JPH0131640B2 - - Google Patents

Description

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

Conventionally known piezoelectric buzzers include those that drive a two-terminal type sounding element by applying an oscillation voltage from an oscillation circuit, and those that combine a three-terminal feedback type sounding element and an amplifier to generate feedback and amplification effects. There are some types that are driven using 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 generate the collector voltage. Since it is only necessary to apply the voltage to the body main electrode, 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 the natural resonant frequency of the sounding body, making it difficult to obtain large sound pressures.Also, to drive the sounding body, it is necessary to incorporate a transistor, multiple resistors, and a board to interconnect them. , a larger component mounting volume is required,
Problems remain, such as that it is difficult to make the piezoelectric buzzer thinner, and furthermore, it is difficult to further reduce costs because an electronic circuit must be assembled.

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 this objective, according to the present invention,
A mechanical contact is provided near the sounding body to prevent the voltage applied to the sounding body via the mechanical contact, the bending movement of the sounding body caused by this, and the contact/separation phenomenon between the sounding body and the mechanical contact. It is designed to be used continuously and to continue pronunciation, and this is exactly what makes it unique.

That is, the mechanical contact type piezoelectric buzzer of the present invention supports a piezoelectric sounding body formed by adhering a conductive elastic thin plate to one surface of a piezoelectric plate near the node of bending vibration, and Mechanical contacts provided at positions other than the joints of the thin plate are positioned so that these mechanical contacts and the elastic thin plate separate when the piezoelectric sounding body is bent and come into contact when the piezoelectric sounding body returns to its original state. In addition, a DC power source is connected between the mechanical contact and a surface electrode provided on the other side of the piezoelectric plate, and a discharge resistor is further connected between this surface electrode and the elastic thin plate. .

Hereinafter, the present invention will be explained based on the drawings.
FIG. 1 is a diagram explaining the principle of the present invention. A piezoelectric sounding body 3, which is made by pasting a piezoelectric plate 2 on a conductive elastic thin plate 1, is mounted on a support 4 near a node of bending vibration.
A mechanical contact 5 is provided near the outer peripheral edge of the elastic thin plate 1, 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, the surface electrode 7 of the piezoelectric plate 2
When no voltage is applied between the power supply terminal 8 connected to the power supply terminal 8 and the power supply terminal 9 connected to the mechanical contact 5, the mechanical contact 5 is positioned so as to be in contact with 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 surfaces of the piezoelectric plate 2 through the mechanical contact 5 and the elastic thin plate 1, and the piezoelectric plate 2 is charged. As indicated by the line, the elastic lamina 1 is bent away from the mechanical contact 5. Then, the electric charge stored in the piezoelectric plate 2 is discharged through the discharge 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 comes into contact with the mechanical contact 5. I come to do it. Therefore, by simply supplying a DC voltage between the power supply terminals 8 and 9, the sounding body 3 repeats the above-mentioned operation, bending and vibrates, and generates sound.

As is clear from the above explanation of the operation, the discharge resistor 6 serves as a discharge route for the electric charge charged between the electrodes of the piezoelectric plate 2, and only by discharging can the sounding body be returned to its original shape. . 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 2 approximately matches the time constant of the mechanical resonance system constituted by the piezoelectric sounding body 3. According to the experimental results, the piezoelectric plate 2 is made of lead zirconate titanate porcelain (PZT) with a diameter of 25 mm.
When using a circular piezoelectric ceramic plate with a thickness of 0.2 mm and a thickness of 0.2 mm,
The suitable resistance value of the discharge resistor 6 was about 510Ω. When the diameter of the piezoelectric plate is small, increase the resistance value,
If the diameter is large, adjust the resistance value to a small value. Good sound was obtained at a DC voltage of about 20 to 50V.

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 FIG. 2, the shape of the elastic thin plate 1 is made such that the tongue portion 1a protrudes from the outer peripheral edge of the disk, and the mechanical contact point is brought into contact with the tongue portion 1a. You can configure it to do so. By providing the tongue portion 1a in this manner, the amplitude of the bending vibration can be increased, and the work of positioning and setting 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 the tongue part.

FIG. 3 is an explanatory diagram showing an embodiment of the piezoelectric buzzer according to the present invention. The configuration of the buzzer body is
Since the principle is the same as that shown in the figure, corresponding parts are given the same reference numerals and detailed description thereof will be omitted. However, in this embodiment, a sounding body having a tongue portion as shown in FIG. 2 is used. The buzzer body 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 5 is supported by a screw 19 on a step 18 formed on the inner wall of the case 17, and when not in operation, the tongue piece 1a come into contact with. The back side of the case 17 is closed by a back cover 20, and the lead wire 21 is drawn out from the back cover 20 or a notch or through hole of the case 17. In this embodiment, a type having a lead wire is installed as the discharge resistor 6, but it is also possible to adopt a technique such as directly forming a chip resistor or a printed resistor on a piezoelectric plate.

As described above, the present invention directly utilizes the bending vibration of the sounding body to turn on the mechanical contact. Since it is a piezoelectric buzzer configured to turn off, bending vibration occurs at the resonance frequency of the sounding body and a large sound pressure can be obtained, and since only one discharge resistor needs to be connected, it is possible to use a piezoelectric buzzer that is configured to turn off. This has excellent practical effects, such as eliminating the need for electronic components and substrates for interconnecting them, allowing cost reduction and thinning.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram of the principle of the present invention, FIG. 2 is a plan view showing an example of a piezoelectric sounding body, and FIG. 3 is an explanatory diagram of an embodiment of a piezoelectric buzzer according to the present invention. DESCRIPTION OF SYMBOLS 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 formed by adhering a thin conductive elastic plate to one surface of a piezoelectric plate is supported in the vicinity of a node of bending vibration thereof, and the node of the elastic thin plate is Mechanical contacts provided at positions other than the parts are positioned so that these mechanical contacts and the elastic thin plate separate when the piezoelectric sounding body is bent and come into contact when the piezoelectric sounding body returns to its original state, and A mechanical contact piezoelectric buzzer comprising: a DC power source connected between a mechanical contact and a surface electrode provided on the other surface of the piezoelectric plate; and a discharge resistor connected between the surface electrode and the elastic thin plate. . 2. Claims in which the thin elastic plate is a thin metal plate and has a shape in which a tongue protrudes from the outer peripheral edge of the disc, and the mechanical contact point comes into contact with and separates from the tongue. The piezoelectric buzzer according to item 1.