A Unified Control Framework with Continuous Speed Adaptation used for Powered Prostheses Control

Abstract

A challenge for lower-limb powered prostheses is developing a seamless control strategy to perform multiple locomotion tasks, such as changes in walking speed. Generally, powered prostheses implement different independent controllers that correspond to a specific task that each contain their own patient-specific control parameters to tune. This paper presents an online parameterize method of providing desired joint kinematic trajectories for a powered knee-ankle prosthesis controller to perform continuously smooth kinematic transitions unified across the gait cycle for level-ground activity. An active Catmull-Rom spline model generates the online desired knee and ankle joint trajectories as a virtual constraint controller that is a function of a phase variable and human desired speed. An offline optimization routine was implemented to produce optimal control point locations for the Catmull-Rom spline model to give transit across different kinematic walking speeds in a continuous manner. Results demonstrate speed adaptation for different walking speeds (i.e., slow, normal, and fast) as well as running to show versatility towards an adaptive unified virtual constraint control.