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Research Papers: Magnetic Storage

Thermal Fly-Height Control Slider Instability and Dynamics at Touchdown: Explanations Using Nonlinear Systems Theory

[+] Author and Article Information
Sripathi Vangipuram Canchi1

Department of Mechanical Engineering, Computer Mechanics Laboratory, University of California, Berkeley, CA 94720vcsripathi@berkeley.edu

David B. Bogy

Department of Mechanical Engineering, University of California, Berkeley, CA 94720

1

Corresponding author.

J. Tribol 133(2), 021902 (Mar 21, 2011) (13 pages) doi:10.1115/1.4003483 History: Received June 06, 2010; Revised December 29, 2010; Published March 21, 2011; Online March 21, 2011

Thermal fly-height control sliders are widely used in current hard disk drives to control and maintain subnanometer level clearance between the read-write head and the disk. The peculiar dynamics observed during touchdown/contact tests for certain slider designs is investigated through experiments and analytical modeling. Nonlinear systems theory is used to highlight slider instabilities arising from an unfavorable coupling of system vibration modes through an internal resonance condition, as well as the favorable suppression of instabilities through a jump condition. Excitation frequencies that may lead to large amplitude slider vibrations and the dominant frequencies at which slider response occurs are also predicted from theory. Using parameters representative of the slider used in experiments, the theoretically predicted frequencies are shown to be in excellent agreement with experimental results. This analytical study highlights some important air bearing surface design considerations that can help prevent slider instability as well as help mitigate unwanted slider vibrations, thereby ensuring the reliability of the head-disk interface at extremely low head-disk clearances.

Copyright © 2011 by American Society of Mechanical Engineers
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Figures

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Figure 1

Spin stand set-up with Candela OSA, AE sensor, and LDV

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Figure 2

Experimental result for the pemto slider: time history of (a) slider’s vertical velocity 3σ, (b) AE signal 3σ, and (c) power supplied to TFC heater

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Figure 3

Frequency spectrum of the slider’s vertical velocity in the unstable zone

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Figure 4

Schematic of the two degree of freedom model for slider-ABS system

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Figure 5

Linear model analysis: (a) ABS first and second pitch mode shapes and (b) first and second pitch mode frequencies as a function of thermal protrusion α

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Figure 6

Displacement-force plot for the trailing edge spring: k21=3.3×105 and α=2.075, — linear: k11=αk21 and k12=k13=0, – – quadratic nonlinearity: k11=αk21, k12≠0, and k13=0, and ⋯ quadratic and cubic nonlinearities: k11=αk21, k12≠0, and k13≠0

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Figure 7

Frequency response plot for the linear damped system and the damped system with only quadratic nonlinearities when ω2≈2ω1: (a) first modal coordinate η and (b) second modal coordinate φ, ⋯ linear case, — nonlinear case with increasing σ2, and – – nonlinear case with decreasing σ2

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Figure 8

Frequency response plot for the first modal coordinate η, ⋯ linear damped case and −⋅− damped case with cubic nonlinearities but no internal resonance

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Figure 9

Frequency response plot for the damped system with quadratic and cubic nonlinearities: (a) first modal coordinate η and (b) second modal coordinate ϕ, −⋅− no internal resonance, — internal resonance (ω2≈2ω1) with increasing σ2, and – – internal resonance (ω2≈2ω1) with decreasing σ2

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Figure 10

Frequency response plot for the damped system with quadratic and cubic nonlinearities showing the effect of α, — internal resonance (ω2≈2ω1) with increasing σ2 and – – internal resonance (ω2≈2ω1) with decreasing σ2

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Figure 11

Effect of thermal protrusion α on the internal resonance detuning parameter σ1

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Figure 12

Response amplitude as function of σ1 for σ2=0 for the damped system with quadratic and cubic nonlinearities: (a) first modal coordinate and (b) second modal coordinate

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Figure 13

Response amplitude as function of σ1 for the damped system with quadratic and cubic nonlinearities showing the effect of σ2: (a) first modal coordinate and (b) second modal coordinate

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Figure 14

Experimental result for the femto slider: time histories of (a) slider’s vertical velocity 3σ, (b) AE signal 3σ, and (c) power supplied to TFC heater

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Figure 15

Time history of response for linear damped system and damped system with quadratic and cubic nonlinearities when α=2.075(σ1=0.046) and σ2=0, ⋯ linear case, — nonlinear case with large amplitude response, and – – nonlinear case with suppressed amplitude response

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Figure 16

Effect of external force on the frequency response plot for the damped system with quadratic and cubic nonlinearities and internal resonance (α=2.075) (a) first modal coordinate and (b) second modal coordinate, — increasing σ2 and – – decreasing σ2

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Figure 17

Effect of damping on the frequency response plot for the damped system with quadratic and cubic nonlinearities and internal resonance (α=2.075) (a) first modal coordinate and (b) second modal coordinate, — increasing σ2 and – – decreasing σ2

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Figure 18

Dynamic and stationary frequency response plots for the damped system with only quadratic nonlinearities and internal resonance (α=2.075): (a) first modal coordinate and (b) second modal coordinate, — increasing σ2 and – – decreasing σ2, bold lines represent the stationary curves

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Figure 19

Dynamic and stationary frequency response plots for the damped system with quadratic and cubic nonlinearities and internal resonance (α=2.075): (a) first modal coordinate and (b) second modal coordinate, — increasing σ2 and – – decreasing σ2, bold lines represent the stationary curves

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