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DESCRIPTION JP2004104327

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DESCRIPTION JP2004104327
An object of the present invention is to improve impact resistance. An actuator in a piezoelectric
speaker having a structure in which an actuator is attached to a panel and the panel is vibrated
by the actuator to radiate a sound wave to a space, the actuator being a plate-like piezoelectric
body and disposed on both sides thereof In an actuator having a structure in which the
longitudinal center of the piezoelectric diaphragms 11 and 12 composed of electrodes is held by
a holder 21 and the holder 21 is attached to a panel, shock absorbers 41 are formed on both
plate surfaces of the piezoelectric diaphragms 11 and 12. Arrange the [Selected figure] Figure 1
Piezoelectric speaker actuator
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
piezoelectric speaker which uses a panel of an apparatus as a diaphragm in an apparatus such as
a portable telephone, and more particularly to a structure of an actuator for vibrating the panel.
[0002] For example, in devices such as mobile phones and personal digital assistants (PDA), a
transparent panel (flat panel) which covers the display surface of a display element such as a
liquid crystal display element and is positioned on the surface of the device ) Is used as a
diaphragm of a piezoelectric speaker, and the panel is vibrated to emit sound waves into space,
and an actuator (piezoelectric actuator) for vibrating the panel is attached to the back of the
panel. It is attached. FIG. 4 shows the structure of an actuator conventionally used by being
attached to a panel in a piezoelectric speaker having such a configuration, and in this example,
the actuator 10 has two piezoelectric vibrations of different lengths. The piezoelectric vibrators
11 and 12 are held by the holder 21 in parallel with each other. Both of the piezoelectric
diaphragms 11 and 12 have a laminated structure as shown in FIG. 5, and a pair of plate-like
piezoelectric members 14 are disposed with the electrode 13 positioned at the center between
them. The electrodes 15 are disposed outside the body 14 respectively. The electrode 13 located
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at the center is formed of, for example, a stainless steel plate, and a piezoelectric body 14 made
of ceramic such as PZT (lead titanium zirconate) is attached to the electrode 13 and attached.
The outer electrode 15 has a two-layer structure of a silver foil 16 and a copper foil 17 in this
example, and the silver foil 16 is formed by printing and applying silver paste on the
piezoelectric body 14, and the copper foil 17 is attached thereon It has been attached. The
piezoelectric diaphragms 11 and 12 having the above-described laminated structure are referred
to as a bimorph type, and are formed in a strip shape. In addition, the convex part 13a for lead
wire connection is provided in the longitudinal direction center one side of the electrode 13. As
shown in FIG. Further, the sizes (areas) of the piezoelectric body 14 and the electrode 15 are
gradually reduced gradually with respect to the electrode 13. The holder 21 is provided with two
slits 22 for sandwiching the piezoelectric diaphragms 11 and 12. The piezoelectric diaphragms
11 and 12 are inserted into the slits 22 and bonded and fixed, and the longitudinal direction
centers thereof are respectively attached to the holder 21. It is held. A wide base portion 23 is
provided on one end side of the holder 21 in the stacking direction of the piezoelectric
diaphragms 11 and 12, and an end face of the base portion 23 parallel to the plate surface of the
piezoelectric diaphragms 11 and 12 ( The bottom surface is the surface to be attached to the
panel.
6 and 7 show a state in which the actuator 10 is attached to the panel 31 covering the display
surface of the mobile phone and a schematic structure of the mobile phone in which the panel 31
to which the actuator 10 is attached is incorporated. 10 is disposed along one side of the panel
31 as shown in FIG. 6, and the base 23 of the holder 21 is attached to the panel 31 by being
attached. The panel 31 is made of a transparent resin plate such as polycarbonate or acrylic. The
peripheral edge of the panel 31 to which the actuator 10 is attached is fixedly held by the main
body case 32 of the portable telephone as shown in FIG. 7 and arranged on the surface of the
portable telephone. A printed wiring board 33 is accommodated in the main body case 32, and
although not shown, a liquid crystal display element, for example, is mounted as a display
element on the printed wiring board 33. In FIG. 7, reference numeral 18 denotes a lead wire for
connecting the actuator 10 to the printed wiring board 33, and two lead wires 18 are drawn out
from the electrodes 13 and 15. The two electrodes 13 and the four electrodes 15 of the two
piezoelectric diaphragms 11 and 12 of the actuator 10 are respectively connected and conducted
by lead wires (not shown). In a mobile phone equipped with a piezoelectric speaker comprising
the actuator 10 and the panel 31 as described above, a large-area panel 31 is used as a vibrating
body to emit a sound wave, so that a good sound can be obtained. Become. Further, the actuator
10 has two piezoelectric vibrating plates 11 and 12 having different lengths, whereby
adjustment / improvement of the frequency characteristic and improvement of the sensitivity are
achieved. As shown in FIG. 7, a shock absorbing material 34 is interposed between the panel 31
and the main body case 32, whereby the transmission of the vibration of the panel 31 to the
main body case 32 is blocked. By the way, in the actuator 10 having the above-mentioned
structure, the piezoelectric body 14 has a thin plate shape, and the ceramic such as PZT which is
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its constituent material is a very fragile material. Because of this, the following problems could
occur. That is, when an impact is applied to the actuator 10 due to a drop or the like, both ends
of the piezoelectric diaphragms 11 and 12 are bent with respect to the central portion held by
the holder 21, and a crack occurs in the piezoelectric body 14 due to the bending Or in contact
with the panel 31, the printed wiring board 33, etc. in a state where the piezoelectric diaphragms
11, 12 are mounted on another member, for example, a portable telephone, or the piezoelectric
diaphragms 11, 12 are in contact with each other As a result, it may occur that the corners of the
piezoelectric body 14 are chipped (broken).
Therefore, the conventional actuator 10 is vulnerable to impact, and in that respect it has become
unreliable. An object of the present invention is to provide an actuator for a piezoelectric speaker
that is resistant to shock and has excellent reliability in that respect. According to the invention
of claim 1, an actuator in a piezoelectric speaker having a structure in which an actuator is
attached to a panel and the panel is vibrated by the actuator to emit a sound wave into a space.
The holder is held by the holder at the longitudinal center of the piezoelectric diaphragm
consisting of a plate-like piezoelectric member and electrodes disposed on both sides of the plate,
and one end surface of the holder parallel to the plate surface of the piezoelectric diaphragm is a
panel In the actuator of the structure attached to the above, shock absorbing materials are
disposed on both plate surfaces of the piezoelectric diaphragm. According to a second aspect of
the present invention, in the first aspect of the present invention, the piezoelectric vibration plate
has a structure including a pair of piezoelectric members with an electrode interposed
therebetween. According to a third aspect of the present invention, in the first aspect or the
second aspect of the present invention, the holder holds two piezoelectric diaphragms of
different lengths in parallel with each other, and a shock absorber located between the
piezoelectric diaphragms. It is assumed that one side of the piezoelectric diaphragm is attached
to one side of the piezoelectric diaphragm, and the other side is in close contact with the other
side. In the invention of claim 4, in the invention of any one of claims 1 to 3, the impact
absorbing material is made of a polyurethane-based or polyethylene-based foam. In the invention
of claim 5, in the invention of any one of claims 1 to 3, the impact absorbing material is made of
polyurethane-based or polyethylene-based rubber. Embodiments of the present invention will be
described by way of examples with reference to the drawings. FIG. 1 shows the construction of
an embodiment of an actuator for a piezoelectric speaker according to the present invention, and
FIGS. 2 and 3 show a state in which the actuator is attached to a panel and a portable telephone
as in FIGS. Shows the states incorporated in the The parts corresponding to those in FIGS. 4 to 7
are denoted by the same reference numerals, and the detailed description thereof is omitted. In
this example, as shown in FIG. 1, in the actuator 40, the shock absorbing material 41 is disposed
on the both plate surfaces of the piezoelectric vibrating plates 11 and 12, respectively. The
piezoelectric diaphragms 11 and 12 are simplified in this figure, but have the same configuration
as in FIGS. 4 and 5. Two shock absorbing materials 41 located outside the piezoelectric
diaphragm 11 are provided with the holder 21 interposed therebetween, and the plate surface of
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the piezoelectric diaphragm 11 is covered with these two shock absorbing materials 41, and The
upper surface (outer surface) of the shock absorbers 41 substantially coincides with the upper
end surface of the holder 21.
Two shock absorbing members 41 located outside the piezoelectric vibrating plate 12 are
provided with the base 23 of the holder 21 interposed therebetween, and the plate surface of the
piezoelectric vibrating plate 12 is covered with these two shock absorbing members 41. The
lower surface (outer surface) of the shock absorbers 41 substantially coincides with the end
surface (bottom surface) of the base 23. Two shock absorbing members 41 positioned between
the piezoelectric diaphragms 11 and 12 are provided with the holder 21 interposed
therebetween, and the size thereof is sized to cover the longer piezoelectric diaphragm 11 so that
piezoelectric vibration is generated. The opposite surface is adhered to the piezoelectric
diaphragm 12. The impact absorbing members 41 located on the outer sides of the piezoelectric
vibrating plates 11 and 12 are attached to the piezoelectric vibrating plates 11 and 12,
respectively. The impact absorbing material 41 is attached before attaching the piezoelectric
diaphragms 11 and 12 to the holder 21. As a constituent material of the shock absorbing
material 41, a polyurethane or polyethylene foam is used as a material that does not disturb the
vibration of the piezoelectric diaphragms 11 and 12. Also, polyurethane or polyethylene rubber
may be used. Furthermore, gel-like impact absorbers can also be used. According to the actuator
40 configured as described above, the shock absorbing material 41 can absorb the shock, that is,
the deformation of the piezoelectric diaphragms 11 and 12 due to the shock can be significantly
reduced. It is possible to prevent the generation of the crack 14 and the generation of a chip
(crack) of the piezoelectric body 14 due to the contact between the piezoelectric vibrators 11 and
12. Further, as shown in FIG. 2, since the shock absorbing material 41 is interposed between the
panel 31 and the piezoelectric diaphragm 12 in a state of being attached to the panel 31, the
piezoelectric diaphragm 12 and the panel 31 by impact are provided. Since the shock absorbing
material 41 exists on the side facing the printed wiring board 33 in the state of being
incorporated in the mobile phone as shown in FIG. 3, for example, the printed wiring board 33
can be avoided. Even if the actuator 40 and the actuator 40 are disposed in close proximity to
each other, the piezoelectric diaphragm 11 can be prevented from coming into contact with the
printed wiring board 33 due to an impact, and thus these contacts cause cracking or chipping of
the piezoelectric body 14 Can be prevented. Incidentally, when the piezoelectric diaphragms 11
and 12 are attached to the holder 21, conventionally, the adhesive is cured and the holder is
supported by the holder 21 only at the central portion until the piezoelectric diaphragms 11 and
12 are fixed. In this example, the shock absorbing material 41 maintains the predetermined state,
while a jig is required so that the piezoelectric diaphragms 11 and 12 being held do not deviate
from the predetermined state (parallel state). The jig is unnecessary, and it is easy to assemble at
that point.
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In addition, since the piezoelectric diaphragms 11 and 12 are covered and protected by the
shock absorbing material 41, the piezoelectric diaphragms 11 and 12 may be touched when
attaching to the panel 31 or assembling into a device such as a mobile phone. Alternatively, it
can be prevented that the piezoelectric diaphragms 11 and 12 are deformed or the piezoelectric
body 14 is damaged due to collision with another member, which makes it easy to handle. In the
embodiment described above, the actuator including two piezoelectric diaphragms has been
described, but the number of piezoelectric diaphragms is not limited to this, and may be one, for
example. Also, the panel to which the actuator is attached is not limited to the one positioned on
the surface of the device as in this example, but may be positioned in the device. As described
above, according to the present invention, even if an impact such as a drop is applied, the impact
is absorbed by the impact absorbing material, thereby preventing the crack and chipping of the
piezoelectric body which conventionally occurred. As a result, it is possible to obtain an actuator
for a piezoelectric speaker which is excellent in impact resistance and highly reliable in that
respect. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective view showing an
embodiment of a piezoelectric speaker actuator according to the present invention. FIG. 2 is a
view showing a state in which the actuator of FIG. 1 is attached to a panel forming a diaphragm,
A is a plan view, B is a side view, and C is a front view. 3 is a schematic cross-sectional view
showing a state in which a panel to which the actuator of FIG. 2 is attached is incorporated in a
mobile phone. FIG. 4 is a perspective view showing a conventional configuration example of a
piezoelectric speaker actuator. 5 is a perspective view showing a laminated structure of the
piezoelectric diaphragm in FIG. 4; 6 is a view showing a state in which the actuator of FIG. 4 is
attached to a panel forming a diaphragm, A is a plan view, B is a side view, and C is a front view.
7 is a schematic cross-sectional view showing a state in which a panel to which the actuator of
FIG. 6 is attached is incorporated in a mobile phone.
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