Designing an Adaptive Prosthetic Socket Controller Using H-Infinity Loop Shaping Synthesis

Abstract

Amputees often find wearing a prosthetic limb for a long period of time uncomfortable. Prosthetic sockets that adjust the socket’s fit automatically, or adaptive sockets, would encourage amputees to wear their prosthesis more frequently. In this work, we simulate the control system design of a Multiple-Input, Multiple-Output (MIMO) adaptive socket using principles of optimal control and robust control. A data-driven model of the socket-limb interface is first obtained by applying regression to open-loop recordings of the socket interacting with the limb during a simulated grasping task. A MIMO controller is then designed to maintain a desired uniform socket fit. An $H_{\infty}$ controller, obtained from loop shaping synthesis using the Glover-McFarlane method, is shown to perform comparably to a Linear Quadratic Gaussian (LQG) controller while maintaining robustness to uncertainties in the socket-limb interface model. This work then outlines a potential procedure on how to develop the control system for a real adaptive prosthetic socket with multiple sensors and actuators.