Dynamic magnetic information storage or retrieval – General processing of a digital signal – Data clocking
Reexamination Certificate
1998-08-14
2001-05-22
Sniezek, Andrew L. (Department: 2651)
Dynamic magnetic information storage or retrieval
General processing of a digital signal
Data clocking
C360S075000, C360S077120, C360S121000
Reexamination Certificate
active
06236525
ABSTRACT:
TECHNICAL FIELD
The present invention relates to writing servo tracks on magnetic storage tape.
BACKGROUND ART
Magnetic tape provides a reliable, cost-efficient, and easy to use means for information storage and retrieval. Ongoing efforts to increase the usefulness and cost-effectiveness of magnetic tape include increasing the ability to store more information for a given width and length of tape. This is generally accomplished by including more data tracks on a given width of tape. Increasing the number of data tracks requires those tracks to be more densely packed onto the tape. As the data tracks are more closely spaced, errors may be more easily introduced into the reading or writing of data. Therefore, an increase in the precision of positioning the tape with respect to the head becomes more critical. The positioning of the tape on the tape head may be affected by variations in the tape or the tape head, and in variations in tape positioning caused by air flow, temperature, humidity, tape shrinkage, and other factors, especially at the outside edges of the tape.
Servo tracks are employed to provide increased accuracy in the placement of data tracks on tape. The one or more servo tracks provide a reference point to maintain correct positioning of the tape head with respect to the tape. Each servo track may have various patterns or frequency regions to allow precise positioning between the tape head and the tape. Servo tracks are generally placed on the tape during tape manufacture and are used by a tape deck to align the read and write heads with the tape. Each servo track may comprise a sequence of one or more servo frames.
Because the servo tracks control precise read and write head positioning, the size and location of servo track fields have a strict tolerance. Also, because the servo pattern will be written in a manufacturing environment, the servo writer head must be capable of writing the patterns in one pass of the tape at high tape speed. Various portions of the servo track pattern are written by different modules in a servo write head. Inaccuracies in pattern size and location may result from variations in tape velocity as the tape passes over the servo write head, in improper gap-to-gap parallelism and azimuth in module location, because the tape is skewed over the servo writer head, or the like. What is needed is to determine the precise position of the tape at each module with respect to the reference module.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide increased accuracy in writing servo tracks on magnetic storage tape.
Another object of the present invention is to minimize the effects of velocity variations of tape passing over the servo write head.
Still another object of the present invention is to minimize gap-to-gap parallelism and azimuth errors in servo track write heads.
Yet another object of the present invention is to minimize the effects of tapes skewed over servo track write heads.
In carrying out the above objects and other objects and features of the present invention, a servo track writer head is provided. The servo track writer head writes servo tracks spaced across the width of a data storage tape as the tape moves along the head in a tape direction, each servo track written along a portion of the tape length. The servo track writer head includes a leading writer for each servo track. Each leading writer writes a synchronization field on the tape at the same tape position in the tape direction as every other leading writer. The servo track writer head also includes a sequence of trailing writers for each servo track. Each trailing writer produces at least one trailing field on the tape. Each trailing field is written a fixed distance in the tape direction behind the synchronization field. Each trailing writer at a particular location in the sequence of trailing writers is positioned at the same distance in the tape direction from a selected leading writer as every other trailing writer at that particular location in the sequence of trailing writers. The servo track writer head also includes at least one timing writer. Each timing writer writes a timing field on the tape at a timing distance in the tape direction from each of the synchronization fields. Further, the servo track writer head includes a sequence of timing readers corresponding to each timing writer. Each timing reader reads the timing field on the tape written by the corresponding timing writer. The number of timing readers in the sequence of timing readers is equal to the number of trailing writers in the sequence of trailing writers. Each timing reader at a particular location in the sequence of timing readers is located the timing distance in the tape direction from the trailing writer having the same particular location in the sequence of trailing writers. The positioning of timing readers permits locations of timing fields to be read, allowing the appropriate fixed distance behind synchronization fields for writing trailing fields to be determined.
In a preferred embodiment, each synchronization field and each timing field is written simultaneously.
In another embodiment, the last trailing writer in each sequence of trailing writers is a track identification writer. Each of the remaining trail of writers in the sequence of trailing writers is an erase writer. Each trailing field is an erased field. In a refinement, the remaining trailing writers are a first erase writer and a second erase writer.
In still another embodiment, a first tape edge and a second tape edge define the tape width. A first timing writer is located closer than any leading writer to the first tape edge. A second timing writer is located closer than any leading writer to the second tape edge.
In yet another embodiment, the fixed timing distance is zero, thereby aligning the start of each timing field with the start of each synchronization field along the tape length.
In a further embodiment, each of the timing writers is a thin film writer including a bottom pole, a top pole, an insulating gap layer interposed between the bottom pole and the top pole, and a plurality of coils between the top and bottom poles. The bottom pole and the top pole form an electromagnet driven by current in the coils. In a refinement, at least one trailing writer has a split top pole, each split top pole trailing writer writing at least two trailing fields simultaneously.
In a still further embodiment, each timing reader is an inductive reader or a magnetoresistive reader.
In yet a further embodiment, each timing writer and each leading writer are constructed on a single substrate. Each timing reader at a particular location in the sequence of timing readers and each trailing writer having the same particular location in the sequence of trailing writers are also constructed on a single substrate.
In yet a still further embodiment, each timing writer writes the timing field at a first frequency. Each timing writer writes a second field following the timing field, the second field including a signal at a second frequency. Each timing reader detects the transition between the timing field and the second field and detects periods of the second frequency signal. The number of periods detected is used to determine the appropriate fixed distance behind synchronization fields for writing trailing fields.
A method for writing at least one servo track on a magnetic storage tape moving relative to a head is also provided. Each servo track has a synchronization field followed by a sequence of trailing field patterns extending for a portion of the tape length. The method includes writing a synchronization field on the tape for each servo track, writing at least one timing field on the tape a fixed distance from a select synchronization field, reading each timing field from the tape, and writing the next trailing field pattern in the sequence on the tape for each servo track. Each of the next trailing field patterns has a location based on when each timing field is read. Reading each timing field and writing t
Cates James C.
Dee Richard H.
Gillingham Ronald D.
Mantey John P.
O'Day Richard L.
Brooks & Kushman P.C.
Sniezek Andrew L.
Storage Technology Corporation
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