In this paper we introduce a design framework that permits task-specific complex geometries in robotic limbs with the minimal power consumption. Additionally we present a optimal gear ratio selection algorithm with realistic constraints, which we use as a subroutine within the geometry optimization. As a case study we optimize the a spatial, hybrid parallel-serial robotic limb structure with a large set of geometric parameters. Optimal design with respect to this mechanism produces three locally optimal families of designs. These are analyzed rigorously and a best design was chosen. A prototype has been constructed from the chosen design family, proving that the approach is practical. This serves as evidence that the design optimization method is an effective tool to minimize the electrical cost of a given task, and thus specialize the design.

With over 600 thousand people each year surviving a stroke, it has become the leading cause of serious long-term disability in the United States [1], [2]. The adverse financial and social conditions attributed to stroke have prompted researchers and entrepreneurs to explore the viability of rehabilitation robots. The Powered Ankle Foot Orthosis (PAFO) utilizes robotic tendon technology and supports motion with a single degree of freedom, ankle rotation in the Sagittal plane. Motion capture data, robot sensor data, and functional 6 minute walk data were collected on three stroke subjects. All subjects had some positive changes in their key gait variables while using the PAFO. These changes were more dramatic while harnessed and using a treadmill as opposed to walking over ground. Robot sensor data showed significant improvements on key variables for the three subjects. Motion capture data showed improvements in knee range of motion for subject 1, and the 6 minute walk data showed an increase in distance walked for subjects 1 and 3. Comfort, stability, and robustness proved to be critical design parameters for developing a gait therapy robot capable of collecting repeatable data with low variability.

With microprocessing power greatly increasing, hardware is no longer a hurdle in the development of controllers for wearable robotic systems, specifically lower limb robots. The challenge remains in developing smart algorithms that are able to detect which task a person is about to perform and then determine the correct desired movements for the robotic system. This paper reflects on four existing control algorithms for the task of level ground walking, and then presents theory and test results of a novel control algorithm based on phase plane invariants. The goal of this paper is to produce the correct motor reference command in a continuous fashion rather than based on determining distinct states for a given task.

There are various methods to control a powered AFO. As different as they are in their approach each of them has certain advantages as well as difficulties. What is still needed is a robust control concept that meets the requirements for ankle gait assistance. A new, stiffness-control model has been developed that divides the stance phase of gait into five zones using either velocity or stiffness control for each zone. The design and implementation of this new control algorithm as well as some first test results are presented.

A portable wearable robotic device that can actively supplement locomotion of partially limited ambulators in their normal environment (variable terrain, weather, man made structures, etc.) seems highly desirable but currently short of attainment due to several key technology gaps. Low energy and power density in current actuation technology, inadequate control schemes and safety of use are leading challenges towards a portable, complementary device. This paper presents the dynamically controlled ankle-foot orthosis (DCO) with regenerative kinetics which seek to incrementally attain portability by solving the energy/power density issue in powered elements by harnessing elastic energy of uniquely tuned mechanical elements and reducing the control problem and increasing safety by introducing compliant elements between the human-machine-environment interfaces.

Repetitive task therapy is an effective form of rehabilitation for people suffering from the debilitating injuries of stroke. Robotic physical therapy devices have been developed in the past, many of which may benefit from the use of bidirectional pneumatic actuators. This paper presents the Robotic Gait Trainer, an ankle rehabilitation device structurally based on a tripod mechanism with one fixed link. The device incorporates two double-acting, compliant Spring Over Muscle (SOM) actuators as actuation links. The kinematic model of the tripod structure and analysis of the workspace of the robotic device are discussed. It is shown that the device is capable of moving the foot about the ankle joint in dorsiflexion and plantarflexion as well as inversion and eversion, a feature unique to the lightweight, compact and easily portable device. Results of the analysis prove that the tripod structure generates a range of motion that matches the safe anatomical range of the ankle joint during gait

This paper presents a new human-based navigation model to guide a mobile robot to intercept ground balls. The new model consists of two strategies: the optical acceleration cancellation (OAC) model, and the lateral alignment strategy. The OAC model uses a linearly decreasing cotangent function of the gaze angle to reduce the distance between the robot and the target on the ground. It determines a set of possible robot positions on the horizontal plane at every time instant. The robot laterally aligns with the target when it moves to the side. The lateral alignment strategy determines a unique robot position at each time instant. The new navigation strategy provides a simple and fast algorithm to navigate mobile robots in an open field to intercept ground balls. Visual servo controllers were designed and simulated. A high-speed mobile robot was developed to conduct interception experiments

In previous work, we demonstrated the feasibility of perceptual navigation algorithms used to intercept fly balls. In this paper we expand the optical acceleration cancellation heuristic to also intercept ground balls. We used computer simulations and experiments with mobile robots with various bail trajectories and different initial positions of the fielder to test our new model. A new robotic system with improved vision and faster processing was developed for experimentally intercepting ground balls. The results support the generality of viewer based interception heuristics for both fly balls and ground balls.

The relationship between input deflection and output force is fixed for constant-force mechanisms. An advantage of a constant-force mechanism is that the control effort is minimized. For example, in grasping applications, if the grasp force is understood and given, then the mechanism will apply the constant-force even if there are small deflections. A double-slider, variable, constant-force mechanism is developed in this paper. The force relationship is analyzed using the virtual network principle. An active control law is used to generate a variable constant-force output. The paper also discusses the experimental validation of the force relationship using springs and also compliant plastic materials. This macro-level research is a step towards developing the technical capability to design micro constant-force mechanisms.

The study of human, upright-balance is often performed by perturbing a base on which a subject is standing. Once a perturbation is initiated, data describing a subject's ability to balance is recorded and analyzed. We introduce a novel perturbation device that can translate and rotate its base in any direction within a 2D plane. This robust perturbation envelope will expand researchers' abilities in the study of upright balance and balance recovery. The heart of the design is the use of four powered casters as the platform's transmission system. The casters' offset insures that the Jacobian matrix describing the system's planar motion is non-singular. A rapid embedded programming method is used to develop the control system. By controlling the orientation and speed of each caster, translation, rotation, or combined perturbations can be easily implemented.

Human based algorithms; to catch fly balls have been research and studied. In the paper, the validity of the human models are tested by catching balls that are dropped vertically downward. The regular OAC (optical acceleration cancellation) and the inverted OAC models are simulated first, and then tested experimentally with a mobile robot. The simulation and the experimental results show that both methods are able to intercept the dropped ball, but the initial and final motions are different. A digital image processing program, DVRobot, was written to process digital images very quickly.

Human based vision algorithms for interception of flying balls in one-dimension have been researched and studied. We develop new perceptual strategies for three-dimensional space that are robust and simple. Results from simulations show the feasibility of human vision algorithms for ball catching. This paper discusses the experimental validation of two perceptual algorithms: linear optical trajectory and the optical acceleration cancellation.

We describe a framework and control algorithms for coordinating multiple mobile robots with manipulators focusing on tasks that require grasping, manipulation and transporting large and possibly flexible objects without special purpose fixtures. Because each robot has an independent controller and is autonomous, the coordination and synergy are realized through sensing and communication. The robots can cooperatively transport objects and march in a tightly controlled formation, while also having the capability to navigate autonomously. We describe the key aspects of the overall hierarchy and the basic algorithms, with specific applications to our experimental testbed consisting of three robots. We describe results from many experiments that demonstrate the ability of the system to carry flexible boards and large boxes as well as the system's robustness to alignment and odometry errors.

Proposes an architecture for tightly coupled multi-robot coordination that is well suited to cooperative manipulation tasks. At all times, a robot is identified as a leader, while the others are designated as followers. The assignment of roles and the coordination between the robots is guaranteed by communication protocols and control algorithms. The key feature is the flexibility that allows changes in leadership and assignment of roles during the execution of a task. We describe the experimental implementation and demonstration in a cooperative transportation task, in which two and three heterogeneous robots cooperate to carry a large object in an environment containing obstacles.

We present a novel modeling framework and control algorithms for multiple mobile manipulators cooperatively grasping and transporting an object. The planning and control tasks are decentralized, and the framework explicitly incorporates the protocols used to coordinate the robots in the team. The framework is flexible in the sense that it scales with the number of robots and controllers. Preliminary experimental results for teams of two-three robots are shown, while simulation results are used to illustrate the extensions of our approach to larger teams.

Human navigational principles are researched and applied to mobile robotic applications. Two principles, constant optical rate and angular constancy, can be used by a fielder or mobile robot to define a trajectory for interception of a projectile without knowledge of the ball's or fielder's world coordinates. Two novel, robust, viewer-centered algorithms, a passive and an active version, are modeled and experimentally validated.

We develop two quality measures for the analysis and optimization of grasps and fixtures. The first metric is a measure of stability and is obtained by analyzing the effect of small perturbations in the position of the grasped object or small disturbance forces on the grasped object The second metric is a measure of robustness to errors in the positions of the fixture elements. In addition, we explore the effect that the stiffness of the fixture elements has on these two quality measures and propose a design optimization approach to maximize stability and robustness to errors.

The main goal of the paper is to present a framework and basic control algorithms for coordinating a small team of robots in tasks that involve grasping large objects and transporting them in a two-dimensional environment with obstacles. Each robot consists of a mobile platform and an arm. Some arms are passive while others are active. Our previous work (1998) addressed the manipulator design, the architecture, and the communication between robots. In this paper we address the control of the manipulators, the coordination between the platforms for a team of two or three cooperating robots, and the handling of flexible large objects.

This paper addresses the design and control of autonomous mobile platforms manipulating and transporting a grasped object. Each platform is equipped with a manipulator arm. In order to hold an object in a stable grasp, the arms have to apply and maintain appropriate contact forces to ensure force closure. We describe an architecture and a real time control system that allow the coordinated control of multiple, heterogeneous, mobile manipulators. In this architecture, a lead robot plans, based on available sensory information, and follows a suitable trajectory. The other robots follow a desired formation with respect to the leader while maintaining a stable grasp. There are three main contributions in this paper. We present the real time control system and our approach to rapidly prototype the control code. We describe a novel, forklift-like arm and a control scheme that allows us to easily control the Cartesian stiffness or impedance. Finally, we describe the details of an experimental testbed and results that demonstrate the robustness of the control scheme.

The authors address force control in overconstrained dynamic systems with special emphasis on robot control. Previous approaches to force control are studied, and many of these are shown to be unsuitable for dynamic force control. Practical and theoretical considerations for designing force control algorithms are discussed. Experimental and simulation results that validate the theoretical findings are presented for a single-degree-of-freedom pneumatic force controller.>

The mechanics, design, control, and experimental results for a 3-DOF (degree-of-freedom) in-parallel, pneumatically actuated manipulator are presented. The manipulator consists of two platforms connected by three serial chains. It is naturally compliant in translation along the approach direction as well as in rotations about axes perpendicular to the approach direction, while it is stiff in other directions. The kinematic design allows the three relative DOF between the two plates of the manipulator to accommodate uncertainties and sustain impacts while contacting and interacting with unknown environments. Experimental results show that, with a sampling rate of 100 Hz, the position control bandwidth of a single actuator servo system is 11 Hz, while the force control bandwidth is 10 Hz. These figures also reflect the bandwidth and the performance of the complete system.>