Improved steering model and integrated robust control for a curved path-tracking controller for headland turns

Abstract

The accuracy of the rice transplanter's curved path-tracking during headland turns significantly impacts the row spacing precision of rice transplanting, especially in the initial stage of each row operation. This study aims to improve the curved path-tracking accuracy of rice transplanters. To achieve this, an improved transplanter steering model and tracking error model are developed based on the transplanter's steering characteristics, using the transplanting arm array centre as the reference point. Building upon the proposed tracking error model, an integrated robust curved path-tracking controller is proposed, combining low-frequency disturbance observer-based feedforward control, Linear Quadratic Regulator control, H-infinity control, and quadratic stability. This controller is robust to perturbation parameters and disturbances caused by uneven paddy field bottom, sideslip, path curvature, and model linearisation, and it also has a rapid convergence rate. Model comparison results indicated that the turning radii predicted by the proposed transplanter steering model closely match the actual turning radii of the rice transplanter, outperforming the conventional Ackermann steering model. Additionally, the controller using the transplanting arm array centre as the reference point exhibited higher tracking accuracy for transplanting arm array centre compared to using the rear axle centre as the reference point. Ablation experiments demonstrated the effectiveness of each component in the proposed control method, among all components, the low-frequency disturbance observer-based feedforward control had the most significant impact on accuracy improvement. Overall, the proposed curved path-tracking controller exhibited high accuracy for curved path-tracking control and effectively meets the operational requirements of the rice transplanter.