A Soft-Switching Type-3 Fuzzy Control for Electrically Driven Nonholonomic Robots

The wheeled mobile robots (WMRs) are used in extensive fields because of their simple structure and high efficiency. Due to the different applications of WMRs in different problems, the control problem of WMRs is challenging. Various frictions and disturbances complicate the dynamics of MRs. To cope with these problems, various control systems have been developed. But, in most of the existing methods, just the structural uncertainties are considered, and non-structural uncertainties such as disturbance and un-modeled dynamics are neglected. Although in some studies, the sliding mode controller (SMC) and its combination with different methods have been presented, however, in most of these controllers, to ensure stability, some coefficients are conservatively set with large values, and as a result, large control signals are generated. These signals are often not within the acceptable range, and their practical implementation is difficult. In this paper, an adaptive controller is designed that is robust under structural/un-structural uncertainties and unknown dynamics. In the designed controller, the coefficients and bounds of uncertainties are adjusted using an adaptive type-3 (T3) fuzzy system (FS). Based on back-stepping kinematic control, new adaptation laws, sufficient conditions for stability, and control signals are derived. Adaptive T3-FS is designed to create a soft-switching mechanism. New learning rules of T3-FS are derived to adjust the upper/lower bounds of structural and un-structural/uncertainties. The stability is mathematically analyzed and proved under uncertainties. Several simulations are given to prove the effectiveness.