A Robot Gripper With Variable Stiffness Actuation for Enhancing Collision Safety

This article presents the design of a two-finger variable stiffness gripper and demonstrates how the adjustable compliance of the fingers can enhance manipulation safety and robustness during collisions. The compliance between actuators and fingers are generated by using repulsive magnets as preloaded nonlinear springs such that by adjusting the air-gaps between the magnets, the position and stiffness of the fingers can be controlled simultaneously. The capability of the proposed design in collision detection and reaction is demonstrated via two collision scenarios. In the first experiment, a momentum-based collision detection algorithm in the context of compliant grasping is investigated. In the second experiment, an optimal reaction strategy is developed that exploits the adjustable stiffness characteristics of the gripper to improve safety during collisions. The experimental results of the two scenarios indicate the effectiveness of the proposed gripper in enhancing collision safety.