Adaptive disturbance observer-based fixed time nonsingular terminal sliding mode control for path-tracking of unmanned agricultural tractors

To address the automatic navigation issue of unmanned agricultural tractors affected by unknown disturbances, a path-tracking control scheme is proposed by utilising fixed-time nonsingular terminal sliding mode and adaptive disturbance observer technique. Firstly, a path-tracking kinematic model is established, which considers the unknown disturbances. Secondly, unlike conventional sliding mode controllers, a novel fixed-time terminal sliding mode controller is proposed for the unmanned agricultural tractor, which effectively enhances the dynamic performance and reduce the chattering effect. Furthermore, to reduce the detrimental effects of unknown disturbances, a new adaptive disturbance observer is designed to estimate and compensate these unknown disturbances. Subsequently, a strict Lyapunov analysis is conducted to confirm that the lateral and heading offsets of the unmanned agricultural tractor under the adaptive disturbance observer-based fixed time nonsingular terminal sliding mode control scheme can be stabilised to the arbitrarily small neighbourhood near the origin within a fixed time. Finally, extensive experiments were carried out to verify the effectiveness and advantages of the proposed control scheme.