A safe joint with a joint torque sensor

In this study, a safe joint with a joint torque sensor is presented. The safe joint, named “Spring-Clutch”, is a simple passive mechanism that consists of a spring, a cam, and a joint torque sensor. When the torque applied is less than a pre-set threshold, the Spring-Clutch acts as a rigid joint between the input and output. However, if the applied torque exceeds the threshold, the Spring-Clutch is released and acts as a revolute joint, which results in reduction of the collision force to prevent damage of human and robot. After the applied torque is removed, the Spring-Clutch is immediately re-engaged. In addition, a compact joint torque sensor is installed in the Spring-Clutch to measure the torque at the joint. This paper describes the design principles and performance evaluation of Spring-Clutch, and discusses practical applications to a joint mechanism for safe manipulator.