Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
2001-10-30
2004-08-31
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
Reexamination Certificate
active
06785085
ABSTRACT:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH
Not Applicable
REFERENCE TO MICROFICHE APPENDIX
Not Applicable
BACKGROUND OF THE INVENTION
The present invention relates to disc memory systems, and more particularly, to positioning information on magnetic disc media for positioning read/write heads.
During normal operation, most computer systems typically require high-capacity, non-volatile data storage resources. One such data storage resource is a disk drive. A disc drive operates by writing user data to, and reading user data from, a disc-shaped magnetic medium that is organized into tracks. Each track forms an annulus bounded by an inner radius and an outer radius on the disk, where the center of the annulus is the axis of rotation of the disk. In addition to the user data within the tracks, positioning information, known in the art as “servo data,” is typically written periodically among the user data within the tracks. Both the user data on the tracks and servo data between the tracks are magnetic markings written on the media by creating spatially varying magnetization patterns on the media. Read/write heads read data from and write data to the disc medium as the disc rotates about its axis of rotation. The servo data are used to guide the read/write heads to an appropriate position relative to the track being read from or written to.
FIG. 1
(Prior Art) shows a prior art head-disc assembly subsystem
10
of a magnetic disc memory system with an associated servo control system
20
. A disc medium
30
attaches to a spindle motor
40
, enabling rotation of the disc medium
30
about an axis of rotation. Multiple tracks
50
(centerlines only are shown) containing information data are written during a manufacturing process. A head
60
attached to a head arm assembly
70
is connected to a positioner assembly
80
. The servo data from the disc medium
30
are read by head
60
and provided to the servo control system
20
after appropriate pre-amplification by pre-amplifier
76
. The servo control system
20
analyzes the servo data and determines an appropriate correction, if necessary, to return the head to its optimum position over the track
50
. The servo control system
20
communicates the head position correction to the positioner assembly
80
via an positioning signal
90
. The positioner assembly
80
adjusts the position of the head
60
as a function of the positioning signal
90
from the servo control system
20
.
FIG. 2
(Prior Art) shows a single track
50
from the disc medium
30
of
FIG. 1
, subdivided into intervals of user information
54
and position information
56
.
FIG. 3
(Prior Art) illustrates how position information
56
of
FIG. 2
is further subdivided into a servo burst
58
and multiple fields
59
that contain Fill, AGC, INDEX, and ADDRESS information. These later multiple fields
59
are beyond the scope of the present invention, and are therefore not described further.
FIG. 4
(Prior Art) shows a more detailed view of the servo bursts
58
of
FIG. 3
, positioned along several adjacent segments
100
of the tracks
50
on a typical magnetic disc medium
30
. Because the segments
100
are very short arcs of the circular tracks
50
, they are shown in
FIG. 4
as straight, without curvature.
FIG. 4
shows that each individual servo burst
58
is offset both perpendicularly from the center of tracks
110
as well as along the track with respect to the adjacent servo bursts. The purpose of this arrangement is described below.
FIG. 5
(Prior Art) illustrates a read/write head
60
from the subsystem of
FIG. 1
, properly positioned directly over a track segment
100
, about to encounter two servo bursts
58
C and
58
D. The disc medium
30
is spinning about an axis of rotation such that the track segment
100
is moving in the direction of the arrow
102
, with respect to the head
60
. The read/write head
60
is properly positioned over the track segment
100
when the head is situated symmetrically about the track center line
110
of the track segment
100
, as shown.
As the servo bursts
58
pass under the read/write head
60
, the head
60
converts the spatially varying magnetic patterns on the medium
30
that form the bursts
58
, into time varying electrical signals (also referred to herein as the “servo burst readback signal”).
FIG. 6
(Prior Art) illustrates electrical signal
120
and
130
, corresponding to servo bursts
58
C and
58
D, respectively, that the read/write head
60
produces as it passes the bursts
58
C and
58
D. Since the head
60
overlaps equal portions of bursts
58
C and
58
D, the amplitudes of the resulting signals
120
and
130
are substantially equal. The servo control system
20
interprets the equal amplitudes of electrical signals
120
and
130
to mean the head
60
is optimally positioned, and therefore no improvement is necessary.
FIG. 7
(Prior Art) illustrates an example of an improperly positioned head
60
from the subsystem
10
of
FIG. 1
, which is perpendicularly offset from the track centerline
110
of the track
100
. Since the head
60
overlaps more of burst
58
C than burst
58
D, the amplitude of the electrical signal
220
is greater than the amplitude of the electrical signal
230
, as shown in
FIG. 8
(Prior Art). The servo control system
20
interprets the discrepancy between the electrical signals
220
and
230
to mean that the head
60
is not optimally positioned about the centerline. The servo control system
20
generates a positioning signal
90
as a function of amplitude differential between the two electrical signals
220
and
230
, and which of the two signals is larger. The amplitude differential indicates how much correction the servo control system
20
should apply to the head
60
, and which of the two is larger indicates which direction the servo control system
20
should move the head
60
.
FIG. 4
shows that four rows of servo bursts should be used (
58
A,
58
B,
58
C and
58
D) to detect a positioning error and generate a positioning signal
90
to compensate this error. Bursts
58
C and
58
D are used to keep the head on track (within an error of +/− one half of a track width), and bursts
58
A and
58
B are used to determine the direction to move the head
60
if the positioning error is greater than or equal to one half of a track width. Bursts must have substantial length (in the direction of track motion) to achieve an acceptable signal to noise ratio. Therefore a significant portion of the track must be dedicated to positioning information. The more that sectors of the disk
30
are used for servo information, the more important it is to reduce the size of bursts area in order to achieve best areal density in the magnetic recording.
FIG. 4
also shows that a substantial part of the disc area used for servo bursts area, nearly 50 percent, is not used at all. Large gaps between bursts in the direction perpendicular to the track centerline are necessary to avoid superposition of servo burst signals (i.e., crosstalk) from adjacent servo bursts.
FIG. 4
thus shows that the prior art servo burst method suffers from significant area penalty. It is therefore desirable to realize a more efficient servo-burst method that will reduce the percentage of the track dedicated to servo bursts.
It is an object of the present invention to substantially overcome the above-identified disadvantages and drawbacks of the prior art.
SUMMARY OF THE INVENTION
The present invention provides a reduction in the percentage of the area dedicated to read/write head positioning information on a magnetic recording medium by employing servo bursts of different frequencies, thus allowing the servo bursts to be located adjacently in the direction perpendicular to the track center line (i.e., transverse to the center line). The servo burst readback signal corresponding to a particular servo burst on the disk medium is distinguished from the readback signal of an adjacent servo burst by analyzing the associated signal frequencies. Therefore, the invention requir
Guzik Nahum
Stein Anatoli B.
Talalai Alex
Guzik Technical Enterprises
Hudspeth David
McDermott Will & Emery LLP
Tzeng Fred F.
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