Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
1997-08-07
2002-09-24
Burgess, Glenton B. (Department: 2753)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
C360S075000, C360S112000
Reexamination Certificate
active
06456449
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates generally to magnetic head servo control systems and, more particularly, to disk drive position control systems that determine the location of a head relative to disk tracks.
2. Description of the Related Art
In a conventional computer disk drive sector servo system, servo information is stored in servo bursts recorded in a magnetic storage material as a series of magnetic flux reversals. When the disk rotates beneath a read/write head, a magnetic read element of the head senses the changes in flux and produces a varying electrical readback signal. The electrical signal can be decoded to indicate the head position relative to tracks of the disk. In this way, the read/write head can be accurately positioned relative to data tracks of the disk for data read and write operations.
Each disk surface of a sector servo disk drive includes concentric or spiral tracks that are divided into radial sectors having a short servo track information area followed by a customer data area. The servo track information area typically includes a sector marker, track identification data, and a servo burst pattern. The sector marker indicates to the data read/write head that servo information immediately follows in the track. The servo read head can be the same head used for reading data or can be a separate, dedicated servo head. The servo pattern readback signal is demodulated to produce a position error sensing (PES) signal. The PES signal is used to generate a corrective input signal that is applied to the read/write head positioning servo.
FIG. 1
shows a conventional disk drive system
20
having a rotatable storage disk
22
and a rotary arm
24
that is moved by a servo motor
26
. The read/write head
28
is suspended over the disk at one end of the arm. The disk
22
has concentric tracks
30
and is divided into sectors that are defined by radially spaced sector marker fields
32
, of which two are shown. It should be understood that conventional disk drives typically contain approximately one hundred sectors and more than 5000 data tracks; fewer are indicated in
FIG. 1
for simplicity of illustration. Customer data is recorded by a user into the track spaces
33
between the sector markers. The read/write head
28
produces a readback signal when reading information from the disk
22
and receives a write signal when recording information onto the disk surface. The readback signal and write signal are carried to and from the read/write head
28
over data and servo lines
34
, which are coupled to a disk drive controller
36
.
When the read/write head
28
is located over servo information recorded into the disk, the disk controller
36
receives position information and in response generates a position error sensing (PES) signal that indicates the position of the head relative to a disk track. The PES signal is used by the disk drive controller
36
to generate servo commands that control the servo motor
26
, and are provided over a servo line
38
to maintain the head in a correct (centered) position.
FIG. 2
shows the read/write head
28
of
FIG. 1
in greater detail. The head
28
comprises what is commonly referred to as a magneto-resistive (M-R) head, which includes an M-R read element
40
and an inductive write element
42
. The M-R read element
40
is placed on a non-magnetic support piece
44
over which is formed the write element
42
. The write element includes a magnetic gap
46
formed at the top of a pair of magnetic pole pieces
41
,
43
joined at the other end
45
, and electromagnetic coils sandwiched therebetween (not shown in FIG.
2
). Two electrical wires
48
,
50
are connected to read contacts
52
,
54
and carry the sensed readback signal from the M-R head read element
40
back to signal processing circuitry
56
. The combined read/write head shown in
FIG. 2
permits a single head to include both read and write elements and thereby simplifies production and design.
The read/write head
28
is shown in
FIG. 2
above a track
60
of the disk
22
. The extent of a data track is represented by the data track width (DTW) shown in FIG.
2
. The servo information is recorded in servo pattern bursts that have a width approximately equal to the track width DTW.
FIG. 2
also shows the extent of the servo sensing width (SSW), the width of the portion of servo information sensed by the head
28
and used by the disk drive controller
36
in maintaining the head centered above a disk track. It should be appreciated that data tracks and servo tracks are located in separate circumferential regions of the disk, as shown in
FIG. 1
, but that the DTW and SSW are shown in
FIG. 2
together, juxtaposed only for illustration of relative size.
The disk controller
36
controls the servo motor
26
(
FIG. 1
) to maintain the read/write head
28
above a track
60
of the disk
22
in response to the head readback signal. The track
60
represents one of the tracks
33
illustrated in
FIG. 1
; therefore, tracks for storing data will be repeated across the disk
22
at an interval of one DTW wide. As noted above, the head readback signal is generated from sensed servo pattern bursts. The servo pattern bursts are recorded in the disk tracks as magnetic field transitions that extend radially across the width of the disk tracks
33
.
FIG. 3A
shows a conventional servo burst pattern comprising an A, B, C, D quadrature burst pattern that is repeated radially within servo information portions of the disk (FIG.
1
). The tracks run horizontally across the sheet, from left to right. The numbers of respective tracks
33
are shown along the left side of the drawing figure and indicate respective track and half-track centerlines. Thus, the horizontal lines aligned with Tracks N and N+1.0 indicate the centerlines of disk track N and N+1, respectively, and the line aligned with N+0.5 indicates the halfway position between these tracks. Each of the quadrature servo bursts A, B, C, D shown in
FIG. 3A
is approximately one full data track width (DTW) across. Thus, the top-left “A” servo burst of
FIG. 3A
extends approximately from track N−1.0 to track N. The adjacent “B” servo burst extends approximately from track N to track N+1.0 and the adjacent “C” servo burst extends approximately from track N−0.5 to track N+0.5. The full “D” servo burst shown in
FIG. 3A
extends approximately from half track position N+0.5 to half track N+1.5.
It should be understood that servo pattern widths other than the one-track width shown in
FIG. 3A
are possible. For example, many disk drive systems currently utilize servo patterns that are two-thirds or one-half width of a data track, rather than the one-track width shown. Moreover, it is not necessary to use the quadrature servo bursts shown in FIG.
3
A. It also is common to use dual burst servo patterns. Dual burst servo patterns generally comprise either the A, B servo bursts or the C, D servo bursts of the quadrature pattern illustrated in FIG.
3
A.
Customer data to be recorded into and read from the data tracks cannot occupy the full width of a data track, because otherwise the magnetic field emitted by the read/write head upon recording data in one track would interfere with data recorded in adjacent tracks. Therefore, the write head is typically less than one data track wide, often approximately 85% of DTW. Recording at less than full width and spacing the customer data apart from track to track by increments of approximately one DTW ensures that data recording can take place safely in adjacent tracks.
In the sector servo disk illustrated in
FIG. 1
, the read element
40
of the read/write head
28
is used to read both servo information and customer data recorded on the disk. The read element is typically optimized for reading the customer data, which will be recorded on the disk
22
with the write element
42
. For improved reading of customer data, the width of the read element
40
should be less than the width of
Belser Karl Arnold
Cheung Wayne Leung
Freitas Dave Anthony
Hong Ju-Hi John
Krounbi Mohamad Towfik
Burgess Glenton B.
Gray Cary Ware & Freidenrich
Kunzler Brian C.
Wang K.
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