Dynamic magnetic information storage or retrieval – Head mounting – For moving head during transducing
Reexamination Certificate
2001-09-13
2004-01-13
Heinz, A. J. (Department: 2653)
Dynamic magnetic information storage or retrieval
Head mounting
For moving head during transducing
Reexamination Certificate
active
06678123
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a magnetic head, a recording and/or playback method for a tape-type magnetic recording medium and a rotary magnetic head mechanism.
Various apparatus for recording and playing back a signal onto and from a tape-type magnetic recording medium are known and widely used. An exemplary one of apparatus of the type mentioned is a video cassette recorder apparatus of a rotary drum type wherein a magnetic head mounted on a rotating drum forms and records a track having an inclination angle on a tape-type magnetic recording medium and further traces and plays back the inclined track. Particularly recently, a video tape recorder (VTR) apparatus compliant with digital standards has been popularized.
One of tape-type magnetic recording media is a coat-type magnetic tape. The coat-type magnetic tape has a structure wherein a magnetic layer or a magnetic face is formed on a plastic base material by applying acicular or particulate magnetic powder to the plastic base material using a binder as an adhesive. The magnetic face of the coat-type magnetic tape has a coercive force Hc and a residual magnetic flux density Br which are inclined to increase as the recording density increases. For example, with an MP tape compliant with the DV standards, the coercive force Hc reaches 2,300 oersted and the residual magnetic flux density reaches 3,000 gauss.
On the other hand, the size of the simple substance of the magnetic powder decreases to 0.1×1.0 &mgr;m with a coat-type metal tape. Further, as regards the tape thickness, while tapes of approximately 10 to 16 &mgr;m thick are conventionally used on editing machines, the tape thickness is decreased in order to satisfy the demand for miniaturization of a tape cassette and for recording and playback for a long period of time. Now, the tape thickness of a tape-type magnetic recording medium for a digital video signal compliant with the DV standards is 7 to 8 &mgr;m.
Therefore, it is necessary for an apparatus for recording/playing back onto/from a magnetic tape of such a characteristic as just described to be contrived in terms of a fluidic interference function relating to control of physical contact with the magnetic tape and a magnetic interference function relating to recording/playback.
An exemplary one of magnetic tape recording/playback apparatus of the type described is a rotary magnetic head mechanism which records/plays back onto/from a magnetic tape medium while rotating. A conventional rotary magnetic head mechanism of the type just mentioned adopts a magnetic head which operates in accordance with the principle of magnetic induction. In the magnetic head, magnetic poles are opposed to each other with a very small head gap left therebetween, and a magnetic face of a magnetic tape medium is disposed perpendicularly to and very close to the head gap. Upon recording, magnetic lines of force generated from the magnetic poles when they are driven magnetize a magnetic substance which forms the magnetic face of the magnetic tape medium while the magnetic lines of force pass from one to the other of the magnetic poles through the head gap and the magnetic face to record on the magnetic tape medium. On the other hand, upon playback, leakage fluxes generated from the magnetic substance which forms the magnetic face of the magnetic tape medium are caught through the head gap by the magnetic poles to detect an electromotive force generated by electromagnetic induction when the leakage fluxes vary as the magnetic tape medium is fed.
In order to raise the recording density and assure a high S/N (signal to noise) ratio, it is necessary for the magnetic tape medium to closely contact with the head gap and besides it is necessary to maintain stable movement of the tape while such close contact of the tape is maintained.
Conventionally, in order to realize the close contacting state described above, the magnetic tape medium is pressed against the head gap to obtain a necessary contact pressure. Particularly with a rotary magnetic head mechanism, the contact pressure is obtained by a tension applied to the magnetic tape medium.
FIGS. 11
to
13
show a configuration of a conventional rotary magnetic head mechanism of the type described.
Referring to
FIGS. 11
to
13
, a rotary magnetic head mechanism
100
shown includes a cylindrical rotary drum
101
having a head window
102
formed in a recessed relationship therein such that it is open on a part of circumferential face of the cylindrical rotary drum
101
, and a magnetic head
104
having a head gap
103
and disposed in the head window
102
. The rotary magnetic head mechanism
100
is rotated at a predetermined speed in a rotational direction
106
. Upon rotation of the rotary magnetic head mechanism
100
, also the magnetic head
104
moves at an equal speed. Tension
107
is applied to a magnetic tape medium
105
which extends along the rotary drum
101
such that the magnetic tape medium
105
is pressed against the head gap
103
by the tension
107
and therefore is fed in the same direction at a speed lower than that of the magnetic head
104
. A cylindrical fixed drum
111
is disposed in a little spaced relationship below the rotary drum
101
.
In order to assure a good contact state between the head gap
103
and the magnetic tape medium
105
, a face
108
of the rotary magnetic head mechanism
100
around the head gap
103
along which the rotary magnetic head mechanism
100
contacts with the magnetic tape medium
105
is formed as a curved face of a curvature
109
which is convex in a recording track direction, that is, a magnetic tape feeding direction and is formed also as a curved face of a curvature
110
which is convex also in a track width direction and besides the face
108
projects from the cylindrical face of the rotary drum
101
together with the head gap
103
.
When the magnetic tape medium
105
contacts with the magnetic head
104
having the configuration just described with a pressing force caused by the tension
107
, the magnetic tape medium
105
is deformed into a convex shape along the face
108
of the magnetic head
104
and a good contact state between the magnetic head
104
and the magnetic tape medium
105
can be assured. Meanwhile, a portion of the magnetic tape medium
105
which does not contact with the magnetic head
104
is sometimes deformed by the gaps between the head window
102
and the rotary drum
101
and fixed drum
111
.
As described above, the rotary magnetic head mechanism
100
of the conventional configuration applies sufficient tension
107
to the magnetic tape medium
105
to compulsorily press the magnetic tape medium
105
against the magnetic head
104
of a convex shape to assure a good contact state between them thereby to make use of magnetic interference between the magnetic head
104
and the magnetic tape medium
105
to effect magnetic recording or playback of the magnetic tape medium
105
.
The rotary magnetic head mechanism
100
, however, has a problem that, since the magnetic tape medium
105
is compulsorily pressed against the magnetic head
104
of a convex shape as described above, the head gap
103
is liable to be abraded by the magnetic tape medium
105
, resulting in reduction of the life of the head gap
103
. Simultaneously, there is another problem that the magnetic face of the magnetic tape medium
105
is liable to be abraded similarly and suffer from irreversible deformation, resulting in reduction of the life of the magnetic tape medium
105
.
Therefore, in order to assure a long life of the head, the rotary magnetic head mechanism
100
is conventionally designed such that the depthwise dimension of the head gap
103
, that is, the gap depth, is set so deep as to have a suitable margin. In particular, for example, the gap depth is initially set as deep as 20 to 30 &mgr;m to assure a long interval of time until the gap depth is decreased to its limit value by abrasion of the magnetic head
104
thereby to assure a long life of the rotary magnetic
Sugizaki Yasuo
Takayama Jun
Frommer William S.
Frommer & Lawrence & Haug LLP
Heinz A. J.
Sony Corporation
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