Decoupling and Tracking Control for Offshore Crane System Effect by Unknown Roll/Heave Wave Motions Disturbances

This paper introduces an output feedback control method for an offshore crane system (OCS) with unknown wave disturbance caused by roll-heave motions. The method combines a backstepping controller and a high-gain observer to achieve the desired tracking trajectories of the cart position and the rope length. The dynamic model of the offshore crane system is initially formulated to account for unknown dynamic friction, dynamic coupling, and external disturbances while ensuring dynamic decoupling of the cart position and hoisting dynamics. The backstepping controller is proposed to stabilize the system and achieve trajectory tracking, where the extended high gain observer is used to estimate the dynamic states and external disturbances. The effectiveness of the proposed control approach is verified through simulations for both the system with disturbances generated by roll-heave motions. The simulation results demonstrate that the proposed approach is capable of achieving the desired trajectories, even under conditions of unknown nonlinearities and wave motion disturbances.