Dynamic magnetic information storage or retrieval – General processing of a digital signal – Data clocking
Reexamination Certificate
1999-05-21
2001-11-27
Sniezek, Andrew L. (Department: 2651)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Data clocking
C360S075000
Reexamination Certificate
active
06324027
ABSTRACT:
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.
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 strive to increase data capacity, 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 did not discuss how to achieve optimum track to track trigger pattern alignment in the presence of random errors. The growth of these errors has thus far prevented the commercial application of various proposed techniques for self-clock generation, since there are precise requirements for timing alignment in modern disk drives.
Therefore, a need still exists for a capability to reduce systematic errors in the writing of timing patterns. In particular, a need exists for an improved capability to:
1) Minimize the effect of velocity jitter without decreasing the interval size, such that a source of random errors is at least reduced.
2) Improve the control of intervals, which in turn reduces random errors during timing pattern generation.
3) Achieve track to track alignment without incurring an additional revolution of the disk. This at the very least reduces the growth of random errors during a single revolution of the disk.
SUMMARY OF THE INVENTION
The shortcomings of the prior art are overcome and additional advantages are provided through the provision of a method for measuring the velocity of a storage medium at a given time. In one example, a time interval between a first trigger pattern and a second trigger pattern is measured prior to the given time. A substantially instantaneous velocity of the storage medium is computed based on the time interval, and a next trigger pattern is written after the given time, at a delay time. The delay time is to correct for a deviation between the substantially instantaneous velocity of the storage medium and an average velocity of the storage medium. The measuring, computing and writing are performed on a same revolution of the storage medium with a single head.
In another embodiment of the invention, a method for determining whether a trigger pattern is misplaced is provided. A first time interval between a first trigger pattern and a second trigger pattern is determined. Additionally, a second time interval between the first trigger pattern and a third trigger pattern is determined. The first and second time intervals are compared to determine whether the first trigger pattern is misplaced.
In yet another embodiment of the present invention, a method of generating timing patterns for self-servowriting of a storage medium of a storage device is provided. A first set of trigger patterns is written at a first radial location of the storage medium. During a single revolution of the storage medium, a second set of trigger patterns is written at a second radial location of the storage medium and one or more random errors in location of the second set of trigger patterns relative to the first set of trigger patterns is determined. One or more correction values is computed to compensate for the one or more random errors, and one or more trigger patterns is written at a subsequent radial location of the storage medium at locations altered by the correction values. The errors in placement of the one or more trigger patterns at the subsequent radial location are reduced.
In another aspect of the present invention, an apparatus for measuring the velocity of a storage medium at a given time is provided. In one example, the apparatus includes a measuring unit adapted to measure a time interval between a first trigger pattern and a second trigger pattern prior to the given time; a controlling unit adapted to compute a substantially instantaneous velocity of the storage medium based on the time interval; and a pattern generator adapted to write a next trigger pattern after the given time at a delay time. The delay time is to correct for a deviation between the substantially instantaneous velocity and an average velocity of the storage medium. The measuring, computing and writing are performed on a same revolution of the storage medium with a single head.
In another aspect of the present invention, an apparatus for determining whether a particular trigger pattern is misplaced is provided. In one example, the apparatus includes a first measuring unit adapted to determine a first time interval between a first trigger pattern and a second trigger pattern; a second measuring unit adapted to determine a second time interval between the first trigger pattern and a third trigger pattern; and a processing unit adapted to compare the first and second time intervals to determine whether the first trigger pattern is misplaced
Chainer Timothy Joseph
Schultz Mark Delorman
Webb Bucknell Chapman
Yarmchuk Edward John
Heslin Rothenberg Farley & & Mesiti P.C.
International Business Machines - Corporation
Raissinia, Esq. Abdy
Schiller, Esq. Blanche E.
Sniezek Andrew L.
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