A sliding mode control approach to reduce the influence of manipulator disturbances on an underwater vehicle's position

Manipulator movement produces force/moment disturbances which act on the underwater vehicle and alter its position, and consequently the manipulator end-effector position. The effect of the manipulator motion, assuming perfect manipulator joint angle tracking, on the vehicle's position and consequently the manipulator end-effector position is investigated assuming no vehicle control. 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. Due to the nonlinear dynamics of the vehicle, Slotine's sliding mode approach has been used. This technique allows the expressions developed for the manipulator disturbances to be incorporated in the control law. This is shown to be beneficial in the regulation of the vehicle's yaw angle, and offers improved performance compared with a sliding mode controller that does not incorporate the manipulator disturbances. This technique also demonstrates superior performance and insensitivity to parameter variations compared with a fixed-gain controller.