Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
2000-02-07
2004-07-06
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
Reexamination Certificate
active
06760184
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 includes concentric or spiral tracks that are divided into sectors having a short servo track information area followed by a customer data area. The servo track information area typically includes a sector mark, track identification data, and a servo burst pattern. The sector mark indicates that servo information immediately follows in the track.
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 circumferentially spaced sector mark fields
32
, of which two are shown. It should be understood that conventional disk drives typically contain approximately one hundred sectors per track and more than 5000 data tracks; fewer are indicated in
FIG. 1
for simplicity. Customer data is recorded by a user into the track spaces
33
between the sector marks. 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 head
28
over a data cable
34
, which is coupled to a disk drive controller
36
.
When the read/write head
28
is 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 to generate servo commands that control the servo motor
26
and are provided over a servo line
38
to maintain the head in a position centered above one of the tracks.
FIG. 2
shows the read/write head
28
of
FIG. 1
in greater detail, shown in an exploded view providing better visualization of the component. 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 gap material
44
located on a magnetic shield piece
45
. The write element of the head includes a magnetic gap
46
containing a magnetic pole piece and electromagnetic coils (not shown in FIG.
2
). A second non-magnetic gap material
47
is placed over the M-R read element
40
and leads. The write element is placed on the second gap material
47
, which is over the MR read element.
Two electrical wires
48
,
50
are connected to read contacts
52
,
54
respectively, and carry the sensed readback signal from the M-R read element to signal processing circuitry
56
. The combined read/write head shown in
FIG. 2
permits a single head assembly to include both read and write elements and thereby simplifies production and design.
The disk controller
36
controls the servo motor
26
(
FIG. 1
) to maintain the read/write head
28
above a magnetic track
60
of the disk
22
in response to the head readback signal. As noted above, the head readback signal is generated from sensed servo pattern bursts recorded in the disk track
60
. The servo pattern bursts are recorded in the disk tracks as magnetic field transitions that extend across the width of the disk tracks.
FIG. 3
shows a conventional servo burst pattern comprising an A, B, C, D quadrature burst pattern that is repeated for each servo sector. The bursts are part of the information following the sector mark (FIG.
1
). Each burst of the quad-burst servo pattern shown in
FIG. 3
is typically made up of two parts, each being one-half of a data track pitch (DTP), as indicated by the data track numbers along the left side of the drawing showing respective data track centerlines. It should be understood that other servo pattern widths are possible. For example, many conventional disk drive systems utilize servo patterns that are two-thirds the width of a data track. In addition to quadburst servo patterns, it is also common to use dual burst patterns, which generally comprise only the A and C servo bursts of the quad-burst pattern illustrated in FIG.
3
.
The servo pattern bursts A, B, C, and D are produced by energizing write coils in the read/write head
28
during a servo writing operation before final disk drive assembly. When the write coils of the read/write head are energized, they do not record flux transitions that correspond exactly to the actual width of the track. To the contrary, the flux transitions typically span about 60% to 90% of the track pitch, depending on the tolerance of the width of the write element and the recorded density. The write coils cannot record a full-width pattern because the width of the write element is less than the data track pitch for data handling purposes. Therefore, to get a servo pattern with bursts that span substantially the full width of a track, it is necessary to make multiple passes.
The servo pattern bursts are typically produced with a two-step servo write process, as shown in FIG.
3
. The process steps are generally referred to as “move and write” because the read/write head is moved, a portion of the servo burst is written to the disk, and the process is repeated. When the read/write head is moved, it is moved radially a predetermined distance that is typically one-half DTP. After the second move and write step, the second portion of the servo pattern burst is recorded.
Because the magnetic flux transitions written by the write element into the disk are usually greater than one-half DTP, the total width of the A burst is now greater than one data track width (DTW), proper size is obtained on the third pass by erasing part of the burst at the next half DTP position, which is commonly called trimming. Thus, with each pass that writes part of the servo pattern, part of the previously written flux transitions are erased or written over. It should be appreciated that the two burst halves making up the servo pattern burst must be aligned radially (that is, the flux transitions must be oriented along the same radial line from the disk center) so the transitions are in phase. The alignment requirement restricts the servo frequency to be significantly lower than the data frequency, which reduces the servo signal-to-noise ratio.
Typically, the read/write head that will be used in reading and writing customer data after the disk has been sold is the same head as the read/write head used in producing the servo pattern bursts. Accordingly, the read/write head is generally optimized for reading and writing customer data, not servo patterns. As a result, the read/write head is generally somewhat more narrow that the DTP to allow for write element size tolerance and servo track following imperfections. Typically, the write element of a read/write head is approximately 85% of DTP and the effective read width of the M-R read element is approximately 50% of DTP. Using a narrow read element causes non-linearity in the response of the read/write head when reading the servo information. The non-linearity can be reduced somewhat by using narrow se
Davidson Dan I
Hitachi Global Storage Technologies
Hudspeth David
LandOfFree
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