Dynamic magnetic information storage or retrieval – General recording or reproducing – Recording-or erasing-prevention
Reexamination Certificate
2002-06-28
2004-09-21
Faber, Alan T. (Department: 2651)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Recording-or erasing-prevention
C360S075000, C360S031000, C360S077020
Reexamination Certificate
active
06795262
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 method of expanding the on-track operational range of a disk drive based upon detection of an external vibration condition.
2. Description of the Related Art
A Disk drive generally includes a control system that implements various on-track-declaration algorithms. Generally speaking, the goal of the conventional on-track-declaration algorithm is data reliability and data integrity. The on-track-declaration algorithms achieve these goals by enabling reading or writing only after the disk drive's transducer head has remained close to track center for some time (e.g. a specified number of servo samples) and, once reading or writing has begun, the on-track-declaration algorithms disable reading or writing if the disk drive's transducer head moves too far away from track center.
1) Typical On-Track-Declaration Algorithms
Before the data transfer begins, whether writing user data to or reading user data from a desired track, the transducer head must seek to and “settle in” to the desired track. The transducer head, however, usually overshoots the desired track. The typical control system addresses overshoot by enabling data transfer only after several successive position error signal (PES) values have fallen within certain prescribed limits, i.e. only after the transducer has remained within a so-called “arrival window” for a sufficient amount of time (servo samples). There are usually two separate arrival windows for reading and writing, a “Read Settle Window” and a “Write Settle Window” The Read Settle Window is relatively liberal since the control system can simply try to re-read the data and apply correction algorithms if it does not correctly read it the first time. The Write Settle Window, on the other hand, is relatively restrictive so that data is written to the target track with minimal risk of sliver error or of corrupting an adjacent track.
After the data transfer has begun, the typical control system stops the transfer under certain conditions. After writing has begun, for example, the typical control system immediately stops writing if the transducer head momentarily exceeds a so-called write unsafe limit (“WUS limit”). The WUS limit enhances data integrity by ensuring that data is written relatively close to track center and by protecting adjacent tracks. The foregoing on-track-declaration algorithms will be discussed in detail below after reviewing the general construction and overall operation of a disk drive.
2) An Exemplary Disk Drive and its Read/Write Elements
The on-track-declaration algorithms described above are best understood with reference to an actual disk drive.
Referring to
FIG. 1
, a conventional disk drive
10
has a head disk assembly (HDA)
20
including 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 foregoing components are generally mounted in an enclosure comprising a base
21
and a cover
24
. A printed circuit board assembly (PCBA)
30
is secured to the base
21
, the PCBA
30
containing suitable circuitry for communicating with a host and controlling the disk drive as is well known in the art.
FIG. 2
is a simplified representation of a magneto-resistive transducer head
80
that has two elements, namely a write element
81
and a read element
82
.
Returning to
FIG. 1
, 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 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.
3) The Servo Control System
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. The servo information permits the servo control system to repeatedly determine the position of the head relative to the written track. In operation, the disk drive's servo control system intermittently processes (read only) the pre-recorded servo information while the actuator assembly
50
moves the head to a desired track and, once there, while the disk drive transfers user data to the data track (i.e. writing) or from the data track (i.e. reading).
4) On-Track Declaration Algorithms for READ READY or WRITE READY
FIG. 3A
is a position profile
85
(position versus time) of a transducer head being positioned for subsequent execution of a read or write operation. In
FIG. 3A
, the seek moves the head from a current track X to a target track Y. As shown, the position profile
85
extends through a seek period
91
during which time the head travels across one or more tracks, into a subsequent read settle period
92
or write settle period
93
during which time the head “settles in” to the TARGET TRACK CENTER of the target track Y.
FIG. 3B
is a graphical representation of the total time it takes to complete a data transfer command in the presence of a vibration state when using a default on-track declaration algorithm. As shown, the time is consumed by the seek time, the settle time, and the actual writing time. In this particular example, it is further shown that the writing is intermittently interrupted due to the existence of the vibration state, thereby extending the overall time to complete the data transfer command.
FIG. 4
is a close-up of the position profile
85
of
FIG. 3A
, illustrating the “settling in” that occurs during the read settle period
91
or write settle period
93
. Here, the servo control system attempts to align the transducer head to the TARGET TRACK CENTER within a read settle window
94
(+R percent from track center) or within a write settle window
95
(+W percent from track center) prior to execution of a read or write command. The read and write settle windows
94
,
95
are sometimes called “arrival windows.” A write operation is more critical than a read operation due to the potential of overwriting and corrupting data on an adjacent track. Accordingly, the settle criteria for execution of a write operation is generally more conservative than the settle criteria for execution of a read operation (i.e. W<R).
The servo system works to bring the transducer head into alignment with TARGET TRACK CENTER during the settling period. Since the transducer head may overshoot TARGET TRACK CENTER at the beginning of the settling period, it is necessary to successively sample the position of the transducer head relative to TARGET TRACK CENTER before starting to execute the read or write operation. Position samples of transducer head relative to TARGET TRACK CENTER are taken by the disk drive servo system at regular time intervals, indicated at T
1
, T
2
, T
3
, T
4
, T
5
, T
6
, T
7
, T
8
, T
9
and T
10
. The corresponding samples on position profile
85
are indicated as S
1
, S
2
, S
3
, S
4
, S
5
, S
6
, S
7
, S
8
, S
9
, and S
10
.
FIG. 4
shows a simple embodiment where a single window parameter is
Codilian Raffi
Gibbons Kent W.
Webb Steven L.
Faber Alan T.
Myers Dawes Andras & Sherman
Shara, Esq. Milad G.
Western Digital Technologies Inc.
LandOfFree
Method of modifying on-track declaration algorithm of a disk... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method of modifying on-track declaration algorithm of a disk..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method of modifying on-track declaration algorithm of a disk... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3242650