Dynamic magnetic information storage or retrieval – General recording or reproducing – Signal switching
Reexamination Certificate
1998-10-20
2001-05-29
Kim, W. Chris (Department: 2651)
Dynamic magnetic information storage or retrieval
General recording or reproducing
Signal switching
C360S077020
Reexamination Certificate
active
06239932
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a method of formatting a magnetizable medium, comprising the recording in one pass of at least a first servo signal in a first servo track by means of a first write head and a second servo signal in a second servo track, adjacent the first servo track, by means of a second write head.
The invention also relates to a magnetizable medium provided with at least a first servo track containing a first servo signal and a second servo track adjacent the first servo track and containing a second servo signal.
Furthermore, the invention relates to a cartridge comprising at least one reel hub on which a magnetic tape has been wound, which magnetic tape has been provided with at least a first servo track containing a first servo signal and a second servo track adjacent the first servo track and containing a second servo signal.
The invention also relates to an arrangement for formatting a magnetizable medium, comprising
a write head unit comprising at least a first write head and a second write head disposed near the first write head,
a mechanism for moving the medium and the write bead unit with respect to one another,
a servo generator for driving the first write head with a first servo signal and for driving the second write head with a second servo signal.
DESCRIPTION OF THE RELATED ART
Such a method, such a medium, such a cartridge and such an arrangement are known from WO 96/30897-A2 (PHN 15250). In the known method a large number of servo tracks are written simultaneously on a magnetic tape by means of a write-head unit having a number of write heads which is the same as the number of tracks. The write-head unit then scans the magnetic tape in its longitudinal direction and the write heads adjoin one another in a direction transverse to said longitudinal direction. The write heads are then driven in such a manner that two adjacent servo tracks always contain a distinguishable servo signal. A magnetic tape thus provided with servo tracks is used in a multi-track linear data recording apparatus. The transitions between two adjacent servo tracks serve to position a recording/reproducing head in the data recording apparatus with respect to the medium. A disadvantage of the known method is that the transition between two adjacent servo tracks is not sharp. As a result of this, the data recording apparatus is not capable of accurately positioning the recording/reproducing head with respect to the medium.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a method of the type defined in the opening paragraph which yields a sharper transition between two adjacent servo tracks than the known method.
The method in accordance with the invention is characterized in that during the pass the medium is magnetized alternately by the first write head and the second write head. The invention is based on the recognition of the fact that the magnetic fields of the first write head and the second write head can interfere with one another as a result of which, amplified by non-linear characteristics of the magnetizable medium, a reduced magnetization of the medium is obtained near the transition between two adjacent servo tracks. Owing to the measures in accordance with the invention it is achieved that the magnetic fields of the first write head and the second write head alternate with one another as a function of time during use. As a result of this, the magnetic fields of the first write head and the second write head influence one another to a relatively small degree and a better magnetization of the medium is obtained near the transition between the first and the second servo track. In the transitional area between the first and the second write head the magnetic field at a given instant is determined almost entirely by the first write head or by the second write head. As a result of this, the transitional area between two adjacent servo tracks is magnetized alternately in accordance with the first servo signal and the second servo signal and a sharp transition between the first servo track and the second servo track is obtained.
A variant of the method in accordance with the invention is characterized in that use is made of a frequency of alternation which is higher than, or substantially equal to, the highest frequency in the first servo signal and the second servo signal. Owing to this measure, the first and the second servo signal, also referred to as tracking signal, can subsequently be recovered more easily from the first and the second servo track by filtering.
A variant of the method in accordance with the invention is characterized in that use is made of a frequency of alternation which is higher than, or substantially equal to, the Nyquist frequency of the medium. Owing to this measure it is achieved that the alternation frequency is recorded on the medium in a strongly attenuated form so that it is no longer necessary to filter out the alternation frequency during the reconstruction of the first and the second servo signal. Moreover, this results in substantially the entire bandwidth of the medium being available for the first and the second servo signal.
A variant of the method in accordance with the invention employs phase displaced periodic bias signals for the respective write heads.
That achieves that the distortion of the first and the second servo signal caused by non-linearity of the magnetization curve of the medium is reduced and at the same time a satisfactory magnetization is obtained near the transition between the first and the second servo track.
The bias signals may include a periodic trivalent signal. That yields the advantage that the first and the second write head are operated efficiently.
By configuring the first and the second servo signals to have phase opposed sinusoidal components, the transition between the first and the second servo track can readily be tracked by means of a servo system. For recording such signals the method in accordance with the invention has a great many advantages because, when this is method is not used, the magnetic fields caused by the first sinusoidal component and the second sinusoidal component counteract one another to a maximal extent because they are in phase opposition.
The two write heads may have a common pole. That has the advantage that the first and the second servo track can be written very close to one another so that the medium can store a large amount of information. When such write beads are used the method in accordance with the invention has a great many advantages because saturation of the common pole is precluded by the alternate write method.
The two servo signals may be recorded alternately in odd and even numbered servo tracks. That has the advantage that the medium can be provided with all the required servo tracks in one pass, as is described in WO 96/30897-A2 (PHN 15250), which is herewith incorporated by reference, and that only two different servo signals and two different bias signals have to be generated.
The medium in accordance with the invention is characterized in that
the first servo track contains a first bias signal and the second servo track contains a second bias signal, and
the first bias signal and the second bias signal alternately assume their respective maximum value.
An advantage of the medium in accordance with the invention is that the transition between the first and the second servo track is sharp, so that the data recording apparatus is capable of accurately positioning the recording/reproducing head with respect to the medium. As a result of this accurate positioning the data can be written and read with a greater reliability. In addition, this accurate positioning enables the density of the data tracks to be higher than with the known system.
The cartridge in accordance with the invention is characterized in that
the first servo track contains a first bias signal and the second servo track contains a second bias signal, and
the first bias signal and the second bias signal alternately assume their respective maxim
Kim W. Chris
Neal Regina Y.
OnStream Inc.
Welsh & Katz Ltd.
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