U.S. patent application number 11/294358 was filed with the patent office on 2006-04-20 for method and apparatus for writing servo data with perpendicular magnetic recording in a disk drive.
This patent application is currently assigned to KABUSHIKI KAISHA TOSHIBA. Invention is credited to Koji Osafune, Kazuhito Shimomura, Koji Yano.
Application Number | 20060082921 11/294358 |
Document ID | / |
Family ID | 34385924 |
Filed Date | 2006-04-20 |
United States Patent
Application |
20060082921 |
Kind Code |
A1 |
Shimomura; Kazuhito ; et
al. |
April 20, 2006 |
Method and apparatus for writing servo data with perpendicular
magnetic recording in a disk drive
Abstract
There is disclosed a servo writing method in which servo data is
recorded by a perpendicular magnetic recording system. In the servo
writing method, at the time of perpendicular magnetic recording of
the servo data on a disk, a servo writing operation is executed
including an offset process set based on the hard-easy transition
shift (HETS) phenomenon.
Inventors: |
Shimomura; Kazuhito;
(Akishima-shi, JP) ; Osafune; Koji; (Ome-shi,
JP) ; Yano; Koji; (Ome-shi, JP) |
Correspondence
Address: |
PILLSBURY WINTHROP SHAW PITTMAN, LLP
P.O. BOX 10500
MCLEAN
VA
22102
US
|
Assignee: |
KABUSHIKI KAISHA TOSHIBA
Tokyo
JP
|
Family ID: |
34385924 |
Appl. No.: |
11/294358 |
Filed: |
December 6, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
10926393 |
Aug 26, 2004 |
|
|
|
11294358 |
Dec 6, 2005 |
|
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Current U.S.
Class: |
360/75 ;
G9B/5.222 |
Current CPC
Class: |
G11B 5/59633
20130101 |
Class at
Publication: |
360/075 |
International
Class: |
G11B 21/02 20060101
G11B021/02 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 29, 2003 |
JP |
2003-306992 |
Claims
1. A disk drive for perpendicular magnetic recording, comprising: a
magnetic head including a write head and a read head suitable for
the perpendicular magnetic recording; and a disk medium which has
an Hn value set based on a relation between inverse magnetic domain
generated magnetic field characteristics (Hn) and hard-easy
transition shift (HETS) phenomenon and on which servo data is
recorded by a perpendicular magnetic recording system
beforehand.
2. The disk drive according to claim 1, wherein the Hn value of the
disk medium is 800 (1/(4.pi.).times.10.sup.3 A/m) or more.
3. The disk drive according to claim 1, wherein the Hn value of the
disk medium is 1000 (1/(4.pi.).times.10.sup.3 A/m) or more.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 10/926,393, filed Aug. 26, 2004, which is based upon and claims
the benefit of priority from prior Japanese Patent Application No.
2003-306992, filed Aug. 29, 2003, the entire contents of both of
which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates generally to a field of a disk
drive of a perpendicular magnetic recording system, particularly to
a servo writing method in which servo data is recorded on a disk
medium by perpendicular magnetic recording.
[0004] 2. Description of the Related Art
[0005] In recent years, practical use of a disk drive of a
perpendicular magnetic recording system has been pushed forward. In
the perpendicular magnetic recording system, a disk drive using a
write head called a single pole type head (SPT) suitable for
perpendicular magnetic recording, and a disk medium (hereinafter
referred to simply as a disk) which is a double-layered
perpendicular recording medium is promising.
[0006] In general, servo data for use in a control for positioning
heads is recorded on disks before shipping the disk drives. In a
servo writing step for recording the servo data, a servo write-only
device called a servo track writer (STW) is used.
[0007] The servo data is roughly classified into an address code
and a servo burst signal. The address code includes a cylinder code
and a sector code.
[0008] Since the servo data is used for correctly positioning the
head at a target position on the disk, a high-precision writing
method is required. In the disk drive, the servo data recorded on
the disk is read by a read head at the time of positioning the
head. At this time, precision in positioning the head depends on
precision in reproducing the servo data.
[0009] For example, when the servo burst signal included in the
servo data is recorded, and when erase bands exist on opposite
sides, the signal-to-noise (S/N) ratio in an operation for
reproducing the servo data sometimes drops because of losses by the
erase bands. To solve this problem, a technique has been proposed
in which the track width of the servo burst signal is expanded to
improve the S/N ratio (see U.S. Pat. No. 6,023,389, for
example).
[0010] In the disk drive of the perpendicular magnetic recording
system, the servo data is recorded on the disk by the write head
using an SPT suitable for the perpendicular magnetic recording.
[0011] Additionally, in the perpendicular magnetic recording
system, a phenomenon has been confirmed in which a recorded
magnetized state changes, when a recording magnetic field having a
polarity opposite to a magnetization polarity magnetically recorded
on the disk beforehand is applied by the write head using the SPT.
This phenomenon is called a hard-easy transition shift (hereinafter
sometimes abbreviated as HETS) or simply a hard transition.
[0012] In HETS, the recording magnetic field from the head
apparently becomes strong, and the magnetization displacement point
shifts, when the magnetization having a pole opposite to that of
the magnetization before the recording on the disk is written.
[0013] It has been confirmed that when an influence of HETS
phenomenon is exerted at the time of a servo writing operation and,
for example, when the servo data is written in a radial direction
from an inner periphery to an outer periphery on the disk, the
servo data shifts in a reverse direction, and is recorded. When the
servo data is recorded in this manner, a reproduction error of the
cylinder code is generated, or the precision in reproducing the
servo burst signal deteriorates. As a result, the precision in
positioning the head deteriorates.
BRIEF SUMMARY OF THE INVENTION
[0014] In accordance with one embodiment of the present invention,
there is provided a servo writing method including facilities to
compensate for a shift of servo data in a radial direction by the
HETS phenomenon in a servo writing step by a perpendicular magnetic
recording system.
[0015] The servo writing method is a method in which servo data is
recorded on a disk medium by use of a write head of a perpendicular
magnetic recording system. The write head is moved to a designated
position of the disk medium in a radial direction. When the servo
data is recorded at the designated position by the use of the write
head, a write operation is executed including an offset process set
based on the hard-easy transition shift (HETS) phenomenon.
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING
[0016] The accompanying drawings, which are incorporated in and
constitute a part of the specification, illustrate embodiments of
the invention, and together with the general description given
above and the detailed description of the embodiments given below,
serve to explain the principles of the invention.
[0017] FIG. 1 is an explanatory view of a servo writing method
according to an embodiment of the present invention;
[0018] FIGS. 2A to 2D are timing charts showing the servo writing
method according to the present embodiment;
[0019] FIG. 3 is a diagram showing a servo track writer according
to the present embodiment;
[0020] FIG. 4 is a diagram showing a main part of a disk drive of a
perpendicular magnetic recording system according to the present
embodiment;
[0021] FIG. 5 is a diagram showing a format of a disk according to
the present embodiment;
[0022] FIG. 6 is a diagram showing a format of servo data according
to the present embodiment;
[0023] FIG. 7 is a diagram showing a structure of a head of the
perpendicular magnetic recording system according to the present
embodiment;
[0024] FIG. 8 is a diagram showing an HETS phenomenon according to
the present embodiment;
[0025] FIG. 9 is a diagram showing an ideal recorded state of the
servo data according to the present embodiment;
[0026] FIGS. 10 and 11 are diagrams showing an actual recorded
state of the servo data according to the present embodiment;
[0027] FIG. 12 is a diagram showing Hn characteristics of the disk
of the perpendicular magnetic recording system according to the
present embodiment;
[0028] FIGS. 13 and 14 are diagrams showing characteristics of an
offset amount with respect to Hn according to the present
embodiment; and
[0029] FIG. 15 is a flowchart showing a procedure of a servo
writing operation according to the present embodiment.
DETAILED DESCRIPTION OF THE INVENTION
[0030] The present embodiment will be described hereinafter with
reference to the drawings.
[0031] A servo writing method of the present embodiment will be
described with reference to FIGS. 1, 2, 3, and 15.
[0032] In the servo writing method of the present embodiment, as
shown in FIG. 3, servo data is recorded with respect to a disk 10
incorporated in an assembled disk drive using a write head 20
mounted on an actuator 12 of the drive under control of an STW 13.
The disk 10 is rotated by a spindle motor 11. An SPT suitable for
perpendicular magnetic recording is used in the write head 20.
[0033] Moreover, the servo writing method of the present embodiment
may be a method in which a multi stack (MS)-STW for recording the
servo data collectively with respect to a plurality of disks by one
servo writing operation is used. Even in this method, the servo
writing operation is performed by the write head using the SPT
suitable for the perpendicular magnetic recording.
[0034] Furthermore, as shown in FIG. 4, a self servo writing system
may also be used in which the servo data is recorded using a head
15 of the drive without using any STW in a disk drive 1 assembled
as a product. The head 15 includes a write head using an SPT, and a
read head usually using a giant magnetoresistive (GMR) element. The
head 15 is mounted on an actuator 16 driven by a voice coil motor
(VCM) 17.
[0035] (Perpendicular Magnetic Recording and HETS Phenomenon)
[0036] Perpendicular magnetic recording and the HETS phenomenon
will be described as an assumption for describing a servo writing
method of the present embodiment.
[0037] As shown in FIG. 5, a large number of tracks 100 are
constituted in a disk 10 incorporated in a disk drive 1. Each track
includes a servo area in which servo data is recorded by the servo
writing method of the present embodiment, and a data area in which
user data is recorded.
[0038] As shown in FIG. 6, the servo data includes a preamble 60, a
servo mark (SM) 61, an address code 62, servo burst signals (bursts
A to D) 63, and a pad (PAD) portion 64. The address code 62 is gray
code data including a cylinder code and a sector code.
[0039] FIG. 9 shows a state of ideal servo data (62, 63) recorded
on the disk 10. In the disk drive 1, a track (cylinder) for
positioning the head 15 is identified using the cylinder code red
by the head 15. A control for positioning the head is executed in
such a manner that an amplitude value at the time of reproduction
of the burst A is equal to that at the time of reproduction of the
burst B. Accordingly, the head 15 is positioned on a track center
line 83. It is to be noted that in FIG. 9, reference numeral 84
denotes a track boundary line.
[0040] In the head (15, 20) in which the SPT suitable for the
perpendicular magnetic recording is used, as shown in FIG. 7, a
magnetic field generated from a main magnetic pole 71 of the write
head is applied to a perpendicular magnetic recording layer 10A of
a double-layered disk 10, passes through a soft magnetic layer 10B,
and is converged into a return yoke 70. That is, a magnetic field
loop is formed in the SPT. Here, in the write head, a magnetic
domain inside the SPT is reversed by a recording current, and
accordingly a direction of generation of the magnetic field
changes.
[0041] Moreover, the head includes a read head including a GMR
element 73 held between reproduction shielding members 72, 74. The
GMR element 73 reproduces a recording magnetic field generated from
the magnetic recording layer 10A on the disk 10. The reproduction
shielding members 72, 74 remove interference magnetic noise at the
time of the reproduction.
[0042] In the perpendicular magnetic recording system, as shown in
FIG. 8, a recording magnetic field having a polarity opposite to a
magnetization polarity (80S) magnetically recorded on the disk
beforehand is applied by a write head 20W which is an SPT in the
perpendicular magnetic recording system, and then a recorded
magnetized state changes. This phenomenon is the HETS
phenomenon.
[0043] Concretely, when the recording magnetic field having the
same polarity as that of magnetization (80N) on the disk before the
recording is applied, magnetization (81N) corresponding to the
shape of the head 20W is recorded. On the other hand, when the
magnetization (81N) opposite to the magnetization (80S) before the
recording is written, the recording magnetic field from the head
apparently becomes strong, a magnetization displacement point
shifts, and a shape of recorded magnetization (82N) becomes larger
than that of the head.
[0044] By this HETS phenomenon, a servo pattern (servo data)
actually recorded on the disk indicates a recorded state shown in
FIG. 10 with respect to an ideal recorded state shown in FIG.
9.
[0045] That is, the address code 62 shifts from the track boundary
84 in a direction (width direction) reverse to a servo writing
direction 21 by an amount S0, and is recorded in a portion (71)
different from a track adjacent to bits. The burst data 63 is
brought into such a recorded state that the bits of the burst A or
the burst B are connected to each other in a width S0 corresponding
to the shift amount in the vicinity of the center line 83 of the
track (see reference numeral 25). When the read head 15 is
positioned in such a manner that amplitude values of the bursts A
and B are equal (positional error is 0) in this recorded state of
the servo data, the head shifts from the center line 83 of the
track (target position) by S1 (S0/2).
[0046] On the other hand, the cylinder code shifts by the shift
amount S0 and is recorded. Therefore, when the read head 15 is
positioned in order to eliminate the positional error (burst
A-burst B=0), the head reads a part (corresponding to the shift
amount S1) of the adjacent cylinder code servo-written later.
Additionally, the amount of the data read from the adjacent track
depends on a reproduction track width of the read head 15.
[0047] Usually, cylinder addresses on the disk 10 are allocated in
such a manner that the address decreases on an outer peripheral
side (e.g., cylinder 0), and increases toward the inner periphery.
Therefore, when the servo writing direction extends toward the
outer periphery from the inner periphery, the cylinder code shifts
on an inner peripheral side, and is recorded. Therefore, a read
head 11R reads a part of the cylinder code of the adjacent track on
a "-1" side with respect to the cylinder code of the track in which
the head is positioned. Conversely, when the servo writing
direction extends toward the inner periphery from the outer
periphery, the read head 11R reads a part of the cylinder code of
the adjacent track on a "+1" side (inner peripheral side) with
respect to the cylinder code of the track in which the head is
positioned.
[0048] FIG. 11 shows a concrete example of an actually recorded
state of the servo data by the HETS phenomenon. As shown in FIG.
11, a noise region (dead region) which does not contribute as the
servo burst signal exists between the bursts A and B. When high
track densification of the disk actually proceeds, the track width
of the read head is reduced. Additionally, the head 15 contacts the
track in a place centering on a dotted line 110 in order to satisfy
a relation "burst A=burst B" in a position offset by SO/2 from a
relation with the dead region. In this place, the regions 25 which
do not contribute as the servo burst signals exist in the bursts A
and B. Therefore, as shown in FIG. 11, a regional portion 120 which
contributes to the head 15 as the servo burst signal is reduced.
Accordingly, a quality of the signal contributing to the control
for positioning the head degrades, and, as a result, a region in
which the relation between a control amount (distance) and a
control signal amount (voltage) has linearity is narrowed. That is,
with a decrease of a dynamic range, a precision in positioning the
head is lowered.
[0049] (Servo Writing Method)
[0050] Next, a servo writing method of the present embodiment using
an STW 13 will be described mainly with reference to FIGS. 1, 2A to
2D, and a flowchart of FIG. 15.
[0051] Basically in the servo writing method in which servo data is
recorded on a disk 10, a write head 20 is positioned, for example,
at a pitch which is 1/3, 1/2, or 1/4 of a track pitch by control of
the STW 13, while the servo data is superimposed upon a part of the
adjacent servo data. The servo data is connected to one another in
this manner, and recorded without any gap.
[0052] FIG. 1 shows a case where the servo data is written, for
example, in a direction (arrow 21) from the inner peripheral side
to the outer periphery of the disk 10. FIGS. 2A to 2D show timing
gate signals SG30 to SG33 necessary for a servo writing operation
in the STW 13. FIG. 15 is a flowchart showing a procedure of the
servo writing of the STW 13.
[0053] The STW 13 records address codes (cylinder codes and sector
codes) 22 in a write timing 300 of SG30 (step S1). A recording area
(26) of the burst B is erased in a write timing 310 of SG30 (step
S2). In this case, by characteristics of the SPT which is the write
head 20 and the disk 10 for the perpendicular magnetic recording,
the erased region shifts from the area 26 in an arrow track
direction (direction reverse to the writing direction 21) by an
amount SO (area 24). This shift amount SO indicates a value
determined based on the above-described HETS phenomenon, and an
amount corresponding to about 10% of the track pitch is
experimentally confirmed (concretely, about 20 nm). In this case,
the same degree of a shift as the shift amount SO is also generated
in the portion of the address code 22.
[0054] Next, the STW 13 records a servo burst signal (27) of the
burst A in a write timing 320 of SG31 (step S3). In the timing 320,
the STW 13 executes an offset writing operation to position the
write head 20 in a position obtained by subtracting an offset
amount (corresponding to the shift amount SO) from an original
feeding pitch and to record the servo burst signal (27) of the
burst A. By this operation, the region 25 which does not contribute
to the servo burst signal by the HETS phenomenon is recorded in a
position offset by the offset amount SO. By these two operations,
the STW 13 records the signal 27 of the burst A, and records the
erased region 26 (including 24) in a timing just after the prior
timing.
[0055] Next, the STW 13 records an erased region 28 of the burst A
in the timing of SG32 (step S4). By this erasing, an unnecessary
signal region on the outer peripheral side of the servo burst
signal 27 of the burst A is erased. Furthermore, the STW 13 records
a servo burst signal 29 of the burst B in a write timing 330 of
SG33 (step S5). Also in this case, the STW 13 executes an offset
writing operation to position the write head 20 in a position
obtained by subtracting the offset amount SO from the original
feeding pitch in the timing 320 and to record the servo burst
signal 29 of the burst B.
[0056] The STW 13 repeats the above-described operation for the
predetermined number of tracks to thereby record the regions 25
which do not contribute to the servo burst signals in the bursts A
and B in positions offset by the offset amount SO. Therefore,
positions corresponding to track center lines in which the bursts A
and B reproduced by the read head have a relation "A=B" are shown
by dotted lines 23 in FIG. 1.
[0057] As described above, in the present embodiment, in the servo
writing method, when the servo burst signals (bursts A and B) are
recorded, an offset writing operation is executed to offset the
position of the write head 20 in a direction reverse to the writing
direction 21 by the offset amount SO and to write the signals.
Therefore, as described above, the recording shift (shift amount
SO) generated by the HETS phenomenon can be compensated for at the
time of the servo writing.
[0058] Therefore, in the disk drive (see FIG. 4) incorporating the
disk 10 on which the servo data is recorded by the servo writing
method of the present embodiment, the head 15 can be brought into
contact with the center line (23 of FIG. 1) on the track based on
the servo data. Accordingly, as a result, the head positioning
precision can be improved.
[0059] Furthermore, since losses of the dynamic range in the head
positioning control or dead zones of the servo burst signals are
eliminated, the head positioning control is not adversely
influenced. Additionally, since all the track widths of the read
head can contribute to the reproduction of the servo burst signals,
the tracks are effectively highly densified.
[0060] Furthermore, since the head 15 can be correctly positioned
based on the servo burst signals, the address code 22 can be
normally reproduced, the reproduction error of the cylinder code
can be inhibited from being generated.
[0061] (HETS and Offset Amount)
[0062] FIGS. 12, 13, and 14 are characteristic diagrams concerning
HETS and offset amounts at the time of servo writing according to
the present embodiment.
[0063] It has been confirmed that the HETS phenomenon is caused by
recording conditions of a write head using an SPT, magnetostatic
characteristics of a disk of a perpendicular magnetic recording
system, and an inverse magnetic domain generated magnetic field Hn.
Hn denotes a magnetic field intensity in an M-H characteristic loop
shown in FIG. 12.
[0064] FIG. 14 shows an example of a measurement result of an HETS
amount with respect to Hn. From measurement results shown in FIG.
14, it can be confirmed that when the disk has an Hn of 800 or 1000
or more, the shift amount is inhibited from being generated by the
HETS phenomenon.
[0065] FIG. 13 shows an example of the measurement result
concerning setting of an offset amount in a case where an offset
writing operation is executed at the time of a servo writing
operation by the STW. That is, the offset amount which is the
measurement result corresponds to a set value, for example, in a
case where the reproduction error of the cylinder code falls within
an allowable range.
[0066] In the servo writing by the STW, it is not practical to
adjust the position of the head with an offset amount which has
been set to a large value. Then, when the measurement result of the
HETS amount with respect to Hn shown in FIG. 14 is considered, and
when Hn of the disk is 800 or more, the HETS amount is suppressed,
and therefore the offset amount does not have to be set to such the
large value. The vicinity of a dotted line shown in FIG. 13 is a
preferable concrete example of an actual offset amount.
[0067] As described above, in the servo writing method of the
present embodiment, it is possible to effectively inhibit the head
positioning precision from being degraded by the HETS in a disk
drive to which the perpendicular magnetic recording system is
applied and which has a high track density exceeding, for example,
100 kTPI.
[0068] It is to be noted that in the present embodiment, only the
bursts A and B have been described as the servo burst signals, but
naturally the present invention may be applied to the servo burst
signals of a usual four-phase bursts A to D system or a six-phase
bursts A to F system. In the servo writing by the STW of the
present embodiment, the direction from the inner periphery to the
outer periphery has been described as the writing direction 21, but
naturally the present invention may be applied to the servo writing
in a reverse direction (from the outer periphery to the inner
periphery). Additionally, in this case, the offset direction is the
direction of the outer periphery.
[0069] As described above, according to the servo writing method of
the present embodiment, since the shift of the servo data in a
radial direction can be compensated based on the HETS phenomenon,
as a result, high-precision servo data can be recorded on the
disk.
[0070] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
representative embodiments shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general invention concept as defined by the
appended claims and their equivalents.
* * * * *