Robust Adaptive Sliding-Mode Control for Permanent Magnet Spherical Actuator with Uncertainty Using Dynamic Surface Approach

This paper presents a position tracking control method for a three degree-of-freedom permanent magnet spherical actuator (PMSA). The control method is designed based on a dynamic model of the PMSA with uncertainties including modelling errors and external disturbance. Sliding-mode surface are adopted to restrain and eliminate the effect of external disturbances. To compensate modelling errors, an adaptive law is employed to estimate unknown model parameters so that model information can be updated in real time. By the use of dynamic surface approach, three first-order filters are introduced to avoid the explosion of derivative terms caused by traditional adaptive backstepping approach. The stability of the closed-loop system using the proposed controller is confirmed through Lyapunov theorem. The test bench consisted of the prototype of PMSA, the host computer, the current controller and the orientation detection device is established for experiments. Simulation and experimental results are provided to validate effectiveness of the proposed method.