Prosthetic legs output feedback control via variable high gain observers

Abstract

This work addresses the modeling, state estimation, and control of a robot/prosthesis system with four joints: vertical hip prismatic joint, thigh, knee, and ankle rotational joints. The full dynamic model is provided, and a simplified version is considered for control/estimator evaluation. Initially, a full-state feedback scheme is implemented using computed torque plus a PID controller, and then a high gain observer is designed to estimate the system states. We propose the implementation of a high gain observer (HGO) to estimate the prosthesis joint velocities with a time-varying HGO gain synthesized from measurable signals designed to reduce the amount of noise in the control effort while keeping an acceptable tracking error transient performance. Simulations are conducted to evaluate the performance using fixed HGO gain in comparison with the proposed variable HGO approach, in the presence of noise and parametric uncertainties.