Development of MorphHand: Design of an underactuated anthropomorphic rubber finger for a prosthetic hand using compliant joints

This paper describes the design of a 3D-printed rubber finger with simple compliant joints for an anthropomorphic prosthetic hand. This hand, called MorphHand, is developed to test a new manufacturing method that combines the ideas of morphological computation, compliant mechanisms, biomimetics, personalization, and rapid manufacturing. In this paper, the essential features and parameters for the design of the finger were investigated with the goal of achieving inherent flexibility and similar, smooth and natural trajectories as the human hand. Five two-joint rubber fingers with nine different structural and material configurations were 3D-printed and tested. Trajectory, joint angle, and force data were acquired by using a motion capture system and a force gauge. Finally, the results were compared to a real finger. The chosen morphological parameters had the expected effects on the fingers' response and three of the configurations resulted in a close to natural response. Also, one of the fingers had closed air pockets behind its joints. This made the finger's extension faster and its cosmesis better, making the structure interesting for further development.