Robust Repetitive Learning Control of Lower Limb Exoskeleton with Hybrid Electro-hydraulic System

In this paper, robust repetitive learning control for lower limb exoskeleton, CASWELL-II, is addressed. A hybrid electro-hydraulic system which consists of unidirectional servo valve and magnetic valve is presented to driven the exoskeleton leg. First, a full state space model of CASWELL-II is worked out by combining both the rigid body and hybrid electro-hydraulic actuators dynamics. Secondly, a robust repetitive learning controller is presented to perform the periodic tracking task of the hybrid electro-hydraulic actuators via backstepping design, and the stability of the closed-loop system is proved by Lyapunov method. Finally, the controller is realized and tested on CASWELL-II by experiment.