Finger Roll-Up Prevention Mechanism for Control of Flexion Rate in a Cable-Driven Grasping Exoskeleton

This paper presents the design and implementation of an Anti-Finger Roll-Up (AFRU) mechanism for a cable-driven grasp assistance exoskeleton. Finger rollup describes the premature flexion of the distal and proximal interphalangeal joints relative to the metacarpophalangeal joint as a result of a cable pulling directly on the fingertip. This leads to unstable pinching grasps or grasps that place the target object outside of the grasp envelope.This device provides a solution to finger roll-up by emulating an increase in joint stiffness in the distal interphalangeal and proximal interphalangeal joints. A passive spring steel leaflet is attached to the anterior side of the exoskeleton to oppose flexion. To evaluate this mechanism, a surrogate hand with elastic joints was fabricated and used as an experimental test bed of the anti-finger roll-up capabilities of the exoskeleton, while emulating biomechanical properties of a human hand. To assist clinicians who want to emulate this mechanism, a dynamic model of the cable-driven exoskeleton, finger, surrogate joints, and spring steel leaflet has been developed to assist in adapting this device to the various pathologies.