Contact Force and Slider Dynamics

1
Tape Edge Wear and Its Relationship to Lateral
Tape Motion
2003 IIP/ISPS Joint Conference, Yokohama, Japan
Jason Wang and Frank Talke Center for Magnetic
Recording Research, University of California,
San Diego Yokohama, June 17, 2003
2
Motivation

• To increase storage density in tapes, track
  density must be increased
• Increase of track density requires better tape
  guiding
• Tape guiding is done by using pressure pads
• Pressure pads cause wear and degradation of
• performance
• Relationship between tape edge wear and lateral
  tape motion is needed

3
Objective

• Study tape edge wear
• Investigate lateral tape motion
• Correlate wear of tape edge and lateral tape
  motion

4
SEM Investigation of tape edge wear

• Investigation of tape edge for new and used tapes
  using
• SEM (Scanning Electron Microscopy)
• (a) top-view investigation
• (b) edge-view investigation

5
Top view comparison
5000 passes
new tape
100 passes
5 um
6
Edge view comparison
5000 passes
new tape
3000 passes
10 um
7

• Note
• Smoothening of tape edge occurs as a function of
  wear cycles

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Semi-quantitative study of tape edge wear
Talke (1971)
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• Question
• How can one measure quantitatively wear of the
  tape edge in the nano-and micro-meter regime?

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• Perform the following procedure
• Make an artificial defect in the tape edge (1um
  in depth, 1um in length)
• characterize this defect using AFM
• perform wear test
• monitor the change of depth of the defect

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• Measurement of tape edge wear

WEAR (? d) INITIAL DEPTH - REMAINING DEPTH
TAPE EDGE
1 um, INITIAL
1 um, INITIAL
10 um
10 um
REMAINING DEPTH
REFERENCE PLANE
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• Measurement of tape edge wear

WEAR (? d) INITIAL DEPTH - REMAINING DEPTH
1.6 mm
GUIDE PAD
TAPE EDGE
1 um, INITIAL
1 um, INITIAL
10 um
10 um
REMAINING DEPTH
REFERENCE PLANE
13
Test drive setup
Rollers without Flanges
Slider
Suspension
Tape
Removed Original Guide Pads
Bottom View
14
AFM measurement
Scanning Tip
Reel of Tape
Camera
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Data processing
AFM image of edge wear at 30-mN guide force
6,000 wear cycles
Initial
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Tape edge wear vs. number of wear cycles
at 4 m/s and 30 mN guide force
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Edge wear vs. tape speed
6k-pass
4k-pass
2k-pass
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Wear vs. guide surface roughness
Ra 126 nm
Ra 49 nm
Ra 15 nm
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Wear vs. tape tension
280 mN (1-oz)
560 mN (2-oz)
840 mN (3-oz)
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• Next
• Measurement of lateral tape motion

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• Evaluation of lateral tape displacement

Edge sensor
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• Edge sensor

Edge sensor
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Experimental setup
- 30-mN guide force from slider - 4 m/s constant
tape speed with a shoe-shine motion - Data were
collected at the same location on tape - Started
with a new LTO tape - Data were collected after
fixed number of wear cycles -
Edge sensor
Slider suspension
24
Lateral tape displacement and its distribution
6s 7.846
100 cycles
6s 7.446
1,000 cycles
6s 10.350
8,000 cycles
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Lateral tape displacement after high-pass
filtering at 1 kHz
6s 0.788
100 cycles
6s 0.796
1,000 cycles
6s 0.870
8,000 cycles
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• Why high pass filtering?
• High pass filtering corresponds to looking
• only at the component of the lateral tape
• motion that is not corrected by tape servo!

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Standard deviation (s) of lateral tape
displacement vs. number of wear cycles
(a) Un-filtered signal
(b) 1 kHz high-pass filtered signal
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Standard deviation (s) of lateral tape
displacement vs. high pass filter frequency
Hz
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Power spectral density of lateral tape
displacement
8,000 cycles
4,000 cycles
100 cycles
1,000 cycles
30
Power spectral density of lateral tape
displacement
4,000 cycles
8,000 cycles
1,000 cycles
100 cycles
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Standard deviation (s) of lateral tape
displacement vs. number of wear cycles
(c) 1.0 to 2.2 kHz band-pass filtered signal
32
Correlation between LTM and tape edge wear
(a) Unfiltered signal
Tape edge smoothening
(b) 1.0 kHz high pass filtered signal
Lateral tape displacement vs. tape edge wear
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Time-frequency images of LTM
(a) After 100 cycles
(b) After 1,000 cycles
Delta-function event
Frequency
Frequency
Time (sec)
Time (sec)
(c) After 4,000 cycles
(d) After 8,000 cycles
Frequency
Frequency
Time (sec)
Time (sec)
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Summary

• Tape edge wear increases with increasing number
  of wear cycles.
• The standard deviation of lateral tape
  displacement decreases initially due to edge
  smoothening and then increases with increasing
  number of wear cycles
• The standard deviation of high frequency lateral
  tape frequency content in the 1.0 to 2.2 kH
  range was found to increase with increasing
  number of wear cycles, causing a potential
  problem as high track densities are implemented