Anthropomorphic Optimization Of A Prosthetic Finger And Its Grasping Force Study

Designing an anthropomorphic multi-finger hand in the aspect of function, appearance and movement feature from the perspective of bionics is a research focus in the prosthetic hand field, which can not only meet the requirements of daily life, but also improve the user’s self-confidence. In this paper, an underactuated prosthetic finger mechanism possessing the characteristic of motion-coupling and self-adaptive grasping function is designed, and an optimization calculation of the structure parameters is conducted in terms of anthropomorphic appearance and motion feature.Firstly, the paper has reviewed the research status of finger mechanism at home and abroad. Combined with the structure and movement characteristic of human finger, an underactuated finger mechanism possessing the motion-coupling feature and self-adaptive grasping function is designed based on spring elements and coupling linkage. Then, the kinematics of the mechanism during natural bending and self-adaptive grasping process are analyzed and validated with simulations.Studies on physical characteristic of human finger movement show that the angel of three phalanxes are coupled with each other, and the fingertip follows a stereotypical trajectory in the process of natural bending, due to the connection and stretching of tendons. The phalange angel of natural moving is collected with the data glove and fitted into mathematical relationships, and then parameters of the finger mechanism are optimized based on it with the compound shape method, in order to mimic the movement characteristic of human finger and extend the work space of the prosthetic finger.According to the structural specialty of the mechanism, the static model of the prosthetic finger in all kinds of grasp configuration is established using the principle of virtual work and validated with ADAMS simulations. Relationships between the driving torque, the stiffness of spring elements and the grasping forces are analyzed. The grasping area of variable grasping posture and the force feature in different areas are studied, which will attribute to the stably grasping function of the prosthetic hand.Finally, the prosthetic finger is manufactured and a physical test platform is built, then the natural bending and grasping experiments of the finger is conducted. Results show that the prosthetic finger can achieve the expected motion-coupling characteristic and grasp objects with different shape and size self-adaptively, and its grasping force feature is similar to the simulation analysis.