This paper presents a novel solution for underwater intention recognition that simultaneously detects head motion and throat vibration, enhancing multimodal human-robot interactions for underwater diving. The system pairs with an underwater supernumerary robotic limb (SuperLimb), providing propulsion assistance to reduce the diver’s physical load and mental fatigue. An inertial measurement unit monitors head motion, while a throat microphone captures vocal vibrations. Learning algorithms process these signals to accurately interpret the diver’s intentions and map them to the SuperLimb for posture management. The system features a compact design optimized for diving scenarios and includes a multimodal, real-time classification algorithm to distinguish various head motions and vocal signals. By collecting and analyzing underwater throat vibration data, the study demonstrates the feasibility of this approach, enabling continuous motion commands for enhanced diving assistance. The results show that the head motion recognition component of the system achieved a high classification accuracy of 95%, and throat vibration classification reached 86% accuracy on land and 89% underwater for various purposes.

As over 11,000 people turn 65 each day in the U.S., our country, like many others, is facing growing challenges in caring for elderly persons, further exacerbated by a major shortfall of care workers. To address this, we introduce an elder-care robot (E-BAR) capable of lifting a human body, assisting with postural changes/ambulation, and catching a user during a fall, all without the use of any wearable device or harness. Our robot is the first to integrate these 3 tasks, and is capable of lifting the full weight of a human outside of the robot's base of support (across gaps and obstacles). In developing E-BAR, we interviewed nurses and care professionals and conducted userexperience tests with elderly persons. Based on their functional requirements, the design parameters were optimized using a computational model and trade-off analysis. We developed a novel 18-bar linkage to lift a person from a floor to a standing position along a natural trajectory, while providing maximal mechanical advantage at key points. An omnidirectional, nonholonomic drive base, in which the wheels could be oriented to passively maximize floor grip, enabled the robot to resist lateral forces without active compensation. With a minimum width of 38 cm, the robot's small footprint allowed it to navigate the typical home environment. Four airbags were used to catch and stabilize a user during a fall in$\leq \mathbf{2 5 0 ~ m s}$. We demonstrate E-BAR's utility in multiple typical home scenarios, including getting into/out of a bathtub, bending to reach for objects, sit-to-stand transitions, and ambulation.

This paper presents a novel design concept of a pair of soft gripper hands that can establish a secure connection between them for bearing a large load with a low air pressure. The design was inspired by dovetail joints in carpentry that enable a tight, strong connection between two pieces of wood. We propose to mimic the dovetail joint mechanism by using soft robotic fingers that interlace to each other for secure connection. The work was motivated by the need for securing a connection between two soft robotic arms for holding a balance-impaired older adult in case of losing balance. First, the design principle of dovetail-like secure soft finger connection is presented, and its potential application to a portable fall prevention system is described. Details of the dovetail soft finger design, its rapid inflation method, and other implementation issues are then discussed. Through experiments of a proof-of-concept prototype, it is validated that the dovetail soft fingers can bear at least 18 kg of load with only 52 kPa of air chamber pressure filled in 250 ms of charging time. At the end, the proposed method is compared to alternative methods using a Pugh chart.

Pneumatic soft everting robotic structures have the potential to facilitate human transfer tasks due to their ability to grow underneath humans without sliding friction and their utility as a flexible sling when deflated. Tubular structures naturally yield circular cross-sections when inflated, whereas a robotic sling must be both thin enough to grow between a human and their resting surface and wide enough to cradle the human. Recent works have achieved flattened cross-sections by including rigid components into the structure, but this reduces conformability to the human. We present a method of mechanically programming the cross-section of soft everting robotic structures using flexible strips that constrain radial expansion between points along the outer membrane. Our method enables simultaneously wide and thin inflated profiles, and maintains the full multi-axis flexibility of traditional slings when deflated. We develop and validate a model relating geometric design specifications to fabrication parameters, and experimentally characterize their effects on growth rate. Finally, we prototype a soft growing robotic sling system and demonstrate its use for assisting a single caregiver in bed-to-chair patient transfer.

This paper proposes the utilization of Supernumerary Robotic Limbs (SuperLimbs) for augmenting astronauts during an Extra-Vehicular Activity (EVA) in a partial-gravity environment. We investigate the effectiveness of SuperLimbs in assisting astronauts to their feet following a fall. Based on preliminary observations from a pilot human study, we categorized post-fall recoveries into a sequence of statically stable poses called "waypoints". The paths between the waypoints can be modeled with a simplified kinetic motion applied about a specific point on the body. Following the characterization of post-fall recoveries, we designed a task-space impedance control with high damping and low stiffness, where the SuperLimbs provide an astronaut with assistance in post-fall recovery while keeping the human-in-the-loop scheme. In order to validate this control scheme, a full-scale wearable analog space suit was constructed and tested with a SuperLimbs prototype. Results from the experimentation found that without assistance, astronauts would impulsively exert themselves to perform a post-fall recovery, which resulted in high energy consumption and instabilities maintaining an upright posture, concurring with prior NASA studies. When the SuperLimbs provided assistance, the astronaut’s energy consumption and deviation in their tracking as they performed a post-fall recovery was reduced considerably.

The navigational abilities of tip-everting soft growing robots, known as vine robots, are compromised when tip-mount devices are added to enable carrying of payloads. We present a new method for securing a vine robot to objects or its environment that exploits the unique eversion-based growth mechanism and flexibility of vine robots, while keeping the tip of the vine robot free of encumbrance. Our implementation is a tip-clutching winch, into which vine robots can insert themselves and anchor to via powerful overlapping belt friction. The device enables passive, high-strength, and reversible fastening, and can easily release the vine robot. This approach enables carrying of loads of at least 28 kg (limited by the tensile strength of the vine robot body material and winch actuator torque capacity), as well as novel material transport and locomotion capabilities.

A global modeling methodology based on Koopman operator theory for the dynamics of rigid bodies that make and break contact is presented. Traditionally, robotic systems that contact with their environment are represented as a system comprised of multiple dynamic equations that are switched depending on the contact state. This switching of governing dynamics has been a challenge in both task planning and control. Here, a Koopman lifting linearization approach is presented to subsume multiple dynamics such that no explicit switching is required for examining the dynamic behaviors across diverse contact states. First, it is shown that contact/non-contact transitions are continuous at a microscopic level. This allows for the application of Koopman operator theory to the class of robotic systems that repeat contact/non-contact transitions. Second, an effective method for finding Koopman operator observables for capturing rapid changes to contact forces is presented. The method is applied to the modeling of dynamic peg insertion where a peg collides against and bounces on the chamfer of the hole. Furthermore, the method is applied to the dynamic modeling of a sliding object subject to complex friction and damping properties. Segmented dynamic equations are unified with the Koopman modeling method.

This paper discusses the incorporation of a pair of Supernumerary Robotic Limbs (SuperLimbs) onto the next generation of NASA space suits. The wearable robots attached to the space suit assist an astronaut in performing Extra-Vehicular Activities (EVAs). The SuperLimbs grab handrails fixed to the outside of a space vehicle to securely hold the astronaut body. The astronaut can use both hands for performing an EVA task, rather than using one hand for securing the body or operating a tether. The SuperLimbs can also assist an astronaut in repositioning the body and stabilizing it during an EVA mission. A control algorithm based on Admittance Control is developed for a) virtually reducing the inertial load of the entire body so that an astronaut can reposition his/her body with reduced effort, and b) bracing the body stably despite reaction forces and disturbances acting on the astronaut during an EVA operation. A full-scale prototype of Space Suit SuperLimbs was constructed and tested. Results from the experimentation indicated that with the aid of SuperLimbs, energy consumption during EVAs is reduced significantly.

Age-related loss of mobility and an increased risk of falling remain major obstacles for older adults to live independently. Many elderly people lack the coordination and strength necessary to perform activities of daily living, such as getting out of bed or stepping into a bathtub. A traditional solution is to install grab bars around the home. For assisting in bathtub transitions, grab bars are fixed to a bathroom wall. However, they are often too far to reach and stably support the user; the installation locations of grab bars are constrained by the room layout and are often suboptimal. In this paper, we present a mobile robot that provides an older adult with a handlebar located anywhere in space - “Handle Anywhere”. The robot consists of an omnidirectional mobile base attached to a reposition able handlebar. We further develop a methodology to optimally place the handle to provide the maximum support for the elderly user while performing common postural changes. A cost function with a trade-off between mechanical advantage and manipulability of the user's arm was optimized in terms of the location of the handlebar relative to the user. The methodology requires only a sagittal plane video of the elderly user performing the postural change, and thus is rapid, scalable, and uniquely customizable to each user. A proof-of-concept prototype was built, and the optimization algorithm for handle location was validated experimentally.

Although telepresence assistive robots have made significant progress, they still lack the sense of realism and physical presence of the remote operator. This results in a lack of trust and adoption of such robots. In this paper, we introduce an Avatar Robot System which is a mixed real/virtual robotic system that physically interacts with a person in proximity of the robot. The robot structure is overlaid with the 3D model of the remote caregiver and visualized through Augmented Reality (AR). In this way, the person receives haptic feedback as the robot touches him/her. We further present an Optimal Non-Iterative Alignment solver that solves for the optimally aligned pose of 3D Human model to the robot (shoulder to the wrist non-iteratively). The proposed alignment solver is stateless, achieves optimal alignment and faster than the baseline solvers (demonstrated in our evaluations). We also propose an evaluation framework that quantifies the alignment quality of the solvers through multifaceted metrics. We show that our solver can consistently produce poses with similar or superior alignments as IK-based baselines without their potential drawbacks.

In providing physical assistance to elderly people, ensuring cooperative behavior from the elderly persons is a critical requirement. In sit-to-stand assistance, for example, an older adult must lean forward, so that the body mass can shift towards the feet before a caregiver starts lifting the body. An experienced caregiver guides the older adult through verbal communications and physical interactions, so that the older adult may be cooperative throughout the process. This guidance is of paramount importance and is a major challenge in introducing a robotic aid to the eldercare environment. The wide-scope goal of the current work is to develop an in-telligent eldercare robot that can a) monitor the mental state of an older adult, and b) guide the older adult through an assisting procedure so that he/she can be cooperative in being assisted. The current work presents a basic modeling framework for describing a human's physical behaviors reflecting an internal mental state, and an algorithm for estimating the mental state through interactive observations. The sit-to-stand assistance problem is considered for the initial study. A simple Kalman Filter is constructed for estimating the level of cooperativeness in response to applied cues, with a thresholding scheme being used to make judgments on the cooperativeness state.

A pair of Supernumerary Robotic Limbs (Super-Limbs) can brace the wearer’s upper body while they work at floor level, and support them during crawling. The SuperLimbs’ motion is synchronized with the operator to mimic natural human crawling. This synchronization relies on experimental data from the operator’s observed crawl. A method for predicting the phase difference between the SuperLimbs’ hand placement and the operators desired hand placement is developed and used to coordinate the SuperLimbs’ motion with the operator’s. The experimental data is also used to design the structure of the SuperLimbs to minimize their energy consumption during crawling and regulate their actuator’s temperatures.The SuperLimbs are designed to mimic the operator’s arms while they crawl, however factors such as their limited number of degrees of freedom (DoF), compared to natural limbs, and the compliance of the connection between the SuperLimbs and the operator means that the SuperLimbs’s may dynamically interact with the wearer differently from how their natural limbs do. A simple dynamic model is constructed to assess the energy consumed by the operator as they crawl with the SuperLimbs under different coordination patterns. An optimal coordination pattern is obtained from this assessment.

Optimization of gear ratios for dual-motor actuators is presented for the development of a walker-type assist robot. The robot is reconfigurable to provide an elderly user with multiple physical support functions; one is to assist sitto-stand transitions and the other is to serve as a walker to aid the user in walking. To avoid falling while walking, the robot must react quickly and reconfigure its footprint for supporting the user. This requires high speed actuators. In contrast, for assisting sit-to-stand transitions, high torque actuators are required. To meet the bimodal, conflicting load conditions, i.e. high-torque, low-speed v.s. high-speed, low-torque, this paper presents a dual-motor actuation solution, where two motors with diverse gear ratios are combined. The system is characterized with two key parameters: an internal gear ratio between a high-speed motor and a torque-booster, and an external gear ratio for connecting the dual motor actuator to the load. The internal and external gear ratios are optimized for performing both sit-to-stand assist and rapid foot reconfiguration.

This paper presents a wheeled wall-climbing robot with a shape-adaptive magnetic adhesion mechanism for large steel structures. To travel up and down various curved ferromagnetic surfaces, we developed a 2 DOF rotational magnetic adhesion mechanism installed on each wheel that can change the orientation of the magnets to keep the magnetic force direction always normal to the contact surface. These magnetic wheels have a spherical shape and can move relative to the main body by a non-elastic suspension mechanism so that the robot can climb up small obstacles on the ground and find contact points for each wheel on a wall with an arbitrary curved shape. Being geometrically stable is important for the robot because this robot is intended to be a mobile base for a welding manipulator. The detailed design of the mechanism and the results of climbing tests are presented.

A control algorithm that allows a human model to crawl using a pair of supernumerary robotic limbs (SuperLimbs) is presented. The human model and SuperLimbs are coupled by a compliant harness. This work is inspired by the need for wearable robotic systems that can support workers engaged in fatiguing tasks. The walking policy is developed based on Lyapunov analysis. The volume of the region of attraction (ROA) of the system is used to quantify robustness and identify the optimal harness compliance. Simulation experiments are used to verify the performance of the algorithm. The presented formulation allows us to guarantee stable locomotion under nominal conditions and define robustness against modeling error and perturbations. This study is also the first, that the authors are aware of, to address cooperative crawling between a human and a wearable robotic system with state feedback.

Supernumerary Robotic Limbs (SRLs) have been successfully applied in bracing and as an assistive technology for people with disabilities. These tasks only require perception internal to the SRL-human system. However, SRLs show promise in applications requiring external perception such as opening a door when one’s hands are full. One path toward developing SRLs that accomplish these tasks is to use human-in-the-loop control, thus leveraging the human’s superior perception system to help the SRLs. However, the effects on the user of controlling additional limbs are unclear. This article presents an experimental study where humans, wearing two single degree of freedom SRLs, were instructed to minimize the position error between the subject’s natural and robotic limbs and the corresponding targets, one for each limb. First, subjects performed worse with their natural limbs when asked to perform the task with two natural and two robotic limbs as opposed to with just their natural limbs, suggesting that shared control could help. Second, subjects moved their natural limbs together followed by moving their SRLs together. This informs both the choice of control scheme for the SRLs and the division of labor within a task. Third, subjects showed significant concurrent use of the natural and robotic limbs.

Aircraft manufacturing, construction, and agricultural production often involve workers maintaining uncomfortable postures, such as stooping and kneeling, for extended periods of time. We present a wearable robot, called MantisBot Alpha, that consists of two expandable robotic arms that brace a worker near the ground and allows them to perform bi-manual tasks. The key component of this new design is a novel linkage mechanism that provides adjustment of both the worker's distance to the ground and their torso tilt. The mechanism link parameters are optimized such that a) its expansion rate is high enough to push off the human body from the ground and fully contract the scissor arm when not used, and b) it allows the worker to reach within a large space while c) it is light enough for wearability. The linkage mechanism also avoids the singularity problem in standard scissor mechanisms. The actuator design provides a fail-safe system. A prototype has been fabricated to demonstrate the feasibility of the system.

Inspection and maintenance of equipment inside buildings, such as exit signs, bared pipelines, air vents, and fire alarms often requires a robot to reach high, hidden, or confined areas that are difficult for humans to access. Even though these tasks are easy and repeatable, they are still not automated. The Mobile Extendable Robot Arm (MERA) is a movable robot arm with a novel 2-DOF scissor mechanism for reaching a high place and positioning an end-effector. MERA is composed of a locomotion vehicle with a rotation table and a 4-DOF extender arm, itself made of two layers of the 2-DOF scissor mechanism arranged in series. Placing the end-effector at an arbitrary point in space, the 4-DOF arm possesses two degrees of redundancy, allowing access to a point from various directions and enabling obstacle avoidance. In this paper, we present the design and analysis of the 2-DOF scissor mechanism. The 2-DOF scissor mechanism has two rotary actuators for driving the base links individually; consequently, the mechanism can elongate the entire body and tilt at the center of the base shaft. However, we found that the 2-DOF scissor mechanism had a singularity; after analyzing the singularity, we propose two novel solutions to the problem.

A novel design concept of expandable robotic arm inspired by plant growth is presented. The robot can construct its own structure by converting a type of fluidized material into a rigid structure at its growing point. The robot can extend its structure in multiple directions, and move through a winding space to reach a point, which is otherwise difficult to access. The robot with the rigid structure can also bear a significant load, has a plate to attach an end-effector, and can transport an object. The robot satisfies three key functional requirements that are characteristic to plant growth. First, the robot is capable of transporting structural materials to its growing point. Second, the robot is capable of transforming the material into a rigid structure. Third, it is capable of steering its growing point so that it is expanded in a desired direction. A proof-of concept prototype is then presented that consists of a special sprocket chain that can be switched between flexible/fluidized and rigid states, a winch that can pull/transport the chain, and a steering system to direct the growing direction. Unlike plants, this growing robot can retract its extended body, and can extend in a different direction. The prototype demonstrates that it meets all the functional requirements, and that it can make sharp turns and move through obstacles.

An intuitive on-site robot programming method for small-lot robotic welding is presented. In current robotic welding, a human operator has to input numerous parameters, including feedrate, swing width, and frequency, by using a teach pendant or a control panel before executing the task. This traditional approach is suitable for mass production, but requires tedious, time-consuming programming, which does not fit low-volume manufacturing, such as shipbuilding. In this paper, a method is developed for acquiring those parameters directly from an on-site human demonstration and seamlessly transitioning from manual operation to automatic control. With this method, a welding worker can directly execute a welding task, and the motion of a welding torch is observed, from which key parameters are identified and the machine performs the rest of the task autonomously. No tedious parameter input is required, but the worker can jump-start the task. The motion of a welding torch is represented as a combination of sinusoidal and linear functions. Discrete Fourier Transform (DFT) and Recursive Least Squares (RLS) estimates are used for identifying the parametric model in real time. Furthermore, an algorithm is developed for determining whether an appropriate estimation result has been obtained and when to switch from manual operation to autonomous control. The method is implemented on a virtual teleoperation system and seamless control transition is demonstrated.

Cells interacting through an extracellular matrix (ECM) exhibit emergent behaviors resulting from collective intercellular interaction. In wound healing and tissue development, characteristic compaction of ECM gel is induced by multiple cells that generate tensions in the ECM fibers and coordinate their actions with other cells. Computational prediction of collective cell-ECM interaction based on first principles is highly complex especially as the number of cells increase. Here, we introduce a computationally-efficient method for predicting nonlinear behaviors of multiple cells interacting mechanically through a 3-D ECM fiber network. The key enabling technique is superposition of single cell computational models to predict multicellular behaviors. While cell-ECM interactions are highly nonlinear, they can be linearized accurately with a unique method, termed Dual-Faceted Linearization. This method recasts the original nonlinear dynamics in an augmented space where the system behaves more linearly. The independent state variables are augmented by combining auxiliary variables that inform nonlinear elements involved in the system. This computational method involves a) expressing the original nonlinear state equations with two sets of linear dynamic equations b) reducing the order of the augmented linear system via principal component analysis and c) superposing individual single cell-ECM dynamics to predict collective behaviors of multiple cells. The method is computationally efficient compared to original nonlinear dynamic simulation and accurate compared to traditional Taylor expansion linearization. Furthermore, we reproduce reported experimental results of multi-cell induced ECM compaction.

When a human performs a task with the assistance of wearable extra limbs, the human movement for performing the task may inadvertently disturb the position and orientation of the robot base, making it difficult for the robot to properly carry out its objective. Therefore, unlike self-standing robots, a wearable robot must not only assist the user without interfering or prohibiting the natural human movement, but also have the capability to detect and reject disturbances caused by the wearer's motion. This paper examines such a situation, where the human attempts to twist open a bottle while a pair of robotic fingers mounted on the same arm holds the bottle in place. As the human arm rotates to twist the cap, the robot and consequently the bottle would rotate in that same direction, which makes separation of the cap from the bottle almost impossible. To compensate for the human induced disturbances, a data-driven latent space impedance control method is developed such that the robot can secure the bottle and at the same time allow natural human movement to be carried out during manipulation. Simulation and experiments have demonstrated the efficacy of the latent space impedance controller to enable single-handed object manipulation with the assistance of wearable robotic fingers.

We present the design of a new robotic human augmentation system that will assist the operator in carrying a heavy payload, reaching and maintaining difficult postures, and ultimately better performing their job. The Extra Robotic Legs (XRL) system is worn by the operator and consists of two articulated robotic legs that move with the operator to bear a heavy payload. The design was driven by a need to increase the effectiveness of hazardous material emergency response personnel who are encumbered by their personal protective equipment (PPE). The legs will ultimately walk, climb stairs, crouch down, and crawl with the operator while eliminating all external PPE loads on the operator. The forces involved in the most extreme loading cases were analyzed to find an effective strategy for reducing actuator loads. The analysis reveals that the maximum torque is exerted during the transition from the crawling to standing mode of motion. Peak torques are significantly reduced by leveraging redundancy in force application resulting from a closed-loop kinematic chain formed by a particular posture of the XRL. The actuators, power systems, and transmission elements were designed from the results of these analyses. Using differential mechanisms to combine the inputs of multiple actuators into a single degree of freedom, the gear reductions needed to bear the heavy loads could be kept at a minimum, enabling high bandwidth force control due to the near-direct-drive transmission. A prototype was fabricated utilizing the insights gained from these analyses and initial tests indicate the feasibility of the XRL system.

A novel wearable robotic device is developed to support the wearer when performing bi-manual tasks near the ground. The device is worn around the upper torso and has two Supernumerary Robotic Limbs (SRLs) that reach the ground when the wearer assumes a crawling-like position, such that neither of the wearer's natural arms are needed to support the body. Rather, both human hands can be engaged in executing a required task. Coordinating actuators at both robotic limbs, the wearer's body is supported stably with a desired impedance. As the wearer moves away from an equilibrium position, restoring forces designated by the impedance act on the wearer. First, the design concept of the SRLs for near-ground work is described, followed by a derivation of the control laws used to produce virtual impedance. A proof-of-concept prototype is then presented along with experimental verification of the derived control laws.

Most of the wearable robots today assist their users by acting in parallel or in series to their natural limbs. We propose a different approach to wearable robotics, consisting of devices that provide users with additional, independent robotic limbs. We present a wearable robot prototype that can achieve these goals with an extremely light weight apparatus. In order to control additional robotic limbs as if they were part of the user's body, we need voluntary signals that are independent of natural limb motions and comfortable to measure. One suitable solution - explored in this study - is the use of muscle activation signals generated by the torso. We hypothesize that a human is competent to move the extra limbs voluntarily and independently without interfering with the natural arms and legs. We developed a wearable suit to measure these signals, and we tested three possible real-time control strategies linking torso muscle contraction to the motions of two simulated extra limbs. The experimental data show that the velocity control strategy yields the highest motion accuracy, minimum muscular effort, maximum independence from the natural limbs and the fastest learning rate. This control strategy has then been applied to the control of the physical robot prototype, worn by human subjects. All of the subjects achieved accurate (normalized tracking error <; 0.5), independent (normalized natural arm motions <; 0.15) control of the extra limbs.

Fulfillment centers located in densely populated urban areas are an ever-growing need for leading online consumer websites. These urban fulfillment centers have limited land mass and must have innovative solutions to transport goods within the available vertical space. This work presents a Multi-Track Elevator (MTE) System, a competitive solution for rapid access and retrieval of goods in high-rise e-commerce fulfillment centers and warehouses. The MTE System consists of multiple vertical rails connected with angular traverse rails that allow multiple carriages to go up and down without collision. A novel turning point system switches track routes so that several carriages can move across the multiple rails for rapidly accessing many floors and collecting diverse goods. Unlike existing vertical-horizontal grid elevators and rail systems, the Roller-coaster type, self-powered carriages on the MTE system do not have to stop at switching points, but can continually move across the network of rails. This work walks through the architecture of the rail network system and techniques for switching multiple rails, followed by the design of vertical turntables for smooth, continuous rail switching. Finally, outlining the use of a simple route optimization algorithm, diverse elevator systems are compared with respect to total traveling time and distance. A proof-of-concept prototype has been built and is presented.

This paper addresses the closed-loop control of an actuator with both a continuous input variable (motor torque) and a discrete input variable (mode selection). In many applications, robots have to bear large loads while moving slowly and also have to move quickly through the air with almost no load, leading to conflicting requirements for their actuators. An actuator with multiple gear ratios, like in a powertrain, can address this issue by allowing an effective use of power over a wide range of output speed. However, having discrete modes of operation adds complexity to the high-level control and planning. Here a controller for two-speed actuators that automatically select both the best gear ratio and the motor torque is developed. The approach is to: first derive a low-dimensional model, then use dynamic programming to find the best actions for all possible situations, and last use regression analysis to extract simplified global feedback laws. This approach produces simple practical nearly-optimal feedback laws. A controller that globally minimizes a quadratic cost function is derived for a two-speed actuator prototype, global stability is proven and performance is demonstrated experimentally.

We present a novel 6 DOF robotic mechanism for reaching high ceilings and positioning an end-effector. The end-effector is supported with three scissor mechanisms that extend towards the ceiling with 6 independent linear actuators moving the base ends of the individual scissors. The top point of each scissor is connected to one of three ball joints located at the three vertices of the top triangular plate holding the end-effector. Coordinated motion of the 6 linear actuators at the base allows the end-effector to reach an arbitrary position with an arbitrary orientation. The design concept of the Triple Scissor Extender is presented, followed by kinematic modeling and analysis of the the Inverse Jacobian relating actuator velocities to the end-effector velocities. The Inverse Jacobian eigenvalues are determined for diverse configurations in order to characterize the kinematic properties. A proof-of-concept prototype has been designed and built. The Inverse Jacobian for use in differential control is evaluated through experiments.

A robot attached to a human body can support the human when performing tasks in dangerous environments or when taking postures that are fatiguing and uncomfortable. This paper presents a new type of supernumerary robotic limbs (SRL) that supports the human body against floors, walls, and surrounding structures so that the human can perform a task safely, comfortably, and stably. First, the use of wearable robots for securing and supporting a human body is discussed, followed by an SRL design concept. The SRL is worn around the waist and can brace the human body by making contact with a wall, grasping a rail, or being anchored to the floor. Quasi-static stability and compliance with which the body is supported are analyzed. Two control methods for stabilizing the body support system are considered: one is null-space stabilization using Hessian matrices, and the other is joint servo stiffness, based on the Jacobian. A prototype robot is designed and tested. Potential applications of the SRL in diverse fields are discussed.

Functionality of a human hand can be augmented with wearable robotic fingers to enable grasping and manipulation of objects with a single hand. Such technology will have applications in manufacturing and construction, as well as health care. This paper presents a method for controlling extra robotic fingers, termed “Supernumerary Robotic Fingers (SR Fingers),” in coordination with human fingers to grasp diverse objects. Two hypotheses are proposed and verified through experiments. One is that humans prefer grasp posture of their fingers and that of the SR Fingers to be highly correlated when working together, which is represented with a few principal components, resembling grasp synergy in neuromotor control. The other hypothesis is that SR Finger posture can be controlled to coordinate with human finger posture via grasp synergy of the hybrid human-robotic hand. Partial least squares regression is used for predicting a desired posture of the SR Fingers from the measurement of human fingers. This method is implemented on a pair of wrist-mounted SR Fingers. Experiments demonstrate that the prototype SR Fingers can assist the human user in performing single-handed grasping tasks without requiring explicit commands.

Cell migration is a fundamental process for the development and maintenance of all multicellular organisms. Accurate cell tracking may lead to better interpretations of long-term cell behaviours. This paper describes an automated system to track multiple cells from experimental phase contrast images, which includes image registration, lumen segmentation, cell candidate detection, and multiple hypothesis Kalman filtering. We incorporate biological knowledge to associate the new observations to existing tracks. We apply our methodology to the problem of tracking endothelial cells in 3D angiogenic vessels. Numerical results indicate that our method associates cells more accurately compared to standard methods for cll association and tracking.

In this paper we present a unique self stabilizing ellipsoidal robot for inspection of underwater structures using the principles of ground effect. Underwater metal structures - whether it is ship hulls or internals of a boiling water reactor - require subsurface inspection to detect internal cracks, hidden cavities and other structural damage. This is usually done with on-contact ultrasonic sensors, a slow process if the structure is not sufficiently smooth. However, ultrasound can also be used with a precisely controlled gap. Such precision is challenging relying solely on actuators for control. This paper exploits near surface hydrodynamics to self stabilize a body at a precise gap. Specifically we show how boundary layer and venturi effects combine to create a stable, zero force position at a very small distance from the surface - conceptually similar to air bearings sliders on hard disk drives. Below the stable point lift force dominates, while above it Venturi suction prevails, each bringing the body back to equilibrium. Limitations in the restoring force are considered in the stability analysis included in the paper. This self stabilization method opens a whole new door for non-contact subsurface inspection of underwater structures by autonomous vehicles as well as precision distance maintenance in underwater environment. Here we present our initial analysis and preliminary experimental results for the method when used with an ellipsoidal robot.

This paper presents a novel approach to balance assistance and joint load reduction for human bipedal walking. We introduce a new type of wearable robot, called Supernumerary Robotic Limbs (SRL), that provides two additional legs for augmenting stability and reducing the loads on human leg joints. Unlike exoskeletons, the SRL is kinematically independent of the human skeletal structure, and can therefore take an arbitrary posture to provide optimal assistance in coordination with human motions. Furthermore, unlike crutches, canes, and other balance assistance equipment, the SRL can provide balancing support autonomously and thereby free the human arms from holding those tools. First, the new design concept and balance assistance strategy are described, followed by kinematic and static modeling. Two gate patterns of the combined human and SRL are discussed. Optimal gate synthesis that maximizes the area of support polygon is discussed. Finally, the gate control strategies are implemented on a prototype SRL, using body motion sensors to enable real-time, seamless coordination between the user and the robot.

Similar to combustion engines comprising multiple cylinders engaged with a crankshaft, multiple piezoelectric stack actuators (PSA) engaged with a common output rod can produce smooth, long stroke motion with desired properties. In particular, when equally spaced multiple units are arranged to push sinusoidal gear teeth on the output rod, the system exhibits unique collective behaviors thanks to “harmonic” effects of the multiple units. For example, although the force-displacement characteristics of individual units are highly nonlinear, the undesirable nonlinearity, including singularity, may be eliminated. Here we present harmonic analysis and control of a class of actuators consisting of multiple driving units engaged with a sinusoidal transmission, termed a harmonic poly-actuator. Through theoretical analysis we obtain 1) conditions on the unit arrangement to eliminate their nonlinearity from the output force, 2) control algorithms for coordinating the multiple units to generate a commanded force with desired force-displacement characteristics, and 3) a method for compensating for output force ripples due to possible misalignment and heterogeneity of individual units. The control algorithms are implemented on a prototype harmonic poly-actuator with six units of PSAs. Experiments demonstrate the unique features of the poly-actuator exploiting the harmonic properties of the system.

Functionality of a human hand can be augmented with extra robotic fingers attached to the forearm. These wearable extra fingers can work together with the human fingers and perform tasks that are usually difficult for a single hand. Such technology may benefit amputees and surviving stroke patients who are forced to live with only one functional arm. In this paper, we present a novel method, exploiting redundancies in the elbow, to control a pair of extra robotic fingers, termed Supernumerary Robotic Fingers or SR Fingers for short, to perform “hold-and-manipulate” tasks. Two control protocols are explored here. One protocol enables discrete transition between different modes of motion, while the other continuously controls grasping behavior of the SR Fingers. Four robot assisted “hold-and-manipulate” tasks are examined, including twisting off the cap of a water bottle, opening the lid of a food container, plugging a cable into an electronic device, and mixing salad in a bowl. Through the successful completion of these tasks, we demonstrate that wearable extra fingers have the potential to provide those with impaired hands the opportunity to live with more independence and work more productively.

In many applications, robots have to bear large loads while moving slowly and also have to move quickly through the air with almost no load. This leads to conflicting requirements for their actuators. Multiple gear ratios, like in a powertrain, address this issue by allowing an effective use of power over a wide range of output speed. However in robotics, as opposed to powertrains, the controlled load is not always inertial and acting as a low-pass filter; hence gear shifting is a more challenging issue in a robotics context. In this paper, it is proposed to address this problem using a dual-speed dual-motor architecture to maintain full control of the output during gear shifting. A dynamic model is developed and a controller using the redundancy of motors is proposed to enable fast seamless gear shifting even when interacting with unknown dynamic environments. Results are demonstrated with a proof-of-concept linear actuator.

The dynamics of filopodia interacting with the surrounding extracellular matrix (ECM) play a key role in various cell-ECM interactions, but their mechanisms of interaction with the ECM in 3D environment remain poorly understood. Based on first principles, here we construct an individual-based, force-based computational model integrating four modules of 1) filopodia penetration dynamics; 2) intracellular mechanics of cellular and nuclear membranes, contractile actin stress fibers, and focal adhesion dynamics; 3) structural mechanics of ECM fiber networks; and 4) reaction-diffusion mass transfers of seven biochemical concentrations in related with chemotaxis, proteolysis, haptotaxis, and degradation in ECM to predict dynamic behaviors of filopodia that penetrate into a 3D ECM fiber network. The tip of each filopodium crawls along ECM fibers, tugs the surrounding fibers, and contracts or retracts depending on the strength of the binding and the ECM stiffness and pore size. This filopodium-ECM interaction is modeled as a stochastic process based on binding kinetics between integrins along the filopodial shaft and the ligands on the surrounding ECM fibers. This filopodia stochastic model is integrated into migratory dynamics of a whole cell in order to predict the cell invasion into 3D ECM in response to chemotaxis, haptotaxis, and durotaxis cues. Predicted average filopodia speed and that of the cell membrane advance agreed with experiments of 3D HUVEC migration at r(2) > 0.95 for diverse ECMs with different pore sizes and stiffness.

A wearable robot secured on the shoulder of a human is developed for assisting its wearer in the execution of tasks in the overhead workspace. Installing a ceiling panel is an example of such a task. During this task the robot can hold the panel or collaborate actively with the human in order to fix the panel with the appropriate equipment. This wearable robot, termed "Supernumerary Robotic Limbs", works closely with the human to streamline the operation and reduce the human workload. First, the design concept of the Robot-on-the-Shoulder system is described, and a new approach to the coordinated control between the wearable robot and the human is presented. A graphical task process representation based on Coloured Petri Nets (CPN) is used to model the concurrent and distributed nature of the human-robot system, which comprises two human hands and two robot hands. The CPN framework is then extended to a type of hybrid control system by imbedding local dynamic controllers in the Transition nodes of the CPN model. Each local dynamic controller collects sensor signals relevant to the target transition and makes a predictive control decision. This allows the robot on the shoulder to take a proactive and preemptive action as well as to confirm a successful Transition. The control parameters for these algorithms are tuned based on "teaching-by-showing" techniques using human demonstration data. Partial Least Squares is used for extracting significant sensor signals from high-dimensional sensor data in order to do real time predictions and control. A prototype robot-on-the-shoulder system is built, and the CPN hybrid control is implemented and tested for a ceiling panel installation task.

In this paper we examine the dynamics of a unique type of jet propelled, spheroidal robot design. This robot uses jets angled inward into a diamond shape to achieve superior planar dynamics. We explore the role of the diamond configuration in avoiding nonminimum phase behavior and we examine the best vehicle aspect ratios for this type of robot design. We use a degree of controllability metric to illustrate the uncontrollable behavior of certain designs and also identify an optimal aspect ratio of 1.4. The paper concludes by incorporating these lessons into a new 5 degree-of-freedom prototype robot that provides substantial improvements over previous designs. This robot uses centrifugal pumps and fluidic valves to achieve high maneuverability and unique motions such as forward and reverse motions, sway translations, and turning in place. In addition, this design can achieve improved forward efficiency through the use of dual output-pumps and can perform these planar motions at various vehicle depths through the use of a closed loop depth control system.

A new type of wearable robot that assists the wearer with extra arms secured around the hips is presented. Supernumerary Robotic Limbs (SRL) can hold objects, clamp them to a fixture, guide and support human hands, and assist the wearer in performing a task as a close co-worker. This paper focuses on a class of tasks where SRL physically interacts with the environment through contact. SRL makes contact with a wall and thereby braces the human body against the environment. SRL also guides the human hands by placing a drill jig over the drilling location. Bracing the human body and guiding the hands, SRL can enhance the drilling task stability and accuracy. The SRL technology is applied to aircraft assembly, where conventional industrial robots failed to perform effectively. First, the basic design concept of SRL is summarized, and task strategies using SRL and their functional requirements are described. Kinematic and static properties resulting from the structural closed loops formed around the SRL, the human, and the environment are analyzed, and effective strategies for physical disturbance rejection and fine positioning are discussed. A prototype robotic arm grasps the aircraft fuselage structure. Another robotic arm places a drill jig precisely on the fuselage structure, and guides and stabilizes a hand drill held by the human user. An optimization method is developed in order to identify the SRL kinematic configuration and joint torques that stabilize the drill and at the same time minimize the human workload.

A new approach to physically assisting the human with a wearable robot is presented. Supernumerary Robotic Limbs (SRLs) attached to the human waist support the body efficiently when the human is taking fatiguing postures, e.g. hunching over, squatting, or reaching the ceiling. Unlike a leg exoskeleton, where powered joints are attached to the human joints and are constrained to move together with the human limb, the SRL can take an arbitrary posture to maximize the load bearing efficiency. Taking a near-singular configuration, the SRL can bear a large load with small power consumption. First, the “bracing” strategy for supporting the human body is described, followed by a mathematical analysis of the load bearing efficiency. The optimal SRL posture and joint torques are then obtained in order to minimize the human load. Numerical and experimental results using a prototype of the SRL demonstrate the effectiveness of the method.

Capacitive actuators, such as piezoelectric stack actuators, provide an efficient solution for robotic and mecha-tronic systems that typically require large forces and minimal velocities over long periods of time. To overcome the stack actuator's limitations, particularly their limited stroke, a harmonic poly-actuator design is presented. This design utilizes a multitude of intermediate buckling amplification mechanisms in a parallel arrangement to create a large stroke, high force actuator. The redundant system architecture combined with a particular spatial and temporal coordination allow for a number of salient features, including robustness to failure, backdrivability, and continuous force control via elementary ON-OFF control. A prototype was built using six intermediate buckling amplification mechanisms and was able to produce over 100 Newtons of force over a stroke of 450 mm.

In this paper we present the dynamic modeling and control of EVIE (Ellipsoidal Vehicle for Inspection and Exploration), an underwater surface contact ROV (Remotely Operated Vehicle) for inspection and exploration. Underwater surface inspection is a challenging and hazardous task that demands sophisticated automation - as in boiling water nuclear reactors, water pipeline, submarine hull and oil pipelines inspection. EVIE is inspired by its predecessor, the Omni Submersible, in its ellipsoidal, streamlined, and appendage free shape. The objective for the robot is to carry inspection sensors - magnetic, acoustics or visual - to determine cracks on submerged surfaces. Unlike a robot moving in a practically boundless fluid, contact forces complicate the dynamics by bringing in normal and frictional forces, both of which are highly non linear in nature. This makes the modeling much more challenging and the development of an integrated controller more difficult. In this paper we will discuss the preliminary design and hydrodynamic modeling of such a robot. We analyze in detail the controls for one of the many transitional states of this robot. Eventually all transitional states need to be integrated to develop a hybrid dynamical system which shall use a controller that can adapt to its different states.

A highly maneuverable, spheroid-shaped, underwater robot using appendage-free, multi-degree of freedom (DOF) propulsion technologies is presented. The vehicle is hydrodynamically unstable due to the Munk moment. The vehicle is stabilized by feedback control, rather than passive fins, which facilitates rapid turns and agile motions. The new design was motivated by nuclear reactor inspection and other applications where external appendages must be avoided. Two technical challenges are addressed in this paper. One is the development of a compact, multi-DOF propulsion system that generates multiaxis water jets and switches them rapidly. The other is the design of a jet configuration and control system that augments stability and achieves high maneuverability. A nonlinear hydrodynamic model is formulated, and its linearized dynamics are analyzed to attain insights into how jet direction influences controllability and stability. A prototype vehicle is built and used to verify these concepts. The integrated design method is implemented and shown to achieve stable motions, high maneuverability, and multidirectional capability.

A novel design concept of piezoelectric actuators producing large displacement while transmitting a significant amount of energy is presented. A rolling-contact buckling mechanism with a novel preload mechanism can amplify the PZT stack's displacement on the order of 100 times while transmitting several times larger work output than conventional flexure-type displacement amplification mechanisms. Existing displacement amplification mechanisms are analyzed in terms of transmissibility and are characterized with two lumped-parameter elements: serial and parallel compliances. The maximum transmissibility is attained when the parallel stiffness and the serial compliance are zero. An existing flexure mechanism using structural buckling, that produces a large displacement but a low transmissibility, is replaced by a rolling-contact mechanism that approaches the maximum criterion. Furthermore, a mechanism is presented to apply a constant preload to each PZT stack despite their movement. A prototype has been built to implement the design concept and verify the theoretical results. Experiments using the prototype demonstrate that it produces a 4.2 mm free displacement with over 60% transmissibility.

In this paper we present a new type of spherical underwater robot that is completely smooth and uses jets to propel and maneuver. This robot is specifically designed for the direct visual inspection of water-filled infrastructure such as the inside of nuclear powerplants. The unique propulsion architecture consists of a single bidirectional centrifugal pump combined with two fluidic valves. The pump is used to produce a high velocity jet while the valves are used to quickly switch the jet between output ports. The spherical shape means that the robot is simple to model and control, maneuverable, and robust to collisions. The propulsion architecture is described in detail along with a rigid body model for maneuvering control. A novel valve PWM controller is used to achieve heading control, and the controller performance is confirmed with both simulation and experiments. Finally, experiments are used to illustrate the turning and diving performance of the robot.

We present the Supernumerary Robotic Limbs (SRL), a wearable robot designed to assist human workers with additional arms and legs attached to the wearer's body. The SRL can work closely with the wearer by holding an object, positioning a workpiece, operating a powered tool, securing the human body, and more. Although the SRL has the potential to provide the wearer with greater strength, higher accuracy, flexibility, and dexterity, its control performance is hindered by unpredictable disturbances due to involuntary motions of the wearer, which include postural sway and physiological tremor. This paper presents 1) a Kalman filter approach to estimate the state of the SRL despite the involuntary wearer's motion, and 2) a method for improving the accuracy and stabilizing the human body and the SRL. The dynamics of the human-SRL system are analyzed, including human-induced disturbance models based on biomechanics literature. A discrete Kalman filter is constructed and its performance is evaluated in terms of error covariance. A “bracing” technique is then introduced to suppress the human-induced disturbances; one robotic limb grasps an environment structure and uses it as a support to attenuate the disturbances. We show how bracing can be used to shape the stiffness parameters at the robot base. This in turn allows to enhance state estimation accuracy in the areas of the workspace where the user needs assistance.

A novel design concept is presented for amplifying the displacement of a PZT stack over 50-fold while transmitting a significant amount of work per cycle. Piezoelectric devices, such as PZT stack actuators, have a competitive power density, while consuming virtually no energy for generating a force at a constant position. Despite the salient features, the actual work usable for activating a load is significantly reduced when displacement amplification mechanisms are used for attaining displacements large enough to drive a macroscopic robotic system. This paper addresses how the work produced by a PZT stack is transmitted to a load without attenuation. The theoretical limit of maximum work is obtained and experimentally verified. Conditions for transmitting the maximum work, i.e. maximum work transmissibility, are obtained based on a simple model. A novel displacement amplification mechanism using a flexure-free, buckling mechanism is then presented as a solution that satisfies the maximum energy transmissibility conditions. A prototype device is designed and tested. Initial experiments show promising results.

An integrative cell migration model incorporating focal adhesion (FA) dynamics, cytoskeleton and nucleus remodeling, actin motor activity, and lamellipodia protrusion is developed for predicting cell spreading and migration behaviors. This work is motivated by two experimental works: (1) cell migration on 2-D substrates under various fibronectin concentrations and (2) cell spreading on 2-D micropatterned geometries. These works suggest (1) cell migration speed takes a maximum at a particular ligand density (∼1140 molecules/µm(2)) and (2) that strong traction forces at the corners of the patterns may exist due to combined effects exerted by actin stress fibers (SFs). The integrative model of this paper successfully reproduced these experimental results and indicates the mechanism of cell migration and spreading. In this paper, the mechanical structure of the cell is modeled as having two elastic membranes: an outer cell membrane and an inner nuclear membrane. The two elastic membranes are connected by SFs, which are extended from focal adhesions on the cortical surface to the nuclear membrane. In addition, the model also includes ventral SFs bridging two focal adhesions on the cell surface. The cell deforms and gains traction as transmembrane integrins distributed over the outer cell membrane bond to ligands on the ECM surface, activate SFs, and form focal adhesions. The relationship between the cell migration speed and fibronectin concentration agrees with existing experimental data for Chinese hamster ovary (CHO) cell migrations on fibronectin coated surfaces. In addition, the integrated model is validated by showing persistent high stress concentrations at sharp geometrically patterned edges. This model will be used as a predictive model to assist in design and data processing of upcoming microfluidic cell migration assays.

This paper presents the design, modeling, and experimental verification of a novel, programmable connection mechanism for robots separated by a surface. The connector uses electropermanent magnets (EPMs) [1] to establish a continuum of clamping force between the robots, enabling the motion of one robot to slave the other during a variety of maneuvers. The authors design a novel, solid-state EPM arrangement capable of generating up to an estimated 890N of clamping force under environmental loading conditions. A relationship between geometric and environmental variables and connection assembly performance is first modeled and subsequently experimentally characterized. By implementing these connectors in a custom manufactured pair of assembly robots, the authors demonstrate the connection assembly and magnetizing hardware can be compactly fit within an autonomous robot application. We offer this mechanism as a repeatable, easily-automated alternative to robotic systems that depend on mechanic means to regulate clamping force [2].

There is an increasing need for the inspection of nuclear power plants worldwide. To access complex underwater structures and perform non-destructive evaluation, robots must be tetherless, compact, highly maneuverable, and have a smooth body shape with minimal appendages. A new water jet propulsion system using fluidic valves coupled with centrifugal pumps is developed for precision maneuvering. A hybrid control system that combines continuous pump regulation and discrete Pulse Width Modulation (PWM) of fluidic valves is proposed. This control scheme provides high accuracy, high bandwidth, and flexibility in maneuvering control. First, the functional requirements for nuclear power plant inspection are discussed, followed by the basic design concept of an inspection robot. Miniaturized Coanda-effect valves are designed and built based on CFD and mathematical analysis. The hybrid control system incorporating the pump/valve system is designed and tested. Experimental results illustrate that the hybrid control scheme holds substantial promise and is capable of very precise orientation control. Based on these, a full 4-DOF robot is designed, and its key components are described.

Visible light communication systems have gained prominence as a method for wireless underwater communications. This is because these systems are capable of long distance communications in water with high bandwidths. A requirement of visible light systems, however, is consistent line of sight to maintain a communication link. This arises from the directional nature of visible light emitters and detectors. One solution to this problem is to implement feedback control in order to “point” visible light emitters and detectors at one another. This in turn requires precise estimation of the relative locations of these two components as a feedback signal. In this work, a system is presented that uses the modulated light signal both as a medium with which to carry data and as a reference upon which to base the localization of a mobile robot. This is therefore a dual-use system, for both communication and localization. First, this paper presents the architecture of a dual-use visible light communication and localization system. The localization is carried out using an Extended Kalman Filter (EKF) algorithm. Then, a planar version of this dual-use system is tested, demonstrating the feasibility and effectiveness of the dual-use approach.

The body representation in the human mind is dynamic, and illusions or traumatic events can modify it to include additional limbs. This remarkable adaptability of the central nervous system to different body configurations opens new possibilities in the field of human augmentation. In order to fully exploit this potential, we developed a new type of wearable co-robot that can perform tasks in close coordination with the human user. The system, named Supernumerary Robotic Limbs (SRL), consists of two additional robotic arms worn through a backpack-like harness. The SRL can assist the user by holding objects, lifting weights and streamlining the execution of a task. If the SRL perform movements closely coordinated with the user and exhibit human-like dynamics, they might be incorporated into the body representation and perceived as parts of the user's body. As a result, the human would be able to extend the range of available skills and manipulation possibilities, performing tasks more effectively and with less effort. This paper presents a communication, estimation and control method for the SRL, aimed to perform tasks in tight coordination with the wearer. The SRL observes the user motion, and actively assists the human by employing a coordinated control algorithm. In particular, skills involving the direct cooperation of two human workers are transferred to the SRL and a single user. Demonstration data of the two humans - a leader and an assistant - are analyzed and a state estimation algorithm is extracted from them. This can be used to control the SRL accordingly with the used end effectors. A causal relationship relating the assistant's motion to the leader's motion is identified based on System Identification methods. This approach is applied to a drilling operation performed by two workers. An effective coordination skill is identified and transferred to the SRL, to make them act like the human follower.

This paper presents a new approach to the estimation of unknown central aortic blood pressure waveform from a directly measured peripheral blood pressure waveform, in which a physics-based model is employed to solve for a subject- and state-specific individualized transfer function (ITF). The ITF provides the means to estimate the unknown central aortic blood pressure from the peripheral blood pressure. Initial proof-of-principle for the ITF is demonstrated experimentally through an in vivo protocol. In swine subjects taken through wide range of physiologic conditions, the ITF was on average able to provide central aortic blood pressure waveforms more accurately than a nonindividualized transfer function. Its usefulness was most evident when the subject's pulse transit time deviated from normative values. In these circumstances, the ITF yielded statistically significant reductions over a nonindividualized transfer function in the following three parameters: 1) 30% reduction in the root-mean-squared error between estimated versus actual central aortic blood pressure waveform (p < 10 (-4)), 2) >50% reduction in the error between estimated versus actual systolic and pulse pressures ( p < 10 (-4)), and 3) a reduction in the overall breakdown rate (i.e., the frequency of estimation errors >3 mmHg, p < 10 (-4)). In conclusion, the ITF may offer an attractive alternative to existing methods that estimates the central aortic blood pressure waveform, and may be particularly useful in nonnormative physiologic conditions.

A paired robot system is developed for a class of tasks where two end-effectors work together; one placed inside and the other outside a confined box. The work was motivated by practical needs for aircraft wing box manufacturing and maintenance. Two robots, each carrying an end-effector, are engaged using strong magnets attracting each other and thereby supporting each body against gravity. The robots must move across the surface of the box, while avoiding interference with obstacles fixed to the surface. A novel paired robot with magnetic feet is presented that can flip and go over an obstacle while tightly holding each body against gravity. Furthermore, the paired robots can automatically be loaded and unloaded from the confined box through a small entry hole by flipping and sliding on the box surface. First the task conditions and functional requirements are described, and then the design concept of the flip-and-slide magnetic paired robots is presented. Kinematic and static models of the system are obtained, and the conditions for successful flipping and sliding are analyzed. Control algorithms for detaching as well as engaging magnetic feet are obtained. A prototype flip-and-slide paired robot system is designed and the feasibility of the approach is demonstrated.

A highly maneuver able, compact vehicle for underwater precision inspection of complex structures is presented. The vehicle will have no appendages such as rudders, screws, and other external thrusters, which might get tangled and interfere with the underwater structure in a cluttered environment. A multi-axis, integrated thruster mechanism using Coanda-effect high-speed valves for switching the direction of jets can be encapsulated in a compact, egg-shaped body. Compared to traditional screw thrusters, these valves have improved dynamic performance in switching the jet stream direction. Furthermore, the reaction forces and moments due to switching can be substantially reduced. First, the principle of Coanda effect water jet valves is introduced, and its governing equations are obtained. Optimal dimensions and parameters producing a maximum of thrust are obtained, and are experimentally verified. Multiple Coanda-effect valves are then integrated into a tree structure to create a multi-axis thrust mechanism. A simple planar proof of concept prototype is built and tested.

Functional muscle tissue holds promise as a practical actuator for use in engineering applications. Previously, functional live-cell muscle actuators used for robotics have not scaled greater than about 10 μm, the size of a single monolayer of cells. We present a method to produce larger scale muscle actuators fully integrated into a mechanical structure. We use manufacturing techniques including printing a mold, pouring a molded part, and deposition of cell suspension. Our method allows for co-fabrication of actuator and mechanism through muscle self-assembly. We incorporate muscle construct technologies such that the muscle is fully 3D, anchored, and aligned, yielding a 10 mm long and 0.5 mm thick aligned muscle actuator. By co-fabricating the mechanism and actuators, the muscles are produced and used in the same environmental conditions, the process is more robust and repeatable, and evaluation of performance is under identical conditions to those in which the actuator is used. By using the presented method, variable geometry and multiple degrees of freedom can all be incorporated in a single mechanical structure.

A Remotely Operated Vehicle (ROV) is developed for use in the inspection of underwater structures in hazardous environments. The vehicle presented can change orientation like an eyeball using a novel gimbal mechanism for moving an internal eccentric mass. Combined with a pair of thrusters, the Eyeball ROV can move in any direction with non-holonomic constraints. In this paper the design concept is presented first, followed by dynamic and hydrodynamic analysis. Due to poor open loop stability characteristics, stability augmentation is implemented using onboard sensors and was designed and tested in simulation. A physical proof-of-concept prototype is also presented.

This paper presents an integrated stochastic approach to tracking multiple live cells that interact with the surrounding gel matrix. Cells migrate in a stochastic manner, forming a functional structure. Tracking the trajectory of each migrating cell and its interactions with the gel and other cells provide useful insights into how a vascular structure is formed as a collection of migratory cells. In micro-fluidic 3-D angiogenic sprouting experiments, two types of images are obtained at discrete time steps using confocal microscopy: a) three-dimensional fluorescent images of stained cell nuclei and b) two dimensional visible light images of the gel matrix. These two sources of images provide supplementary information as the outline of the conduit or lumen formed in the matrix by the migrating cells can be seen in the images of the gel. A Bayesian filtering framework is developed which augments both the cell and conduit parameters to the same state vector, allowing mathematically consistent simultaneous observation updates from both channels. Issues encountered include the high dimensional state vector and non-Gaussian cell state updates. Results demonstrate that our method based on Rao-Blackwellized particle filtering treats these issues effectively.

A pair of mobile robots acting on opposite sides of a thin plate is developed for a class of tasks where robots have to work together, carrying a pair of end-effectors and traversing across a plate surface. Using powerful magnets, the paired robots attract each other, support themselves against gravity, and generate traction force to move across the panel. First, the design concept of paired mobile robots is presented, followed by dynamic modeling and magnetic analysis. Conditions for preventing the robot from falling as well as from slipping on the plate surface are examined. Time-optimal control of the paired robots subject to the no-fall, no-slip conditions is formulated and solved numerically. Precision positioning control using a laser beacon is designed and tested. A prototype of the paired robots using Halbach array permanent magnets and Lorentz force actuators is developed, and the control methods are implemented and tested on the prototype.

A simple, under-actuated robotic winch, called the “Winch-Bot,” is developed for surface inspection of a large object. The Winch-Bot, placed over an object surface, has only one actuator for tracing a free geometric path in a vertical plane. The cable length is controlled in relation to the direction of the cable so that the inspection end-effecter hanging at the tip of the cable can follow the path dynamically despite the lack of full degrees of freedom. We analyze the tracing dynamics, address under what conditions a given geometric path can be traced (traceability conditions), and prove under what conditions the tracing motion is repetitive. A controller utilizing partial feedback linearization is proposed, and simulations are used to validate the explored traceability criteria and to confirm the controller's performance improvement.

Novel designs of an array of piezoelectric stack actuators using a unique buckling mechanism are presented in this paper. Multiple PZT actuator units with high gain displacement amplification mechanisms are arranged in parallel with spatial phase differences. Having an inherent kinematic singularity, the buckling mechanism provides not only an extremely high gain of displacement amplification, but also varying stiffness and nonlinear force-displacement characteristics. The phased array PZT actuator exploits this nonlinearity for gaining a large output displacement as well as for combining multiple PZT stacks in parallel without conflicting with each other. Three specific designs of arrayed buckling actuators are presented. The aggregate output force-displacement relationship is analyzed and its profile is shaped with respect to spatial phase differences and nonlinear stiffness and force characteristics of individual PZT buckling actuator units.

This paper presents new experimental results from a human-size robotic forearm, created to demonstrate the effectiveness of recruitment-based control architectures for large actuators made from shape memory alloys (SMA) and other active materials. The robot arm is actuated antagonistically by two actuators made up of 60 small SMA springs arranged in parallel, which are activated in an on/off fashion using Joule heating. The force and stiffness of each actuator is controlled by recruiting a desired number of springs to contract. The joint position is then controlled using equilibrium point servo control. The results presented in this paper show that the combination of equilibrium point control of the arm joint and recruitment-based control of each actuator's stiffness solve some of the major problems of scalability and response speed often associated with active material actuators.

Variable stiffness actuation and energy harvesting have been important yet separate challenges in robotics. Both functions are needed, however, for mobile robots on extended missions when actuators and generators must be used together. In this paper, we present a unique piezoelectric cellular system that combines motion generation and energy harvesting capabilities into a single, scalable device. Each of the discrete cellular units provides linear, contractile motion at 10% strain using the converse piezoelectric effect. These units may also be back-driven from environmental loading and thereby generate energy using the direct piezoelectric effect. Furthermore, each cell has the capability to toggle between a low stiffness ON state and a high stiffness OFF state, which allows an assembly of individual cells to tune both their static stiffness and structural resonant frequencies online. We demonstrate the effectiveness of our device for tuning both locomotion speed and the harvested power of an underwater flapping fin system.

A new approach to a variable stiffness actuator with tunable resonant frequencies is presented in this paper. Variable stiffness actuators have become increasingly important to meet safety requirements and achieve adaptive manipulation or locomotion. For cyclic motion, exploiting dynamic resonance can lead to high power transmission, high energy efficiency, and large motion amplitude. Resonance and variable stiffness characteristics have yet to be incorporated into a single actuator design. In this paper, a cellular artificial muscle actuator that achieves both variable stiffness and variable resonance capabilities is presented. The design is based on piezoelectric stack actuators. First, the principle of variable stiffness and variable resonant frequencies is described. The static and dynamic performance are then quantified with theoretical models. Theoretical analysis reveals that the proposed actuator can be tuned over a broad range of resonant frequencies by selectively turning specific units on or off. Initial prototypes are tested experimentally and exhibit 15% static strain, over 300% static stiffness tunability, and over 100% dynamic resonance tunability.

A simple, compact, yet powerful robotic winch, called ldquoWinch-Bot,rdquo is presented in this paper. The Winch-Bot is an underactuated robot having only one controllable axis. Although hanging a load with merely one cable, it is capable of moving it in a large workspace by swinging the load dynamically based on parametric self-excitation. The generated trajectories can be used for a variety of tasks, from moving material to cyclic inspection of surfaces. The basic principle and design concept of the Winch-Bot are first described, followed by dynamic modeling and analysis. Two trajectory generation problems are solved. One is point-to-point transfer of a load, and the other is the tracking of a continuous path. It will be shown that the system can track a given geometric trajectory, although the tracking velocity cannot be determined arbitrarily due to the underactuated nature of dynamics. A prototype Winch-Bot is designed and built, and point-to-point, continuous path, and parametric excitation control are implemented.

A passive mobile robot carrying a heavy manufacturing tool is activated from across a thin wall. The mobile robot placed within a confined space has no tether and no local battery, but is powered from an outside robot through magnetic coupling. A pair of magnetic feet allows the passive inside robot to hang from a ceiling and walk across a wall. A heavy manufacturing tool held in the middle of the passive inside robot is activated with a Lorentz force actuator-this is also activated from the outside robot. A set of Hall effect sensors on the outside robot detect the magnetic field created by the passive robot in order to estimate the position of the inside robot. First, the task conditions and functional requirements are described, and the design concept of the passive mobile robot is presented. An electro-magnetic model for predicting magnetic field strength and load bearing capacity is used to facilitate design as well as to estimate and control the position of the passive inside robot. A proof-of-concept prototype system is designed and built for application to aircraft manufacturing.

Buckling is a highly nonlinear and singular phenomenon in thin beams, and is usually an undesired characteristic that must be prevented from occurring in engineered systems. Buckling, however, can be a useful mechanism for gaining extremely large displacement amplification, since a tiny displacement in the axial direction of the beam may lead to a large defection in the middle of the beam. This paper presents a novel large-strain piezoelectric actuator exploiting the buckling of a structure with imbedded PZT stacks. Although the free displacement of a PZT stack is only 0.1% of the stack length, the buckling mechanism, controlled with an effective algorithm and strategically placed redirecting stiffness, can produce a large bi-polar displacement that is approximately 150 times larger than the original PZT displacement. Furthermore, the structural buckling produces a pronounced nonlinearity in output impedance; the effective stiffness viewed from the output port varies as a function of output displacement, which can be a useful property for those applications where actuator stiffness needs to vary.

A simple and efficient approach for varying the inherent stiffness and impedance of a muscle-like actuator is presented. The basic architecture of PZT cellular actuators has already achieved a large effective strain (10-20%). This architecture is modified and extended so that each cellular unit can be switched between a zero compliance state and constant compliance state. The effective stiffness of the cellular actuator is varied by changing the distribution of cellular units in the rigid versus compliant state. Furthermore, by placing a multitude of these cellular units in series or parallel, the stiffness can vary within a large set of discrete values. This paper also demonstrates the viability of the variable stiffness cellular actuator for cyclic tasks such as running and flapping. The basic principle and design concept for the actuator is described, followed by force-displacement analysis. A dynamic model is then constructed to demonstrate the variable resonance properties of the actuator under load.

A legged robot that moves across a steel structure is developed for steel bridge inspection. Powerful permanent magnets imbedded in each foot allow the robot to hang from a steel ceiling powerlessly. Although the magnets are passive, the attractive force is modulated by tilting the foot against the steel surface. This allows the robot to slide its feet along the surface using ¿Moonwalk¿ and ¿Shuffle¿ gait patterns. The robot can also detach its feet and swing them over small obstacles. These diverse walking patterns are created with a single servoed joint and 2 sets of simple locking mechanisms. Kinematic and static conditions are obtained for the under-actuated legged robot to perform each gait pattern safely and stably. A proof-of-concept prototype robot is designed, built, and tested. Experiments demonstrate the feasibility of the design concept and verify the analytical results.

A nonlinear feedback scheme for a gravity-assisted underactuated manipulator with second-order nonholonomic constraints is presented in this paper. The joints of the hyper articulated arm have no dedicated actuators but are activated by gravity. By tilting the base link appropriately, the gravitational torque drives the unactuated links to a desired angular position. With simple locking mechanisms, the hyperarticulated arm can change its configuration using only one actuator at the base. This underactuated arm design was motivated by the need for a compact snake-like robot that can go into aircraft wings and perform assembly operations using heavy end-effectors. The dynamics of the unactuated links are essentially second-order nonholonomic constraints for which there are no general methods to design closed-loop control. We propose a nonlinear closed-loop control law that is guaranteed to be stable in positioning one unactuated joint at a time. We synthesize a Lyapunov function to prove the convergence of this control scheme. The Lyapunov function also generates estimates of the domain of convergence of the control law for various control gains. The control algorithm is implemented on a prototype three-link system. Finally, we provide some experimental results to demonstrate the efficacy of the control scheme.

A new approach to the design and control of multi-fingered hands using hybrid DC motor - shape memory alloy (SMA) array actuators is presented in this paper. The fundamental design concept is based on the principle of motor control "synergy", a biomechanics terminology of coordinated motion generation. A couple of DC motors are used for driving multiple fingers with a particular velocity distribution over a vast number of finger joints corresponding to the direction of the most significant synergy. Principal component analysis is used for determining the most significant direction and the residual directions. SMA array actuators are used for driving the fingers in the residual directions. Although many actuator axes are needed for spanning the residual space, the required strokes are much shorter than the most significant direction. Compact and high energy-density SMA actuators meet these requirements. The paper presents synergistic integration of these two types of actuators having diverse characteristics. This allows us to embed all the actuators and transmission mechanisms in the palm, eliminating a bundle of tendons crossing over the wrist joints. An initial prototype hand is designed and built.

This paper presents algorithms for concurrent deployment of multiple links of a gravity-assisted underactuated robot arm. The joints of the hyper-articulated arm have no dedicated actuators, but are activated with gravity. By tilting the base link appropriately, multiple unactuated links may be steered simultaneously to desired angular positions. This underactuated arm design was motivated by the need for a compact snake-like robot that can go into aircraft wings and perform assembly operations using heavy end-effecters. The dynamics of the unactuated links are essentially 2ndorder non- holonomic constraints, for which there are no general control algorithms. We perform a controllability analysis to establish the feasibility of multi-link positioning using the available inputs, viz., the biaxial tilts of the base link. We propose a feed-forward control algorithm for simultaneous positioning of multiple links. We also propose an intermittent feedback control scheme to compensate for disturbances acting on the system. We built a 4 link prototype where the base is tilted using a Stewart Platform. The proposed control schemes are implemented on our prototype system. The experimental results indicate the efficacy of the control schemes.

This paper presents the dynamic analysis of an artificial muscle actuator designed for high-bandwidth, power-law strain amplification. The actuator is based on a nested cellular architecture of PZT stack actuators. Most smart material actuators have seen limited use in mobile robotic applications because of their small strain, low stress capacity, low bandwidth, and stringent input requirements. The proposed actuator design overcomes these limitations and can serve as a high-bandwidth multifunctional artificial muscle. The dynamic characteristics of the actuator design are derived analytically and validated experimentally. A test system mimicking flapping flight is then used to illustrate the actuator dynamics.

A static lumped parameter model is proposed for the design and analysis of nested piezoelectric cellular actuators with exponential strain amplification mechanisms. Piezoelectric ceramic material, such as Lead Zirconate Titanate (PZT), has large stress and bandwidth, but its extremely small strain, i.e. only 0.1%, has been a major bottleneck for broad applications. We have proposed a "nested rhombus" multi-layer mechanism for PZT actuators, which increases strain exponentially through its hierarchical cellular structure, for over 20% effective strain. To drive a large load, however, care must be taken in the design of the strain amplification structure. Through kinematic and static analysis this paper addresses how the output force and displacement are attenuated by the joint stiffness and beam compliance involved in the strain amplification mechanism. An insightful lumped parameter model is developed to quantify the performance degradation and facilitate design trade-offs. A prototype nested PZT cellular actuator that weighs only 15 g has produced 21% effective strain (2.49 mm displacement from 12 mm actuator length) and 1.7 N blocking force.

Precise robot positioning is important for many applications in indoor environments. Current solutions to the indoor localization problem are either both unreliable and inaccurate, or very expensive. In this paper we propose, design and build a low-cost, robust and accurate indoor localization system using laser light sources. The system calculates the coordinates of a robotic arm by using triangulation algorithms with precisely measured values of the angles of the receiver with respect to the three laser emitters. A system of three rotating lasers and receiver unit was built and deployed in the wing of an aircraft. Using this system, a robotic arm could be localized accurately within error margins defined approximately by Gaussian distributions centered at the object’s true coordinate values and with standard deviations of 0.19 mm, 0.11 mm and 0.34 mm in the x, y and z coordinate directions respectively. The system was also used to detect vertical drop in the robotic arm due to its weight as it extends to perform fitting operations on the skin of the wing. Feedback from the laser localization system was used to adjust the position of the tip of the robotic arm in order to perform a sequence of high precision docking tasks within the aircraft wing

We present an initial design of a mobile robotic system for automated assembly inside an aircraft body. This system allows for the positioning control of a heavy duty end effector that is working on the far side of a thin wall at any orientation. It utilizes electromagnets to hold the end effector against the wall, as well as linear motor type actuation for locomotion. Initial testing on a prototype verifies the effectiveness of some of the chosen design parameters.

This paper presents a lightweight robotic hand that uses an SMA actuator array. The SMA wires are activated via joule heating, implementing SBC. A coordinate transformation architecture which reduces activation signal dimensionality, known as C-segmentation, is presented. A robotic hand with 16 controlled DOF and 32 independent SMA axes was developed to demonstrate the advantages of joule-heated SBC; the total weight of the robotic hand system was less than 800 grams. 16 different grasping postures were successfully recreated by using only 8 C-segments. It was concluded that a very lightweight robotic hand with simple controls can effectively reproduce the necessary configurations for conventional grasping situations.

This paper presents a control architecture for artificial muscle materials such as shape memory alloys and polymer actuators. The active material is broken up into many small independent cells that can be regulated in a binary fashion into ON and OFF states, so that the actuator displacement is determined by the number of ON cells. In order to control the number of cells that contract, a novel closed loop feedback control method is employed. Each cell is given a small stochastic finite state machine that governs its transition between ON and OFF states. A central controller globally varies the probabilistic rate with which all of the cells make state transitions. Using this architecture, actuator displacement can be controlled in a stable, robust fashion. Different feedback laws are compared using the fixed policy value iteration algorithm to calculate expected settling time in response to a step reference. A simple law based on calculating expected future behavior is found to be very close to the optimal law computed using the value iteration algorithm. The performance of the control laws is verified on a 50 cell shape memory alloy cellular actuator.

This paper describes the design and analysis of a humanoid foot constructed using polypyrrole (PPy) conducting polymer (CP) actuators. The compliance and damping of natural muscles plays an important role in natural human gait. Conducting polymers actuators and other smart structure actuators can store energy by means of inherent mechanical compliance that traditional DC motor actuators do not possess. This paper presents a method for optimizing the inherent compliance and damping of the actuators in order to minimize the active control effort required to generate a natural human gait. A simplified kinematic model of the design is evaluated using biomechanical joint angle and ground reaction force (GRF) data to yield the desired force versus displacement characteristics of the posterior and dorsal actuators. Numerical simulations illustrate the multifunctional nature of the PPy actuators and the overall power requirements of the system during the stance phase of walking gait.

In this paper, the concept of broadcast feedback for stochastic cellular control systems is expanded to a system with nonuniform cellular length and nonuniform transition probability. The cellular control architecture was originally inspired by skeletal muscles comprising a vast number of tiny functional units, called sarcomeres. The output of the actuator system is an aggregate effect of numerous cellular units, each taking a bistable ON-OFF state. A central controller broadcasts the error between the aggregate output and a reference input. Rather than dictating the individual units to take specific states, the central controller merely broadcasts the overall error signal to all the cellular units uniformly. In turn each cellular unit makes a stochastic decision with a state transition probability, which is modulated in relation to the broadcasted error. Stability conditions of the broadcast feedback system are obtained by using a stochastic Lyapunov function. It is demonstrated that, even in the presence of the distribution of the cell length and/or the distribution of the transition probability generated in each cell, the aggregate output of the cellular units can track a given trajectory stably and robustly.

Human hands employ characteristic patterns of actuation, or synergies, that contain much of the information required to describe an entire hand shape. In some cases, 80% or more of the total information can be described with only two scalar component values. Robotic hands, however, commonly only couple intra-finger joints, and rarely take advantage of this inter-finger coordination. In this paper, real-world data on a variety of human hand postures was collected using a data glove, and principal components analysis was used to calculate these synergies, resulting in what we call eigenpostures. A novel mechanism design is presented to combine the eigenpostures and drive a 17-degree-of-freedom 5-fingered robot hand. The hand uses only 2 DC motors to accurately recreate a wide range of hand shapes. We also present a design improvement that allows us to distinguish between high-precision and low-precision tasks, as well as greatly reduce overall error.

The demand for high-force and compact actuators with large strain is increasing in robotics. PZT is known as one of the promising materials for this purpose with respect to bandwidth, stress, and reliability. However, the most critical drawback of PZT is its extremely small strain, i.e. only 0.1 %. This paper presents a nested rhombus structure for strain amplification of PZT stack actuators. This structure provides a "power-law" strain amplification, resulting in over 20 % strain, which is particularly useful for gaining a large strain in a compact body, appropriate for many robotic applications. The notational convention and fundamental force-displacement analysis will be presented. In addition, the feasibility of the design concept will be addressed through the design of a proof- of-concept prototype.

This paper presents a cellular actuator design for a robotic hand. Although the motions of robotic hands are complex, a design of cellular actuator segmentation can be simplified by extracting the features of given postures and using them to design and control the actuator. A method of using captured hand posture data to design the actuator segmentation is proposed. Data from the eight most frequently used hand grips in a daily living, as defined in the sollerman hand function test, is used in this design. The gathered joint angle data is transformed into actuator displacement data and used to generate a segmentation design of the actuator. For segmentation design, feature extraction method, called non-negative matrix factorization with constraints is proposed. The actuator system has 12 SMA actuators each with eight segments, resulting in 96 configurable segments before the coupled segmentation design is applied. The coupling segmentation design effectively groups the segments into clusters which are simultaneously controlled. The segmentation design reduces 96 separately controlled segments to 8, while maintaining the ability to accomplish all desired postures. A robotic hand with five fingers, designed and fabricated using the FDM process, is driven with this actuator system, and eight hand postures are reproduced with the robotic hand

We propose a novel concept for the actuation of a hyper-articulated robot arm for assembly operations inside an aircraft wing-box. Traditional electromechanical actuators powering individual joints are unsuitable for our purpose, because of limited space and large payload requirements. We propose an underactuated system which uses a single actuator at the base for the deployment of a multi d.o.f. serial linkage structure. Our proposed system exploits gravitational and gyroscopic torques in the system dynamics to rapidly deploy the system. There are no general techniques for the control of such underactuated systems. We develop and compare two approaches for determining the input required for a desired output trajectory and verify the results through simulation and experiments

A broadcast-probability approach for the coordination of a vast number of actuators is proposed. We consider an actuator that consists of many "cellular" actuator units like human muscles. Each local unit has a decision-making unit which decides whether to accept or ignore the broadcasted control signal in a stochastic manner. We demonstrate through simulation that centralized coordination is unnecessary, and redundancy and randomness of the system improve the performance

A new approach to artificial muscle actuator design is presented, and is implemented using shape memory alloys (SMA). An array of SMA actuators is segmented into many independently controlled, spatially discrete volumes, each contributing a small displacement to create a large motion. The segmented cellular architecture of SMA wires is extended to a multiaxis actuator array by arranging the segments in a two-dimensional (2-D) array. The multiaxis control is streamlined and coordinated using a 2-D segmentation method in order to activate multiple links of a robot mechanism in a coordinated manner. The basic principle of segmented binary control (SBC) is first presented, followed by multiaxis segmentation theory and a design procedure. The method is applied to a five-fingered robotic hand capable of taking a variety of postures. A 10-axis SMA actuator array is built, and SBC is implemented using Peltier-effect thermoelectric devices for selective local heating and cooling. Experiments demonstrate the feasibility and effectiveness of the new method.

A novel multi-axis Shape Memory Alloy (SMA) array actuator has been developed for driving five-fingered anthropomorphic robot hand. The new actuator array uses Segmented Binary Control (SBC), which controls the SMA wires segment by segment in a digital manner. Normally, SMA wires are hard to control and require nonlinear controllers to control each wire. SBC simplifies the control of SMA wire but increases the complexity of the design and the number of control loops. A multi-axis segmentation theory has been developed to reduce the design complexity and the number of control loops by reducing the number of segments. Segmentation architecture of an actuator array is designed for five-fingered robotic hand that performs fourteen different postures. The segmentation architecture is implemented with ten SMA wires sandwiched between a layer of thermoelectric modules embedded on a printed circuit board and a layer of acrylic substrate board with grooves. Initial results of the segmented binary controlled SMA wire are verified with minimum segment architecture of a single axis.

We present a design concept and two initial prototypes of a robot arm for assembly operations inside an aircraft wing-box. The wing-box has a large span, but is only accessible through multiple small portholes along its length. The arm is compact enough to enter the wing-box through the small portholes and is capable of subsequent reconfiguration so as to access a number of assembly points inside the wing-box. Traditional electromechanical actuators are unsuitable for our purpose, because of limited space and large payload requirements. We use an actuator module comprising Shape Memory Alloy (SMA) wires, which are known for their high stress to volume ratio. Our design also addresses the issue of limited strain of SMA wires through a displacement amplification mechanism. Our compact, high displacement actuator module can be readily integrated into the structure of the robot arm. We also discuss a deployment scheme for the robot arm, which eliminates gravity loading during the reconfiguration phase, and also helps to position the end effecter at the various assembly points inside the wing-box.

This paper describes a new approach to the control of highly nonlinear shape memory alloy (SMA) actuator systems, in which SMA wires are divided into many segments and their thermal states are controlled individually as a group of finite state machines. Instead of driving a current to the entire SMA wire and controlling the wire length based on the analogue strain-temperature characteristics, the new method controls the discrete state (austenite or martensite) of individual segments and thereby controls the total displacement proportional to the number of the austenite segments. Although the inherent property of SMA is highly nonlinear and uncertain with a prominent hysteresis, this Hysteresis Loop Control is robust and stable, providing characteristics similar to a stepping motor. Furthermore, this method can apparently eliminate the latency time associated with phase transition of SMA actuators. Coordination of the multitude of segments having independent thermal states allows for fast response with zero latency time even for thick SMA wires. The new control method is implemented using the Peltier effect thermoelectric devices for selective segment-by-segment heating and cooling. Experiments demonstrate effectiveness of the proposed method, which exploits the inherent hysteresis and nonlinearity of SMA rather than compensating for the nonlinearity.

We propose a novel concept for the actuation of a hyper-articulated robot arm for assembly operations inside an aircraft wing-box. The wing-box has a large span, but is only accessible through multiple small portholes along its length. The arm should be compact enough to enter the wing-box through the small portholes, yet capable of subsequent reconfiguration so as to access a number of assembly points inside the wing-box. Traditional electromechanical actuators powering individual joints are unsuitable for our purpose, because of limited space and large payload requirements. We propose an underactuated system which uses a single actuator at the base for the deployment of a multi d.o.f. serial linkage structure. Our proposed system exploits gravitational and gyroscopic torques in the system dynamics to rapidly deploy the system. We develop a methodology for determining the input required for a desired output trajectory and verify the results through simulation.

In recent years, wearable sensing networks have been the focus of the biotechnology industry. A continuing the question is how best to integrate electronic components with the human body. The authors have devised a body area network that relies on two innovations; the use of conductive fabrics, and the use of DC powerline communication. By combining these innovations, we have created a truly wearable network that allows full generality of sensor location, spatial distribution of the medium to reduce overall bulk, and maintains sufficiently low line impedance for simultaneous power and data delivery over a single conductor. We have created a method for analysis of the transmission properties of conductive fabric garments. In addition, we evaluate the basic transmission line characteristics of the garment. Finally, we present a verification of our model and initial experimental results.

A new method for repositioning a rigid body with a flexible sheet is developed and is applied to a rehabilitation bed for turning and transferring a bedridden patient to alleviate bedsores and other ailments. The patient position and orientation are fully controlled by manipulating a flexible bed sheet under no-slip conditions. The use of a flexible sheet and the untethered nature of manipulation make the repositioning method particularly well suited to handling the human body. First, the basic design concept of the rehabilitation bed for automated patient repositioning is presented. The kinematic and static behaviors of body-sheet interactions are analyzed, and conditions for no-slip, quasi-static repositioning are obtained. In order to prevent injury to the patient's fragile skin, it must be ensured that the patient does not slip on the sheet during repositioning. A prototype bed with a pair of servoed arms for manipulating the bed sheet is developed, and the no-slip conditions and the repositioning method are experimentally verified. A closed-loop control based on the measurement of a patient's position and orientation is implemented and tested. Note to Practitioners-This work was motivated by the problems faced by bedridden patients as well as caregivers in the healthcare industry. The labor-intensive repositioning and transfer of bedridden patients are performed with a robotic system supervised by a single caregiver. Our repositioning scheme uses the bed sheet for rolling and moving the patient and closely mimics the current practice prevalent in nursing homes and hospitals. Our approach will be a natural alternative to manual repositioning and transfer and will be acceptable for most caregivers and patients. Initial prototyping and experiments have been completed in consultation with a professional caregiver.

Long hours of driving cause the tissues to be pressurized for an extended period and result in considerable discomfort and driver fatigue. Periodically stimulating the tissues in contact with the car seat, as well as providing adequate ventilation and pressure relief may alleviate these problems. In this paper, we describe the design of a robotic car seat capable of actively redistributing the contact pressure on the tissue and thus providing relief to the weary driver. The distributed nature of the surface actuation and space limitations necessitate the use of a large number of actuators that must be confined to a small volume. We design and use Shape Memory Alloy actuator units, which can accomplish the above goals by virtue of their high power to weight ratio. Matrix architecture is used for the drive amplifier that can drive N/sup 2/ actuator units using only 2N switches and is thus suitable for vast degree of freedom systems in terms of scalability. The prototype car seat uses 16 SMA actuator units, which are driven in a matrix architecture using 8 switches. The actuators are compactly housed under the car seat and the force and displacements are transmitted to the flexible seat surface through a novel routing scheme. We create a distributed lifting motion of the seat surface in order to stimulate the tissue. A complementary distributed sinking motion of the seat surface is created in order to provide pressure relief and ventilation.

This paper describes a technique that uses conductive fibers as part of a wearable sensor for continuous monitoring of joint movements. Conductive fibers are incorporated into flexible fabrics that fit tightly around a joint, and resistance changes in the fibers caused by skin extension can be measured, and related to joint motion. An overview of the sensor design, including functional requirements and design parameters, are presented, as well as preliminary results from a prototype sensor design. A single-axis joint model is also presented to illustrate the implementation of an extended Kalman filter to estimate joint angle. The Kalman filter also estimates parameters associated with misalignment errors that may be created every time the subject takes off and puts on the wearable sensor, allowing a sensor to be calibrated only once, with no need for re-calibration for all future uses.

A new approach to the design and control of shape memory alloy (SMA) actuators is presented. SMA wires are divided into many segments and their thermal states are controlled individually in a binary manner. The Peltier effect is used for heating and cooling individual segments of the SMA. Unlike the traditional way of controlling the wire length by driving a current to the entire SMA wire, the new method controls the binary state (hot or cold) state of each segment. The total displacement is then proportional to the number of the segments having the heated state, i.e. austenite phase. This architecture has three salient features, which would overcome fundamental difficulties of SMA. 1) Although the inherent property of SMA is highly nonlinear and uncertain with a prominent hysteresis, the binary state/phase control does not depend on the complexity of SMA state transition. 2) With use of the Peltier effect thermoelectric devices the response of SMA becomes more controllable, stable, and more accurate compared to the traditional air cooling and electric wire heating. 3) By operating at the heated state, SMA shows considerable load disturbance rejection compared to traditional methods. First, the basic principle and architecture of the segmented SMA actuator system are described. Initial implementation and feasibility tests are then presented, followed by discussion of the experimental results.

A wearable DC power line communication network is proposed for health sensing and rehabilitation. This system provides a network through which multiple sensors and actuators can send and receive both information and power. With such a network, sensors placed at many remote locations on the human body can send and receive information to a centralized power/data coordinator. This system consists of three main components: (1) the centralized power/data coordinator which coordinates communication among the nodes, (2) smart sensors and actuators, which have some localized data processing, and (3) the communications bus, which consists of two electrical conductors. The system operates using a two-tiered protocol, which relies on both polling and prioritization. During normal operation, the centralized coordinator constantly polls the sensors and actuators, obtaining biological information; When an emergency signal is generated by one of the nodes, it immediately notifies the central components, which in turn notify an Internet provider in order to alert a doctor, paramedic, or other safety personnel. First, a unique DC power line communication system is reviewed. Next, the details of our wearable DC power line communication network is discussed. Next, the design process for such a system is discussed in terms of the medium type and the number of sensor nodes in the network. Finally, a preliminary design of the proposed system is presented.

A new approach to artificial muscle actuators assimilating the morphological and kinesiological structure of biological muscles is presented and is implemented using shape memory alloys. Like a biological muscle consisting of short muscle fibers arranged in an overlapping series, an array of SMA actuators are segmented into many independently controlled, spatially discrete volumes, each contributing a small displacement to create a large motion. Furthermore, the segmented architecture of SMA wires is extended to a multi-axis actuator array by arranging them in a two-dimensional array. The multi-axis control is streamlined and coordinated using a two-dimensional segmentation method in order to activate multiple bones (links) of a skeletal robot structure in a coordinated manner. Moreover, the 2-D segmentation is so designed that coordinated gross motion as well as independent fine movements may be generated with minimum complexity and minimum control loops.

When the human fingertip is pressed against a surface or bent, the hemodynamic state of the fingertip is altered due to mechanical interactions between the fingernail and bone. Normal force, shear force, and finger extension/flexion all result in different patterns of blood volume beneath the fingernail. This phenomenon has been exploited in order to detect finger forces and finger posture by creating a photoplethysmograph "fingernail sensor," which measures the two-dimensional pattern of blood volume beneath the fingernail. In this paper, a filter is designed to predict the normal force, lateral shear force, longitudinal shear force, and bending angle based on readings from the fingernail sensor. Linear, polynomial, and neural network models relating the bending angle and touch forces to optical sensor outputs are developed and tested. A method is developed to uniformly calibrate the predictor for each user. Calibration experiments are performed to train and validate the predictor for seven human subjects. Results show that on average, shear forces can be predicted with 0.5 N root mean square (rms) error, normal force with 1 N rms error, and posture angle with 10 degrees rms error. Applications and methods for improving performance are discussed.

Traditionally, a dedicated power amplifier is used for driving each actuator. For a system with a large number of actuator, this one-to-one architecture may be inefficient and costly. This paper presents a new, scalable architecture, called networked actuation architecture, for the power drive and control of large-scale actuation systems. The networked actuation architecture allows sharing of the drive amplifiers among many actuators, and thereby reducing the number of the drive amplifiers and wiring requirements. Since several actuators are sharing a drive amplifier, traditional control algorithms are not applicable. Several new control algorithms for large-scale actuation are presented and compared. Simulation is performed for different types of control algorithm for different types of inputs.

A new type of actuator is presented where shape memory alloy (SMA) wires are embedded within artificial "blood vessels." Fluid flowing through vessels allows the SMA wires to be rapidly cooled by convection, resulting in greater bandwidth than ordinarily possible. Combinations of electric, fluidic, and thermal inputs can be used to control the contraction/extension of the SMA wires within the compliant vessels. These wet vascular SMA actuators can be used as robotic muscle or even embedded in a compliant rubber material to create an active vasculated robotic flesh. This paper begins by proposing a type of biomimetics where robots and machines are imbued with a vasculature or network of blood vessels. The concept of a wet SMA actuator is then introduced as an immediate application of a vasculated robot. A wet SMA actuator is then designed and implemented. Initial prototypes are 3 mm in diameter and are capable of 2% strain at 2 Hz by pulsing 2 A of current and 3 mL/s of water. Reservoirs of hot and cold water are also used to recycle the thermal energy and allow the actuators to exert static force with no electric current. Finally, multiple vascular SMA actuators are imbedded within a 4 mm thick rubber sheet to implement the active vasculated robotic flesh.

The marionette bed presents a new method for rolling and repositioning a bedridden patient using a pair of actuated rollers attached to both sides of the bedsheet in order to lift and manipulate the patient body. This prevents development of painful bedsores and of pneumonia. This paper builds a simple kinematic model to create trajectories for generation of desired body motion. It also addresses a closed loop control strategy, based on patient position and orientation feedback, for the marionette bed. Closed loop control provides flexibility and safety in the various modes of operation of the bed. The bed can now handle patients of various sizes when supplied with some parameters. The safety of the patient is also ensured because the position and orientation is continuously monitored. A prototype is built and initial experiments demonstrate that a human body is rolled and manipulated by the assist device, as desired.

A novel material transport and handling system utilizing simultaneous information and power delivery is proposed. This system provides a convenient and unobtrusive method of sending documents, specimens, and material to multiple locations within a single building. It consists of a fixed track, central controller, central power supply, and multiple 'smart-carriers'. By using a fixed track, the system can be placed out of the way of normal ground level activity. The system allows for horizontal, as well as vertical travel. The 'smart-carriers' carry parcels along the tracks to and from various locations at the user's command. The 'smart-carriers' each have their own onboard micro-modem and controller. The track itself delivers the power and information signals to the smart-carriers. This design allows for a very simple and flexible system. Equation reduction was used to model a generic system with "n" smart carriers. Next, a powerline communication system was built and tested to evaluate the characteristics of the track. Protocols for communicating between the centralized controller and the carriers are introduced. Finally, a preliminary design of the proposed system is presented.

A new concept for an actuator array is presented where a vast number of actuators are contained within a small volume and are controlled in a scalable sense. This vast degree-of-freedom system utilizes an array of shape memory alloy wires embedded within a network of fluidic vessels. A matrix manifold and valve (MMV) system routes fluid from hot and cold reservoirs in order to control an array of N/sup 2/ SMA actuators using only 2N valves. A prototype MMV system containing a 4 by 4 array of wet SMA actuators is designed and implemented. Control strategies suitable for controlling MMV system that uses 2N valves to control N/sup 2/ actuators are presented. Two different protocols are presented and evaluated. The system error increases without bound under certain input conditions, since all the actuators cannot be activated at the same time. Simulations show that system error starts to go out of bound when the individual actuator is activated 25% of the time for the 4 by 4 arrays of the actuators.

A new method for manipulation of a rigid body with a flexible sheet is presented, and the method is applied to repositioning of bedridden patients. A key feature of the proposed system is that the body is not securely connected to the sheet and the contact region between the body and the sheet changes dynamically during manipulation. The use of a soft flexible sheet and the untethered nature of manipulation, makes the system particularly well suited to handling the human body. We present an application to a rehabilitation bed for repositioning a bedridden patient to alleviate secondary ailments such as bedsores. In order to prevent injury to the patient's fragile skin, it must be ensured that the patient does not slip on the sheet during repositioning. We model the system and present a no-slip condition based on system parameters. The model is used to develop a closed loop control strategy for coordinating the motions of multiple actuators of the prototype bed. The prototype bed can successfully reposition test subjects using the control strategy developed.

A system of networked smart motors is developed to reduce complex cable harnesses. Motor control signals are sent over the DC power bus line and receiver by motors with integrated power amplifiers and controller. Unlike traditional AC power line communication, the noise level and signal attenuation are much lower for the DC power bus communication. This allows for high fidelity, broadband communication among many smart motors without bulky, costly cables. A modem is designed to exploit the features of the DC power bus communication. Experimentation is done to verify that the DC bus line is indeed useful for communication. An experimental setup was developed to identify the noise spectrum and signal transmissibility of the consolidated power-signal line. Optimal carrier frequency and filter parameters are then obtained based on the experiments.

A design for rolling and repositioning a bedridden patient is presented. A pair of actuated rollers are attached to both sides of the bedsheet in order to lift and manipulate the patient body, like a marionette. The patient is gently supported on a hammock-like active bedsheet, creating virtually no shear forces on the patient body. Therefore, the patient can safely and easily be maneuvered with minimal physical assistance! by the caregiver. This prevents development of painful bedsores and of pneumonia. In the paper, functional requirements and design issues are addressed, followed by the basic design concept, mechanism, and control strategy. A prototype is built and initial experiments demonstrate that a human body is rolled and manipulated by the marionette device, providing proof of concept. A simple kinematic model is built to create trajectories for generation of desired body motion. Extended functionalities including bed-to-chair and bed-to-bed transfers, are described at the end.

When the human fingertip is pressed against a surface or bent, the hemodynamic state of the fingertip is altered due to mechanical interactions between the fingernail and bone. Normal force, shear force, and finger extension/flexion all result in different patterns of blood volume beneath the fingernail. This phenomenon has been exploited in order to detect finger forces and finger posture by creating a photoplethysmograph "fingernail sensor," which measures the two-dimensional pattern of blood volume beneath the fingernail. In this paper, a filter is designed to predict the normal force, lateral shear force, longitudinal shear force, and bending angle based on readings from the fingernail sensor. Linear, polynomial and neural network models are proposed as candidates for the predictor framework. A method is developed to uniformly calibrate the predictor for each user. Calibration experiments are performed to train and validate the predictor for seven human subjects. Results indicate that a simple linear model performs best, predicting shear forces with an average of 0.5 N r.m.s. error and normal force with an average of 1.0 N r.m.s. error.

A system of multi-axis networked smart motors is developed to reduce complex cable harnesses. Motor control signals are sent over the DC power bus line and received by motors with integrated power amplifiers and controllers. The noise level and signal attenuation are low, allowing for high fidelity, broadband communication among many smart motors without bulky, costly cables. A modem is designed to exploit the features of the DC power bus communication. A power-signal coupling circuit with an impedance trap filter is designed for superimposing control signals over the DC power bus line with a maximum of signal transmissibility and reduced line noise. An experimental setup was developed to identify the noise spectrum and signal transmissibility of the consolidated power-signal line. Optimal carrier frequency and filter parameters are then obtained based on the experiments. A simple protocol for bi-directional communication between the motors and the central controller is designed and tested. Finally, the design of a joint undergoing continuous rotation is proposed utilizing the consolidated power-signal cable connected to endlessly spinning smart motors.

This article explains a modeling methodology of human physiology. An agent-based approach to a physiological digital human is proposed, and its design concept and architectural framework are discussed. The modeling is based on two types of agents: stationary agents which model human physiology, and mobile agents that model parameter interaction between the user and the human physiological model. The human thermoregulatory system is chosen as an example of model functions. A Java-based agent system is shown as an implementation of the model.

A new source coded modulation algorithm optimizing the energy efficiency in information transmission is presented. Wireless communication devices transmit nonuniform-probability messages using nonuniform-energy signal sequences. Hence, energy-optimal information transmission can be achieved by representing higher-probability messages by lower-energy signal sequences. In this paper, first this source coded modulation problem is formulated and an optimization algorithm for designing energy-optimal modulation systems is proposed. Then, a new sub-optimal source coded modulation algorithm achieving energy efficient information transmission at a reduced system complexity is introduced. Finally, extensions of this algorithm are investigated for improving the energy efficiency.

A servomotor design that is powered and controlled through only one wire is presented. A traditional servomotor needs both a power cable and a control cable connecting the motor to a control amplifier. Cables are bulky, heavy, and expensive and, more importantly, difficult to install and maintain in many applications. Particularly for multi-axis applications, like robots and machine tools, cable harnesses become thick and long, and are difficult to run through a stack of many axes, this is a major burden and bottleneck in electromechanical drives. The objective of this research is to eliminate such bulky cables by integrating and consolidating power cables and signal cables into a single wire, and transmitting control signals through the signal wire. Signals are coded by using a CDMA protocol and are superimposed on the single wire that supplies a DC voltage to each motor. In the paper first the principle of reduced-cable smart motors is described, followed by the architecture of the signal transmission system using direct sequence spread spectrum. A prototype system is designed, and the signal transmission line is simulated to verify the principle.

A new method for measuring both the posture of human fingers and shear force at human fingertips is presented. Instead of using a traditional electronic glove with bending sensors embedded along the finger and shear sensors embedded beneath the fingertip, a wearable fingernail sensor is used to measure resulting changes in coloration of the fingernail. Since the sensor is mounted on the fingernail, finger posture can be measured without wearing a glove that hampers the motion of the fingers. Similarly, shear forces can be measured without covering the finger pad and obstructing the human's natural haptic sense. In the past, fingernail sensors with a one-dimensional array of photodetectors have been used to measure normal touching forces at the fingertip. A new fingernail sensor with a two-dimensional spatial array of photodetectors is constructed in order to measure finger posture and shear forces. Experiments are performed in order to measure the outputs of the photodetectors in response to changes in finger posture and applied normal and shear forces. Analysis is then performed to correlate the outputs to the inputs and provide a means of estimating normal forces, shear forces, and changes in finger posture.

A new type of touch sensor for detecting contact pressure at human fingertips is presented. This new sensor allows the fingers to directly contact the environment without obstructing the human's natural haptic senses. The finger touch force is detected by measuring changes in the coloration of the fingernail; hence the sensor is mounted on the fingernail rather than on the fingertip. Specifically, the fingernail is instrumented with miniature light emitting diodes (LEDs) and photodetectors in order to measure changes in the reflection intensity when the fingertip is pressed against a surface. The changes in intensity are then used to determine changes in the blood volume under the fingernail, a technique termed "reflectance photoplethysmography". A hemodynamic model is used to investigate the dynamics of the blood volume at two locations under the fingernail. A miniaturized prototype nail sensor is designed, built, and tested. The theoretical analysis is verified through experiment and simulation.

A unified approach to general constraint motion control is presented. Robotic systems interacting with the task environment having complex dynamics are described as a set of state equations and algebraic constraints; the former represents the dynamics of the individual robots and task processes, and the latter describes the constraints and boundary conditions created by the interactions among the robots and the task processes. The resultant mathematical model of the constrained system is high-index differential-algebraic equations (DAE). This paper provides a powerful solver for this class of high-index DAE by using sliding mode control and singular perturbation theories. The singularly perturbed sliding manifolds method guarantees computational stability and accuracy. A numerical example illustrates the modeling and realization procedure and its computational performance.

A method of detecting human mistakes and misperception for assisting humans in operating complex systems is presented. The method is developed in the context of operating iPASS (Integrative Physical Assists and Seamless Services) system which provides a patient diverse physical aids without changing equipment. The system can serve as a bed, a walker, a stand-up and seating assistance, as well as a wheelchair. iPASS needs special care for its operations because human mistakes and misperception might lead to serious consequences such as injury and costly repair. In order to detect human mistakes and misperception in a human motion, it is important to monitor a human motion and to understand human intention. In this paper, processes of human perception and motion are treated as stochastic processes, and they are modeled by using hybrid hidden Markov models. Finally, an application of this method to stand-up assistance for iPASS is described.

Advancements on a new type of touch sensor for detecting contact pressure at human fingertips are presented. A fingernail is instrumented with miniature LEDs and photodetectors in order to measure changes in the nail color when the fingertip is pressed against a surface. The fingernail sensor allows the fingers to directly contact the environment without obstructing the human's natural haptic senses. Reflectance photoplethysmography is used to measure the pattern of nail color, i.e., the blood content under the fingernail. Hemodynamic modeling, based on actual fingertip anatomy and physiology, is used to investigate the dynamics of the change in blood volume at multiple locations under the fingernail. An optical model is created to relate the blood volume to the light intensity measured by the photodetectors. The theoretical analysis is verified through model simulation and experimentation using a prototype fingernail sensor.

Natural surface waves, created by periodic circular motion of material particles, can transfer a long object placed upon the crests of the waves in an arbitrary direction within the horizontal plane. Inspired by this natural behavior, a surface wave distributed actuation method and its potential for transporting bedridden patients is explored in this paper. First, the basic principle of surface wave distributed actuation is presented, followed by kinematic modeling and analysis. Based on the analysis, modifications to natural wave transport are made to enhance transport efficiency and human comfort. Further kinematic analysis reveals that an object can be transferred by a simplified actuator architecture that makes the concept amenable to hardware realization. Finally, design trade-offs and guidelines for developing a feasible and practical surface wave bed are discussed based on the prototyping and experiments.

This paper presents kinematic and dynamic analysis of a holonomic vehicle with continuously-variable transmission. Four ball wheels, independently actuated by DC motors, enable for moving the vehicle in any direction within the plane and rotating it around its center. The angle between the two beams holding the balls can be changed to alter the gear ratio and other dynamical characteristics of the vehicle. This feature is exploited in augmenting the vehicle stability, optimizing output power, selecting an appropriate gear ratio, and in impedance matching. A simple adaptive friction-compensation-based controller is proposed to handle the complex friction properties.

A surface wave distributed actuation method and its potential for transporting bedridden patients is explored. First, the basic principle of surface wave distributed actuation is presented, followed by kinematic modeling and analysis. Based on the analysis, modifications to natural wave transport are made to enhance transport efficiency and human comfort. Further kinematic analysis reveals that an object can be transferred by a simplified actuator architecture that makes the concept amenable to hardware realization. Two proof-of-concept prototypes are designed, built, and tested. The first is a powered water bed consisting of a water vat, a flexible mat placed on the water surface, and an exciter creating surface waves at resonant frequencies. The other is a powered mechanical bed having an array of coordinated active nodes that generate psuedo-continuum surface waves. Experiments demonstrate the surface wave actuation concept and verify the analytical results.

A new mechanism for transporting a bedridden patient in an arbitrary direction while lying comfortably on the bed is developed. A wave-like periodic motion is generated on a mattress surface by activating the individual coil springs which constitute the mattress. The whole or part of the patient body is moved by this periodic surface movement. Varying the periodic trajectory and coordination pattern yields various movements of the patient, i.e. translation and rotation of the whole body, changing the posture of the limbs, etc. First, functional requirements for active mattresses are provided, and a prototype system is designed and built. A variety of control algorithms are developed for moving a patient in various ways. Periodic trajectory and coordination patterns are designed in order to move the patient smoothly despite uncertainties in load distribution and actuator dynamics. A discrete-event control system using a Petri net is developed for coordinating and synchronizing many axes of motion. Furthermore, a high-level controller is developed to perform closed-loop positioning of the human body, based on the estimation of the body's location using pressure sensors distributed across the bed surface. Experiments using a prototype mattress demonstrate smooth body motion in both the x and y directions and rotation within the plane of the mattress surface.

A novel human-machine interface using wearable sensors is presented. Fingernail sensors that detect touch forces at the fingertip are used as a means to acquire human intentions of pressing buttons and switches. The sensor is worn on the fingernail (and looks like an ornamental fingernail). Combined with a magnetic tracker detecting the position of the human hand, it identifies which switch the human wishes to push and when the switch has been pushed. This allows traditional physical switches, embedded in a wall, control panel, etc., to be replaced by "virtual switches" that contain no electrical circuits or mechanical parts, but are merely pictures showing the location of the switch. In the virtual switch system, the location and functionality of switches are determined by software and can thereby be changed flexibly depending on the progress of task performance, environmental conditions, and context. The virtual switch method is combined with a "hyper manual" that stores task-procedure and operational information on a computer. Monitoring the human task performance allows the digital hyper manual to better guide the human, detect errors, and provide a safer environment.

A new type of touch sensor for detecting contact pressure at human fingertips is presented. A fingernail is instrumented with miniature LEDs and photodetectors in order to measure changes in the nail color pattern when the fingertip is pressed against a surface. Unlike traditional electronic gloves, in which sensor pads are placed between the fingers and the environment surface, this new sensor allows the fingers to directly contact the environment without obstructing the human's natural haptic senses. The finger touch force is detected by measuring changes in the nail color, hence the sensor is mounted on the fingernail rather than on the fingertip. Photo-reflective plethysmography is used to measure the nail color. Haemodynamic modeling is used to investigate the dynamics of the change in blood volume under the fingernail. The model is simulated and then evaluated by comparison with the experimental dynamic response of the sensor. Applications to human-machine interaction are discussed.

Bedridden patients and elastic bodies are transported by a novel ball transfer mechanism about their support surface. A series of spherical balls are constrained in their position in the support surface, but are allowed to rotate freely in three dimensions. A series of 'bed bugs' are coordinated to provide flexible support and tangential motion patterns of the human patient. This ball drive actuation allows a bedridden patient to move freely while lying upon the bed. First, the design concept is explained, then a description of the important parameters and performance measures is made. Interactions between the soft tissue and the bed surface with a ball transfer mechanism are addressed, and technical requirements for transporting humans and elastic bodies will be obtained. A proof-of-concept prototype has been designed and will be tested to verify model results and the manipulation concept.

Bedridden patients and elastic bodies are transported by generating surface waves on an active bed. Surface waves are shown to be a viable transport mechanism for large-scale, elastic bodies given certain conditions and constraints on the design. Surface wave actuation allows a bedridden patient to move freely while lying comfortably upon the bed. The motion of each node on the bed surface is coordinated such that it follows a circular trajectory with a certain phase lag from adjacent nodes. Basic properties of surface waves are presented. Based on these properties a new, concept, the extender, is added to the design to take advantage to the inherent rotational component of surface wave points. Kinematic analysis is performed to characterize the actuation concept. Sensitivity of design parameters on critical human transport issues is presented. Transport speed and efficiency are analyzed as well. A proof-of-concept prototype is designed, built and tested. It is demonstrated that a human is moved along the bed surface while lying on the bed.

A intelligent control architecture for semi-autonomous systems is presented. This has been motivated by the need for an architecture to differentiate between users of different perceptual and cognitive capabilities when interacting and using machines with automatic features. A good example for that is a robotic wheelchair. The proposed architecture evolves around three variables: degree of autonomy to reflect the user capabilities, user's level of confidence in commanding the machine, and strength of conflict between the user's command and the machine's autonomous response. The analogy between this architecture and horseback riding is demonstrated.

A source coding algorithm minimizing the battery power needed for RF transmission is presented. Digital RF transmitters in portable devices consume energy only when high bits are sent and virtually no energy is consumed when low bits are sent. Therefore, energy consumption can be minimized by devising a source coding algorithm that minimizes the occurrence of high bits in transmitting information. In this paper, we first formulate the minimum energy source coding problem for RF transmission. We then derive the optimal memoryless coding algorithm from the source statistics. Finally, we improve the memoryless coding performance via a novel technique that utilizes a simple memory mechanism. Overall, we take a first step towards a novel energy saving wireless communication protocol.

Force guided robot control is a control scheme based on the interpretation of measured force acting on the robot end effector. A functional map relating the correction of motion to force measurements is generated based on the geometry of the workpiece and its kinematic behavior in interacting with the environment. In the traditional force guided control schemes, the contact force measured by a force sensor is directly fed back to a feedback controller to generate a motion correction signal. In the paper, instead of simply measuring contact forces, we take positive actions by giving perturbation to the end effector and observing the reaction forces to the perturbation in order to obtain much richer and more reliable information. By the correlation between the input perturbation and the resultant reaction forces, we can determine the gradient of the force profile and guide the part correctly. By applying a type of direct adaptive control, the contact force is maintained at the lowest level. This algorithm is applied to a pipe insertion task, in which the insertion force is minimized during the insertion. Based on the process model and stability analysis using the Popov stability criterion, conditions for stable, successful insertion despite nonlinearities and uncertainties in the environment are obtained. The theoretical results are verified using the experimental data. To generate high frequency perturbation, a vibratory end effector using piezoelectric actuators is designed and built. Through both simulations and experiments, the feasibility and usefulness of these methods are demonstrated.

A reconfigurable mechanism for varying the footprint of a four-wheeled omnidirectional vehicle is developed and applied to wheelchairs. The variable footprint mechanism consists of a pair of beams intersecting at a pivotal point in the middle. Two pairs of bad wheels at the diagonal positions of the vehicle chassis are mounted, respectively, on the two beams intersecting in the middle. The angle between the two beams varies actively so that the ratio of the wheel base to the tread may change. Four independent servo motors driving the four ball wheels allow the vehicle to move in an arbitrary direction from an arbitrary configuration as well as to change the angle between the two beams and thereby change the footprint. The objective of controlling the beam angle is threefold. One is to augment static stability by varying the footprint so that the mass centroid of the vehicle may be kept within the footprint at all times. The second is to reduce the width of the vehicle when going through a narrow doorway. The third is to apparently change the gear ratio relating the vehicle speed to individual actuator speeds. First the concept of the varying footprint mechanism is described, and its kinematic behavior is analyzed, followed by the three control algorithms for varying the footprint. A prototype vehicle for an application as a wheelchair platform is designed, built, and tested.

A method for docking a vehicle with a fixture is developed and applied to a hybrid wheelchair/bed system. A powered wheelchair is docked to a bed portion and reconfigured to a flat stationary bed so that the bedridden person does not have to change seating when transferring between the chair and bed. A holonomic omnidirectional vehicle with a ball wheel mechanism is used for the wheelchair. The high maneuverability and holonomic nature of the vehicle allow the wheelchair to be docked precisely with a fixture. An instrumented bumper is developed to detect contacts with the fixture and ensure rider comfort. Using sensor information from the bumpers, the contact state of the vehicle is recognized at all times. Moreover, the orientation of the fixture is estimated from the contact information, and using a framework of discrete event control, the vehicle is aligned and guided towards the fixture despite large misalignments. A prototype system was designed and tested. The vehicle was successfully docked to the bed despite a small clearance ratio as well as large lateral and angular initial misalignments.

An approach to interactive control of human-robot systems using dual Petri nets is presented. A human and robot(s) work side by side by sharing the task goal and part of the process state. The human is instrumented with a type of data glove so that the robot can monitor the human state and coordinate its action with the human. First, the class of interactive tasks performed by a human and robot is described as a dual-agent, concurrent, event-driven system, and represented by two Petri nets interacting to each other. One Petri net represents the human side task process, while the other represents the robot side. Both sides proceed with their assigned tasks concurrently through state transitions within each Petri net. They observe the partner's state and coordinate each step of task performance as specified by the conditional state transition involved in the Petri nets. A distributed control system is directly derived from the dual Petri net representation. As an exemplary case study, a cable connection task is considered. The task is first decomposed into two subtasks, which are assigned to the human and the robot. A data glove worn by the human is developed for measuring the hand location as well as the force and position of each finger tip. A decentralized controller is built and a proof-of-concept experiment is described.

A new reconfigurable mechanism for varying the footprint of a four-wheeled omnidirectional vehicle is presented. A chair is mounted on a moving platform with four ball-wheels allowing holonomic, omnidirectional motion. Two pairs of ball-wheels at the diagonal positions of the chassis are mounted, respectively, on two beams that intersect at a pivotal point in the middle. The angle between the two beams crossing at the pivotal point is varied actively so that the ratio of the wheel base to the tread may change. Four independent servomotors driving the four ball-wheels allow the vehicle to exhibit holonomic motion. The beam angle is controlled based on the measurement of the mass centroid position in such a way that the mass centroid can be kept within the footprint at all times. The concept of the reconfigurable footprint mechanism is described, and its kinematics is analyzed followed by the control design for augmenting vehicle stability. A prototype vehicle for wheelchair platform application is designed.

This paper presents the development of the ring sensor to monitor a patient 24 hours a day for a tele-nursing system. The ring sensor is worn by the patient at all times, hence the health status is monitored 24 hours a day. The sensors packed into the ring include LEDs with different wavelengths, and technologies of photoplethysmography and pulse oximetry are implemented on the ring. The sensor data are transmitted to a computer through the digital wireless communication link and the patient status is analyzed continually and remotely. Any trait of abnormal health status and possible accidents is detected by analyzing the sensor data. A combination of a global receiver and multiple local ones are used to estimate the patient's location and activity. Both the physiological data and the position information can be used to make an accurate decision as to whether a warning signal must be sent to a medical professional caring the patient. An issue of power reduction for miniaturization of the ring sensor is also addressed.

An approach for overcoming the difficulties in force-guided assembly for real manufacturing applications is presented. The perturbation/correlation based control for a robot system is generalized, and then applied to the pipe insertion task which is difficult using conventional force guided control. Based on the analytic model of this controller, a Popov stability criterion is applied to cope with the unknown nonlinearity in the environment. Several critical assumptions are verified based on the experimental data, and the guide line to select parameters involved in this method is presented. Through an experiment, the feasibility and usefulness of this approach are demonstrated. A vibratory end-effector using a piezoelectric actuator was designed and implemented.

A hybrid wheelchair/bed system for bedridden persons is developed and tested. A powered wheelchair can be docked to a bed portion and reconfigured to a flat stationary bed so that the bedridden person does not have to change seating when transferring between the chair and bed. Moreover the wheelchair can also be docked to a toilet directly and automatically. A holonomic omnidirectional vehicle with a ball wheel mechanism is used for the wheelchair. The high maneuverability and holonomic nature of the vehicle allow the chair to be docked easily and precisely against a fixture. The wheelchair is equipped with teleconferencing facility so that the bedridden patient may communicate face-to-face with a distal caregiver, friends and relatives. This paper describes the basic concept of the reconfigurable holonomic omnidirectional mobile bed with unified seating (RHOMBUS). Issues on the mechanical design of the vehicle, chair, and bed are addressed, followed by control issues. A force-guided docking control method using force sensors embedded in the bumper of the vehicle is developed. A prototype system is designed and tested.

In this paper, we present a new approach to learning robot impedance control parameters from a logic task description. In this approach, we first describe the desired behaviour of a robot for performing a given task at a logic level. A simple logic branch control using a quasi-static force-to-motion map is created based on the logic description. The progressive learning method is then applied to this logic branch control in order to create a dynamic control, i.e. impedance control, for performing the task quickly and dynamically. Starting with a simple logic description about the robot behaviour, the system can develop a fully dynamic impedance control by progressively learning the process dynamics. The problem is formulated in the context of high-speed insertion, and the proposed approach is verified through simulation.

In the traditional force-guided control schemes, the contact force measured by a force sensor is directly fed back to a feedback controller to generate a motion correction signal. The issue central to force guided robot control is how to obtain reliable, consistent and copious force signals and extract useful information in order to successfully guide the robot while keeping the contact force at a desired level. In this paper, instead of simply measuring contact forces, we take positive actions by giving perturbation to the end effector and observing the reaction forces to the perturbation in order to obtain much richer and more reliable information. By taking the correlation between the input perturbation and the resultant reaction forces, we can determine the gradient of the force profile and guide the part correctly. This algorithm is applied to a pipe insertion task, and connector assembly task. Based on the process model and stability analysis using the Popov stability criterion, conditions for stable, successful insertion despite nonlinearities and uncertainties in the environment are obtained. The theoretical results are verified using the experimental data.

A novel approach to the design of trajectories for automatic tuning of non-collocated sensor/actuator systems is presented. This approach uses the progressive learning theory, a method for tuning many control parameters in a particular sequence so that all the parameters can be tuned stably and effectively. Using this progressive learning method a sequence of training trajectories can be designed, which not only satisfy geometric constraints for performing a task but also take into account the dynamics of the machine to better perform the task. This approach is implemented on a single degree-of-freedom high speed linear slider, and experimental results and discussions are presented at the end.

An approach to learning control using an excitation scheduling technique is developed and applied to an impedance learning problem for fast robotic assembly. Traditional adaptive and learning controls incur instability depending on the reference inputs provided to the system. This technique avoids instability by progressively increasing the level of system excitation. Called progressive learning, it uses scheduled excitation inputs that allow the system to learn quasistatic parameters associated with slow input commands first, followed by the learning of dynamic parameters excited by fast input commands. As learning progresses, the system is exposed to a broader range of input excitation, which nonetheless does not incur instability and unwanted erratic responses. In robotic assembly, learning starts with a slow, quasistatic motion and goes to a fast, dynamic motion. During this process, the stiffness terms involved in the impedance controller are learned first, then the damping terms and finally by the inertial terms. The impedance learning problem is formulated as a model-based, gradient following reinforcement learning. The method allows the suppression of excessive parameter changes and thereby stabilizes learning. By gradually increasing the motion speed command, the internal model as well as the control parameters can be learned effectively within a focused, local area in the large parameter space, which is then gradually expanded as speed increases. Several strategies for motion speed scheduling are also addressed.

This paper describes an experimental recursive method for simultaneously changing both the mechanical structure and control of a positioning system in order to improve the system's overall control performance. A method is devised which allows a robotic system to improve its control performance through concurrent repetitive reinforcement of its structure and optimization of its control gains. To expedite the process of modifying a prototype structure, a method for coating the structure with steel-reinforced epoxy is developed. A recursive algorithm, based on a gradient descent method and a parameter estimation theory, is developed to determine both the optimal incremental structure changes and the required control parameter changes. The resultant changes are then immediately implemented by using the epoxy reinforcement coating method as well as by changing the control gains. The entire process consisting of experimental evaluation, data analysis, and structure reinforcement is repeated until the task performance is improved to the desired level.

A new class of ball wheel mechanisms for omnidirectional vehicles is presented. This ball wheel mechanism can be designed to yield fully mobile vehicles that are not only free of any kinematic singularity but are configuration invariant in kinematic behavior. Invariant kinematics greatly simplifies the control of smooth and precise vehicle motion. Multiple displacement sensors are easily incorporated into each ball wheel mechanism. This unique feature enables the detection of slip between tires and the floor and also indicates at which tire the slip occurs. This allows traction control to be implemented to fully exploit the available floor friction while accurate dead reckoning navigation continues from two non slipping tires. A prototype vehicle with three ball wheel mechanisms is implemented. Smooth motion and precise dead reckoning are accomplished.

A novel approach to stable learning control is developed inspired by human learning behavior, and applied to an impedance learning problem for high-speed dynamic robotic assembly. The new method termed "progressive learning" uses scheduled excitation inputs that allow the system to learn quasi-static, slow modes in the beginning, followed by the learning of faster modes. This new method is presented in the context of high speed robotic assembly, where an impedance control law is learned with this excitation scheduling method. Extensive simulation results are provided to demonstrate the effectiveness of this method. A detailed analysis of the mechanism of progressive learning is also provided and verified through simulation.

Friction and stick/slip phenomena are a major source of disturbance in assembly tasks, especially under low velocity or frequent start/stop conditions. These friction effects are highly nonlinear, dependent on environmental parameters, and the resulting forces are extremely difficult to model accurately under all conditions. This paper discusses frictional contacts in the context of robotic assembly based on the underlying physics of the phenomenon. A technique employing a high frequency dither is presented which reduces the effect of friction between parts in relative motion. The parameters of this dither are tuned on-line to account for changes in the operating conditions. This tuning algorithm adjusts the dither parameters based on force feedback measurements and a model for the desired forces. Analysis shows that a set of optimal parameters exists. Experimentation demonstrates the algorithm's success, even in the presence of uncertain or varying system model parameters. The discussion includes consideration of previous friction studies and combination with force-guided control.

A new approach to force guided assembly is developed for the assembly of unsurfaced parts having sharp burrs and irregular surfaces. Due to friction at burrs and irregular surfaces, force signals are very noisy and erratic, preventing reliable sensing and monitoring of the assembly process. In this paper, instead of simply measuring contact forces, we take positive actions by actively shaking the end effector and observing the reaction forces to the perturbation in order to obtain rich, reliable information. By taking the correlation between the input perturbation and the resultant reaction forces, we can determine the direction of the part surface and guide the hand-held part correctly despite burrs and poor surface finish. The principle of active force sensing using a correlation technique is described. An algorithm for guiding an assembly part by using the correlation information is developed based on the theory of direct adaptive control. The method is then applied to a practical task: the assembly of sheet metal parts with sharp edges and burrs. Experiments demonstrate the effectiveness and feasibility of the active force sensing method.>

Optimal task sequence planning using a simulated annealing technique is developed for a high throughput chip placement machine. To minimize tact time, chips are mounted by multiple robots on moving PC boards being transferred by a precision conveyer. To avoid both geometric and dynamic interferences among multiple robots, while minimizing the tact time, the sequence of operations as well as the allocation of the multiple robots are optimized by using simulated annealing. The optimization problem is a type of traveling salesman problem, but is highly complicated because the target destinations for placing individual chips keep moving together with the PC board. First, the configuration of the new chip placement system is described. The task sequence optimization problem is then formulated, followed by the application of simulated annealing to solving the problem. An efficient algorithm for perturbing a task sequence is developed and applied to practical chip placement tasks.>

This paper describes an experimental recursive method for changing the hardware construction of a plastic robot arm in order to improve the system's dynamic performance. A system is implemented which allows the robot to improve its task performance through repetitive reinforcement of its structure. The structure reinforcement occurs using a coating method developed from stereolithographic rapid prototyping technology. A recursive algorithm, based on a gradient descent method and a parameter estimation theory, is developed to determine the optimal incremental structure changes. The resulting structure changes are then immediately executed by the stereolithographic reinforcement coating method. The entire process consisting of task execution, data analysis, and structure reinforcement is repeated until the task performance is improved to the desired level. An experimental system implementing the proposed technique was developed for building a high speed robot. The system is applied successfully in building a polycarbonate robot arm, showing a significant improvement in the arm dynamics.>

A new approach to compliant motion control using neural networks is presented. In the paper, "compliance" is treated as a nonlinear mapping from a measured force to a corrected motion. The nonlinear mapping by a multilayer neural network is outlined, this allows one to deal with complex control strategies that cannot be represented by linear compliance, such as in stiffness and damping control.>

An integrated approach to the concurrent design of arm structure and control is presented. To achieve high-speed positioning, a technique is developed in which comprehensive design parameters describing arm link geometry, actuator locations, and feedback gains are optimized with respect to the settling time of the system. First, a two-link, nonrigid arm is analyzed, and a simple dynamic model representing rapid positioning processes is obtained. A PD control system is designed for the dynamic model. Optimal feedback gains minimizing the settling time are obtained as functions of structural parameters involved in the dynamic model. The structural parameters are then optimized by using an optimization technique in order to obtain an overall optimal performance. The resultant arm design shows an outstanding performance, which is unattainable if the structure and control are designed separately.>

A novel design of a holonomic omnidirectional vehicle is introduced. The holonomic mechanism allows the vehicle to maneuver in an arbitrary direction from an arbitrary configuration on a plane. This significantly simplifies control problems and improves positioning accuracy. A fundamental method of obtaining omnidirectional motion with holonomic constraints with the floor, using a mechanism with spherical tires, is presented. Kinematic analysis of this mechanism gives the vehicle Jacobian relating actuator velocities to the vehicle velocity components. Analysis of lateral tire slip during vehicle rotation allows slip reduction methods. A prototype vehicle using this special mechanism and a computerized control system is designed and tested. In addition to rotation, the vehicle can perform very accurate translational motions, in two orthogonal directions, arbitrarily termed forward and sideways. Motions in these two degrees of freedom are decoupled from each other and are insensitive to variations in ground friction coefficient.>

The authors develop a method of modeling a human manipulative skill using human linguistic knowledge about the task. A global nonlinear structure of human control behavior is constructed based on the linguistic information, and all functionalities used by the linguistic structure are identified from human demonstration data. Mapping between sensor space and human mental space for input signals is discussed to elucidate human skills. Techniques for selecting significant features extracted from sensor signals and reducing the dimension of the sensor space are developed. The techniques were applied to a direct-drive deburring robot to verify the feasibility of the method.>

paper takes a new approach to robotic assembly, treating assembly as a discrete event system. A discrete event in assembly is defined as a change in contact state reflecting a change in a ge- ometric constraint. The discrete event modelling is ac~complished using Petri nets. The problems of task-level planning .and syn- thesis are addressed. Using the Petri net modelling, a discrete event controller (DEC) is developed. The DEC is a task-level controller that directs the assembly process to the desired end state. The DEC outputs both a desired velocity and it desired force command. The desired velocity commands insure consis- tency with geometric constraints while simultaneouslly directing the system toward the next desired discrete state. The desired force commands attempt to maintain the current state of contact. Task-level planning is accomplished using dynamic programming to deterimine the optimal sequence of discrete states for success- ful assembly. This desired sequence of discrete states is then used as a reference input to the DEC. 1 Iintroduction In discrete automation, assembly is one of the most error-prone, unreliablle processes. There is an increasing need for efficient methods of increased robustness and reliability in :the face of tolerancing errors and uncertainties in the workpieces and the environment. The control of assembly, including task level tra- jectories and on-line task level control, is a key component to improving the success of robotic assembly. The goal of this paper is to present a new approach to the control of robotic assembly tasks, treating assembly as a discrete event dynamic system. The abstraction to discrete event modelling highlights the necessary transitions for successful assembly. Additionally, the abstraction allows for planning on a task level rather than the cumbersome process of exact trajectory planning. Various methods have been proposed for the control of assem- bly processes. (Whitney, 19821 derives quasi-static con.dit,ions for a successful insertion operations. (Mason, 19821 (Raibert and Craig, 19811 describe a hybrid position/force control for various tasks. Other work has included using force feedback as a source of task preformance information (Hannaford, 19871. However, unlike most force-feedback applications, the state of contact changes during an assembly process. These discrete changes in state should be the focal point of the control procedure In order t,o incorporate the state changes, we will model assembly as a discrete event dynamic system. The discrete state vector will be the discrete states of contact in the assembhly process. The discrete events (occurring at discrete instances in time) are the since they indicate significant changes in the system dynamics. changes in contact state. Typically, discrete event dynamic sys- tem models arise from certain aspects of manufacturing systems and data network protocols. In contrast to these applications, this paper presents the discrete event modelling and control of robotic assembly. The difficulty of modelling and designing discrete event control systems has long been recognized in the literature. Moreover, there is apparently no unifying theory for the control of discrete event systems. Numerous methods have been proposed for the modelling and analysis of discrete event systems, each having different characteristics. Some of these include formal languages (Ramadge, 19891, finite state machines (Tadmor and Maimon, 19891, and Petri nets (Peterson, 19811. The goal of this paper is to present a new approach to robotic assembly, treating assembly as a discrete event dynamic system. The discrete event modelling is accomplished using Petri nets. The abstraction of assembly to Petri net modelling highlights the key transitions necessary for successful insertion. Additionally, the abstraction allows for planning on a task level rather than the cumbersome process of exact trajectory planning. Using the Petri net modelling, a discrete event controller (DEC) is developed. The DEC is a task-level controller that directs the assembly process to the desired end state. Two condi- tions are derived that perform this function. First, a closed form solution is given for the desired velocity commands. Desired ve- locity commands insure consistency with geometric constraints while simultaneously directing the system toward the next de- sired discrete state. Second, an equation is derived the specifies the desired force commands, The desired force commands are the forces that attempt to maintain the current state of contact. Lastly, an optimal sequence of discrete events (changes of con- tact) leading to successful insertion is determined using dynamic programming, thus completing the specificaiions for the DEC.

The focus of this study is to examine the teaching data for training the neural network: whether or not the sample data provide a consistent mapping from inputs to outputs, whether some significant information is missing in the measurement of human operations, and whether the network may converge to the global minimum where the network produces a correct mapping. Conditions for a given data sample to satisfy in order to generate a consistent mapping are obtained by using Lipschitz's condition, which is known as a condition for the continuity of functions. Prior to the training of neural networks, sample data are examined and validated with Lipschitz's condition, which guarantees the consistency. This validation method is applied to a skill transfer problem of deburring robots in order to demonstrate the approach.>

The integrated structure/control design of flexible robot arms is presented. The open loop, poles, and zeros are relocated by modifying the geometry and the structure of the arm. To determine the geometry and structure in a systematic manner, an inverse mapping method based on finite-element modeling and sensitivity analysis is applied to the flexible arm design. Using this method, a beam geometry that allows for a significantly high natural frequency is obtained. In order to relocate zeros, the torque transmission technique is applied. It makes it possible to remove nonminimum-phase zeros and make the endpoint control robustly stable. Based on the theoretical analysis and computation, a prototype arm was designed and built, and its performance was evaluated.>

A methodology for accounting for distributed workpiece compliance which simplifies the task-planning process is presented. The authors examine hybrid position/force control and its limitations, and they extend it to account for the natural compliance of parts. They introduce the concept of buffer zones as a geometric representation of the effects of part compliance. Using buffer zones and simple geometric reasoning they plan assembly tasks involving compliant parts with bounded geometric uncertainties. A systematic method is presented for using workpiece compliance by which it is possible to determine when the part compliance is sufficient and only simple position control is required, and when force sensing is needed. The traditional formulation of configuration space is extended to include the regions where part deformation occurs. The task of assembling a flexible two-dimensional box is planned with the use of buffer zones.>

A new approach to the representation and learning of compliance control laws using neural networks is presented. Compliance is treated as a nonlinear mapping from a measured force to a corrected motion. The nonlinear mapping is represented by a multilayered neural network, which makes it possible to deal with complex strategies of force feedback. This network representation provides not only linear compliance, as represented by stiffness and damping matrices, but also nonlinear compliance, which has never been explored extensively. This network approach also makes it possible to teach a desired compliance from teaching data by using an iterative learning algorithm. Conventional methods of compliant motion control are reviewed, linear compliance and its limits are discussed, and nonlinear compliance based on the network representation is introduced. An analysis is made of the nonlinearity of compliance that arises in performing assembly tasks, and the network structure that meets the requirements for representing a group of nonlinear compliances necessary for performing the assembly tasks is obtained.>

A flexible arm with a special transmission mechanism is analyzed, and a method for integrated design of the arm structure and controller is presented. Control of flexible arms is a difficult problem because of the complicated dynamic coupled with the nonminimum-phase nature which is due to the noncollocated construction of sensor and actuator. The transmission mechanism developed relocates the torque-actuation point on the arm and modifies the flexible arm to a minimum-phase system. The resulting flexible arm is analyzed in terms of poles and zeros that are changed by relocating the torque-actuation point. A simple prototype arm is designed and compared with a nonminimum-phase arm. The effectiveness of the special transmission is discussed with regard to control performance, and an integrated structure/control design methodology is proposed.>

An approach to the teaching of manipulative skills is developed and applied to a deburring robot. Teaching data acquired from a human expert, who can perform an efficient job, are processed on a computer to attain his skilful manipulation strategies. The strategies are described by a group of control laws that relate sensor signals to motion commands. Sensor signals are processed by using pattern recognition techniques to interpret sensor information and to allow the robot to recognize the state of the process. The control laws designate which control action the robot should take in response to each signal pattern generated in the process. A method for driving a compact set of discrimination functions for real-time recognition of signal patterns is also discussed. The method is implemented on a direct-drive deburring robot. It is demonstrated that the robot can mimic the skilful manipulation of the human expert and perform the task efficiently.>

An efficient method is developed to generate programs for the hybrid position/force control of robots from teaching data. An operator's motion is measured in terms of the force exerted by the operator and the position of the end-effector. The acquired data are then analyzed in order to understand what the operator intended to do, and necessary information is obtained to generate the hybrid control program. Determinations are made of which control mode, position or force, should be taken in each direction, how much force should be exerted, and what trajectory the end-effector should follow. The interpreted motion is then translated into a robot language, which explicitly describes the motion strategy that the human operator conceived. The method was implemented on a direct-drive arm and a personal computer, and the efficiency of the method was demonstrated through experiments.>

A novel approach to the teaching of skills that human workers have acquired in performing specific tasks is presented. A skilled worker shows how to perform a given task, and his motions are measured. The force exerted by the worker and the displacement of the tool manipulated by the worker are monitored and stored in a computer. The data are analyzed to find the control law of the human expert. The functional relationship between the force and the displacement is derived from the data by using a curve-fitting technique. The identified relationship is used as a reference model for controlling a manipulator arm to replicate the expert motion. The method is applied to the impedance control of a simple grinding robot.>

The design and analysis of a high-speed insertion hand, the dynamic RCC hand, are presented. The dynamic behavior of a peg in high-speed insertion is analyzed. Conditions for the peg to be guided along the chamfer without bouncing on the surface are derived. Mass properties of the peg and its supporting mechanism that enable successful insertion are determined. A high-speed insertion hand is designed on the basis of the dynamic analysis. Experiments demonstrate the feasibility and usefulness of the dynamic insertion hand.>

A methodology for the automatic generation. of robot programs for hybrid position/force control is presented. While hybrid control allows a robot to perform skillful manipulations, its programing is more complex and intricate than simple position control schemes. In hybrid control, control modes must be designated to individual C-frame axes, in such a way that the robot motion conform to geometrical or natural constraints. Both position and force reference inputs must be provided as artifical constraints. This is difficult , since it requires the interpretation of a given task and the translation into a set of commands used in the hybrid position/force control. In this paper, an efficient method is developed to eliminate manual programming and task interpretation/translation. The operator teaches a given task by "teaching-by-showing", in which the operator contacts the robot end effector to the environment, and accommodates the contact force. During the operator's motion, the force applied by the operator as well as the position of the end effector are measured, The acquired motion data are then processed and interpreted so that necessary information to generate robot programs is obtained. The choice of control modes as well as reference inputs to the robot controller are derived from the motion data. Then the result is translated into a robot program. First, the principle of this method is described. The algorithm to interpret motion data is then developed for a simple palletizing job. The method is implemented on a force-controlled direct-drive arm using a personal computer.

Dynamic behavior of a manipulator arm and its end effector that interact with the environment is analyzed. Inertial properties of the arm and the end effector are represented with respect to a point of contact between the end effector and the environment. Virtual mass is then defined to be the equivalent mass of the arm and the end effector reflected to the point of contact, and is given by the ratio of a force acting on the point to the acceleration caused by the force at the point. Unlike a real mass, the virtual mass varies depending on the direction of the applied force and the location of the contact point. The maximum and minimum values of the virtual mass are then obtained and the physical meanings are discussed. Next, the rotational motion of the end effector is considered. A single rigid body possesses a centroid; a particular point at which rotation and translation of the rigid body are separated. The concept of the centroid is extended to the one for a system of rigid bodies such as arm links and the members of the end effector. The point is referred to as the generalized centroid, at which a linear force causes only a linear acceleration and a pure moment causes only an angular acceleration, hence separated. The virtual mass and the generalized centroid are then applied to task planning for chipping, hard surface contact, and dynamic insertion operations. The orientation of a tool and the configuration of the manipulator arm are optimized so that a desired dynamic behavior can be accomplished by having an appropriate virtual mass and the generalized centroid at an appropriate point.

A manipulator design theory for reduced dynamic complexity is presented. The kinematic structure and mass distribution of a manipulator arm are designed so that the inertia matrix in the equation of motion becomes diagonal and/or invariant for an arbitrary arm configuration. For the decoupled and invariant inertia matrix, the system can be treated as linear, single-input, single-output systems with constant parameters. As a result, the control of the manipulator arm is simplified, and, more importantly, control performance can be improved due to the reduced dynamic complexity. First, the problem of designing such an arm with the decoupled and/or configuration-invariant inertia matrix is defined. The inertia matrix is then analyzed in relation to the kinematic structure and mass properties of the arm links. Necessary conditions for the manipulator arm to possess a decoupled and/or configuration-invariant inertia matrix are obtained. Using the necessary conditions, we find the kinematic structure and mass properties for which the inertia matrix reduces to a constant, diagonal form. For 2 and 3 degree-of-freedom arms, possible arm designs for decoupled and/or invariant inertia matrices are then determined.

The concept of an adaptable fixturing system and its hardware implementation are first presented. The system employs reconfigurable fixture elements that are used to locate and hold various workparts for assembly. A key feature of this approach is that the fixture configuration can be changed automatically depending upon the workpart geometry and the assembly operations required. In the later half of this paper, basic analytic tools are developed to support the automation of fixture layout design. Kinematic modeling, analysis and characterization of workpart fixturing are presented. The condition for a fixture layout to locate a given workpart uniquely and to constrain its motion completely are derived. Desirable fixture layout characteristics are obtained for loading and unloading the workpart successfully despite errors in workpart manipulation.

The instantaneous kinematic and static characteristics of wrist joints are analyzed. Velocity ratio and mechanical advantage have been used for characterizing single-input-single-output mechanisms. These concepts are extended to multi-input-multi-output mechanisms in order to analyze robotic devices, specifically, wrist joints. The kinematic and static performance of wrist joints and their singularities are analyzed in terms of the generalized velocity ratio and the generalized mechanical advantage. Methods for avoiding singularities and improving the kinematic and static performances are then presented. The kinematic and static performance is optimized by varying the kinematic structure and the geometry of wrist joints. In particular the geometry of the last link, on which the end effector is mounted, is modified so that the singular points are moved from the middle of the workspace to its boundaries. The kinematic and static performance is further improved by determining the optimal configuration for performing a given task. An optimization method is developed to find the configuration that provides the most uniform velocity ratio and an adequate mechanical advantage in all directions. The kinematic and static performance of two different wrist joints are then evaluated and improved using this design methodology.

A simple and effective solution to the robot grinding problem is introduced, which significantly reduces vibrations during grinding without additional actuators or active control. The objective is to determine the optimal compliance design for grinding robot tool holders. It is found that the degree of correlation between the dynamic behavior of the wheel in the directions normal and tangent to the desired workpiece surface has a direct effect on the grinding performance. This fact is utilized to determine the optimal tool holder compliance design through analysis, simulation and experimentation. The resulting design conclusions have been incorporated in an end-effector which was successfully tested for the grinding of weld seams.

A new method for the design of hybrid position/force controllers for constrained manipulators is derived. This method can be applied to all types of constraint due to contact with the environmcnt; including constraint due to contact at the end effector, constraint due to more than one robot manipulating a workpiece, and constraint due to the bracing of a robot arm against a work surface. The manipulator and its contact with the environment are modeled in terms of lower order pairs. From this model a general equation describing the constraint on the motion of the arm is derived. The task is modeled as a set of essential position vectors and a set of essential force vectors. A hybrid position/force controller is derived to control the position and force at the joints of a manipulator such that the motion of the the robot conforms to the constraints imposed on it due to contact with the environment; and the motion at the end effector, and the force at the contact with the environment are those required for the performance of the task. The method is illustrated by a simple three degree of freedom example.

The basic concept of an adaptable fixturing system and its hardware implementation are described. The system employs reconfigurable fixture elements that are used to locate and hold various workparts for assembly. The fixture configuration can be changed automatically depending upon the workpart geometry and the assembly operations required. Analytic tools are developed for designing fixture layouts. Kinematic modeling, analysis, and characterization of workpart fixturing are presented. The condition for a fixture layout to locate a given workpart uniquely at a desired location is derived. Desirable fixture layout characteristics are obtained for loading and unloading the workpart successfully despite errors in workpart manipulation. The fixturing of a plastic cover of an electrical appliance with complex shape is used as an example to verify the analytic results and for demonstrating the concept.

An analysis of robot arm dynamics and a graphical method of representing these dynamics suitable for computer aided design is presented. The inertia ellipsoid, which is used for graphically representing the mass properties of a single rigid body, is extended to a generalized ellipsoid for a series of rigid bodies such as a robot arm. By drawing the Generalized Inertia Ellipsoid (GIE) on a computer display, one can visualize the mass properties and dynamic behaviour of a robot manipulator. This method is applied to aid the design of a mechanical arm; the dimensions of the arm structure and its mass distribution are optimized on the basis of the evaluation of the arm dynamics displayed on a graphics terminal.