Sliding Mode Controller Based on Disturbance Separation Dynamic Model for Offshore 6-Dof Parallel Platform With Active Wave Compensation

The parallel platform has been increasingly employed in offshore crane and active wave compensation systems, as it offers excellent load-bearing capacity and six-degree-of-freedom (6-dof) motion capability. However, the uncertainty of the load, the motion of the ship caused by the wave, and the interference forces caused by wind pose challenges to the controller design. This research proposes a sliding mode controller (DSM-SMC) based on a dynamic model with interference force and load inertia uncertainty separation, aiming to enhance the system’s robustness and trajectory tracking performance. Based on the model developed using the Newton-Euler method, the uncertainty in the load inertia and the external interference forces are uniformly separated. Furthermore, by reformulating the model in terms of relative motion within a non-inertial reference frame, a disturbance-separated dynamic model (DSM) is ultimately derived. Then, a robust sliding mode controller is designed, and its asymptotic stability under bounded disturbances is theoretically proven using Lyapunov stability theory. To validate the proposed DSM-SMC, a simulation model is constructed using the MWORKS software platform. The simulation results demonstrate satisfactory trajectory tracking performance and validate the effectiveness of the proposed control strategy.