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.