Dynamic magnetic information storage or retrieval – General processing of a digital signal – Data in specific format
Reexamination Certificate
2001-04-19
2004-06-22
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Data in specific format
C360S046000, C360S077080
Reexamination Certificate
active
06754016
ABSTRACT:
BACKGROUND
1. Technical Field
The invention relates generally to disk drive assemblies and, more particularly to frequency modulation read-back signal generation patterns for generating position error signals in accordance therewith for disk drive assemblies.
2. Description of Related Art
A magnetic disk drive assembly is a machine that is typically used to read data from and write data onto a magnetic disk.
FIG. 1
illustrates a conventional magnetic disk drive assembly
32
. The assembly
32
includes a storage medium
12
(e.g., a disk), an actuator
38
, a head assembly
18
and a voice coil motor
40
. The head assembly
18
is attached to the actuator
38
that is connected to the voice coil motor
40
(e.g., a servo motor). The voice coil motor
40
is used to move the head assembly
18
in order to keep it over a desired portion of the storage medium
12
.
Information is recorded on the storage medium
12
in one or more tracks
34
and in one or more servo sectors
36
. Typically, the tracks
34
store data, and for the disk drive assembly
32
to work properly, the head assembly
18
must lie within a small distance of the centerline of the track
34
being accessed. If the head assembly
18
deviates to either side of the center of the track, mistakes can occur in writing or reading information to and from the storage medium
12
.
To determine the position of the head assembly
18
on the storage medium
12
, special patterns are created on the storage medium
12
in one or more of the sectors
36
. The head assembly
18
is used for reading the special patterns encoded on the sectors
36
of the storage medium
12
and for generating a signal that is indicative of the location of the head assembly
18
relative to the track
34
as well as the actual track number. This signal is called a position error signal (PES). Using a servo loop based on the PES, the voice coil motor
40
positions the head assembly
18
closer to the centerline of the track
34
being accessed. Accordingly, the sectors
36
are often referred to as “servo sectors.”
FIG. 2
generally illustrates a disk drive system
10
including a storage medium
12
and a head assembly
18
for writing and reading information to and from the storage medium
12
. The head assembly
18
includes a write head
20
for writing the information to the storage medium
12
and a read head
22
for reading information from the storage medium
12
. As discussed hereinbefore, in order to maximize the accuracy with which the head assembly
18
writes and reads information to and from the storage medium
12
, the position of the head assembly
18
, and in particular the read head
22
, should be controlled with the highest achievable accuracy in order to maximize storage density and accuracy of writing and reading data to and from the disk. The control information that is provided on the servo sectors
36
of the storage medium
12
, as discussed hereinbefore, is dedicated for determining the position of the head assembly
18
, the read head
22
or the write head
20
.
The storage medium
12
typically is a magnetic disk comprising two layers: a magnetizable recording layer
14
and a substrate layer
16
. Information is written or recorded on the storage medium
12
by magnetizing small regions within the recording layer
14
generally referred to as magnetic domains
28
. As part of a write operation, as the storage medium
12
rotates in a given direction
30
, the write head
20
is used to create the magnetic domains
28
on the recording layer
14
, thereby creating a number of flux changes within the recording layer
14
. In contrast, during a read operation, the read head
22
detects the magnetic domains
28
. The total number of magnetic domains
28
that can be accommodated on a disk is indicative of the storage capacity or bit density of the storage medium
12
.
The write head
20
is generally a thin film inductive head, which generally includes a coil
19
and a magnet
21
having a small gap
23
. The magnet
21
is formed of a soft magnetic layer and the coil
19
is wrapped around one of the pole pieces of the magnet
21
, such that when an electric current
24
is passed through the coil
19
, a magnetic field
25
is created across the gap
23
. The portion of the magnetic field
25
that fringes out from the gap
23
magnetizes the magnetizable recording layer
14
and thus creates the magnetic domains
28
. The direction of the current
24
flowing through the coil
19
determines the polarity of each of the magnetic domains
28
. Current flowing in one direction forms a magnetic domain
28
having a polarity representative of logic “one.” Conversely, current
24
flowing in an opposite direction forms a magnetic domain
28
having an opposite polarity representative of logic “zero.” The magnetic domains
28
form boundary regions when they are written in a contiguous pattern. The boundary regions are detected using the read head
22
.
The read head
22
of the head assembly
18
generally senses the magnetic domains
28
created on the recording layer
14
of the storage medium
12
and produces an electrical signal in response thereto. In one example, the read head
22
can be a magneto resistive head, which operates on the principle of the magneto resistive effect or the giant magneto resistive effect. In its simplest form, a magneto resistive element undergoes a change in its internal resistance when it is aligned with the flux lines of a magnetic field. If a constant electrical current is provided as an input to a magneto resistive element, a change in its internal resistance will create a corresponding change in output voltage.
At the transition of the contiguous magnetic domains
28
there exist magnetic flux fields. When the read head
22
passes over a boundary region it senses the flux field present at the transition between two contiguous magnetic domains. The read head
22
responds to the magnetic flux by producing an output signal
26
(e.g., a read-back signal) corresponding to the encoded signal written to that portion of the storage medium
12
. Accordingly, as the storage medium
12
moves relative to the read head
22
, the read head
22
produces a series of output signals
26
representative of the information recorded on the storage medium
12
. The disk drive system
10
therefore typically includes signal processing electronic circuits, such as a servo demodulator, a disk drive controller and a servo controller, for decoding the information.
FIG. 3
illustrates generally a conventional schematic representation of information encoded on a track
34
of a storage medium. As discussed previously, the track
34
may include a data portion
42
and a servo sector
36
. As discussed previously, the servo sector
36
typically includes information encoded thereon, which is used to control the position of the read head
22
relative to the track
34
. Those skilled in the art will appreciate that the information written to the servo sector
36
by the disk manufacturer must never be corrupted. Otherwise, it will be virtually impossible to determine the position of the read head
22
and, hence, it will be difficult to read the information stored on the storage medium
12
.
The servo sector
36
typically includes a number of sub-portions, each including specially encoded patterns, which the read head
22
encounters in turn as it moves along the track
34
. Generally the first special pattern in the servo sector
36
is a write recovery pattern
44
. The second special pattern is a track identification pattern
46
. The track identification pattern
46
merely provides information about which track
34
the read head
22
is located on, but does not provide information about the read head's
22
relative position within the track
34
. Thus, the track identification pattern
46
alone is insufficient to determine the position of the read head
22
because the read head
22
is commonly somewhat narrower than the width of the track. Therefore, the read head
22
may be located
Lin Xiangdong
Messner William C.
Zhu Jian-Gang
Carnegie Mellon University
Hudspeth David
Kirkpatrick & Lockhart LLP
Rodriguez Glenda P.
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