Dynamic magnetic information storage or retrieval – General processing of a digital signal – Data in specific format
Reexamination Certificate
2002-09-30
2003-12-02
Hudspeth, David (Department: 2697)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Data in specific format
C360S077020, C360S077010, C360S077060, C360S077080
Reexamination Certificate
active
06657801
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to magnetic disk drives (disk drives), and more particularly to a disk drive with an improved characterization segment pattern that reduces the test time associated with multiple profile scans used to determine reader and writer magnetic widths, and to a method of recording such pattern.
2. Description of the Related Art
This application is directed to a disk drive
10
like that exemplified by FIG.
1
. As shown, a conventional disk drive
10
has a head disk assembly (HDA)
20
housed within an enclosure formed from a base
21
and a cover
24
. The HDA
20
includes at least one disk
23
, a spindle motor
22
for rapidly rotating the disk
23
, and a head stack assembly (HSA)
40
that includes an actuator assembly
50
and a head gimbal assembly (HGA) (not numbered) with a transducer head
80
for reading and writing data. The HSA
40
is part of a servo control system that positions the transducer head
80
over a particular track on the disk to read or write information from that track. The HSA
40
earns its name from the fact that it generally includes a plurality of HGAs that collectively provide a vertical arrangement of heads called a “head stack”.
The industry presently prefers a “rotary” or “swing-type” actuator assembly
50
that conventionally comprises an actuator body
51
which rotates on a pivot assembly between limited positions, a coil
52
that extends from one side of the actuator body to interact with a pair of permanent magnets
60
to form a voice coil motor (VCM), and an actuator arm
54
that extends from the opposite side of the actuator body to support the HGA.
A controller circuit board
30
suitably positions the actuator assembly
50
and then reads or writes user data in accordance with commands from a host system (not shown).
A disk drive is ultimately used to store user data in one or more “data tracks” that are most commonly arranged as a plurality of concentric data tracks on the surface of its disk or disks. Special servo information is factory-recorded on at least one disk surface so that the disk drive's servo control system may control the actuator assembly
50
, via the VCM, to accurately position the transducer head to read or write user data to or from the data tracks. In operation, the disk drive's servo control system processes (read only) the pre-recorded servo information while the disk drive processes (reads or writes) user data in the data tracks.
Earlier disk early drives used a “dedicated servo” system where one head and one disk surface provide the servo information for all of the other heads and disk surfaces. As shown in
FIG. 2
, however, the industry presently prefers an “embedded servo” system where the servo information is interspersed amongst the data on each surface of each disk. The factory-recorded servo information is contained in servo wedges
211
that are each divided into a plurality of servo sectors
511
. The servo sectors
511
are recorded concentrically in order to provide numerous servo tracks formed from an entire rotation of servo sectors
511
.
The servo information is factory recorded at the time of manufacture using a relatively expensive and low-throughput manufacturing fixture called a servo track writer (STW). The STW records the servo tracks containing the servo information on each surface of each disk for later use by the servo control system when the drive is in the hands of the user. The servo tracks are generally used throughout the life of the disk drive without modification. The operation of an STW is well known to those of ordinary skill in the art.
As shown, each servo wedge
211
generally comprises a header region HDR followed by a plurality of servo bursts (two are shown, but four is common). The header region HDR generally includes several fields (none of which are separately shown in
FIG. 2
) such as a setup or write splice field WRITE SPLICE, an address mark field AM, an automatic gain control/phase locked oscillator field AGC/PLO, a servo sync mark field SSM, a track identification field TKID, and a wedge number field W#. The header region HDR is followed by at least two servo bursts (an A burst and B burst are shown) that are circumferentially sequential and radially offset relative to a burst pair centerline. The servo format used is not critical and is explained here only for background purposes. The purpose of these various fields and available variations are well known to those of ordinary skill in the art.
Today, the transducer head
80
of
FIG. 1
is usually provided in the form of a so-called magnetoresistive transducer that includes a separate reader and a separate writer. As the market continues to demand increased storage capacity and overall performance at reduced cost, the industry has steadily reduced the widths of the reader and writer in order to increase the track pitch and overall a real density of the disk drive. Due to normal manufacturing variations with respect to physical width, sensitivity and linearity, it has become more and more critical to characterize the reader width and writer width of individual transducers in order to optimize the capacity or performance of an individual drive and increase overall yield.
The conventional approach to characterizing the reader width is with a so-called “micro-track profile” that is enabled by writing a full-width track and then erasing a portion of that track to leave a continuous, partial width characterization track
101
to the surface of the disk
23
, as suggested by FIG.
3
A. In developing the micro-track profile, the reader is scanned radially across the partial width characterization track
101
to produce a series of signal amplitude data points that can be analyzed with conventional techniques to establish the reader width.
The conventional approach to characterizing the writer width is with a so-called “full-track profile” that is enabled by writing a continuous, full width characterization track
102
to the surface of the disk, as suggested by FIG.
3
B. In developing the full-track profile, the reader is scanned radially across the full width characterization track
102
to produce a series of signal amplitude data points that can be analyzed with conventional techniques to establish the writer width.
The concepts of full-track and micro-track profiles are well known to those of ordinary skill in the art. It is also well known that the characterization takes an appreciable amount of time in the STW because the reader is successively moved to a plurality of different radial positions and, for each such position, the characterization track
101
or
102
is revolved beneath the reader for one full revolution so that the signal amplitude may be averaged over that one revolution in order to produce a track average amplitude or TAA for that particular position of the reader. The conventional process must be affected for the full-track profile and then separately affected for the micro-track profile.
FIGS. 4A and 4B
are simplified illustrations of a conventional “sectorization” of the partial-width and full-width characterization tracks
101
,
102
that provides improved accuracy in making track profile measurements. It still remains necessary, however, to take the time required to separately process the partial-width and full-width characterization tracks
101
,
202
.
U.S. Pat. No. 6,404,576 entitled “METHOD AND SYSTEM FOR COMPENSATION OF NONLINEARITY OR FLUCTUATION OF HEAD POSITION SIGNAL” (hereafter the “'576 Patent”), and issued Jun. 11, 2002, is an example of a method for obtaining the micro-track and full-track profiles in the field rather than in the STW. In the '576 Patent, using multiple passes in the STW, special patterns are written in a reserved areas of the disk before shipping so that after the disk drive is in the field, the disk drive can detect a full-track profile or a micro-track profile by locating the reader at a suitable radial position while rotating these speci
Chue Jack M.
Tipton, II William C.
Figueroa Natalia
Hudspeth David
Myers Dawes Andras & Sherman
Shara, Esq. Milad G.
Western Digital Technologies Inc.
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