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JP2007074062

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DESCRIPTION JP2007074062
PROBLEM TO BE SOLVED: To improve unevenness of frequency characteristics. SOLUTION: The
exciter 1 for a panel type speaker is a piezoelectric bimorph 4 composed of a shim 2 which is a
plate member made of metal, resin or ceramic, and a piezoelectric ceramic 3 deposited on both
sides except an outer edge portion and a rear portion. Is insert-molded while being held in a
cantilever shape by the rear portion of the resin holding portion 5. The holding portion 5 is
integrally formed with a protruding portion 5 a that protrudes downward. The holding portion 5
holds the shim 2 by including the first holding portion 5 b including the protrusion 5 a directly
holding the shim 2 and a portion of the piezoelectric ceramic 3 along the longitudinal direction
of the piezoelectric bimorph 4 And a second holding unit 5c. The protrusion 5a is fixed in the
vicinity of one end of the diaphragm to constitute a panel type speaker. [Selected figure] Figure 1
Exciter for panel type speaker and panel type speaker
[0001]
The present invention relates to a panel-type speaker exciter and a panel-type speaker for use in
a small portable device such as a mobile phone.
[0002]
In recent years, in small portable devices such as mobile phones, a small exciter is fixed to the
end of a display panel such as a transparent acrylic plate as a diaphragm, and a display device
such as an LCD is disposed in the main part of the display panel. A panel-type speaker aiming at
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the effect that the image and the sound exist at the same position is used.
The applicant has proposed a structure of a box-shaped piezoelectric exciter and a structure of a
fixing portion of a piezoelectric bimorph incorporated therein as an exciter used for such a panel
type speaker (see, for example, Patent Document 1).
[0003]
FIG. 5 is a cross-sectional view showing an example of the structure of such a conventional
piezoelectric exciter. FIG. 6 is a partially enlarged cross-sectional view showing the structure of a
bimorph fixing portion of another conventional piezoelectric exciter. FIG. 7 is a graph for
comparing and displaying the frequency characteristics of panel type speakers using
piezoelectric exciters of various structures.
[0004]
In the case shown in FIG. 5, two beams b1 and b2 are fixed to the inside of a box-shaped case C
with one end portion intervened by an adhesive layer f, and a flexural vibration having a basic
structure of a cantilever beam It is a type of exciter. The beams b1 and b2 are piezoelectric
bimorphs in which ceramic piezoelectric layers are formed on both sides of a metal plate called
shim. Fixing of the piezoelectric bimorph is ceramic holding. When an alternating current signal
is supplied through the signal input terminals t1 and t2 formed in the case C, the stacked
piezoelectric layers expand and contract in the longitudinal direction of the beam and a
deflection signal is excited by the beams b1 and b2. Moreover, what is shown in FIG. 6 is a
bending vibration type exciter in which the fixing method of the piezoelectric bimorph is
different. In this case, the fixation of the piezoelectric bimorph is a shim holding that holds the
protruding shim portion directly. The signal input terminal t1 is a negative terminal, and t2 is a
positive terminal connected to the electrode surface of the beam b1 by a metal spring. Japanese
Patent Application No. 2004-305840 (FIG. 6, paragraph number 0006)
[0005]
A panel-type speaker forms a speaker with high sound pressure by utilizing resonance of an
exciter having a cantilever structure and deflection resonance of a panel which is a plate-like
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body, but between a plurality of resonance points, Since the sound pressure is low, the frequency
characteristic is considerably uneven as shown by the solid line in FIG. 7 as compared with the
conventional cone speaker. If the drop in sound pressure is large, it is difficult to hear the
playback sound. Loudspeakers employing the ceramic holding exciter shown in FIG. 5 have good
frequency sound pressure characteristics in the low band (1 kHz or less) but high band (above
the second resonance frequency of the cantilever) and sound pressure level There is a place
where the On the other hand, the frequency sound pressure characteristic of the speaker
employing the shim holding exciter shown in FIG. 6 is good in the high region but insufficient in
the low region.
[0006]
The present invention has been made to solve such conventional problems, and an object thereof
is to provide a panel-type speaker exciter and a panel-type speaker that do not cause a decrease
in the sound pressure of the speaker near the resonance point. It is.
[0007]
The means of the present invention for achieving the above-mentioned object comprises a
rectangular piezoelectric bimorph having a piezoelectric ceramic layer deposited on both sides of
a shim, and a holding portion for holding the piezoelectric bimorph in a cantilevered manner. In
the exciter for panel type speaker, the holding portion extends in the longitudinal direction of the
piezoelectric bimorph from the first holding portion directly holding the shim extended from one
end of the piezoelectric bimorph and from the first holding portion And a second holding unit for
holding the bimorph including the piezoelectric ceramic layer.
[0008]
Further, the holding portion is characterized in that it has a plate-like portion which is extended
in the length direction of the bimorph from the first holding portion and does not contact the
second holding portion.
[0009]
Further, the outer periphery of the first holding portion is inscribed in one end of a tubular body
having a square cross section, and the cylindrical body is extended to the tip of the bimorph
without contacting the second holding portion and the bimorph. It is characterized by
[0010]
Further, an elastic body such as a sponge or rubber is interposed in a space below the second
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holding portion.
[0011]
Further, the first holding portion is characterized by having a protruding portion which is a
portion protruding in the thickness direction with respect to the second holding portion.
[0012]
Further, the plate-like portion, the cylindrical body, or the protrusion may be separately formed
and then fixed to the first holding portion.
[0013]
Another means of the present invention for achieving the above-mentioned object is
characterized in that the exciter for a panel type speaker according to any one of claims 1 to 6 is
provided on a plate-like diaphragm, or the projection or It is characterized in that a plate portion
or the cylindrical body is fixed.
[0014]
According to the present invention, there is provided an exciter for a panel type speaker,
comprising: a rectangular piezoelectric bimorph formed by depositing a piezoelectric ceramic
layer on both sides of a shim; and a holding portion for holding the piezoelectric bimorph in a
cantilever shape. The holding portion includes a first holding portion directly holding a shim
portion extended from one end of the piezoelectric bimorph, and the piezoelectric ceramic layer
extending from the first holding portion along the longitudinal direction of the piezoelectric
bimorph. Since the second holding portion holds the bimorph, the presence of the second holding
portion damps the resonance vibration of the piezoelectric bimorph, so that the sharpness Q of
the resonance of the exciter can be lowered, and the resonance frequency characteristic is
obtained. An exciter for a panel type speaker without unevenness was obtained.
[0015]
Hereinafter, a panel-type speaker exciter according to an embodiment of the present invention
will be described in detail with reference to the drawings.
FIG. 1 is a cross-sectional view and a right side view showing a panel type speaker exciter
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according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view showing a panel type speaker using this exciter.
[0016]
First, the configuration of the panel-type speaker exciter according to the first embodiment of the
present invention will be described.
In FIG. 1, reference numeral 1 denotes a panel type speaker exciter.
2 shows a shim which is a plate member made of metal, resin or ceramic.
3 shows a piezoelectric ceramic deposited on both sides except the outer edge and the rear of the
shim 2.
4 shows a piezoelectric bimorph composed of the shim 2 and the piezoelectric ceramic 3.
Reference numeral 5 denotes a resin-made holding portion in which the piezoelectric bimorph 4
is held in a cantilever shape and insert-molded.
In addition, the holding part 5 may be metal, and when the shim 2 is a metal, an insulation
process is required.
At the rear of the holding portion 5, a projection 5a projecting downward is integrally formed.
The protrusion 5a may be separately formed and then fixed to the main body. The holding
portion 5 holds the shim 2 including the first holding portion 5 b including the protrusion 5 a
directly holding the shim 2 and a portion of the piezoelectric ceramic 3 along the longitudinal
direction of the piezoelectric bimorph 4 It consists of the 2nd holding | maintenance part 5c. The
rear end portion of the shim 2 slightly protrudes from the end face of the first holding portion
5b.
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[0017]
In FIG. 2, 6 indicates a substantially rectangular diaphragm made of a plastic plate or a metal
plate or the like, and 7 indicates a panel type speaker. In the vicinity of one short side of the
diaphragm 6 of the panel type speaker 7, the projection 5a of the holding portion 5 of the panel
type speaker exciter 1 is fixed by means such as adhesion, welding, adhesion. In the space
between the diaphragm 6 and the second holding portion 5c, an elastic body such as sponge or
rubber (not shown) having a hardness sufficiently smaller than the members of the holding
portion 5 may be disposed.
[0018]
Next, the effect of the first embodiment of the present invention will be described. Since the
presence of the second holding portion 5 c damps the resonance vibration of the piezoelectric
bimorph 4, the sharpness Q of the resonance of the exciter 1 can be lowered. In addition, the
second holding unit 5c further widens the interval between the first and second resonance
frequencies obtained from the conventional simple beam structure. The presence of a member
such as sponge or rubber in the space under the second holding portion 5c improves the impact
resistance and effectively transmits the force generated by the piezoelectric element to the case
side or the panel side. Thus, the exciter 1 can provide a panel type speaker having flatter
frequency characteristics, as shown by the dotted line in FIG.
[0019]
Next, an exciter for a panel type speaker according to a second embodiment of the present
invention will be described in detail with reference to the drawings. FIG. 3 is a cross-sectional
view showing a panel type speaker exciter according to a second embodiment of the present
invention.
[0020]
In FIG. 3, reference numeral 11 denotes a panel type speaker exciter according to a second
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embodiment of the present invention. Reference numeral 15 denotes a resin-formed holding
portion. The holding portion 15 is composed of a first holding portion 15 b directly holding the
shim 2 and a second holding portion 15 c containing the piezoelectric ceramic 3 and holding the
shim 2. One end of a plate-like portion 15d is joined to the first holding portion 15b. The platelike portion 15d is integrally formed with the holding portion 15, but may be separately formed
and then joined. In addition, when making it a separate body, the division position may be any.
The plate-like portion 15d of the exciter 11 is fixed to the diaphragm to constitute a panel type
speaker. In the space between the diaphragm and the second holding portion 25c, an elastic
body (not shown) such as sponge or rubber having a hardness sufficiently smaller than that of
the members of the holding portion 15 may be disposed. The other configuration is the same as
that of the exciter 1 according to the first embodiment, so the same reference numerals and
names are given to the same components and the detailed description is omitted.
[0021]
Next, the effects of the second embodiment of the present invention will be described. Since the
plate-like portion 15d is provided in the holding portion 15, the fixing to the diaphragm is easy
and strong. The other effects are the same as in the first embodiment.
[0022]
Next, a panel type speaker exciter according to a third embodiment of the present invention will
be described in detail with reference to the drawings. FIG. 4 is a cross-sectional view showing a
panel type speaker exciter according to a third embodiment of the present invention.
[0023]
In FIG. 4, reference numeral 21 denotes a panel type speaker exciter according to a third
embodiment of the present invention. The reference numeral 25 denotes a resin molded holding
portion. The holding portion 25 is composed of a first holding portion 25 b holding the shim 2
directly and a second holding portion 25 c holding the shim 2 including the piezoelectric ceramic
3. The reference numeral 26 denotes a tubular member having a square cross section whose one
end is inscribed in the outer periphery of the first holding portion 25b and does not contact the
second holding portion 25c and the piezoelectric bimorph 4 and extends to the tip of the
piezoelectric bimorph 4 An enclosure is shown. The enclosure 26 is integrally formed with the
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holding portion 25 but may be separately formed and then joined. In addition, when making it a
separate body, the division position may be any. The enclosure 26 of the exciter 21 is fixed to the
diaphragm to constitute a panel type speaker. The other configuration is the same as that of the
exciter 1 according to the first embodiment, so the same reference numerals and names are
given to the same components and the detailed description is omitted.
[0024]
Next, the effects of the third embodiment of the present invention will be described. Since the
fragile piezoelectric bimorph 4 is protected by the enclosure 26, breakage of the piezoelectric
bimorph 4 can be prevented. The other effects are the same as in the first embodiment.
[0025]
The exciter for a panel type speaker according to the present invention can be widely applied to
a panel type speaker of a small portable device.
[0026]
It is sectional drawing and the right view which show the exciter for panel type speakers which is
the 1st Embodiment of this invention.
It is sectional drawing which shows the panel type speaker which used the exciter of FIG. It is
sectional drawing and the right view which show the exciter for panel type speakers which is the
2nd Embodiment of this invention. It is sectional drawing and the right view which show the
exciter for panel type speakers which is 3rd Embodiment of this invention. It is sectional drawing
which shows the conventional exciter for panel type speakers. FIG. 6 is a cross-sectional view
showing another conventional panel-type speaker exciter. It is a graph which shows the
frequency characteristic for panel type speakers.
Explanation of sign
[0027]
DESCRIPTION OF SYMBOLS 1, 11, 21 Exciter 2 Shim 3 Piezoelectric ceramic 4 Piezoelectric
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bimorph 5, 15, 25 Holding part 5a Projection part 5b, 15b, 25b 1st holding part 5c, 15c, 25c
2nd holding part 6 Diaphragm 7 Panel type Speaker 15d plate-like part 26 enclosure
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