Evaluation and reduction of the dynamic coupling between a manipulator and an underwater vehicle

The formulation of the dynamic coupling between a manipulator and an underwater vehicle is presented. Results from a simulation of a particular manipulator-vehicle configuration illustrate the nature and extent of the dynamic coupling. The modeling processes for the underwater vehicle and the manipulator are described with an evaluation of the simple hydrodynamic effects that can be incorporated in the dynamic equations of the manipulator. The equations are formulated for the combination of a 6-degrees-of-freedom vehicle and a 3-degrees-of-freedom manipulator. The effect of the manipulator motion, assuming perfect manipulator joint angle tracking, on the vehicle's position/orientation and consequently the manipulator end-effector position is investigated assuming no vehicle control. Slotine's sliding mode approach has been used to reduce the effect of the manipulator disturbances. This technique allows the expressions developed for the manipulator disturbances to be incorporated in the control law. Control of the vehicle's yaw angle, in this particular manipulator-vehicle configuration, has been determined to be the single most important factor in reducing the end-effector error variation. This is shown to be beneficial in the regulation of the vehicle's yaw angle and offers improved performance compared to a sliding mode controller that does not incorporate the manipulator disturbances. This technique also demonstrates superior performance and insensitivity to parameter variations compared to a fixed-gain controller.