Dynamic magnetic information storage or retrieval – General processing of a digital signal – Data in specific format
Reexamination Certificate
2000-07-13
2004-07-06
Hudspeth, David (Department: 2697)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Data in specific format
C360S077080, C360S078140
Reexamination Certificate
active
06760172
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an information recording apparatus provided with a magnetic head and a magnetic disk; and, more particularly, the invention relates to a magnetic disk drive whose track density is significantly improved.
A magnetic disk drive positions its head by use of a rotary actuator on a magnetic disk rotated by a spindle motor, thereby recording/reproducing information magnetically from/on many tracks formed on the magnetic disk concentrically. In order to follow a target data track, it is required to precisely measure the relative position between each head and the magnetic disk, thereby reducing any misalignment caused by a difference in thermal expansion, as well as the influence of such disturbances as the vibration of the spindle motor and the vibration rotary actuator during rotation. The information which indicates the relative position between the head and the magnetic disk is provided in the form of a head position signal. It is essential to produce this head position signal as accurately as possible so as to improve the track density. To achieve this object, there is a technique employed widely, as disclosed in Japanese Patent Prepublication No. 58-222468. The technique obtains the head position signal from each shipment pattern written on the magnetic disk before the delivery of the magnetic disk drive. The special pattern is referred to as a servo pattern.
FIGS. 13A
to
13
D show how a servo pattern is formed up in a servo area
31
with use of a servo track writer. The servo track writer, as disclosed, for example, in Japanese Patent Prepublication No. 64-48276, is used to write tracks at equal pitches on a magnetic disk. In this case, a description will be given of a conventional technique that has been employed widely; wherein, one track is divided into two so as to write a servo pattern therein respectively.
How servo patterns are written in three consecutive tracks on the magnetic disk sequentially is shown in
FIGS. 13A
,
13
B,
13
C, and
13
D. Usually, because the core width of the write element of the magnetic head is wider than a half of a track, a servo pattern becomes wider than the target track just after the pattern writing. For example, the width of the servo pattern newly written in track
16
-
2
in
FIG. 13A
is wider than the width of the servo pattern written in the track
16
-
1
. Following this process, a servo pattern written at the previous rotation of the magnetic disk is erased at one side before another servo pattern is written as shown in
FIGS. 13B and 13C
.
Then, as shown in
FIG. 14A
, after the magnetic disk is rotated several times, four patterns from A burst
43
-
1
to D burst
43
-
4
are formed into the same width as that of one track. An ISG part
40
and an AM (Address Mark) part
41
are formed as consecutive patterns in the track width direction. When a servo pattern is written actually, it needs a time for moving the head only by a half of the track pitch in the track width direction. In the case of a method of rotating the magnetic disk idly once between the states in the charts
13
A and
13
B,
13
B and
13
C, and
13
C and
13
D, respectively, servo patterns are written in the servo areas of one track while the magnetic disk is rotated twice.
FIGS. 14B and 14C
show how a head position signal is generated from a servo pattern formed in the servo area
31
. In the pattern shown in
FIG. 14A
, the ISG part
40
is a continuous pattern formed so as to reduce the influence of the magnetic irregularities of the medium or the fluctuation of the flying height of the magnetic disk. A servo decoder block activates an auto gain control (AGC) so as to reproduce the ISG part
40
. The AGC is turned off when the AM part
41
is detected, thereby providing a function for normalizing the following reproduced width of the following burst part
43
at an amplitude of the ISG part
40
. A Gray code part
42
describes the track number of each track
16
with a Gray code. In this part there is often described sector number information, as well. The burst part
43
is formed as a checker-like pattern so as to obtain accurate information on the target position in the radial direction of the magnetic disk. It is necessary for the head to follow the center of each track accurately. This pattern is formed so that the center between A burst
43
-
1
and B burst
43
-
2
or between C burst
43
-
3
and D burst
43
-
4
is aligned with the center of each track
16
. A pad part
44
is formed so as to absorb the delay of the decoder block system so that clock generation is maintained, while the servo decoder block reproduces the servo area
31
.
The head
11
provided with a read element reproduces servo patterns while running on the position A from left to right as shown in FIG.
14
A.
FIG. 14B
shows an example of the reproduced waveform at this time. The reproduced waveforms of the AM part
41
, the Gray code part
42
, and the pad part
44
are omitted here so as to simplify the description. The servo decoder block detects the amplitudes of the four bursts from A burst
43
-
1
to D burst
43
-
4
. The amplitude of each burst is converted to a digital value by an A/D converter and transferred to a CPU. The CPU calculates the difference between amplitudes of the A burst
43
-
1
and the B burst
43
-
2
, thereby calculating a position signal N. In
FIGS. 14A-14C
, expressions are also shown. Each expression normalizes such a difference between amplitudes with the ISG amplitude.
To provide this function of normalization, the servo decoder block controls the AGC so as to fix the amplitude of the ISG
40
. In the same way, the Q position signal is calculated from the difference of amplitude between the C burst
43
-
3
and the D burst
43
-
4
.
FIG. 14C
shows a head position signal generated as described above. The position signal N becomes 0 at position B where the center of the head is positioned at equal distances to both the A burst
43
-
1
and the B burst
43
-
2
. The N position signal is switched between positive and negative in proportion to the misalignment distance from this center position. For example, the position signal N is obtained from the reproduced waveform of the position C shown in
FIG. 14A
at the position C shown in FIG.
14
C. The CPU compares the absolute value of the position signal N with the absolute value of the position signal Q, thereby inverting the positive
egative states of those position signals N and Q and linking them so as to generate continuous position signals, respectively. In many servo patterns, the position where the position signal N becomes 0 is set as a following center, thereby controlling the voice coil motor for driving the head. If there is no misalignment between the write element and the read element in the track width direction, the edge of each of A burst
43
-
1
and B burst
43
-
2
is aligned to the center of each track
16
.
The use of the above conventional technique can therefore reduce the misalignment caused by the difference in thermal expansion, as well as the influence of such disturbance as the vibration of the spindle motor and the rotary actuator during rotation. Consequently, the accuracy of following each target data track can be improved, thereby further improving the track density.
However, the above conventional technique has an inherent a problem; that is, when a servo area is written with use of a servo track writer, the vibration of the servo track writer is fixed on the magnetic disk as a difference in position between servo patterns in servo areas. In particular, because the non-repeatable run-out that does not depend on the rotational position of the disk adds up error components that are different among tracks, there is no effective method for removing the non-repeatable run-out. Because a servo area, once it is formed, cannot be rewritten after the shipment of the magnetic disk drive, the head comes to follow servo patterns in each of which error components are added up. According to a technique disclosed in
Hamaguchi Takehiko
Tomiyama Futoshi
Zaitsu Hideki
Antonelli Terry Stout & Kraus LLP
Hudspeth David
Rodriguez Glenda
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