Dynamic magnetic information storage or retrieval – Head – Head accessory
Reexamination Certificate
2001-04-05
2003-09-23
Davis, David (Department: 2652)
Dynamic magnetic information storage or retrieval
Head
Head accessory
Reexamination Certificate
active
06624973
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a magnetic head for use in a floppy disc drive (FDD) and a hard disc drive (HDD).
2. Description of the Related Art
An example of a conventional magnetic head that is used in an FDD is shown in FIG.
10
.
In
FIG. 10
, a magnetic head
1
′ is, in general, composed of a slider
2
sliding on a magnetic recording medium (not shown), a substantially rectangular opening
3
formed in the slider
2
, a magnetic core
6
having gaps (a read/write gap
4
and an erasing gap
5
), inserted into the opening
3
and sealed up with a sealing material such as glass, a back yoke
7
made of a magnetic material and joined to the magnetic core
6
to thereby form a closed magnetic path, and a read/write coil
11
and an erasing coil
12
respectively provided on leg portions
8
,
10
of the back yoke
7
.
The magnetic core
6
, which is inserted in the opening
3
formed in the slider
2
, is sealed up with glass, etc. which is molten and poured into gaps formed between the magnetic core
6
and inner walls of the slider
2
in order to prevent it from happening that foreign substances like dusts get in the gaps and deteriorate characteristics.
The slider
2
including the opening
3
is formed by press-molding and then sintering. However, the opening
3
formed with this method does not always have a precise rectangular shape. As shown in
FIG. 11
, the opening
3
may be deformed in such a manner as to have an increased width at the middle or its longitudinal direction (
FIG. 11
) or a decreased width to the contrary. The magnetic core
6
inserted in the opening
3
with such a deformation is apt to move freely when molten glass is poured thereinto, making it difficult to determine an appropriate position of the magnetic core
6
.
FIG. 12
shows an embodiment in which projections
30
a
,
31
a
and
31
b
are provided on some of the inner walls of the opening
3
as a means for locating the magnetic core
6
at an appropriate position.
Of four inner walls
30
,
31
,
32
and
33
, which define the opening
3
, the inner wall
30
is provided at its middle with the projection
30
a
extending in a depth direction (in a direction perpendicular to the paper of
FIG. 12
) of the opening
3
. The inner wall
31
is provided with the two projections
31
a
,
31
b
having the same height as the projection
30
a
and extending in a depth direction of the opening
3
like the projection
30
a.
In a magnetic head shown in
FIG. 12
, when molten glass is poured into the opening
3
, gaps between the magnetic core
6
and the inner walls
30
,
31
provided with the projections
30
a
,
31
a
,
31
b
are to receive more molten glass than those between the magnetic core
6
and the inner walls
32
,
33
provided with no projection. Accordingly, there is generated an imbalance of surface tension in the poured glass, and the magnetic core
6
is moved toward the inner walls
32
,
33
to be duly positioned. However, the amount of glass poured between the magnetic core
6
and the inner walls
30
,
31
provided with the projections
30
a
,
31
a
,
31
b
is different from the amount of glass poured between the magnetic core
6
and the inner walls
32
,
33
provided with no projection. Therefore, if the viscosity of the glass is smaller than the optimum, the glass is too fluid and may flow out in an undesirable way when poured between the magnetic core
6
and the inner walls
30
,
31
. On the other hand, if the viscosity of the glass is larger than the optimum, the glass may not satisfactorily flow between the magnetic core
6
and the inner walls
32
,
33
.
In order to solve such problems, a magnetic head shown in
FIG. 13
is provided with projections
32
a
,
33
a
,
33
b
on the inner walls
32
,
33
, which are located to oppose respectively the projections
30
a
,
31
a
,
31
b
on the inner walls
30
,
31
. According to this magnetic head, the glass can be easily poured between all the inner walls
30
to
33
and a magnetic core
6
. However, it is still impossible to determine an appropriate position of the magnetic core
6
because there are gaps existing between the respective projections and the magnetic core
6
, in other words, the width and length of the magnetic core
6
are different from the distances between the projections
31
a
and
33
a
, and
31
b
and
33
b
and between the projections
30
a
and
32
a
, respectively.
Now, in a magnetic head shown in
FIG. 14
, of projections provided on the four inner walls
30
to
33
, projections
30
a
′,
33
a
′ and
33
b
′ on the inner walls
30
and
33
are formed such that their heights from the inner walls are smaller than those of the projections
31
a
,
31
b
and
32
a
on the inner walls
31
and
32
. With this formation, when glass is poured into an opening
3
, the glass is to flow in a larger amount into gaps between the magnetic core
6
and the inner wall
31
provided with higher projections and between the magnetic core
6
and the inner wall
32
provided with a higher projection, than into gaps between the magnetic core
6
and the inner wall
30
provided with a lower projection and between the magnetic core
6
and the inner wall
33
provided with lower projections. Therefore, a difference is generated in surface tension of the glass, and the magnetic core
6
is moved toward the inner walls
30
and
33
. As a result, the magnetic core
6
at one side is aligned to the heights of the projections
30
a
′,
33
a
′ and
33
b
′ to be duly positioned. Since the projections
30
a
′,
33
a
′ and
33
b
′ exist on the inner wall
30
and
33
, toward which the magnetic core
6
is moved, gaps are secured between the inner walls
30
and
33
and the magnetic core
6
, thereby allowing the glass to appropriately flow.
In a composite type magnetic head for an HDD, a metal spacer maybe used as a means of positioning a magnetic core. For instance, a thin plate spring made of phosphorous bronze, beryllium copper or the like is put as a spacer between the magnetic core and the inner walls or the opening to determine an appropriate position of the magnetic core. However, the thermal expansion coefficient of metal as a spacer is greatly different from that of the glass to be poured in the opening to seal up the magnetic core, so cracks are easily generated in the glass. Further, if the metal used as a spacer is exposed at a surface sliding on a recording medium, since the hardness of the metal is lower than that of the glass and of ceramics as a magnetic core material, the metal part is worn away more quickly due to friction, which causes a partial abrasion in the slider. As a result, there is a deterioration easily generated with regard to a contact with a recording medium and a posture thereto.
As a density of a recording medium becomes higher, it is required to increase a track density in order to increase a writing capacity of a unit track, forcing its track width to be decreased. While this reduces the thickness of a magnetic core contributing to cost reduction, the wall thickness of a molding die for a slider into which the magnetic core is inserted has to be also reduced creating problems with the strength and life of the molding die. Specifically in a magnetic head for a high recording density FDD of 120 MB type, its track width is about 8 &mgr;m, so the thickness of the magnetic core is about 0.08 to 0.1 mm. This means the magnetic head is about ½ as thick as a magnetic head for a standard recording density FOD of 2 MB type. Further, if the thickness of the magnetic core is reduced, it becomes accordingly possible to reduce (narrower) the size of the opening of the slider formed to accept the magnetic core. However, for making the opening of the slider narrower, it is necessary to reduce the thickness of a molding die for forming the opening, whereby the molding die can be easily deformed. This makes it difficult to keep the same precision in the shape of the openi
Egawa Motoji
Oishi Shigeyuki
Davis David
Minebea Co. Ltd.
Oliff & Berridg,e PLC
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