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Technical Briefs

Design and Optimization of Mechanically Resonant Torsional Spring Mechanism for Laser Light Dispersion Applications

[+] Author and Article Information
Loke Kean Koay1

School of Mechanical Engineering, Engineering Campus, Universiti Sains Malaysia, Nibong Tebal, Penang 14300, Malaysialkean85@hotmail.com klkean85@yahoo.com

Horizon Gitano-Briggs

School of Mechanical Engineering, Engineering Campus, Universiti Sains Malaysia, Nibong Tebal, Penang 14300, Malaysiahorizonusm@yahoo.com

1

Corresponding author.

J. Mech. Des 133(1), 014504 (Jan 10, 2011) (6 pages) doi:10.1115/1.4003143 History: Received July 22, 2010; Revised November 16, 2010; Published January 10, 2011; Online January 10, 2011

A laser light scanning device consisting of an electronically driven mechanically resonant torsional spring-mirror system was developed for display applications. The original design suffers fatigue failure due to the repeated rotation of the torsional spring. The torsional spring design is investigated and analyzed to attain the lowest possible stress level while maintaining a constant resonant frequency. The finite element analysis model of the torsional spring was created and the stress was minimized by changing the geometrical parameters of the spring. Spring geometric optimization resulted in a maximum stress of 0.632 GPa, that is 12% reduction in stress from the original design, which should give an extended life span of 1 month for the intended application.

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Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Torsional spring and device components

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Figure 2

Experimental setup

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Figure 3

Schematic showing the twist axis and the displacement distribution of the torsional spring

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Figure 5

Angular displacement of the mirror-spring at the extremity of motion (plan view)

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Figure 7

The coil voltage and the photodiode voltage/position sensor voltage

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Figure 8

Torsional amplitude versus driven frequency of initial spring design

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Figure 4

Light pattern: (a) static and (b) during scanning

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Figure 6

Peak-to-peak deflection of the suspended plate versus the distance between the coil and the permanent magnet measured for a drive current of 0.15 A

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Figure 9

Stress distribution of original torsional spring. Maximum stress is 0.72 GPa at the tip of the screw hole.

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Figure 10

Maximum stress versus width

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Figure 11

Maximum stress versus thickness

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Figure 12

Maximum stress versus length

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Figure 13

Stress versus change width and thickness at constant length

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Figure 14

(a) Worst case spring with a maximum stress of 0.90 GPa and (b) optimized spring with a maximum stress of 0.63 GPa

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