Force sensor

Abstract

An end effector comprises a force sensor cooperating with an output flange at the wrist of a robot arm. The force sensor includes a cylinder mounted in the robot arm having a piston whose outer end is attached to the output flange of the arm at its outer end; its inner end comprising one side of a pressure chamber pressurized to a known level. The piston is mounted on bushings for sliding linear movement within the sleeve of the piston along the axis of vertical movement of the arm, but levers or other mechanisms may be used to provide the required motion. The pressure in the chamber is calibrated to a known level of a pressure which is to be applied to the part being worked by the end effector. The piston carries a position encoder; when the pressure within the pressure chamber is exceeded, movement of the position encoder is detected and signaled to a position controlling computer. Depending on the choice of the operator, the pressure may increase or the movement of the end effector may be stopped, eliminating possible damage to the part or robot. An ear is positioned adjacent to the end effector extending to be held in place between two rollers mounted on the robot arm or quill. These rollers may be tightened against the end of the ear, so that the ear may move freely vertically along the axis of movement of the end effector, while effectively bracing the end effector so that with rotation of the robot quill, the force of rotation of the quill is accurately and positively transmitted to the end effector. The position encoder comprises a linear strip mounted to pass between the phototransistor and light of a photodetector. Slotting of the linear strip will provide a quadrature data output indicating both direction and speed of movement of the shaft carrying the strip.