Hybrid position/force control of a hydraulic underwater manipulator

Current generation underwater remotely operated vehicles equipped with robotic manipulators are teleoperated and consequently place a large workload burden on the human operator. A greater degree of automation could improve the efficiency and accuracy with which underwater tasks are carried out. A hybrid position/force control scheme is proposed to control an industrial hydraulic underwater manipulator, modified to include a force/torque sensor, for tasks such as weld inspection. Modelling of the hydraulic actuation mechanism is performed and the resulting model is easily incorporated in the standard robot dynamic equations. An experimental facility using a PC-based digital signal processor is used to produce practical hybrid position/force results for a Slingsby TA9 hydraulic arm. Results are presented for the manipulator sliding across a planar surface in different parts of its work envelope. Good general agreement is obtained between the simulated and practical systems. A fixed gain control strategy is shown to work well, provided it is tuned for the arm configuration when sliding occurs