Dynamic magnetic information storage or retrieval – General processing of a digital signal – Data in specific format
Reexamination Certificate
2000-10-06
2003-07-08
Holder, Regina N. (Department: 2651)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Data in specific format
C360S077080
Reexamination Certificate
active
06590729
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic disk drive, more specifically to a magnetic disk drive such as a flexible magnetic disk drive and a rigid magnetic disk drive which acquires information for positioning a magnetic head from a reproduced signal of a servo pattern recorded on a magnetic disk.
2. Description of the Related Art
The most general servo pattern used for positioning a magnetic head of a magnetic disk drive comprises servo bits which are arranged in a staggered layout along the centerline, and a method for positioning (tracking) a magnetic head is known, in which difference between each of the servo bits amplitude is generated to acquire the information on the position in the track-width direction, as described in Japanese Patent Publication No. 47-32012.
FIGS.
2
(
a
) and
2
(
b
) are diagrams illustrating the outline of the conventional “amplitude-detecting servo” system. FIG.
2
(
a
) is a diagram showing the relationship between tracks and a servo pattern, and FIG.
2
(
b
) is a diagram showing an example of reproduced signals obtained from a magnetic head moving on the servo pattern. The case of positioning a magnetic head
10
having a track width of T
wr
on the track #N is considered. As shown in FIG.
2
(
a
), when the magnetic head
10
moves in the direction x in the drawing and passes on patterns P and A to D, the reproduced signals as shown in FIG.
2
(
b
) are obtained. The white and black portions of each of the patterns P and A to D show that the direction of magnetization on the portions of one color of the servo pattern recorded on a magnetic recording medium is opposite to the direction of magnetization on the portions of the other color. That is, in the case of longitudinal recording, the directions of magnetization on the white and black portions are vectors pointing to the opposite directions to each other which have track-direction (x-direction) components in the surface of a medium, while in the case of perpendicular recording, the directions of magnetization on the white and black portions are vectors pointing to the opposite directions to each other which have components perpendicular to the surface of the medium. The pattern of FIG.
2
(
a
) is schematic and actually agrees with the signal period of FIG.
2
(
b
).
When a difference between the amplitude S
A
of the reproduced signal of the pattern A and the amplitude S
B
of the reproduced signal of the pattern B, S
A
−S
B
, is calculated and the magnetic head
10
is caused to move in the track-width direction y, the calculation results in N-POS signal as shown on the right side of FIG.
2
(
a
). Similarly, when a difference between the amplitude S
C
of the reproduced signal of the pattern C and the amplitude S
D
of the reproduced signal of the pattern D, S
C
−S
D
, is calculated and the magnetic head
10
is caused to move in the track-width direction y, the calculation results in Q-POS signal as shown on the right side of FIG.
2
(
a
). By using the above calculated N-POS and Q-POS signals of desired portions as positional signals, the current position of the magnetic head
10
can be known.
Meanwhile, as a servo system different from the above servo system, the so-called “phase-detecting servo” system is disclosed, for example, in Japanese Patent Laid-Open No. 60-10472. FIGS.
3
(
a
) and
3
(
b
) are diagrams illustrating the outline of the conventional “phase-detecting servo” system. The case of positioning the magnetic head
10
having a track width of T
wr
on the track #N is considered. When the magnetic head
10
moves in the direction x and passes on patterns P and A to C shown in FIG.
3
(
a
), the reproduced signals as shown in FIG.
3
(
b
) are obtained, for example. The representation of the white and black portions of each of the patterns P and A to C is the same as that of FIG.
2
. The patterns are at azimuth angles with respect to the magnetic head
10
. Since these angles are too small to make the degradation (azimuth loss) in the reproduced signal a problem, the shapes of the reproduced signals of the patterns are not so different from those of FIG.
2
(
b
). However, the phases of the patterns A, B and C relative to the pattern P vary depending on the position of the magnetic head
10
in the track-width direction y. The phases of the patterns A, B and C on the track #N are defined as P
A
, P
B
and P
C
, respectively. The pattern of FIG.
3
(
a
) is schematic and actually agrees with the signal period of FIG.
3
(
b
).
When the phase shifts P
B
−P
A
and P
C
−P
B
are calculated, an example of the results of the calculations is shown on the right side of FIG.
3
(
a
). By using the above calculated P
B
−P
A
and P
C
−P
B
signals appropriately as positional signals, the current position of the magnetic head
10
can be known. As a method for obtaining the phases P
A
, P
B
and P
C
from the reproduced signals of FIG.
3
(
b
), a method which is disclosed in Japanese Patent Laid-Open No. 6-231552 can be employed, for example.
Further, an example of an amplitude pattern in combination with a method comprising detecting a phase change by distorting the waveform is disclosed in Japanese Patent Laid-Open No. 9-251736. This pattern records a pattern which includes not only the characteristic properties of the conventional amplitude pattern but also the change-with-time property that a portion of a waveform changes while another portion does not. Because of this pattern, the patterns C and D of FIG.
2
(
a
) can be omitted.
Along with an increase in the track density of a magnetic disk drive, a variety of technical factors or factors associated with the production of the magnetic disk drive come to the surface as the factors inhibiting the increase in the track density. Of such factors, geometrical factors ascribed to the track width of a magnetic head and the shape of a servo pattern appears in the form of non-linearity in a positional signal. This includes the effect of a difference between a geometrical track width and an effective track width in a recording pattern in the track-width direction. Further, as for noise in a recording medium or reproduction circuit system, it can be gradually recognized as a relative reduction in signal-to-noise ratio (S/N) relative to the reproduced signal. Further, as for disturbance, the track density can reach its limit when the error for track following control exceeds a margin.
Further, as for the prior art in which the method for detecting a change in a portion of a waveform with time by distorting the waveform is employed together with the amplitude pattern, it has such a defect that as a result of distorting the waveform, other harmonic content is produced other than the harmonic content in the fundamental wave or the waveform before distortion, thereby decoding noise increases.
The present invention has been invented in view of the above points, and the object of the present invention is to provide a method and a device that exhibit better performance against the above factors inhibiting the increase in the track density than that of the current system.
BRIEF SUMMARY OF THE INVENTION
To solve the above problems, in the present invention, the information on the servo pattern or on the position for positioning a magnetic head is multiplexed. That is, the improvement of positioning accuracy is intended by acquiring both the information on the amplitude and the information on the phase from the servo pattern simultaneously and using them effectively while having them complement each other.
It has been recognized that the non-linearity in the positional signal is caused by the mismatch between the width of the servo pattern and the track width of a reproducing head, particularly in the amplitude-detecting system. However, the positions where the non-linearity is liable to occur are limited to some local portions. Thus, by acquiring the information on the phase which is not susceptible to non-linearity together with the infor
Akagi Kyo
Seo Yosuke
Antonelli Terry Stout & Kraus LLP
Holder Regina N.
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