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.

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 a general method for exact distance computation between convex objects represented as intersections of implicit surfaces. Exact distance computation algorithms are particularly important for applications involving objects that make intermittent contact, such as in dynamic simulations and in haptic interactions. They can also be used in the narrow phase of hierarchical collision detection. In contrast to geometric approaches developed for polyhedral objects, we formulate the distance computation problem as a convex optimization problem. We use an interior point method to solve the optimization problem and demonstrate that, for general convex objects represented as implicit surfaces, interior point approaches are globally convergent, and fast in practice. Further, they provide polynomial-time guarantees for implicit surface objects when the implicit surfaces have self-concordant barrier functions. We use a primal-dual interior point algorithm that solves the Karush-Kuhn-Tucker (KKT) conditions obtained from the convex programming formulation. For the case of polyhedra and quadrics, we establish a theoretical time complexity of O(n1.5), where n is the number of constraints. We present implementation results for example implicit surface objects, including polyhedra, quadrics, and generalizations of quadrics such as superquadrics and hyperquadrics, as well as intersections of these surfaces. We demonstrate that in practice, the algorithm takes time linear in the number of constraints, and that distance computation rates of about 1 kHz can be achieved. We also extend the approach to proximity queries between deforming convex objects. Finally, we show that continuous collision detection for linearly translating objects can be performed by solving two related convex optimization problems. For polyhedra and quadrics, we establish that the computational complexity of this problem is also O(n1.5).

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.

In this paper, we present an interior point approach to exact distance computation between convex objects represented as intersections of implicit surfaces. The implicit surfaces considered include planes (polyhedra), quadrics, and generalizations of quadrics including superquadrics and hyperquadrics, as well as intersections of these surfaces. Exact distance computation algorithms are particularly important for applications involving objects that make contact, such as in dynamic simulations and in contact point prediction for dextrous manipulation. They can also be used in the narrow phase of hierarchical collision detection. In contrast to geometric approaches developed for polyhedral objects, we formulate the distance computation problem as a convex optimization problem; this optimization formulation has been previously described for polyhedral objects. We demonstrate that for general convex objects represented as implicit surfaces, interior point approaches are reasonably fast and in some cases, owing to their global convergence properties, are the only probably good choice for solving proximity query problems. We use an interior point algorithm that solves the KKT conditions obtained from the convex programming formulation. We present implementation results for example implicit surface objects and demonstrate that distance computation rates of about 1 kHz can be achieved