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Robust Optimum Design of Fluid Dynamic Bearing for Hard Disk Drive Spindle Motors

[+] Author and Article Information
Hiromu Hashimoto

 Tokai University, 4-1-1 Kitakaname, Hiratsuka-shi Kanagawa-ken, 259-1292, Japanhiromu@keyaki.cc.u-tokai.ac.jp

Masayuki Ochiai, Yuta Sunami

 Tokai University, 4-1-1 Kitakaname, Hiratsuka-shi Kanagawa-ken, 259-1292, Japan

J. Tribol 134(4), 041102 (Aug 23, 2012) (11 pages) doi:10.1115/1.4007246 History: Received July 08, 2011; Revised July 11, 2012; Published August 23, 2012; Online August 23, 2012

This paper describes the robust optimum design considering dimensional tolerances for fluid dynamic bearings (FDBs) of 2.5 in. hard disk drives (HDDs). Recently, 2.5 in. HDDs are widely used for mobile devices such as laptops, video cameras, and car navigation systems. Therefore, in mobile devices, high durability toward external vibrations is essential for high HDD performance. On the other hand, FDBs for HDD spindle motors are generally manufactured by mass production processes which will eventually require reduction of production costs. Consequently, the FDBs are demanded to be easily manufactured and expected to have an insensitive design with low variability of bearing characteristics due to manufacturing errors. In this paper, first, the vibration model of the spindle motor is constructed, and then the vibration experiment was carried out in order to verify the appropriateness of the vibration model. Second, the bearing characteristics are calculated considering dimensional tolerance using optimum design combined with the statistical method in which the dimensional tolerance is assumed to distribute according to the Gaussian distribution. The bearing characteristics are estimated by expectation and standard deviation. Finally, the results of this robust optimum design compared with ones of optimum design neglecting tolerance, and the validity of this technique, were clarified. It was found from the results that the tolerances of radial clearance and groove depth are important factors to be considered to reduce the variability of the amplitude and friction torque. In addition, the variability of the amplitude strongly depends on the groove depth.

Copyright © 2012 by American Society of Mechanical Engineers
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References

Figures

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Figure 3

Vibration experimental test rig

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Figure 5

Amplitude versus frequency under acceleration 5 G and rotational speed 4200 rpm

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Figure 6

Lissajous waveforms of shaft inclination angle

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Figure 9

Probability density function

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Figure 10

Schematic diagram of conical whirling motion of the shaft

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Figure 11

Sensitivity analysis of each bearing dimension

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Figure 12

Flowchart of present robust optimum design

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Figure 13

Flowchart of calculation of objective function by conventional optimum design neglecting tolerance

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Figure 14

Objective function values of each bearing clearance

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Figure 15

Objective function values of each optimum design

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Figure 16

Expectation and standard deviation of vibration amplitude

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Figure 17

Expectation and standard deviation of friction torque

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Figure 18

Maximum value of eccentricity ratio by each groove depth tolerance

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Figure 19

Relationship between eccentricity ratio and groove depth by each optimum design

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Figure 20

Maximum value of friction torque by each groove depth tolerance

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Figure 21

Relationship between friction torque and groove depth by each optimum design

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Figure 1

Schematic diagram of spindle motor for 2.5 in. HDD

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Figure 2

Four degrees of freedom for shaft-bearing system

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Figure 4

Specifications of journal bearing and shaft

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Figure 7

Variability of design variable and bearing performance (minimization problem)

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Figure 8

Trade-off correlation between bearing performance and variability

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