Design and Control of a Three Finger Hand Exoskeleton for Translation and Rotation of a Slender Object

Abstract

A three-finger exoskeleton is designed and controlled to translate and or rotate a slender object held between the fingertips. Each finger exoskeleton comprises of three serially concatenated planar external four-bar linkages, all on one plane, except for the thumb exoskeleton, for which one linkage is out of plane. Linkages are constrained to be on the dorsal side (sagittal plane) of each finger. To design each linkage, when performing coordinated translation and rotation, trajectories of all phalanges of the index and middle fingers and the thumb are obtained through video capture and post-processing that involves coordinate transformation. Optimal kinematic synthesis for each linkage is then performed via the three accuracy point method coupled with a stochastic search algorithm. Post manufacturing, the exoskeleton is mounted on the dorsal side of the hand using Velcro bands. Fastening is accomplished on each phalanx, palm and forearm via a fixture designed to house all three exoskeletons. Nine micro-servo motors are employed for actuation. To perform coordinated translation and rotation tasks, trajectory following is accomplished using open loop position control, incorporating artificial neural network to convert known finger joint angles into the required driving link angles. Based on experimental tests conducted, the exoskeleton is found to be successful in reproducing the requisite finger motions involved in coordinated object manipulation.