Independent Long Fingers are not Essential for a Grasping Hand

Abstract

The human hand is a complex integrated system with motor and sensory components that provides individuals with high functionality and elegant behaviour. In direct connection with the brain, the hand is capable of performing countless actions ranging from fine digit manipulation to the handling of heavy objects. However the question of which movements mostly contribute to the manipulation skills of the hand, and thus should be included in prosthetic hands, is yet to be answered. Building from our previous work, and assuming that a hand with independent long fingers allowed performance comparable to a hand with coupled fingers, here we explored the actual contribution of independent fingers while performing activities of daily living using custom built orthoses. Our findings show that, when an opposable thumb is present, independent long fingers provide a measureable advantage in performing activities of daily living only when precision grasps are involved. In addition, the results suggest that the remarkable grasping skills of the human hand rely more on the independent abduction/adduction of the fingers than on their independent flexion/extension. These findings are of interest to the designers of artificial hands, including biomimetic prostheses and exoskeletons.

Investigation into reducing anthropomorphic hand degrees of freedom while maintaining human hand grasping functions

“…Finger abduction/adduction fails to show either a strong coordination or group coupling with other joint movements (sections ''Coordinated joint movements'' and ''Determining the minimum number of DoAs''), which may indicate that adduction movements need to be included in anthropomorphic hand design. This finding is also consistent with the overall findings of Montagnani et al, 19 which suggest that independent abduction/adduction of hand fingers have a significant role in grasping skills. In addition, some prosthetic hands neglect finger DIP joints.…”

Design and Evaluation of a Bowden-Cable-Based Remote Actuation System for Wearable Robotics

“…The finger mechanism requires an accurately controlled input force of 30 N per finger. To provide dexterity but maintain a compact and lightweight mechanical design, we decided to couple the motion of all fingers except for the thumb as suggested in [27]. Consequently, the needed force adds up to a total of 120 N for the four coupled fingers.…”

Improvement of hand functions of spinal cord injury patients with electromyography-driven hand exoskeleton: A feasibility study

“…We demonstrated that by taking advantage of compliance in the design of hand exoskeletons, the number of essential target hand poses can be reduced, resulting in easier and more robust control of the device in real-time. Grasping skills mainly rely on independent abduction/adduction of the thumb and flexion/extension of the thumb and fingers (Tavakoli et al, 2015;Montagnani et al, 2016). Therefore, optimizing the number of target poses is a crucial component for an sEMG-driven hand orthosis.…”