Safe joint module for safe robot arm based on passive and active compliance method

In recent years, collision safety between humans and robots has drawn much attention as service robots are being increasingly used in human environments. Since various types of collisions can occur during a robot’s operation, multiple safety methods should be implemented to ensure human safety. The most common and practical solutions are the active and passive compliance methods and each has its own merits and disadvantages. To combine the active and passive compliance methods to achieve higher reliability, 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 be used to detect a collision; then the actuator appropriately reacts to minimize the impact. However, if the collision detection by the embedded joint torque sensor and the subsequent reaction fail due to the limited bandwidth of the 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, the combined active and passive compliance method can ensure collision safety. Moreover, the embedded torque sensor can be used for force control. The embedded harmonic drive can achieve high gear reduction and low backlash. Several experiments on static and dynamic collisions showed that the proposed module can guarantee safety while maintaining good performance.