Dynamic magnetic information storage or retrieval – Head – Plural gaps
Reexamination Certificate
2000-03-15
2002-11-05
Klimowicz, William (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Plural gaps
Reexamination Certificate
active
06477003
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a system for recording and/or reproducing information, comprising
a magnetizable medium provided with a track pattern comprising
buried servotracks of a first type containing a first signal, and
buried servotracks of a second type containing a second signal,
which servotracks extend substantially in a longitudinal direction and which track pattern, in a transverse direction perpendicular to the longitudinal direction, alternately comprises a servotrack of the first type followed by a servotrack of the second type, and an apparatus comprising
a magnetic head unit comprising a plurality of heads at different positions in the transverse direction,
means for moving the medium relative to the magnetic head unit in the longitudinal direction,
an actuator for moving the magnetic head unit relative to the medium in the transverse direction, and
a control unit for controlling the actuator, which control unit is adapted to generate a position signal based on the difference between the signals of two heads.
The invention also relates to a medium for such a system.
The invention further relates to a magnetic write head comprising a head face with a longitudinal direction in which a magnetizable medium is movable relative to the magnetic write head, and a transverse direction oriented transversely to the longitudinal direction, and further comprising a structure of integrated write units, which structure terminates in the head face, which write units are disposed adjacent one another in the transverse direction, extend substantially in the transverse direction and each have a write gap.
The invention also relates to an arrangement comprising such a magnetic write head and means for scanning a magnetizable medium with the head.
2. Description of the Related Art
Such a medium, such a system and such a magnetic write head are known from WO 96/30897-A2. The known medium is a magnetic tape on which seven servotracks have been written by means of the known magnetic write head, the signal in the first servotrack being in phase with the signal in the third, the fifth and the seventh servotrack and the signals in the second, the fourth and the sixth servotrack being in phase opposition to the signals in the first, the third and the fifth servotrack. By means of an apparatus forming part of the known system it is possible to write information signals over the servotracks on the magnetic tape thus formatted. For this purpose, the apparatus comprises a magnetic head unit having four heads and means for moving the magnetic tape past the magnetic head unit in a longitudinal direction. The known apparatus further comprises an actuator for positioning the magnetic head unit in a transverse direction and a control unit for controlling the actuator. The control circuit comprises a comparator for generating a position signal based on the difference between the signal supplied by a first head and the signal supplied by a second head. The magnetic head unit follows the servotracks on the magnetic tape on the basis of the position signal. A disadvantage of the known system, the known medium and the known magnetic write head is that after the whole magnetic tape has been written or read the magnetic tape is to be rewound in order to return it into its initial position. Another disadvantage of the known system is that only one half of the number of heads supplies information about the position of the servotracks relative to the magnetic head unit.
SUMMARY OF THE INVENTION
It is an object of the invention to provide a system, a medium, a magnetic write head and an arrangement of the types defined in the opening paragraphs, by means of which it is possible to achieve a high accuracy of positioning the magnetic head unit relative to the track pattern on the medium and by means of which it is possible to read and/or write the information from/on the track pattern in an even number of passes. To this end, the system in accordance with the invention is characterized in that the track pattern comprises a group of at least two bands of a first type separated by a band of a second type, which bands of the first type adjoin a servotrack at their sides remote from the band of the second type,
the bands of the first type comprising N
1
servotracks having a first typical width W
1
,
the bands of the second type comprising N
2
servotracks having a second typical width W
2
, which complies with
N
2
=2, 4, 6 etc. and W
2
=(k+½)W
1
or
N
2
=1, 3, 5 etc. and W
2
=2 k.
where k=1,2 etc.,
and the center-to-center distance p between the heads complies with the relationship p=n·W
1
, where n=2, 4, 6, . . . etc.
By means of the measures in accordance with the invention it is achieved that the information can be read from and/or written on the track pattern in an even number of passes of the magnetic head unit relative to the medium and the position signal is immune to tolerances in the servotrack width and to amplitude differences between the first signal and the second signal. This immunity is achieved in that there are always at least two heads disposed on a boundary between two adjacent servotracks and in that these heads read a servotrack of the same one type by means of their facing parts and in that they read a servotrack of the other type by means of their parts which are remote from one another. The above-mentioned tolerances influence the signals read by means of these heads to the same extent, as a result of which these tolerances are cancelled in the actuator drive because this drive is based on the difference between the signals read by the relevant heads. If the apparatus is required to have a write capability, the heads are adapted to read servosignals and write information signals at the same time.
An embodiment of the system in accordance with the invention is characterized in that the medium has at least one servotrack having a width of at least n·W
1
. Owing to these measures one head can be disposed wholly on the n·W
1
wide servotrack during all passes, thereby enabling this head to be used for reading a speed signal representative of the speed of the medium with respect to the magnetic head unit in the longitudinal direction. Owing to said measures the magnetic head unit need not be positioned accurately in the transverse direction in order to generate the speed signal. This simplifies starting of the system in accordance with the invention.
The medium in accordance with the invention is characterized in that the track pattern comprises a group of at least two bands of a first type separated by a band of a second type, which bands of the first type adjoin a servotrack at their sides remote from the band of the second type,
which bands of the first type comprising N
1
servotracks having a first typical width W
1
,
the bands of the second type comprising N
2
servotracks having a second typical width W
2
, which complies with
N
2
=2, 4, 6 etc. and W
2
=(k+½)W
1
or
N
2
=1, 3, 5 etc. and W
2
=2k.W
1
,
where k=1, 2 etc.
The medium in accordance with the invention can be used in the system in accordance with the invention with the advantages outlined above.
An embodiment of the medium in accordance with the invention is characterized in that N
2
=1 and k=1. By means of an apparatus comprising, for example, three heads disposed at a center-to-center distance of at least 2·W
1
and having a recording width of approximately W
1
this track pattern can be provided wholly with information tracks in an even number of passes. For example, if N
1
=1 this can be effected in two passes. The track pattern can be repeated several times in the transverse direction of the medium, as a result of which the magnetic head unit can inscribe a following track pattern with information after a displacement in the transverse direction. In a preferred embodiment N
1
=7, three of such track patterns are juxtaposed in the transvers
Hoogendoorn Abraham
Kalfs Johannes J. W.
Klimowicz William
Welsh & Katz Ltd.
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