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We present a novel hybrid knee prosthesis that uses a motor, transmission and control system only for active dynamics tasks, while relying on a spring/damper system for passive dynamics activities. Active dynamics tasks require higher torque, lower speed, and occur less frequently than passive dynamic activities. By designing the actuation system around active tasks alone, we achieved a lightweight design (1.7 Kg w/o battery) without sacrificing peak torque (85Nm repetitive). Preliminary tests performed by an able-bodied person using a bypass orthosis show that the hybrid knee can support reciprocal stairs ambulation with low electrical energy consumption.

Abstract-Body-powered prostheses use a cable-operated system to generate forces and move prosthetic joints. However, this control system can only generate forces in one direction, so current body-powered prehensor designs allow the user either to voluntarily open or voluntarily close the tongs. Both voluntary opening (VO) and voluntary closing (VC) modes of operation have advantages for certain tasks, and many endusers desire a terminal device (TD) that can switch between the two modes. However, such a TD must maintain the same thumb position (i.e., point of Bowden cable attachment) and movement direction in both modes in order to avoid the need to readjust the harness after every mode switch. In this study, we demonstrate a simple design that fulfills these requirements while allowing the user to switch easily between modes. We describe the design concept, describe a rugged split-hook prototype, provide specifications (size, weight, efficiency, etc.), and present a pilot study in which five subjects with intact arms and two subjects with amputation used the VO and VC splithook prehensor to perform the Southampton Hand Assessment Procedure. Subjects performed an average of 4 to 7 (+/-0.2) points better when they could choose to switch between modes on a task-by-task basis than when they were constrained to using only VO or VC modes.

Absrrocr -This study is an extension of earlier work to incorporate walker handle dynamometers with a video motion analysis system. The purpose of this study is to more fully address the quantitative metrics identified in the pilot study with a more sophisticated biomechanical model and instrumentation system, and a larger subject population. Preliminary findings of walker comparisons indicate differences in shoulder and elbow angles when comparing anterior and posterior walkers.'