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Technical Briefs

A Tristable Mechanism Configuration Employing Orthogonal Compliant Mechanisms

[+] Author and Article Information
Guimin Chen1

School of Mechatronics, Xidian University, Xi’an, Shaanxi 710071, Chinaguimin.chen@gmail.com

Quentin T. Aten

Department of Mechanical Engineering, Brigham Young University, Provo, UT 84602quentinaten@yahoo.com

Shannon Zirbel

Department of Mechanical Engineering, Brigham Young University, Provo, UT 84602sazirbel@gmail.com

Brian D. Jensen

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

Larry L. Howell

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

1

Corresponding author. Present address: P. O. Box 181, No. 2 Taibai South Road, Xi’an, Shaanxi 710071, China.

J. Mechanisms Robotics 2(1), 014501 (Nov 19, 2009) (6 pages) doi:10.1115/1.4000529 History: Received July 17, 2009; Revised September 26, 2009; Published November 19, 2009

Tristable mechanisms, or devices with three distinct stable equilibrium positions, have promise for future applications, but the complexities of the tristable behavior have made it difficult to identify configurations that can achieve tristable behavior while meeting practical stress and fabrication constraints. This paper describes a new tristable configuration that employs orthogonally oriented compliant mechanisms that result in tristable mechanics that are readily visualized. The functional principles are described and design models are derived. Feasibility is conclusively demonstrated by the successful operation of four embodiments covering a range of size regimes, materials, and fabrication processes. Tested devices include an in-plane tristable macroscale mechanism, a tristable lamina emergent mechanism, a tristable micromechanism made using a carbon nanotube-based fabrication process, and a polycrystalline silicon micromechanism.

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Copyright © 2010 by American Society of Mechanical Engineers
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Figures

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Figure 1

A design example (device A): (a) end-effector; (b) bistable mechanism

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Figure 2

A tristable mechanism illustrated in its three stable equilibrium positions, including its as-fabricated (left), second stable (middle), and third stable (right) positions

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Figure 3

(a) As-fabricated position, (b) deformed position, and (c) free-body diagram of one-half and (d) one-quarter of the end-effector

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Figure 4

Force-deflection curves of device A

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Figure 5

Dimensions of bistable mechanism employed in the test devices

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Figure 6

Planar tristable mechanism: (a) fabricated, or first, (b) second, and (c) third stable equilibrium positions

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Figure 7

Lamina emergent tristable mechanism: (a) fabricated, or first, (b) second, and (c) third stable equilibrium positions

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Figure 8

Force-deflection curves of device B

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Figure 9

A tristable micromechanism made using a carbon nanotube-based fabrication process

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Figure 10

Scanning electron micrographs of the tristable micromechanism fabricated from polycrystalline silicon. The inset optical image shows the device in its undeflected state and the other two images demonstrate the second and third stable equilibrium positions.

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