Towards Safe Physical Human-Robot Interaction by Exploring the Rapid Stiffness Switching Feature of Discrete Variable Stiffness Actuation

Safety holds the prime importance in direct physical human-robot interaction (pHRI) tasks. Robots should have the ability to handle unexpected collisions in unstructured environments. Collision avoidance based on exteroceptive sensors can work in these scenarios. However, it may not be sufficient, especially considering that the relative motion between robots and humans can be fast and hardly predictable. This highlights the importance of fast and reliable detection and reaction techniques for the collisions. Rapid switching to intrinsic complaint mode upon collisions is a promising solution for this requirement. Recently, we have proposed a new design of the discrete variable stiffness actuator (DVSA), which has the capability of instantaneously switching its stiffness between different predefined levels. We believe that this rapid stiffness switching feature can significantly improve safety during collisions. In this letter, we combined a software-based collision detection method with a hardware-based rapid stiffness switching technique. The proposed strategy has been implemented on a DVSA-based manipulator to evaluate its safety performance in the sudden dynamic collision and static near-singular clamping collision scenarios. The results clearly indicate that the proposed strategy can significantly mitigate the impact of unexpected collisions and improve safety during pHRI.