Adaptive dual closed-loop trajectory tracking control for a wheeled mobile robot on rough ground

In this paper, a trajectory tracking problem is investigated for a wheeled mobile robot on rough ground. Firstly, a more accurate dynamic model is developed by introducing a direct current motor model. Secondly, an improved fixed-time extended state observer (FXESO) is applied to estimate the states of the system and lumped disturbances containing the unmodeled dynamics of the system and the unknown external disturbances including slight bumps and dips caused by rough ground. Thirdly, a dual closed-loop control strategy is proposed. For the outer loop control, an adaptive kinematic controller is presented, which reduces the difficulty of parameter tuning and improves the steady-state accuracy of the position errors. For the inner loop control, an adaptive non-singular terminal sliding mode control method based on the improved FXESO is designed, in which the velocity errors converge in finite time. Finally, numerical simulations and experiment results are carried out to illustrate the effectiveness of the proposed control strategy.