JPH0820226B2 - Head flying height measurement method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention will be described in the following order.

A Industrial Field B Outline of the Invention C Conventional Technology D Problems to be Solved by the Invention E Means for Solving Problems (FIGS. 1 and 6 to 8) F Action (First Fig. 6 to Fig. 8) G Example (Figs. 1 to 8) H Effect of the invention A Industrial field of application The present invention relates to a method for measuring the head flying height, and particularly to a so-called hard disk or the like. This is applicable when measuring the flying height of the head.

B. Summary of the Invention The present invention provides an optical interference fringe between a rotating disk and a head arranged so as to levitate by utilizing the air flow generated on the surface of the disk. In the head flying height measuring method for measuring the flying height of, the optical interference fringes are generated by irradiating monochromatic light, and the brightness at any point of the optical interference fringes corresponds to the flying height of the head part. By utilizing the variation, the flying height of the measurement point is calculated from the maximum value and the minimum value, so that the head flying height can be measured with high accuracy.

C Prior Art In an information recording / reproducing apparatus using a so-called hard disk, information is recorded at high density on a magnetic disk by allowing a magnetic head to face a magnetic disk rotating at a high speed while maintaining a minute gap. Or, the magnetic head is levitated by the air flow that is accompanied by the high-speed rotation of the magnetic disk as a method of facing the magnetic head to the surface of the magnetic disk while keeping a minute gap. The method has been adopted.

In this type of information recording / reproducing apparatus, if there is a means for grasping the floating mode in detail when the magnetic head is floated, it is possible to evaluate whether or not the head is stably floating as designed, and It is considered to be effective in taking measures to improve the problem. Based on this idea, a device that measures the flying stability of the head,
It is disclosed in JP-A-60-124071 and JP-A-60-124072.

D. Problems to be Solved by the Invention This conventional levitation stability measuring apparatus has a transparent glass plate rotating at high speed in place of the magnetic disk to which the magnetic head should face, and the surface of the magnetic head is exposed through this transparent glass plate. Take an image with a video camera. As a result, optical interference fringes corresponding to the air gap between the magnetic head and the transparent glass plate are generated, and if this is imaged by a video camera and recorded in the recording means, the floating stability of the magnetic head can be judged. You can get information.

However, this conventional device is designed to measure the determination of the flying height by visually confirming the color of the color interference fringes.Therefore, there is a problem that the measurement accuracy cannot be improved so much, and it is practically 0.05. There is a problem in that an accuracy of only about [μm] can be obtained.

Therefore, in order to determine the flying mode of the head in detail, when it is necessary to measure the flying height with higher accuracy when trying to obtain the judgment data for various parameters, the conventional head floating method is used. The quantity measurement method is still insufficient.

The present invention has been made in consideration of the above points, and by using monochromatic light as the irradiation light for generating the optical interference fringes, the detection signal obtained from the measurement point of the head portion is used to compare with the conventional case. Then, it is intended to propose a head flying height measuring method capable of obtaining the head flying height with higher accuracy.

E Means for Solving the Problems In the present invention for solving the problems, the rotating disk 3 and the head arranged so as to float by utilizing the air flow generated on the surface of the disk 3. In the head flying height measuring method for measuring the flying height of the head section 4 by the optical interference fringes generated between the disk section 4 and the head section 4, irradiating the disk 3 and the head section 4 with irradiation light of monochromatic light. The optical interference fringes are generated by, and for the measurement point x ₀ set at a point within the optical interference fringes, image data Q2 representing the brightness of the optical interference fringes is obtained, and the brightness representing the image data Q2 is By utilizing the fact that the flying height of the head portion 4 at the measurement point X ₀ is increased and it changes cyclically, the change is approximated as a sine wave shape, and a dark point and a bright point that appear periodically. For the cycle range between = 0,
1, 2, ...) are assigned, the order m to which the flying height h ₀ of the above measurement point belongs is specified, and based on the maximum and minimum values of the brightness on both sides of the sine wave shape change within the cycle range,
The head flying height h ₀ at the measurement point X _0, floating representing the difference between the flying height h ₁ corresponding to the scotoma and or bright points on either side of the cycle range, until the flying height h ₀ of the flying height h ₁ approximated calculated as the sum h ₀ = h ₁ + h ₂ and the amount h _2, where the determined as an integer multiple of utilizing the periodicity of the dark points and bright point the flying height h ₁ lambda / 4, and The flying height h ₂ is obtained as the phase of the sine waveform change within the m-th cycle range.

F action If the measurement point X ₀ is set at a point within the optical interference fringes generated by the irradiation light I ₁ of monochromatic light, and the flying height of the head section 4 at this measurement point X ₀ is gradually increased, The brightness value detected as the video data changes periodically. By approximating the change to a sinusoidal shape, the flying height corresponding to the measurement point X ₀ can be approximately calculated based on the maximum value R _max and the minimum value R _min of brightness according to the periodicity. . Thus, the head flying height h ₀ can be calculated with high accuracy, and the flying height h ₀ can be approximately calculated as the phase of the sine wave shape change, so that even the difference between the maximum value R _max and the minimum value R _min (that is, the contrast). Even if becomes smaller, the head flying height can be calculated without being affected by it.

G Embodiment One embodiment of the present invention will be described in detail below with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a flying head measuring device as a whole, and a head portion 4 is arranged so as to face a transparent disk 3 made of a glass material which is rotationally driven by a motor 2, and the head portion 4 is The root portion is fixed to the tip of an elastic member 6 fixed to the head support plate 5.

The head support plate 5 is fixed on a moving member 9 which moves forward and backward in a direction (X direction and Y direction) indicated by an arrow a on a stage 8 fixed to a fixed portion 7, and the moving member 9 is moved by a stage feed driver 10. When the drive output S1 advances or retreats in the direction of arrow a, the head portion 4 is positionally controlled at a predetermined position of the transparent disk 3 in response to this.

The motor 2 is rotationally driven by the drive output S2 of the rotation control circuit 11, and a pulse output having a pulse interval corresponding to the rotational speed of the transparent disk 3 is provided by a rotation sensor 12 provided in association with its output shaft. S3 is generated, which is converted by the tachometer 13 into a rotation speed detection output S4 having a DC level corresponding to the rotation speed and fed back to the rotation control circuit 11.

Thus, a servo system for the motor 2 is formed so that the transparent control disk 11 is rotated at a high speed at a speed corresponding to the speed reference signal S5 supplied from the central processing unit 15 having a microcomputer configuration.

The rotation speed detection output S4 is input to the central processing unit 15 as data representing the current rotation speed of the motor 2.

When the transparent disc 3 rotates at a high speed, the air flow in contact with the surface is entrained, so that the air flow between the head portion 4 and the surface of the transparent disc 3 is increased as shown in FIG.
AR is generated, and the head portion 4 is given a levitation force by the air flow AR, and thus the head portion 4 floats in the direction away from the transparent disk 3 against the pressing force of the elastic member 6.

The head portion 4 has a structure shown in FIG. 3 so that it can float above the air flow AR by a predetermined amount as needed.

That is, the head portion 4 has a slider 4A made of an opaque material having a concave vertical cross section, and a pair of slide surfaces 4L and 4R facing the surface of the transparent disk 3 are formed on the surface. The slide surfaces 4L and 4R extend in parallel in a direction along the air flow AR across the groove 4B, and the surfaces thereof are mirror-finished.

At the rear end of the slide surface 4L and / or 4R, the magnetic head 4C
Is installed. In the case of FIG. 3, the head portion 4 is formed by inserting a block including one magnetic head 4C into a groove 4D formed in the trailing edge of one slide surface 4R, and using a glue to slide the slider. It is glued to 4A.

The structure of the head portion 4 is called a monolithic structure. On the other hand, as shown by a broken line in FIG. 3, it is possible to form a so-called composite structure in which the magnetic head 4E is mounted on the slide surface 4L side.

At the tip of the slide surfaces 4L and 4R of the slider 4A, obliquely chamfered airflow inflow slopes 4M and 4N are formed.
The air flow AR flowing from the slopes 4M and 4N for inflow of this air flow
However, while pushing the airflow inflowing slopes 4M and 4N in a direction away from the magnetic disk 3, the airflow inflowing slopes 4M and 4N flow into between the slide surfaces 4L and 4R and the transparent disk 3.

Here, the slide surfaces 4L and 4R of the slider 4A are mirror-finished, whereas the inner surface of the groove 4B is not mirror-finished. Therefore, as shown in FIG. 2, when the irradiation light I ₁ is irradiated from above the transparent disk 3, a part of the light passing through the transparent disk 3 is reflected by the inner surface of the transparent disk 3. _The light reflected as ₂₂ and transmitted through the transparent disk 3 is reflected as reflected light I _{21 on} the surfaces of the slide surfaces 4L and 4R. Thus, the reflected light I ₂₁ and I
The synthetic reflected light R of ₂₂ produces optical interference fringes by the two-beam interference method.

Actually, the slider 4A is, as shown in FIG.
While the front end edge into which the magnetic field flows in rises relatively large, the gap between the rear end part on which the magnetic head 4C is mounted and the transparent disk 3 becomes narrow (for example, 0.2 to 0.3 [μ
m] to 0.5 [μm]). Thus, by actually increasing the recording level and the reproducing level on the magnetic disk as much as possible, the high density recording and the reproducing can be surely achieved.

The transparent disk 3 has a microscope 21 arranged above it.
Irradiation light I ₁ is emitted from (FIG. 1) through the objective lens 21A, and this irradiation light I ₁ can pass through the transparent disk 3 and reach the surface of the head portion 4.

On the other hand, of the light emitted from the light source 22 (FIG. 1), monochromatic light of a predetermined wavelength is filtered by the color filter 23, and then the half mirror 21 provided in the microscope 21.
Irradiation light I ₁ from the objective lens 21A to the transparent disk 3 via B ₁
And irradiate.

As a result, the combined reflected light R causing the two-beam interference is
It is incident on the television camera 24 (which is an image pickup means using a photoelectric conversion means such as CCD) through the objective lens 21A and the half mirror 21B and is converted into a raster video signal VD _IN . This raster video signal VD _IN is given to the monitor 30,
As shown in FIG. 4 (B), on the display screen DIS, together with the slide surfaces 4L and 4R of the slider 4A, the slide surfaces 4L and 4R.
The optical interference fringes generated above are displayed.

Further, the raster video signal VD _IN is given to the 1H cutout circuit 31. The 1H cutting circuit 31 extracts the video signal for one scanning line from the raster video signal VD _IN.
The 1H video signal VD _H is converted into a digital signal in the analog / digital conversion circuit 32 and taken into the central processing unit 15. As shown in FIG. 4 (B), this 1H video signal VD _H contains the video signal on one scanning line SCH on one of the slide surfaces 4L or 4R (for example, 4R) of the display screen DIS. Thus, the data on the position of the interference fringes and the interval of the interference fringes can be taken into the central processing unit 15 from the 1H video signal VD _H.

A display signal S7 for displaying the scan line SCH is provided from the 1H cutout circuit 31 to the monitor 30 on the display screen DIS of the monitor 30.

The central processing unit 15 transfers the data to the floppy disk,
The data is stored in an external storage device 35 such as a hard disk, read as needed and used as calculation data, and is printed out by a printer 36.

The central processing unit 15 uses the data on the lightness and darkness of the optical interference fringes to determine the slide surface 4L of the head unit 4L.
For each of the points 4 and 4R, the distance between the surface of the transparent disk 3 and the surface of the opposing transparent disk 3 (hence the flying height h) is obtained by calculation based on the following principle, and the evaluation processing is executed.

First, in FIG. 2, the combined reflected light R (that is, interference light) obtained by combining the reflected lights I ₂₁ and I ₂₂ is as follows. It is represented by. Where δ is the phase difference between the reflected lights I ₂₁ and I ₂₂ , It is represented by. Further, λ is the wavelength of the monochromatic light emitted (for example,
0.4 to 0.8 [μm]), I ₂₁ represents the amplitude of the reflected light I ₂₁ from the surface of the slider 4A, and I ₂₂ represents the amplitude of the reflected light I ₂₂ from the surface of the transparent disk 3.

Therefore, synthetic reflected light R when the wavelength λ of monochromatic light is fixed
The value of is the phase difference δ of the reflected lights I ₂₁ and I ₂₂ for each part of the slide surfaces 4L and 4R (FIG. 4 (B)) (hence the floating of the slide surfaces 4L and 4R from the surface of the transparent disk 3). Quantity h (4th
It has a brightness corresponding to that of FIG. Therefore, the value R _{0 of the} reflected light R is fixed by fixing an arbitrary coordinate position X ₀ of the coordinate position X in the extending direction of the slide surfaces 4L and 4R (for example, the coordinate position of the gear of the head 4C (this is called a head position)). And the flying height h ₀ corresponding to this value R ₀ is calculated by the equation (1) and (2)
Based on the formula, fixed position X ₀ (that is, head 4C
The flying height of the gear position) can be measured.

When the surfaces of the slide surfaces 4L and 4R are flat, the flying height h in equation (2) changes in proportion to the coordinate position X of the slide surfaces 4L and 4R. When the change in brightness is observed along the coordinate position X in the direction, the change in brightness of the combined reflected light R at each position of the slide surfaces 4L and 4R becomes a sine wave shape (Fig. 4 (A)). .

On the other hand, when the surface is not a flat surface but has some unevenness, the phase of the sine waveform changes so as to be partially shifted depending on the characteristics.

The brightness of the surfaces of the slide surfaces 4L and 4R is the darkest part DP (Fig. 4 (B)) (or the brightest part).
The difference between the flying heights h of the corresponding coordinate positions is
It represents λ / 2 for the wavelength λ of I ₁ .

By the way, in equations (1) and (2), the fixed position
Given the flying height h ₀ of the head portion 4 and the variable h for X _0,
As shown in FIG. 5, if the flying height h at the fixed position X ₀ increases, the brightness at the fixed position can be expressed as a graph that periodically changes in a sinusoidal shape. Therefore, in order to know the flying height h ₀ of the head portion 4 at the fixed position X ₀ to be measured, it is determined whether the flying height h ₀ falls within the cycle range of the change in brightness. Further, the phase within the determined cycle range may be measured.

Practically, the information that can be used for the calculation in the central processing unit 15 is the maximum value R _max and the minimum value R _min of the combined reflected light R, and the head flying height h ₀ corresponding to the brightness R ₀ at the fixed position X ₀ is calculated. , The maximum value R _max and the minimum value R _min can be used as follows.

That is, in FIG. 5, the combined reflected light R has the maximum value R _max.
Is the phase difference δ of the reflected lights I ₂₁ and I _{22 according to} the equation (1).
Is 0, 2π, 4π, etc. (the point on the graph where the combined reflected light R is brightest in this way is hereinafter referred to as the bright point), and the flying height h _{max at} this time is λ / 4, 3λ / 4, 5λ / 4 ...
…become.

Further, the synthetic reflected light R becomes the minimum value R _{min because} the phase difference δ between the reflected lights I ₂₁ and I ₂₂ is π, 3π,
5π ... (The point on the graph where the combined reflected light R is darkest is referred to as a dark point hereinafter), and the flying height h _{min at} this time is 0, λ / 2, λ, 3λ / 2. ……become.

Therefore, dark points and bright points appear alternately and periodically at λ / 4 intervals in FIG. In order to obtain the flying height h ₀ at an arbitrary brightness R ₀ using this relationship, the order m (m = m =
0, 1, 2 ...), and the order m to which the flying height h ₀ belongs
And the flying height h ₁ (that is, h _max or h _min ) corresponding to the dark and / or bright points on both sides of the cycle range,
If the sum of the flying height h ₁ and the flying height h ₂ that represents the difference from the flying height h ₀ , that is, h ₀ = h ₁ + h ₂ (3) is obtained, a relatively simple calculation is performed. Therefore, the flying height h ₀ can be obtained.

Here, the flying height h ₁ can be easily obtained as a value that is an integral multiple of λ / 4 by utilizing the periodicity of dark points and bright points,
Also, the flying height h ₂ is (1) for the m-th cycle range.
It can be obtained by executing an operation for solving the term of cos δ included in the equation and the equation (2) for h.

The _{first method} for calculating the flying height h ₂ that is the non-periodic component is based on the bright point (that is, the flying height h _max = λ / 4, 3λ / 4, 5λ / 4 ...). And a second method for obtaining a dark point (that is, a point of flying height h _min = 0, λ / 2, λ, 3λ / 2 ...) As a reference, and a dark point and a bright point are alternately used as reference points. (Ie (h _max , h _min ) = 0, λ / 4, λ / 2, 3
The third method or the like can be applied in which the points of λ / 4 ...

In the case of this embodiment, using the first method, the head flying height h ₀ is calculated based on the flying height h _{max of the} bright point as follows: Approximate calculation is performed according to. here, Becomes

In the case of the embodiment shown in FIG. 1, the order m of the cycle range including the flying height h ₀ is determined by replacing the filter of the color filter 23. That is, prior to the measurement of the levitated state, the central processing unit 14 gives a filter replacement command S10 to the color filter driver 43, and the output S11 replaces the two color filters 23 so that the irradiation light I ₁ has a wavelength λ ₁ Or by changing to monochromatic light of λ ₂ , the flying height h _max of each monochromatic light
And the change of h _min determines the order m.

Thus, in equation (4), the values R ₀ , R _min , R _max , m,
Since the wavelength λ of the irradiation light I ₁ is all known, the brightness between the maximum value R _max and the minimum value R _min adjacent to each other is calculated by this equation.
The flying height h ₀ corresponding to R ₀ can be approximately calculated.

The central processing unit 15 can store the calculation result in the external storage device 35 as needed.

On the other hand, the monitor 30 gives the image processing circuit 44 a planar video signal PIC representing the video displayed on the display screen DIS. The image processing circuit 44 has a frame memory, and the monitor 30
The planar video signal PIC of is converted into digital data and written in the frame memory. The data DPIC written in the frame memory is transferred to the central processing unit 15 in response to a read command from the central processing unit 15, and stored in the external storage device 35 as needed.

In the above-described structure, the head portion 4 whose floating mode is to be determined is mounted so as to face the transparent disk 3, and the microscope 21 emits the irradiation light I ₁ so as to pass through the transparent disk 3. The data relating to the levitation of the head section 4 is fetched into the central processing unit 15 via the image processing circuit 44 as image data of its optical interference fringes on the basis of the combined reflected light R, and after being processed, it is stored in the external storage device. Stored in 35. Thus, the central processing unit 15 can obtain the floating mode of the head part 4 from the slide surfaces 4L and 4R for 1H.
The flying mode of the head portion 4 can be comprehensively determined based on the planar floating information for one minute or one frame.

That is, the central processing unit 15 reads out the video data representing the optical interference fringes for 1H fetched from the 1H clipping circuit 31 for the pixels along the scanning line SCH (FIG. 4 (B)), and if necessary, , The flying height h ₀ for one measurement point X ₀ on the slide surfaces 4L and 4R can be calculated to evaluate the flying height of the head section 4.

Further, the central processing unit 15 reads out the video data representing the planar optical interference fringes fetched from the image processing circuit 44 for each of the pixels along the scanning lines SCH1, SCH2 ... slide surface 4L of the flying height h ₀ of the measurement points X ₀ by calculating head unit 4 may assess floating manner for the entire 4R.

In the ideal case where the maximum value R _max and the minimum value R _min of the brightness of the combined reflected light R are constant, the flying height h ₀ corresponding to the measurement point X ₀ can be obtained as described above. . On the other hand, actually, as shown by the chain lines K1 and K2 in FIG. 7, the difference between the maximum value R _max and the minimum value R _min tends to decrease as the head flying height h increases.

The reason why this phenomenon occurs is, firstly, as in the case where a halogen lamp is used as the light source 22, for example, a point light source cannot be actually obtained, so that the irradiation light I ₁ irradiating the disk 3 and the head portion 4 is Unavoidably spread to
Therefore, when the flying height h increases, the difference between the maximum value R _max and the minimum value R _min , that is, the contrast decreases.

The second reason is that the monochromatic light that can be obtained by the color filter 23 cannot practically ideally obtain the irradiation light I ₁ having a single wavelength, and therefore the synthetic reflected light R causes interference. When this occurs, the result is that the contrast is deteriorated.

As described above, it is practically difficult for the combined reflected light R to obtain the ideal characteristic curve Q1 shown by the solid line in FIG. 7, and as the head flying height h increases as shown by the broken line in FIG. A characteristic curve Q2 that weakens the contrast will be drawn.

Therefore, the central processing unit 15 needs to calculate the head flying height corresponding to the intersection of the brightness R ₀ and the characteristic curve Q2 when calculating the head flying height h ₀ .

With respect to this point, the central processing unit 15 uses the maximum value R _max and the minimum value R _min at both end positions of the cycle range to which the brightness R ₀ corresponding to the measurement point X ₀ belongs, as described above, to obtain the head flying height. Since the approximate calculation of h ₀ is performed, even if the contrast deteriorates according to the head flying height h ₀ , the influence can be effectively avoided.

As described above, according to the embodiment of FIG. 1, the head flying height h ₀ corresponding to the measurement point X ₀ in the optical interference fringe includes the brightness of the combined reflected light R at the measurement point X ₀ . By performing an approximate calculation based on the maximum value R _max and the minimum value R _min of the brightness on both sides of the cycle range, the combined reflected light R
Even if the contrast of the head deteriorates, it is possible to obtain a calculation result that effectively avoids the effect, and as a result, it is possible to measure the head flying height with high accuracy.

According to the experiment, the accuracy of the flying height measurement result is 0.01
It was possible to obtain a measurement result of about [μm] (it was about 0.05 [μm] in the conventional case).

In the above description, the head portion 4 is opposed to the transparent disk 3 to generate the optical interference fringes. Instead, the head portion 4 made of a transparent material is opposed to the opaque disk 3. Even when the optical interference fringes are generated by doing so, the same effect as the above case can be obtained.

Further, in the above description, the slider 4A having the configuration having the two slide surfaces 4L and 4R is used, but the same effect as the above case can be obtained even if the number and the shape thereof are changed as necessary. You can

According to the present invention as described above the effect of the H invention, per calculates the head flying height h ₀ at the measurement point X _0, brightness R varies cyclically when head flying height measurement point X ₀ is changed By utilizing this, the cycle range to which the brightness of the measurement point X ₀ belongs is determined, and the head flying height is approximately calculated based on the maximum value R _max and the minimum value R _min on both sides of this cycle range. As a result, the head flying height can be measured with higher accuracy compared to the case where the wavelength is measured by color interference fringes as in the conventional case, and the flying height is approximated as the phase of the sine waveform change. As a result, even if the difference (that is, the contrast) between the maximum value R _max and the minimum value R _min becomes small, the head flying height can be measured without being affected by the difference.

[Brief description of drawings]

FIG. 1 is a block diagram showing a head flying height measuring apparatus for carrying out an embodiment of the head flying height measuring method according to the present invention, and FIG. 2 is an explanation of the flying principle of the head portion 4 and the generation of optical interference fringes. 3 is a schematic perspective view showing the detailed structure of the head portion 4, and FIG. 4 is a schematic line used for explaining optical interference fringes generated on the slide surfaces 4L and 4R of the head portion 4. 5 and 5 are characteristic curve diagrams showing the relationship between the head flying height and optical interference fringes, FIG. 6 is a schematic diagram used to explain planar image data, and FIG. 7 is a diagram when measurement data fluctuates. FIG. 6 is a characteristic curve diagram for explaining a correction operation. 1 ... Head flying height measuring device, 2 ... Motor, 3 ... Transparent disk, 4 ... Head part, 5 ... Head support plate, 6
...... Elastic member, 15 ...... Central processing unit, 21 ...... Microscope, 22 ...... Light source, 23 ...... Color filter, 24 ...... Television camera, 30 ...... Monitor, 31 ...... 1H cut-off circuit, 32 ......
Analog / digital conversion circuit, 35 ... External storage device,
36 ... Printer, 44 ... Image processing circuit.

Claims (1)

[Claims] 1. Floating of the head portion by optical interference fringes generated between a rotating disc and a head portion arranged so as to levitate by utilizing an air flow generated on the surface of the disc. In the head flying height measuring method for measuring the amount, the optical interference fringes are generated by irradiating the disk and the head portion with irradiation light of monochromatic light, and the optical interference fringes are set at points within the optical interference fringes. Video data representing the brightness of the optical interference fringes is obtained at the measurement point, and the brightness represented by the video data changes periodically when the flying height of the head portion at the measurement point is increased. By taking advantage of the fact, the change is approximated as a sine wave shape, and the order m (m = 0, 1, 2, ...) Is assigned to the cycle range between the dark point and the bright point that appear periodically,
Specify the order m to which the flying height h _{0 at the} above measurement point belongs,
Based on the maximum and minimum values of brightness on both sides of the sine wave shape change in the cycle range, the head flying height h ₀ at the measurement point is set to a dark point and / or a bright point on both sides of the cycle range. the flying height h ₁ corresponding to this flying height h ₁
To the flying height h _0, which is the sum of the flying height h ₂ and h ₀ = h ₁ + h ₂ , and approximates the flying height h ₁ using the periodicity of the dark point and the bright point.
A head flying height measuring method, characterized in that the flying height h ₂ is obtained as an integer multiple of / 4, and the flying height h ₂ is obtained as the phase of the sinusoidal waveform change within the m-th cycle range.