| With the deepening exploration of the underwater world,research on the unmanned underwa-ter vehicles which perform tasks of repairing,exploring,collecting in the inaccessible underwater area have become the focus of oceanographic research institutions in many countries.In this con-text,the underwater vehicle-manipulator system(UVMS)which is equipped with the underwater manipulator emerges as the times require.The UVMS can precisely control the position of the end effector,and at the same time has the advantages of small volume,flexible movement,low energy consumption and less operating costs,which are unparalleled by large underwater submarines.Underwater Vehicle-Manipulator System has many characteristics such as strong coupling,highly nonlinearity,degree of freedom redundancy,which bring difficulties for the motion control of the system.Coupling force and moment caused by the movement of the manipulator will obvi-ously affect the stability of the vehicle.Meanwhile,different from the traditional arm,the effects of speed and acceleration of the underwater vehicle can be transfer to the end effector through the arms.Research of coordinated control of UVMS is presented in this thesis aimed at the coupling between the underwater vehicle and the manipulator.Firstly,the kinematics equations of the vehicle and manipulator are discussed and the 6 degree of freedom motion equations of the vehicle is presented.The force of the underwater vehicle and thruster’s configuration are analyzed in detail.Then the dynamic equations of the manipulator is generated through the Newton-Euler iteration.As the stability control of the vehicle is the basis for the implementation of the underwater mission,a PID controller based on thruster space is designed for the motion control of the under-water vehicle.When the configuration of thrusters changes,only part of the PID parameters needs to be retuned,which is conducive to project’s implementation.The simulation proves that the PID controller based on thruster space has a good performance on the motion control of the vehicle.Aiming at the coupling between underwater manipulator and the underwater vehicle,this the-sis proposes a quasi-sliding mode controller(QSMC),using the saturation function as the switching function in the sliding mode control law.Meanwhile,we use the Newton-Euler iteration to get the force and moment of the manipulator acting on the base(underwater vehicle),and compensate it to the controller’s output,which improves the control precision and restrain chatting problem effectively while retaining the robustness of sliding mode controller.Through the simulation of hovering,pick-up mission in the still water and the flowing water,it is verified that the proposed control scheme can ensure that the system can accomplish the pre-designed underwater mission precisely and maintain the robustness to external disturbances such as the movement of manipula-tor and water flow. |
