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JP2003163994

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JP2003163994
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
method of manufacturing a piezoelectric diaphragm used in a piezoelectric speaker.
[0002]
2. Description of the Related Art It is known to use a piezoelectric diaphragm as a sound source
of audio equipment such as a speaker. In this type of speaker, a piezoelectric diaphragm is
attached to one side of an acoustic diaphragm made of a plastic material via a columnar
mounting member, and the piezoelectric diaphragm is vibrated by applying an audio signal to the
piezoelectric diaphragm. The vibration is transmitted to the acoustic diaphragm through the
mounting member to obtain the generation of the sound corresponding to the audio signal. The
piezoelectric diaphragm has a ceramic layer attached to one side or both sides of a thin metal
plate, and the ceramic layer is bent by causing a potential difference across the ceramic layer to
cause the ceramic layer to bend. The piezoelectric diaphragm is vibrated. By changing the
potential difference formed between the two side surfaces of the ceramic layer in accordance
with the audio signal, the piezoelectric diaphragm vibrates in accordance with the audio signal.
As described above, in order to form a potential difference between both sides of the
piezoelectric diaphragm and vibrate the piezoelectric diaphragm in accordance with the audio
signal, conductive layers are formed on both sides of the piezoelectric diaphragm by silver
plating or the like.
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[0003]
[Problems to be Solved by the Invention] Conventionally, after pasting a ceramic layer not formed
with holes in the central part on both sides of a metal plate not formed with holes in the central
part, three layers are pierced with a punch. There is a method of forming a central hole. This
method has the advantage that the relative positioning of the holes in each layer can be perfect,
as compared to attaching and forming the holes in advance in the metal plate and the ceramic
layer. However, when the punch penetrates the metal plate, the central region of the metal plate
bulges and deforms in the advancing direction of the punch, causing a problem that the central
region of the lower ceramic layer is broken more than a desired size.
[0004]
In order to solve this, a center hole is formed in the center of a thin metal plate molded into a
predetermined shape, a ceramic layer is attached to both sides of the thin metal plate, and a
punch having an outer diameter equal to or smaller than the inner diameter of the center hole. Is
positioned relative to the center hole on the surface of one ceramic layer attached to the metal
thin plate, and the punch is penetrated from the surface of the one ceramic layer to the other
ceramic layer through the center hole to center Methods of forming the holes have been
proposed. However, in this method, when the central hole is formed in the ceramic layer, shorts
may occur between the conductive layers on both sides of the ceramic layer due to particles of
the conductive layer adhering to the inner surface of the central hole of the ceramic layer, etc. .
[0005]
The present invention has as its technical object the solution of the problems of the prior art, and
the object of the present invention is to provide a method of manufacturing a piezoelectric
diaphragm in which a short circuit accident occurring in a central hole of a ceramic layer is
prevented or reduced.
[0006]
According to the present invention, a piezoelectric diaphragm having a ceramic layer attached to
at least one side surface of a metal plate is supported at its center and attached to an acoustic
diaphragm. Forming a central hole at the center of the metal plate, attaching a ceramic layer
having a conductive layer formed on both sides thereof to the metal plate, and Forming in the
ceramic layer a central hole concentric with the central hole of the metal plate, wherein the
central hole of the ceramic layer is formed by a conical drilling tool that converges in the distal
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direction, and the central hole of the ceramic layer A method of manufacturing a piezoelectric
diaphragm is characterized in that the distance between the conductive layers along the inner
surface of the above is increased.
[0007]
DETAILED DESCRIPTION OF THE INVENTION Preferred embodiments of the invention will now
be described with reference to the accompanying drawings.
First, referring to FIG. 4, the piezoelectric speaker according to the preferred embodiment of the
present invention comprises the piezoelectric diaphragm 10, which is supported at a central
position by the mounting member 18 and thus the acoustic diaphragm 20. Is attached to
The piezoelectric diaphragm 10 is composed of, for example, a circular metal thin plate 12 made
of a metal thin plate such as brass, and a circular ceramic layer 14 attached to both sides of the
metal thin plate 12 with a suitable adhesive.
[0008]
Referring to FIG. 3, the ceramic layer 14 can be formed in a circular thin plate shape from a
ferroelectric ceramic material such as barium titanate or lead zirconate titanate, and conductive
layers are formed on both sides by a method such as silver plating. 16a, 16b are formed. The
conductive layers 16a and 16b are formed in a circle having a diameter smaller than that of the
ceramic layer 14 disposed concentrically with the ceramic layer 14, and the outer conductive
layer 16a faces the outside of the piezoelectric diaphragm 10 when assembled; It comprises an
inner conductive layer 16 b in contact with the thin metal plate 12. In one embodiment, ceramic
layer 14 has a thickness of about 0.12 mm and conductive layers 16a, 16b have a thickness of
about 0.005 mm.
[0009]
Wires (not shown) are connected to the thin metal plate 12 and the outer conductive layer 16a of
the ceramic layer 14, respectively, and the piezoelectric diaphragm 10 is connected to an
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amplifier (not shown) via the wires. ing. Then, by applying an audio signal between the thin metal
plate 12 and the ceramic layer 14, the piezoelectric diaphragm vibrates or bends in accordance
with the audio signal.
[0010]
As described above, the piezoelectric vibration plate 10 is attached to the acoustic vibration plate
20 at its central portion by the mounting member 18 including the rod 18a having an external
thread, the nut 18b, and the bracket 18c. The bracket 18c can preferably be attached to the
acoustic diaphragm 20 with a suitable adhesive or double-sided tape. The acoustic diaphragm 20
is preferably made of a composite material obtained by molding polystyrene foam or a suitable
plastic material such as boron, silicon carbide, alumina, carbon, aramid fibers or the like with a
plastic matrix such as nylon, polyester or epoxy. . Further, an annular vibration control piece 22
may be attached to one side surface of the piezoelectric diaphragm. The vibration control piece
22 is made of an elastic material, preferably an elastomeric material such as synthetic rubber,
natural rubber, low density polyethylene, soft vinyl chloride plastic and the like. The vibration
control piece 22 is not a single annular member, but a plurality of members formed in a
rectangular, triangular, trapezoidal, etc. shape, preferably, a pair of members disposed at point
symmetrical positions across the center of the piezoelectric diaphragm. It is also good.
[0011]
By applying an audio signal to the piezoelectric diaphragm 10, the peripheral portion of the
piezoelectric diaphragm repeats bending operation back and forth, and its vibration is
transmitted to the acoustic diaphragm 20 from the central portion of the piezoelectric diaphragm
via the mounting member 18. The vibration is transmitted from the acoustic diaphragm 20 to the
ambient air. The piezoelectric diaphragm 10 does not use a heavy magnet as compared to a
dynamic type speaker, so it has a high ability to follow high-frequency audio signals, and in
particular, can obtain a high sound pressure without distortion in a high sound area. It becomes
possible.
[0012]
The piezoelectric diaphragm 10 has center holes 10 a and 10 b for passing the mounting
member 18 through the piezoelectric diaphragm 10 in order to center the mounting of the
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mounting member 18. The central hole comprises a portion 10 a formed in the thin metal plate
12 and a portion 10 b formed in the ceramic layer 14. When the ceramic layer 14 is attached to
the thin metal plate 12 after forming the central hole 10 b in the ceramic layer 14, positioning of
the portion 10 a formed on the thin metal plate 12 in the central hole and the portion 10 b
formed on the ceramic layer 14 Is a problem. Since the ceramic layer 14 is formed of a brittle
material, care must be taken not to damage the ceramic layer 14 when assembling the
piezoelectric diaphragm 10, but if the above-mentioned positioning is insufficient, the mounting
member 18, in particular When the rod 18a is inserted into the central holes 10a and 10b, the
rod 18a may interfere with the inner peripheral surface of the portion 10b formed on the
ceramic layer 14 at the central hole to damage the ceramic layer 14. In order to prevent this,
according to the present embodiment, after attaching the ceramic layer 14 in which the central
hole 10b is not formed to the thin metal plate 12, the central hole 10b is formed in the ceramic
layer 14 by the drilling tool 50. Be done. Although it is difficult to position the ceramic layer 14
in which the central hole 10b is formed with respect to the thin metal plate 12, it is relatively
easy to position the drilling tool 50 with respect to the central axis O of the thin metal plate 12.
For this reason, it is possible to increase the concentricity of the portions 10a and 10b of the
central hole by forming the central hole 10b after attaching the ceramic layer 14 in which the
central hole 10b is not formed to the metal thin plate 12 It becomes.
[0013]
The drilling tool 50 used when forming the central hole 10b in the ceramic layer 14 is preferably
a tool having a conical processing portion 54 that converges at one end of the shank 52 with the
tip angle α, preferably a rotary grindstone . As a result, as shown in FIG. 1, the central hole
portion 10b formed in the ceramic layer 14 has a mortar shape. Thus, the distance L between the
conductive layers 16a and 16b along the inner surface of the central hole 10b can be increased,
and the occurrence of a short circuit between the conductive layers 16a and 16b can be reduced.
The tip angle α is preferably 90 degrees or 120 degrees.
[0014]
Furthermore, when bonding the ceramic layer 14 to the metal plate 12, the ceramic layer 14 is
pressed against the metal plate 12 so that the adhesive is pushed out from between the two, and
as shown in FIG. It is further preferable to form an insulating protective portion 24 along the
outer peripheral edge portion of 14. This makes it possible to prevent a short circuit in the outer
peripheral portion of the ceramic layer 14.
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