JPS61214285A - Formation of servo pattern - Google Patents

Abstract

PURPOSE:To form first and second servo patterns and third and fourth servo patterns, respectively and position a head correctly by moving the head in a + direction and in a - direction by an odd number and an even number tracks by half the width of the track. CONSTITUTION:Disks 20, 21 are set, and in opposite thereto, a magnetic head 12 is disposed. The head 12 is moved to a prescribed track by moving and controlling a carriage 51 by a mu CPU59. A position of the head 12 is measured by a laser length measuring device 52 and a mirror 50 attached to the carriage 51. In the track of an even number of the servo area (including 0), a head 12-1 is moved in the + direction and the - direction by almost half the width of the track to form servo patterns 13, 14. In the track of the odd number, a head 12-2 is moved in the + direction and in the - direction by almost the half the width of the track to form servo patterns 15, 16. In this manner, a correct positioning of the magnetic head can be carried out.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a servo pattern forming method in an index servo system of a magnetic disk device.

[Technical background of the invention and its problems]

In the open-loop magnetic head positioning method using a stepper motor, if the track density is increased, large off-tracks occur due to expansion and contraction of the disk due to temperature and humidity and errors in the positioning mechanism, making it impossible to write/write data accurately. There's a problem.

Therefore, an index servo system has been proposed as a relatively simple magnetic head positioning system that solves these problems. In this servo method, a simple servo pattern is embedded in the index area of the disk, and when reading/writing data, the servo signal from this servo pattern is used to determine the off-track amount of the magnetic head. In addition, the phase current of the stepper Tanabata is changed to correct the position of the magnetic head so that it can be accurately on-track.

Conventionally, this servo pattern has been formed using a magnetic head of a dedicated servo writing device called a servo writer, which is separate from the magnetic head of the magnetic disk device. However, for example, in the index servo method, which requires forming servo pattern tracks in accordance with the stepper motor, it is necessary to align the origin of the magnetic disk device (the beginning of writing the servo pattern) and to perform servo writing in accordance with the movement of the stepper motor. It must be made.

In other words, servo writing takes a lot of time, the servo writer is loaded into the magnetic disk device, so the shape of the magnetic disk device needs to be specially designed, and the head must be loaded into a narrow space between disks. There are many problems with forming servo patterns using a servo writer, such as the need for a special loading mechanism.

Therefore, there has been an attempt to solve the above problem by using a method (% 1982-121182) of forming a servo pattern using only the magnetic head of a magnetic disk drive, as shown in FIG. 1X9. This method is equipped with means for switching modes between 1-phase excitation and 2-phase excitation, writes servo patterns using 1-phase excitation, and reads/writes data.
It is characterized by writing using two-phase excitation. However, although this method can solve the above problems, 1
, it cannot be used for read/write using two-phase excitation, and it only worsens the seek time.

Furthermore, the part shown at (90) in the figure is the track pitch.

The servo patterns (91') and (92) change each time as the track width changes.In other words, when these servo patterns (91') and (92) are read out with the magnetic head (93), the readout IJ near area (of the magnetic head) used for position control changes. There are various servo pattern forming methods described above for accurate magnetic head positioning without using a dedicated servo writing device called a servo writer. Many problems still remain.

[Purpose of the invention]

This invention was made in view of the above-mentioned problems, and its purpose is to use only the magnetic head of a magnetic disk device to accurately position the magnetic head, without using a dedicated servo writing device called a servo writer. The present invention provides a method for forming a servo pattern for

[Summary of the invention]

The present invention uses a servo pattern formed embedded in a predetermined area provided on a disk plate in a servo pattern forming method of an index servo method for controlling the position of a head. The head is moved approximately half the track width in the + direction and the one direction to form first and second servo patterns, and the difference signal when reading the first and second servo patterns causes the head to The position can be corrected, and in odd-numbered tracks, the head is moved approximately half the track width in the ten directions and in the one direction to form third and fourth servo patterns, and the third and fourth servo patterns The position of the head can be corrected based on the difference signal when the head is read.

〔Effect of the invention〕

Therefore, according to the servo pattern forming method of the present invention, a servo pattern can be formed using the head of a magnetic disk device, so there is no need for a dedicated head or loading mechanism for servo writing, and there is no need to perform servo writing in accordance with a stepper motor. Otherwise, there is no need to align the origin.

In addition, by forming the first and second servo patterns on even-numbered tracks (including O) and the third and fourth servo patterns on odd-numbered tracks, position signals necessary for head position control can be generated. There is no non-linearity in the signal obtained when reading the servo pattern, which means that the head can be accurately moved to the desired position, which is extremely effective in practice. This will be explained in detail with reference to.

FIG. 2 is a diagram schematically showing the positional relationship between the servo sector area (11) on the disk and the data area circle in the index servo method.The servo pattern is written in the servo sector area α1, and the present invention is applied to the servo sector area OI. This clarifies the method of forming the servo pattern to be written, and this servo pattern is written by the head of the magnetic disk device.

Figure 3 is a schematic configuration diagram of a magnetic disk device for writing servo patterns.As shown in the figure, two Q disks (21Q1) are set, and magnetic Head α is arranged. For this magnetic head αa, the microprocessor μCPU (59) instructs the stepper motor control circuit (b) to move a predetermined track via the I10 board (58), and the stepper motor (to) rotates with one-phase or two-phase current balance. By moving the carriage 61) to which the magnetic head is attached, it moves to this predetermined track.Also, when the microprocessor μCPU 51 commands a certain amount of movement, the stepper motor 63 moves between the 1st phase and 2nd phase. The current lance is broken and the carriage f51 is moved by the amount of movement. Each time, the position of the magnetic head α is determined by the mirror 5G attached to the laser sub-length device 53 and the carriage 51).
This measurement data is sent as a position feedback amount to the stepper motor control circuit via the I10 port (to) and the microprocessor μCPUt51, and is used to accurately move the magnetic head (13) to a predetermined position. It is used for.

The signal is supplied to the top pattern generation circuit 6η, which operates the read/write amplifier (to), and is performed by the magnetic head (13).The read/write amplifier (to) is also operated according to the writing, and the servo decoder (to) performs this processing each time. The information is decoded by the microprocessor μCP via the I10 board.
0 input to U'S FIG. 1 is a diagram showing an example of a servo pattern formed by the above-described mechanism. There is a servo area (11) between the data areas 1υ, and in this servo area α, there is a servo pattern forming method 9 formed by the magnetic head α of the magnetic disk device, as described later.

The method of forming a servo sector area according to the present invention will be described below with reference to FIGS. 4 to 6.

The upper part in the figure is defined as the child direction, and the lower part is defined as one direction.

First, in Fig. 4, servo patterns a3 and I on track O
is written as follows. The microprocessor μC
When the PU commands track O, the magnetic head is positioned at the center of track O, that is, at position (12-1). Next, the magnetic head is moved approximately in the direction of half the track width to the position (3-1). To measure this track width, set the magnetic head (12-1) in advance.
), write an appropriate magnetization pattern, read this magnetization pattern while moving the magnetic head in the child direction, and move the magnetic head in one direction, so that the output signal is 1/2 in the child direction and 1/2 in the one direction.
The distance until it becomes! ! 1 (movement amount) is measured using a laser length measuring device. This distance (amount of movement) is the track width. At this position, the servo area is first DC erased to align the magnetization direction to the right on the paper. When the magnetic head returns to the servo area as the disk rotates again, the magnetic head returns to RZ.

The servo pattern (13) at position A is written in the servo pattern (Zero) format.The magnetization direction of this written servo pattern (13) is to the left on the paper.As is well known, the above-mentioned RZ format starts from the O level ( This is a writing format using an information signal (or falling).

Next, move the magnetic head in one direction by about half the track width to position (3-2), DC erase the servo area in the same way, and then move the magnetic head again to the DC erased servo area. When it arrives, write servo pattern I at position B.

In Figure 5, for tracks 1 and above, track O (
It's a little different from the track where I started writing the servo pattern. When the microprocessor μCPU commands track 1, the position of the magnetic head becomes the center of track 1 at (12-2). When the servo information is read through the servo decoder in this state, the written servo pattern I
A part of the data is read out. Move the magnetic head in one direction to the position (3-3) where the read output signal is no longer obtained, and in this state DC erase the servo area. Next, move the magnetic head to the position (3-4) ((12 When the magnetic head comes to the servo area again, the servo pattern (I5 is written in R, Z format) at position C.

Since this writing is in the R, Z format as described above, it has no effect on the servo pattern α that has already been written.

Furthermore, move the magnetic head to position (3-5) (position approximately half the track width in one direction from position (12-2))
Move to DC erase the servo area. Then, when the magnetic head comes to this servo area again, the servo pattern αυ at position D is written in R, Z format.

In FIG. 6, for track 2, by repeating the same operation as for track 1, the magnetic head is moved to (3-7).
At the position (3-8), the servo pattern η is written, and at the position (3-8), the servo pattern α is written.

By repeating the same steps, servo patterns for the necessary tracks can be formed.

Figure 7 shows the signal waveform obtained from the formed servo pattern, (a) is track 01, (b) is track 1, (C)
are the respective signal waveforms of track 2. It is determined whether the magnetic head is in the correct position when it indicates an on-track state. In this case, even numbered tracks (including 0)
Then, when the difference between the peak value of the signal at position A and the peak value of the signal at position B is O, and on odd-numbered tracks, when the difference between the peak value of the signal at position C and the peak value of the signal at position D is O. It is.

As described above, by forming a magnetization pattern (servo pattern) corresponding to the track width over four phases using the magnetic head of the magnetic disk device according to the method of the present invention, the servo head of the servo writing specialized device is not used.

Therefore, a servo pattern can be formed without requiring a mechanism for loading a servo head between disks, and without requiring any processing on the frame of the magnetic disk device.

Moreover, the readout signal of this servo pattern used for positioning the magnetic head does not change, and is always read out as a +J near region, allowing accurate movement to a predetermined position.

[Other embodiments of the invention]

Note that this invention is not limited to the above embodiments. The shape of the servo pattern is the erase part (the part that detects the beginning of each sector) for detecting the servo area, and the AGC part (
A pattern for an AGC signal used for signal level adjustment between tracks and between sectors may also be included.

Furthermore, the servo patterns are not limited to one dibit pattern each, but can be written in multiple patterns as shown in Fig. 10 (for example, two such as (100) and (110) in Fig. 6) to obtain the average value of each. By taking the difference, the error due to signal fluctuation can be reduced and the single position accuracy can be made even more accurate.

An example of a schematic partial configuration diagram of a magnetic disk device was previously shown in FIG. 3, but a mechanism that does not use a laser length measuring device and a mirror as shown in FIG. 8 may also be used. In this case, the position measurement, which was previously performed using a laser length measuring device and a mirror, is performed by determining the relationship between the movement position due to the rotation of the stepper motor and the current ratio. This brings about effects such as reducing the cost of the magnetic disk device.

In addition, various changes and modifications can be made without departing from the gist of the present invention.

[Brief explanation of drawings]

FIG. 1 is a diagram showing servo pattern formation according to an embodiment of the present invention, FIG. 2 is a view of a disk plate viewed from above, FIG. 3 is a partial schematic diagram of a magnetic disk, and FIGS. 4 to 6 7 is a diagram showing a method for forming a servo pattern according to an embodiment of the present invention, FIG. 7 is a diagram showing pulses obtained by reading the servo pattern of the present invention, and FIG. 8 is a diagram illustrating another embodiment of a magnetic disk. FIG. 9 is a diagram showing conventional servo pattern formation, and FIG. 10 is a diagram showing servo pattern formation according to another embodiment of the present invention. 10... Servo area, 11... Data area, 12.
...Head, 13-19...Servo pattern, addition...
・Disk plate, blade...mirror, 55...read/write amplifier 0 Figure 1 Figure 2 Figure n Figure 4 Figure 5
Figure 6, Figure 7, Figure 9, Figure 10 Procedural amendment (self-motivated) 1986-6.1 night Japan Patent Office Commissioner's Palace 1, case display patent application 1988-54322 No. 2, Name of the invention Servo pattern forming method and its disk plate 3, Relationship with the amended case Patent applicant (307) Toshiba Corporation 4, Agent Address: 1-1 Shibaura-chome, Minato-ku, Tokyo 105 Japan 7. Contents of the amendment The method and its disc plate shall be amended. (2) The entire specification shall be corrected as shown in the attached sheet. Amended Description 1, Title of Invention Servo pattern forming method and its disk plate 2, Claims (1) Servo pattern formation for positioning a head using a servo pattern embedded in a servo area on a disk plate In the method, in the even-numbered (including 0) servo track of the servo area, the head is moved 100,000 times in one direction and approximately half the track width to generate servo tracks each consisting of first and second position information. A pattern is formed, and in odd-numbered tracks, the head is moved approximately half the track width in the + direction and in the one direction to form servo patterns formed from the third and fourth position information, respectively. Servo pattern formation method. (2) The servo pattern forming method according to claim 1, wherein the gl and fourth servo patterns are dibit patterns. (3) The servo pattern forming method according to claim M1 or claim 2, wherein each of the first to fourth servo patterns consists of a plurality of dibit patterns. (4) A plurality of data tracks for recording data are provided approximately half a track apart from the data track in which the servo pattern is embedded so that the head can position the head on each data track in the data area. What is claimed is: 1. A disk plate formed with a servo track and a servo pattern for positioning a head, characterized in that a servo pattern is formed. 3. Detailed Description of the Invention [Technical Field of the Invention] - The present invention relates to a servo pattern forming method for positioning a head and a disk plate thereof. [Technical background of the invention and its problems] In an open-loose magnetic head positioning method using a stepper motor, when the track density is increased,
Due to expansion and contraction of the disk due to temperature and humidity and errors in the positioning mechanism, a large off-track occurs, making it impossible to read/write accurate data. Therefore, an index tab system has been proposed as a relatively simple magnetic head positioning system that solves these problems. In this servo method, a simple servo pattern is embedded in the index area of the disk, and when reading/writing data, the servo signal from this servo pattern is used to determine the off-track amount of the magnetic head. The phase current of the stepper motor is changed to correct the position of the magnetic head so that it can be accurately on-track. Conventionally, this servo pattern has been formed using a magnetic head of a dedicated servo writing device called a servo writer, which is separate from the magnetic head of the magnetic disk device. However, for example, servo writing must be performed in accordance with the positioning of the origin (servo pattern writing IM) of the stepper motor disk device and the movement of the stepper motor. However, since servo writing takes a lot of time, and because the servo writer is loaded into the magnetic disk drive, the shape of the magnetic disk drive needs to be special, and the head cannot be loaded into a narrow space between disks. There are a number of problems with forming servo patterns using a servo writer, such as the need for a special loading mechanism. Therefore, for example, as shown in FIG. 9, there is a method (
There was an attempt to solve the above problem using Japanese Patent Laid-Open No. 58-121182. This method is characterized by providing means for mode switching between l-phase excitation and two-phase excitation, writing servo patterns by one-phase excitation, and reading/writing data by two-phase excitation. However, although this method can solve the above problems, ■
It cannot be used for read/write using two-phase excitation, and it only worsens the seek time. Furthermore, the part indicated by ■ in the figure changes each time according to changes in track pitch and track width, and when this servo pattern (9υ, 嬶) is read out with a magnetic head, it is used for position control. The servo pattern for accurate positioning of the magnetic head without using a dedicated servo writing device called a servo writer, such as changing the read linear area (area used to determine whether or not the magnetic head is used), is However, many of the above-mentioned problems still remain. [Objective of the Invention] This invention was made in view of the above-mentioned problems, and its purpose is to solve the problem without using a dedicated servo writing device called a servo writer. The present invention provides a method for forming a servo pattern and a disk plate thereof, which enables accurate positioning of the head from a servo pattern formed using the head of a disk device. , a servo pattern that is not embedded is used to position the head, and in the even numbered (including O) servo track, the head of the disk device is moved in the + direction and in the one direction by about half the track width. , each form a servo pattern consisting of first and second position information, and the position of the head can be corrected by the difference signal when reading the first and second servo patterns. Similarly to the above, the head of the disk device is moved approximately half the track width in the + direction and the one direction to form a servo pattern consisting of third and fourth position information, and the third and fourth servo patterns are read. Accordingly, the servo pattern of the present invention can be formed using the head of a magnetic disk device, so that the position of the head can be corrected by using a difference signal when the servo pattern is There is no need for a dedicated writing head or load mechanism, there is no need for servo writing in accordance with the stepper motor, and there is no need for origin alignment. Also, the first and second By forming the third and g4 servo patterns on odd-numbered tracks, nonlinearity does not occur in the position signal (signal obtained when reading the servo pattern) necessary for head position control, and This has extremely great practical effects, such as being able to move the head accurately to a desired position. [Embodiment of the Invention] An embodiment of the present invention will be described in detail with reference to the drawings. FIG. 2 is a diagram schematically showing the positional relationship between the servo area and the data area αυ on the disk in the Intex servo system. The servo pattern is written in the servo area H. This invention clarifies the servo pattern to be written in this servo area aω, and this servo pattern is written by the head of the magnetic disk device. FIG. 3 is a schematic diagram of a magnetic disk device for writing servo patterns. As shown in the figure, for example, two disks (19 (21)) are set, and a magnetic head α2 is arranged opposite to them.
The stepper motor □□□ rotates with l-phase or 2-phase current balance, and the magnetic head αa
The carriage 6υ on which is attached moves to this predetermined track. Also, Mike a7'o Sera? When a certain amount of movement is commanded from the pressure 69, the stepper motor hammer breaks the current balance between phase 1 and phase 2, and the carriage moves by that amount of movement (f51).
move. Each time, the position of the magnetic head cIz is measured by a laser length measuring device 52 and a mirror ω attached to a carriage 51), and this measurement data is used as a feedback amount of the position I 10 Ho )(
The signal is sent to the stepper motor control circuit (incorporated) via the microprocessor μCPU (support) and the microprocessor μCPU, and is used to accurately move the magnetic head α2 to a predetermined position. Writing of servo patterns, etc. is performed using the microprocessor μ.
Commands from the CPU t5■ are supplied to the servo pattern generation circuit 67) via the I10 board (g), and the read/
The write amplifier (to) is activated and the magnetic head α2 performs the write operation. Also, read/write amplifier (
), this information is decoded each time by the servo decoder and sent to the microprocessor μ via the I10 boat.
It is input to the CPU 69. FIG. 1 is a diagram showing an example of a servo pattern formed by the above-mentioned mechanism on a disk plate. A data area αυ consisting of a plurality of data tracks for recording data, and a servo area consisting of a plurality of servo tacks provided approximately half a track width apart from the data tracks of this data area aυ. In this servo area CLI, there is a servo pattern α formed by the magnetic disk device head α as described later:
Servo patterns are formed on the servo tracks at the top and bottom of the drawing as shown in 1-(19). For example, servo patterns (13 and α) are provided with one line sandwiched between them. The servo pattern forming method of the present invention will be explained below with reference to FIGS. In Figure 4, the servo pattern (13 and α4) on track O is written as follows. When the microprocessor μCPU commands track 0, the magnetic head is positioned at the center of track O. In other words, (12- This is the position of 1).Next, move the magnetic head to (
3-1) in the direction of approximately half the track width. To measure this track width, write an appropriate magnetization pattern in advance with the magnetic head at position (12-1), read this magnetization pattern while moving the magnetic head in one direction, and the output signal is 1
72. Measure the distance (amount of movement) until it becomes 1/2 in one direction with a laser length measuring device. This distance (amount of movement) is the track width. At this position, the servo area is first DC erased to align the magnetization direction to the right on the paper. Then, when the magnetic head comes to the servo area again due to the rotation of the disk, the magnetic head returns to RZ (Return to
Write servo pattern 0 at position A in (Zero) format. The magnetization direction of this written servo pattern 0 is to the left on the paper. As is well known, the above-mentioned RZ format is
This is a writing format using an information signal that rises (or falls) from 0 level. Next, move the magnetic head in one direction by about half the track width to position (3-2), perform T)C erasing on the servo area in the same way, and then move the magnetic head again to this DC erased servo area. When it arrives, write servo pattern α4 at position B. In FIG. 5, for tracks 1 and above, track O(
It's a little different from the track where I started writing the servo pattern. When the microprocessor μCPU commands track 1, the position of the magnetic head becomes the center of track 1 (12-2). When the servo information is read through the servo decoder in this state, the written servo pattern a
Part of 4 is read out. The magnetic head is moved in one direction to a position (3-3) where the read output signal is no longer obtained, and in this state, the servo area is DC erased. Next, move the magnetic head to position (3-4) (a position moved roughly in the direction of half the track width from position (12-2)), and when the magnetic head comes to the servo area again, move to position C. Write servo pattern a9 in RZ format. As described above, this writing has no effect on the already written servo pattern a4 because of the RZ format. Furthermore, move the magnetic head to position (3-5) (position approximately half the track width in one direction from position (12-2))
Move to DC erase the servo area. Then, when the magnetic head comes to this servo area again, the servo pattern αe at position D is written in the RZ format. In FIG. 6, for track 2, repeating the same operation as for track 1 causes the magnetic head to move to (3-7).
At the position, the servo pattern αη is written, and at the position (3-8), the servo pattern (181) is written. By repeating the same process, servo patterns for the required tracks can be formed. fa7 The figure shows the signal waveform obtained from the formed servo pattern, (a) is track 0, (b) is track 11 (c
) are the respective signal waveforms of track 2. Determination of whether the magnetic head is accurately located at a predetermined position, that is, the on-track state can be determined as follows. When the difference between the peak value of the signal at position A and the peak value of the signal at position B is 0 on even-numbered tracks (including 0), the difference between the peak value of the signal at position C and the peak value of the signal at position D on odd-numbered tracks is 0. When off-track, where the difference between As mentioned above, in the magnetic disk device of the present invention. By forming a magnetization pattern (servo pattern) corresponding to the track width over four phases using the magnetic head of the device, there is no need for a servo head of a device dedicated to servo writing. Therefore, a servo pattern can be formed without requiring a mechanism for loading a servo head between disks, and without requiring any processing on the frame of the magnetic disk device. Moreover, the readout signal of this servo pattern used for positioning the magnetic head does not change, and is always read out as a linear area, allowing accurate movement to a predetermined position. [Other Examples of the Invention] Note that the present invention is not limited to the above embodiments. The servo pattern is formed using the erase part for detecting the servo area (the part that detects the beginning of the servo area) and the AGC.
(a pattern for an AGC signal used as a signal when performing inter-track signal level adjustment). Also, the servo pattern is not limited to one Guibit pattern, but by writing multiple servo patterns (for example, two such as (100) and (110) in the figure) as shown in Figure 1O, the average value of each servo pattern can be calculated. By taking the difference, errors due to signal fluctuation can be reduced, and the position accuracy will be even more accurate. An example of a schematic partial configuration diagram of a magnetic disk device was previously shown in FIG. 3, but a mechanism that does not use a laser length measuring device and a mirror as shown in FIG. 8 may also be used. In this case, the position measurement, which was previously performed using a laser length measuring device and a mirror, is performed by determining the relationship between the movement position due to the rotation of the stepper motor and the current ratio. This brings about effects such as reducing the cost of the magnetic disk device. In addition, in the above embodiment, the index servo side and the other 1
Various changes and modifications can be made without departing from the spirit of the invention. 4. Brief description of the drawings Fig. 1 is a diagram showing servo pattern formation according to an embodiment of the present invention, Fig. 2 is a view of a disk plate viewed from above, and Fig. 3 is a partial schematic diagram of a magnetic disk. , Figures 4 to 6 are diagrams showing a method of forming a servo pattern according to an embodiment of the present invention. Figure 7 is a diagram showing pulses obtained by reading the servo pattern of the present invention, and Figure 8 is a diagram showing a method of forming a servo pattern according to an embodiment of the present invention. FIG. 9 is a diagram showing a conventional servo pattern formation, and FIG. 1O is a diagram showing a servo pattern formation according to another embodiment of the present invention. 10... Servo area, 11... Data area, 12.
...Head, 13-19...Servo pattern. 20...Disk board, 50...Mirror 55...Read/write amplifier.

Claims (3)

[Claims] (1) In an index servo type servo pattern forming method that uses a servo pattern embedded in a predetermined area provided on a disk plate to control the position of the head, the servo pattern is recorded by the head of a disk device. At the same time, in the even-numbered tracks (including 0), the head is moved approximately half the track width in the ten directions and in the one direction to form the first and second servo patterns, and in the odd-numbered tracks, A servo pattern forming method characterized in that the head is moved approximately half the track width in the ten directions and in the one direction on the corresponding track to form third and fourth servo patterns. (2) The servo pattern forming method according to claim 1, wherein the first to fourth servo patterns are dibit patterns. (3) Claim 1 or 2, characterized in that each of the first to fourth servo patterns consists of a plurality of patterns.
The servo pattern forming method described in section.