U.S. patent application number 14/177826 was filed with the patent office on 2015-04-16 for head position demodulating method and magnetic disk device.
This patent application is currently assigned to KABUSHIKI KAISHA TOSHIBA. The applicant listed for this patent is KABUSHIKI KAISHA TOSHIBA. Invention is credited to Tatsuhiko KOSUGI, Kazunori MORI, Hiroshi OOYABU.
Application Number | 20150103435 14/177826 |
Document ID | / |
Family ID | 52809449 |
Filed Date | 2015-04-16 |
United States Patent
Application |
20150103435 |
Kind Code |
A1 |
KOSUGI; Tatsuhiko ; et
al. |
April 16, 2015 |
HEAD POSITION DEMODULATING METHOD AND MAGNETIC DISK DEVICE
Abstract
According to one embodiment, a head position demodulating method
and a magnetic disk device switch a demodulation window such that
an amplitude of a fundamental wave component of a null-type burst
pattern transitions from a decreasing direction to an increasing
direction along with an increase in seek speed during demodulation
of the null-type burst pattern recorded on a magnetic disk.
Inventors: |
KOSUGI; Tatsuhiko;
(Yokohama-shi, JP) ; MORI; Kazunori; (Tokyo,
JP) ; OOYABU; Hiroshi; (Fujisawa-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
KABUSHIKI KAISHA TOSHIBA |
Tokyo |
|
JP |
|
|
Assignee: |
KABUSHIKI KAISHA TOSHIBA
Tokyo
JP
|
Family ID: |
52809449 |
Appl. No.: |
14/177826 |
Filed: |
February 11, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61891121 |
Oct 15, 2013 |
|
|
|
Current U.S.
Class: |
360/77.08 |
Current CPC
Class: |
G11B 5/5547 20130101;
G11B 5/59688 20130101 |
Class at
Publication: |
360/77.08 |
International
Class: |
G11B 5/596 20060101
G11B005/596 |
Claims
1. A head position demodulating method, comprising switching a
demodulation window with respect to a null-type burst pattern
recorded on a magnetic disk such that an amplitude of a fundamental
wave component of the null-type burst pattern transitions from a
decreasing direction to an increasing direction corresponding to
seek speed during demodulation of the null-type burst pattern.
2. The method according to claim 1, wherein the demodulation window
is switched such that the amplitude of the fundamental wave
component of the null-type burst pattern does not become
indefinite.
3. The method according to claim 1, further comprising: setting a
first demodulation window during demodulation of the null-type
burst pattern; and switching to a second demodulation window
different from the first demodulation window in a case where the
amplitude of the fundamental wave component of the null-type burst
pattern calculated based on the first demodulation window is within
a predetermined range of a seek speed including a turning point
that turns from a decreasing direction to an increasing direction
along with an increase in seek speed.
4. The method according to claim 3, further comprising switching to
a third demodulation window different from the windows in a case
where the amplitude of the fundamental wave component of the
null-type burst pattern calculated based on the second demodulation
window is within a predetermined range of a seek speed including a
turning point that turns from a decreasing direction to an
increasing direction along with an increase in seek speed.
5. The method according to claim 1, wherein the fundamental wave
component of the null-type burst pattern is a sine component or a
cosine component when a DFT (discrete Fourier transform) operation
is performed on a signal obtained by reading out the null-type
burst pattern using a magnetic head.
6. The method according to claim 1, wherein the demodulation window
is switched to have a different time from a burst center to a
center of the demodulation window, the burst center being a
boundary between an N-phase and a Q-phase of the null-type burst
pattern.
7. The method according to claim 1, wherein respective demodulation
windows of an N-phase and a Q-phase of the null-type burst pattern
are set to be mutually symmetrical with respect to a burst center
as a boundary between the N-phase and the Q-phase of the null-type
burst pattern.
8. The method according to claim 1, wherein the demodulation window
is switched before respective amplitudes of the fundamental wave
component with respect to the seek speed coincide with each other
between the demodulation windows.
9. The method according to claim 1, further comprising performing
speed compensation on the fundamental wave component of the
null-type burst pattern extracted from a signal read out by a
magnetic head in a state where a gain due to a seek speed is
ignored.
10. The method according to claim 9, wherein assuming that a
rotation correction angle due to the seek speed is denoted as
.theta., the gain is given by 1/(cos.sup.2 .theta.-sin.sup.2
.theta.).
11. A magnetic disk device, comprising: a magnetic head; a magnetic
disk that records a null-type burst pattern to determine a position
of the magnetic head on a track based on a read result by the
magnetic head; and a magnetic recording controller configured to:
switch a demodulation window with respect to the null-type burst
pattern such that an amplitude of a fundamental wave component of
the null-type burst pattern transitions from a decreasing direction
to an increasing direction corresponding to seek speed during
demodulation of the null-type burst pattern read by the magnetic
head; and calculate a demodulation position of the magnetic head
based on the fundamental wave component of the null-type burst
pattern.
12. The magnetic disk device according to claim 11, wherein the
magnetic recording controller is configured to switch the
demodulation window such that the amplitude of the fundamental wave
component of the null-type burst pattern does not become
indefinite.
13. The magnetic disk device according to claim 11, wherein the
magnetic recording controller is configured to: set a first
demodulation window during demodulation of the null-type burst
pattern recorded on the magnetic disk; and switch to a second
demodulation window different from the first demodulation window in
a case where the amplitude of the fundamental wave component of the
null-type burst pattern calculated based on the first demodulation
window is within a predetermined range of a seek speed including a
turning point that turns from a decreasing direction to an
increasing direction along with an increase in seek speed.
14. The magnetic disk device according to claim 13, wherein the
magnetic recording controller is configured to switch to a third
demodulation window different from the windows in a case where the
amplitude of the fundamental wave component of the null-type burst
pattern calculated based on the second demodulation window is
within a predetermined range of a seek speed including a turning
point that turns from a decreasing direction to an increasing
direction along with an increase in seek speed.
15. The magnetic disk device according to claim 11, wherein the
fundamental wave component of the null-type burst pattern is a sine
component or a cosine component when a DFT (discrete Fourier
transform) operation is performed on a signal obtained by reading
out the null-type burst pattern using a magnetic head.
16. The magnetic disk device according to claim 11, wherein the
demodulation window is switched to have a different time from a
burst center to a center of the demodulation window, the burst
center being a boundary between an N-phase and a Q-phase of the
null-type burst pattern.
17. The magnetic disk device according to claim 11, wherein
respective demodulation windows of an N-phase and a Q-phase of the
null-type burst pattern are set to be mutually symmetrical with
respect to a burst center as a boundary between the N-phase and the
Q-phase of the null-type burst pattern.
18. The magnetic disk device according to claim 11, wherein the
magnetic recording controller is configured to switch the
demodulation window before respective amplitudes of the fundamental
wave component with respect to the seek speed coincide with each
other between the demodulation windows.
19. The magnetic disk device according to claim 11, wherein the
magnetic recording controller is configured to perform speed
compensation on the fundamental wave component of the null-type
burst pattern extracted from a signal read out by a magnetic head
in a state where a gain due to a seek speed is ignored.
20. The magnetic disk device according to claim 19, wherein
assuming that a rotation correction angle due to the seek speed is
denoted as .theta., the gain is given by 1/(cos.sup.2
.theta.-sin.sup.2 .theta.).
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is based upon and claims the benefit of
priority from Provisional Patent Application No. 61/891,121, filed
on Oct. 15, 2013; the entire contents of which are incorporated
herein by reference.
FIELD
[0002] Embodiments described herein relate generally to a head
position demodulating method and a magnetic disk device.
BACKGROUND
[0003] The magnetic disk device retrieves the sector-cylinder
number in servo data and burst data indicative of location
information on a track, and performs positioning of a magnetic head
based on these information.
BRIEF DESCRIPTION OF THE DRAWINGS
[0004] FIG. 1 is a block diagram illustrating a schematic
configuration of a magnetic disk device according to one
embodiment;
[0005] FIG. 2A is a plan view illustrating a track arrangement in
the magnetic disk of FIG. 1;
[0006] FIG. 2B is a diagram illustrating an exemplary configuration
of a servo area of FIG. 2A;
[0007] FIG. 3 is a diagram illustrating a setting method of a
demodulation window during a seek in the magnetic disk device
according to one embodiment;
[0008] FIG. 4 is a diagram illustrating a waveform of a fundamental
wave component when a null-type burst pattern is scanned in a track
direction in the magnetic disk device according to one
embodiment;
[0009] FIG. 5A is a diagram illustrating a position Lissajous
figure of the fundamental wave component in FIG. 4;
[0010] FIG. 5B is a diagram illustrating a position Lissajous
figure of the fundamental wave component during a seek;
[0011] FIG. 6 is a diagram illustrating a relationship between time
from the burst center and a demodulation window in the magnetic
disk device according to one embodiment;
[0012] FIG. 7A is a diagram illustrating a relationship between a
seek speed and an attenuation rate of a DFT integration value when
the time from the burst center is changed;
[0013] FIG. 7B is a diagram illustrating a switching method of the
demodulation window corresponding to the seek speed;
[0014] FIG. 8 is a diagram illustrating a switching method of
demodulation window corresponding to acceleration or
deceleration;
[0015] FIG. 9A is a diagram illustrating a voice coil current and a
head-position predictive error when the demodulation window is
fixed corresponding to the seek speed; and
[0016] FIG. 9B is a diagram illustrating a voice coil current and a
head-position predictive error when the demodulation window is
switched corresponding to the seek speed.
DETAILED DESCRIPTION
[0017] According to one embodiment, during demodulation of a
null-type burst pattern recorded on a magnetic disk, a demodulation
window is switched such that the amplitude of the fundamental wave
component of the null-type burst pattern transitions from a
decreasing direction to an increasing direction along with an
increase in seek speed.
[0018] Exemplary embodiments of a head position demodulating method
and a magnetic disk device will be explained below in detail with
reference to the accompanying drawings. The present invention is
not limited to the following embodiments.
First Embodiment
[0019] FIG. 1 is a block diagram illustrating a schematic
configuration of a magnetic disk device according to a first
embodiment. FIG. 2A is a plan view illustrating track arrangement
in the magnetic disk of FIG. 1. FIG. 2B is a diagram illustrating
an exemplary configuration of a servo area of FIG. 2A.
[0020] In FIG. 1, the magnetic disk device includes a magnetic disk
2. The magnetic disk 2 is supported via a spindle 10. The magnetic
disk device also includes a magnetic head HM. The magnetic head HM
includes a write head HW and a read head HR. The write head HW and
the read head HR are arranged facing the magnetic disk 2. Here, the
magnetic head HM is held on the magnetic disk 2 via an arm A. The
arm A can slide the magnetic head HM within the horizontal surface,
for example, during a seek.
[0021] Here, as illustrated in FIG. 2A and FIG. 2B, the magnetic
disk 2 includes tracks T along a down-track direction DE. On each
track T, a data area DA to which user data is written and a servo
area SS to which servo data is written are disposed. Here, the
servo areas SS are radially arranged. The data area DA is arranged
between the servo areas SS along the down-track direction DE. To
the servo area SS, as illustrated in FIG. 2B, a preamble 20, a
servo-area mark 21, sector/cylinder information 22, and a burst
pattern 23 are written. The sector/cylinder information 22 can
provide a servo address in a circumferential direction and a radial
direction of the magnetic disk 2, and can be used for seek control
that moves the magnetic head HM to a target track. The burst
pattern 23 can be used for tracking control that positions the
magnetic head HM within a target range of the target track. These
portions of servo data may be recorded on the magnetic disk 2 by
self-servo write or may be recorded on the magnetic disk 2 by a
dedicated servo writer.
[0022] Here, the burst pattern 23 can employ a null-type burst
pattern formed of an N-phase and a Q-phase. For the N-phase and the
Q-phase, magnetized patterns can be disposed such that the
polarities (the N-pole and the S-pole) are alternately inverted at
intervals of 180 degrees (=1 cyl) along a cross-track direction DC.
Furthermore, the N-phase and the Q-phase are arranged to each have
phases mutually shifted by 90 degrees (=0.5 cyl) along the
cross-track direction DC at their boundaries. For example, the
N-phase is arranged to have polarities inverted at the boundaries
between mutually adjacent tracks T1 to T4. The Q-phase is arranged
to have polarities inverted in each center of the tracks T1 to
T4.
[0023] Referring again to FIG. 1, the magnetic disk device includes
a voice coil motor 4 that drives the arm A and a spindle motor 3
that rotates the magnetic disk 2 via the spindle 10. The magnetic
disk 2, the magnetic head HM, the arm A, the voice coil motor 4,
the spindle motor 3, and the spindle 10 are housed in a case 1.
[0024] The magnetic disk device includes a magnetic recording
controller 5. The magnetic recording controller 5 includes a head
controller 6, a power controller 7, a read/write channel 8, and a
hard disk controller 9. Here, the magnetic recording controller 5
can calculate a demodulation position of the magnetic head HM based
on the burst pattern 23 read by the read head HR. At this time, the
magnetic recording controller 5 can switch the demodulation window
such that the amplitude of the fundamental wave component of the
burst pattern 23 transitions from a decreasing direction to an
increasing direction along with an increase in seek speed, during
demodulation of the burst pattern 23 read by the read head HR.
Here, this seek speed is a speed of the magnetic head HM along the
cross-track direction DC when the magnetic disk 2 rotates at a
constant speed.
[0025] The head controller 6 includes a write current controller 6A
and a readout signal detector 6B. The power controller 7 includes a
spindle-motor controller 7A and a voice-coil-motor controller 7B.
The read/write channel 8 includes a discrete Fourier transform
(DFT) demodulator 8A. The hard disk controller 9 includes an
initial-phase correction unit 9A, a speed correction unit 9B, an
azimuth correction unit 9C, a gamma correction unit 9D, a
demodulation-position calculator 9E, and a head-position controller
9F.
[0026] The head controller 6 can amplify and detect a signal during
recording/reading. The write current controller 6A can control a
write current flowing to the write head HW. The readout signal
detector 6B can detect a signal read by the read head HR.
[0027] The power controller 7 can drive the voice coil motor 4 and
the spindle motor 3. The spindle-motor controller 7A can control
rotation of the spindle motor 3. The voice-coil-motor controller 7B
can control driving of the voice coil motor 4.
[0028] The read/write channel 8 exchanges data between the head
controller 6 and the hard disk controller 9. The data includes read
data, write data, and servo data. For example, the read/write
channel 8 can convert a signal read out by the read head HR into a
data format handled by the host HS and can convert data output from
the host HS into a signal format recorded by the write head HW.
These format conversions include DA conversion and encoding. The
read/write channel 8 can perform decode processing on a signal read
out by the read head HR and can perform code modulation on data
output from the host HS. The DFT demodulator 8A can extract the
fundamental wave component when a DFT operation is performed on the
burst pattern 23 with respect to a signal read out by the read head
HR. This fundamental wave component can be the sine component or
the cosine component in the N-phase and the Q-phase of the burst
pattern 23. In the following description, a curved line by
expressing on the phase plane, a relationship between the sine
component of the N-phase and the sine component of the Q-phase in
the burst pattern 23 or a relationship between the cosine component
of the N-phase and the cosine component of the Q-phase in the burst
pattern 23 is referred to as a position Lissajous figure. A curved
line by expressing, on the phase plane, a relationship between the
sine component and the cosine component of the N-phase in the burst
pattern 23 or a relationship between the sine component and the
cosine component of the Q-phase in the burst pattern 23 is referred
to as a complex Lissajous figure. This complex Lissajous figure
draws a real part and an imaginary part of the fundamental wave
component in the burst pattern 23 read out by the read head HR.
[0029] The hard disk controller 9 can perform recording/reading
control based on a command from outside and can exchange data
between the outside and the read/write channel 8. The initial-phase
correction unit 9A rotates the complex Lissajous figure in the
N-phase and the Q-phase of the burst pattern 23, which is read by
the read head HR, by a predetermined angle so as to perform initial
phase correction.
[0030] The speed correction unit 9B performs speed compensation so
as to reduce the ellipticity of the position Lissajous figure of
the fundamental wave component in the burst pattern 23 read by the
read head HR. That is, the phase of the fundamental wave component
in the burst pattern 23 is corrected such that the position
Lissajous figure deformed into an elliptical shape by seeking has a
shape close to a circular shape. The speed correction unit 9B can
switch the demodulation window such that the amplitude of the
fundamental wave component of the burst pattern 23 transitions from
the decreasing direction to the increasing direction along with an
increase in seek speed, during demodulation of the burst pattern
23. Here, the speed correction unit 9B includes a seek-speed
determiner 9G and a demodulation-window switcher 9H. The seek-speed
determiner 9G can determine the seek speed of the magnetic head HM.
The demodulation-window switcher 9H can switch the demodulation
window with respect to the burst pattern 23. At this time, the
demodulation-window switcher 9H can switch the demodulation window
such that the amplitude of the fundamental wave component of the
burst pattern 23 does not become indefinite.
[0031] The azimuth correction unit 9C rotates the position
Lissajous figure of the fundamental wave component of the burst
pattern 23 by a predetermined angle so as to reduce the gradient of
the position Lissajous figure deformed into a rectangular shape due
to the read position of the burst pattern 23 on the magnetic disk
2. The gamma correction unit 9D corrects the arithmetic expression
for obtaining the position of the magnetic head HM from the
fundamental wave component of the burst pattern 23 so as to improve
the linearity of a change in position of the magnetic head HM with
respect to a change in fundamental wave component of the burst
pattern 23. The demodulation-position calculator 9E calculates the
demodulation position of the magnetic head HM based on the
fundamental wave component of the burst pattern 23. The
head-position controller 9F controls the position of the magnetic
head HM based on the calculation result of the demodulation
position of the magnetic head HM.
[0032] The magnetic recording controller 5 is coupled to the host
HS. The host HS may be a personal computer that issues a write
command, a read command, and similar command to the magnetic disk
device, or may be an external interface.
[0033] The following describes operation of the magnetic disk
device in FIG. 1.
[0034] While the spindle motor 3 rotates the magnetic disk 2, a
signal is read out from the magnetic disk 2 via the read head HR
and is detected by the readout signal detector 6B. The signal
detected by the readout signal detector 6B undergoes data
conversion by the read/write channel 8 and then is transmitted to
the hard disk controller 9. In this data convert, the DFT
demodulator 8A performs a DFT operation on the burst pattern 23
with respect to a signal read out by the read head HR so as to
extract the sine components and the cosine components of the
N-phase and the Q-phase in the burst pattern 23. Subsequently, the
hard disk controller 9 calculates the demodulation position of the
magnetic head HM based on the sine components or the cosine
components of the N-phase and the Q-phase in the burst pattern 23
detected by the readout signal detector 6B. In the following
description, a description will be given of an example where the
demodulation position of the magnetic head HM is calculated based
on the sine components of the N-phase and the Q-phase in the burst
pattern 23.
[0035] At this time, the initial-phase correction unit 9A rotates
the complex Lissajous figure by a predetermined angle so as to
reduce the gradient of the long axis of the complex Lissajous
figure in the N-phase and the Q-phase of the burst pattern 23. The
speed correction unit 9B switches the demodulation window such that
the amplitude of the fundamental wave component of the burst
pattern 23 does not become indefinite corresponding to the seek
speed. Subsequently, the speed compensation is performed so as to
reduce the ellipticity of the position Lissajous figure of the sine
components of the N-phase and the Q-phase of the burst pattern 23.
This speed compensation can correct the phase relationship between
the sine components of the N-phase and the Q-phase of the burst
pattern 23. In case of correcting this phase relationship, the gain
due to the seek speed can be ignored. Furthermore, the azimuth
correction unit 9C rotates the position Lissajous figure of the
sine components of the N-phase and the Q-phase of the burst pattern
23 by a predetermined angle so as to reduce the gradient of the
position Lissajous figure deformed into a rectangular shape.
Furthermore, the gamma correction unit 9D corrects the arithmetic
expression for obtaining the position of the magnetic head HM from
the fundamental wave component of the burst pattern 23 so as to
improve the linearity of the change in position of the magnetic
head HM with respect to the change in fundamental wave component of
the burst pattern 23. Subsequently, the demodulation-position
calculator 9E applies the arithmetic expression corrected by the
gamma correction unit 9D to calculate the demodulation position of
the magnetic head HM. Subsequently, the head-position controller 9F
controls the position of the magnetic head HM during a seek based
on the calculation result of the demodulation position of the
magnetic head HM.
[0036] Here, by the switching of the demodulation window such that
the amplitude of the fundamental wave component of the burst
pattern 23 transitions from the decreasing direction to the
increasing direction along with the increase in seek speed, the
amplitude of the fundamental wave component of the burst pattern 23
can be set not to be indefinite even in the case where the seek
speed has increased. This allows improving the linearity during
demodulation of the head position even in the case where the seek
speed increases, thus improving stability at the time of the
termination of seeking. For example, in the case where the
demodulation window is fixed, the limit of the seek speed that
ensures the linearity during demodulation of the head position has
been about 0.3 m/sec. Even in the case where the demodulation
window is narrowed, the limit of the seek speed that ensures the
linearity during demodulation of the head position has been around
0.5 m/sec. In contrast, by switching the demodulation window such
that the amplitude of the fundamental wave component of the burst
pattern 23 transitions from the decreasing direction to the
increasing direction along with the increase in seek speed, the
seek speed that ensures the linearity during demodulation of the
head position can be improved up to around 3 m/sec.
[0037] FIG. 3 is a diagram illustrating a setting method of the
demodulation window during a seek in the magnetic disk device
according to one embodiment.
[0038] In FIG. 3, the magnetic head HM diagonally crosses tracks
2n-1 to 2n+1 (where "n" is a positive integer) during a seek.
Accordingly, at trace points PN and PQ, the magnetic head HM is
located on the boundary between the N-pole and the S-pole.
Therefore, the amplitude of the fundamental wave component of the
burst pattern 23 becomes zero. Here, assuming that the demodulation
windows are denoted by WN and WQ, the trace points PN and PQ are
included. This reduces the amplitude of the fundamental wave
component of the burst pattern 23, thus reducing the linearity
during demodulation of the head position. In contrast, when the
demodulation windows are switched from WN and WQ to WN' and WQ',
the trace points PN and PQ are not included. This increases the
amplitude of the fundamental wave component of the burst pattern
23, thus improving the linearity during demodulation of the head
position compared with the case where the demodulation windows are
WN and WQ.
[0039] FIG. 4 is a diagram illustrating a waveform of the
fundamental wave component when a null-type burst pattern is
scanned along the down-track direction DE in the magnetic disk
device according to one embodiment.
[0040] In FIG. 4, in the case where the magnetic head HM scans the
track T along the down-track direction DE, the sine components of
the N-phase and the Q-phase are shifted by 90.degree. in a phase
relationship.
[0041] FIG. 5A is a diagram illustrating the position Lissajous
figure of the fundamental wave component in FIG. 4. FIG. 5B is a
diagram illustrating the position Lissajous figure of the
fundamental wave component during a seek.
[0042] As illustrated in FIG. 5A, the position Lissajous figure
becomes a circle when the Q-phase is plotted on the X-axis of the
phase plane while the N-phase is plotted on the Y-axis of the phase
plane in the waveform of FIG. 4. Points A to D in FIG. 5A
correspond to respective points A to D in FIG. 4. On the other
hand, during a seek, as illustrated in FIG. 5B, the phase of the
Q-phase and the phase of the N-phase rotate in mutually opposite
directions. Thus, the position Lissajous figure is flattened. At
this time, a rotation angle .theta. is proportional to the seek
speed. Flattening the position Lissajous figure reduces the
linearity of the phase relationship between the sine components of
the N-phase and the Q-phase, thus reducing the demodulation
accuracy of the head position. Accordingly, speed compensation is
performed so as to reduce the ellipticity of the position Lissajous
figure in the speed correction unit 9B.
[0043] Here, assuming that the vector of the sine components of the
N-phase and the Q-phase before the correction is (X, Y) and the
vector of the sine components of the N-phase and the Q-phase after
the correction is (Ux, Uy), the relationship between (X, Y) and
(Ux, Uy) can be given by the following formula.
( X Y ) = ( cos .theta. - sin .theta. sin .theta. cos .theta. ) (
Ux 0 ) + ( cos .theta. sin .theta. - sin .theta. cos .theta. ) ( 0
Uy ) = ( cos .theta. sin .theta. sin .theta. cos .theta. ) ( Ux Uy
) ##EQU00001##
[0044] As illustrated below, inverse conversion on the above
formula allows obtaining (Ux, Uy).
( Ux Uy ) = 1 cos 2 .theta. - sin 2 .theta. ( cos .theta. - sin
.theta. - sin .theta. cos .theta. ) ( X Y ) ##EQU00002##
[0045] With this formula, when .theta.=45+90m ("m" is a positive
integer), (Ux, Uy) becomes indefinite and the head position cannot
be demodulated. Here, the rotation angle .theta. (rad) can be given
by the following formula.
.theta.=Vel/TW.times..pi..times.TB
Here, Vel (m/sec) indicates a seek speed, TW (m) indicates a track
width, TB (sec) indicates time from the burst center (the boundary
between the N-phase and the Q-phase) to the center of the
demodulation window.
[0046] Here, switching the demodulation window allows changing the
time TB from the burst center. Accordingly, also in the case where
the seek speed increases, switching the demodulation window allows
avoiding the state where .theta.=45+90m, thus preventing (Ux, Uy)
from being indefinite.
[0047] FIG. 6 is a diagram illustrating a relationship between the
time from the burst center and the demodulation window in the
magnetic disk device according to one embodiment.
[0048] In FIG. 6, setting respective demodulation windows WN1 and
WQ1 with respect to the N-phase and the Q-phase allows setting the
time TB from the burst center CB to be 40 nsec. Additionally,
setting respective demodulation windows WN2 and WQ2 with respect to
the N-phase and the Q-phase allows setting the time TB from the
burst center CB to be 25 nsec. Additionally, setting respective
demodulation windows WN3 and WQ3 with respect to the N-phase and
the Q-phase allows setting the time TB from the burst center CB to
be 35 nsec. These values of the time TB are examples and the time
TB is not limited to these values.
[0049] Accordingly, switching the demodulation window allows
changing the time TB from the burst center CB so as to prevent (Ux,
Uy) from being indefinite also in the case where the seek speed
increases.
[0050] In order to reduce level difference along with switching of
the demodulation window, the respective demodulation windows WN1,
WQ1, WN2, WQ2, WN3, and WQ3 are preferred to be set with respect to
the N-phase and the Q-phase so as to be mutually symmetrical with
respect to the burst center CB.
[0051] FIG. 7A is a diagram illustrating a relationship between the
seek speed and the attenuation rate of a DFT integration value when
the time from the burst center is changed. FIG. 7B is a diagram
illustrating a switching method of the demodulation window
corresponding to the seek speed. FIG. 7A illustrates respective
attenuation rates of the demodulation windows WN1, WQ1, WN2, WQ2,
WN3, and WQ3 in FIG. 6. This attenuation rate corresponds to the
amplitude of the fundamental wave component of the burst pattern
23. The increase and the decrease in attenuation rate here can
correspond to the increase and the decrease in amplitude of the
fundamental wave component of the burst pattern 23.
[0052] In FIG. 7A, in case of the demodulation windows WN1 and WQ1
(TB=40 nsec), turning points A1 to A3 occur. At the turning points
A1 to A3, the attenuation rate turns from the decreasing direction
to the increasing direction along with the increase in seek speed.
In case of the demodulation windows WN2 and WQ2 (TB=25 nsec),
turning points B1 and B2 occur. At the turning points B1 and B2,
the attenuation rate turns from the decreasing direction to the
increasing direction along with the increase in seek speed. In case
of the demodulation windows WN3 and WQ3 (TB=35 nsec), turning
points C1 to C4 occur. At the turning points C1 to C4, the
attenuation rate turns from the decreasing direction to the
increasing direction along with the increase in seek speed.
[0053] Here, for example, in the case where the demodulation
windows WN1 and WQ1 are fixed, the attenuation rate becomes close
to zero at the turning points A1 to A3. Thus, a seek speed where
(Ux, Uy) becomes indefinite exists. Accordingly, in the case where
the seek speed becomes close to the turning points A1 to A3 when
the demodulation windows WN1 and WQ1 are set, the demodulation
windows are switched to the demodulation windows WN3 and WQ3 or the
demodulation windows WN2 and WQ2 so as to prevent (Ux, Uy) from
being indefinite.
[0054] Accordingly, as illustrated in FIG. 7B, the seek speed is
divided such that a seek speed in the vicinity of the turning point
per each time TB from the burst center CB (hereinafter referred to
as a blank speed) is not included. The vicinity of the turning
point can be set in a range where the attenuation rate is equal to
or less than a predetermined value. For example, in case of the
demodulation windows WN1 and WQ1 (TB=40 nsec), the seek speed is
divided such that a seek speed in the vicinity of the turning
points A1 to A3 is not included. In case of the demodulation
windows WN2 and WQ2 (TB=25 nsec), the seek speed is divided such
that a seek speed in the vicinity of the turning points B1 and B2
is not included. In case of demodulation windows WN3 and WQ3 (TB=35
nsec), the seek speed is divided such that a seek speed in the
vicinity of the turning points C1 to C4 is not included. At the
blank speed of each demodulation window, switching to other
demodulation windows can prevent the attenuation rate from being
equal to or less than a predetermined value.
[0055] For example, a first speed to a sixth speed can be set to a
divided section of the seek speed. The first speed and the third
speed can be assigned to the demodulation windows WN1 and WQ1
(TB=40 nsec). The second speed, the fourth speed, and the sixth
speed can be assigned to the demodulation windows WN2 and WQ2
(TB=25 nsec). The fifth speed can be assigned to the demodulation
windows WN3 and WQ3 (TB=35 nsec). When the seek speed is the first
speed or the third speed, the demodulation windows WN1 and WQ1 can
be selected. When the seek speed is the second speed, the fourth
speed, or the sixth speed, the demodulation windows WN2 and WQ2 can
be selected. When the seek speed is the fifth speed, the
demodulation windows WN3 and WQ3 can be selected.
[0056] Here, in the adjacent speed sections from the first speed to
the sixth speed, overlap portions can be disposed. This allows
switching the demodulation window before the respective amplitudes
of the fundamental wave component of the burst pattern 23 with
respect to the seek speed coincides with each other between the
demodulation windows. For example, in the case where the seek speed
increases when the seek speed is the first speed, the demodulation
windows WN1 and WQ1 can be switched to the demodulation windows WN2
and WQ2 so as to shift the seek speed to the second speed before
the seek speed reaches the upper limit of the first speed. On the
other hand, in the case where the seek speed decreases when the
second speed is the seek speed, the demodulation windows WN2 and
WQ2 can be switched to the demodulation windows WN1 and WQ1 so as
to shift the seek speed to the first speed before the seek speed
reaches the lower limit of the second speed.
[0057] FIG. 8 is a diagram illustrating a switching method of the
demodulation window corresponding to acceleration or
deceleration.
[0058] In FIG. 8, in the case where the seek speed is equal to or
less than the start speed of the second speed during deceleration,
the seek speed transitions from the second speed to the first speed
when the seek speed is equal to or less than the upper limit speed
of the first speed. In the case where the seek speed is equal to or
more than the upper limit speed of the first speed during
acceleration, the seek speed transitions from the first speed to
the second speed when the seek speed is equal to or more than the
start speed of the second speed. In the case where the seek speed
is equal to or less than the start speed of the third speed during
deceleration, the seek speed transitions from the third speed to
the second speed when the seek speed is equal to or less than the
upper limit speed of the second speed. In the case where the seek
speed is equal to or more than the upper limit speed of the second
speed during acceleration, the seek speed transitions from the
second speed to the third speed when the seek speed is equal to or
more than the start speed of the third speed. In the example of
FIG. 8, the first speed to the third speed in FIG. 7B are
described. The same applies to the speed after the third speed.
[0059] FIG. 9A is a diagram illustrating a voice coil current and a
head-position predictive error when the demodulation window is
fixed regardless of the seek speed. FIG. 9B is a diagram
illustrating a voice coil current and a head-position predictive
error when the demodulation window is switched corresponding to the
seek speed.
[0060] In FIG. 9A, respective currents IA, IB, IC, and ID flow to
the voice coil motor 4 when the seeking is turned on. Here, the
current IA is a forward current during acceleration, the current IB
is a reverse current during acceleration, the current IC is a
forward current during deceleration, and the current ID is a
reverse current during deceleration. At this time, fixing the
demodulation window increases respective variations of predictive
errors EA, EB, EC, and ED of the head position. The predictive
errors EA, EB, EC, and ED correspond to the respective currents IA,
IB, IC, and ID. Here, the predictive errors EA, EB, EC, and ED are
differences between an estimated position and a measured position
of the magnetic head HM. The estimated position of the magnetic
head HM can be obtained from the previous measured position and
estimated speed of the magnetic head HM. This estimated speed can
be obtained using an observer that simulates the operation of the
magnetic head HM. The measured position of the magnetic head HM can
be obtained based on the demodulation result of the burst pattern
23 read by the read head HR.
[0061] On the other hand, switching the demodulation window
corresponding to the seek speed allows reducing the variations of
the predictive errors EA, EB, EC, and ED of the head position as
illustrated in FIG. 9B.
[0062] With the above-described embodiment, the demodulation window
is switched such that the amplitude of the fundamental wave
component of the burst pattern 23 transitions from the decreasing
direction to the increasing direction along with the increase in
seek speed, so as to increase the seek speed that ensures the
linearity during demodulation of the head position.
* * * * *