Sliding mode control of a dual-trolley mobile harbor crane in the presence of wave-induced ship motions

In this paper, a robust dual stage trolley control scheme is proposed for mobile harbor crane system. The purpose of the mobile harbor crane is to load/unload cargos in the open sea and transport them to shallower water where they can be offloaded at existing conventional ports. During the loading and unloading operations, wave-induced motions of the mobile harbor cause deteriorating sway motions of cargo. Therefore, in the proposed control method, sliding-mode controllers based on the nonlinear and underactuated mobile harbor crane model is designed to suppress the longitudinal and lateral sway motions. The decoupling law is applied to incorporate unactuated dynamics with actuated dynamics and the asymptotic stability of the closed loop system is guaranteed by the proposed control law. Simulation results are included to discuss the efficiency of the proposed controller.