Research Papers

A Family of Butterfly Flexural Joints: Q-LITF Pivots

[+] Author and Article Information
Xu Pei

e-mail: peixu@buaa.edu.cn

Shusheng Bi

School of Mechanical Engineering and Automation,
Beihang University,
Beijing 100191, R.P. China

1Corresponding author.

Contributed by the Design Innovation and Devices of ASME for publication in the Journal of Mechanical Design. Manuscript received October 18, 2011; final manuscript received September 24, 2012; published online November 15, 2012. Assoc. Editor: Alexander Slocum.

J. Mech. Des 134(12), 121005 (Nov 15, 2012) (8 pages) doi:10.1115/1.4007917 History: Received October 18, 2011; Revised September 24, 2012

The typical leaf-type isosceles-trapezoidal flexural (LITF) pivot consists of two flexural beams and two rigid-bodies. The single LITF pivot has the small range of motion and relatively large center shift. However, the vacancy in the pivot point makes LITF pivots much easier to be cascaded than other commonly used flexure joints. The performances of LITF pivots will be greatly improved by connecting them together in series. This paper presents an innovative design of LITF pivots. The single LITF pivot is regarded as a basic configurable module, and four of them can be used to construct new types of flexure joint, which are referred to here as quadri-LITF (Q-LITF) pivot. Ten types of Q-LITF pivots are synthesized in this paper. Compared with a single LIFT pivot, the stroke of a Q-LITF pivot is larger, and stiffness of the mechanism becomes smaller. The center-shift of the Q-LIFT pivot can be optimized by tuning geometric parameters of its single LITF modules. Based on the pseudorigid-body (PRB) model of the single LITF pivot, the method for analyzing the Q-LITF pivots is proposed. One type of the Q-LITF pivots is selected as an example to demonstrate the proposed method for the Q-LITF pivot analysis. The comparison between the results of PRB model analysis and the finite element analysis (FEA) shows the feasibility and efficiency of the analysis procedure.

Copyright © 2012 by ASME
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Fig. 1

Leaf-type flexure joint. (a) A LITF pivot (consisting of two flexural beams and two rigid-bodies); (b) ADLIF [19], a double-LITF pivot (consisting of two LITF pivots); (c) butterfly flexural pivot [14], a Q-LITF pivot (consisting of four LITF pivots)

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Fig. 2

A LITF pivot and equivalent four-bar model, pin-joint model

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Fig. 3

The four-bar PRB model for case TI

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Fig. 4

The four-bar PRB model for case TII

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Fig. 5

Cascade of two D-LITF Pivots. IE indicates intermediate element; S indicates stand; ME indicates moveable element. (a) Select two pivots and (b) make the virtual centers coincident, then combine them.

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Fig. 6

The butterfly flexural pivot. (a) Embodiment; (b) schematic; and (c) PRB model

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Fig. 7

Experimental setup and the butterfly pivot

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Fig. 8

Moment–displacement results for butterfly pivot

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Fig. 9

Stress results for butterfly pivot

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Fig. 10

Center-shift results for butterfly pivot

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Fig. 11

Center-shift results comparison

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Fig. 12

Center-shifts of ten types of Q-LITF pivot




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