Dynamic magnetic information storage or retrieval – Automatic control of a recorder mechanism – Controlling the head
Reexamination Certificate
1998-04-03
2001-08-14
Sniezek, Andrew L. (Department: 2651)
Dynamic magnetic information storage or retrieval
Automatic control of a recorder mechanism
Controlling the head
C360S121000
Reexamination Certificate
active
06275350
ABSTRACT:
TECHNICAL FIELD
The invention relates generally to positioning magnetic heads in magnetic storage devices used for data storage and retrieval, and relates more particularly to the positioning of the magnetic heads to compensate for transducer-to-tape alignment errors caused by dimensional instability of the tape.
DESCRIPTION OF THE RELATED ART
Magnetic tape data storage devices are used to backup data stored on non-removable disk drives in computers, so that data will not be lost in the event of an operator or electrical error, or a mechanical failure. The use of magnetic tape data storage devices is commonplace, since the cost per unit of stored data is low compared to other forms of electronic data storage. Due to the increasing density and volume of data stored on non-removable disk drives, there is an increasing need for tape data storage devices that provide greater data storage capacity and higher data transfer rates. To satisfy the requirement for data storage, higher track densities on the magnetic tape are sought. To satisfy the need for higher transfer rates, magnetic heads that have multiple read and write transducers which operate simultaneously are used.
There are a number of factors that must be considered in determining the maximum tape track density of a storage device, including the need to compensate for data track alignment errors caused by small manufacturing variations in the tape storage devices or caused by environmental factors that affect the dimensional stability of the tape. Dimensional changes affect the relative position of a magnetic head and data tracks on the tape. Dimensional changes in tape, particularly for tape formed using polymer substrates, such as the commonly used PET (polyethylene terephthalate) substrate, are generally a function of temperature, humidity and the internal structure of the tape. Many kinds of tape have been found to shrink over the useful life of the tape, as a function of age. Compensating for dimensional instability of tape has become more stringent as track densities increase.
For purposes of recording and reading numerous tracks simultaneously, many prior art magnetic tape data storage devices use multi-transducer heads that extend across all or a significant portion of the width of the tape. In such devices, fabrication difficulties and physical limits often require that the individual transducers on the multi-transducer head must be separated by significantly more than the width of a single track.
Referring to
FIG. 1
(Prior Art), a conventional configuration of a multi-transducer magnetic head
100
is shown as extending over a portion of the width of a magnetic tape referenced by the number
102
and addressed by the magnetic head. The portion of the tape
102
shown has a width of W
1
, which is the width prior to any age related shrinkage. A number of transducer pairs
104
are arrayed along the magnetic head
100
. Each transducer pair
104
includes one write transducer
106
, which has a length approximately as wide as the data track
110
, and one read transducer
108
, which is spaced apart from the write transducer along the longitudinal axis of the tape. The read transducer has a length that is less than the length of the write transducer
106
in order to provide a margin
118
on each side of the read transducer
108
. The difference in the lengths of the two transducers within each pair
104
is intended to compensate for sources of track alignment error, including some tolerance for age-related tape shrinkage.
A number of data tracks
110
are shown, with one data track
110
being located beneath each of the transducer pairs
104
. Each data track
110
has a centerline
116
that is aligned with centerlines passing through a read transducer
108
and a corresponding write transducer
106
. The direction of motion of the tape
102
is from right to left. In the spaces between the data tracks
110
, currently unaccessed regions
114
exist and are available for subsequently formed tracks. Separate electronic channels for the read and write transducers permit control of simultaneous read and write operations. Simultaneous read and write operations are used to confirm that data recorded on tape
102
by a write transducer is accessible by a read transducer. The position of the transducer pairs
104
relative to the tape
102
is shown in
FIG. 1
before any age-related shrinkage has occurred. The pitch of the adjacent read transducers
108
is consistent through the entire transducer array. Similarly, the pitches of the write transducers
106
and the data tracks
110
are consistent. The term “pitch” is defined herein as the center-to-center spacing between adjacent elements.
The width of the multi-transducer head
100
and the width of the magnetic tape may be more than one hundred times the width of an individual data track
110
. Therefore, shrinkage of only a few tenths of a percent in the width of a tape can cause the spacing between recorded data tracks
110
to change sufficiently, relative to the spacing at the time that the tracks were recorded, potentially causing a track misalignment between read transducers
108
of the magnetic head
100
and the data track
110
intended to be read. In
FIG. 2
(Prior Art) the width of the portion of the tape
102
has a reduced width W
2
, as compared to the original width W
1
of FIG.
1
. As shown in
FIG. 2
, shrinkage may cause some of read transducers
108
to extend significantly beyond the data tracks
110
to be read. If age-related shrinkage is not compensated for, or is insufficiently compensated for, the read transducers
108
of the outermost transducer pairs
104
will no longer align with the data tracks
110
sufficiently to enable the read transducers to reliably read the stored data.
Servo tracking techniques have been developed to reduce the effects of tracking error and thus increase the possible track density of tape systems. Known servo tracking techniques vary widely, but most involve methods of dynamically moving the magnetic head to reposition the transducers over the correct data tracks. However, such servo mechanisms are not necessarily effective in compensating for age-related shrinkage when used on conventional multi-transducer heads because simultaneous alignment of the outermost transducers over the appropriate data tracks may be prevented after tape shrinkage. For example, after shrinkage, the distance between the outermost tracks read by the magnetic head will be less than the distance between the outermost read transducers. Thus, displacing the read transducers on one end of a head to align with the appropriate data tracks will displace the read transducers on the opposite end of the head away from alignment with the appropriate data tracks. Consequently, servo tracking conventional heads does not directly address the adverse effects of dimensional instabilities of magnetic tapes.
What is needed is a magnetic head and transducer arrangement and method which allow the use of multi-transducer magnetic heads for simultaneously writing and reading an array of data tracks of a data storage tape and which have read transducers positioned to compensate for age-related dimensional tape instabilities.
SUMMARY OF THE INVENTION
A magnetic head and transducer arrangement and method include providing a progressive offset of a position of a read transducer relative to a corresponding write transducer in an array of transducer pairs. More specifically, a distance between a centerline through a read transducer and a centerline through a write transducer of the same pair will be greater with the distance of the pair from a head positioning reference point on the magnetic head. While not critical, the head positioning reference point is preferably along a track-following plane that is defined by operation of a servo mechanism.
In one embodiment, the array of transducer pairs is fixed to a magnetic head that extends across at least a portion of the width of a magnetic tape. In a preferred embodiment, the head positioning reference point
Hewlett--Packard Company
Sniezek Andrew L.
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