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Research Papers

Stiffness Compensation Mechanism for Body Powered Hand Prostheses with Cosmetic Covering

[+] Author and Article Information
Nima Tolou1

Faculty of Mechanical, Maritime and Materials Engineering, Department of Biomechanical Engineering,  Delft University of Technology (TU Delft), Mekelweg 2, 2628 CD Delft, The Netherlandsn.tolou@tudelft.nl

Gerwin Smit, Ali A. Nikooyan, Dick H. Plettenburg, Just L. Herder

Faculty of Mechanical, Maritime and Materials Engineering, Department of Biomechanical Engineering,  Delft University of Technology (TU Delft), Mekelweg 2, 2628 CD Delft, The Netherlands

1

Corresponding author.

J. Med. Devices 6(1), 011004 (Mar 13, 2012) (5 pages) doi:10.1115/1.4005781 History: Received February 28, 2011; Revised November 04, 2011; Published March 12, 2012; Online March 13, 2012

Body powered hand prostheses require high physical user effort. This is caused by the stiffness of the cosmetic covering, or cosmetic glove. This paper aims to present a new concept of a mechanism for the compensation of the nonlinear stiffness of body powered hand prostheses by using static balancers with a nonlinear behavior. This concept is based on a cooperative action of snap-through behavior in multiple bi-stable spring mechanisms to create the nonlinear balancing force. To demonstrate the efficiency of the concept, an optimized design for a case study of a child-size hand prosthesis is also presented. A pattern search method was applied for the optimization. As a result, the calculated stiffness and thereby the operating effort was reduced by 96%. It can be concluded from the conceptual and numerical results that the presented concept provides a highly efficient solution to the discussed problem.

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Copyright © 2012 by American Society of Mechanical Engineers
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Figures

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Figure 1

The (a) top view real and (b) schematic test setup: The stiffness characteristic of a cosmetic glove was determined by applying it to the hand mechanism. The activation force (Fact ) and displacement (Xact ) were measured and recorded, during opening and closing of the hand.

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Figure 2

The reference force-displacement curve (reference ds) is approximated by two linear parts for the voluntary-opening hand prosthesis. The nonlinear part of force-displacement curves of four different Otto Bock 8S6 gloves (ds 1 to ds 4) are also shown. ds: dataset.

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Figure 3

The mechanism of voluntary-opening hand prosthesis considered in presented work

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Figure 4

Full sketch of the presented concept for partially statically balanced hand prosthesis. Note that this diagram is not to scale: deflections are exaggerated.

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Figure 5

Force diagram (support forces not shown) of nonlinear SB; the force system is repeated n times so that the total force is F = nPcos(ϕ)

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Figure 6

Dimensionless force-displacement behavior for SB I and SB II

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Figure 7

Phases of balancing system indicated in Fig. 6; continues line (–) and dash line (––) correspond to SB I and SB II respectively. Note that these diagrams are not to scale: deflections are exaggerated.

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Figure 8

Compensation error for 60 sets of bound limits (intervals); interval 1 corresponds to the widest (0.7 LB and 1.3 UB) and interval 60 corresponds to the tightest (1.3 LB and 0.7 UB) bound limit

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Figure 9

Comparison of dimensionless hand prosthesis, balancing and residual forces versus displacement for interval 31

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