Dynamic magnetic information storage or retrieval – General processing of a digital signal – Data clocking
Reexamination Certificate
1999-07-01
2001-01-09
Kim, W. Chris (Department: 2753)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Data clocking
C360S075000
Reexamination Certificate
active
06172830
ABSTRACT:
The present invention relates to a method and apparatus for writing a clock track on a storage medium.
Information for systems such as data processing systems is typically stored on storage media. Particular use is made of storage disks such as magnetic disks, opto-magnetic disks, and the like. One type of magnetic disk is a so-called “hard disk assembly” which is intended normally to be permanently fixed in a data processing system; the hard disk assembly includes the magnetic disk medium itself and the associated read and write head or heads which write data to the disk and read data from the disk. Another type of magnetic disk is of a type known as “removable media” which normally consists of a magnetic disk medium in a protective plastics case which can be used to transfer data between data processing systems by physical transfer of the disk itself from one machine to another.
In manufacturing storage media such as hard disk drives, a hard disk assembly consisting of the head(s), the disk or disks, the motor and arm electronics, is mounted in a mastering station known as a servo-writer. The servo-writer writes a pattern of magnetic information (the “servo track pattern”) onto the disk. The servo track pattern becomes the master reference which is used by the disk drive during normal operation in order to locate the tracks and sectors on the disk for data storage and retrieval.
In order to be able to write the servo track onto the correct positions on the disk during manufacture of the disk, it is necessary to write a (usually temporary) clock track onto the disk which serves as a timing reference during writing of the servo pattern. Conventionally, a separate clock head is used to write the clock track onto the disk. However, the use of a dedicated clock track writing head is an expensive addition to the manufacturing process.
U.S. Pat. No. 5,485,322 discloses a method and system for writing a clock track on a storage medium using an internal recording head of a hard disk drive. A timing pattern is generated on the storage medium with the internal recording head and a radial positioning value used in radially positioning the internal recording head is determined. The servo pattern is written at the locations determined by the generated timing pattern and radial positioning value. In effect, in this prior art system, the clock pattern is written in an iterative manner across the disk. However, there is a problem in that this method can introduce phase differences in a clock pattern between respective tracks on the disk. As a disk will often require many thousands of clock tracks across the disk, even very small phase errors in the clock track can cumulatively become very large.
U.S. Pat. No. 5,448,429 discloses another example of a system for writing clock tracks across a disk in which a written clock signal is read to provide a reference for the writing of the clock signal to a subsequent track.
According to a first aspect of the present invention, there is provided a method of writing clock data to a storage medium having tracks on which data are stored, the method comprising the steps of:
(A) writing clock data to a present track on the storage medium;
(B) reading said written clock data from said present track;
(C) generating clock data for a subsequent track on the storage medium from the clock data read from said present track;
(D) comparing the phase of the generated clock data for the subsequent track with a reference timing signal and adjusting the phase of the generated clock data for the subsequent track in accordance with said comparison; and,
(E) writing said phase adjusted clock data for the subsequent track to said subsequent track.
The use of the reference timing signal means that phase errors, arising for example from variations in the phase owing to various effects (such as propagation delays in the write circuit, the magnetic effects of writing the transitions to the disk and reading the transitions from the disk within the magnetic head, and the read channel and decode circuitry) can be significantly reduced and, for practical purposes, substantially eliminated. It is not necessary to provide a dedicated clock read/write head as required in some prior art systems.
The subsequent track may be the track immediately following the present track.
The steps (B) to (E) may be repeated across the tracks on the storage medium, with the clock data read from a certain track in a step (B) being the clock data written in a step (E) for that track. Thus, the clock data for a track is generated from the phase corrected clock data read from a previous track, the phase adjustment being made in accordance with the reference timing signal.
Steps (B) to (E) can be repeated for every track on the storage medium. Alternatively, phase adjustment may only have to be carried out for some of the tracks, such as every second or every third track.
In the comparison step (D), the phase of the generated clock data to be written to a present track may be adjusted by an amount which takes into account the phase adjustment used for clock data written to a previous track, the phase difference between the reference timing signal and the generated clock data to be written to the present track, and the phase difference between the reference timing signal and the generated clock data to be written to said previous track.
In a particularly preferred embodiment, in the comparison step (D), the phase of the generated clock data to be written to a present track n is adjusted by an amount T(n) substantially equal to (T(n−1)−2T
error
(n)+T
error
(n−1)), where T(n−1) is the phase adjustment used for clock data written to the previous track n−1, T
error
(n) is the phase difference between the reference timing signal and the generated clock data to be written to the present track n, and T
error
(n−1) is the phase difference between the reference timing signal and the generated clock data to be written to the previous track n−1.
Said previous track may be the track which immediately precedes the present track.
The storage medium may be a disk.
The disk may be a magnetic disk.
The disk may have a motor for rotating the disk. Conveniently, the timing reference signal may be obtained from the back emf (electromotive force) of said rotating motor.
Alternatively or additionally, the timing reference signal may be obtained from a probe which detects movement past the probe of an index or indices on a rotating part of a disk drive which includes a disk as a storage medium during rotation of the disk. The index may be an optically detectable mark on the disk and the probe may be an optical sensor.
Alternatively or additionally, the probe may be a non-contact inductive probe which detects movement therepast of features on a rotating part of a disk drive. Such features may be screws on the hub associated with the rotating part of the disk drive. A suitable non-contact inductive probe is a Hall effect probe.
The timing reference signal actually used may be a statistical average in the time domain of a plurality of such timing reference signals. This serves to reduce the problem of variations in the timing reference signal which may occur. The average may be taken over several clock track copying cycles.
According to a second aspect of the present invention, there is provided apparatus for writing clock data to a storage medium having tracks on which data are stored, the apparatus comprising:
writing means for writing clock data to a present track on a storage medium;
reading means for reading said written clock data from said present track;
generating means for generating clock data for a subsequent track on the storage medium from the clock data read from said present track;
comparing and adjusting means for comparing the phase of the generated clock data for the subsequent track with a reference timing signal and adjusting the phase of the generated clock data for the subsequent track in accordance with said comparison; and,
means for writing said phase adjusted
Havant International Ltd.
Kim W. Chris
Pillsbury Madison & Sutro Intellectual Property Group
LandOfFree
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