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Technical Brief

Synthesis of Constant Torque Compliant Mechanisms

[+] Author and Article Information
Hari Nair Prakashah

Department of Mechanical Engineering,
Texas A&M University-Kingsville,
Kingsville, TX 78363
e-mail: hari.nair9@gmail.com

Hong Zhou

Department of Mechanical Engineering,
Texas A&M University-Kingsville,
Kingsville, TX 78363
e-mail: hong.zhou@tamuk.edu

Manuscript received May 22, 2016; final manuscript received September 26, 2016; published online October 25, 2016. Assoc. Editor: Larry L Howell.

J. Mechanisms Robotics 8(6), 064503 (Oct 25, 2016) (8 pages) Paper No: JMR-16-1148; doi: 10.1115/1.4034885 History: Received May 22, 2016; Revised September 26, 2016

Constant torque compliant mechanisms produce an output torque that does not change in a large range of input rotation. They have wide applications in aerospace, automobile, timing, gardening, medical, and healthcare devices. Unlike constant force compliant mechanisms, the synthesis of constant torque compliant mechanisms has not been extensively investigated yet. In this paper, a method is presented for synthesizing constant torque compliant mechanisms that have coaxial input rotation and output torque. The same shaft is employed for both input rotation and output torque. A synthesized constant torque compliant mechanism is modeled as a set of variable width spline curves within an annular design domain formed between a rotation shaft and a fixed ring. Interpolation circles are used to define variable width spline curves. The synthesis of constant torque compliant mechanisms is systematized as optimizing the control parameters of the interpolation circles of the variable width spline curves. The presented method is demonstrated by the synthesis of constant torque compliant mechanisms that have different number of variable width spline curves in this paper.

Copyright © 2016 by ASME
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References

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Figures

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Fig. 1

Three typical T–θ relationship curves

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Fig. 2

The realistic T–θ relationship curve

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Fig. 3

The output torque deviation from its desired constant value

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Fig. 4

The annular design domain with outside fixed ring

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Fig. 5

The annular design domain with inside fixed ring

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Fig. 6

Five interpolation points and their interpolation polyline

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Fig. 7

The cubic spline curve from the interpolation points of Fig. 6

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Fig. 8

The wide cubic spline curve from the cubic spline curve of Fig. 7

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Fig. 9

The wide cubic spline curve with cusp

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Fig. 10

Five interpolation circles and their interpolation polyline

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Fig. 11

The variable width spline curve from the interpolation circles of Fig. 10

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Fig. 12

The design domain of the synthesized compliant mechanism

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Fig. 13

The synthesis result for the topology of three curved beams

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Fig. 14

The actual output torque curve for the topology of three curved beams

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Fig. 15

The undeformed and deformed compliant mechanisms for the topology of three curved beams

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Fig. 16

The stress distribution for the topology of three curved beams

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Fig. 17

The synthesis result for the topology of four curved beams

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Fig. 18

The actual output torque curve for the topology of four curved beams

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Fig. 19

The undeformed and deformed compliant mechanisms for the topology of four curved beams

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Fig. 20

The stress distribution for the topology of four curved beams

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Fig. 21

The front and back views of the modeled compliant mechanism

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Fig. 22

The front and back views of the modeled base plate

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Fig. 23

The assembly model of the compliant mechanism and base plate

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Fig. 24

The physical model of the assembled compliant mechanism and base plate

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Fig. 25

TSD-50 digital torque screwdriver

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Fig. 26

The hex tip of the screwdriver and the hex socket in the rotation shaft

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Fig. 27

The measured output torque values of the three-beam compliant mechanism

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