Nonlinear control of an underwater vehicle/manipulator with composite dynamics

This paper is devoted to the problem of control design of an underwater veh icle/manipulator (UVM) system composed of a free navigating platform equipp ed with a robot manipulator This composite system is driven by actuators an d sensors having substantially different bandwidth characteristics due to t heir nature. Such difference allows for a mathematical setup which can be n aturally treated by standard singular perturbation theory, On the basis of this analysis, two control laws are proposed. The first is a simplification of the computed torque control law which only requires partial compensatio n for the slow-subsystem (vehicle dynamics). Feedback compensation is only needed to overcome the coupling effects from the arm to the basis. The seco nd aims at replacing this partial compensation by a robust nonlinear contro l that does not depend on the model parameters. The closed-loop performance of this controller is close to that of the model-based Compensation. Both control laws are shown to be closed-loop stable in the sense of the perturb ation theory. A comparative study between a linear partial derivative (PD) controller, a partial model-based compensation, and the nonlinear robust fe edback is presented at the end of this paper.