JPH09293342A - Magnetic disk device, position sensing method used for the device and servo-pattern writing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a servo-pattern, from which a position error signal having high accuracy is obtained at an arbitrary place, in a magnetic disk device using an MR head. SOLUTION: A data servo-pattern is constituted so as to be shown in the Fig.1, width in the radial direction of four servo-bursts A2, B3, C4, D5 is set in two third of data track pitches, and each servo-burst A2, B3, C4, D5 is arranged while being displaced by every one third of the data track pitches in the radial direction. A dead band by positional error signals (A-B), (C-D) as the differential signals of the output amplitude of each servo-burst A2, B3, C4, D5 is removed and a magnetic disk device can be used in a continuous linear region by changing over the positional error signals in response to the place of a head.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a sector servo technique for a magnetic disk device, and more particularly to a sector servo technique for a magnetic disk device using a composite head of a thin film head and an MR head.

[0002]

2. Description of the Related Art A magnetic disk apparatus, as shown in FIG. 10, has a magnetic disk 101 having a magnetic surface and supported on a spindle (not shown) for rotation, and at least movable with respect to the disk surface. One magnetic head 10
3 and a spindle motor 10 for driving the spindle
4, a head support mechanism 105 coupled to the magnetic head 103, and the magnetic head 1 along the magnetic disk surface.
03 for moving the head supporting mechanism 105, which is made to move the head 03, and servo information recorded on the magnetic disk surface.
A servo system 107 for reading out at 03 and controlling the actuator 106 to move the position of the magnetic head 103 to a target position or hold it at the target position.

[0003] Recent magnetic disk devices generally perform positioning of the magnetic head, that is, tracking control, by a so-called sector servo system.

In the sector servo system, as shown in FIG. 10, about 30 to 100 servo sectors 102 are arranged in a circle so as to traverse a plurality of concentric data recording tracks on the magnetic disk 101 at equal time intervals. .
Here, the servo sectors 102 are not aligned linearly in the radial direction and are curved because the locus of movement of the head is not a straight line but an arc centered on the pivot.

In a typical example, the servo area 102 has an AGC section 110 and a rough position information section (cylinder address information section) 111 in a time sequence of passing under a head (circumferential direction of the disk) as shown in FIG. And servo burst A11
2, servo burst B113, servo burst C11
4 and a precise position information section including four servo bursts D115. Each servo burst is a repetition (eg 10 cycles) of a signal of a single frequency. The radial width of each servo burst is the data track pitch Tp.
The burst pattern is repeated at a 2-cylinder width cycle with an erase portion (non-signal portion) having a data track pitch width interposed therebetween in the radial direction. Further, each burst of A, B, C, and D is 1 / of the data track pitch Tp in the radial direction.
It is arranged so as to be offset by an integral multiple of two. In FIG. 11, B is offset by Tp based on A, and C is Tp /
The two offsets and D are arranged with a 3/2 Tp offset (or Tp / 2 offset in the opposite direction to C in another expression).

The sector servo pattern is written by precision equipment called a servo track writer (STW) using the magnetic head 103 itself used for reading and writing data. The width of the write head is the data track pitch Tp
Since it is narrower, it is necessary to continue writing in order to write a servo pattern of one track pitch width. The servo pattern is formed by continuously writing at a position shifted by 1/2 of the data track pitch Tp, and the width of excess writing is further 1/2 of Tp.
DC erase at the offset position. Therefore, when observing the pattern of one track width by the Bitter method or the like, it can be seen that there is a thin erase band formed when data is continuously written in the center. (FIG. 11 omits rewriting.) For positioning control, the position is detected and the actuator is controlled so that the difference becomes smaller than the target position.
The position is detected as follows. First, the cylinder address is recognized by decoding the code of the coarse position information section. Next, the four bursts A, B, C, of the precision position information section
Detect the amplitudes Sa, Sb, Sc and Sd of D. Since the output amplitude of the magnetic head 103 is almost proportional to the size of the recording pattern width that passes directly under the magnetic head 103, when the magnetic head 103 is on the line of the track center Tc, Sa and S
It can be easily understood from FIG. 10 that b is about half of the maximum value, Sc is the maximum value, and Sd is the minimum value (nearly zero). So Figure 1
As shown in FIG. 1, Sa-Sb and Sc-Sd are used as position error signals 120 and 121 to obtain a precise position within one cylinder.

Two position signals are generated here because the linearity of the position signal is lost in the vicinity of the maximum / minimum of one position signal, the sensitivity of the position is lowered, and a dead zone is generated. In that case, accurate position information can be obtained by using another position signal. The cause of the dead zone is that the read width Tr of the magnetic head 103 is narrower than the recorded burst pattern width Tp. When the burst amplitude is near the maximum value, the output amplitude hardly changes because the recording pattern exists right under the head even if the head is offset to the left or right (track crossing direction) by a small amount (± (Tp-Tr) / 2 or less). Further, even in the vicinity of the minimum burst amplitude, even if a small amount of offset is applied, the area directly below the head is the erase portion and the amplitude remains almost zero.

When the magnetic head 103 is off-tracked by 1/2 Tp from the track center Tc, a position signal (Sa-S
b) Since the dead zone appears in 120, the position error signal (Sc-Sd) 121 is obtained at the position 1/4 Tp off-track.
By switching to and using the magnetic head 103 at any position, the magnetic head 103 outputs a position error signal corresponding to the position, and the magnetic head 103 can be positioned.

Incidentally, today, the amplitude detection output Sa of the servo burst A and that Sb of the servo burst B are AD respectively.
After conversion, the microprocessor calculates (Sa-S
b) is often calculated, and the position error signal does not always exist as an analog signal.

[0010]

The magnetic disk device is rapidly increasing the recording density year by year, and an MR head having a high reading sensitivity is being used to achieve a high recording density. Since the MR head is read-only, the thin film head (TF head) is used for writing as in the conventional case. Therefore, the magnetic head is a combination of a thin film head and an MR head.

The problem with the conventional servo pattern is that when a composite head having a read-only MR head is used, a position error signal (Sa-S) generated from the servo burst signal is used.
b). Since the linear region of (Sc-Sd) becomes narrow and the dead zone region becomes large, it is impossible to stably and accurately position at an arbitrary position, for example, a 1/4 off-track position.

One of the reasons for this is that in the case of the TF-MR composite head, the track widths of TF and MR are changed in order to reduce the read error for off-track, and the design is made for wide write / narrow read. It is narrower than the TFH for both reading and writing, which means that the dead zone is widened.

Another reason is that in a reproducing MR head, the off-track sensitivity characteristic is non-linear, and the hem and shoulder of the off-track profile deviate from a straight line.

Another reason is that the MR head is essentially asymmetric in the left and right off-track characteristics.

For these reasons, the position error signals (Sa-Sb), (Sc-Sd) created by the burst reproduction output.
It becomes difficult to maintain the ratio of the linear area to the data track pitch Tp at 50% (± 1/4 Tp), and it is difficult to secure the linear area by switching at the position where the 1/4 cylinder is off-tracked. Positioning control becomes difficult.

FIG. 6 shows the basic arrangement of the servo burst pattern. FIG. 7 shows the relative positional relationship between the burst pattern and the reproducing MR head. FIG. 8 shows the result of the off-track profile when the reproducing MR head is off-tracked in FIG.

Considering a trapezoid formed by a straight line approximating the slope of the profile, a line with standardized output Y = 0, and a line with standardized output Y = 1, the lower left and upper right of the profile are rounded and rounded. There is. In the reproducing MR head having the off-track profile shown in FIG. 9, the amplitude S of the two bursts A12 and B13 arranged in FIG.
The profile when a and Sb are taken out and the position error signal (Sa-Sb) is produced is shown. Position error signal (Sa-
The interval between the points P and Q where Sb) = 0 is the burst A in FIG.
12 and burst B13. Position error signal (S
a-Sb) = 0, the linear region is the reproduction MR.
Only about 80% of the reproducing track width of the head can be secured. This is because the reproducing MR head has a sensitivity distribution in the track width direction.

When the relationship between the track width Tr and the reproducing track width Rw of the reproducing MR head is 1 / 2Tr> 0.8 × Rw (1), the position error signal (when the servo burst pattern is offset by 1 / 2Tr) is arranged ( Sa-Sb), (Sc
A dead zone that cannot be positioned by either of Sd) is created.

However, as described above, the reproduction M is generally performed.
The R head has a reproduction track width shortened to secure a margin when recording and reproducing data. If the reproduction track width is 70% of the track width Tr, there is no problem from the above equation (1), but 6
At 0%, the track width is 1/2 from the relationship of the above formula (1).
Positioning becomes difficult with offset servo burst patterns.

As a countermeasure, the servo burst is changed to A, B,
There is a method to increase from C and D to 6 servo bursts or 8 bursts so that the non-linear part is not used.
Then, the data area corresponding to the increased servo burst decreases and the data utilization efficiency decreases. Moreover, the number of channels and the processing time of the AD converter are increased, which leads to an increase in cost and a decrease in performance.

An object of the present invention is to provide a servo pattern suitable for a wide write narrow read type composite head. According to the present invention, the recording length of servo information can be increased to improve the accuracy of position information without deteriorating the utilization efficiency of the data surface, and the same detection circuit as in the prior art can perform accurate and stable positioning at any position. It becomes possible.

The radial width of each burst is set to ⅔ of the data track width, and the servo bursts are arranged offset in the radial direction by ⅓ of the data track width. In this case, the width of the MR head becomes relatively large with respect to the width of the servo burst information with respect to the width of the MR head, and the basic idea is to avoid the dead zone.

By setting the burst pattern width to 2/3 data track pitch, the cycle of the pattern can be doubled to 4 Cyl and the linearity can be improved with the same four servo bursts.

[0024]

A magnetic disk device according to the present invention is a magnetic disk having a magnetic surface and supported on a spindle for rotation, and at least one magnetic head movable with respect to the surface of the magnetic disk. A spindle motor that drives the spindle, a head support mechanism that supports the magnetic head and operates to move the head along the disk surface, an actuator that moves the head support mechanism, and the magnetic A magnetic disk device including a servo system that reads servo information recorded on a disk surface with the magnetic head, moves the position of the magnetic head to a target position by controlling the actuator, and holds the position at the target position. In the above, the servo information includes rough position information indicating a rough position of the head and precise position information. The precise position information is composed of four position information patterns A, B, C and D, each position information pattern is recorded in order in the track direction including at least two magnetization reversals, and the recording width in the track crossing direction is data. The position information pattern is about ⅔ of the track pitch, and each position information pattern has an erase portion having a width of about ⅔ of the data track pitch in the cross-track direction, that is, every 4/3 of the data track pitch with a portion without magnetization reversal interposed. The four pieces of position information A, B, C, D are recorded at positions shifted from each other by 1/3 times or 2/3 times or equal to the data track pitch in the track crossing direction. It is characterized by

In the magnetic disk device of the present invention, the rough position information includes cylinder address information, and one recording end of the cylinder address information in the track crossing direction is one of the four recording ends of the fine position information. It is characterized in that they are arranged on the same radius as.

The servo pattern writing method of the present invention is
3. A method of writing a sector servo pattern including rough position information and fine position information on the magnetic disk of the magnetic disk device according to claim 1 or 2 by a servo track writer, after writing one round, 1/3 of a data track pitch. By repeating the operation of shifting by the pitch and writing again, the coarse position information and the fine position information are rewritten according to the timing information generated by the clock head synchronized with the rotation of the magnetic disk, and 1/3 is written. When writing by shifting the pitch, the rough position information is continuously written in the same pattern every three times, and the fine position information is divided into four pieces of position information A, B, C, D, The information pattern is written twice in succession, and the DC erase operation is performed twice in succession. Position of the track transverse to write is characterized to keep shifting one time feed pitch of the head or twice or three times to each other at their four position information.

The servo pattern writing method of the present invention is
3. A method of writing a sector servo pattern including rough position information and fine position information on the magnetic disk of the magnetic disk device according to claim 1 or 2 by a servo track writer, after writing one round, 1/3 of a data track pitch. By repeating the operation of shifting by the pitch and writing again, the coarse position information and the fine position information are rewritten according to the timing information generated by the clock head synchronized with the rotation of the magnetic disk, and 1/3 is written. When writing while shifting by pitch, the coarse position information is written once when the pattern is written, and then the write date is closed twice to prevent overwriting, and the precise position information is the four position information A, It is divided into B, C, and D, and the position information pattern is written once for each of the position information described above. The write gate is closed to prevent overwriting, the next one time is DC erased, and the next one time is DC erased or the write gate is closed by repeating the operation, and the precise position information is written. The position in the cross-track direction to write is characterized in that the head feed pitch is offset by one, two, or three times based on these four position information.

According to the position detecting method of the present invention, when the coarse position information and the fine position information are used in the magnetic disk device according to the second aspect, the four pieces of precision position information are overlapped with each other in the radial direction of the disk. Select two pairs that do not exist, and use the difference between the amplitudes of the two position signals belonging to each pair as the first position error information and the second position error information, and calculate the absolute value of the first position error information and the second position error information. The smaller one of the two is used as the position error information, and the position error information and the maximum or minimum of the four precise position information,
Alternatively, the position is detected by using the polarity of the larger absolute value of the first position error information and the second position error information and the cylinder address information of the position information as a criterion for determining a rough position within one track. Is characterized by.

As shown in FIG. 1, the servo pattern has four track cycles of N, N + 1, N + 2, and N + 3 repeated, and the magnetic head uses a position error signal (Sa-Sb).
By switching the position error signal (Sc-Sd) as shown in FIG. 4, the use range of the slope of one position error signal can be set to ± 1/6 cylinder width, which is ± 1/4 that of the conventional pattern. Since the width is narrower than the cylinder width, the dead zone due to the position error signal can be eliminated and a continuous linear region can be secured for positioning.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an embodiment of the present invention will be described in detail with reference to FIGS.

The structure of the magnetic disk drive is the same as the conventional one and is as shown in FIG. FIG. 1 shows the structure of coarse position information and fine position information of the sector servo of the magnetic disk device of the present invention. The servo sector 102 of FIG. 10 includes the position information of FIG.

In FIG. 1, 1 is an AGC portion and a coarse position information portion (address portion), 2 to 5 are precise position information portions, 2 is a servo burst A, 3 is a servo burst B, 4 is a servo burst C, and 5 is a servo. It is burst D. The width of the rough position information portion is almost equal to the track pitch Tp. On the other hand, the width of each burst in the precision information section is 2/3 Tp, and the blank portions on the left and right of each burst are in the DC erase (erase) state. As is apparent from FIG. 1, the pattern arrangements of N to N + 3 are all different. Focusing only on the precise position information part, the burst pattern repeats 4 / 3Tp cycles, but the relationship between the boundary of the coarse position information part and the burst pattern is 4 / 3T.
p-destination and 8 / 3Tp-destination are different, 12 / 3Tp = 4
It returns to the same arrangement for the first time at Tp. Therefore, it is possible to discriminate which part of the adjacent four cylinders is located from the value of the lower two bits of the address information (coarse position information) and the magnitude relationship of the four bursts.

2 and 3 show two methods of writing the servo pattern having the arrangement shown in FIG. FIG. 2 shows a standard writing method. Some kind of writing is performed every 1/3 Tp pitch every servo sector. The width of the rough position information is Tp, and the same pattern is written three times. Therefore, two thin erase bands are formed in the width of Tp due to the spread of the magnetic field at the edge of the write head.
It should be noted that the timing of magnetization reversal must be aligned at the time of rewriting, but for that reason, in the servo track writer, a clock head is used separately from the write head to obtain a reference clock synchronized with the rotation.

FIG. 3 shows a writing method in which the written pattern is not spliced. After positioning the write head at the NCyl position using a laser length measuring machine or the like with a servo track writer, the data specified at the servo pattern write timing N in FIG. 3 is written. In case of N, AGC + coarse position information and servo burst A are written, and servo burst B is DC erased. At this time, writing is not performed at the timing of servo bursts C and D, and the gate is closed and passed. Next, move the write head 1/3 of the data track pitch and position it at N + 1/3.
Data is written at the servo pattern write timing of +1/3. At N + 1/3, servo burst C is written and servo burst D is DC erased. In other areas, the gate is closed and passed. Next, the write head is fed by 1/3 of the data track pitch, positioned at N + 2/3, and data is written at the servo burst write timing of N + 2/3. At N + 2/3, servo burst A is DC erased and servo burst B is written. Otherwise, the area closes the gate and passes through. Further, the write head is positioned at 1/3 feed N + 1 of the data track pitch, and AGC + coarse position information and the servo burst D are written, and the servo burst C is DC erased.

As described above, the gate is controlled at the write timing shown in FIG. 3 and the write head is fed by 1/3 data track pitch from N to N + 3 + 2/3 to write the specified data, whereby AGC + coarse position information and servo burst A servo pattern without an erase band due to continuous writing, the radial width of the four servo bursts is set to ⅔ of the data track pitch, and the servo bursts are arranged offset in the radial direction by ⅓ of the data track pitch. Create a 2/3 track pitch burst pattern.

The magnetic head (reproducing MR head) 6 has the above-mentioned 4
Positioning is performed using a position error signal generated by using the servo pasts.

A method of processing position information by the servo burst pattern is shown in FIGS.

The servo burst pattern shown in FIG. 1 is read by the reproducing MR head 6 having a narrow track width, and the position error signal (Sa-Sb) 7 and the position error signal (Sc-Sd) 8 are generated from the difference in the amplitudes. It becomes like 4.

FIG. 5 shows the position error signal to be used in each track depending on the position of the magnetic head in the track crossing direction. The position signal to be used in this way can be switched depending on the zone in which the head is located. Thus, the dead zone due to the position error signal is eliminated, a continuous linear region is secured, and accurate position information can be obtained regardless of the position of the magnetic head (reproducing MR head) 6 on the track.

[0040] It should be noted that is not to detect the actual to the position from the position information, we do not know is located in advance anywhere in the zone. In that case, in order to realize the usage of the position error signal of FIG. 5 and obtain the position, the following may be done.

When the position X is represented with reference to O thin lida, X
= Tp (4N + m−f) + KθS Here, Tp is the track pitch, 4N + m is the cylinder address, and m is the lower 2 bits of the cylinder address, which is 0 to 3. f is the offset of the center line of the position error signal from the track center, -1/2, -1/6, +1/6, + 1 /
It is either 2. S is Sa-Sb, Sc-Sd,
It is either Sb-Sa or Sd-Sc. Kθ is the sensitivity (distance / voltage) of the position error signal. The selection of f and S is determined as shown in the following table according to the magnitude relation between m and Sa-Sb, Sc-Sd. If | Sa-Sb |> | Sc-Sd | and Sa-Sb> 0, then S = Sc-Sdf is +1/6 if m = 0, + 1/6, m if m = 1.
= 2 if +1/2, m = 3 if f = -1 / 2 | Sa-Sb |> | Sc-Sd | and if Sa-Sb <0 then S = Sd-Scf If m = 0 then +1/2 , M = 1, -1/2, m
If = 2, then-1 / 6, if m == 3, then f = + 1/6 If | Sa-Sb | <| Sc-Sd | and Sc-Sd> 0, then S = Sa-Sb f is further + 1 / 6, m = 1, + 1/2, m
= 2, -1/2; m == 3, f = -1 / 6 | Sa-Sb | <| Sc-Sd | and Sc-Sd <0, S = Sb-Sa f further m = 0- If 1/2, m = 1, then -1/6, m
= 2, +1/6, m == 3, f = + 1/2 Note that | Sa-Sb |> | Sc-Sd | and Sa-Sb>
0 means burst A is the maximum, or burst B
Is equivalent to the minimum of Sa, Sb, Sc,
S and f may be selected by obtaining the maximum or minimum of Sd.

[0042]

As described above, by using the 2/3 track width servo pattern of the present invention, the reproduction M
Positional error signals (Sa-Sb),-(Sa-Sb), (Sc-
By switching between Sd) and-(Sc-Sd), the dead zone of the position error signal can be eliminated and a continuous linear region can be secured.

As a result, positioning can be performed even if the reproducing track width of the reproducing MR head is about 60% of the track width.

In addition, the conventional 1-track-width burst pattern has a half the conventional 1 / 4-track pitch and doubles the conventional 8
Although the same effect can be obtained by using the individual pieces, there is a drawback that the length of the burst pattern is doubled and the occupation ratio of the servo information on the data recording surface is increased to reduce the data recording capacity. Further, since the servo pattern is written at a finer pitch as compared with the present invention, the processing time of the servo track writer, which is an expensive facility, is extended and the productivity is deteriorated. As described above, there is an effect that the utilization efficiency and the production efficiency on the data side are superior to those of the simple extension of the conventional technique.

[Brief description of drawings]

FIG. 1 is a configuration diagram showing a servo pattern showing an embodiment of a servo signal writing system and a positioning system of the present invention.

FIG. 2 is a timing diagram of writing a servo pattern according to FIG.

FIG. 3 is a timing diagram of a servo pattern that does not cause overwriting.

FIG. 4 is a waveform diagram of a position error signal including the servo pattern shown in FIG.

FIG. 5 is a diagram showing a relationship between a magnetic head (reproducing MR head) position and a position error signal to be used.

FIG. 6 is a schematic diagram of a servo pattern.

FIG. 7 is a relative positional relationship diagram between a reproducing MR head and a recording pattern.

FIG. 8 is a reproduction MR output profile diagram for an off-track position.

FIG. 9 is a profile diagram of a position error signal (AB).

FIG. 10 is an external view of a conventional magnetic disk device.

FIG. 11 is a configuration diagram showing a conventional servo pattern.

FIG. 12 is a waveform diagram of a position error signal composed of a conventional servo pattern.

[Explanation of symbols]

 1 AGC + coarse position information 2 Servo burst A 3 Servo burst B 4 Servo burst C 5 Servo burst D 6 Magnetic head (reproducing MR head) 7 Position error signal (Sa-Sb) 8 Position error signal (Sc-Sd) 11 MR head Playback track width 12 Burst A 13 Burst B 14 Burst 101 Magnetic disk 102 Servo sector 103 Magnetic head 104 Spindle and spindle motor 105 Head support mechanism 106 Actuator 107 Servo system 110 AGC section 111 Coarse position information section 112 Servo burst A 113 Servo burst B 114 Servo burst C 115 Servo burst D 120 Position error signal (Sa-Sb) 121 Position error signal (Sc-Sd)

Claims (5)

[Claims] 1. A magnetic disk having a magnetic surface and supported on a spindle for rotation, at least one magnetic head movable with respect to the surface of the magnetic disk, and a spindle motor for driving the spindle. A head support mechanism that supports the magnetic head and operates to move the head along the disk surface, an actuator for moving the head support mechanism, and servo information recorded on the magnetic disk surface to the magnetic information. In a magnetic disk device including a servo system for reading with a head and moving the position of the magnetic head to a target position by controlling the actuator, and holding the servo system at the target position, the servo information is a rough position of the head. It includes coarse position information and precision position information, and the precision position information is four position information. Each position information pattern is composed of turns A, B, C, D, and is sequentially recorded in the track direction including at least two magnetization reversals. The recording width in the track crossing direction is about 2/3 of the data track pitch. Each position information pattern is arranged so as to be repeated every 4/3 of the data track pitch with an erase portion having a width of about 2/3 of the data track pitch, that is, a portion having no magnetization reversal sandwiched between the position information patterns. The four pieces of position information A, B, C, and D are 1/3 times or 2 / the data track pitch in the track crossing direction.
A magnetic disk device characterized in that the data is recorded at a position which is deviated by a factor of 3 or 1. 2. The rough position information includes cylinder address information, and one recording end of the cylinder address information in a track crossing direction is on the same radius as one of the four recording ends of the fine position information. 2. The magnetic disk drive according to claim 1, wherein the magnetic disk drive is arranged as described above. 3. A method of writing a sector servo pattern including rough position information and fine position information on the magnetic disk of the magnetic disk device according to claim 1 or 2 by a servo track writer, wherein after writing for one turn, a data track is written. The rough position information and the fine position information are rewritten according to the timing information generated by the clock head synchronized with the rotation of the magnetic disk by repeating the operation of shifting again by 1/3 pitch and writing again. When writing with shifting by 1/3 pitch, the rough position information is the same pattern written continuously every three times, and the precise position information is the four position information A, B, C, D.
And write the position information pattern twice,
It is characterized in that the position in the track crossing direction in which the precise position information is written is shifted by one, two, or three head feed pitches from each other by repeating the operation of continuously performing DC erase. Servo pattern writing method. 4. A method of writing a sector servo pattern including coarse position information and fine position information on the magnetic disk of the magnetic disk device according to claim 1 or 2 by a servo track writer, wherein after writing for one revolution, a data track is written. The rough position information and the fine position information are rewritten according to the timing information generated by the clock head synchronized with the rotation of the magnetic disk by repeating the operation of shifting again by 1/3 pitch and writing again. The coarse position information is written once when the pattern is written once, and the write gate is closed twice to prevent overwriting. The position information A, B, C, D
If the position information pattern is written once for each of the position information, the write gate is closed the next time to prevent overwriting, and the next time the DC erase is performed. One time of writing is performed by repeating the operation of DC erasing or closing the write gate, and the position in the cross-track direction in which the precise position information is written is the head feed pitch of one or two times with the four position information or A servo pattern writing method, which is characterized by being shifted three times. 5. When using the rough position information and the fine position information in the magnetic disk device according to claim 2, two pairs of the four pieces of fine position information which do not overlap each other in the radial direction of the disk are formed. The difference between the amplitudes of the two position signals belonging to each pair is selected as the first position error information and the second position error information.
The position error information is used, and the smaller one of the first position error information and the second position error information is used as the position error information, and the position error information and the maximum or minimum of the four precise position information are used. Or the polarity of the larger absolute value of the first position error information and the second position error information and the cylinder address information of the position information as a criterion for determining the rough position within one track. A position detecting method characterized by detecting.