Development and evaluation of the Hybrid Hand, a prosthetic hand with force assist

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Active hand
prostheses aid people, who suffer from an upper limb deficiency, in performing
activities of daily living. The two types of active hand prostheses available
are the myo-electric prosthesis and body-powered prosthesis. Even though both
allow a user to grasp objects, the downsides are major. The high actuation
force required for the operation of body-powered prostheses and the high costs
and low feedback of the myo-electric prostheses lead to high abandon rates. A
hybrid solution could combine the best of both worlds: high output force and
transparent feedback. In this study we introduce a body-powered prosthetic hand
with force assist, that allows for user operation without muscle fatigue, while
still providing the user with transparent feedback.   Design
requirements are set up following parameters from literature. For this study
the outer shell and closing mechanism of the 100-Dollar Hand have been used and
adapted to purpose. An extensive mechanical analyses, a new conceptual design
and the addition of a micro controller led to the new closing mechanism of the
Hybrid Hand. The proposed prototype has been tested on a test bench and results
have been compared to the conventional body-powered 100-Dollar Hand. The Hybrid
Hand decreases the actuation forces needed for a pinch force of 15 N with 33%
in comparison to the 100-Dollar Hand. Moreover, the system increases the output
pinch force at 80 N actuation force with almost 80%. With a weight of 320 gram
and costs of under 200 dollar, the hand can amplify the pinch force with a
maximum of 29 N. However, due to the low efficiency of the worm gear, the
opening time of the hand (3.5 s) has to be improved. This paper presents the
first 3D printed hand prosthesis with force assist that allows for user
operation without muscle fatigue. With a low weight, low cost, high pinch force
the prosthesis is accessible to and could aid people with an upper limb
deficiency all over the world. Future research should further investigate the
durability of the system and should introduce ways to improve and optimize the
efficiency of the transmission of the system.