U.S. patent application number 09/833143 was filed with the patent office on 2001-11-01 for method and apparatus for fly height testing using light emitting diodes.
Invention is credited to Johnston, Matthew M..
Application Number | 20010035960 09/833143 |
Document ID | / |
Family ID | 26903576 |
Filed Date | 2001-11-01 |
United States Patent
Application |
20010035960 |
Kind Code |
A1 |
Johnston, Matthew M. |
November 1, 2001 |
Method and apparatus for fly height testing using light emitting
diodes
Abstract
A method and fly-height tester include a moving medium and a
slider mount that holds a slider in proximity with the medium so
that the slider flies relative to the medium. At least one light
emitting diode generates a light that is directed by optics so that
it reflects off the medium and the slider. The reflected light is
directed by second optics to at least one detector, where each
detector is capable of generating an electrical signal based on the
amplitude of at least one wavelength of light in the reflected
light. A distance calculator then determines the distance from the
slider to the medium based on the at least one electrical
signal.
Inventors: |
Johnston, Matthew M.;
(Edina, MN) |
Correspondence
Address: |
Theodore M. Magee
WESTMAN CHAMPLIN & KELLY
International Center-Suite 1600
900 South Second Avenue
Minneapolis
MN
55402-3319
US
|
Family ID: |
26903576 |
Appl. No.: |
09/833143 |
Filed: |
April 11, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60208875 |
Jun 1, 2000 |
|
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Current U.S.
Class: |
356/507 ;
G9B/5.145 |
Current CPC
Class: |
G01B 11/14 20130101;
G11B 5/455 20130101 |
Class at
Publication: |
356/507 |
International
Class: |
G01B 009/02 |
Claims
What is claimed is:
1. A method of testing the fly-height of a slider for a disc drive,
the method comprising steps of: (a) flying the slider over a
transparent disc; (b) generating light from an array of light
emitting diodes; (c) directing the light so that it reflects off
the disc and the slider to thereby produce reflected light; (d)
detecting the amplitude of at least one wavelength of light in the
reflected light; and (e) calculating the distance between the
slider and the transparent disc from the amplitude of the at least
one wavelength of light.
2. The method of claim 1 wherein generating step (b) comprises
generating light from an array of light emitting diodes that
produce white light.
3. The method of claim 2 wherein generating step (b) further
comprises using the amplitude of at least one wavelength of light
in the reflected light to set the intensity of the light produced
by the light emitting diodes.
4. The method of claim 1 wherein generating step (b) further
comprises generating light from an array of light emitting diodes
that comprises at least two types of diodes, each type of diode
being capable of generating a different wavelength of light.
5. The method of claim 4 wherein the array of diodes comprises
three types of diodes.
6. The method of claim 5 wherein detecting step (d) comprises
detecting the amplitudes of three wavelengths of light in the
reflected light, each of the three wavelengths having been
generated by a separate type of light emitting diode in the array
of diodes.
7. The method of claim 6 wherein generating step (b) further
comprises using a detected amplitude of a wavelength of light
produced by a type of light emitting diode in the array of diodes
to control the intensity of light emitted by that type of light
emitting diode.
8. The method of claim 1 wherein generating step (b) comprises
generating light from an array of light emitting diodes that
comprises two stacked levels of light emitting diodes.
9. A fly-height tester for testing the fly height of sliders used
in storage devices, the tester comprising: a moving medium; a
slider mount for holding the slider in proximity to the moving
medium such that the slider flies relative to the medium; at least
one light emitting diode for generating light; first optics for
directing the light so that it reflects off the moving medium and
the slider to form reflected light; second optics for directing the
reflected light to at least one detector, each detector being
capable of generating an electrical signal based on the amplitude
of at least one wavelength of light in the reflected light; and a
distance calculator that calculates the distance between the slider
and the moving medium based on at least one electrical signal
generated by the at least one detector.
10. The fly-height tester of claim 9 wherein the at least one light
emitting diode comprises an array of light emitting diodes.
11. The fly-height tester of claim 10 wherein the array of light
emitting diodes comprises light emitting diodes that are stacked on
two different levels in the array.
12. The fly-height tester of claim 10 wherein the array of light
emitting diodes comprises diodes that generate a broad spectrum of
light wavelengths.
13. The fly-height tester of claim 10 wherein the array of light
emitting diodes comprises at least two different colors of light
emitting diodes.
14. The fly-height tester of claim 13 wherein the array of light
emitting diodes comprises three different colors of light emitting
diodes.
15. The fly-height test of claim 14 wherein the at least one
detector comprises three different detectors, each detector
designed to detect a different color of light produced by a
different color light emitting diode.
16. The fly-height tester of claim 9 further comprising a feedback
circuit for controlling the intensity of the light produced by the
at least one light emitting diode based on at least one electrical
signal produced by at least one detector.
17. The fly-height tester of claim 16 wherein the at least one
light emitting diode comprises an array of colored light emitting
diodes, the array having three different colors of light emitting
diodes.
18. The fly-height tester of claim 17 wherein the at least one
detector comprises three detectors, each detector being capable of
generating an electrical signal based on the amplitude of a
different color of light.
19. The fly-height tester of claim 18 wherein the feedback circuit
comprises three separate feedback circuits, each separate feedback
circuit for controlling the intensity of the light produced by one
of the colors of light emitting diodes based on an electrical
signal produced by at least one detector.
20. A fly-height tester, for testing the fly-height of a slider
relative to a medium, the fly-height tester comprising: a slider
mount for positioning the slider proximate the medium; and
interferometer means for generating light, reflecting the light off
the slider and medium to produce reflected light, detecting the
reflected light and calculating a distance between the slider and
the medium based on the reflected light.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims priority from U.S. provisional
patent application Ser. No. 60/208,875, filed Jun. 1, 2000, and
entitled "FLY HEIGHT VARIANCE TECHNIQUE FLY HEIGHT TESTING".
FIELD OF THE INVENTION
[0002] The present invention relates to fly-height testing in
storage devices. In particular, the present invention relates to
interferometer fly-height testing.
BACKGROUND OF THE INVENTION
[0003] In many storage devices, a slider containing a read or write
head flies above a moving medium, such as a disc, in order to read
or write data to various parts of the medium. The fly-height of the
slider, the distance between the slider's bottom surface and the
surface of the medium, affects the head's ability to read and write
data to the medium. To ensure that the fly-height of a slider is
within specifications, the slider is tested using a fly-height
tester before it is placed in a drive.
[0004] Most fly-height testers determine the distance between the
slider and a test medium using a technique known as interferometry.
Under this technique, a beam of light is passed through the medium
and onto the slider as the slider flies over the medium. This
causes the light to be reflected twice, once at the surface of the
medium and once at the slider. These two reflective beams interfere
with each other such that some wavelengths of light have a high
amplitude in the combined reflected light while other wavelengths
of light have zero amplitude. By measuring the intensity of the
light at particular wavelengths, it is possible to determine the
distance between the slider and the disc surface.
[0005] Because the distance measurement is dependent on the
amplitude of the reflected light, any noise that affects the
amplitude of the reflected light will affect the accuracy of the
measurement. In prior art systems, one major source of optic noise
has been the light source used to generate the light beam. For
example, some testers use arc lamps that produce a noisy light beam
due to the manner in which they generate light. Other fly-height
testers use lasers that generate a light that is initially
relatively clean but that is prone to speckling when it reflects
off a surface.
[0006] Arc lamps and lasers are also undesirable because they are
inefficient and produce a large amount of heat. This adds to the
cost of the tester because the tester must be designed to vent the
heat.
[0007] The present invention provides a solution to this and other
problems and offers other advantages over the prior art.
SUMMARY OF THE INVENTION
[0008] A method and fly-height tester include a moving medium and a
slider mount that holds a slider in proximity with the medium so
that the slider flies relative to the medium. At least one light
emitting diode generates a light that is directed by optics so that
it reflects off the medium and the slider. The reflected light is
directed by second optics to at least one detector, where each
detector is capable of generating an electrical signal based on the
amplitude of at least one wavelength of light in the reflected
light. A distance calculator then determines the distance from the
slider to the medium based on the at least one electrical
signal.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] FIG. 1 is block diagram of one embodiment of a storage
device under the present invention.
[0010] FIG. 2 is a block diagram of a fly-height tester under one
embodiment of the present invention.
[0011] FIG. 3 is a circuit diagram of an LED array under one
embodiment of the present invention
[0012] FIG. 4 is a top view of an LED array under one embodiment of
the present invention
[0013] FIG. 5 is a block diagram of a second embodiment of a
fly-height tester under the present invention
[0014] FIG. 6 is a top view of an LED array under a second
embodiment of the present invention.
DETAILED DESCRIPTION OF ILLUSTRATIVE EMBODIMENTS
[0015] FIG. 1 is a perspective view of a disc drive 100 in which
the present invention is useful. Disc drive 100 includes a housing
with a base 102 and a top cover (not shown). Disc drive 100 further
includes a disc pack 106, which is mounted on a spindle motor (not
shown), by a disc clamp 108. Disc pack 106 includes a plurality of
individual discs 107, which are mounted for co-rotation about
central axis 109. Each disc surface has an associated disc
head-slider 110 that is mounted to disc drive 100 for communication
with the confronting disc surface. Head-slider 110 includes a
slider structure arranged to fly above the associated disc surface
of an individual disc of disc pack 106, and a transducing head 111
arranged to write data to, and read data from, concentric tracks on
the confronting disc surface. The concentric tracks are, in effect,
parallel to each other at different radii on the disc. In the
example shown in FIG. 1, head-sliders 110 are supported by
suspensions 112 which are in turn attached to track accessing arms
114 of an actuator 116. Actuator 116 is driven by a voice coil
motor (VCM) 118 to rotate the actuator, and its attached heads 110,
about a pivot shaft 120. Rotation of actuator 116 moves the heads
along an arcuate path 122 to position the heads over a desired data
track between a disc inner diameter 124 and a disc outer diameter
126. Voice coil motor 118 is driven by servo electronics included
on circuit board 130 based on signals generated by the heads of
head-sliders 110 and a host computer (not shown). Read and write
electronics are also included on circuit board 130 to supply
signals to the host computer based on data read from disc pack 106
by the read heads of head-sliders 110, and to supply write signals
to the write head of head-sliders 110 to write data to the
discs.
[0016] The fly heights of head-sliders 110 are tested before the
sliders are placed in a disc drive. Under the present invention,
the fly-heights are tested using an interferometer that has an
improved light source constructed of light emitting diodes
(LEDs).
[0017] FIG. 2 provides a block diagram of a fly-height tester 200
of one embodiment of the present invention. Fly height tester 200
includes an LED light source 202 that generates a light 204. The
light passes through an optic system 206, where it is collimated
into a beam of light that is reflected by a splitter 208 toward a
second optic system 210. Optic system 210 directs the beam of light
toward a transparent disc 212 and a slider 214. Disc 212 is rotated
by a motor 216 and a spindle 218. Slider 214 is mounted in a slider
mount 220 that places a positive but resilient force against slider
214 to force it into contact with disc 212. As the disc is rotated
by motor 216, an air bearing develops between slider 214 and disc
212 causing slider 214 to fly below disc 212.
[0018] The beam of light from optics 210 reflected off surface 222
of disc 212 and the surface of slider 214. This generates reflected
light 224 from slider 214 and reflected light 226 from disc
212.
[0019] Reflected light 224 and 226 are combined to form a total
reflected beam that is formed from the interference between
reflected light 224 and reflected light 226. This total reflected
beam passes through optics 210 and splitter 208 to optics 230,
which direct the reflected beam onto a set of detectors 231, 232,
and 233. Each detector generates an electrical signal that has an
amplitude that tracks the amplitude of a wavelength of light in the
reflected beam. Under most embodiments, detectors 231, 232, and 233
detect different wavelengths of light. The three electrical signals
234, 235, and 237 produced by the detectors are provided to a
fly-height calculator 236, which determines the distance between
the head 214 and disc 212 based on the amplitude of the signals.
Systems for performing such fly-height calculations are well known
in the art.
[0020] At least one of the electrical signals, such as electrical
signal 234, is also provided to a sample and hold 238, which is
gated to hold the electrical signal at a constant level during the
fly height measurement period. Because it is held constant by the
sample and hold 238 during measurement, as the distance between
slider 214 and disc 212 changes, the amplitude provided by the
sample and hold 238 indicates the intensity of the light provided
by LED 202. The gated signal is provided to an inverting amplifier
which inverts and amplifies the signal in order to provide negative
feedback. During non-measurement periods, the inverting amplifier
240 is able to generate a feedback signal 244 that can be used to
control a power source 246 for LED 202. For example, if the
amplitude is too high, comparator 240 will generate a feedback
signal 244 that will lower the power provided by power source 246.
In this manner, feedback signal 244 will reduce the intensity of
the light output by LED 202. Similarly, if the amplitude provided
by sample and hold 238 is too low, comparator 240 will increase
feedback signal 244 so that the power provided to LED 202
increases. Thus, the present invention provides a feedback
mechanism for stabilizing the intensity of the light provided by
LED 202, thereby limiting the noise in the light provided to
detectors 231, 232, and 233.
[0021] Under most embodiments of the invention, LED 202 is an array
of LEDs. FIG. 3 provides a circuit diagram for such an array. In
FIG. 3, the array is constructed from bias resistors and LEDs that
extend in parallel between power supply 246 and a ground 302. For
example, bias resistor 304 is in series with LED 306 between power
supply 246 and ground 302. Similarly, bias resistor 308 is in
series with LED 310 between power supply 246 and ground 302.
[0022] The bias resistors of the array, such as bias resistors 304
and 308, are selected based on the voltage provided by power supply
246 and the desired operating current for the LEDs. Under one
embodiment, the LEDs are white gallium nitride (GaN) LEDs from
Nichia Corporation in Tokushima, Japan having part number
NSPW500BS. For such LEDs, power supply 246 typically provides five
volts and the LEDs are biased with 200 ohm resistors. The number of
LEDs in the array is determined based on the amount of light that
is needed for the fly-height testing. Under one embodiment, 300
LEDs are provided in the array.
[0023] Although gallium nitride LEDs were used in one embodiment of
the present invention, LEDs formed from other materials may be used
in the present invention as long as they provide sufficient light
for the fly-height testing.
[0024] FIG. 4 provides a top view of a layout for the LEDs in one
light source of the present invention. In the embodiment of FIG. 4,
the LEDs are stacked in two layers, with the bottom layer being
represented by solid circles, such as LED circle 400 and the top
layer being represented by dashed circles such as LED circle 402.
In this manner, the spaces between the LEDs in the top layer are
filled with LEDs from the bottom layer. Note that in the embodiment
of FIG. 4, the light from the LED tends to be concentrated in the
center of the LED and is highly directional such that the light
emitted from the LED would be directed almost entirely out of the
page of FIG. 4.
[0025] FIG. 5 provides a block diagram of a second embodiment of
the present invention, in which three different colors of LEDs are
provided in the LED array, with each color providing a different
wavelength of light. In FIG. 5, the elements that are common to
FIG. 2 are numbered the same.
[0026] In FIG. 5, the different colored light emitting diodes in
LED array 202 are each provided with their own feedback
stabilization circuit. For example, sample and hold 238, comparator
240, and power supply 246 provide a stabilization feedback circuit
for LEDs of one color, sample and hold 500, comparator 502, and
power supply 504 provide a stabilization feedback circuit for LEDs
of a second color, and sample and hold 506, comparator 508 and
power supply 510 provide a stabilization feedback circuit for LEDs
of a third color. In the stabilization feedback circuits, the
reference voltage used by comparators 240, 502 and 508 can be
different for different LEDs.
[0027] Under most embodiments, detectors 231, 232, and 233 are
selected so that they will each detect light from a different one
of the colored LEDs. For example, if red, blue and green LEDs were
found in LED array 202, detector 231 would detect red light,
detector 232 would detect blue light and detector 233 would detect
green light. Under some embodiments, these detectors are
specifically selected to match the LEDs of LED array 202, in that
they are formed using the same technology as the LED to which they
are matched. In other embodiments, the only difference between the
detectors is the use of a different filter before the actual
detector so that the particular wavelength of light for a
particular LED can be selected
[0028] FIG. 6 shows a layout for LEDs in an LED array in one
embodiment of the present invention in which different colored LEDs
are provided in the LED array. In particular, LED array 600 of FIG.
6 includes red LEDs, blue LEDs and green LEDs as exemplified by red
LED 602, blue LED 604, and green LED 606. In FIG. 6, red LEDs are
shown with vertical hatching, blue LEDs are shown with horizontal
hatching, and green LEDs are shown with diagonal hatching. Although
an equal number of each LED is shown in the embodiment of FIG. 6,
in other embodiments, different colors will have different numbers
of LEDs in the LED array based on the intensity of the light
provided by each LED.
[0029] In summary, a method of testing the fly-height of a slider
214 includes generating light 204 from an array of light emitting
diodes 202 and directing the light 204 so that it reflects off the
slider 214 and a transparent disc 212, over which slider 214 is
flying. The amplitude of at least one wavelength of light in
reflected light 224, 226 from the slider 214 and the disc 216 is
detected. This amplitude is then used to calculate the distance
between the slider 214 and the disc 212.
[0030] In other embodiments of the invention, a fly-height tester
200 includes a moving medium 212 and a slider mount 220 that holds
a slider 214 in proximity with medium 212 so that slider 214 flies
relative to medium 212. At least one light emitting diode 202
generates light 204, that is directed by first optics 206, 208, and
210 so that it reflects off medium 212 and slider 214. The
reflected light 224, 226 is directed by second optics 210, 208, 230
to at least one detector 231, 232, 233, where each detector is
capable of generating an electrical signal 234, 235, 237 based on
the amplitude of at least one wavelength of light in the reflected
light 224, 226. A distance calculator 236 then determines the
distance between slider 214 and medium 212 based on the at least
one electrical signal 234, 235, 237.
[0031] It is to be understood that even though numerous
characteristics and advantages of various embodiments of the
invention have been set forth in the foregoing description,
together with details of the structure and function of various
embodiments of the invention, this disclosure is illustrative only,
and changes may be made in detail, especially in matters of
structure and arrangement of parts within the principles of the
present invention to the full extent indicated by the broad general
meaning of the terms in which the appended claims are expressed.
For example, the particular elements may vary depending on the
particular application for the interferometer while maintaining
substantially the same functionality without departing from the
scope and spirit of the present invention. In addition, although
the preferred embodiment described herein is directed to a
fly-height tester for a slider in a disc drive system, it will be
appreciated by those skilled in the art that the teachings of the
present invention can be applied to other systems, like tape-drive
or optical drive systems, without departing from the scope and
spirit of the present invention.
* * * * *