Back-stepping control design for an underwater robot with tilting thrusters

A hovering control design based on back-stepping method is proposed for a dynamic model of an underwater robot with tilting thrusters. In order to achieve various underwater tasks, a robotic platform must be able to maintain its position and orientation against ocean currents and reaction forces from the manipulator's operation. The underwater robot which has four tilting thrusters can carry out six degrees-of-freedom (DOF) motion. A dynamic model is derived for the underwater robot based on hydrodynamic analysis and nonlinear thrust vector mapping. A hovering controller based on a dynamic model is derived by using a back-stepping control method, and disturbance models, such as ocean currents and reaction from the attached manipulator, are designed. Simulations show reasonable results of the control system under disturbance.