Multi-finger hydraulic end effector

Abstract

An end effector for use with a robotic mechanism is disclosed which is capable of grasping cylindrical workpieces having a varying diameter off center and holding it with six degrees of freedom. The end effector has a plurality of sets of fingers, each set having three fingers which radially approach and retract from the workpiece with a spacing of 120 degrees between the movement direction of the fingers. The movement of each of the fingers in a set are coplanar, and the planar movement of each set of fingers are parallel with each other. Each finger is actuated by its own hydraulic cylinder which causes it to independently engage the workpiece. The cylinders are hydraulically operated by a hydraulic system having a pressurizing pump for flowing fluid from a tank through a bidirectional valve to a series of pilot operated check valves and then to the cylinders. The setting of the bidirectional valve determines whether the fingers grasp the workpiece or release it. Only after all fingers have made contact with the workpiece does the pressure in the system increase to cause the fingers to grip it with a predetermined force. The pilot operated check valves prevent the fluid from flowing back through them, thus enabling the end effector to support the workpiece without need for continual pump pressure. The bidirectional valve is then centered, so that the pump may be unloaded to save power. By reversing the bidirectional valve, the pilots of the check valves are actuated allowing flow reversal which retracts the fingers.