A walking controller for a powered ankle prosthesis

Abstract

This paper describes a walking controller implemented on a powered ankle prosthesis prototype and assessed by a below-knee amputee subject on a treadmill at three speeds. The walking controller is a finite state machine which emulates a series of passive impedance functions at the joint in order to reproduce the behavior of a healthy joint. The assessments performed demonstrate the ability of the powered prosthesis prototype and walking controller to reproduce essential biomechanical aspects (i.e. joint angle, torque, and power profiles) of the healthy joint, especially relative to a passive prosthesis.

Fig. 1

Powered prosthesis prototype.

Fig. 2

The finite state machine executed by the prosthesis for walking. θ_a is the ankle angle, which is compared to predetermined thresholds θ_th,01, θ_th,12, and θ_th,3, respectively. ${\stackrel{.}{\theta }}_a$ is the angular velocity of the ankle, and ${\stackrel{.}{\theta }}_f$ is the angular velocity of the foot with respect to the ground

Fig. 3

Kinematics and kinetics for slow, normal, and fast cadences. Healthy subject data ± 1 standard deviation are shaded in gray, powered prosthesis data are shown by blue (dark) lines, and passive prosthesis data are shown by red (light) lines.