Design of a Novel Compliant Safe Robot Joint with Multiple Working States

This paper presents the design and development of a novel compliant safe joint (CSJ). The principle of operation of the CSJ is based on a cam-like transmission mechanism, which we call the bridge. The cam profile on the stationary bridge is designed to have multiple regions, which allow the CSJ to passively achieve multiple working states. The proposed joint behaves as a normal rigid joint when the load is smaller than a preset threshold, shifts into the flexible state when the load exceeds the threshold, and switches into the free state in which the motion cannot be transmitted from the motor to the output shaft. In order to achieve a compact modular assembly, the joint's components are designed to have the shape of a hollow cylinder and to be installed around the motor. We analyze how the key dimension parameters affect the torque threshold and the joint's stiffness. Experiments are conducted to validate the working principle and verify the performance of the joint.