Trajectory Tracking Control of Parking Automated Guided Vehicles Using Nonlinear Disturbance Observer-based Sliding Mode

Abstract Automated valet parking systems based on parking automated guided vehicles (P-AGVs) are effective for improving parking convenience and increasing parking density. The ability of P-AGVs to move towards any position and attain any orientation simultaneously due to their mecanum wheels makes it convenient to transport vehicles in a parking lot. In this study, a nonlinear disturbance observer-based sliding mode controller for the trajectory tracking problem of a P-AGV is proposed. The kinematic and dynamic models for a P-AGV tracking trajectory are first analyzed in sequence and the influences of disturbing forces considered. Subsequently, a nonlinear disturbance observer (NDO) is designed to estimate the disturbing forces and torques generated by the caster wheels. Based on the designed NDO, a robust nonsingular terminal sliding-mode (NTSM) controller is used to track reference trajectories. The stabilities of the NDO and NDO-NTSM control systems are theoretically verified using their Lyapunov functions. Finally, simulations and experiments are performed to verify the effectiveness of the proposed control scheme. The experimental results show that the proposed NDO-NTSM controller can improve the trajectory tracking stability by 42–68% compared to a traditional NTSM controller. The NDO-based sliding mode controller for trajectory tracking proposed in this study can effectively reduce the impact of disturbances on trajectory tracking accuracy.