Higher-order sliding mode backstepping control for an omnidirectional rehabilitation training robot*

Aiming at the grounded nonlinear disturbance suppression problem in the trajectory tracking control of omnidirectional wheel rehabilitation robot, this article proposes a composite control scheme that combines high-order sliding mode control with a disturbance estimation mechanism. Firstly, Utilizing a recursive backstepping approach, this work develops a layered sliding surface that facilitates the implementation of a finite-time convergent higher-order sliding mode control scheme; secondly, a nonlinear disturbance observer is constructed to realize disturbance compensation for the perturbation triggered by the grounding characteristics of the omni-directional wheel; and the global asymptotic stability of the closed-loop system is analytically established through the construction of an appropriate Lyapunov function.