Finger Shape Design based on the Center of Percussion Theory for High-Speed Contact Grasping of Highly-backdrivable Grippers

In recent years, grippers that can make high-speed contact and grip objects have been proposed utilizing the high back-drivability of the low reduction ratio geared motors or direct drive motors. However, with simple rotational back-drive phenomena alone, the impact force applied to the rotation axis when the fingertips come into contact with the environment can- not be avoided. Repeated impact forces applying on the actuator could lead to significant damage. Therefore, in this study, the center of percussion (CoP) theory is applied to the finger design of two-fingerd rotational opening-and-closing gripper, which has two highly-backdrivable actuators to independently drive them. This finger shape design theory can lead to the impact force mitigation. In this paper, the impact transmission ratio is considered and the results of experiments that demonstrate the validity and usefulness of the design theory based on the dynamics was presented. The finger design theory was modeled using Newton-Euler equations. As an initial step in the research, the collision experiments at a maximum speed of 1 m/s with a single finger attached to a robot arm were executed. As a result, the proposed CoP-based finger achieved an impact transmission ratio of approximately 0.2, indicating that about 80 % of the impact force was mitigated. Comparisons with other finger shapes further demonstrated the experimental validity and effectiveness of the proposed design.