JPH0410798B2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a piezoelectric diaphragm for a buzzer in which a piezoelectric ceramic plate is attached to a thin elastic plate such as a metal plate, and in particular, it is used to support the vibration nodes of the piezoelectric diaphragm. This relates to a piezoelectric diaphragm used in a piezoelectric buzzer.

Conventional configuration and its problems A piezoelectric buzzer with a structure that supports the nodes of the diaphragm is
The piezoelectric diaphragm has a three-terminal structure with a feedback electrode, supports the nodal part of vibration at the resonant wave number of the piezoelectric diaphragm, and obtains sharp resonance characteristics. A so-called self-oscillation type device that generates sound near the resonance frequency of a piezoelectric diaphragm by configuring an excitation oscillation circuit is widely used. A cross-sectional view of an example of a conventional piezoelectric buzzer of this type is shown in FIG. In this conventional piezoelectric buzzer, the nodal part of the vibration at the resonance frequency when the piezoelectric diaphragm 1 is allowed to vibrate freely is attached to the ring-shaped piezoelectric vibrator mounting part 3 protruding from the case 2 of the piezoelectric sounding body by gluing or the like. It has a supporting structure.
A typical example of the piezoelectric diaphragm 1 used here is the one whose plan view is shown in FIG. 2, and has a structure in which a piezoelectric ceramic plate 5 is integrated with a conductive elastic flat plate 4 such as a metal plate. A main electrode 6 and a return electrode 7 are provided on the front surface of the piezoelectric ceramic plate 5, and the electrode provided on the back surface is electrically connected to the metal plate 4.
For example, lead wires 8, 9, and 10 are connected to the main electrode 6, the return electrode 7, and the metal plate 4 as means for connecting to an oscillation circuit. As an example of a self-excited oscillation circuit that drives this piezoelectric buzzer, the third
The one shown in the figure is often used.

This type of piezoelectric buzzer has a simple drive circuit and high sound pressure, so it is often used for various alarm sounds.However, as the devices used in recent years have become smaller, there has been a strong demand for smaller piezoelectric buzzers. There is also a demand for a relatively low sounding frequency. However, in order to miniaturize the piezoelectric buzzer, the diameter of the piezoelectric diaphragm must be reduced, which is a condition that contradicts the reduction in the sound frequency, so it is possible to simultaneously reduce the size of the piezoelectric buzzer and reduce the sound frequency. It has become a major challenge to do so.

In order to lower the resonant frequency without increasing the diameter of the piezoelectric diaphragm, there is a method of making the piezoelectric diaphragm thinner, but this method also has its limits and is insufficient. Furthermore, if the outer periphery of the piezoelectric diaphragm is supported, the resonance frequency will be lowered, but the Q at resonance will be lowered, making it unsuitable for self-oscillation.

Purpose of the Invention The present invention eliminates these conventional drawbacks and realizes a piezoelectric buzzer that is small and has a relatively low sounding frequency. The purpose is to reduce the

Structure of the Invention In order to achieve this object, the piezoelectric diaphragm according to the present invention is made by bending the outer periphery of a flat disk to make it into a tray shape with a U-shaped cross section. , is characterized by providing a notch in the bent portion, and has a configuration in which a piezoelectric ceramic plate is attached to a flat disk portion of the metal plate.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. In FIG. 4, the same parts as in FIG. 2 of the conventional example are indicated by the same symbols. In FIG. 4, reference numeral 11 denotes a metal plate whose outer peripheral portion is bent at right angles, and a notch 13 is provided in the bent portion 12.
A piezoelectric ceramic plate 5 is attached to the upper surface of the metal plate 11, and a main electrode 6 and a return electrode 7 are provided on the piezoelectric ceramic plate 5. Further, lead wires 8, 9, and 10 are connected to each electrode and the metal plate.

An embodiment of a self-oscillation type buzzer incorporating this piezoelectric diaphragm into a case is shown in cross-section in FIG. In FIG. 5, the same parts as in FIG. 1 of the conventional example are indicated by the same symbols. As is clear from Fig. 5, the piezoelectric diaphragm 5
The bent portion 12 is bent in the direction of entering the inside of the case 2.

Effects of the Invention By bending the outer periphery of the metal plate of the piezoelectric diaphragm into a U-shape and making cuts in the bent portion to divide the bent portion as in the present invention, the bent portion can also vibrate freely. Therefore, an effect equivalent to an apparent increase in the diameter of the diaphragm can be obtained without increasing the actual diameter of the diaphragm, and the resonant frequency of the piezoelectric diaphragm according to the present invention is achieved by increasing the bending part of the outer periphery. The resonance frequency drops to almost the same as when it is stretched and made into a flat plate. Since the resonant frequency of the piezoelectric diaphragm is inversely proportional to the square of the diameter, its effect is very large. Therefore, even if the diameter of the diaphragm is the same, the resonant frequency can be changed by changing the length of the bent portion, and the resonant frequency can also be changed by changing the width of the cut in the bent portion (width of the bent portion). It can be changed. Therefore, the degree of freedom in designing piezoelectric diaphragms with the same diameter is greatly increased. Furthermore, since the bent portion is divided into many parts and can freely vibrate, the bent portion does not suppress vibration and reduce the Q of the piezoelectric diaphragm, making it ideal for self-excited oscillation. In addition, when this piezoelectric diaphragm is incorporated into a case, the bent portion of the metal plate enters the conventional dead space inside the case, so it is possible to reduce only the sound frequency without increasing the size of the piezoelectric buzzer. As described above, the present invention is very useful for downsizing and lowering the frequency of piezoelectric buzzers.

[Brief explanation of drawings]

Fig. 1 is a sectional view of a conventional self-oscillation type piezoelectric buzzer with node support, Fig. 2 is a plan view showing an example of a piezoelectric diaphragm used in the piezoelectric buzzer of Fig. 1, and Fig. 3 is Circuit diagram showing an example of an oscillation circuit that drives a self-oscillation type piezoelectric buzzer, Figures 4a and b
5 is a plan view and a side view of a piezoelectric diaphragm for a buzzer according to an embodiment of the present invention, and FIG. 5 is a sectional side view of a self-oscillation type piezoelectric buzzer using the same piezoelectric diaphragm. 5...Piezoelectric diaphragm, 12...Bending portion, 13
...notch.

Claims (1)

[Claims] 1. It has a thin elastic plate made of metal, etc., which has a U-shaped cross section and is divided into a plurality of pieces by making a plurality of cuts on the outer side, and a piezoelectric ceramic is attached to the flat part of the elastic thin plate. A piezoelectric diaphragm for buzzers made by pasting a plate.