Output feedback trajectory tracking control of wheeled mobile robots with position measurements

To cope with the difficulty in posture angle measurement of wheeled mobile robots (WMRs), we investigate the trajectory tracking control problem with only position measurements in this work. Firstly, a reduced-order state observer for posture angle is designed using position information, ensuring exponential convergence of the observing error provided that the linear velocity of the robot keeps strictly positive. Under certain excitation conditions of the reference trajectory, we then propose a trajectory tracking control law using state feedback approach, guaranteeing the linear velocity of the robot strictly positive and the tracking errors globally convergent to zero. The proposed observer and state feedback control law are further combined to obtain the output feedback trajectory tracking control law. Theoretical analysis shows that, under certain excitation conditions of the reference trajectory, the obtained output feedback control law ensures that the tracking errors globally asymptotically tend to zero. Finally, numerical simulations are carried out to validate the proposed schemes, showing that the posture observer, the state and output feedback trajectory tracking control laws are all effective, and furthermore, the output feedback tracking control law can still achieve practical tracking of the reference trajectory in the presence of position measurement errors.