But due to the complexity of a dynamic integral model and the difficulty of making necessary measurements, these mechanism-based control laws have been difficult to be directly applied to real WMRs so far. They intended to reveal the mechanism of the occurrence of slippage and skid, and thus, the control model can be theoretically accurate. Some researchers performed a series of studies on the dynamic interaction between WMRs’ wheels and unstructured terrain. However, when WMRs locomote on soft or rugged terrain, which is a nonholonomic constraint system as in, control laws developed with the ideal assumptions may not ensure a decent real-time performance of tracking trajectories. Many current researchers make assumptions that the wheels and the ground have no relative slip or skidding, to simplify the description and analysis of the external uncertainty. Wheeled mobile robots (WMRs) have been widely utilized for exploration tasks on both earth and extraterrestrial bodies. The feasibility of the proposed method in the real world is demonstrated by experiments with a skid-steered WMR on the loose-soil terrain. Simulation results show that the proposed method can greatly suppress chattering and improve the robustness of trajectory tracking. A complete control loop with active slip compensation and adaptive SMC is thus established. This method combines the adaptive control method and a fast double-power reaching law with the SMC method. And a new adaptive SMC method is proposed to guide a WMR in trajectory tracking missions based on the kinematic model of a general WMR. In this paper, a kinematic-based feed-forward control model is designed for WMRs with longitudinal slippage and applied to the closed-loop control system for active compensation of time-varying slip rates. Traditional SMC has some potential problems, such as slow convergence, poor robustness, and excessive output chattering.

Methods based on sliding mode control (SMC) are popular approaches for these situations.

Wheeled mobile robots (WMRs) in real complex environments such as on extraterrestrial planets are confronted with uncertain external disturbances and strong coupling of wheel-ground interactions while tracking commanded trajectories.

Smc fan control 2019