Six-degree-of-freedom hovering control of an underwater robotic platform with four tilting thrusters via selective switching control

Abstract

We introduce a new underwater robotic platform with a tilting thruster mechanism for hovering motion. The tilting thruster mechanism can implement six-degree-of-freedom (DOF) motion with only four thrusters, but tilting motion makes the system nonlinear. We designed a selective switching controller in order to solve the nonlinear problem, and applied it to the robot system. The selective switching controller divides the six-DOF system into two three-DOF subsystems, and switches between subcontrollers according to the error in real time. Dynamic models of a robotic platform and a disturbance model of an attached manipulator are derived for the control design. Using simulation, the stability condition of control is determined, and the validity of the derived dynamic model of the robotic platform and manipulator is verified through comparison between simulation and experiment. A hovering experiment under a disturbance from the manipulator is performed to verify the robustness of the controller. The experimental results validate the successful hovering ability of the proposed robot.