Reduction of the dynamic coupling in an underwater vehicle-manipulator system using an inverse dynamic model approach

This paper proposes a control strategy for station keeping of an underwater vehicle- manipulator system when the manipulator is asked to perform a certain task. The control structure consists of an inverse dynamic feedforward controller, the interaction forces between subsystems and a PILIM feedback controller for pitch control of the vehicle. The UVMS includes a 6-DOF vehicle and a 3-link manipulator, where the manipulator has a significant mass compared to the vehicle. The equations of motion are based on a tree representation of the UVMS and are described with the Newton-Euler algorithm. Hydrodynamic effects and friction considerations are taken into account in the forward dynamic model, while in the inverse dynamic model they are ignored. Simulation results show the validity of the inverse dynamic model approach without perfect knowledge of the system for station keeping of the vehicle. A key contribution of the study is that it is based on a lightweight underwater system. The main problem addressed in this paper is the station keeping of an underwater vehicle when the attached manipulator is moving. It is demonstrated that an inverse dynamic model used as a feedforward controller is a viable solution in the presence of system uncertainties.