Development of an individual finger abduction and adduction mechanism for a prosthetic hand

Abstract

Hand amputations can occur as a result of accidents, illness, or even war, and that can be physically and psychologically challenging for the amputee. To help individuals with their daily activities and increase their independence, prosthetic hands are used to replace missing hands. Silicone-based cosmetic covers can be used to replicate the aesthetic view of the human hands. In the human hand, there are different finger motions like abduction and adduction, flexion and extension, and opposition and retroposition. Over the years, several mechanisms have been developed for finger flexion and extension. However, finger abduction and adduction are also required to achieve grasping patterns such as power and precision grasping patterns. In this research, the finger abduction and adduction mechanism was developed, and the mechanism is powered by a cam, gear, clutch, and tendon systems. The proposed cam system was designed using six abduction and adduction finger patterns. The middle finger is rigidly attached to the palm, while the little, ring, and index fingers perform individual abduction and adduction motions. A five-bar mechanism is used for the little, ring, middle, and index fingers, and a four-bar mechanism is used for the thumb for the flexion and extension motions. A kinematic study and mobility analysis were conducted on the five-bar mechanism. Furthermore, motion simulation proved that the finger mechanism is capable of flexion and extension motions. Static stress simulations were performed on stress-critical components of the proposed mechanism using a CAD package to ensure mechanical reliability. The prosthetic hand was assembled using 3D-printed and CNC-machined components and actuated by eight micro metal gear motors to get the 18 DOF. Experimental validation proved the capability of individual finger abduction and adduction with grasping patterns like Tripod, Quadpod, and Adduction Grip