Opposition Movement of the Little Finger Enhances the Grasping Function of Robotic Hands

Abstract

Most contemporary hand robots only consider the palmar opposition as the thumb opposition, while ignoring the important role of the opposition of little finger. Consequently, the back of the hand is considered as a rigid, immovable structure. This letter investigated the influence of little finger opposition on hand grip performance through several research endeavors, including mechanical modeling and analysis of palmar opposition, optimization of the palmar-driving strategy, and prototype experiments on hand grip. First, we developed a kinematic model of palmar opposition based on the hand's anatomy and function of the transverse arch. We then employed elastic mechanics analysis methods to investigate the potential energy variations of the model during gripping. Second, we proposed an integrated palm-driving strategy and measured the deformation of the hand during the grasping process. Third, we designed and manufactured a hand rehabilitation exoskeleton that incorporates both the palmar opposition of the thumb and little finger. Finally, we conducted comparative experiments on grasping performance using the hand exoskeleton. Analysis results confirm the important role of the little finger opposition in maintaining hand grasping stability and enhancing grasping strength. These findings offer valuable insights for the research of hand function rehabilitation and high-performance robotic hands.