Motion-inhibition control of a multi-robot mooring system using an actuating force fuzzy control method

The multi-robot mooring system (MRMS) composed of robots and a moored ship has characteristics of strong fluid-structure coupling, high nonlinear, complex disturbance, and difficulty in establishing models accurately. Thus, the conventional model-based control method is difficult to be implemented for motion-inhibition control. In the paper, the displacement gain coefficient and velocity gain coefficient of the local feedback PD control law are defined as the actuating restoring force (ARF) coefficient and the actuating damping force (ADF) coefficient, respectively, and a local feedback PD motion-inhibition control law is given. Then a mapping relationship from moored-ship motions to the ARF and ADF coefficients is developed using a maximum normalized deviation index and fuzzy reasoning logic, and an actuating force fuzzy control (AFFC) method is proposed. An optimization approach is proposed to solve the problem that too many fuzzy control parameters are not easy to adjust. An MRMS composed of a ship model (266000 m3 LNG ship of 1:60 scale) and a dual parallel elastic underactuated mooring robot is used to conduct experiments in terms of different motion-inhibition control methods. The results show that the proposed method can effectively inhibit the surge, sway, and yaw motions of the ship under different wave directions.