Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the record
Reexamination Certificate
2000-05-22
2003-10-14
Hudspeth, David (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the record
C360S130210
Reexamination Certificate
active
06633449
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to magnetic tape read/write devices, and more particularly to methods and apparatus for dynamically positioning a magnetic tape with respect to a tape head in such a device.
BACKGROUND OF THE INVENTION
Despite recent advances in techniques for storing data on high density data storage devices such as compact disks (CDs) and magnetic disks, there still exists a need to store data on magnetic tape. Such data can comprise for example a database of information, such as survey information, as well as a computer program. Magnetic tape provides a low cost alternative to other high density data storage devices. Further, data on magnetic tape can be easily erased and modified, unlike read-only CDs. An additional advantage of magnetic tape over other data storage media is that data can be recorded in analog format, as well as digital format. One example of the use of magnetic tapes is in recording data from a seismic survey.
Magnetic tapes of data are accessed by a tape processing device, which can perform one or both of storing (“writing”) data onto the tape, or accessing (“reading”) data previously stored on the tape. A generic term for a tape processing device is a “tape drive”. A tape processing device comprises a tape head for one or both of reading and/or writing data from or to the magnetic tape. The tape head comprises tape head elements, which can perform one or both of these functions. Tape processing devices typically further include at least one, and typically more, guides for supporting the tape as it moves across the tape head. The guides can either be fixed or stationary guides such as spindles, or rollers which roll with the tape as the tape moves across the tape head. The guides help to align the tape with respect to the tape head. The tape support guides can also be powered rollers to rotate either in the direction of, or opposite to the direction of, the tape travel to assist in transport of the tape across the tape head, and to provide proper tensioning of the tape.
Magnetic tapes are stored on reels, which are typically mounted within a cassette housing. The cassette provides mechanical protection for the tape, and facilitates ease of handling the tape. While some cassettes contain both the tape source reel and a take-up reel onto which the tape is wound as it passes over the tape head, another practice is to configure the cassette with only the tape source reel. In this latter configuration, a free end of the tape is connected to a take-up-reel which is part of the tape processing device. This single-reel cassette design reduces the storage area required to store the tapes, as compared to the storage area requirements for a two-reel cassette.
FIG. 1
shows a simplified plan view of a prior-art design of a tape processing apparatus
1
having a tape head
11
, a first tape support guide
12
, a second tape support guide
14
, and a take-up-reel
16
. A single-reel cassette
18
containing a source reel
15
of magnetic tape “T” can be mounted on the tape processing apparatus
1
. The free end of the tape “T” is passed over the first tape guide
12
, the tape head
11
, and the second tape guide
14
, and is then connected to the take-up-reel
16
. Drive motors (not shown) control the winding of the tape “T” onto the take-up reel, or rewinding the tape onto the source reel
15
.
FIG. 2
shows a front elevation view of the tape processing apparatus
1
of FIG.
1
. In
FIG. 2
, the tape “T” is shown in partial view to allow the face of the tape head
11
to be displayed. It is understood, however, that the tape “T” passes in front of the tape head in this view.
FIG. 2
shows the tape guides
12
and
14
. Each tape guide is typically provided with an upper flange
17
and a lower flange
18
. The purpose of the tape guide flanges is to keep the tape guided into a relatively fixed position with respect to the tape head
11
. As the tape moves past the tape head in either direction “A” or “B”, a tape head element
21
can magnetically encode (“write”) data onto the tape, or it can read data from the tape, depending on how the element is electronically configured. It is possible to electronically configure a tape head element to perform both read and write functions merely by electronic circuit switching within the tape processing apparatus. The process and apparatus for recording magnetic data onto, and reading data from, a magnetic tape are well known in the art, and generally will not be discussed further herein.
In order to increase the density of data storage onto magnetic tape, the data can be recorded onto the tape in “tracks” or “channels”. In a linear tape drive, this essentially consists of segmenting the tape into a plurality of tracks, or horizontal zones, were data is recorded, and separating these data zones with zones where no data is recorded. This separation of the data zones (tracks) allows the data from one track to be distinctly read by the tape head element, without magnetic interference from an adjacent data track. In order to read or write data from or to a multi-track tape, the tape head element needs to be able to access the various tracks. Common practice is to provide the tape head with a plurality of tape head elements. Such a configuration is known as an element array, or merely an “array”. One example of an 8-channel element array is shown in FIG.
2
. The tape head
11
comprises a first array
22
having 8 elements, and an adjacent second array
23
also having 8 elements. The use of an element array allows data to be simultaneously recorded on, or read from, up to eight tracks. The use of two element arrays allows data to be recorded onto the tape by the first array, and then immediately read from the tape by the second array. In this manner the accuracy of data recorded onto the tape can be verified through comparison of the recorded and read data. By electronic switching within the tape drive, the functions of the arrays can be switched from recording data to reading data, and visa versa.
In one commercial example, a tape drive can have two tape head arrays of eight elements each. Each element is configured to record data onto a track which is 1500 microns (&mgr;) high (in the vertical direction of the tape, i.e., in the direction perpendicular to the primary direction of travel of the tape). Each track is separated by a 28 &mgr;band.
One drawback to tape drives is that the tape tends to “wander” as it moves across the tape head in the primary direction. That is, viewing
FIG. 2
, as the tape
30
generally moves across the tape head in the horizontal direction, indicated by the arrow “H”, the tapes also tends to randomly move up and down in the vertical direction “V”. Such vertical movement is typically relatively slow as compared to movement in the horizontal direction, although notable exceptions do occur, as described further below. The effect of tape wander is that data recorded at a given location on a magnetic tape may not be readable if that location wanders away from the read-element when the tape is being read. Tape wander results from inconsistencies in the tape, such as thickness and tension, inconsistencies between tape reels, minor misalignment and tolerances of components within the tape drive itself, and a variety of other factors, collectively making it impractical if not impossible to eliminate tape wander through design changes. One prior art method for accommodating the effects of tape wander is to size the head elements and their spacing (in an array) within the limits of wander. That is, if a head element is big enough, and far enough away from a neighboring element, then the path of tape associated with the corresponding data track will always be in contact with the element, even as the tape wanders. However, this solution has the undesirable effect of reducing the density of data which can be stored on a tape of a given width, since the data channels or tracks are necessarily wider, and fewer tracks can thus be placed onto a tape of a given width.
Another known tech
Anderson James C.
Gonzales Curtis P.
McAllister Jeffrey S.
Hewlett-Packard Development L.P.
Hudspeth David
Tzeng Fred F.
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