Design and Control of Transfemoral Powered Prosthesis

Abstract

An impedance-based control strategy to enable a user to walk at a pre-defined speed on the treadmill using a two degree of freedom transfemoral prosthesis with powered knee and ankle joints is presented. The strategy is based on segmenting level walking gait into four distinct modes or finite states and assigning appropriate dynamic behavior to the joints in each of these states. The form of impedance functions are developed from population biomechanical data provided by Winter [1]. Appropriate parameters for impedance functions for a particular user are obtained by experimental tuning through user feedback and recorded gait variables. The final results from a treadmill walk with a user fitted with an able-bodied adapter at 1.8mph are presented, and compares well to normal walking pattern.