Design of Hyperextension Mechanism to Enhance Fingertip Force of Multi-Joint Linkage Mechanism Body-Powered Finger Prosthesis

Abstract

The multi-joint linkage body powered finger prosthesis has a linkage mechanism that converts the flexion and extension movements of the residual finger end into flexion and extension movements of the prosthetic finger. However, as the motion magnification ratio increases, the prosthetic finger does not provide sufficient grasping force at the fingertip. Therefore, the research objective was set to improve the grasping ability by implementing the prosthetic finger with a hyperextension mechanism. A hyperextension mechanism consisting of a 3-joints link mechanism and an elastic band was designed. To evaluate the stability of grasping, fingertip force was measured when applying rotational torque to the model finger with a conventional prosthetic finger setup and a finger with the hyperextension mechanism. As a result, the prosthetic finger with the new mechanism showed 6 and 13 % greater fingertip force in the shallow-flexed and flexed positions, accordingly. However, the force decreased 23 % in the deep-flexed position. Modification of the elasticity design of the band should be made to adjustment.