JP2004056450A - Ultrasonic sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inexpensively provide an ultrasonic sensor in which dispersion of an initial characteristic is reduced, which is neither easily affected by a temperature difference, nor deteriorated by an environment. <P>SOLUTION: A base and a cylindrical part of a case is integrally formed of piezoelectric ceramics. A crossed finger electrode and a spiral electrode are formed on the base. The piezoelectric ceramics between the electrodes are polarized, and set to be driving sources. <P>COPYRIGHT: (C)2004,JPO

Description

【００１９】
実施の形態は、従来構造と電極構成が異なるために、同じ値の静電容量と感度は得られないが、静電容量と感度のそれぞれの平均値に対するばらつきの大きさの比を比較すると、実施の形態は比較例の半分以下で、ばらつきが小さいことが分かる。
【００２０】
また、前述の超音波センサについて、マイナス４０℃とプラス１００℃の温度を繰り返す熱衝撃試験を実施し、超音波センサの静電容量の変化を観測した。前記静電容量は、圧電セラミックスの誘電率と電極間距離、電極面積よって決まる値であるが、熱衝撃試験にて接着層に劣化があると振動子と振動板の間の拘束に変化が生じるため、前記静電容量が下がる傾向がある。比較のため、図７に示した従来構造の超音波センサについても、同様の試験を実施した。熱衝撃試験経過に伴う静電容量の変化率を図６に示す。
【００２１】
図６から、従来構造では、５００サイクル経過時点で５％程度の静電容量の変化があるのに対し、本発明による構造では、ほとんど劣化は見られなかった。この実験結果から、本構造では温度差による特性の劣化は従来構造に比し少ないことが確認された。
【００２２】
更に、前述の超音波センサを１０００個試作するときの１個当りの製造時間とコストを従来構造品と比較し、比較結果を表２に示した。
【００２３】
【表２】

【００２４】
表２から、本発明の超音波センサは比較例に比べ、約６０％の低コストで製造することが可能であることが分かる。
【００２５】
【発明の効果】
上記のように、本発明によれば、ケースの底面と円筒部分を圧電セラミックスで一体成型することで、初期特性のばらつきが少ない超音波センサを安価に提供すると同時に、底面に交差指電極や渦巻き状の電極を形成して、電極間の圧電セラミックスを分極して駆動源とすることによって、温度差の影響を受けにくく、環境による劣化を起こすことの少ない超音波センサを得ることが可能となった。
【図面の簡単な説明】
【図１】本発明による超音波センサの一実施の形態を示す断面図。
【図２】吸音材や弾性材料を充填する前の図１に示した有底筒状ケースの平面図。
【図３】交差指電極に電圧を印加した時の振動板の分極状態を示す図。
【図４】２本以上の同心円状の交差指電極を示す図。
【図５】一定間隔で２本の渦巻き状の電極を示す図。
【図６】熱衝撃試験経過に伴う静電容量の変化率を示す図。
【図７】公知文献に記載されている超音波センサの構造を示す図。
【符号の説明】
１，２５　　有底筒状ケース
２　　振動板
２ａ　　振動板の内面
３，４　　交差指電極
５，６　　ランド電極
７　　吸音材
８　　弾性材料
９，１０　　リード線
１１，１２　　信号線
２１　　分極方向を示す矢印
２６　　振動板
２７　　圧電振動素子
２８ａ，２８ｂ　　素子電極
２９　　吸音材
３０　　弾性体
３１　　はんだ点
３２，３３　　リード線
３４，３５　　信号線[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an ultrasonic sensor that transmits an ultrasonic signal and detects a presence of an obstacle by receiving a reflected wave from the obstacle, and is particularly suitable for a back sonar and a corner sonar of an automobile. The present invention relates to an ultrasonic sensor.
[0002]
[Prior art]
An ultrasonic sensor performs sensing using ultrasonic waves. By vibrating a diaphragm using a piezoelectric vibrating element as a driving source, an ultrasonic pulse signal is intermittently transmitted, and a detected object existing in front is detected. The object is detected by receiving the reflected wave from the object through the diaphragm and the piezoelectric vibrating element.
[0003]
Conventionally, as a publicly known document regarding this type of ultrasonic sensor, there is JP-A-2001-169392. FIG. 7 shows the structure of the ultrasonic sensor described in the known document. The ultrasonic sensor has a structure in which a bottom surface of a bottomed cylindrical case 25 made of metal such as aluminum is a diaphragm 26, and a piezoelectric vibrating element 27 is joined to an inner surface of the diaphragm 26. ing. Electrical connection from the piezoelectric vibrating element 27 is made by lead wires 32 and 33. One lead wire 32 is joined to the element electrode 28 a facing the joint surface of the piezoelectric vibration element 27 by soldering. The other lead wire 33 is soldered to the metal case 25, and is electrically connected via the metal case 25 to the element electrode 28 b on the bonding surface of the piezoelectric vibration element 27. The inside of the bottomed cylindrical case 25 is filled with a sound absorbing material 29 made of sponge or the like so as not to restrain the piezoelectric vibrating element 27, and in order to prevent raindrops or the like from entering the case from above the sound absorbing material 29. Is filled with an elastic body 30 such as a silicone resin. The lead wires 32 and 33 are electrically connected to the signal lines 34 and 35 by soldering inside the resin.
[0004]
The ultrasonic sensor operates as follows. When a drive voltage is intermittently applied to the piezoelectric vibrating element 27 from the signal lines 34 and 35 to vibrate the piezoelectric vibrating element 27, the diaphragm 26 vibrates in film, and the ultrasonic wave is emitted forward from the diaphragm. Since the driving is performed intermittently, the ultrasonic wave reflected from the object reaches the piezoelectric vibrating element 27 via the vibrating plate 26 after a predetermined time has elapsed within the time when the transmission is stopped. Then, the received ultrasonic wave is converted into a voltage signal by the piezoelectric vibrating element 27 and output from the signal lines 34 and 35. Here, since the time until the reflected wave returns and the distance to the object are in a proportional relationship, the distance to the object can be measured by observing the elapsed time from transmission to reception. .
[0005]
[Problems to be solved by the invention]
As a requirement for an ultrasonic sensor used to detect an obstacle around a car, it is required that the sensitivity and the directional angle of the ultrasonic sensor do not change due to environmental changes such as temperature difference and humidity. In addition, it is required that the above-mentioned properties do not change or deteriorate due to the entry of raindrops, that is, drip-proof properties.
[0006]
However, in a structure in which a piezoelectric vibrating element is bonded to a metal case such as aluminum as disclosed in Japanese Patent Application Laid-Open No. 2001-169392, since aluminum and piezoelectric ceramics having different coefficients of thermal expansion by about 10 times are bonded, In the use environment, stress is concentrated on the adhesive layer between the aluminum and the piezoelectric ceramic due to repeated temperature changes, and the adhesive force gradually decreases. This type of ultrasonic sensor emits ultrasonic waves by vibrating the diaphragm on the bottom of the case using the expansion and contraction of the piezoelectric ceramic by the AC voltage as a drive source, and emits ultrasonic waves. There is a problem in that the transmission changes, and as a result, the performance of the ultrasonic sensor, such as the sound pressure, sensitivity, and directional angle, changes from an initial value due to environmental fluctuations and time and does not return to the original value.
[0007]
In general, such a metal case is manufactured by shaving, and the thickness and undulation of the bottom surface of the bottomed cylindrical case that becomes the diaphragm are caused by the resonance frequency, sensitivity, reverberation characteristics, etc. of the ultrasonic sensor. Greatly affects the various characteristics of Therefore, in order to reduce the variation in the initial characteristics, it is necessary to process the metal case with high accuracy, resulting in a problem that the metal case is expensive.
[0008]
Accordingly, the present invention has been made to solve the above-described problems, and provides an inexpensive ultrasonic sensor that has less variation in initial characteristics, is less susceptible to temperature differences, and is less likely to deteriorate due to the environment. The purpose is to do.
[0009]
[Means for Solving the Problems]
According to the present invention, there is provided an ultrasonic sensor for transmitting and receiving ultrasonic waves using the bottom surface of a bottomed cylindrical case as a vibration plate, wherein the bottom surface and the cylindrical portion of the bottomed cylindrical case are integrally formed of a piezoelectric ceramic material. An ultrasonic sensor having a structure in which a counter electrode is formed on a portion of the bottom surface to impart piezoelectricity, and a portion of the bottom surface is used as a driving source for vibration and a receiving source for reflected waves.
[0010]
Further, according to the present invention, on the bottom surface of the bottomed cylindrical case, there are provided three or more parallel linear or concentric interdigital electrodes or a pair of spiral electrodes each having a land electrode at an end. An ultrasonic sensor is obtained.
[0011]
In the present invention, the bottom surface and the cylindrical portion of the bottomed cylindrical case are integrally formed of piezoelectric ceramics, a counter electrode is formed on the bottom surface of the bottomed cylindrical case made of the piezoelectric ceramic, and the counter electrode is used by using the counter electrode. The piezoelectric ceramic is polarized to impart piezoelectricity to form a diaphragm, and an alternating voltage is applied between the counter electrodes to vibrate the diaphragm. Since the outer surface of the diaphragm and the surroundings have no piezoelectricity, the diaphragm vibrates irregularly due to expansion and contraction of piezoelectric ceramics on the inner surface of the fixed outer peripheral diaphragm, and emits ultrasonic waves in front of the outer surface, and , Reflected waves can be detected.
[0012]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.
[0013]
FIG. 1 is a sectional view showing an embodiment of the ultrasonic sensor according to the present invention. In FIG. 1, a bottomed cylindrical case 1 having an outer diameter of 20 mm and a height of 10 mm is obtained by firing a molded body of a lead zirconate titanate-based piezoelectric ceramic material. A 1.5 mm vibrating plate 2 is integrally formed, interdigital electrodes 3 and 4 are formed on the inner surface 2 a of the vibrating plate 2 by sputtering, and land electrodes 5 formed at the ends of the interdigital electrodes 3 and 4. 6 are soldered with lead wires 9 and 10, and the inside of the bottomed cylindrical case 1 is filled with a sound absorbing material 7 such as sponge or felt provided with a hole for passing the lead wires 9 and 10. The sound absorbing material 7 is filled with an insulating elastic material 8 such as a silicone resin or a urethane resin in order to prevent humidity and raindrops from entering.
[0014]
FIG. 2 is a plan view of the bottomed cylindrical case shown in FIG. 1 before the sound absorbing material 7 and the elastic material 8 are filled. The lead wires 9 and 10 are soldered to the signal wires 11 and 12 in the elastic material 8.
[0015]
FIG. 3 shows the polarization state of the diaphragm when a voltage is applied to the interdigital electrodes 3 and 4 of FIG. When an AC voltage is applied to the interdigital electrodes 3 and 4 by polarizing the piezoelectric ceramics on the inner surface side of the diaphragm 2 as shown by an arrow 21 in FIG. 3, the piezoelectric ceramics vibrate due to expansion and contraction of the piezoelectric ceramics on the inner surface side of the diaphragm. The plate vibrates unevenly, and can excite the vibration.
[0016]
In the above-described embodiment, the electrode formed on the inner surface of the diaphragm has been described as an interdigital electrode. However, two or more concentric interdigital electrodes or two spiral electrodes arranged at regular intervals may be used. Similarly, the diaphragm can be vibrated unevenly due to the expansion and contraction of the piezoelectric ceramic on the inner surface side of the diaphragm by application of the AC voltage, and the vibration can be excited, so that an ultrasonic sensor can be configured. One example of the two or more concentric interdigital electrodes is shown in FIG. FIG. 5 shows an example of the two spiral electrodes arranged at a constant interval.
[0017]
The initial characteristics of the capacitance and the sensitivity of the ultrasonic sensor prototyped in the above-described embodiment were measured. For comparison, the same measurement was performed for the ultrasonic sensor having the same configuration and the conventional structure shown in FIG. The number of measurement samples is 20, respectively. The results are shown in Table 1. The capacitance is a value determined by the dielectric constant of the piezoelectric ceramic, the distance between the electrodes, and the electrode area, but a stress is generated with the curing of the adhesive in the bonding process, and the stress affects the dielectric constant of the piezoelectric ceramic. Therefore, the capacitance tends to change.
[0018]
[Table 1]

[0019]
In the embodiment, the capacitance and sensitivity of the same value cannot be obtained because the electrode structure is different from that of the conventional structure.However, when comparing the ratio of the magnitude of the variation to the average value of the capacitance and the sensitivity, It can be seen that the embodiment is less than half of the comparative example and the variation is small.
[0020]
Further, a thermal shock test in which the temperature of minus 40 ° C. and plus 100 ° C. were repeated was performed on the above-described ultrasonic sensor, and a change in capacitance of the ultrasonic sensor was observed. The capacitance is a value determined by the dielectric constant of the piezoelectric ceramics and the distance between the electrodes, the electrode area, but if the adhesive layer is deteriorated in the thermal shock test, the constraint between the vibrator and the diaphragm changes, The capacitance tends to decrease. For comparison, a similar test was performed on the ultrasonic sensor having the conventional structure shown in FIG. FIG. 6 shows the rate of change of the capacitance with the progress of the thermal shock test.
[0021]
As shown in FIG. 6, the capacitance of the conventional structure changes by about 5% after 500 cycles, whereas the structure according to the present invention shows almost no deterioration. From this experimental result, it was confirmed that the characteristics of the present structure were less deteriorated due to the temperature difference than the conventional structure.
[0022]
Furthermore, the manufacturing time and cost per unit when 1,000 ultrasonic sensors were prototyped were compared with those of the conventional structure, and the comparison results are shown in Table 2.
[0023]
[Table 2]

[0024]
Table 2 shows that the ultrasonic sensor of the present invention can be manufactured at a low cost of about 60% as compared with the comparative example.
[0025]
【The invention's effect】
As described above, according to the present invention, by integrally molding the bottom surface and the cylindrical portion of the case with piezoelectric ceramics, it is possible to provide an ultrasonic sensor with less variation in initial characteristics at low cost, and at the same time, to intersect a finger electrode or a spiral on the bottom surface. By forming piezoelectric electrodes and polarizing the piezoelectric ceramics between the electrodes as a drive source, it is possible to obtain an ultrasonic sensor that is less susceptible to temperature differences and less likely to degrade due to the environment. Was.
[Brief description of the drawings]
FIG. 1 is a sectional view showing an embodiment of an ultrasonic sensor according to the present invention.
FIG. 2 is a plan view of the bottomed cylindrical case shown in FIG. 1 before filling with a sound absorbing material or an elastic material.
FIG. 3 is a diagram showing a polarization state of a diaphragm when a voltage is applied to an interdigital electrode.
FIG. 4 is a diagram showing two or more concentric interdigital electrodes.
FIG. 5 is a diagram showing two spiral electrodes at regular intervals.
FIG. 6 is a diagram showing a rate of change in capacitance with the progress of a thermal shock test.
FIG. 7 is a diagram showing a structure of an ultrasonic sensor described in a known document.
[Explanation of symbols]
1,25 bottomed cylindrical case 2 diaphragm 2a inner surface 3,4 interdigital electrode 5,6 land electrode 7 sound absorbing material 8, elastic material 9,10 lead wire 11,12 signal line 21 polarization direction arrow 26 Vibrating plate 27 Piezoelectric vibrating elements 28a, 28b Element electrode 29 Sound absorbing material 30 Elastic body 31 Solder points 32, 33 Lead wires 34, 35 Signal wires

Claims (5)

An ultrasonic sensor for transmitting and receiving ultrasonic waves using the bottom surface of a bottomed cylindrical case as a vibration plate, wherein the bottom surface and the cylindrical portion of the bottomed cylindrical case are integrally formed of a piezoelectric ceramic material, An ultrasonic sensor having a structure in which a counter electrode is formed on a portion of the bottom surface to impart piezoelectricity, and a portion of the bottom surface is used as a driving source for vibration and a receiving source for reflected waves. 2. The ultrasonic sensor according to claim 1, wherein three or more parallel linear interdigital electrodes are provided on a bottom surface of the bottomed cylindrical case. 2. The ultrasonic sensor according to claim 1, wherein two or more concentric interdigital electrodes are provided on the bottom surface of the bottomed cylindrical case. 2. The ultrasonic sensor according to claim 1, wherein two spiral electrodes are provided at regular intervals on the bottom surface of the bottomed cylindrical case. 5. The ultrasonic sensor according to claim 2, wherein a land electrode is provided at an end of an electrode formed on a bottom surface of the bottomed cylindrical case. 6.

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