JPH04236600

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DESCRIPTION JPH04236600
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
piezoelectric vibration device which generates an oscillating sound by a clock frequency
electronic circuit using a clock frequency electronic circuit and a method of manufacturing the
same.
[0002]
2. Description of the Related Art Conventionally, an electric product such as a microwave oven or
an electric washing machine is provided with a clock frequency circuit for performing various
controls. Further, products using a clock frequency of this clock frequency circuit to emit a
confirmation sound and an alarm sound are widely spread. There are an electromagnetic type
and a piezoelectric type as a sounding body that emits this alarm sound etc. However, since the
electromagnetic type has a large amount of power consumption and is easily affected by the
electromagnetic field, these problems have recently been observed. There are many piezoelectric
types that can be miniaturized with less.
[0003]
The diaphragm of this piezoelectric vibrator is formed by providing electrodes made of silver,
nickel, etc. on both sides of a thin metal disk and concentrically bonding polarized piezoelectric
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ceramic disks. It is. And this diaphragm is accommodated in the exterior case which had the
sound emission hole in the closed part. The outer case has a ring-shaped step on the inner
periphery, and the diaphragm is held and fixed by the step and a ring-shaped projection of the
bottom lid closing the opening of the outer case. At the time of fixing, they may be joined by an
elastic adhesive to ensure stability.
[0004]
The piezoelectric vibration apparatus oscillates by applying an alternating electric field to the
diaphragm, and an oscillation sound of a Helmholtz resonance frequency specified by the outer
case and its sound emission hole is emitted. In addition, when the drive frequency matches the
resonance frequency of the diaphragm, the highest sound pressure is obtained. In this
piezoelectric vibration device, the sound of the Helmholtz resonance frequency and the sound of
the resonance frequency of the diaphragm are obtained. An oscillating sound having a peak of
sound pressure is obtained. The Helmholtz resonance frequency fc is given by the following
equation 1:
[0005]
[Equation 1]
[0006]
Here, in the above equation, h1: length of sound emission hole, b: radius of sound emission hole,
S1: area of end face of sound emission hole, h2: formation of sound emission hole with
diaphragm in outer case The length of the cavity between the face and the surface, S2: the area
of the end face of the cavity, C: the speed of sound in air.
[0007]
In the above-mentioned prior art, when the Helmholtz resonance frequency is made closer to the
resonance frequency of the diaphragm, the sound pressure initially increases gradually, but the
lower frequency from a certain point in time There is a phenomenon that the higher the
frequency becomes larger and the sound pressure is reduced.
As a result, conventionally, there has been a problem that the oscillation frequency is reduced or
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the sound pressure is reduced even by a slight dimensional error or a deviation of assembly
conditions.
Moreover, conventionally, in consideration of dimensional errors, etc., the inner diameter of the
sound emission hole is designed to be smaller, and the optimum oscillation conditions are found
and manufactured while gradually expanding the diameter. Therefore, for adjustment from
design to manufacturing There is a problem that it takes a lot of man-hours. This frequency
fluctuation is considered to be caused by coupled vibration between the Helmholtz frequency
and the resonance frequency of the diaphragm.
[0008]
The present invention has been made in view of the above-mentioned problems of the prior art,
and in view of the above-mentioned coupled vibration, a piezoelectric vibrating device capable of
reliably obtaining stable oscillation with a simple configuration and the same The purpose is to
provide a manufacturing method.
[0009]
SUMMARY OF THE INVENTION In the present invention, the ratio ωb / ωa of the Helmholtz
angular frequency ωa to the resonant angular frequency ωb of the diaphragm is approximately
between 0.7 and 1.0. It is a piezoelectric vibration device in which the diameter of the sound
emission hole and the shape of the outer case are set as described above.
[0010]
Further, according to the present invention, the sound emission hole is set such that the ratio ωb
/ ωa of the Helmholtz angular frequency ωa to the resonant angular frequency ωb of the
diaphragm is approximately between 0.7 and 1.0 before assembly. This is a method of
manufacturing a piezoelectric vibration device in which the diameter of the case and the shape of
the outer case are set and provided, and a predetermined diaphragm is attached and fixed to the
outer case.
[0011]
In the piezoelectric vibration device according to the present invention, the ratio between the
resonant frequency of the diaphragm and the Helmholtz resonant frequency is set in advance to
an optimum value, and the number of labor steps such as troublesome adjustment can be
significantly reduced. It is a thing.
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[0012]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A piezoelectric vibration device
according to an embodiment of the present invention will be described below based on the
drawings.
The piezoelectric vibration device of this embodiment has a diaphragm 10 and an outer case 12
accommodating the same, and the diaphragm 10 is obtained by sticking a piezoelectric ceramic
16 to a metal disk 14.
The outer case 12 is closed at one end face of a cylindrical shape, and a sound output hole 18 is
formed at the center of the closed portion.
Further, a ring-shaped step 20 is formed on the inner peripheral surface of the outer case 12,
and the diaphragm 10 is mounted on the step 20.
The opening of the outer case 12 is closed by the bottom lid 24 and accommodates the
diaphragm 10, and the diaphragm 10 is held and fixed by the step portion 20 and the doughnutshaped projection 22 formed on the bottom lid 24. ing. Furthermore, mounting pieces 26 for
mounting are provided to protrude on both sides of the outer case 12.
[0013]
As shown in FIG. 3, the frequency characteristic of the above-mentioned vibration system has two
peak values of the resonance frequency of the diaphragm 10 and the Helmholtz resonance
frequency. Here, it is assumed that the vibration system formed by the diaphragm 10 and the
vibration system formed by the hollow portion in the outer case 12 and the sound emission hole
18 are coupled by a capacitance Cm, and the equivalent inductance of the Helmholtz resonance
angular frequency ωa Let L1 be the equivalent capacitance C1, the equivalent inductance of the
resonant angular frequency ωb of the diaphragm 10 be L2, and the equivalent capacitance be
C2, and the equivalent resistance is neglected because it has nothing to do with resonance.
Considering each of the angular resonant frequencies ωa and ωb and the coupling coefficient K
are expressed by the following equations.
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[0014]
[Equation 2] [Equation 3] [Equation 4]
[0015]
Accordingly, the angular resonant frequency as the whole equivalent circuit of FIG. 4 is expressed
by the following equation.
[Equation 5]
[0016]
Here, when Eq. 5 is solved with .omega.b / .omega.a = P and K = .mu., Two peak values .omega.1
and .omega.2 of the resonance frequency are expressed by the following equations. [Equation 6]
[Equation 7]
[0017]
Now, with the coupling coefficient μ = 0.1, the resonance frequency ωb / 2π of the diaphragm
10 is fixed to the clock frequency 2.048 KHz, and the inner diameter of the sound emission hole
18 is changed to change the Helmholtz angular frequency ωa. Resonant frequencies f1 and f2
obtained by Equations 6 and 7 in the above case are indicated by solid lines in FIG. Here, f1 and
f2 are ω1 / 2π and ω2 / 2π. Similarly, the values of the resonance frequencies f1 and f2 when
the resonance frequency ωb / 2π of the diaphragm 10 is fixed to the clock frequency 4.096
KHz are shown by the broken lines in FIG. As understood from the theoretical calculation value,
in the state where the Helmholtz angular frequency ωa is lower than the resonant angular
frequency ωb of the diaphragm 10, that is, in the state where P is larger than 1, the second peak
value f2 of the resonant frequency is the above clock frequency The constant value becomes
constant at approximately the same value, and the lower resonance frequency f1 tends to
gradually change. Also, when P is 0.9 or less, the resonance frequency f2 of the second peak
value changes in inverse proportion to P, and the resonance frequency f1 of the first peak value
is substantially lower than the above-mentioned fixed value of f2 It becomes constant. That is, the
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portion of constant values of f1 and f2 in the graph of FIG. 5 is a region governed by the
resonance frequency of the diaphragm 10, and the portion influenced by the Helmholtz
resonance frequency has a correlation with P. Therefore, it can be said that f1 and f2 are parts of
the changing resonance frequency. Therefore, as if the resonance frequency controlled by each
vibration system crosses in the part of P = 1, it resonates in the form of jumping and exchanging
each other in the vicinity of P = 1 is there.
[0018]
Based on the above theoretical calculation, the resonance frequency of the diaphragm 10 is set
near the clock frequency, and the diameter of the sound release hole 18 of the outer case 12 is
changed. The result of the experiment is shown below. The measurement was performed in an
anechoic box by applying a sine wave of 3.0 V peak-to-peak to make the distance between the
sound source and the microphone 10 cm. The outer case 12 had an outer diameter of 30 mm,
and the diaphragm 10 had a diameter of 27 mm. The inner diameter of the sound output hole 18
was changed to measure the respective resonance frequencies f1 and f2. The clock frequency for
driving was 2.048 KHz and 4.096 KHz as in the case of the theoretical calculation, and the
resonance frequency of the diaphragm 10 was 2.07 KHz and 4.05 KHz. The measurement results
are shown in Table 1, Table 2 and FIG.
[0019]
[Table 1]
[0020]
[Table 2]
[0021]
As a result, as can be seen by comparing FIG. 5 and FIG. 6, the measurement result and the
calculated value are in good agreement, and based on this, the theoretically calculated optimal
sound emission hole diameter is first It is understood that the piezoelectric vibration device can
be manufactured by setting.
Further, FIG. 7 shows values obtained by measuring the sound pressures Pf1 and Pf2 of the
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resonance frequencies f1 and f2 when the clock frequency is 2.048 KHz by changing ωb / ωa =
P.
[0022]
Thus, as can be seen from Tables 1 and 2 and FIGS. 5, 6 and 7, when ωb / ωa is 1 or more, the
frequency and sound pressure of f1 are unfavorably lowered.
In addition, when ωb / ωa = P is 0.7 or less, the frequency of f2 is greatly increased, and the
sound pressure of f2 is significantly reduced, which is not preferable. Therefore, ωb / ωa = P is
approximately between 0.7 and 1.0, and by setting the diameter of the sound release hole 10 or
the like so as to be within this range, The oscillation frequency can be optimized from the
beginning of production. In this embodiment, based on the above results, each parameter for
determining the oscillation frequency of the piezoelectric vibration device is set in advance so as
to fall within the range of the above P condition, and the diaphragm 10 is attached to the outer
case 12 It is a thing.
[0023]
The piezoelectric vibration device according to the present invention is not limited to the above
embodiment, and the size and number of the sound emission holes can be set appropriately.
[0024]
The piezoelectric vibration device of the present invention is designed and assembled in advance
so that the oscillation frequency is at the optimum value, so that frequency deviation due to
dimensional error or assembly error can be minimized. There is no need to adjust the frequency
during assembly.
Moreover, since there is no adjustment at the time of assembly as in the prior art, the number of
assembly steps and costs can be reduced, and the yield at the time of manufacturing can be
improved.
[0025]
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Brief description of the drawings
[0026]
1 is a longitudinal sectional view of an embodiment of the piezoelectric vibration device of the
present invention.
[0027]
2 is a perspective view of an embodiment of the piezoelectric vibration device of the present
invention.
[0028]
3 is a diagram showing the resonance frequency characteristics of the piezoelectric vibration
device of this embodiment.
[0029]
4 is a circuit diagram of an equivalent circuit of the piezoelectric vibration device of this
embodiment.
[0030]
5 is a graph showing the calculated value of the resonant frequency of the piezoelectric vibration
device of this example.
[0031]
6 is a graph showing the actual value of the resonant frequency of the piezoelectric vibration
device of this embodiment.
[0032]
7 is a graph showing the sound pressure characteristics of the resonant frequency of the
piezoelectric vibration device of this embodiment.
[0033]
Explanation of sign
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[0034]
10 diaphragm 12 exterior case 14 metal disc 18 sound emission hole
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