Adaptive integral sliding mode control for a crane system with swing-angle sensor offset

Cranes are essential for transporting heavy loads in various industries, but controlling them remains challenging due to the difficulty of suppressing payload sway. Accurate calibration of the sway angle sensor, particularly zero-point calibration, is crucial. However, previous studies have not addressed the effects of insufficient zero-point calibration, caused by residual payload sway before the feedback controller is activated. We theoretically demonstrate that such a calibration error partially acts as a constant unmatched disturbance, which conventional sliding mode control cannot compensate for. This study proposes an adaptive integral sliding mode control (AISMC) method combined with an integral-type servomechanism to address constant unmatched disturbances. Furthermore, to cope with significant uncertainty during the initial control phase and reduce chattering near the equilibrium point after the transient phase, the gain of the discontinuous control term is adjusted adaptively. The proposed method effectively handles both matched and unmatched disturbances, ensuring precise trolley positioning with suppressed payload sway. The robustness and effectiveness of the approach are verified through numerical simulations and real-world experiments.