Lightweight hand motion mechanism was developed to achieve high speed pitching. It is indicated that humans have increased fingers stiffness when putting a spin on a ball. By focusing on this feature, fingers have been made motor-less and lightweight. Specifically, the mechanism that fixing PIP angles of index and middle fingers when grasping a ball and switching to elastic joints by release fixation when putting a spin on the ball was developed. Stiffness was considered from a finger model when pitching a fast ball. Pitching experiments confirmed that the robot was able to grasp a ball and put a spin on the ball.
Aoki et al. (Thu,) studied this question.