Fuzzy sliding mode control of an upper limb exoskeleton for robot-assisted rehabilitation

Robot-assisted therapy has become an important technology used to restore and reinforce the motor functions of the patients with neuromuscular disorders. In this paper, we proposed an upper-limb exoskeleton intended to assist the rehabilitation training of shoulder, elbow and wrist. The proposed therapeutic exoskeleton has an anthropomorphic structure able to match the upper-limb anatomy and enable natural human-robot interaction. A modified sliding mode control (SMC) strategy consisting of a proportional-integral-derivative (PID) sliding surface and a fuzzy hitting control law is developed to guarantee robust tracking performance and reduce the chattering effect. The Lyapunov theorem is utilized to demonstrate the system stability. In order to evaluate the effectiveness of proposed algorithm, several trajectory tracking experiments were conducted based on a real-time control system. Experimental results are presented to prove that, when compared to the conventional PID controller, the fuzzy SMC strategy can effectively reduce the tracking errors and achieve favorable control performance.