A Hybrid Systems and Optimization-Based Control Approach to Realizing Multi-Contact Locomotion on Transfemoral Prostheses

Abstract

This paper presents a systematic methodology utilizing multi-domain hybrid system models and optimization based controllers to achieve human-like multi-contact prosthetic walking experimentally on a custom-built prosthesis: AMPRO. Inspired by previous work that realized multi-contact locomotion on a bipedal robot AMBER2, a hybrid system based optimization problem is proposed leveraging the framework of multi-domain hybrid systems. Utilizing a reference human gait coupled with physical constraints, the end result of this optimization problem is stable multi-contact prosthetic gaits that can be implemented on the prostheses directly. Leveraging control methods that stabilize bipedal walking robots- control Lyapunov function based quadratic programs coupled with variable impedance control-an online optimization-based controller is formulated to realize the designed gait in both simulation and experimentally on AMPRO. Improved tracking and energy efficiency are seen when this methodology is implemented experimentally. Additionally, the resulting multi-contact prosthetic walking captures the essentials of natural human walking both kinematically and kinetically.