JPH1175297A - Ultrasonic wave microphone and its frequency adjustment method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a ultrasonic wave microphone whose resonance frequency is easily adjusted where re-adjustment is attained even when adjustment of the resonance frequency is failed. SOLUTION: The ultrasonic microphone is made up of a cylindrical vibration case 1, a diaphragm 2 forming the bottom of the vibration case 1, a piezoelectric element 3 fitted to an inner face 2a of the diaphragm 2, an insulation plug 8 sealing an opening 1b of the vibration case 1, and a lead pin 4 connecting to an electrode of a positive side face of the piezoelectric element 3. Thus, the resonance frequency is easily adjusted in a short time at an inexpensive installation without cutting the diaphragm 2 by removing part of the lead pin. Furthermore, in the case that the frequency adjustment is failed, since re-adjustment is attained by replacing the lead pin excessively cut off with other lead pin and generation of a defective microphone is prevented. Since the weight of the lead pin 4 acts like an added weight to increase the amplitude at resonance comparatively larger, the sound pressure characteristic is enhanced.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic microphone used for an ultrasonic sensor and a method for adjusting the frequency of the microphone.

[0002]

2. Description of the Related Art Generally, an ultrasonic microphone of a transmission / reception type and of an integrated type transmits an ultrasonic wave and receives an ultrasonic wave rebounding from an object. At this time, the distance from the transmission location to the object can be measured by measuring the time from transmission to reception. As an application of such an ultrasonic microphone, a back sonar of an automobile, a corner sensor, a security intruder detection sensor, and the like are known.

[0003]

By the way, the ultrasonic microphone as described above efficiently obtains sound pressure.
A vibrating portion is formed by integrally attaching a vibration plate and a piezoelectric element, and is used with an optimum resonance frequency. However, there are cases where it is necessary to adjust the resonance frequency due to variations in processing accuracy in manufacturing the vibration plate and the piezoelectric element, variations in adhesion between the vibrating body and the piezoelectric element, and the like.

Therefore, as an ultrasonic microphone having resonance frequency adjusting means, a diaphragm is cut to change the thickness of the diaphragm, or, for example, disclosed in Japanese Patent Publication No. 5-1290 and Japanese Patent Laid-Open No. 4-56597. As disclosed, there is known an ultrasonic microphone that adjusts a resonance frequency by cutting a peripheral fixed portion of a diaphragm. Further, as disclosed in Japanese Patent Application Laid-Open No. 4-323999, there is known an ultrasonic microphone in which a resonance frequency is adjusted by adding another component to a vibrating portion.

However, in the ultrasonic microphone disclosed in Japanese Patent Publication No. 5-1290 and Japanese Patent Laid-Open No. 4-56597, if the fulcrum of the diaphragm is excessively cut, it cannot be returned to the original position. Was sometimes defective. In addition, in the ultrasonic microphone disclosed in Japanese Patent Application Laid-Open No. 4-323999, it is necessary to prepare various kinds of additional parts for addition, and it is necessary to prepare other parts for obtaining an appropriate resonance frequency. If not,
In some cases, the ultrasonic microphone has a resonance frequency deviated from a target resonance frequency.

Further, it is necessary to increase the sound pressure in order to widen the detection accuracy and measurement range of the ultrasonic microphone. However, in the conventional ultrasonic microphone, the sound pressure is determined by the characteristics of the piezoelectric element, the dimensions of the diaphragm, the voltage applied to the piezoelectric element, the frequency, and the like, and it is difficult to expand the detection accuracy and the measurement range. . The present invention has been made to solve such a problem, and an object of the present invention is to provide an ultrasonic microphone that can easily adjust a resonance frequency.

Another object of the present invention is to provide an ultrasonic microphone capable of readjusting the resonance frequency when the adjustment of the resonance frequency fails. Still another object of the present invention is to provide an ultrasonic microphone that can improve sound pressure.

[0008]

According to an ultrasonic microphone according to the present invention, a cylindrical vibration case, a vibration plate forming a bottom thereof, a piezoelectric element mounted on an inner surface thereof, and an opening of the vibration case are provided. And a conductive resonance frequency adjusting means having one end side joined to the free end and the other end side joined to the anti-vibration plate side of the piezoelectric element. Therefore, the resonance frequency can be adjusted by removing a part of the resonance frequency adjusting means without cutting the diaphragm. Therefore, the resonance frequency can be easily adjusted in a short time with inexpensive equipment. Further, the weight of the resonance frequency adjusting means becomes an additional load, and the amplitude of the vibrating body at the time of resonance can be relatively increased, so that the sound pressure can be improved.

According to the ultrasonic microphone of the second aspect, the resonance frequency adjusting means has a curved portion between the one end side and the other end side. It is difficult to be transmitted to. Therefore, reverberation after transmission can be quickly converged, and noise at the time of measurement can be reduced. Furthermore, when a part of the resonance frequency adjusting means is deleted during the adjustment of the resonance frequency, it is difficult for an external force to be transmitted to the joint between the resonance frequency adjusting means and the piezoelectric element, so that the joint can be prevented from being damaged.

According to the ultrasonic microphone of the third aspect, at least the other end of the resonance frequency adjusting means is detachable from the piezoelectric element. Therefore, if the adjustment of the resonance frequency fails, the resonance frequency adjusting means is replaced. By doing so, the resonance frequency can be readjusted. Therefore, occurrence of defective products can be prevented. According to the method of adjusting the frequency of the ultrasonic microphone according to the fourth aspect, the resonance frequency is adjusted by removing at least a part of the resonance frequency adjustment means. Therefore, the resonance frequency can be easily adjusted in a short time with inexpensive equipment. Can be.

According to the ultrasonic microphone frequency adjusting method of the present invention, the resonance frequency is adjusted by replacing the resonance frequency adjusting means with another weighted resonance frequency adjusting means, so that the resonance frequency can be easily adjusted. And the occurrence of defective products can be prevented. According to the frequency adjustment method of the ultrasonic microphone according to the sixth aspect, after measuring the resonance frequency, at least a part of the resonance frequency adjustment unit is deleted, and when the resonance frequency adjustment unit is excessively deleted, the resonance frequency adjustment unit is turned off. The resonance frequency is adjusted by replacing the resonance frequency adjusting means with another weight and removing at least a part of the resonance frequency adjusting means having another weight. For this reason, since the resonance frequency can be readjusted, the occurrence of defective products can be prevented.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. (First Embodiment) FIG. 1 shows an ultrasonic microphone according to a first embodiment of the present invention. The ultrasonic microphone according to the first embodiment includes a cylindrical vibration case 1, a vibration plate 2 forming the bottom of the vibration case 1, a piezoelectric element 3 attached to an inner surface 2a of the vibration plate 2, and positive and negative leads. An insulating plug 8 having two terminals 7 electrically connected to the wires 5 and 6 as sealing means for sealing the opening 1b of the vibration case 1; The end side 4b comprises a lead pin 4 as a conductive resonance frequency adjusting means joined to the anti-vibration plate side of the piezoelectric element 3.

The vibrating case 1 and the vibrating plate 2 are integrally formed and have a bottomed cylindrical shape. The material of the vibration case 1 and the vibration plate 2 is preferably aluminum, but may be stainless steel (SUS) or Kovar. Vibration case 1
Is determined according to the frequency and directivity of the transmitted and received ultrasonic waves. A negative lead wire 6 is electrically connected to the inner wall surface 1a of the vibration case 1. Diaphragm 2
Is formed thinner than the side wall of the vibration case 1, and the plate thickness is determined according to the frequency of the transmitted / received ultrasonic wave, the required sound pressure and the sensitivity. A piezoelectric element 3 is adhered to the inner surface 2a of the diaphragm 2. The method of manufacturing the vibration case 1 and the vibration plate 2 may be any of cutting, drawing, punching, forging, die casting, pressing and the like.

The piezoelectric element 3 is made of lead zirconate titanate (P
ZT) or the like, and is adhered to the center of the inner surface 2a of the diaphragm 2 with a conductive adhesive or the like. Electrodes formed by silver printing or the like are formed on both sides of the piezoelectric element 3. The electrode on the negative side surface of the piezoelectric element 3 is attached to the diaphragm 2 and serves as a body ground. A lead pin 4 is bonded to the surface of the piezoelectric element 3 on the side opposite to the vibration plate, that is, the electrode on the plus side surface. When an AC voltage is applied to the piezoelectric element 3, the piezoelectric element 3 vibrates, and the diaphragm 2 vibrates due to the movement of the piezoelectric element 3 at this time. The frequency of the AC voltage applied to the piezoelectric element 3 is near the eigenvalue of the system including the diaphragm 2, the piezoelectric element 3, and the plus and minus lead wires 5 and 6, and therefore, the sensitivity of the microphone is efficiently increased. be able to.

The conductive lead pin 4 has one free end 4a and the other free end 4b joined to the joint 9 of the electrode on the positive side surface of the piezoelectric element 3 by soldering. A positive lead wire 5 is connected to one end 4a of the lead pin 4. Lead pin 4 is 0.4 to 1.0 mmφ
It has a pigtail shape having a curved portion 4c between one end 4a and the other end 4b. As the lead pins 4, it is preferable to use a copper-plated solder wire in consideration of solderability, but any conductive wire may be used.

The positive lead wire 5 is connected to the lead pin 4
And the terminal 7 are electrically connected, and are connected to one end 4a of the lead pin 4 and the end face 7a of the terminal 7 by soldering. The negative lead wire 6
The vibration case 1 is electrically connected to the terminal 7, and is connected to the inner wall surface 1 a of the vibration case 1 and the end face 7 b of the terminal 7 by soldering. The plus and minus lead wires 5 and 6 are thin wires so as not to hinder the vibration of the diaphragm 2 and the piezoelectric element 3.

The two terminals 7 are metal pins,
These are input / output terminals for transferring electric signals to and from an external circuit (not shown). The insulating plug 8 fixes the two terminals 7 respectively.
In addition to being insulated, the inside of the vibration case 1 is sealed. The insulating plug 8 is made of resin, and the vibration case 1
Is bonded and fixed to the opening 1b to seal the opening 1b.

Next, a method of adjusting the resonance frequency of the ultrasonic microphone will be described below. First, as shown in FIG. 2, a negative lead wire 6 is soldered to the inner wall surface 1a of the vibration case 1. Next, as shown in FIG. 3, the piezoelectric element 3 is bonded to the center of the inner surface 2a of the diaphragm 2 so that the minus side of the polarized piezoelectric element 3 having electrodes formed on both side surfaces is in close contact with the diaphragm 2. I do.

Next, as shown in FIG.
Is joined to the joint 9 of the electrode on the positive side surface of the piezoelectric element 3 by soldering. The measurement of the resonance frequency is performed using the negative lead wire 6 and the lead pin 40. At this time, the dimensions of the diaphragm 2 and the lead pins 40
Are set such that the measured resonance frequency is lower than the target value. Since the length of the lead pin to be deleted is substantially determined from the measured resonance frequency and a predetermined adjustment map, the one end 40a of the lead pin 40 is deleted by that length. Here, by removing the one end 40a of the lead pin 40, the weight of the lead pin is reduced, and the applied load is reduced, so that the measured resonance frequency is increased.

Thereafter, the resonance frequency is measured again, and it is confirmed that the measured resonance frequency is within the target range. Here, if the measured resonance frequency is lower than the target value, the length to be deleted from the adjustment map is obtained again, and the end of the lead pin is deleted again. If the measured resonance frequency is higher than the target value, remove the lead pin and repeat the above with a new lead pin. At this time,
Use another adjustment map for lead pin replacement.

Next, as shown in FIG. 1, a positive lead wire 5 is attached to one end 4a of the lead pin 4 whose length has been adjusted. The two terminals 7 and the insulating plate 8 are integrally formed in advance, and the end face 7a of the terminal 7 and the positive lead wire 5 are connected by soldering.
b and the negative lead wire 6 are connected by soldering. After that, the insulating plate 8 is connected to the opening 1b of the vibration case 1.
Glue and fix to According to the above method, an ultrasonic microphone whose resonance frequency is adjusted can be obtained.

According to the first embodiment of the present invention, the resonance frequency can be easily adjusted in a short time with inexpensive equipment without cutting the diaphragm 2 by removing a part of the lead pin. . Furthermore, if the frequency adjustment fails,
Replacing a lead pin that has been excessively deleted with another lead pin makes redoing effective, thereby preventing the occurrence of defective products. Furthermore, the weight of the lead pin 4 becomes an additional load, and the amplitude of the diaphragm 2 and the piezoelectric element 3 at the time of resonance can be made relatively large, so that the sound pressure can be improved.

Further, according to the first embodiment, the lead pins 4
Has a pigtail shape having a curved portion 4c between the one end 4a and the other end 4b, so that the curved portion 4c
The vibration of the vibration plate 2 becomes difficult to be transmitted to the terminal 7 due to the dynamic vibration absorber characteristics of the vibration damper. Therefore, reverberation after transmission can be quickly converged, and noise at the time of measurement can be reduced. Further, when a part of the lead pin is deleted at the time of adjusting the resonance frequency, it is difficult for the stress to be transmitted to the joint 9 between the lead pin and the piezoelectric element 3, so that the joint can be prevented from being damaged. Further, since the lead pin is joined to the piezoelectric element 3 by soldering, if the frequency adjustment fails during the resonance frequency adjustment, the lead pin can be easily replaced with another lead pin.

In the first embodiment, the lead pin 4 has a pigtail shape, but may have a spiral shape or an S-shape. Further, in the first embodiment, the frequency adjustment was performed by removing a part of the lead pin, that is, by increasing the resonance frequency, but by replacing the lead pin with a heavy one, that is, by reducing the resonance frequency. It is also possible to adjust the frequency.

(Second Embodiment) FIG. 5 shows a second embodiment of the present invention.
Shown in The lead pin 14 has a linear shape. One end 14a is a free end and the other end 14b is joined to the joint 9 of the electrode on the plus side surface of the piezoelectric element 3 by soldering. In addition, the same reference numerals are given to substantially the same parts as in the first embodiment.

In the second embodiment, it is not possible to obtain the dynamic vibration damping property by the lead pin, but by removing a part of the lead pin, the resonance frequency can be easily adjusted in a short time with inexpensive equipment. Further, when the frequency adjustment fails, redoing is effective by replacing the lead pin that has been excessively deleted with another lead pin, thereby preventing the occurrence of defective products.

In a plurality of embodiments of the present invention, the vibration case 1
And the vibration plate 2 are integrally formed, but in the present invention, the vibration case and the vibration plate may be a combination of two parts,
In the case of a combination of two parts, the manufacturing method may be any of brazing, press fitting, welding, bonding and the like. Further, in the present invention, instead of connecting the positive lead wire to the lead pin, it is directly connected to the electrode on the positive side surface of the piezoelectric element, and the lead pin does not have a role of a conductor, but has only a role of adjusting the resonance frequency. It may be configured.

[Brief description of the drawings]

FIG. 1 is a sectional view showing an ultrasonic microphone according to a first embodiment of the present invention.

FIG. 2 is a sectional view for explaining a method of adjusting a resonance frequency according to the first embodiment.

FIG. 3 is a cross-sectional view for explaining a method of adjusting a resonance frequency according to the first embodiment.

FIG. 4 is a sectional view for explaining a method of adjusting a resonance frequency according to the first embodiment.

FIG. 5 is a sectional view illustrating an ultrasonic microphone according to a second embodiment of the present invention.

[Description of Signs] 1 Vibration case 1a Inner wall surface 1b Opening 2 Vibration plate 2a Inner surface 3 Piezoelectric element 4 Lead pin (resonance frequency adjusting means) 4a One end side 4b One end side 4c Curved portion 5 Positive lead wire 6 Negative lead Wire 7 Terminal 8 Insulation plug (sealing means) 9 Joint

Claims (6)

[Claims] 1. A cylindrical vibrating case, a vibrating plate forming a bottom of the vibrating case, a piezoelectric element mounted on an inner surface of the vibrating plate, and sealing means for sealing an opening of the vibrating case. An ultrasonic microphone comprising: a conductive resonance frequency adjusting means, one end of which is a free end, and the other end of which is joined to the anti-vibration plate side of the piezoelectric element. 2. The ultrasonic microphone according to claim 1, wherein said resonance frequency adjusting means has a curved portion between said one end and said other end. 3. The ultrasonic microphone according to claim 1, wherein at least said other end side of said resonance frequency adjusting means is detachably connected to said piezoelectric element. 4. A method for adjusting a resonance frequency of an ultrasonic microphone according to claim 1, wherein the resonance frequency adjustment unit is connected to an opposite side of the piezoelectric element from the vibration plate. A method for adjusting the frequency of an ultrasonic microphone, comprising: a step of measuring a resonance frequency; and a step of removing at least a part of the resonance frequency adjustment unit. 5. A method for adjusting a resonance frequency of an ultrasonic microphone according to claim 3, wherein the resonance frequency adjustment means is connected to an opposite side of the piezoelectric element from the vibration plate, and the resonance frequency is measured. And a step of replacing the resonance frequency adjusting means with a different weight of the resonance frequency adjusting means. 6. A method for adjusting a resonance frequency of an ultrasonic microphone according to claim 3, wherein the resonance frequency adjusting means is connected to an anti-vibration plate side of the piezoelectric element, and the resonance frequency is measured. Removing the at least part of the resonance frequency adjusting means; and, when the resonance frequency adjusting means is excessively deleted, replacing the resonance frequency adjusting means with another resonance frequency adjusting means having a different weight. Removing at least a part of the resonance frequency adjusting means.