MIMO Sliding Mode Controller for Gait Exoskeleton Driven by Pneumatic Muscles

In the past decade, pneumatic muscle (PM) actuated rehabilitation robotic devices have been widely researched, mainly due to the actuators' intrinsic compliance and high power to weight ratio. However, the PMs are highly nonlinear and subject to hysteresis behavior. Hence, robust trajectory and compliance control are important to realize different training strategies and modes for improving the effectiveness of the rehabilitation robots. This paper presents a multi-input-multioutput sliding mode controller, which is developed to simultaneously control the angular trajectory and compliance of the knee joint mechanism of a gait rehabilitation exoskeleton. Experimental results indicate good multivariable tracking performance of this controller, which provides a good foundation for the further development of assist-as-needed training strategies in gait rehabilitation.