Design, Control, and Assessment of a Semi-Powered Prosthetic Ankle

Abstract

The current state of the art in ankle-foot prostheses is a leaf-spring-like device typically constructed from carbon fiber. While passive leaf-spring-like prosthetic ankles perform well on level terrains, they lack the behavioral adaptability to accommodate other terrains such as stairs and slopes. Recently, fully powered prosthesis have been developed to address this lack of versatility, however, these fully-powered devices require sizeable motors, transmissions, and batteries, increasing the size and weight of the prosthesis relative to the spring-like standard-of-care. This thesis describes the development of an ankle prosthesis that attempts to provide behavioral adaptability across activities and terrains while minimizing the size and weight of the device relative to fully powered prostheses. This functionality is provided via the design of a semi-powered ankle that is able to control its configuration (spring equilibrium angle) and its resistance (damping). This semi-powered prosthesis leverages a low-power electromechanical drive system in conjunction with a high dissipative power hydraulic actuator to provide the intended mechanical functionality. The mechanical design of the prosthetic ankle is described and control algorithms are developed for functionality across common activities such as stair descent, sloped walking, and sloped standing. The device and controllers are assessed on a single transtibial amputee subject and both kinematic and kinetic outcome measures are presented.