Control of a Transfemoral Prosthesis on Sloped Terrain using Continuous and Nonlinear Impedance Parameters

Abstract

The design of impedance controllers for sloped walking with a transfemoral prosthesis is a complex control problem that generally results in numerous tuning parameters. This study proposes an easy-to-tune sloped walking control scheme. While the ankle is controlled using impedance control, the knee is controlled using a hybrid strategy of impedance control and trajectory tracking. This study derived continuous, nonlinear impedance functions for the ankle and knee joints using optimization. Principal component analysis of the impedance functions revealed trends that can be used to design impedance controllers for any given slope angle. Said trends were further used to establish a tuning regime which was subsequently tested on a transfemoral prosthesis in an emulator study. The generated gait kinematics and kinetics were found to follow the trends of healthy sloped walking data.