An Improved Linear Quadratic Regulator of Shipborne Stewart Platform for Wave Compensation

Ocean-operating ships in rough sea conditions are highly susceptible to wave disturbance. A shipborne Stewart platform with a gangway offers an effective means to enhance the safety of operator and extend the window period for offshore activities. However, the Stewart platform faces time-varying disturbance from ship motions, while the gangway endures off-center loads. These problems make it difficult to design the controller and confirm its parameters of the shipborne Stewart platform. Therefore, an improved linear quadratic regulator with a linear extended state observer is proposed. Specifically, the inverse kinematic model of the Stewart platform's chain limbs and the hybrid Jacobian matrix are developed. The proposed controller is developed in joint-space, and its stability is verified using the Lyapunov theory. On this basis, simulations of random motion signals are carried out in the roll, pitch, and heave directions. Simulation results confirm that the proposed scheme effectively addresses the previous challenges in adjusting parameters without overshooting and oscillation, exhibiting excellent performance in anti-disturbance and decoupling.