Programmable, variable data track pitch

Details Programmable, variable data track pitch Programmable, variable data track pitch

1998-08-13

2001-07-03

Hudspeth, David (Department: 2651)

Dynamic magnetic information storage or retrieval

General processing of a digital signal

Data in specific format

C360S077080, C360S078140

Reexamination Certificate

active

06256160

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to magnetic storage devices and, more particularly, to computer disk drives.
BACKGROUND OF THE INVENTION
A disk drive system is a digital data storage device that stores information within concentric tracks on a storage disk. The storage disk is coated with a magnetic material that is capable of changing its magnetic orientation in response to an applied magnetic field.
During operation of a disk drive,the disk is rotated about a central axis at a substantially constant rate. To read data from or write data to the disk, a magnetic transducer is positioned above a desired track of the disk while the disk is spinning.
Writing is performed by delivering a write signal having a variable current to the transducer while the transducer is held close to the desired track. The write signal creates a variable magnetic field at a gap portion of the transducer that induces magnetic polarity transitions into the desired track. The magnetic polarity transitions are representative of the data being stored.
Reading is performed by sensing the magnetic polarity transitions on a track with the transducer. As the disk spins below the transducer, the magnetic polarity transitions on the track present a varying magnetic field to the transducer. The transducer converts the varying magnetic field into an analog read signal that is then delivered to a read channel for appropriate processing. The read channel converts the analog read signal into a properly timed digital signal that can be further processed and then provided to a host computer system.
The transducer can include a single element, such as an inductive read/write element for use in both reading and writing, or it can include separate read and write elements. Transducers that include separate elements for reading and writing are known as “dual element heads” and usually include a magneto-resistive (MR) read element for performing the read function.
Dual element heads are advantageous because each element of the transducer can be optimized to perform its particular function. For example, MR read elements are more sensitive to small variable magnetic fields than are inductive heads and, thus, can read much fainter signals from the disk surface. Because MR elements are more sensitive, data can be more densely packed on the surface with no loss of read performance.
MR read elements generally include a strip of magneto-resistive material that is held between two magnetic shields. The resistance of the magneto-resistive material varies almost linearly with the applied magnetic field. During a read operation the MR strip is held near a desired track, specifically, within the varying magnetic field caused by the magnetic transitions on the track. A constant current is passed through the strip resulting in a variable voltage across the strip. By Ohm's law (i.e., V=IR), the variable voltage is proportional to the varying resistance of the MR strip and, hence, is representative of the data stored within the desired track. The variable voltage signal (which is the analog read signal) is then processed and converted to digital form for use by the host.
A standard disk drive, generally designated
10
, is illustrated in FIG.
1
. The disk drive comprises a disk
12
that is rotated by a spin motor
14
. The spin motor
14
is mounted to a base plate
16
. An actuator arm assembly
18
is also mounted to the base plate
16
.
The actuator arm assembly
18
includes a transducer
20
mounted to a flexure arm
22
, which is attached to an actuator arm
24
that can rotate about a bearing assembly
26
. The actuator arm assembly
18
includes a voice coil motor (VCM)
28
, which moves the transducer
20
relative to the disk
12
. The spin motor
14
, VCM
28
and transducer
20
are coupled to a number of electronic circuits
30
mounted to a printed circuit board
32
. The electronic circuits
30
typically include one or more read channel chips, a microprocessor-based controller and a random access memory (RAM), among other things.
Instead of having a single disk
12
as shown in
FIG. 1
, as is well-known in the art, the disk drive
10
may include a plurality of disks
12
. In such case, each of the plurality of disks
12
would have two sides, with magnetic material on each of those sides. Therefore, two actuator arm assemblies
18
would be provided for each disk
12
.
Referring now to
FIG. 2
, data is stored on the disk
12
within a number of concentric radial tracks
40
(or cylinders). Each track is divided into a plurality of sectors
42
. Each sector
42
is further divided into a servo region
44
and a data region
46
.
The servo regions
44
of the disk
12
are used to, among other things, accurately position the transducer
20
so that data can be properly written onto and read from the disk
12
. The data regions
46
are where non-servo related data (i.e., user data) is stored and retrieved. Such data, upon proper conditions, may be overwritten.
FIG. 3
shows portions of tracks
40
for a disk
12
drawn in a straight, rather than arcuate, fashion for ease of depiction. To accurately write data to and read data from the data region
46
of the disk
12
(see FIG.
2
), it is desirable to maintain the transducer
20
in a relatively fixed position with respect to a given track's centerline
48
during each of the writing and reading procedures. Tracks n−1 through n+4, including their corresponding centerlines
48
, are shown in FIG.
3
.
To assist in controlling the position of the transducer
20
relate to the track centerline
48
, the servo region
44
contains, among other things, servo information in the form of servo patterns
50
comprised of one or more groups of servo bursts, as is well-known in the art. First, second, third and fourth servo bursts
52
,
54
,
56
,
58
(commonly referred to as A, B, C and D servo bursts, respectively) are shown in FIG.
3
. The servo bursts
52
,
54
,
56
,
58
are accurately positioned relative to the centerline
48
of each track
40
. Unike information in the data region
46
, servo bursts
52
,
54
,
56
,
58
may not be overwritten or erased during normal operation of the disk drive
10
.
As the transducer
20
is positioned over a track
40
(i.e., during a track following procedure), it reads the servo information contained in the servo regions
44
of the track
40
, one servo region
44
at a time. The servo information is used to, among other things, generate a position error signal (PES) as a function of the misalignment between the transducer
12
and a desired position relative to the track centerline
48
. As is well-known in the art, the PES signals are input to a servo control loop (not shown) which performs calculations and outputs a servo compensation signal which controls the VCM
28
to, ideally, place the transducer
12
at the desired position relative to the track centerline
48
.
In addition to performing the track following procedure described above, each track's servo region
44
contains information which is used to position the transducer
20
over an appropriate track
40
and servo region
44
(i.e., to perform seek operations) so that user data may be read from that track's data region
46
. More specifically, as shown in
FIG. 4
, each servo region
44
contains a write/read (W/R) recovery field
60
, an automatic gain control (AGC) field
62
, a synchronization field
64
, a sector number field
66
, a cylinder number field
68
and a PES field
70
. (The PES field
70
is comprised of servo patterns
50
, as described above with reference to FIG.
3
).
The W/R field
60
is used by the disk drive
10
to transition from writing data to a previous data region
46
to reading the servo information in the present servo region
44
. The AGC field
62
is used to set the gain of the read/write channel (not shown) of the disk drive
10
for optimal performance. The synchronization field
64
is used in synchronizing a system clock so that the sector and cylinder number fiel

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