Powered lower-limb exoskeletons have been shown to assist and augment walking, but most such devices do not currently have the ability to explicitly accommodate a stumble perturbation. A major challenge in doing so is identifying a stumble event and selecting in real-time which recovery strategy (elevating or lowering) to employ, particularly since the exoskeleton should ideally select the same strategy selected by the user. In order to do so, the authors conducted experiments involving five young, healthy adults wearing a knee exoskeleton. Each participant underwent a stumble experiment in order to collect an exoskeleton sensor dataset of stumbles throughout swing phase, which was used for stumble detection and recovery strategy identification algorithm development and testing. Overall, the proposed detection and identification algorithms provide improved accuracy with fewer required sensors relative to previous works, and were tested on the largest exoskeleton sensor stumble dataset to date, showing the feasibility of such algorithms for real-time implementation, which is an essential first step in developing lower-limb assistive devices that are robust to stumbles.

This paper presents preliminary results assessing the efficacy of a backpack-worn cold-gas thruster to potentially arrest impending backwards falls. Specifically, a nitrogen-based cold gas thruster system was integrated into a backpack-worn prototype device, and experiments were conducted to assess the effect of the wearable device on backwards falls. Although the device is eventually intended for individuals at fall risk, these preliminary experiments were conducted on three healthy subjects. The experiments compared each subject's ability to recover from an impending fall with and without assistance from the thruster. Results suggest that the likelihood of a fall was substantially reduced with the thruster assistance.

While lower limb exoskeletons for above-ground locomotion have been emerging, few attempts have been made to develop an exoskeleton to augment human swimming. Such efforts are hindered by a lack of knowledge surrounding the kinematics and kinetics of human swimming. This paper presents the design of a robotic platform to be used as a finned swimming testbed; describes a controller to generate finned swimming movement; and presents experiments and associated experimental results conducted to explore thrust production resulting from a flutter kick swimming motion.

This paper explores the effects of a swing phase stumble recovery controller in a swing-assist prosthesis. The prosthesis detects a stumble event and employs either a lowering recovery response - wherein the user's swing is truncated, and the leg is prepared for loading- or an elevating recovery response - wherein an amplified swing flexion is employed to step over the obstacle causing the perturbation. The controller described in this paper choses which of these responses to use based on the perturbation timing within the gait cycle, where stumble events which occur prior to an estimated 35 percent of the way through swing trigger an elevating response, and later stumbles trigger a lowering response. The potential efficacy of this approach was assessed in a preliminary study with two participants with transfemoral amputation; wherein each participant's walking was perturbed in early, mid, and late swing phase when wearing both their prescribed prosthesis and the swing-assist prosthesis prototype. When wearing the swing- assist device, 0 of the 13 perturbations resulted in falls, with none of the trials being classifiable as “near falls”. Conversely, when using their prescribed device, one participant had a fall rate of 3 out of 6 perturbations, with 1 of the 3 recoveries being classifiable as a “near fall”; the second participant had a fall rate of 0 of 3 trials, with 2 of the 3 recoveries being classifiable as “near falls”. For both participants, when recovery was achieved, it was accompanied by significantly longer periods of irregularity and asymmetry in gait when using their prescribed devices, as compared to the test device. These results suggest the possibility of substantial benefit provided by a low-power, reflex- based stumble recovery feature in knee prostheses.

This paper presents a stumble recovery controller for a knee exoskeleton that detects a stumble perturbation; selects an anticipated recovery strategy; and provides appropriate recovery assistance. In order to assess the efficacy of the controller in providing an assistive response to a stumble perturbation, the controller was implemented in a knee exoskeleton and evaluated in a single healthy adult participant against several other controller reactions, and against the participant’s response without an exoskeleton. Results show that the stumble recovery controller successfully detected the perturbation and correctly selected the strategy that matched the participant’s response for all 29 trials in which the exoskeleton was used. Further, results show improvements in stumble recovery metrics when using the exoskeleton with the stumble recovery controller, compared to the control cases of: 1) no change in the nominal controller when stumble is detected; 2) turning off exoskeleton torque when a stumble is detected; and 3) not wearing an exoskeleton.

This paper presents the design and implementation of a controller for stair ascent and descent in a primarily-passive stance-controlled swing-assist (SCSA) prosthesis. The prosthesis and controller enable users to perform both step-over and step-to stair ascent and descent. The efficacy of the controller and SCSA prosthesis prototype in providing improved stair ambulation was tested on a unilateral transfemoral amputee in experiments that employed motion capture apparatus to compare joint kinematics with the SCSA prosthesis, relative to performing the same activity with a microprocessor-controlled daily-use passive prosthesis. Results suggest that the SCSA knee significantly decreases compensatory motion during stair activity when compared to the passive prosthesis.

This paper presents a control approach for an overground lower limb exoskeleton that is intended to provide guidance and assistance to poorly ambulatory individuals during walking without unduly interfering with their ability to maintain balance. The control approach achieves these objectives by emulating a viscous flow field acting on the lower limb joints. The extent to which the control approach achieves the objectives was assessed in experiments, conducted on five healthy subjects, comparing guidance and disturbance characteristics of the velocity-based controller to a potential-field-based controller. Results show that the flow controller provides a combination of lower guidance error and lower disturbance to the user, relative to the potential-field-based controller. The paper also discusses various potentially beneficial characteristics of the flow controller, such as first-order homogeneous behavior, implicitly combined guidance and assistance behaviors, and improved directionality in error correction relative to a potential-field-based controller.

This paper describes a lower limb exoskeleton control approach that facilitates a desired movement coordination between the hip and knee joints during the swing phase of gait. An important feature of the proposed controller is that it provides movement guidance while allowing a user to control step time and step length. Specifically, control of step time is enabled by the use of time-invariant movement constraints, while control of step length is enabled by a real-time path-planning feature. As such, the controller provides movement coordination, but still enables a user to retain the step-to-step variability required to maintain balance during walking. The controller was implemented on a lower limb exoskeleton and tested on five healthy subjects. The subjects walked overground in the exoskeleton without a stability aid under two conditions: with the proposed coordination controller (i.e., with sagittal plane movement constraints) and with no control implemented (i.e., without sagittal plane movement constraints). Data from these assessments indicate that the controller provided substantial movement coordination while still allowing subjects substantive control of step time and length across a range of walking speeds.

This paper introduces the SCCA Hand, a five motor robot hand developed using a minimalist design approach that focused on grasping abilities in real-world environments. Notable features include a novel bidirectional tendon underactuated finger design that biases actuator force toward finger flexion, an additive manufactured monocoque steel construction that enabled enhanced feature density and a low parts count, low grasp impedance by means of series elastic actuation, shock absorption for protection from impacts, and anthropomorphic speed, strength, and size. In addition to a description of its design, experimental characterizations of speed and force capabilities as well as demonstrated achievement of eight canonical grasps and postures are provided.

A controller for a powered transfemoral prosthesis is presented, which can coordinate power delivery at the knee with the motion of the crankshaft on a bicycle. The controller continuously estimates the lengths of a four-bar linkage model through the application of a recursive least squares algorithm. The link lengths are used to estimate the angle of the bicycle crankshaft. With this measure, the delivery of knee torque is coordinated with the motion of the user. The controller is implemented on a prosthesis prototype and assessed on a transfemoral amputee subject ( N = 1). The subject exhibited a bilateral work asymmetry of 83.5% when cycling with his daily use prosthesis in a free-swing mode. When 60-N·m peak assistance was provided by the powered prosthesis, the bilateral work asymmetry was reduced to 11.4%. The subject's metabolic energy rate was measured for speed and power-matched cycling while the powered prosthesis provided zero assistance (i.e., turned off and providing its back-drive resistance) or 30-N·m peak assistance. Subject's metabolic energy rate decreased by 16.5% when receiving powered assistance relative to the zero-assistance condition.

This paper presents a control approach for myoelectric transhumeral prostheses that coordinates the movement of the elbow joint with the movement of the (intact) shoulder. The method combines input from a pair of surface electromyograms (EMG) inputs with information from an inertia measurement unit (IMU) to provide coordinated control of the joints, as described in the paper. In order to assess the efficacy of the control method, experiments were conducted on six healthy subjects using a virtual environment, comparing their ability to perform various pick-and-place tasks, specifically requiring that they pick a virtual ball from a given location and place it in a virtual box, which changed location randomly. The time required to complete a series of pick-and-place tasks using the coordinated control approach was compared to the time required to complete the tasks using a conventional sequential control approach. For these experiments, the average task completion time across all sessions and subjects was 12.8 s using the conventional sequential control approach, versus 8.7 s using the coordinated control approach (i.e., subjects performed the task 32% faster with the proposed approach), indicating that the proposed approach provides improved performance relative to the conventional approach.

Repeated tree traversals are ubiquitous in many domains such as scientific simulation, data mining and graphics. Modern commodity processors support SIMD instructions, and using these instructions to process multiple traversals at once has the potential to provide substantial performance improvements. Unfortunately these algorithms often feature highly diverging traversals which inhibit efficient SIMD utilization, to the point that other, less profitable sources of vectorization must be exploited instead. Previous work has proposed traversal splicing, a locality transformation for tree traversals, which dynamically reorders traversals based on previous behavior, based on the insight that traversals which have behaved similarly so far are likely to behave similarly in the future. In this work, we cast this dynamic reordering as a scheduling for efficient SIMD execution, and show that it can dramatically improve the SIMD utilization of diverging traversals, close to ideal utilization. For five irregular tree traversal algorithms, our techniques are able to deliver speedups of 2.78 on average over baseline implementations. Furthermore our techniques can effectively SIMDize algorithms that prior, manual vectorization attempts could not.

This work presents a functional assessment of the Vanderbilt Multigrasp Hand prosthesis and Multigrasp Myoelectric Control method which the authors have previously described. In the study, a transradial amputee utilized the prosthetic system to perform the Southampton Hand Assessment Procedure (SHAP), which involves manipulation tasks designed to simulate the activities of daily living. The results of the study indicate 81% restoration of typical hand function and compare favorably to recently published SHAP results for commercially available single-grasp and multigrasp prosthetic hands. A video of the assessment is included as supplementary material.

The authors present a control system for a pair of powered prostheses that leverages communication between the devices in order to enhance awareness and improve stability for the user. The control system is implemented on a pair of powered knee and ankle prostheses previously developed by the authors and tested on a healthy subject using able body adapters. The healthy subject also walked on a pair of passive prostheses, with both cases being monitored through motion capture. The kinematic data from the powered system closely match those seen in healthy subjects and show a marked improvement over the passive devices.

This paper describes a level walking controller for a powered ankle prosthesis. The controller was implemented on a powered prosthesis prototype and evaluated on a healthy subject by means of able-bodied adapters on a treadmill walking at 1.2 m/s (4.3 km/h). The ankle joint kinematics provided by the powered prosthesis were compared to that provided by a passive (dynamic elastic response) prosthesis, and both compared to the typical kinematics of healthy gait. The comparison indicates the powered prosthesis better reproduces the kinematics of healthy gait, relative to the passive prosthesis. The torque, energy transfer, and power provided by the powered prosthesis were additionally compared to that of a typical healthy subject.

With the advent of programmer-friendly GPU computing environments, there has been much interest in offloading workloads that can exploit the high degree of parallelism available on modern GPUs. Exploiting this parallelism and optimizing for the GPU memory hierarchy is well-understood for regular applications that operate on dense data structures such as arrays and matrices. However, there has been significantly less work in the area of irregular algorithms and even less so when pointer-based dynamic data structures are involved. Recently, irregular algorithms such as Barnes-Hut and kd-tree traversals have been implemented on GPUs, yielding significant performance gains over CPU implementations. However, the implementations often rely on exploiting application-specific semantics to get acceptable performance. We argue that there are general-purpose techniques for implementing irregular algorithms on GPUs that exploit similarities in algorithmic structure rather than application-specific knowledge. We demonstrate these techniques on several tree traversal algorithms, achieving speedups of up to 38x over 32--thread CPU versions.

The mechanical and electronics design of a quadrupedal walking robot featuring 12 pneumatically actuated degrees of freedom is presented. Control of the robot's joint motions incorporates open-loop damping into the actuation and uses a stance/swing gain scheduler in the joint position controller. The inclusion of these two attributes enables stable and robust joint-level control while attenuating the undesirable oscillatory modes that are commonly associated with pneumatically actuated walking robots. Joint motion trajectories that permit stable walking are developed and implemented in the robot. The combination of these features and techniques is experimentally shown to enable stable walking locomotion of the robot that is not inhibited by unwanted oscillations of significant magnitude.

This paper presents the design of an electrically-actuated, proportional brake that provides a significantly greater torque-to-weight ratio than a magnetic particle brake (considered a benchmark of the state-of-the-art) without sacrificing other characteristics such as dynamic range, bandwidth, or electrical power consumption. The multi-disc brake provides resistive torque through a stack of friction discs which are compressed by a dc-motor-driven ball screw. Unlike nearly all other proportional brakes, which operate in a normally unlocked mode, the brake presented here is designed such that it may be configured in either a normally unlocked or normally locked mode. The latter enables lower electrical energy consumption and added safety in the event of electrical power failure in certain applications. Following the device description, experimental data is presented to characterize the performance of the brake. The performance characteristics are subsequently compared to those of a commercially available magnetic particle brake of comparable size.

A hybrid functional electrical stimulation (FES)/orthosis system is being developed which combines two channels of (surface-electrode-based) electrical stimulation with a computer-controlled orthosis for the purpose of restoring gait to spinal cord injured (SCI) individuals (albeit with a stability aid, such as a walker). The orthosis is an energetically passive, controllable device which 1) unidirectionally couples hip to knee flexion; 2) aids hip and knee flexion with a spring assist; and 3) incorporates sensors and modulated friction brakes, which are used in conjunction with electrical stimulation for the feedback control of joint (and therefore limb) trajectories. This paper describes the hybrid FES approach and the design of the joint coupled orthosis. A dynamic simulation of an SCI individual using the hybrid approach is described, and results from the simulation are presented that indicate the promise of the JCO approach.

This paper presents an approach for the closed-loop control of actuated biped that allows natural looking and energy efficient walking. Rather than prescribe kinematic trajectories or kinematic constraints, the approach is based on the prescription of state dependent torques that ¿encourage¿ patterned movement. Some of the prescribed torques are referenced to the inertial reference frame, which largely decouples the angular dynamics of the robot, and as such greatly simplifies the selection of control parameters. Implementation of torques from the inertial coordinate frames is enabled by a joint torque computation which is motivated by Gauss's principle of least constraint. The proposed approach is implemented in simulation on an anthropomorphic biped, and is shown to quickly converge to a natural looking gait limit cycle. Simulations are conducted with various control parameters and different initial conditions. The authors also show that walking speed can be altered in a simple manner by varying two intuitive controller parameters. The mechanical cost of transport computed on a representative dynamic walk is used to validate energy efficiency of the proposed control approach.

This paper presents an approach for the closed-loop control of a fully actuated biped robot that leverages its natural dynamics when walking. Rather than prescribing kinematic trajectories, the approach proposes a set of state-dependent torques, each of which can be constructed from a combination of low-gain spring-damper couples. Accordingly, the limb motion is determined by interaction of the passive control elements and the natural dynamics of the biped, rather than being dictated by a reference trajectory. In order to implement the proposed approach, the authors develop a model-based transformation from the control torques that are defined in a mixed reference frame to the actuator joint torques. The proposed approach is implemented in simulation on an anthropomorphic biped. The simulated biped is shown to converge to a stable, natural-looking walk from a variety of initial configurations. Based on these simulations, the mechanical cost of transport is computed and shown to be significantly lower than that of trajectory-tracking approaches to biped control, thus validating the ability of the proposed idea to provide efficient dynamic walking. Simulations further demonstrate walking at varying speeds and on varying ground slopes. Finally, controller robustness is demonstrated with respect to forward and backward push-type disturbances and with respect to uncertainty in model parameters.

This paper presents the design of a 14 degree-of-motion forearm actuation unit for an upper extremity prosthesis. The forearm utilizes pneumatic type actuators which use the reaction products of a monopropellant gas generator as a working fluid. The use of pneumatic type actuators provides a near-human power density, such that the fourteen actuator forearm unit can deliver approximately one half of the force and power capability of a human arm, with a total package size that fits within the volumetric constraints of a 50thpercentile female forearm (excluding the cartridge of liquid propellant). This paper describes the design of the forearm. The design has been fabricated, and experimental results are presented that demonstrate the closed-loop force tracking capability. An accompanying video further demonstrates the forearm performance.

This paper presents the design of a gas-actuated anthropomorphic arm prosthesis with 21 degrees of freedom and nine independent actuators. The prosthesis utilizes the monopropellant hydrogen peroxide as a gas generator to power nine pneumatic type actuators. Of the nine independent actuators, one provides direct- drive actuation of the elbow, three provide direct-drive actuation for the wrist, and the remaining five actuate an underactuated 17 degree of freedom hand. This paper describes the design of the prosthesis, including the design of small-scale high-performance servovalves, which enable the implementation of the monopropellant concept in a transhumeral prosthesis. Experimental results are given characterizing both the servovalve performance and the force and/or motion control of various joints under closed-loop control.

This paper presents the design of an anthropomorphic 21 degree-of-freedom, 9 degree-of-actuation arm prosthesis for use by transhumeral amputees. The design leverages the power density of pneumatic actuation with the energy density of liquid propellants to obtain a self-powered dexterous prosthesis in which all of the requisite power, actuation, and sensing is packaged within the volumetric envelope of a normal human arm. Specifically, the arm utilizes a monopropellant as a gas generator to power nine pneumatic-type actuators that drive an elbow, three wrist degrees-of-freedom, and a 17 degree-of-freedom compliant hand. The design considerations discussed in this work include the design of compact, low-power servovalves; the choice of actuators based on energetic requirements of a normal arm; the design of compact elbow and wrist joints with integrated position and force sensing; and the components of the compliant hand design. The liquid-fueled prosthesis is expected to approach the dexterity of an anatomical arm and is projected to deliver half of the force and power output of an average human arm.

This paper describes the design and control of a transfemoral prosthesis with pneumatically powered knee and ankle joints. The current version of the prosthesis serves as a laboratory testbed for purposes of controller development and testing, and as such is tethered for both power and control. A subsequent version will be self-contained, with on-board control and hot gas (monopropellant) actuation. This paper presents the design of the prosthesis prototype, which is in essence a two degree-of-freedom powered robot mechanically attached to a user, and describes an impedance-based control approach that coordinates the motion of the prosthesis and user for the control of level walking. The control approach is implemented on the prosthesis prototype, and experimental results are shown that indicate the effectiveness of the active prosthesis and control approach in restoring fully powered level walking to the user. Finally, an accompanying video demonstrates the functioning prosthesis in level walking.

This paper presents a method for the control of locomotion in a robot hexapod. The approach is based on the WalkNet structure, which in turn is based on the neural control structure of the insect Carausius morosus. Though the WalkNet structure has been shown to function well in kinematic (i.e., non-dynamic) simulations, the authors found that the approach to coordinated control of hexapedal locomotion entailed several significant problems when simulated in the presence of dynamic effects, including gravitational effects, inertial dynamics, and ground contact dynamics. As such, the authors propose several variations on the WalkNet structure that provides stable and robust locomotion in the presence of dynamics, while still maintaining the attributes of WalkNet coordinated control, including self-selection of gait and associated emergent behaviors. The approach is simulated in the presence of dynamics and shown to provide stable gait with emergent characteristics.

The stable simulation of high-stiffness surfaces remains a challenge in impedance-type haptic simulations of mechanical environments. In this paper, the authors propose an approach to achieving a stable, high-stiffness surface in a haptic interface by leveraging the open-loop properties of pneumatic actuators. By using the open-loop component of the actuator stiffness as a primary component of stiffness simulation in a haptic interface, the system requires a comparatively small component of simulated stiffness from the closed-loop control of the actuator. A passivity analysis is presented describing how the presence of an open-loop stiffness enhances the range of passivity of haptically simulated high-stiffness surfaces. Experimental results both with and without a human operator are presented that demonstrate the effectiveness of the approach and its enhanced passivity relative to motor-actuated devices.

This paper proposes a control approach that controls the stiffness and force of pneumatic actuator independently. This independent control of stiffness and force removes a primary cause of contact instability when utilizing stiffness or impedance based force control during interaction with stiff environments. Specifically, in typical stiffness or impedance control, since the force is defined in terms of motion variables, the desired force term appears as high gain position feedback when a manipulator is in contact with a stiff environment. In the proposed approach, since stiffness and force are controlled independently, the force appears as an exogenous input rather than as high gain position feedback, and therefore this source of instability is removed. The paper describes the control approach for independent stiffness and force control, which is based on an MIMO sliding mode controller design. Experimental results are presented that demonstrate the effectiveness of the control approach.

This paper describes a direct-injection, liquid monopropellant powered actuation system, which was developed for the purpose of providing mechanical power to self-powered human-scale robots. The actuation system utilizes the catalytic decomposition of a monopropellant as a hot gas generator for powering pneumatic-type actuators. Specifically, pressurization of a pneumatic actuator is provided via solenoid injection valves, which control the flow of the monopropellant through a catalyst pack into the respective sides of the cylinder. Depressurization is provided by a three-way proportional spool valve, which can exhaust one of the two cylinder chambers. A prototype of the actuation system is described, and experimental data is presented that demonstrates good force and motion tracking performance. Experimental results characterizing the energetic performance of the system demonstrate that the prototype provides an energetic figure of merit an order of magnitude greater than that of battery-powered servomotors.

This paper presents and experimentally demonstrates a control methodology that provides transparency and stability robustness in bilateral telemanipulator systems. The approach is based upon a previously published method that structures the human-manipulators-environment system in a manner that enables the application of frequency-domain loop-shaping methods. This paper reformulates the human-manipulator interaction described in the previously published work, and experimentally demonstrates the approach on a single degree-of-freedom telemanipulation system. Experimental measurements indicate significant improvements offered by the method in both the stability robustness and transparency of the human-manipulators-environment system. Finally, experimental results are presented that demonstrate the robustness in the transparency to significant changes in the environment dynamics.

This work describes the modeling and control of a proposed actuation system that is capable of pressurizing a chamber volume via the catalytic decomposition of a liquid monopropellant controlled by a binary on/off propellant valve. Two design configurations of the actuation system are presented and common portions of both are energetically modeled. The parameters of the resulting dynamic model are meaningful physical properties of either the propellant or the system. A model-based switching controller is then applied to the task of pressure tracking. Model validation and controller performance are shown experimentally.

This paper describes the design of a liquid-propellant-powered hot-gas actuator appropriate for human-scale power-autonomous robots. A prototype of the actuation system is described, and closed-loop tracking data is shown that demonstrates good motion control. Experiments to characterize the energetic performance of the actuation system indicate that the proposed system with a diluted propellant offers an energetic figure of merit five times greater than a battery-powered by undiluted propellant would offer an energetic figure of merit an order of magnitude greater than battery-powered DC motor actuated systems.

This paper presents a liquid-fuel powered pneumatic actuator appropriate for human-scale autonomous robotics. The motivation for this work is the development of a lightweight actuation system with system energy and power densities significantly greater than a DC motor and battery combination. For the scale of interest, the design tradeoffs between complexity of an energy conversion system and fuel specific energy density make many conventional approaches inappropriate. Conventional actuation, such as a battery powered DC motor system, does not possess adequate energy storage to perform significant amounts of mechanical work for significant periods of time autonomously. A system design comparison for a six-degree of freedom walking robot is presented which compares the expected performance of a monopropellant powered actuation system to a battery powered DC motor system. Results from this comparison demonstrate the viability of such an approach and indicate significant increases in energy and power densities. A single-degree of freedom manipulator was constructed to demonstrate this approach. Experimental results corroborate the expected energetic advantages.

This paper presents a two-part study of the effects of virtual surface stiffness on haptic perception. First, size identification experiments were performed to determine the effects of system quality, in terms of surface stiffness, on the ability of a human to identify square cross-section ridges by size in a simulated environment. Then, discrimination experiments were performed to determine relationships between virtual surface stiffness and simulation quality in terms of perceived surface hardness. Results of experiments to test human haptic perception for varying virtual surface stiffnesses indicate that haptic interface hardware may be able to convey sufficient perceptual information to the user at relatively low levels of virtual surface stiffness. Subjects, however, can perceive improvements in perceived simulated surface hardness as stiffness levels are increased in the range of achievable parameters for this hardware. The authors draw several conclusions about the allowable time delays in a haptic interface system based on the results of the surface stiffness experiments.

This paper describes the implementation of a two-channel position-force control architecture on a three degree-of-freedom scaled master-slave telemanipulation system. The architecture enables the authors to address both the transparency bandwidth and stability robustness of the system. First, the uncompensated transparency and stability robustness of the bilateral telemanipulation system are experimentally assessed. Then, loop-shaping compensators are used to increase the transparency bandwidth, while maintaining the stability robustness of the system, and the results are compared with those of the uncompensated system.

This paper presents a two-part study of the effects of maximum endpoint force and system bandwidth on haptic perception. First, size identification experiments were performed to determine the effects of system quality, in terms of these two system parameters, on the ability of a human to identify square cross-section ridges by size in a simulated environment. Then, discrimination experiments were performed to determine the relationships between haptic interface machine parameters and simulation quality in terms of perceived surface hardness. Results indicate that haptic interface hardware may be able to convey sufficient perceptual information to the user with relatively low levels of force feedback and system bandwidth, yet subjects can perceive improvements in simulated surface quality as levels are further increased.

Describes a design technique for simultaneously increasing the transparency bandwidth and stability robustness of a two-channel position-force bilateral teleoperation architecture. Specifically, the stability and performance enhancements are obtained by introducing a dynamic compensator into the system to shape the frequency-domain properties of the human-teleoperator-environment loop. This design technique is demonstrated in a single degree-of-freedom numerical example.

This paper addresses the modeling and control of a compliant micromanipulator for use in such fields as microsurgery, telesurgery, and microassembly. The unique flexure-based manipulator utilizes revolute flexure joints in achieving well-behaved kinematic characteristics, without the backlash and stick-slip phenomena that would otherwise impede precision control. A mathematical model of the micromanipulator is formulated, and a controller for positioning of the manipulator is derived. The model and resulting controller are unlike typical manipulator models and controllers since this manipulator is actually a controlled large range-of-motion structure with nonlinear structural dynamics. Following the development of the controller, computer simulations of the proposed controller on the manipulator are used to verify the positioning performance.

An inchworm robotic insect is presented that can displace on a smooth horizontal surface. It consists of a piezoelectric unimorph and two custom-designed limbs. A two-module lumped-parameter model is formulated to assist in the design/analysis process. The geometry of deformation is analyzed first by superimposing the unimorph's elastic deformation to a rigid-body rotation around the limb/ground contact point A geometry configuration is thus identified that maximizes the horizontal displacement of the robot over one motion's cycle. The dynamic module allows simple evaluation of the ground reaction forces and horizontal velocity of the robot's center of gravity. A prototype inchworm robotic insect was designed whose behavior exhibited good agreement with theoretical predictions.

This paper addresses the issue of dynamic similarity and intensive property invariance in scaled bilateral manipulation, and offers a design methodology based on these considerations. Dimensional analysis methods are utilized to form the basis of a constrained optimization problem that enables selection of a force scaling factor that minimizes the intensive distortion of the environment. The proposed formulation is applicable to any physical environment, including those that are nonlinear and contain multiple degrees of freedom. Furthermore, the formulation does not require an exact environmental model, provided the parameters that influence the environment are known. The proposed techniques are particularly relevant to bilateral manipulation of a microscopic environment (i.e., macro-micro bilateral manipulation), since such environments are difficult to model exactly and are largely influenced by nonlinear effects.

A piezoelectric (PZT) stack-based actuator was developed to provide a means of actuation with dynamic characteristics appropriate for small-scale manipulation. In particular, the design incorporates a highly nonlinear, large-ratio transmission that provides approximately two orders of magnitude motion amplification from the PZT stack. In addition to motion amplification, the nonlinear transmission was designed via optimization methods to distort the highly non-uniform properties of a piezoelectric actuator so that the achievable actuation force is nearly constant throughout the actuator workspace. The package also includes sensors that independently measure actuator output force and displacement, so that a manipulator structure need not incorporate sensors nor the associated wires. Specifically, the actuator was designed to output a maximum force of at least one Newton through a stroke of at least one millimeter. For purposes of small-scale precision position and/or force control, the actuator/sensor package was designed to eliminate stick-slip friction and backlash. The overall dimensions of the actuator/sensor package are approximately 40/spl times/65/spl times/25 mm.

This paper describes the fundamental physical motivations for small-scale minimum surface-effect design, and presents a three degree-of-freedom micromanipulator design that incorporates a minimum surface-effect approach. The primary focus of the design is the split-tube flexure, a unique small-scale revolute joint that exhibits a considerably larger range of motion and significantly better multi-axis revolute joint characteristics than a conventional flexure. The development of this joint enables the implementation of a small-scale spatially-loaded revolute joint-based manipulator with well-behaved kinematic characteristics and without the backlash and stick-slip behavior that would otherwise prevent precision control.

A lumped-parameter model of a piezoelectric stack actuator has been developed to describe actuator behavior for purposes of control system analysis and design, and in particular for microrobotic applications requiring accurate position and/or force control. In addition to describing the input-output dynamic behavior, the proposed model explains aspects of non-intuitive behavioral phenomena evinced by piezoelectric actuators, such as the input-output rate-independent hysteresis and the change in mechanical stiffness that results from altering electrical load. The authors incorporate a generalized Maxwell resistive capacitor as a lumped parameter causal representation of rate-independent hysteresis. Model formulation is validated by comparing results of numerical simulations to experimental data.