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Research Papers: Magnetic Storage

A Simplified Dynamic Model for the Analysis of the Slider Off-Track Motion Due to Head-Disk Interactions

[+] Author and Article Information
Yanhui Yuan, Shao Wang

School of Mechanical and Aerospace Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore

J. Tribol 131(2), 021902 (Mar 03, 2009) (9 pages) doi:10.1115/1.3063808 History: Received September 30, 2007; Revised August 31, 2008; Published March 03, 2009

A five-degree-of-freedom model was developed for the analysis of the off-track motion of the magnetic head slider in a hard disk drive. The air bearing was integrated into the dynamic system by combining its stiffness and damping matrices with those of the suspension. Simulation was conducted for the slider in intermittent contact with circumferentially located bumps on a rotating magnetic disk. For a single bump, the excitation to the transverse displacement of the slider is close to that of an impulse. However, for multiple bumps in a sequence, the excitation gives an effect similar to that of a step force function. The maximum transverse displacement increases almost linearly with both the coefficient of friction and the skew angle. The average contact force is determined by the maximum contact force, the contact time ratio, and the shape factor of the contact force, which change with the bump spacing and the rotational speed of the disk. The steady-state transverse displacement is related to the average contact force. As the bump spacing decreases, the average contact force increases, resulting in a greater transverse displacement. Based on the system dynamic characteristics alone, changing the rotational speed of the disk has only a small impact on the average contact force and, thus, on the transverse displacement. At zero skew angle with the bump path close to a rear pad edge, significant transverse motion occurs because of the excited roll mode and the coupling between the roll angle and the transverse displacement. The off-track motion of the slider is dominated by the rotational mode of the actuator arm and the sway mode of the suspension, as verified by comparing the results of the transverse displacement from the 5DOF model to that from a 2DOF model of the transverse motions of the actuator arm and suspension. The effects of the roll angle on the transverse displacement through coupling were found to be responsible for the difference in the transverse displacements obtained from the two models.

Copyright © 2009 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

5DOF model of a head-arm assembly: (a) a head-arm assembly and (b) equivalent dynamic model in the transverse direction

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Figure 2

Schematic diagrams of the contacting portion of the slider and the disk surface: (a) slider and disk in separation and (b) slider and disk in contact

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Figure 3

Geometry of the bottom surface of the slider and a bump on the disk

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Figure 4

Response of the slider to a single bump: (a) normal contact force, (b) transverse displacement of the slider, (c) flying height, (d) pitch angle, and (e) roll angle

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Figure 5

Maximum transverse displacement of the slider versus the coefficient of friction for different rotational speeds of the disk

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Figure 6

Normal contact force for a single bump versus time

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Figure 7

Maximum transverse displacement of the slider versus the skew angle for different rotational speeds of the disk

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Figure 8

Response of the slider to a large number of bumps: (a) normal contact force, (b) flying height, and (c) pitch angle (θ0=190 μrad)

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Figure 9

Response of the slider to a large number of bumps: (a) transverse displacement and (b) roll angle

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Figure 10

Bump paths on a slider at a zero skew angle: (a) bumps moving along the center line and (b) bumps moving parallel to the center line

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Figure 11

Transverse displacement versus time for the slider flying at a zero skew angle

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Figure 12

Roll angle versus time for the slider flying at a zero skew angle

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Figure 13

Transverse displacement versus time for different bump spacings

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Figure 14

Effects of the bump spacing on the contact force: (a) maximum contact force, (b) contact time ratio, (c) product of the shape factor and contact time ratio, and (d) average contact force

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Figure 15

Transverse displacement versus time for different disk rotational speeds

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Figure 16

Two consecutive impulses of the contact force under steady state for different disk rotational speeds

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Figure 17

Effects of the disk rotational speed on the contact force: (a) maximum contact force, (b) contact time ratio, (c) shape factor, and (d) average contact force

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Figure 18

Transverse displacements of the slider from the 2DOF and 5DOF models

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