Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
1998-08-13
2004-01-13
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
C360S078140
Reexamination Certificate
active
06678109
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a disk drive, a servo control unit, and a control unit, and more particularly to a disk drive, a servo controller, and a controller which have realized high-degree control by lightening processing load to a microprocessor unit (MPU) without increasing cost.
2. Description of Related Art
In hard-disk drives (HDDs) employing magnetic disks as data storage media, concentric circular recording tracks are formed on the magnetic disk. In a conventional HDD, as shown for example in
FIG. 2
, circular tracks
202
with a predetermined width are formed concentrically on the recording surface of a magnetic disk
201
. The recording surface is provided at predetermined-angle intervals with servo areas on which servo patterns
203
are recorded. In addition, between adjacent servo areas there is provided a data sector
205
on which a data area
204
is recorded.
In the aforementioned conventional HDD, if a sector is specified from an outside unit and recording/regeneration is instructed, the head
206
will be moved to a target track on which the sector specified for recording/regeneration has been recorded (seek control). After the head
206
has arrived at the target track, the head position is adjusted so that the head
206
follows the target track (following control). The servo control, such as seek control and following control, is performed by driving a head arm
207
with the head
206
attached thereto by means of a voice coil motor (VCM)
208
.
A description will hereinafter be made of the following control.
Each servo sector
303
, as shown in
FIG. 3
, records a cylinder ID number (CYLID) indicating a track number, a physical sector number (SECCNT) indicating a servo pattern number, burst patterns (WEDGE-A, WEDGE-B, WEDGE-C, WEDGE-D) for tracking (following) control, and so on.
The cylinder ID number CYLID is recorded with special notation called a gray number code. Unlike normal binary-coded notation, the gray number code is defined so that each time a value increases by 1, only a single point in a bit pattern changes. In the gray number code, even when the head
306
flies between the cylinder ID numbers CYLIDn and CYLIDn−1, either value is always obtained.
The physical sector number SECCNT is a number for identifying each individual servo pattern. Even when the radial position varies, this number does not change, so it is recorded with binary-coded notation.
The burst patterns (WEDGE-A, WEDGE-B, WEDGE-C, WEDGE-D) are magnetic patterns for removing the uncertainty of the cylinder ID number CYLID such as described above, deciding over which track the head is positioned among adjacent tracks, and also detecting a detail position on a track. The burst patterns, as shown in
FIG. 3
, are recorded so that the radial recorded positions of the burst patterns each having the width of two track pitches as one cycle differ from each other by half the track pitch.
If the head
306
passes over tracks constructed as described above, the regenerated outputs CYLID, SECCNT, WEDGE-A, WEDGE-B, WEDGE-C, and WEDGE-D will appear in this order on the output of the magnetic head
306
. The regenerated levels A, B, C, and D of these burst patterns WEDGE-A, WEDGE-B, WEDGE-C, and WEDGE-D change in correspondence with the position of the head
306
.
FIG. 4
shows a change in the regenerated level of each burst pattern in the case where the center position of the head
306
(as shown in
FIG. 3
) changes from one end of a track n−1 to one end of a track n+2. Each of the regenerated levels A, B, C, and D changes linearly in correspondence with the position of the head
306
when the head
306
is in a predetermined range. Also, A+B and C+D are nearly constant, respectively. For this reason, from the regenerated output levels of the burst patterns a position error signal (PES) can be detected. On this PES, there are two kinds: a master PES (MPES) employing the aforementioned A and B and a slave PES (SPES) employing C and D. The MPES and the SPES are computed by the following equations:
M
P
E
S
=
A
-
B
A
+
B
×
H
+
80
h
=
2
A
A
+
B
×
H
+
80
h
-
H
(
1
)
S
P
E
S
=
C
-
D
C
+
D
×
H
+
80
h
=
2
C
C
+
D
×
H
+
80
h
-
H
(
2
)
where 00h≦A, B, C, and D≦FFh and H is the head coefficient (00h≦H≦7Fh, 7F and vicinity). The value areas of the master position error signal MPES and the slave position error signal SPES are both greater than 01h and less than FFh.
In the case where the magnetic head
306
passes over the center of a track n, A and B become equal to each other, so 2A/(A+B) becomes 1 and MPES becomes 80h. Also, in the case where the magnetic head
306
is offset from the center of the track n in the downward direction in
FIG. 3
, does not pass over WEDGE-A, and passes over only WEDGE-B, A becomes 0, so 2A/(A+B) becomes 0 and MPES becomes 0h. Conversely, in the case where the magnetic head
306
is offset from the center of the track n in the upward direction in
FIG. 3
, passes over only WEDGE-A, and does not pass over WEDGE-B, B becomes 0, so 2A/(A+B) becomes 2 and MPES becomes FFh (or CYLID become 00h on a track n+1).
Referring again to
FIG. 2
, the aforementioned calculation is performed by an MPU equipped in a hard disk controller (HDC)×9, or a digital signal processor (DSP) or an MPU (hereafter referred to as simply an MPU and the like) provided separately from the HDC
209
. Also, the MPU and the like compute an operational parameter based on the computed MPES and SPES, compute control data (DACOUT) for driving the VCM
208
, based on the operational parameter, and supply the control data to the VCM
208
. The VCM
208
changes the position of the head
206
, based on the supplied control data. In this way, the head
206
follows the track
202
. By controlling the timing of recording/regeneration in such a state, recording/regeneration can be performed on a target sector.
Based on the cylinder ID number CYLID regenerated in the aforementioned way, a track number TRK over which the current head is positioned is detected. Also, the PES obtained in the aforementioned way is added to the track number TRK and the added value is supplied to the HDC
209
as position information (POS) indicating the position of the head.
The HDC
209
generates servo data based on the specified target track and the current head position, controls an operation of the VCM×8, and moves the head
206
to the target track. If the head
206
arrives over the target track, the HDC
209
will execute following control such as described above and perform control of recording/regeneration. An enhancement in the track density and a reduction in the seek time can be realized by executing the aforementioned following control and seek control precisely or at high speed.
However, as described above, in the case where servo control, such as seek control and following control, is performed by the MPU provided in the HDC, if operating speed and control precision are attempted to be enhanced, control load to the MPU within the HDC will be increased. For this reason, there are limits to enhancements in the operating speed and the control precision.
Also, in the case where a DSP or an MPU is provided separately from the MPU provided within the HDC for seek control and following control, the device fabrication cost will be raised to more than necessary, because the DSP or the MPU includes functions not needed for servo control.
It can be seen that there is a need for a disk drive which is capable of enhancing operating speed and control precision without increasing cost.
SUMMARY OF THE INVENTION
To overcome the limitations in the prior art described above, and to overcome other limitations that will become apparent upon reading and understanding the present specification, the present invention discloses a disk d
Kagami Naoyuki
Murakami Masayuki
Nakagawa Yuzo
Sakai Tatsuya
Crawford & Maunu PLLC
Davidson Dan I.
Hitachi Global Technologies
Hudspeth David
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