Design of Safe Joint Module for Safe Robot Arm based on Passive and Active Compliance Methods

In recent years, collision safety between humans and robots has drawn much attention because service robots are being increasingly used in human environments. Since various types of collisions can occur during robot operation, multiple safety methods should be required. To achieve the safety strategy based on both active and passive compliance methods, we propose a novel safe joint module composed of a speed reducer, a torque sensor, and a safety mechanism. The torque sensor embedded in the safe joint module can detect collision, and then the actuator is properly controlled to react against collision. However, if collision detection and reaction using a joint torque sensor fail due to the low bandwidth of a sensor, the safety mechanism composed of purely mechanical elements, such as springs and a cam follower, absorbs the collision force. With the proposed safety joint module, collision safety can be ensured by both active and passive compliance methods. Moreover, the external force applied to the robot arm can be measured for force control. High gear reduction and low backlash can be provided by the embedded harmonic drive. Several experiments on static and dynamic collisions show good performance of the safe joint module with active and passive compliance methods. Keywords— Joint module, manipulator design, collision safety