Method of manufacturing a head unit

Details Method of manufacturing a head unit Method of manufacturing a head unit

2001-07-31

2003-11-04

Vo, Peter (Department: 3729)

Metal working

Method of mechanical manufacture

Electrical device making

C029S835000, C360S122000, C360S271500

Reexamination Certificate

active

06640418

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a method of manufacturing a head unit of a magnetic head to be mounted in a magnetic recording/reproducing apparatus such as a VTR.
BACKGROUND ART
A conventional method of manufacturing a head unit will hereinafter be described with reference to the appended figures.
FIG. 3
is a side view of an example of a conventional head unit. As shown in
FIG. 3
, two right and left head chips
2
and
3
(hereinafter referred to as “chips”) are bonded to a base
1
. The chips
2
and
3
are formed of pairs of metal plates (cores)
5
and
6
, respectively. Each pair is formed of two metal plates joined to each other and a coil
4
is wound around each metal plate.
Gaps
7
and
8
are gaps formed in the joints between the metal plates
5
and the metal plates
6
of the respective chips. Curved surfaces
2
a
and
3
a
are formed as the front faces of the chips
2
and
3
. Gaps on the curved surfaces
2
a
and
3
a
are head gaps
7
a
and
8
a,
respectively. In the figure, GD indicates a gap depth dimension of the gaps
7
and
8
in the side portions of the chips
2
and
3
.
The base
1
eventually is attached to a rotating cylinder (not shown in the figure), and the curved surfaces
2
a
and
3
a
of the front faces of the chips
2
and
3
slide on a magnetic tape. Numeral
9
indicates a rotation center of the rotating cylinder.
FIG. 4A
is a front view of an example of chip front faces before they are ground. Though the following description is directed to the chip
3
, the same is true for the chip
2
. Numeral
10
indicates contour lines of the curved surface
3
a
of the chip
3
, more specifically, contour lines of the curved surface
3
a
when the head gap
8
a
is seen from an extension of a straight line
11
extending between the head gap
8
a
and the rotation center
9
of the rotating cylinder as shown in FIG.
3
. Numeral
12
indicates a vertex of the curved surface
3
a.
The vertex
12
corresponds to a center of the contour lines
10
. Bo indicates a distance between the vertex
12
and the head gap
8
a.
Y indicates a difference of heights between the chip
2
and the chip
3
from a chip-attached surface
1
a
of the base
1
, namely, a relative height (hereinafter referred to as “a head relative height”) of the two chips
2
and
3
. In other words, the head relative height corresponds to a difference in level between the chips in a direction orthogonal to a chip-traveling direction.
FIG. 5
is a perspective view showing a chip grinding process. In the grinding process, a head unit
13
including the chips
2
and
3
is installed in a rotating drum
14
. Accordingly, the chips
2
and
3
rotate coincidentally with the rotating drum
14
(rotating in a direction indicated by an arrow b). The front faces of the chips
2
and
3
are ground during rotation with a grinding tape
15
brought into contact therewith. Since the grinding is carried out with the grinding tape
15
traveling vertically, the front faces of the chips are ground always with an unused surface of the grinding tape
15
.
In such a grinding process, as shown in
FIG. 4A
, the vertex
12
as a reference used to indicate Bo shifts in a direction indicated by an arrow a depending on the grinding amount.
FIG. 4B
shows a state where the grinding of the chip front faces is completed after the foregoing grinding process. A comparison of
FIGS. 4A and 4B
shows that the vertex
12
in
FIG. 4B
shifts in the arrow a direction. In the figures, S indicates a shift amount of the vertex
12
during the grinding.
The portion of the vertex
12
is to be brought into an excellent state of contact with a magnetic tape. Thus, it is preferable that the vertex
12
be as close to the head gaps
7
a
and
8
a
as possible. Ideally, the vertex
12
falls on the head gaps
7
a
and
8
a,
namely, Bo=0. Hence, Bo is a key factor affecting magnetic head performance, and thus, in the manufacturing process, it is necessary to selectively use a magnetic head in which Bo falls within the range of predetermined standard values that meet a required level of performance.
However, in the conventional manufacturing method as mentioned above, the shift amount S of the vertex
12
varies depending on the type of a head unit, and thus it is difficult to make the value of Bo fall in a target range. This has been a factor allowing the manufacturing yield to be decreased.
DISCLOSURE OF THE INVENTION
This invention is intended to solve the conventional problem as mentioned above. It is an object of the present invention to provide a method of manufacturing a head unit, wherein a predetermined distance is obtained between a vertex of a curved surface as a chip front face and a head gap after the chip front face is ground.
In order to achieve the above object, a method of manufacturing a head unit with a plurality of head chips mounted on one base according to the present invention is characterized as follows. That is, with respect to a head chip of the plurality of head chips fixed to the base, assume a distance between a vertex of a curved surface as a front face of the head chip and a head gap is indicated as Bo, a gap depth dimension in the head chip as GD, a value of Bo before grinding the front face of the head chip as Bo
1
, a value of Bo after grinding the front face as Bo
2
, a value of GD before grinding the front face of the head chip as GD
1
, a value of GD after grinding the front face as GD
2
, a grinding amount corresponding to a difference between GD
1
and GD
2
as &Dgr;GD, and a head relative height that is a difference in height from the base between two adjacent head chips of the plurality of head chips as Y,
in processing the head chips in which the head relative height Y is Y′ with the grinding amount &Dgr;GD of &Dgr;GD′, a value of Bo
1
corresponding to a target value of Bo
2
is determined through: a relationship between Bo and GD that has been determined with respect to a head unit in which the head relative height is substantially equal to Y′; the target value of Bo
2
; and the value of &Dgr;GD′, and the value of Bo
1
thus determined is used as Bo
1
of the head chips in which the head relative height Y is Y′.
According to the foregoing method of manufacturing a head unit, grinding of the front faces of the head chips is conducted after Bo
1
corresponding to the target value of Bo
2
is determined. Hence, a head unit with the value of Bo
2
falling within the range of standard values can be manufactured efficiently, and accordingly the yield can be improved.
In the foregoing method of manufacturing a head unit, it is preferable that the relationship between Bo and GD be predetermined in a form of a characteristic straight line. The foregoing method of manufacturing a head unit allows the value of Bo
1
corresponding to the target value of Bo
2
to be determined easily through a relative formula of the characteristic straight line, the target value of Bo
2
and &Dgr;GD.
Furthermore, it is preferable that the characteristic straight line is a straight line showing a correlation between coordinate axes determined using a distribution of coordinates (GD
1
, Bo
1
) and (GD
2
, Bo
2
).
Furthermore, preferably, the target value of Bo
2
is zero. According to the foregoing method of manufacturing a head unit, the value of Bo
1
is determined with the target value of Bo
2
set to zero as an ideal value, so that the value of Bo
2
easily distributes itself in the vicinity of zero, and thus the yield can be improved. This provides an advantageous manufacturing method.
Furthermore, preferably, the head chip before grinding the front face is so formed that a target value of the distance between the vertex of the curved surface as the front face of the head chip and the head gap before the head chip is fixed to the base is set to the value of Bo
1
corresponding to the target value of Bo
2
. The foregoing method of manufacturing a head unit allows the value of Bo
1
to be obtained with high accuracy by bonding the chips to the

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