Research Papers

Double-Young Tristable Mechanisms

[+] Author and Article Information
Guimin Chen

e-mail: guimin.chen@gmail.com

Yunlei Du

School of Mechatronics,
Xidian University,
Xi'an, Shaanxi 710071, China

1Corresponding author.

Contributed by the Mechanisms and Robotics Committee of ASME for publication in the Journal of Mechanisms and Robotics. Manuscript received May 17, 2012; final manuscript received August 22, 2012; published online November 28, 2012. Assoc. Editor: Anupam Saxena.

J. Mechanisms Robotics 5(1), 011007 (Nov 28, 2012) (7 pages) Paper No: JMR-12-1058; doi: 10.1115/1.4007941 History: Received May 17, 2012; Revised August 22, 2012

In this work, we present a new class of tristable mechanism called double Young tristable mechanisms (DYTMs), which connect two prestrained Young bistable mechanisms to create three distinct stable equilibrium positions. A three-degree-of-freedom pseudorigid-body (RPB) model is proposed to accurately predict the kinetostatic behaviors of both Young mechanisms and DYTMs. An optimization-based design method is also presented for DYTMs. Two DYTM prototypes were designed based on the method and machined out of polypropylene sheets. Both of the prototypes exhibit tristability, which demonstrate the feasibility of achieving tristability through connecting two prestrained Young mechanisms. The successful prototyping also indicates that the proposed three degree-of-freedom (3DOF) model is capable of identifying feasible designs for DYTMs.

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Fig. 1

Young mechanism. (a) A Young mechanism of Class I in its two stable equilibrium positions (with the second stable position shown in dashed lines), (b) its single-degree-of-freedom pseudorigid-body model, and (c) its three degree-of-freedom pseudorigid-body model.

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Fig. 2

Young mechanism at a deflected position and its PRBM

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Fig. 3

The curves of the input torque and the potential energy predicted by the 3DOF model for a Young bistable mechanism (with the potential energy curves obtained using the 1DOF model and the FE model shown for comparision purpose). The sharp corner on the input torque curve is associated with the buckling of l4.

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Fig. 4

Schematic of a DYTM

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Fig. 5

Illustration of the potential energy summation of two identical Young mechanisms at different prestrained angle, (a) β=0 deg (before assembly), (b) β=78 deg, (c) β=80 deg, and (d) β=82 deg. The curves are created as follows: Vr is shifted to the right by β and VT is obtained by adding the curves of Vf and Vr together.

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Fig. 6

The total input torque of the DYTM at β=82 deg obtained using the 3DOF model

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Fig. 7

Photographs of the DYTM prototype for proof-of-concept at its three stable positions

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Fig. 8

Cirtical points and energy barriers on the potential energy curves

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Fig. 9

The strain energy curves of the optimized Young bistable mechanism and the resulting DYTM

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Fig. 10

The total input torque of the optimized DYTM (β=82 deg)

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Fig. 11

Photographs of the optimized DYTM at its three stable positions




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