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Research Papers: Hydrodynamic Lubrication

Design and Evaluation of Damped Air Bearings at Head-Disk Interface

[+] Author and Article Information
Jianhua Li

Mechanical Engineering Research Laboratory, Hitachi Ltd., 1, Kirihara, Fujisawa, Kanagawa, 252-0888, Japanjianh.li.we@hitachi.com

Junguo Xu, Yuki Shimizu, Kyosuke Ono, Yukio Kato

Mechanical Engineering Research Laboratory, Hitachi Ltd., 1, Kirihara, Fujisawa, Kanagawa, 252-0888, Japan

Masayuki Honchi

 Hitachi GST, 1, Kirihara, Fujisawa, Kanagawa, 252-0888, Japan

J. Tribol 132(3), 031702 (Jun 24, 2010) (13 pages) doi:10.1115/1.4001812 History: Received June 10, 2009; Revised May 11, 2010; Published June 24, 2010; Online June 24, 2010

Perturbation and modal-analysis methods were employed to systematically study a damped slider’s dynamic characteristics, including an air-bearing slider’s stiffness, damping coefficient, frequency response to translation and wavy motion, natural frequencies, damping ratios, and modal shape-node line. We found that a design with grooves distributed on a trailing pad effectively improved the slider’s damping ratio in the second pitch mode; however, parametric studies revealed that the damping ratio was dependent on the number of grooves, their depth, location, width, length, distribution, orientation, and types. A higher damping ratio could be obtained by optimizing these parameters. The femto slider we designed with distributed damped grooves on a trailing pad had a higher damping ratio in the second pitch mode, and hence, its responses in the second pitch mode were greatly reduced, which were clarified through simulation and an experiment. Some issues on air-bearing stiffness reduction and negative damping at low frequency and contamination and lube pickup on the damped grooves were also evaluated in the experiment. No degradation could be found in the damped slider.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Schematic of flying motion of slider on disk

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Figure 2

Conventional pico slider and its various domains marked with group numbers

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Figure 3

Slider’s damping characteristics: (a) in translation motion and (b) in pitch motion

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Figure 4

Slider design (pico) with DP grooves on trailing pad

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Figure 5

Damping characteristics in translation and pitch motions of (a) slider in Fig. 2 and (b) slider in Fig. 4

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Figure 6

Slider design (pico) to increase damping at higher frequencies

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Figure 7

Damping distribution in pitch mode of slider design in Fig. 6 at frequency of 200 kHz

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Figure 8

(a) Damping characteristics in translation mode for various domains of slider design in Fig. 6 versus frequency. (b) Damping characteristics in pitch mode for various domains of slider design in Fig. 6 versus frequency.

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Figure 9

Air-bearing slider (femto long) used in this study

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Figure 10

Air-bearing slider with five grooves on trailing pad and their assigned numbers

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Figure 11

(a) Damping ratio and (b) element flying height of air-bearing slider versus number of grooves on trailing pad

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Figure 12

(a) Damping ratio, (b) element flying height, and (c) pitch angle of air-bearing slider with five grooves on trailing pad shown in Fig. 1 versus groove depths

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Figure 13

(a) Damping ratio and (b) element flying height of air-bearing slider with one groove on trailing pad versus groove distance to trailing edge

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Figure 14

(a) Damping ratio and (b) element flying height of air-bearing slider with one groove on trailing pad versus groove width

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Figure 15

(a) Damping ratio and (b) element flying height of air-bearing slider with one groove on trailing pad versus groove length

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Figure 16

Groove designs and their damping ratios for air-bearing slider: (a) designs A and B and (b) damping ratio versus groove design

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Figure 17

Groove designs for air-bearing slider with various orientations and shapes

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Figure 18

(a) Damping ratio in second pitch mode of air-bearing slider with groove designs of various orientations and shapes in Fig. 1

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Figure 19

Slider designs (a) without (original) and with various grooves distributed on (b) trailing pad, (c) trailing and side pads, and (d) trailing, side, and front pads

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Figure 20

Damping ratio in roll, first, and second pitch modes versus groove type in Fig. 1

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Figure 21

Stiffness ((a) NDP slider and (b) DP slider) and damping ((c) NDP slider and (d) DP slider) in translation, pitch, and roll modes

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Figure 22

Nodal lines of three mode shapes of (a) NDP slider and (b) DP slider

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Figure 23

NDP and DP sliders’ damping ratios in roll, first (P1), and second (P2) pitch modes

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Figure 24

NDP and DP sliders’ natural frequencies in roll, first (P1), and second (P2) pitch modes

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Figure 25

Flying height (FH) and pitch and roll angle responses to translation motion of (a) NDP slider and (b) DP slider at outer diameter

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Figure 26

Flying-height response to wavy motion of NDP slider and DP slider at outer diameter

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Figure 27

Air-bearing stiffness of NDP and DP sliders versus TFC heater power at interdiameter in (a) translation, (b) pitch, and (c) roll modes

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Figure 28

Flying height (FH) and second pitch damping ratio (DR) of NDP and DP slider versus TFC heater power at interdiameter

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Figure 29

Experimentally measured velocity responses by LDV versus frequency of NDP and DP sliders

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Figure 30

Experimentally measured gain by LDV versus frequency of NDP and DP sliders

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Figure 31

Experimentally measured gain by LDV versus frequency of NDP and DP slider

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Figure 32

Experimentally measured gain by LDV versus frequency of NDP and DP slider

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Figure 33

Disk surface image after touchdown testing with NDP and DP sliders

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