Sliding Mode Control of an Exoskeleton Gait Rehabilitation Robot Driven by Pneumatic Muscle Actuators

This paper firstly summarizes a newly developed knee joint mechanism of a gait rehabilitation robot, as well as a modified dynamics model for pneumatic muscle actuators (PMAs). The major sections focus on the development of single-input-single-output sliding mode trajectory tracking controller for the knee mechanism. The sliding mode controller takes the models of the whole system, which include the pneumatic flow dynamics of the analogue valves and PMAs, dynamic model of the PMAs and dynamics of the mechanism, into account. It controls the voltage applied to the valves to track desired angular trajectories of the knee joint. The preliminary experiments on the sliding mode controller have been conducted and the results have indicated that the knee mechanism’s successful tracking of sinusoidal waves with frequencies and magnitudes closed to actual human gait. Currently, the researchers are working on the development of multi-inputs-multi-outputs control of the mechanism for both trajectory tracking and compliance adjustments.