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JPS54129977

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DESCRIPTION JPS54129977
BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view showing the structure,
operation and support method of a piezoelectric vibrator. FIG. 2 is a cross-sectional view showing
the structure, operation and other supporting method of the piezoelectric vibrator. FIG. 3 is a
diagram showing frequency characteristics of generated sound pressure of the conventional
piezoelectric vibrator. FIG. 4 is a sectional view showing an embodiment according to the present
invention. FIG. 5 is a diagram showing frequency characteristics of generated sound pressure of a
piezoelectric buzzer sounding body and another sounding body according to an embodiment of
the present invention. In the figure, 3 is a piezoelectric vibrator, 8 is an acoustic cylinder.
[Detailed description of the invention])? The present invention relates to the improvement of a
piezoelectric buzzer sounding body used for various alarms and notifications. In this type of
piezoelectric buzzer sounding body, as shown in FIG. 1, a piezoelectric element 1 provided with
electrodes on both sides is bonded to a diaphragm 2 with an adhesive to form a piezoelectric
vibrator 3. The vibrator 3 is bent and vibrated to generate a sound wave by applying an AC
voltage of The oscillation circuit used to obtain this alternating voltage includes a white snow
oscillation circuit and a separately excited oscillation circuit. The self-help oscillation (1-k-729Q
′ ′) circuit is a circuit that takes out the feedback signal from the piezoelectric vibrator by
some means, oscillates at the fundamental resonance frequency of the piezoelectric vibrator in a
self-excited manner, and drives the piezoelectric vibrator. is there. The separately excited
oscillation circuit is a circuit that does not use the feedback signal as described above, and the
oscillation circuit determines a frequency and oscillates to drive the piezoelectric vibrator in a
separately excited manner. In addition, as a method of supporting the piezoelectric vibrator, as
shown in FIG. 1, the method of supporting the support table 5 in the vicinity of the free
fundamental resonance node of the piezoelectric vibrator 3 and the piezoelectric vibrator 3 as
shown in FIG. And a method of supporting on the support base 7 at the outer periphery of Next,
general characteristics and the like of the piezoelectric vibrator will be briefly described. The
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characteristics of the piezoelectric vibrator differ depending on the above two supporting
methods. That is, when supported in the vicinity of the node of the free fundamental resonance
as shown in FIG. 1, the vibration state as shown by the broken line 4.4 'is obtained, and the
center of gravity of the piezoelectric vibrator 3 does not move at resonance. Are prone to
vibration and so the input impedance is low. As shown in FIG. 2, when supported on the outer
periphery of the same piezoelectric vibrator as in FIG. 1, the vibration state as shown by the
broken line 6.6 'is obtained, and the center of gravity of the piezoelectric vibrator 30 moves at
resonance. The vibrator 3 vibrates less easily than the support in the vicinity of the abovementioned node, so the input impedance becomes relatively high. As apparent from the vibration
mode, if the same vibrator is used, the resonance frequency is better when supported at the outer
periphery of the piezoelectric vibrator as shown in FIG. 2 than when supported near the node of
free fundamental resonance as shown in FIG. Becomes lower. In addition, when supporting in the
vicinity of a node as shown in FIG. 1, the self-oscillation circuit is easy to use because the manual
impedance of the piezoelectric vibrator at that resonance frequency is low, but the outer
periphery as shown in FIG. When supported, it is difficult to use a self-oscillation circuit because
the human impedance of the piezoelectric vibrator) 4 at that resonance frequency is high.-The
frequency characteristic of the sound pressure generated from the piezoelectric vibrator is the
above two support methods Although there is a slight difference, the curve is as shown by the
solid line in FIG.
fr is the resonance frequency of this piezoelectric vibrator, and the sound pressure is maximized
at that frequency, and the generated sound pressure drops sharply when the drive frequency
deviates from the resonance frequency fr. Therefore, in order to increase the generated sound
pressure, it is desirable to drive the piezoelectric vibrator at its resonance frequency. 3-Thus, for
example, the resonance frequency of the disk-like piezoelectric vibrator is expressed by the
following equation. where: t is the thickness of the piezoelectric vibrator, r is the radius of the
piezoelectric vibrator. E is the Young's modulus of the piezoelectric vibrator, ρ is the density of
the piezoelectric vibrator. [sigma] is a Poa-Kaan ratio, and [alpha] is a constant determined by the
vibration mode and the I-positive Poisson's ratio. 7η: 2) Therefore, the resonant frequency fr
varies due to variations in the dimensions and materials of the piezoelectric element 1 and the
diaphragm 2, and the temperature coefficient of the resonant frequency fr of the piezoelectric
vibrator takes a negative value, so the resonant frequency fr fluctuates. Therefore, it is preferable
to drive the piezoelectric vibrator by the self-oscillation circuit so as to always drive at the
resonance frequency fr of the piezoelectric vibrator. However, for example, there is an oscillation
circuit in a device to which a buzzer is attached, such as a quartz oscillation type watch, and the
output is used to drive the buzzer or 4-the separately excited oscillation circuit as in the case
where the outer periphery of the piezoelectric vibrator is supported. In many cases it is better to
use However, when using a separately excited oscillation circuit, as described above, the
resonance frequency of the piezoelectric vibrator is dispersed or fluctuates, and the oscillation
frequency of the oscillation circuit is dispersed due to the dispersion of constants of oscillation
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circuit components and temperature characteristics. The sound pressure fluctuates widely, as is
clear from FIG. In addition, even if only the piezoelectric vibrator is driven and vibrated, the
sound pressure is small and in many cases it is not suitable as a buzzer for alarm fist notification.
The object of the present invention is to eliminate the above-mentioned drawbacks and to use a
separately excited oscillation circuit in a piezoelectric buzzer sounding body in which a pressure
b-type vibrator is supported at its outer periphery. To reduce the variation in sound pressure,
increase the generated sound pressure, and to use a self-oscillation circuit, it is possible to
provide a piezoelectric buzzer sounding body capable of increasing the sound pressure.
Hereinafter, the present invention will be described in detail based on embodiments according to
the present invention. As shown in FIG. 4, the piezoelectric vibrator 3 is supported by a support 9
at its outer periphery. The acoustic cylinder 8 is provided such that the support base 9 is
extended and the support 5 has the same diameter and length l and the diameter of the sound
wave emitting hole 10 is d, and the sound pipe 8 is sealed except the sound wave emitting hole
10 It is done. now! The acoustic oscillator 8 of 5 o'clock and d of 5 o'clock is provided, and the
resonance frequency fr of the piezoelectric oscillator when supported on the outer periphery as
described above is approximately 4 KHz. When the piezoelectric vibrator is driven, the frequency
characteristic of the generated sound pressure is as shown by a solid line in FIG.
That is, the resonance frequency fr of the piezoelectric vibrator 3 is in the vicinity of 4 KHz, and
there is a peak 11 of the sound pressure at that frequency. Also, there is another moon 3 of the
other sound pressure in the vicinity of 2.5 KHz), which is the acoustic stop frequency fa. In other
words, in the case of an acoustic cylinder with a length l of 5 麿, an inner diameter of about 27 鳳
and a diameter d of the sound wave emitting hole of 5 闘, when the piezoelectric vibrator is
vibrated at about 2.5 KHz, the sound cylinder Resonates and the sound pressure is amplified. The
acoustic resonance frequency fa can be arbitrarily set by the inner diameter length of the
acoustic cylinder and the size and shape of the sound wave emitting hole. However, in the case of
the sound pressure frequency characteristics as shown by the solid line in FIG. 5, the sound
pressure when the difference between the sound pressure valley 12 and the 6-sound pressure
peak 11 is 15 horns or more and there is no acoustic cylinder. And the frequency characteristics
of the sound pressure (for example, as indicated by the solid line in FIG. 3). Therefore, when the
separately excited oscillation circuit is used, the generated sound pressure will vary by more than
15 h because the oscillation frequency etc. varies. Also when using a self-oscillation circuit, the
peak 11 of the sound pressure at the resonance frequency fr of the piezoelectric vibrator is not
very large. Therefore, the two sound pressure peaks 11.13. That is, the resonant frequency fr of
the piezoelectric vibrator and the acoustic resonant frequency fa are made to approach each
other. Now, as shown in Fig. 2, the piezoelectric vibrator consisting of a disc-shaped piezoelectric
element with a diameter of 20 mm and a thickness of 0.2 F- and a disc-shaped diaphragm with a
diameter of 27 mm and a thickness of 0.2 mm For example, its resonant frequency fr is about 2.5
KHz. If the above-mentioned acoustic cylinder 8 having an inner diameter of 27 m and a length
of 5 mm and a diameter of 5 am of the sound wave emitting hole 10 is used, the acoustic
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resonance frequency fa should be about 2.5 KHz. Therefore, the acoustic resonance frequency fa
is 2.5 KHz 7-for the disk-like piezoelectric vibrator whose resonance frequency fr is 2.5 KHz. The
piezoelectric speaker supported by the acoustic cylinder should have such a frequency
characteristic as to have a single sound pressure peak at 2.5 KHz as shown in FIG. Actually,
however, the frequency characteristic of the generated sound pressure of the piezoelectric
sounding body is a curve as shown by a broken line in FIG. 5, and draws a curve in which two
peaks of the sound pressure exist. That is, when the resonance frequency fr of the piezoelectric
vibrator is slightly higher than the acoustic resonance frequency, the respective resonance
frequencies repel each other from the original 2.5 KHz, and the resonance frequency fr ′ of the
piezoelectric vibrator is the original 2. The acoustic resonance frequency fa 'shifts to about 4-2.7
KHz, which is lower than the original 2.5 KHz, to about 2.7 KHz, which is higher than 5 KHz. The
resonance of the piezoelectric vibrator to the truth!
Even if the frequency fr is slightly lower than the acoustic resonance frequency, the respective
resonance frequencies repel each other from the original 2.5 KHz, and the resonance frequency
fr "of the piezoelectric vibrator is about 2.3 KHz lower than the original 2.5 KHz Also, the
acoustic resonance frequency fa "moves to about 2.7 KHz higher than the original 2.5 KHz, and
has substantially the same frequency characteristics as the frequency characteristics of the
generated sound pressure shown by the broken line in FIG. Therefore, even if the resonance
frequency of the 8-piezoelectric vibrator varies due to the variation of the size and shape of the
piezoelectric vibrator, or the resonance frequency of the piezoelectric vibrator fluctuates due to
the temperature change, the frequency characteristic of the generated sound pressure does not
largely change . Moreover, the difference between the sound pressure peak 14 or 16 and the
sound pressure valley 15 becomes several horns, and the frequency characteristic of the sound
pressure from around 2.2 K) lz to around 2.8 KHz is greatly improved and becomes flat. The
sound pressure peak 14.16 is 10 horns or more more than the sound pressure peak 11 or 13
when the resonance frequency fr of the piezoelectric vibrator is separated from the acoustic
resonance frequency fa as shown by the solid line in FIG. The pressure increases. Here, although
the resonance frequency and the acoustic resonance frequency of the piezoelectric vibrator have
been described to be the same as desired, even in the piezoelectric buzzer sounding body in
which the difference between these resonance frequencies is about IKHz, the frequency
characteristic of the sound pressure is slightly Although it is reduced, the desired effect is
obtained. Therefore, according to the present invention, when the separately excited oscillation
circuit is used, even if the oscillation frequency is fluctuated or fluctuated, or even if the
resonance frequency of the piezoelectric vibrator is slightly fluctuated, the generated sound
pressure is 9-And the sound pressure increases without much variation. Also in the case of using
a self-oscillation circuit, the peak 14 of the sound pressure at the resonance frequency of the
piezoelectric vibrator is increased to obtain a piezoelectric buzzer sounding body that generates a
large sound pressure. In the above description, the shape of the sound wave emitting holes 10 is
circular and is described in the case of-. However, the shape of the sound wave emitting holes
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may be any shape, and may be a plurality of emissive holes it is obvious. Further, the shape of the
piezoelectric vibrator is not limited to the disk shape. As described above, according to the
present invention, by providing a very simple sound cylinder, the standing sound pressure, the
nine frequency characteristics are flat, the variation of the generated sound pressure is reduced,
and the generated sound pressure is large. Since a piezoelectric buzzer sounding body is
obtained, it is extremely useful practically.
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