Electrical audio signal processing systems and devices – Electro-acoustic audio transducer – Electromagnetic
Reexamination Certificate
1999-11-15
2001-05-15
Le, Huyen (Department: 2743)
Electrical audio signal processing systems and devices
Electro-acoustic audio transducer
Electromagnetic
C381S420000, C381S433000
Reexamination Certificate
active
06233346
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a surface-mounted electromagnetic sound generator in which sound is generated by vibrating a vibration plate using an electromagnet. More particularly, the invention relates to an electromagnetic sound generator in which a yoke used in the electromagnet is insert-molded when the case of the sound generator is molded.
2. Description of the Related Art
A yoke employed in a surface-mounted electromagnetic sound generator of this kind according to the prior art usually is fixed within a case by means of a bonding agent. In order to reduce the thickness of the case, however, a yoke
4
is integrated with a case
2
made of plastic, as shown in
FIGS. 3 and 4
. Specifically, when a lower case
2
b
of the box-shaped case
2
is molded, a magnetic-circuit board
4
a
of the yoke
4
is imbedded by being insert-molded into side walls
2
c
and a bottom
2
d
of the case, as shown in FIG.
3
. As a result, the magnetic-circuit board
4
a
is secured by being integrally molded with the lower case
2
b.
When the case
4
is integrated with the lower case
2
b
in the manner described above, the bottom
2
d
of the lower case
2
b
is capable of being reinforced by the magnetic-circuit board
4
a
of the yoke
4
. This makes it possible to reduce the thickness T of the bottom
2
d.
As a result, it is possible to reduce the thickness of the case housing the surface-mounted electromagnetic sound generator having this structure.
In the example of the prior art described above, it is possible to reduce the thickness of the bottom
2
d
of lower case
2
b.
However, if the thickness T is reduced to 0.3 mm, the bottom
2
d
may not be filled with molding material adequately when the lower case
2
b
is injection molded. Molding can be difficult to carry out. Consequently, even it is attempted to achieve a thinner device by thinning the bottom
2
d
of the lower case
2
b,
a major reduction in thickness is not possible.
Further, problems arise in a case where it is attempted to deal with this situation by insert-molding the yoke. Specifically, the thickness of both the side wall
2
c
and bottom
2
d
of the lower case
2
b
is small and, in addition, the magnetic-circuit board
4
a
of the yoke
4
is insert-molded with its outer peripheral portion being only slightly inserted into the side wall
2
c.
The result is that the yoke
4
is surrounded only by a molded portion of small thickness. This means that it is difficult to acquire sufficient strength to fix the yoke
4
and to provide enough strength to resist impact. A high strength is required especially since a coil
6
, a ring-shaped magnet
8
and a vibration-plate supporting ring
12
, which supports a vibration plate
10
, are attached to the yoke
4
.
SUMMARY OF THE INVENTION
Accordingly, an object of the present invention is to provide a surface-mounted electromagnetic sound generator in which yoke fixing strength can be increased and the thickness of the magnetic sound generator reduced.
According to the present invention, the foregoing object is attained by providing a surface-mounted electromagnetic sound generator for generating sound by causing a vibration plate to vibrate by an opposing electromagnet which includes a yoke and a coil housed in a case, wherein the yoke has a magnetic-circuit board an outer circumferential portion of which is provided with a drawn portion, the drawn portion being imbedded in the case by insert-molding when the case is molded.
Further, the drawn portion is formed by raising the outer circumferential portion of the magnetic-circuit board and bending a leading edge of this portion in an outward direction.
Thus, the surface-mounted electromagnetic sound generator according to the present invention includes a yoke having a magnetic-circuit board formed to have a drawn portion. The drawn portion is formed by raising the outer circumferential portion of the magnetic-circuit board and bending a leading edge of this portion in the outward direction. In the present invention, the drawn portion is insert-molded in the lower case when the lower case, which constitutes part of the case, is molded, thereby imbedding the drawn portion in the lower part of the side wall of the lower case. As a result, the drawn portion of the yoke is inserted deeply into the lower case along the side wall thereof to increase the thickness of the portion that surrounds the drawn portion. The strength with which the drawn portion is anchored is thus increased, thereby making it unnecessary to envelope the magnetic-circuit board of the yoke by forming a bottom portion across the entirety of the lower part of the lower case. Accordingly, even if a thin-wall area such as the bottom of the lower case is reduced, sufficient strength is assured and it is unnecessary to mold resin for the entire underside of the lower case. Inadequate filling of resin when the lower case is molded can be eliminated.
Other features and advantages of the present invention will be apparent from the following description taken in conjunction with the accompanying drawings, in which like reference characters designate the same or similar parts throughout the figures thereof.
REFERENCES:
patent: 4251807 (1981-02-01), Hofer et al.
patent: 5467323 (1995-11-01), Sone
Citizen Electronics Co. Ltd.
Koda & Androlia
Le Huyen
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