Prosthetic Legs Output Feedback Control via Variable High Gain Observer

This paper addresses the state estimation and control of a robot/prosthesis control system with four joints: vertical hip displacement, thigh, knee and ankle angles. The motivation was inspired by several drawbacks regarding the usage of load cells and/or sensors in robots and prosthetic legs to capture gait data, external forces (GRFs) and moments during walking. 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. Numerical simulations analyze the robustness of the closed-loop control with respect to parametric errors and measurement noise.