JP2001195714A - Method for measuring head flying height - Google Patents

Abstract

PROBLEM TO BE SOLVED: To easily and exactly measure the floating height H of a head 12 over a wide range. SOLUTION: A unit 50 is lowered stepwise and in the positions of the respective steps, the interference light intensity for one circumference of a disk 14 is detected. The position of the unit 50 where the interference light intensity peaks relating to the measurement point set for the disk 14 is searched out. Namely, the first peak of the interference light intensity based on the reflected light from the rear surface of the disk 14 and the second peak of the interference light intensity based on the reflected light from the head 12 are detected and the first and second positions of the unit 50 corresponding to the first and second peaks are detected. The spacing between the first and second positions is calculated as the floating height H.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for measuring a flying height of a head, and more particularly, to a method for measuring, for example, a hard disk or
The present invention relates to a method of measuring the flying height of a head, which measures the flying height of a head applied to a magnetic recording apparatus such as eto Optical) with respect to a disk.

[0002]

2. Description of the Related Art In a magnetic recording apparatus of this type, recording density has been increased with an increase in the amount of information. However, in this density increase, the distance between the disk and the head, that is, the flying height of the head, has been increased. One of the important factors is to lower the level. Among the recording media, in the case of hard disks having relatively high rigidity, the flying height of the head is decreasing year by year due to the increase in recording density. The flying principle of the head is to lift the head using the lift due to the air flow accompanying the rotation of the disk, and to keep the flying height of the head minute. Therefore, as the flying height decreases, it is necessary to stabilize the flying characteristics of the head with higher precision. With this requirement, a device that can easily and accurately measure the flying height of the head is required.

A conventional head flying height measuring apparatus 1 shown in FIG. 9 has been developed to meet such a demand. In this measuring device 1, a disk 3 is mounted on a spindle motor 2, and a light source is provided above the disk 3 as a light source.
For example, a HeNe laser 4 having a wavelength of about 632 nm is provided. The light emitted from the HeNe laser 4 irradiates the disk 3 and the head 5 disposed below the disk 3, is reflected by the disk 3 and the head 5, and is detected by the light receiving unit 6.

When measuring the flying height H of the head 5 at a predetermined number of revolutions using the measuring device 1, first, the number of revolutions of the spindle motor 2 is temporarily reduced, and the head 5 is brought close to the disk 3. The flying height of the head 5 is gradually increased by increasing the rotation speed of the spindle motor 2, and the intensity of the interference light between the reflected light from the lower surface of the disk 3 and the reflected light from the head 5 is detected by the light receiving unit 6. To detect. Thereby, the relationship between the rotation speed of the spindle motor 2 and the interference light intensity is obtained. When the interference distance calculated from the wavelength is set on the horizontal axis and the interference light intensity is set on the vertical axis, a graph as shown in FIG. 10 is obtained. In this case, since the measurement is performed after the flying height of the head 5 is reduced to near the 0th order of the wave number, the rotation speed corresponds to the 0th order of the wave number.
Therefore, the order and the interference light intensity at the rotation speed to be measured are determined, the interference distance is determined based on the order and the interference light intensity, and the flying height H is determined based on the interference distance.
(H = interference distance / 2) is obtained.

[0005]

The conventional method of measuring the flying height of the head using the measuring device 1 can be applied to a head having a relatively low flying height H (for example, 0.2 μm or less), but is not limited to MO or the like. However, it cannot be applied to a head having a high flying height H, such as a head used in Example 1. In other words, in a head having a higher flying height H, the order of the wave corresponding to the flying height H is higher, so that the head can be lowered to a position corresponding to the 0th order of the wave number even if the rotation speed is reduced. Without
Further, the order of the wave corresponding to the measured interference light intensity could not be determined, and the flying height H could not be calculated.

On the other hand, by using a plurality of lights (light sources) having different wavelengths or a plurality of lights (light sources) having different incident angles to the head, the order of the waves is obtained by utilizing the difference in the period of the intensity of the interference light. A known measuring method is known. However, even with these methods, the flying height was measured only up to about 5 μm, and practically up to about 2 μm.

[0007] Therefore, a main object of the present invention is to accurately measure the flying height of a head over a wide range.
An object of the present invention is to provide a head flying height measuring device.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a method for measuring the flying height of a head with respect to a disk rotated by a motor, the method comprising measuring the flying height of a head. The light from the light source is split into the measurement light and the reference light using the light separating means, and the measurement light is reflected by the disk and the head, respectively, and is irradiated on the light receiving unit. Then, the reference light is reflected by the reflection means and radiated to the light receiving portion, and the optical path length of one of the measurement light and the reference light is changed stepwise, and the intensity of the interference light obtained at the light receiving portion becomes a peak.
Find the flying height of the head based on the difference between the two optical path lengths,
This is a method of measuring the head flying height.

[0009]

The light emitted from the light source is split into reference light and measurement light by the spectral means. The reference light is condensed on the light receiving portion after being reflected by the reflection means, and the measurement light is condensed on the light receiving portion after being reflected on each of the disk and the head. The light receiving section outputs a signal having a magnitude corresponding to the intensity of the interference light between the reference light and the measurement light. When the spectroscopic means is stepped down together with the reflecting means by the displacement means (piezo element, etc.), when the spectroscopic means is at the first position, the measuring light reflected on the lower surface of the disk (head facing surface) and the reflecting light on the reflecting means A first peak appears in the intensity of the interference light with the reference light. Then, when the spectroscopic unit is further lowered in a stepwise manner, when the spectroscopic unit is at the second position, the second peak of the interference light intensity between the measuring light reflected by the head and the reference light reflected by the reflecting unit is obtained. Appears. Therefore, from the first position to the second position
When the distance to the position is calculated, the distance is the distance between the lower surface of the disk and the head, that is, the flying height of the head.
That is, the flying height is determined based on the difference between the two optical path lengths when the interference light intensity reaches a peak. The first light source
And a coherence length short enough to detect the second peak is used. Note that the same measurement can be performed when the reflecting means is displaced stepwise while the spectroscopic means is fixed.

In addition, a reference point is set on the disk based on the index signal output from the encoder of the motor, and at least one measurement point is set on the disk based on the reference point. When the flying height of the disk is measured, accurate measurement can be performed in consideration of the runout of the disk.

[0011]

According to the present invention, the flying height of the head can be measured simply and accurately over a wide range.

The above objects, other objects, features and advantages of the present invention will become more apparent from the following detailed description of embodiments with reference to the drawings.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The head flying height measuring method of this embodiment is as follows.
The flying height H (0. 0) of the head with respect to a glass disk applied to a magnetic recording device such as a hard disk or MO.
(About 1 to 300 μm), and is used, for example, in a measuring apparatus 10 as shown in FIG.

The measuring apparatus 10 (FIG. 1) includes a spindle motor 12, and the spindle motor 12 is provided with an encoder (not shown). Then, the encoder outputs one index signal for one rotation of the spindle motor 12, and outputs a pulse signal (angle signal) obtained by dividing the index signals at equal intervals.

The rotating shaft of the spindle motor 12 has a disk 1 as a virtual medium such as a glass disk.
4 is attached. As shown in FIG. 3, “undulations” or “runouts” exist on the surface of the disk 14, and when the displacement of the runout becomes steep, the behavior of the head 16 cannot follow the surface of the disk 14, so that the flying height Accurate measurement of H becomes difficult. Therefore, the amplitude and cycle of the run-out are measured in advance by using a dedicated measuring device, and only the disk 14 that satisfies a certain standard is adopted.

Then, a head 16 to be measured is arranged below the disk 14. The term “downward” is used to indicate a relative positional relationship with other components, and may be “upward” or “lateral” in practice. The head 16 includes a slider 18 and a suspension 20, and the suspension 20 is fixed to a head mount block 22. Therefore, the head 16
The disk 14 can be displaced in the radial direction by operating the head mount block 22.

Above the disk 14, a beam splitter 24 and an objective lens 26 as spectral means are arranged in this order, and above the objective lens 26, two beam splitters 28 and 30 and a light source 32 are arranged in this order. Be placed. Then, a power supply 34 is connected to the light source 32. As the light source 32, a light source having a short coherence length (about 500 μm or less) such as a halogen lamp, a metal halide lamp, a xenon lamp, a super luminescent diode (SLD), an end-face reflection type light emitting diode, a white LED or an EL panel is used. Can be
Here, the “coherence length” refers to a point from a point where the intensity of the interference light reaches a peak to a point where the intensity of the interference light becomes 3% or less of the peak in a graph (FIG. 4) showing a relationship between the interference distance and the intensity of the interference light. Means the distance L.

A correction plate 36 and a reference mirror 38 as reflection means are provided beside the beam splitter 24.
Are arranged in this order, a light receiving unit 40 is arranged beside the beam splitter 28, and a CCD camera 42 is arranged beside the beam splitter 30.

The correction plate 36 is for optically correcting the optical path length, and is formed of the same material and the same thickness as the disk 14.

As the light receiving section 40, a silicon photodiode, a PIN silicon photodiode, a photomultiplier (so-called photomultiplier) or the like is used.
Receives the interference light and performs photoelectric conversion. A signal based on the interference light (interference light signal) is supplied to an amplifier 44, amplified, and converted into a digital signal by an A / D converter 46.

The CCD camera 42 captures the state of interference between the measurement light and the reference light by video, and the video signal output from the CCD camera 42 is given to a monitor 48 to be displayed as an image.

Among these components, the beam splitter 24, the objective lens 26, the correction plate 36, and the reference mirror 38 are integrally incorporated into a casing 52 as a unit 50.
Is attached to a frame (not shown) so as to be vertically displaceable. In addition, a piezo element (PZT) 54 as a displacement unit is fixed on the upper part of the unit 50. Therefore, when a voltage is applied to the piezo element 54, the wall pressure of the piezo element 54 is changed according to the magnitude of the voltage, and the unit 50 is vertically displaced accordingly.

Further, drivers 56a to 56c for driving these are connected to the spindle motor 12, the head mount block 22, and the piezo element 54, respectively.
These drivers 56a to 56c, A / D converter 46 and output device 58 are connected to computer 60. The output device 58 is for outputting a measurement result, and specifically, a printer, a floppy disk, or the like is used.

Although not shown, it goes without saying that the unit 50 and the like can be displaced in the horizontal direction following the head 12.

In operation, when light is emitted from the light source 32, the light is provided to the beam splitter 24 via the beam splitters 30 and 28 and the objective lens 26, and is split into reference light and measurement light. Then, the reference light is provided to the reference mirror 38 through the correction plate 36, and the measurement light is provided to the disk 14 and the head 16 thereunder. The reference light reflected by the reference mirror 38 is applied to the beam splitter 24, the objective lens 26, and the beam splitter 28.
Then, the measurement light reflected by the disk 14 and the head 16 is focused on the light receiving unit 40 via the beam splitter 24, the objective lens 26, and the beam splitter 28. Therefore, the light receiving unit 40
In, the reference light and the measurement light interfere with each other, and an interference light signal having a magnitude corresponding to the intensity of the interference light is given to the amplifier 44.
It is provided to the computer 60 through the / D converter 46. Also, a part of each reflected light (reference light and measurement light)
CCD camera 4 via beam splitters 28 and 30
2, the interference state (interference fringe) of each reflected light is displayed on the monitor 48 as an image.

In the measuring device 10, when the optical path difference between the measuring light reflected on the lower surface of the disk 14 (the surface facing the head) and the reference light reflected on the reference mirror 38 is “0”, the light receiving unit 40 detects the difference. A first peak appears in the intensity of the interference light. When the optical path difference between the measurement light reflected by the head 16 and the reference light reflected by the reference mirror 38 is “0”, a second peak appears in the interference light intensity. Therefore, if the position of the unit 50 where the first peak appears is the first position, and the position of the unit 50 where the second peak appears is the second position,
The distance from the first position to the second position is the distance from the disk 14 to the head 16, that is, the flying height H of the head 16. That is, half the difference between the optical path length of the measurement light when the unit 50 is at the first position and the optical path length of the measurement light when the unit 50 is at the second position is the flying height H. However, since the disk 14 is rotated and a runout is present on the surface thereof, in this embodiment, at least one measurement point is set on the disk 14 and the flying height H is determined for the measurement point. .

Hereinafter, a method of measuring the flying height of the head will be described with reference to the flowchart of FIG. In addition,
The assumed head flying height H is about 5 μm, and a halogen lamp (coherence length: about 1 μm) is used as the light source 32.

When a start switch (not shown) of the measuring device 10 is turned on, first, in step S1, the computer 16 controls the head 16 and the unit 50 by using a computer.
Is positioned at the initial position, the spindle motor 12 (disk 14) is rotated at a predetermined rotation speed, and the light source 32 emits light. Here, the initial position of the unit 50 is set so that the interval between the spectral point of the beam splitter 24 (FIG. 2) and the lower surface of the disk 14 is longer than the interval between the spectral point of the beam splitter 24 and the reference mirror 38. You.

In step S3, a predetermined voltage is applied to the piezo element 54, and the unit 50 is displaced (down) by a predetermined width. When the unit 50 is displaced, the optical path length of the measurement light becomes shorter and approaches the optical path length of the reference light, so that the optical path difference approaches “0”. That is,
According to the graph of FIG. 4, the interference light intensity approaches the peak. Here, if the displacement width of the unit 50 is too small, the measurement time becomes long, and if it is too large, the peak of the interference light intensity cannot be detected accurately. In this embodiment, the displacement width is set to 20 nm in consideration of the balance between the two. Is set (FIG. 2). However, this value may be changed as appropriate.

In step S5, the interference light intensity corresponding to one round of the disk 14 is detected with the unit 50 stopped. That is, as shown in FIGS. 6 and 7, a reference point is set based on the index signal output from the encoder of the spindle motor 12, and the interference light intensity corresponding to one rotation of the disk 14 starting from this reference point is determined. Is detected. Also, a measurement point (for example, θ = 0) based on the angle signal generated from the index signal
, 90, 180, and 270 degrees), and the relationship between the position of the unit 50, the position of the measurement point (angle θ), and the interference light intensity is stored in a storage device (not shown). At least one measurement point is sufficient, but the behavior of the head 16 can be grasped more accurately as the number of measurement points increases.

In the next step S7, it is determined whether or not the measurement has been completed. That is, it is determined whether or not the unit 50 has been displaced by a preset displacement distance (FIG. 2). Then, if "YES" is determined, the process proceeds to step S9.

The operations from step S1 to step S7 are for obtaining the first and second positions of the unit 50 where the peak of the interference light intensity appears for one rotation of the disk 14. Therefore, the displacement distance of the unit 50 must be sufficiently longer than the head flying height H. In this embodiment, the displacement distance is set to about twice, that is, 10 μm.
Therefore, in step S7, when a voltage corresponding to 10 μm is applied to the piezo element 54, “YE
S "is determined.

If "NO" is determined in the step S7, the process returns to the step S3, and the step feed of the unit 50 and the measurement of the interference light intensity are repeated.

In step S9, the head flying height H is calculated. That is, the first and second peaks of the interference light intensity at the measurement point are detected from the relationship (FIG. 7) between the position of the unit 50, the position of the measurement point (angle θ), and the interference light intensity,
The first and second positions of the unit 50 where the first and second peaks appear are detected, and the distance from the first position to the second position is calculated as the head flying height H.

For example, as shown in FIG. 7, when the reference point is set as a measurement point (θ = 0 degree), the position (1
00), a first peak P1 appears at a position (350).
, A second peak P2 appears. Therefore, the distance from the position (100) to the position (350) is the flying height H
Becomes That is, 100 × 20 nm (= 2 μm) from the origin
m) The head flying height H at the measurement point (θ = 0 °) is 5 μm between the lowered position and the position lowered by 350 × 20 nm (= 7 μm). Similarly, the head flying height H can be obtained for other measurement points, and θ = 90
In the measurement point which becomes the degree, the position (140) and the position (400)
5.2 μm is the flying height H.

When the flying height H is obtained for each measurement point, the measurement operation is completed.

According to this embodiment, since the unit 50 is lowered stepwise to detect the interference light intensity for one round of the disk 14 at each stage, even when a plurality of measurement points are set. The head flying height H at each measurement point can be easily and accurately obtained. Also,
As long as the interference light intensity can be detected, the flying height H
Is relatively high.

Further, by setting a plurality of (for example, 2048) measurement points at equal intervals around one circumference of the disk 14, dynamic characteristics (changes in the flying height H at each measurement point) can be measured.

In the above embodiment, the optical path length of the measurement light is changed stepwise while the optical path length of the reference light is kept constant. Conversely, the optical path length of the measurement light is changed. The optical path length of the reference light may be changed stepwise while keeping the length constant. That is, as shown in FIG. 8, for example, with the beam splitter 24 fixed, the reference mirror 38 is displaced stepwise by the piezo element 62,
The interference light intensity may be detected at each stage position, and the flying height H may be obtained based on the position of the reference mirror 38 when the interference light intensity has a peak.

Further, in each of the above-described embodiments, FIG.
As shown by a two-dot chain line in FIG. 8, a light shielding member 64 having a fine hole such as a circle or a rectangle is arranged between the light receiving unit 40 and the beam splitter 24, and only the light passing through the fine hole is received by the light receiving unit. Irradiation may be performed on 40. In this case, since the light is narrowed by the fine holes, the measurement sensitivity can be increased, and the measurement location can be set finely with respect to the head 12.

[Brief description of the drawings]

FIG. 1 is an illustrative view showing a head flying height measuring apparatus to which the present invention is applied;

FIG. 2 is an illustrative view showing a displacement distance of a lens unit;

FIG. 3 is a graph showing runout of a disk and displacement of a head.

FIG. 4 is a graph showing a relationship between an interference distance and an interference light intensity.

FIG. 5 is a flowchart showing one embodiment of the present invention.

FIG. 6 is a perspective view showing a positional relationship between a disk and a head.

FIG. 7 is a graph showing the intensity of interference light for one rotation of the disk at each position of the unit.

FIG. 8 is an illustrative view showing another head flying height measuring apparatus to which the present invention is applied;

FIG. 9 is an illustrative view showing a conventional technique;

FIG. 10 is a graph showing the relationship between the interference distance and the interference light intensity in the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Head floating height measuring device 12 ... Spindle motor 14 ... Disk 16 ... Head 24 ... Beam splitter 26 ... Objective lens 32 ... Light source 38 ... Reference mirror 40 ... Light receiving unit 50 ... Unit 54 ... Piezo element 60 ... Computer

Continued on the front page (72) Inventor Motohiro Terao 5-10-10 Okuhata, Itami-shi, Hyogo Prefecture Inside Kubota Corporation (72) Inventor Toyofumi Inoue 5-10-10 Okuhata, Itami-shi, Hyogo Prefecture Inside Kubota Corporation (72) Inventor Hiroshi Mita 4-2-18 Hiranocho, Chuo-ku, Osaka-shi Kubota Comps Co., Ltd. (72) Inventor Yoshiki Saeki 4-2-18 Hiranocho, Chuo-ku, Osaka-shi Kubota Comps Co., Ltd.

Claims (5)

[Claims] 1. A head flying height measuring method for measuring a flying height of a head with respect to a disk rotated by a motor, comprising: disposing the head below the disk and dispersing means above the disk. Rotating the disk with the motor, splitting light from a light source into measurement light and reference light using the spectroscopic means, and reflecting the measurement light on the disk and the head, respectively, to the light receiving unit. Irradiating, irradiating the reference light with a reflection unit to irradiate the light receiving unit, and changing the optical path length of one of the measurement light and the reference light in a stepwise manner. Determining the flying height of the head based on the difference between the two optical path lengths that form a peak,
Measurement method of head flying height. 2. The motor includes an encoder, a reference point is set on the disk based on an index signal output from the encoder, and at least one measurement point is set on the disk based on the reference point. 2. The method for measuring the head flying height according to claim 1, wherein the head flying height is measured at the measurement point. 3. The head flying height measuring method according to claim 2, wherein an angle signal is generated based on said index signal, and said measurement point is set based on said angle signal. 4. The head according to claim 1, wherein the optical path length of the measurement light is changed by gradually displacing the spectroscopic means with respect to the disk and the head. How to measure flying height. 5. The head flying height according to claim 1, wherein said optical path length of said reference light is changed by stepwise displacing said reflecting means with respect to said spectral means. How to measure.