Coupled Sliding Mode Control of an Omnidirectional Mobile Robot with Variable Modes

Adequate tracking flexibility and accuracy of the omnidirectional mobile robot are difficult to be achieved with one fixed control frame due to the time-varying dynamics. This paper presents a coupled sliding mode control (CSMC) method, which is able to switch the alternative modes to adapt to operational conditions and perform a satisfactory tracking control. The design begins with constructing a unified state error model for the considered multiple modes. Then, by exploiting novel coupled sliding surfaces, a CSMC is formulated which can effectively alleviate the chattering. Meanwhile, based on the desired and current state information, a two-stage fuzzy switching mechanism is proposed to accomplish an autonomous switched tracking control. Theoretical analysis reveals that the system reaches the sliding manifold in finite time, and the convergence of the state errors can be guaranteed. Experiments on a real-life four-wheeled mobile robot validate the effectiveness and superiority of this control method comparing with single-mode control scheme or conventional methods.