Nonlinear coordination control of offshore boom cranes with bounded control inputs

Offshore cranes are complicated underactuated systems, which work in harsh sea conditions. Due to the various severe disturbances, the control of offshore cranes has always been a great challenge, which is made even more complicated when considering some practical issues such as actuator saturation and coordination. Until now, few results have been published in the literature on this topic. To address this problem, an efficient nonlinear control method is proposed for offshore boom cranes suffering from both ship roll and heave motion in this paper, which takes full consideration of actuator saturation, as well as the coordination problem between actuators. Furthermore, regarding the various extra nonvanishing disturbances, such as winds, frictions, and unmodeled dynamics, a disturbance observer is designed to estimate and eliminate these uncertainties. The asymptotic stability of the desired equilibrium point is rigorously guaranteed by Lyapunov techniques and LaSalle's invariance theorem. Finally, extensive hardware experimental tests are carried out to demonstrate the feasibility and efficiency of the proposed method. To the best of our knowledge, this paper proposes the first method that considers the saturation and coordination problem for offshore cranes while guaranteeing the asymptotic stability of the desired equilibrium point.