Dynamic magnetic information storage or retrieval – Monitoring or testing the progress of recording
Reexamination Certificate
2002-03-22
2004-04-06
Faber, Alan T. (Department: 2651)
Dynamic magnetic information storage or retrieval
Monitoring or testing the progress of recording
C360S077080, C360S048000, C360S046000
Reexamination Certificate
active
06717760
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an information recording apparatus provided with a magnetic conversion head and a magnetic recording medium, more particularly to a magnetic recording disk apparatus that has improved its track density.
Generally, in order to make a head follow up an object data track on a magnetic recording disk medium, the magnetic recording disk apparatus must enable relative positional information between the head and the magnetic recording disk medium to be kept measured accurately and a positional deviation caused by a thermal expansion difference between both magnetic recording disk medium and the arm that supports the head, as well as an influence of such a disturbance as rotation vibration of the spindle motor and the rotary actuator to be reduced. This is why special patterns for positioning the head are recorded on the magnetic recording disk medium before the shipping. The area in which such a pattern is recorded as shown in
FIG. 6
is referred to as a servo area
31
. The servo area
31
is formed between data areas
33
via a gap area
32
. After the shipping, it is inhibited that the user records data in this servo area
31
. In the servo area
31
is recorded data continuously between adjacent tracks
16
in the radial direction. The servo track width
311
is equal to the track pitch of the tracks
16
. On the other hand, in a data area
33
, recorded data on each track
16
is separated from another. The recording track width
331
is narrower than the track pitch of the tracks
16
. Actually, 60 to 100 servo areas
31
are formed at equal pitches on a round of track
16
of the magnetic recording disk medium.
FIG. 7
shows a configuration of such a servo area
31
. An ISG part
40
is a continuous pattern provided so as to reduce the influence of the distribution of the magnetic property in the recording film and the distribution of the flying height of the magnetic recording disk medium. The servo decoder circuit reads back the ISG part
40
by turning on the auto gain control (AGC). Upon detecting an AM part
41
, the AGC is turned off, thereby the magnetic recording disk apparatus of the present invention normalizes the read-back amplitude of the subsequent burst parts
43
with the amplitude of the ISG part
40
. A gray code part
42
describes the track number information of each track
16
with a gray code. This part
42
often describes sector number information, as well. The burst part
43
makes a houndstooth check pattern for obtaining accurate positional information in the radial direction. This part
43
is indispensable for following up the center of each track
16
accurately. This pattern
43
consists of a pair of A-burst
43
-
1
and B-burst
43
-
2
that are provided as straddle the center of each track
16
alternately, as well as C-burst
43
-
3
and D-burst
43
-
4
that are provided as straddle the edge of each track
16
alternately. A pad part
44
is a pattern provided so as to absorb the delay of the decoder circuit system to keep generating a clock while the servo decoder circuit reads back the servo area
31
.
The head
11
reads back the servo areas
31
while running on the position C shown with an arrow from left to right in FIG.
7
. FIG.
8
(A) shows an example of the read-back waveform at that time. To simplify the description, the read-back waveforms of the AM part
41
, the gray code part
42
, and the pad part
44
are omitted here. The servo decoder circuit
44
detects the amplitudes of the four burst parts (from the A-burst part
43
-
1
to the D-burst part
43
-
4
). The amplitude value of each burst part is converted to a digital value in the AD converter, then entered to a CPU. The CPU then calculates the difference between the amplitudes of the A-burst part
43
-
1
and the B-burst part
43
-
2
, thereby finding the N position signal. Although an equation for normalizing the difference with the amplitude of the ASG part
40
is described in
FIG. 7
, this function is realized by hardware in which the servo decoder circuit locks the AGC so as to fix the amplitude of the ISG part
40
. In the same way, the CPU obtains the Q position signal from the difference between the amplitude values of the C-burst part
43
-
3
and the D-burst part
43
-
4
.
FIG. 8B
shows the position signals of the head, which are generated as described above. The N position signal becomes
0
at a position where the center of the head
11
straddles the A-burst part
43
-
1
and the B-burst part
43
-
2
equally. The N position signal becomes positive or negative almost in proportion to a deviation from this center position. For example, the N position signal at the position C shown in
FIG. 8B
can be obtained from the read-back waveform shown in FIG.
8
(A) at the position C shown in FIG.
7
. Usually, it is assumed that the edges of both A-burst part
43
-
1
and B-burst part
43
-
2
match with the center of each track
16
.
The CPU inverts the status (positive
egative) of the N or Q position signal, whichever is smaller in absolute value, then links the signals, thereby generating a continuous position signal. This position signal is then compared with a target position, thereby finding an optimal current value to be applied to a voice coil motor
14
so as to perform such predetermined operations as following-up and seeking.
A technique for forming a spiral data track itself is disclosed in Japanese Published Unexamined Patent Application No.62-204476, No.63-112874, and No.61-296531 respectively. A technique for forming spiral servo information itself is disclosed in FIG. 1 of Japanese Published Unexamined Patent Application No.62-204476.
BRIEF SUMMARY OF THE INVENTION
The above conventional techniques, however, have been confronted with a problem that non-uniformity of the direction of magnetization in the read-back element degrades the linear accuracy of the position signal, thereby the radial position of the head cannot be controlled accurately. In addition, those conventional techniques have also been confronted with a problem that because the detection accuracy of the position signal is degraded by a property variation of the read-back element, the radial position of the head cannot be-controlled accurately.
In the recent years, however, it is common that a high read sensitivity head is used to increase the recording density of the object magnetic recording disk apparatus. For example, there are well-known techniques for using a read-back head that employs a magnetoresistive element (MR element) that makes good use of the magnetoresistive effect of the magnetic film itself, a giant magnetoresistive element (GMR element) that has improved the magnetoresistive effect with a non-magnetic film sandwiched by magnetic films, or a tunnel magnetoresistive element (TMR element) that has improved the magnetoresistive effect more with use of a phenomenon that a tunnel current is changed by an external magnetic field significantly. Those techniques are all effective, since each of those magnetoresistive elements can obtain a favorable SN ratio even in reading back fine recorded patterns on magnetic recording disks, thereby the bit density of the object magnetic recording disk apparatus can be improved.
Generally, both ends of a magnetoresistive element are structured so as to enable a bias magnetic field (vertical bias magnetic field) to be applied in the width direction of the track, thereby forming the magnetic film of the element in a single magnetic domain structure. Consequently, the read-back sensitivity is degraded with respect to the strength of the leakage magnetic field of the object disk at both ends of the element, thereby the output is not made in uniform in the width direction of the track. In addition, because the magnetizing direction is disturbed at both ends of the element, the amplitude value may differ significantly between positive side and negative side of the read-back waveform. And furthermore, the non-uniformity of the magnetizing direction, which is a problem mentioned h
Hamaguchi Takehiko
Takano Hisashi
Tomiyama Futoshi
Zaitsu Hideki
Faber Alan T.
Hitachi Global Storage Technologies Japan Ltd.
Mattingly Stanger & Malur, P.C.
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