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Session: Poster session I
Session starts: Thursday 24 January, 15:00

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Gerwin Smit (Delft University of Technology)
Dick Plettenburg (Delft University of Technology)

Abstract:
Problem: Rejection rates of body-powered hand prostheses are high (26-45%).1 Current body powered hands are inefficient. They require an uncomfortable high activation force, and produce a relatively low pinch force in return (<15 N).2 They have stiff fingers, which do not adapt to the shape of the grasped object. Despite all these drawbacks, the design of body powered hand prostheses hardly has improved since the 1950’s.3 The activation force has not been reduced and the pinch force is still low. Another major problem is the mass of the devices, which is still high (≥350 gram). There have been attempts to increase the efficiency of body powered hand prostheses, by using hydraulics. However, these studies have not resulted in the commercial application of hydraulics in body powered arm prostheses. Goal: The goal of this study was to design a new body-powered, voluntary closing, hand prosthesis, which has articulating fingers. This hand should have a much lower mass than current prosthetic hands, be energy efficient and be able to provide sufficient pinch force. Results: A low mass (152 gram) articulating hydraulic hand was constructed and tested. The hand has 7 active DoF’s which are activated by miniature hydraulic cylinders inside the hand. The hand is controlled by a shoulder strap, connected to a miniature master cylinder. The hydraulic system enables an efficient energy transmission from the master cylinder to the slave cylinders at the finger joints (n=8). This enables a high pinch force (>30 N) and a low user effort. The hand successfully passed the mechanical and functional tests. Discussion and conclusion: The new developed hand prototype with articulating fingers is anthropomorphic, slender, fast, efficient and silent. The hand mass is much lower than the lightest commercially available prosthetic hand. The hand therefore meets one of the most important user demands in upper limb prosthetics, which is a low hand mass. Significance: Its low mass, high efficiency and easy operation makes the new prosthetic hand useful for a large group of upper limb amputees. The light and compact design enables fitting on a very long or very short residual arm. The new prototype might therefore also be an option for people that cannot be fitted with current available prosthetic hands.