Dynamic magnetic information storage or retrieval – General processing of a digital signal – Data clocking
Reexamination Certificate
2000-05-04
2001-07-10
Huber, Paul W. (Department: 2651)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Data clocking
C369S053440
Reexamination Certificate
active
06259574
ABSTRACT:
This application is related to U.S. Pat. No. 5,485,322 of T. Chainer et al. issued on Jan. 16, 1996 entitled, “Method and System for writing a Clock Track on a Storage Medium”, which is a divisional application of application Ser. No. 08/028,044, filed Mar. 8, 1993, now abandoned. U.S. Pat. No. 5,485,322 is commonly assigned herewith, and hereby incorporated herein by reference in its entirety. It is also related to U.S. Pat. No. 5,612,833 of E. Yarmchuk et. al., Attorney Docket No. Y0994-253A, issued on Mar. 18, 1997 entitled, “Radial Self-Propagation Pattern Generation for Disk File Servowriting,” which is also hereby incorporated herein by reference in its entirety.
1. Technical Field
The invention relates generally to hard disk drive memory storage devices for computers. More particularly, it relates to disk drive apparatus and to a method for writing servotrack information therein. More specifically it relates to alleviating the need for a complex mechanical and/or optical positioning system to establish servopatterns on the recording surfaces of the recording media.
2. Background Art
Increased levels of storage capacity in floppy and hard disk drives are a direct result of the higher track densities possible with voice-coil and other types of servo positioners, as well as the ability to read and write narrower tracks by using, for example, magnetoresistive (MR) head technology. Previously, low track density disk drives were able to achieve satisfactory head positioning with leadscrew and stepper motor mechanisms. However, when track densities become so great that the mechanical error of a leadscrew stepper motor combination is significant compared to track-to-track spacing, an embedded servo is needed so that the position of the head can be determined from the signals it reads.
Conventional servo-patterns (also referred to as servo-data) typically include short bursts of a constant frequency signal, very precisely located offset from a data track's center line, on either side. The bursts are written in a sector header area, and can be used to find the center line of a track. Staying on center is desired during both reading and writing. Since there can be sixty, or even more, sectors per track, that same number of servo-data areas must be dispersed around a data track. These servo-data areas allow a head to follow a track center line around a disk, even when the track is out of round, as can occur with spindle wobble, disk slip and/or thermal expansion. As technology advances to provide smaller disk drives, and increased track densities, the placement of servo-data must also be proportionately more accurate.
One example of servo-data is shown in
FIG. 1
, which includes a sector header
2
followed by a pattern to provide radial position information. The sector header includes a Servo ID (SID) Field
4
and a Grey Code Field
6
, which require precise alignment track to track. Misalignment in these patterns results in destructive interference of the magnetic pattern and reduces the amplitude of the signal which leads to errors. Specifications on the alignment in modern disk drives is approximately 25 nanosec (3 sigma) track to track for a disk rotation period of roughly 11 milliseconds or 2.3 ppm. This narrow time window therefore requires precise measurement of the disk angular position over many revolutions of the disk.
As disk drives become smaller and track densities increase, there is a desire to reduce the size of the servo-data areas, such that they take up less space on the disk. In order to reduce the size, however, the servo-data are written at higher and higher frequencies. These higher frequencies require tighter timing tolerances from track to track.
In one example, timing is provided by writing trigger patterns at various locations of the disk. It is understood that in writing a trigger pattern a specified time after a trigger, the presence of electronic delays in the trigger and write circuitry is taken into consideration. This is described in IBM Technical Disclosure Bulletin, Vol. 33, No. 5 (October 1990), where the delay between A and B clock areas is measured and stored. This delay value is used to advance the write timing of all subsequent servo-tracks and clock areas.
Although, the IBM Technical Disclosure Bulletin, Vol. 33, No. 5 (October 1990) discussed the presence of electronic delays, it does not appear to discuss how to achieve optimum track to track trigger pattern alignment. In particular, it does not discuss how to achieve optimum track to track trigger pattern alignment in the presence of media defects (e.g., physical defects on the storage media), media noise and electronics noise. Further, the TDB does not teach how to minimize the size of the clock areas (e.g., trigger patterns).
Therefore, a need still exists for a capability to detect and correct for media defects in the writing of timing patterns. In particular, a need exists for an improved capability to:
1) Detect whether a trigger pattern is at an expected location on a storage medium.
2) Remove extraneous noise during the writing of trigger patterns.
3) Determine whether a trigger pattern is within an expected trigger pattern region.
SUMMARY OF THE INVENTION
The shortcomings of the prior art are overcome and additional advantages are provided through the provision of a method for detecting trigger patterns. A trigger pattern is written on a storage medium of a storage device, and a detector is used to detect whether the trigger pattern is at an expected location on the storage medium, at a given time. In one example, when the detector does not detect the trigger pattern at the given time, a false trigger pattern is generated.
In a further example of the present invention, a time interval is measured between the trigger pattern and another trigger pattern written on the storage medium, and a determination is made as to whether the measured time interval is valid. If the measured time interval is invalid, then, in one embodiment, it is corrected.
In another embodiment of the present invention, a method for determining whether a trigger pattern is within an expected trigger pattern region is provided. An interval is measured at the trigger pattern, and the measured interval is corrected for any previous invalid trigger patterns. Thereafter, a determination is made as to whether the corrected measured interval is valid. A valid corrected measured interval indicates the trigger pattern is within the expected trigger pattern region.
In one example, the determination of whether the corrected measured interval is valid includes subtracting a target interval value for the trigger pattern from the measured interval to obtain a resulting value, and comparing an absolute value of the resulting value to a valid interval window to determine whether the corrected measured interval is valid. The corrected measured interval is valid when is the absolute value of the resulting value is less than or equal to the valid interval window.
In another aspect of the present invention, an apparatus for detecting trigger patterns is provided. In one example, the apparatus includes a generator adapted to write a trigger pattern on a storage medium of a storage device; and a detector adapted to detect whether the trigger pattern is at an expected location on the storage medium at a given time.
In yet a Further aspect of the present invention, an apparatus for determining whether a trigger pattern is within an expected trigger pattern region is provided. In one example, the apparatus includes a measuring unit adapted to measure an interval at the trigger pattern; and a controlling unit adapted to correct the measured interval for any previous invalid trigger patterns, and to determine whether the corrected measured interval is valid. A valid corrected measured interval indicates the trigger pattern is within the expected trigger pattern region.
The present invention advantageously detects whether a trigger pattern is at an expected location on the storage medium. In one example, this detection is performed
Chainer Timothy Joseph
Schultz Mark Delorman
Webb Bucknell Chapman
Yarmchuk Edward John
Heslin & Rothenberg, P.C.
Huber Paul W.
International Business Machines - Corporation
Raissinia, Esq. Abdy
Schiller, Esq. Blanche E.
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