Underwater Robotics: control of marine manipulator-vehicle systems

Abstract

For using underwater vehicle-manipulator systems (UVMS) in a challenging envi-ronment, it is important to have a good mathematical description of the systemwhich accounts for disturbances such as ocean currents. The dynamics equation onmatrix form is therefore derived and different properties such as positive definitenessand skew symmetry is obtained. Based on the derived equations, a sliding modecontroller has been designed in order to track trajectories in the configuration spaceof the UVMS. The controller is robust when it comes to uncertainties in dynamicsparameters and uncertainties in ocean current, yielding global asymptotic stabilityas long as the uncertainties are bounded.Furthermore, a kinematic control system has been designed for facilitating humanoperation of a UVMS, by allowing an operator to only control the end effectormotion. The rest of the motion is then resolved through a weighted least-normpseudo inverse solution of the Jacobian matrix, in order to avoid mechanical jointlimits. Moreover, the vehicle s motion is controlled by an event based algorithm tolimit the motion of the vehicle. This is done by attaching a 3D meshed polygon tothe vehicle frame and check if the end effector is inside or outside this mesh. Themesh then represents the space, relative to the manipulator, were the end effectoris fully dexterous. The vehicle will then be commanded to move only when the endeffector reaches the outside of the meshed polygon.A simulator has been implemented, based on the derived equations. The simula-tions of the UVMS, with the two controllers, yields good tracking results for trackingtrajectories both in the workspace of the end effector and in the configuration spaceof the UVMS.