Low-gain feedback controller for a real soft actuated knee rehabilitation device using a state observer

Abstract

Rehabilitation devices using soft actuation have been designed recently due to their characteristics in the human-robot interaction. Though, the analysis and control of these kinds of systems are challenging. We have designed a five-link knee rehabilitation device actuated in two of the five joints. This system can be reconfigured to attend a wide range of patients according to their height. We use elastic actuation to help the motion at the knee joint. In this work, we simplify the rehabilitation device modelling into a one-degree of freedom (DoF) soft actuated system. We present the design and implementation of a dynamic feedback controller to track a desired reference. For the proposed controller, we require an estimation of the system stiffness and some of the states, so we propose a state observer as part of the design. As a result, we present the design and implementation of the controller with a state observer that follows a desired angular joint trajectory with the desired stiffness. We demonstrate in simulation, by performing different tests oriented to carry out rehabilitation routines, the effectiveness, and stability of the controlled system which responds effectively to disturbances.