Dynamic magnetic information storage or retrieval – Monitoring or testing the progress of recording
Reexamination Certificate
2001-02-23
2003-11-18
Faber, Alan T. (Department: 2651)
Dynamic magnetic information storage or retrieval
Monitoring or testing the progress of recording
C360S053000, C360S077020, C360S078040
Reexamination Certificate
active
06650491
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field
The present invention relates to a system and method for setting a RW (read/write) offset in a hard disk device (HDD) to cancel the offset between the read and write heads of the disk device. This disk device includes a rotary actuator where both the write and read heads access a sector-servo type disk recording medium. The present invention also includes a system and method for recovering a read data error of data recorded in a disk device accessing a disk recording medium with a head section implemented in a rotary actuator.
2. Description of the Related Art
A hard disk device (HDD) (including a sector-servo type disk D) surface, as shown in
FIG. 2
, is divided into data areas DF and servo areas SF. A combination type head section H (see
FIGS. 1 and 4
) that includes a write head Hw for writing user data on the disk D, a read head Hr for reading data, and a rotary actuator
2
(see
FIG. 1
) for moving the head section H along in a radial direction of the disk D is also included in HDD. A RW offset &Dgr;W, as shown in
FIG. 4
, is the offset amount of read head Hr from the reference position at the time of data writing.
A control unit of the disk device recognizes only a position of read head Hr on the basis of a read signal of servo information area by read head Hr. It is necessary to require write head Hw to track a desired position while compensating for the RW offset when user data is recorded by write head Hw. Read head Hr must also track a desired position while shifted by the RW offset when user data is read by read head Hr. It is necessary to set the RW offset in the disk device before disk operation. Additionally, the dimensions and positional relations of write head Hw and read head Hr differ with every head section H and it becomes necessary to calculate the RW offset for every head section H.
As shown in
FIG. 4
, a yaw angle &phgr; between the longitudinal direction (disk-circumferential direction) of a track and head section H changes depending on a position of the track (radius from a disk center). The RW offset has a different value for every track. The RW offset must be set for every track in the disk device before disk operation.
Furthermore, since the RW offset varies for every disk device and for every head section H, the RW offset is set in the disk device by individually finding the RW offset by measuring and calculating a value from a test.
In the following description, the tracking position is a position in a radial direction (the direction of track width) of the disk where write head Hw or read head Hr is positioned. Additionally, an on-track position is a target position where data is recorded by write head Hw. The on-track position is also the target tracking position of the read head Hr when the data is read from the disk. Furthermore, an off-track position is every tracking position that is not an on-track position.
The write offset is an offset amount of read head Hr from a reference position (for example, a center of track width) when the data is read from the disk. The RW offset is the shift amount between write head Hw and read head Hr in a radial direction. If the write offset is zero, the offset amount of read head Hr from a reference position when the data is read, and the shift amount between write head Hw and read head Hr become equal. In addition, if the write offset is not zero, the offset amount of read head Hr from the reference position at the time of data reproduction has a value found by adding the write offset to the shift amount between write head Hw and read head Hr. In the RW offset, the shift amount between write head Hw and read head Hr is the critical value. Therefore, it is assumed that the RW offset refers to the shift amount between write head Hw and read head Hr in a radial direction of a disk.
For example, in
FIG. 5
, a reference position of a track T(j) is a position of r=r(j), and since, at the time of data recording as shown in
FIG. 5A
, read head Hr tracks to the reference position, the write offset is 0. In
FIG. 5A
, data is recorded by write head Hw at the on-track position which separates write head Hw and read head Hr from the reference position by the shift amount &Dgr;W (=RW offset). During a data read, read head Hr tracks to a position separating from the reference position by the RW offset &Dgr;W. If the write offset is not zero, read head Hr tracks to a position found by adding the write offset to the shift amount &Dgr;W between write head Hw and read head Hr.
It is well-known in the art that the MSE (Mean Square Error) method is utilized for setting the RW offset in a disk device. The MSE method includes the steps of:
writing a predetermined test pattern in each data area within tracks selected to be measured;
finding a corresponding value of difference between real read signals and ideal response signals of the test patterns at a plurality of different tracking positions;
searching a tracking position where the MSE value minimizes; and
finding a RW offset for the track to be measured, on the basis of this tracking position where the MSE value is minimal.
Furthermore, as described above, the RW offsets of the plurality of tracks to be measured are found by an interpolation of these RW offsets of the tracks to be measured and are set in the disk device.
If a recording position is unintentionally shifted, user data is recorded at a position that is shifted from an on-track position for a data sector. In this case, if a set RW offset is used, a read data error may occur since the data recorded in the data sector cannot be read correctly. In a disk device, if an error occurs at the time of read operation, a error recovery procedure is executed about the data sector where the read data error occurs. The error recovery procedure (ERP) includes the steps of retrying the data read at the same position where the error occurred or by shifting the disk slightly to attempt to find the requested data in adjacent tracks.
However, setting a RW offset by the MSE method, a skill well-known in the art, the data area used for a test pattern is usually limited to a few data sectors. It is not possible to measure all points in a data track area. Because of this, the precision of the MSE values is poor, and frequently, the error due to this imprecise value is included in a set RW offset. Therefore, it is necessary to increase the number of data sectors and tracks that are measured in order to increase the precision of RW offsets. This, however, increases the time latency for RW offset calculations. Also, if the number of data sectors and the number of tracks measured are increased, the precision of the MSE values becomes especially degraded when a GMR head is used for a read head or when there is an extremely fine track pitch.
Additionally, in a method well-known in the art of setting a RW offset on the basis of a tracking position where a level of a read back signal maximizes, precision is insufficient only when means for approximately finding the RW offset is simply given as a maximum.
As described above, if the RW offsets in a disk device include measurement errors, the disk device cannot continue to read data at optimum positions, and errors may frequently occur at the time of read operation.
In the error recovery procedure (ERP), an error recovery may require a large time latency, because it is not feasible to find a lost track smoothly if the recording position is shifted unintentionally.
The present invention solves such conventional problems, and its object is to reduce the occurrence of read data errors by enhancing the setting precision of RW offsets. In addition, another object of the present invention is to reduce time latency required for error recovery handling.
SUMMARY OF THE INVENTION
All objects, features, and advantages of the present invention will become apparent in the following detailed written description.
The RW offset setting method of the present invention includes the steps of:
[A] recording a test pattern by a write head in
Endoh Tatsuya
Hashimoto Junji
Ikeda Masaomi
Matsui Takao
Shibata Akira
Bracewell & Patterson L.L.P.
Faber Alan T.
Raissinia Abdy
LandOfFree
System and method for setting a read/write offset and for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with System and method for setting a read/write offset and for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and System and method for setting a read/write offset and for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3131959