Prescribed Performance Control for the Lower Limb Exoskeleton With Time-varying State Constraints and Input Saturation

Abstract

This paper studies the problem of prescribed performance tracking control for the lower limb exoskeleton under time-varying state constraints and input saturation. A prescribed performance control method is proposed to achieve the specified tracking accuracy within a preset time. Under the framework of system transformation, the control problem with specified performance and state constraints is transformed into the boundedness problem of auxiliary variables. Meanwhile, the hyperbolic tangent function is employed to deal with the input saturation. Through rigorous theoretical analysis, it can conclude that the tracking error converges to a prescribed region near the origin within a given time and all signals of the closed-loop system are bounded. The superiority of this control scheme is verified through a practical simulation example.