Spring-Clutch: A safe torque limiter based on a spring and CAM mechanism with the ability to reinitialize its position

Service robots are anticipated to be used in unstructured areas such as homes, hospitals, and public areas in the near future. However, safety issues need to be addressed before this can occur. In particular, robot manipulators that handle objects by physical contact run the risk of colliding with people or objects. Thus, it is important to prevent collisions that could injure people and damage robot manipulators. In this study, a safe joint mechanism is developed to ensure the safe use of a manipulator. This mechanism, termed `Spring-Clutch,' is a simple passive mechanism that consists of a coil spring and a CAM mechanism. When a torque is applied that is less than a threshold value, Spring-Clutch functions as a rigid joint between the input and the output. However, when an applied torque exceeds the threshold, angular displacement occurs between the input and output to reduce the collision force. If the applied torque is removed, Spring-Clutch immediately returns to its nominal position without the need for additional operations. This paper describes the design principles and performance of Spring-Clutch, and discusses the possibility of its practical use as a joint mechanism for safe manipulation.