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Research Papers: Mechanisms and Robotics

Compliant Wireform Mechanisms

[+] Author and Article Information
Tyler M. Pendleton

Department of Mechanical Engineering, Brigham Young University, Provo, UT 84602

Brian D. Jensen1

Department of Mechanical Engineering, Brigham Young University, Provo, UT 84602bdjensen@byu.edu

Ron Mongeon, Spring Works, Salt Lake City, Utah, January, 2006.

1

Corresponding author.

J. Mech. Des 130(12), 122302 (Oct 21, 2008) (6 pages) doi:10.1115/1.2991132 History: Received November 13, 2007; Revised July 22, 2008; Published October 21, 2008

This paper presents an alternative to fabrication methods commonly used in compliant mechanisms research, resulting in a new class of compliant mechanisms called wireform mechanisms. This technique integrates torsional springs made of formed wire into compliant mechanisms. In this way the desired force, stiffness, and motion can be achieved from a single piece of formed wire. Two techniques of integrating torsion springs are fabricated and modeled: helical coil torsion springs and torsion bars. Because the mechanisms are more complex than ordinary springs, simplified models, which aid in design, are presented, which represent the wireform mechanisms as rigid-body mechanisms using the pseudo-rigid-body model. The method is demonstrated through the design of a mechanically tristable mechanism. The validity of the simplified models is discussed by comparison to finite element models and, in the case of the torsion-bar mechanism, to experimental measurements.

FIGURES IN THIS ARTICLE
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Copyright © 2008 by American Society of Mechanical Engineers
Topics: Mechanisms , Springs , Torsion , Wire
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Figures

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Figure 1

Dimensions (in millimeters) of the original tristable mechanism, fabricated by milling polypropylene sheets

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Figure 2

Schematic (a) of a wireform mechanism and (b) its model

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Figure 3

Dimensions (in millimeters) of the large coil mechanism

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Figure 4

Dimensions (in millimeters) of the small coil mechanism

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Figure 5

Comparison of the predicted moment-angular deflection curves of the two coil mechanism models (the PRBM and the FEA model) for the large coil mechanism. The moment is applied to the wire section between the two coil springs.

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Figure 6

Comparison of the predicted moment-angular deflection curves of the two coil mechanism models for the small coil mechanism. The moment is applied to the wire section between the two coil springs.

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Figure 7

Photographs of two different tristable compliant mechanisms with torsional springs

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Figure 8

Isometric, auxiliary, and front views of the torsion-bar mechanism, showing model parameters (shading is added for clarity to describe how the mechanism works)

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Figure 9

Photographs of the torsion-bar mechanism prototype hinge. Dashed lines in the closeup show parts of the mechanism obscured by the plastic.

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Figure 10

Experimental setup for force-deflection measurements of the compliant tristable torsion-bar mechanism

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Figure 11

Force-deflection curves comparing the measured values to the values predicted by the models

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