Model-free prescribed performance fixed-time control for wearable exoskeletons

Abstract

Abstract In this paper, a model-free fixed-time control strategy with prescribed performance is proposed for the wearable exoskeleton angle tracking control. Firstly, an ultra-local model is employed to formulate the plant dynamic relation between control input and output. Then, an intelligent-proportional-derivative controller is designed based on the time delay estimation technique. To improve the tracking precision, a prescribed performance sliding mode controller is designed and a uniform robust exact disturbance observer is employed to compensate the controller. Besides, based on the universal barrier Lyapunov function, the stability is analyzed for the closed-loop system and the prescribed performance is proved. Finally, a 5 degree-of-freedom wearable exoskeleton virtual prototype is developed in SOLIDWORKS and transferred to MATLAB/SimMechanics as the controlled object of visualization simulation, simulation results show the effectiveness of the proposed control strategy.