Abstract: To study the influence of the disturbance of castor wheel's torsion on the trajectory tracking of wheeled mobile robots, a trajectory tracking control method considering the friction disturbance of the castor at the front of the robot and the noncoincidence between the centroid and the geometric center of the robot is proposed. First, the dynamic model of the wheeled mobile robot with castor wheel's disturbance is established. Then, according to the pose error model, the virtual velocity controller is designed by backstepping method to make the pose error converge. Next, combined with the disturbance observer, the friction disturbance caused by the torsion of the castor wheel during the robot's moving process is estimated. A torque controller based on the integral sliding mode idea is constructed to ensure the speed tracking. Finally, the stability and asymptotic convergence of the system are proved using the Lyapunov stability theory. Simulation and experimental results show that the load of the controller can be reduced when the disturbance caused by the castor wheel friction is fed back into the dynamic control controller. Compared with the control method which ignores the disturbance of the castor wheel, the root-mean-square of the maximum position error of the wheeled mobile robot is reduced by 37.37%, and the stability of the motion system can be improved.

Key words: wheeled mobile robots, trajectory tracking, dynamics, castor wheel, disturbance observer