MOTION PLANNING AND CONTACT CONTROL FOR A TELE-ASSISTED HYDRAULIC UNDERWATER ROBOT

Implementing tele-assistance or supervisory control for autonomous sub sea robots requires atomic actions that can be called from high level task planners or mission managers. This paper reports on the design an d implementation of a particular atomic action for the case of a subse a robot carrying out tasks in contact with the surrounding environment . Subsea vehicles equipped with manipulators can have upward of 11 deg rees of freedom (DOF), with degenerate and redundant inverse kinematic s. Distributed local motion planning is presented as a means to specif y the motion of each robot DOF given a goal point or trajectory. Resul ts are presented to show the effectiveness of the distributed versus n on-distributed approach, a means to deal with local minima difficultie s, and the performance for trajectory following with and without satur ated joint angles on a robot arm. Consideration is also given to the m odelling of hydraulic underwater robots and to the resulting design of hybrid position/force control strategies. A model for a hydraulically actuated robot is developed, taking into account the electrohydraulic servovalve, the bulk modulus of oil, piston area, friction, hose comp liance and other arm parameters. Open and closed-loop control results are reported for simulated and real systems. Finally, the use of distr ibuted motion planning and sequential position/force control of a Slin gsby TA-9 hydraulic underwater manipulator is described, to implement an atomic action for tele-assistance. The specific task of automatical ly positioning and inserting a Tronic subsea mateable connector is ill ustrated, with results showing the contact conditions during insertion .