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TECHNICAL PAPERS

Optimizing Vibration Isolation of Flex Circuits in Hard Disk Drives

[+] Author and Article Information
M. R. Brake

wickert@cmu.edu Department of Mechanical Engineering, Data Storage Systems Center,  Carnegie Mellon University, Pittsburgh, PA 15213

J. A. Wickert1

wickert@cmu.edu Department of Mechanical Engineering, Data Storage Systems Center,  Carnegie Mellon University, Pittsburgh, PA 15213

1

Corresponding author.

J. Vib. Acoust 127(2), 165-172 (Jun 03, 2004) (8 pages) doi:10.1115/1.1891813 History: Received May 30, 2003; Revised June 03, 2004

A “flex circuit” is a laminate of polyimide substrate, adhesive, and copper conductors that is used to connect the stationary electronic components in a computer hard disk drive to the rotating arm that positions read/write heads above the disks. The flex circuit’s transverse and longitudinal vibrations couple with the arm, and those motions, although seemingly small, degrade performance during seek operations from one data track to another. The flex circuit and arm mechanism is defined by a number of geometric parameters, and some latitude is available at the design stage for choosing dimensions and angles so as to minimize vibration transmission from the flex circuit to the arm. In this paper, the results of parameter, optimization, and experimental studies are discussed with a view toward improving isolation of the arm from vibration of the flex circuit in one or several modes. Particularly for the mechanism’s odd modes, the flex circuit’s free length and the relative attachment angle between the arm’s centerline and the circuit can each be chosen to significantly reduce vibration transmission. A genetic algorithm was applied to minimize a metric of vibration coupling in several vibration modes, and, in the case study examined, vibration isolation was improved by over 80%.

Copyright © 2005 by American Society of Mechanical Engineers
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Figures

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Figure 2

First four vibration modes (—) shown superposed on the flex circuit’s equilibrium shape (---). The mode shapes are annotated with the corresponding natural frequency and displacement ratio η.

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Figure 4

Illustration of the mock arm and flex circuit test stand

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Figure 5

Comparison of measured (⋯) and predicted (—) second mode shapes. The normal and tangential components are shown on the same scale. Multiple points indicate separate trials.

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Figure 6

Comparison of measured (⋯) and predicted (—) third mode shapes. The normal and tangential components are shown on the same scale. Multiple points indicate separate trials.

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Figure 7

Comparison of measured (⋯) and predicted (—) fourth mode shapes. The normal and tangential components are shown on the same scale. Multiple points indicate separate trials.

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Figure 8

Predicted (bars) and measured (points) displacement ratios for the mock flex circuit test stand in the second, third, and fourth vibration modes. The measured values are averages of three independent trials. Data ranges are indicated by the narrow bars through each point.

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Figure 9

Dependence of the (a) second and (b) third mode displacement ratios on the flex circuit’s free length, for arm positions at the disk’s inner (ID), middle, and outer (OD) diameters

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Figure 10

Comparison of measured (⋯) and predicted (—) natural frequencies of the mock arm and flex circuit test stand in the third vibration mode. Multiple points indicate separate trials.

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Figure 1

Schematic of the vibration model for the arm and flex circuit mechanism in a hard disk drive

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Figure 3

Dependence of the displacement ratios for the second and third modes on the arm’s position between the disk’s inner (60deg) and outer diameters (30deg)

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Figure 11

Comparison of measured (⋯) and predicted (—) displacement ratios of the mock arm and flex circuit test stand in the third vibration mode. Multiple points indicate separate trials.

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Figure 12

Dependence of the (a) second and (b) third mode displacement ratios on the relative attachment angle between the flex circuit and arm, for arm positions at the disk’s inner (ID), middle, and outer (OD) diameters.

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Figure 13

Dependence of the (a) second and (b) third mode displacement ratios on the orientation angle of the arm electronics block, for arm positions at the disk’s inner (ID), middle, and outer (OD) diameters

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Figure 14

Dependence of the (a) second and (b) third mode displacement ratios on the offset angle between the flex circuit and arm, for arm positions at the disk’s inner (ID), middle, and outer (OD) diameters

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Figure 15

(a) Cross section of the weighted displacement ratio’s surface along the plane L-β in the design space, indicating the presence of multiple local minima. (b) Cross-section of the weighted displacement ratio along L for β=80°.

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Figure 16

Progress of the genetic algorithm toward the optimal (—) solution with each successive generation compared to the baseline solution (---)

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Figure 17

Comparison of the displacement ratios of the baseline (---) and optimized (—) flex circuit shapes on the arm’s position between the disk’s inner (60deg) and outer diameters (30deg) for the second (a), third (b), and fourth (c) modes

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