JPS589200A - Mechanical contact type piezo-electric buzzer - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a piezoelectric buzzer having a mechanical contact structure.

Conventionally known piezoelectric buzzers χ include one in which a two-terminal four-type sounding element is driven by applying an oscillation voltage from an oscillation circuit, and one in which a three-terminal feedback type sounding element and an amplifier are combined to drive the sounding element and their feedback effects. There are also types that are driven using amplification and amplification. In particular, the latter type basically uses a simple amplifier consisting of one transistor and several resistors, and applies the feedback voltage from the feedback electrode of the sounding body to the base of the transistor to adjust the collector voltage. Since it is only necessary to apply the voltage to the main electrode of the sounding body, there is an advantage that the number of parts can be reduced compared to the former type.

However, as mentioned above, the latter type uses the amplification effect of the transistor and the feedback effect of the sounding body to generate oscillation, so a phase shift occurs due to the equivalent capacitance of the sounding body. It oscillates at a frequency lower than its own natural resonance frequency, which results in a large sound pressure.
In addition, in order to drive the sounding element, a transistor, multiple resistors, and a board for interconnecting them must be incorporated, which requires a large component mounting volume. Problems remained, such as the fact that the circuits had to be assembled, making it difficult to further reduce costs.

An object of the present invention is to eliminate the drawbacks of the prior art as described above, and to create a device that does not require the use of any electronic components other than just one resistor, is therefore suitable for thinning, and can realize cost reduction. Our goal is to provide a piezoelectric buzzer with a completely new structure.

In order to achieve such an object, according to the present invention, a mechanical contact is provided near the sounding body to control the voltage applied to the sounding body via the mechanical contact and the bending motion of the sounding body caused by the voltage. In addition, it is configured to continue sounding by utilizing the phenomenon of contact and separation between the sounding body and the mechanical contact point, and this is exactly what makes it unique.

The present invention will be explained below based on the drawings.

Figure 1 is an explanatory diagram of the principle of the present invention. A piezoelectric sounding body 3 consisting of a piezoelectric plate 2 adhered to a conductive elastic thin plate 1 is supported by a support 4 near the bending vibration node, and a mechanical A contact point 5 is provided, and a discharge resistor 6 is connected between the electrodes of the piezoelectric plate 2. The thin elastic plate 1 is used to improve the mechanical strength of the piezoelectric sounding body 3, increase the amplitude of bending vibration, and provide electrical continuity to the electrode on the side to which the piezoelectric plate is attached, and is generally preferably a thin metal plate. However, it may also be a synthetic resin plate with a conductive layer formed on its surface. As shown in the figure, the piezoelectric plate 2 may most simply be a so-called unimorph type in which silver electrodes are printed and baked on the front or both sides of a thin piezoelectric ceramic plate and polarized in the thickness direction, but it may have a bimorph structure. can also be adopted.

Now, in FIG. 1, when no voltage is applied between the power terminal 8 connected to the surface electrode 7 of the piezoelectric plate 2 and the power terminal 9 connected to the mechanical contact 5, the mechanical contact 5
is positioned so as to contact the elastic thin plate 1. Therefore, when a DC voltage is applied between the power supply terminals 8 and 9, voltage is applied to both the front and back sides of the piezoelectric plate 20 through the mechanical contact 5 and the elastic thin plate 1, and the piezoelectric plate 20 is charged. As shown in , the elastic thin plate 1 is bent away from the mechanical contact 6 . Then, the electric charge stored in the piezoelectric plate 2 is discharged through the discharging resistor 6, and the sounding body 3 returns to its original state as shown by the solid line in the figure, and the elastic thin plate 1 is brought into contact with one mechanical liquid point. Comes into contact with 5. Therefore, power terminal 8
．． By simply supplying a DC voltage between the two terminals 9, the sounding body 3 repeats the above-mentioned operation, bending and vibrates, and generates sound.

As is clear from the above operation description, the discharge resistor 6 is 3,
This serves as a discharge route for the electric charge accumulated between the electrodes of the piezoelectric plate 2, and the sounding body can only be returned to its original shape by discharging. If there is no discharge resistance, the bent sounding body will not recover and therefore cannot be vibrated. The resistance value of the discharge resistor 6 is preferably selected so that the time constant between it and the equivalent capacitance of the piezoelectric plate 20 approximately matches the time constant of the mechanical resonance system constituted by the piezoelectric sounding body 3.

According to the experimental results, when a circular piezoelectric ceramic plate made of lead zirconate titanate ceramic (1) ZT) with a diameter of 25 rim and a thickness of 0.2 mm is used as the piezoelectric plate 2, the discharge resistance The resistance value of No. 6 was preferably about 510Ω. When the diameter of the piezoelectric plate is small, the resistance value is increased, and when the diameter is large, the resistance value is 1! Adjust it small. , +1'+ /#, t
Good pronunciation was obtained at about lf, It about 7(+-14(1\゛).

In a sounding body in which the piezoelectric plate 2 is circular and the elastic thin plate 1 is a circular disk with a slightly larger diameter, the amplitude of the bending vibration at the mechanical contact 5 is too small. In such a case, as shown in Figures 1 and 2, the shape of the thin elastic plate 1 is such that the tongue portion 1a protrudes from the outer peripheral edge of the disk, and the mechanical contact point is provided on the tongue portion 1a. What is necessary is just to configure it so that they are in contact with each other.

By providing the tongue portion 1a in this way, the amplitude of the bending vibration can be increased, and the positioning and setting work of the mechanical contacts becomes easier. However, by providing the tongue portion 1a, the mechanical resonance frequency of the sounding body shifts to a lower side, and if it is too long, it will vibrate at the mechanical resonance frequency of the tongue portion, reducing sound production efficiency. There is a limit to the length of each piece.

Figures 1 and 3 are explanatory diagrams showing one embodiment of the piezoelectric buzzer according to the present invention.The configuration of the buzzer body is the same as the principle diagram shown in Figure 1, so corresponding parts are the same. A detailed description of them will be omitted. However,
In this embodiment, a sounding body having a tongue portion as shown in Fig. 2 is used. The main body of the buzzer is housed in a dish-shaped case 17 having a sound emitting port 15 opening in the center and mounting portions 16 on both sides. The sounding body 3 is supported at the nodal position of its bending vibration, and the mechanical contact point 5 is
It is supported by a screw 19 on a stepped portion 18 formed on the inner wall of the case 17, and comes into contact with the tongue portion 1a during non-operation. The back side of the case 17 is closed by a back cover 20, and a lead wire 21
is pulled out from the back cover 20 or the notch or through hole of the case 17. Although the discharge resistor 6 of this embodiment is of a type having a lead wire, it is also possible to directly form a printed resistor on a chip resistor or a piezoelectric plate.

As described above, the present invention is a piezoelectric buzzer configured to directly utilize the bending vibration of the sounding body to turn on and off mechanical contacts. Since only one discharge resistor needs to be connected, there is no need for electronic components such as transistors and multiple resistors, and substrates for interconnecting them, making it possible to reduce costs and reduce thickness. 3. It has excellent effects.

[Brief explanation of the drawing]

Figure 1 is an explanatory diagram of the principle of the present invention, Figure 2 is a plan view showing an example of a piezoelectric sounding body, and Figure 3 is an explanatory diagram of an embodiment of a piezoelectric buzzer according to the present invention. 1...Elastic thin plate, 2...Piezoelectric plate, 3...Sounding body,
4... Support body, 5... Mechanical contact, 6... Discharge resistance.

Claims (1)

[Scope of Claims] 1. A piezoelectric sounding body made of a piezoelectric plate attached to a conductive elastic thin plate is supported near the nodes of bending vibration, and mechanical contacts are provided at positions other than the nodes. A mechanical contact type piezoelectric buzzer is provided, and a discharge resistor is connected between the electrodes of the piezoelectric plate, and a DC power source is connected between the mechanical contact and the sounding body electrode that is not electrically conductive. 2. Claims in which the electrically conductive elastic thin plate is a metal thin plate, has a shape in which a tongue protrudes from the outer periphery of the disk, and a mechanical contact is brought into contact with and separated from the tongue. The piezoelectric buzzer according to item 1.