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The level walking process for an above knee (A/K) amputee with a conventional prosthesis greatly compromises the amputee’s mobility. The fact that conventional prostheses lock in hyperextension during the stance phase, in contrast to the extend-flexextend pattern during stance for the natural limb, has been suggested as a source of the amputee’s uncosmetic gait and high energy expenditure. While the lock in hyperextension during stance provides stability to prevent buckling, it requires the person to vault over the prosthetic limb. This vaulting during level walking may cause higher vertical displacements of the body center of gravity (c.g.) and accompanying higher energy requirements for the amputee. This investigation employs an amputee-interactive prosthesis simulator system to evaluate the viability of controlling the prosthetic knee joint to follow a normal knee position pattern. In order to insure that the amputee-interactive prosthesis simulator system does not introduce gait anomalies, the system was controlled to simulate a conventional prosthesis. This showed that the simulator system has no undesired side effects since data from walking trials with the simulator system in “conventional prosthesis mode” are very similar to data from conventional prostheses in the literature. Then, an active position control scheme which controls the prosthetic knee joint to follow a normal knee position pattern was tested by two young, active amputees in level walking trials. The subjects experienced very little difficulty in walking with the active control scheme and preferred the simulator with the active control scheme to their conventional prostheses. Measured knee power requirements for the scheme indicate that this type of control is feasible without external power sources. However, measurements of the vertical displacement of the body c.g. show little difference between gait with the active control scheme and gait with a conventional prosthesis. It appears that the increased energy requirements for A/K amputees are not due in total to the lack of the extend-flex-extend position profile at the prosthetic knee joint.

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A new approach for evaluating advanced concepts for knee-joint control in above-knee prostheses involves the use of a simulator prosthesis which can be worn by an amputee and controlled electronically to emulate proposed future prostheses. A critical element in this system is the knee-torque controller. Realization of a powerful, lightweight, easily controlled transducer was essential to the successful development of the simulator system. This paper presents the design of such a controller and evaluates its performance. Brief examples of studies in which the new system has been applied are given. The proven viability of the device suggests that similar actuators might aid other prosthesis/orthesis studies.

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