JPH10206528A - Ultrasonic sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic sensor that allows correct position detection without being affected by a short range or temperature change, has not a complex driving circuit, is suited to a wide range of position detection, and excels in maintainability. SOLUTION: A case 1 is furnished with a body section 1a of nearly depressed form in the upper section and a sensor head section 1b that protrudes downward from the bottom section of the body section 1a, and is generally in inverted protrusion form. The sensor head section 1b is made up of an acoustic matching section 1b1 to which a piezoelectric vibrator 2 is fastened and a vibration resonance section 1b2 that is formed between the acoustic matching section 1b1 and the body section 1a. The sensor head 1b is thinner than the body section 1a provided in the upper section. Especially a valve structure that absorbs the reverberant vibration of the piezoelectric vibrator 2 is formed by forming a vibration resonance section 1b2 as a side face thinner than the acoustic matching section 1b1 as a bottom section.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an ultrasonic sensor, and more particularly, to an ultrasonic sensor which can detect the position of an object by ultrasonic waves.

[0002]

2. Description of the Related Art Conventionally, the characteristics of an ultrasonic wave have a strong directivity in which the ultrasonic wave travels in a certain direction.
It has the property of reflecting almost 100%. As a typical ultrasonic sensor that detects this reflected frequency,
An ultrasonic sensor in which a piezoelectric vibrator is formed of ceramic is generally known. Among these types of ultrasonic sensors, those that are capable of both transmitting and receiving are sensors that detect a signal from a change in capacitance due to vibration, and include an element that transmits and receives an ultrasonic wave.

[0003] As described above, by transmitting an ultrasonic wave from the ultrasonic sensor and measuring the time until the ultrasonic wave is reflected and returned from the object to be detected, the distance to the object and the existing position are determined. There is an ultrasonic measuring device as a device for measuring. For example, Japanese Patent Application Laid-Open No. 61-120599 or Japanese Patent Application Laid-Open No. 2-138883 describes the prior art of this type of apparatus.

FIG. 2 is a cross-sectional view showing the structure of a conventional ultrasonic sensor for transmitting and receiving, which is provided with such a transmitting section and a receiving section. As shown in FIG. 2, a piezoelectric vibrator 120 is adhesively fixed to the bottom surface inside the case 100 having a substantially concave cross section. A lead wire 130 for supplying a voltage is connected to the upper surface of the piezoelectric vibrator 120 by solder 150 and wired.

[0005] A lid 11 is provided in an opening on the upper surface of the case 100.
0, and the lid 110 is attached to the case 1
A lid portion 110b for sealing the upper surface portion;
and a screw portion 110a extending vertically upward from the center of the upper surface of the upper surface b.

[0006] At the center of the lid 110, an opening is formed to penetrate from the tip of the screw 110a to the bottom of the lid 110b. The lead wire 130 soldered to the upper surface of the piezoelectric vibrator 120 is taken out through an opening provided in the center of the lid 110, and a voltage is applied to the externally provided piezoelectric vibrator to generate an ultrasonic wave. (Not shown)
It is connected to the. In this drive circuit, in addition to the function of generating ultrasonic waves from the piezoelectric vibrator, a correction circuit for correcting a change in the characteristics of the sensor due to temperature or the like is incorporated to keep the reverberation amount and the sensor sensitivity constant.

When using the conventional ultrasonic sensor configured as described above, this ultrasonic sensor is fixed at an arbitrary position by a screw portion 110a provided on the lid 110, and the lead wire 130 is connected to a drive circuit. I do. By driving the ultrasonic sensor fixed at a predetermined place, the piezoelectric vibrator 12 provided on the bottom of the case 100 is driven.
A vibration is generated at 0, and an ultrasonic wave is transmitted to the outside through the bottom surface of the case 100.

As a result, when the pulsed ultrasonic wave hits the object to be detected and returns, the reflected ultrasonic wave is received, and the time from transmission to return is measured to measure the time. The distance to the detection object and the existing position are detected without contact.

[0009]

However, in the conventional transmitting / receiving ultrasonic sensor shown in FIG.
The vibration generated by the zero causes the side surface and the lid of the case 100 to resonate, and the vibration of the case remains as reverberant vibration for a long time even after the ultrasonic wave is transmitted. As a result, when the position of an object at a short distance is detected by the ultrasonic sensor, a reflected wave reflected from the detected object is buried in reverberant vibration, and there is a problem that position detection becomes difficult. Therefore, if position detection is performed at a short distance, a function of removing the effect of reverberation vibration must be added on the drive circuit side, and the drive circuit becomes complicated.

Further, since the characteristics of the ultrasonic sensor change depending on the temperature, it has been necessary to correct the characteristic by a drive circuit.
However, when temperature correction is performed by the drive circuit, generally, data input from the ultrasonic sensor is corrected according to the value of the temperature sensor provided in the drive circuit. For this reason, the driving circuit becomes complicated, and a temperature difference is inevitably generated between the ultrasonic sensor and the driving circuit, so that there is a problem that an accurate measurement result cannot be obtained.

The present invention solves the above-mentioned problems of the prior art, enables accurate position detection without being affected by short distances and temperature changes, and has a simple driving circuit and a wide range of position detection. It is an object of the present invention to provide an ultrasonic sensor that is suitable for maintenance and has high maintainability.

[0012]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a transmitting / receiving piezoelectric vibrator for transmitting an ultrasonic wave by an applied voltage and receiving a reflected wave of the ultrasonic wave. A case to which the piezoelectric vibrator is fixed. The case includes a main body and a sensor head. The sensor head includes an acoustic matching section to which the piezoelectric vibrator is fixed, and a vibration resonance section formed between the acoustic matching section and the main body. Then, by making at least the thickness of the vibration resonance portion smaller than the thickness of the main body portion, the resonance of the sensor head portion is increased, and the time of reverberation vibration generated when the piezoelectric vibrator transmits ultrasonic waves is shortened.

According to the present invention, a transmitting / receiving piezoelectric vibrator for transmitting an ultrasonic wave by an applied voltage and receiving a reflected wave of the ultrasonic wave and a case to which the piezoelectric vibrator is fixed are provided. Have. The case includes a main body in which a control circuit for performing temperature correction of the piezoelectric vibrator is provided,
The sensor head includes an acoustic matching section to which the piezoelectric vibrator is fixed, and a vibration resonance section formed between the acoustic matching section and the main body.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, an embodiment of an ultrasonic sensor according to the present invention will be described in detail with reference to the accompanying drawings. FIG.
1 is a cross-sectional view of a transmission / reception ultrasonic sensor showing a structure of a first embodiment of an ultrasonic sensor according to the present invention. FIG.
FIG. 2 is a perspective view illustrating an appearance of the ultrasonic sensor illustrated in FIG. 1.
3, the same components as those of the ultrasonic sensor shown in FIG. 1 are denoted by the same reference numerals. In the following description, for convenience of explanation, the upper position in the drawing is the upper part, and the lower position is the lower part or the bottom part, but of course it does not indicate the upper and lower parts in actual use.

As shown in FIG. 1, a substantially cylindrical case 1
Is a main body 1a having a substantially concave shape at the top, and a sensor head 1b projecting further downward from the bottom of the main body 1a.
, And has a shape in which the convex shape is inverted as a whole. The sensor head section 1b includes an acoustic matching section 1b1 to which the piezoelectric vibrator 2 is fixed, and a vibration resonance section 1b2 formed between the acoustic matching section 1b1 and the main body and 1a. The sensor head portion 1b is formed to be thinner than the thickness of the main body portion 1a provided on the upper portion. In particular, the thickness of the vibration resonance portion 1b2 which is a side surface portion is formed thinner than the acoustic matching portion 1b1 which is a bottom surface portion. ing.

As described above, according to the present embodiment, the acoustic matching portion 1b1 vibrates by the piezoelectric vibrator 2 adhered to the bottom portion inside the sensor head portion 1b to form an acoustic matching layer, and the vibration resonance portion 1b2 is a vibration resonance layer of the acoustic matching section 1b1. Since the thickness of the vibration resonance layer of the vibration resonance portion 1b2 is made smaller than that of the acoustic matching layer of the acoustic matching portion 1b1 of the sensor head portion 1b, the load on the piezoelectric vibrator 2 is reduced, and the structure becomes easy to vibrate. ing. Thus, in the ultrasonic sensor shown in FIG. 1, the sensor head 1b
Are projected, and the thickness of the portion is reduced, thereby forming a valve structure that absorbs the reverberation vibration of the piezoelectric vibrator 2.

Inside the sensor head 1b, a silicon elastic body 4 is filled above the piezoelectric vibrator 2 provided on the bottom surface,
The upper part of the silicon elastic body 4 is filled with a glass fiber sound absorbing material 6. The glass fiber sound absorbing material 6
A sound-absorbing material made by processing a glass material into a fibrous shape so as to have excellent reverberation absorption properties. Ultrasonic waves generated from the bonded surface of the piezoelectric vibrator 2 are absorbed by the silicon elastic body 4 and the glass fiber sound absorbing material 6.

The main body 1a formed above the sensor head 1b is formed to have a diameter larger than the diameter of the sensor head 1b due to a substantially crank-shaped step. The outer periphery of the silicon plate 10 is mounted on the step of the sensor head 1b.

A control board 12 for performing temperature correction is fixed on the upper portion of the silicon plate 10. This control board 12
A thermistor for detecting a temperature change of a sensor, and a capacitor having a predetermined temperature characteristic and a capacitance value (neither is shown)
Are connected in series. By combining such a thermistor and a capacitor, a stable reflection sensitivity characteristic and a low reverberation characteristic can be expected, and an ultrasonic sensor capable of high-accuracy and wide-range detection can be realized.

The control board 12 is connected to an external lead wire 20 which is a twisted pair wire connected to a driving circuit (not shown), and is connected to the piezoelectric vibrator through a hole formed in the silicon board 10 and the control board 12. 2 is connected to a lead wire 18 connected to the same. One of the lead wires 18 is soldered to the + terminal of the piezoelectric vibrator 2 with the solder 14, and the other is connected to the negative terminal of the piezoelectric vibrator 2 with the solder 14.

Further, on the inner side of the sensor head 1b,
Silicon plate 10, control board 12, and external lead wire 20
Is filled with a silicon material 22 so as to fix the above.
The silicon material 22 is formed of silicon, rubber, or the like, and has a drip-proof structure for preventing moisture inside the case 1. As described above, the inside of the case 1 is constituted by the sensor head 1b provided with the piezoelectric vibrator 2 and the main body 1a provided with the control board 12.

A cover 30 is provided on the upper and side surfaces of the case 1.
Are fitted so as to cover from above. This lid 30
Is a noise damper 3 covering the side surface of the case 1 and made of resin.
0c and a flange portion 3 made of a metal material on the upper surface of the case 1
0b and a screw portion 30a.

In the flange portion 30b, two flange-like metals are horizontally arranged side by side.
The cover 30 is formed by integrally fitting the noise damper 30c therebetween. By making the shapes of the flange portion 30b and the noise damper 30c as shown in FIG. 1, the bonding area of the flange portion is increased and the adhesion strength is increased.

On the upper surface of the flange portion 30b, a screw portion 30a made of a metal material is disposed in a vertically extended shape so that the screw portion 30a can be fixed to a desired mounting place by a screw. From the tip of the screw portion 30a, the flange portion 30
A hollow portion through which the external lead wire 20 passes is formed up to the bottom surface of b. The lid 30 is configured as described above, and the case 1
Is fitted so as to cover from the upper surface.

When the ultrasonic sensor is attached by the screw portion 30a, the screw portion 30a may be pushed and adversely affect the inside of the main body 1a. Further, a load may be applied to the control board 12 due to bending stress from the external lead wire 20. Therefore, an absorption damper 24 is provided between the case 1 and the lid 30 to absorb the stress applied to the control board 12 or the inside of the case 1.

Next, a second embodiment of the ultrasonic sensor according to the present invention will be described in detail with reference to FIG. FIG. 4 is a sectional view showing a second embodiment of the ultrasonic sensor according to the present invention. 4, the same components as those of the ultrasonic sensor shown in FIG. 1 are denoted by the same reference numerals.

The ultrasonic sensor shown in FIG. 4 has the same structure as the ultrasonic sensor shown in FIG. 1 except that the case portion of the ultrasonic sensor shown in FIG.

As shown in FIG. 4, the case 40, which is cylindrical and has a convex cross-sectional side surface, has a circuit portion 40a having a concave upper portion, and further projects downward from the bottom portion of the circuit portion 40a. And a sensor head 40b.

Between the circuit portion 40a of the case 1 and the sensor head portion 40b, there is formed a stepped portion 40d having a crank shape inside.
Taper 40 having an outer taper angle of 10 to 60 degrees
e.

In the second embodiment of the ultrasonic sensor according to the present invention having such a structure, the same effects as those of the ultrasonic sensor shown in FIG. 1 can be expected, and the taper 40e is provided on the outside of the case 1. The dirt is less likely to adhere to the steps, and the adhered dirt is easily cleaned. Also, by providing the taper angle, the sensor head 4
The ultrasonic wave transmitted from 0b is diffused over a wide range, and a wider range can be detected.

Next, a third embodiment of the ultrasonic sensor according to the present invention will be described in detail with reference to FIG. FIG. 5 is a sectional view showing a narrow-angle ultrasonic sensor according to a third embodiment of the present invention. 5, the same components as those of the first ultrasonic sensor shown in FIG. 1 are denoted by the same reference numerals.

As shown in FIG. 5, the structure other than the lid 50 and the outer case 55 is the same as the structure shown in FIG. 1, and a duplicate description will be omitted. As shown in FIG. 5, in this embodiment, the case 1 is fitted to the lid 50, and the case 1 and the lid 50 are further housed in the outer case 55 and protected from the outside. It has become.

The lid 50 has a plate-like flange 50b made of a metal material on the upper surface of the case 1 and a flange 5b.
The cover 50 is provided with a screw portion 50a extending vertically from the center of Ob and a noise damper 50c covering the side surface of the case 1 at the bottom of the flange portion 50b.

The lid 50 penetrates from the center of the flange portion 50b to the tip of the screw portion 50a, and has an external lead wire 20 provided therein. The noise damper 50 c of the lid 50 is filled in the upper surface and the outer peripheral portion so as to absorb the vibration around the case 1. Such a lid 50
Is surrounded and protected by an outer case 60.

The outer case 60 has a concave shape.
The case 1 is fitted so as to cover from the bottom portion to the flange portion 50b of the lid 50, and is fixed by drawing around the outer peripheral edge portion of the flange portion 50b.

At this time, an opening having a diameter larger than the bottom surface of the case 1 is formed in the bottom surface of the outer case 60, and the bottom surface of the case 1 is exposed to the outside through the bottom opening of the outer case 60.

In the third embodiment of the ultrasonic sensor according to the present invention having such a structure, since the ultrasonic sensor is always covered with the noise damper 50c, a high damping effect of reducing reverberation vibration when generating ultrasonic waves can be obtained. Sensor head 1
External stress can be reduced from being directly applied to the b side surface. Further, since the sensor head 1b has the same structure as that of the first embodiment, the same effect as the ultrasonic sensor shown in FIG. 1 can be expected.

Next, a fourth embodiment of the ultrasonic sensor according to the present invention will be described in detail with reference to FIG. FIG. 6 is a partial sectional view showing a fourth embodiment of the ultrasonic sensor according to the present invention. As shown in FIG. 6, components other than a nut head 60b provided on the lid 60 are the same as those shown in FIG. 5, and a duplicate description will be omitted.

In the ultrasonic sensor shown in FIG. 6, a lid 60 has a plate-like flange portion 60c made of a metal material and a screw portion 60a extending vertically from the center of the flange portion 60c.
The bottom of the flange portion 60c is filled with a noise damper 50c that covers the side surface of the case 1. An upper surface of the flange portion 60c is provided with an I-cut portion (not shown) or a head portion of a nut portion 80b.

The ultrasonic sensor according to the fourth embodiment of the present invention having such a structure can expect the same effect as the ultrasonic sensor shown in FIG. 5, and can improve the mounting work by providing the nut head 60b. You can expect.

That is, the nut head 60b and the screw portion 60a
With this arrangement, the problem that the engagement portion between the flange portion 60c and the noise damper is disengaged due to a load at the time of attachment and the idle portion rotates, making it difficult to fix the ultrasonic sensor in a predetermined place is eliminated.

FIG. 7 is a graph showing a comparison of reverberation temperature characteristics between the ultrasonic sensor according to the present embodiment having the control board 12 for performing temperature compensation and a conventional ultrasonic sensor. FIG.
As shown in the graph, changes in reverberation rates of these ultrasonic sensors in a temperature range of -30 to 65 ° C are shown by curves. The horizontal axis represents temperature, and the vertical axis represents the reverberation change rate due to temperature change.

The curve shown by the arrow C represents the theoretical correction value of the ultrasonic sensor according to the present embodiment. Also, arrow B
The curve shown in FIG. 1 represents a change in reverberation rate due to a temperature change of the conventional ultrasonic sensor. Further, the curve indicated by arrow A represents a change in reverberation rate due to a temperature change of the ultrasonic sensor according to the present embodiment.

As shown in FIG. 7, in the conventional ultrasonic sensor, the range of the change rate of the reverberation amount due to the temperature change is as large as 200% over the entire temperature range of -30.degree. C. to + 65.degree. Significantly increases. In correcting the reverberation level that changes with temperature as described above, in the related art, the reverberation amount and the sensor sensitivity are kept constant by arbitrarily combining the inductance and the resistance on the circuit board. For this reason, the circuit configuration is complicated and the processing speed is reduced.

On the other hand, in the ultrasonic sensor according to the present embodiment, the range of the change rate of the reverberation amount due to the temperature change in the range of −30 ° C. to + 65 ° C. is kept constant, and is theoretically 50%.
Below (20% or less in experimental data). Therefore, the ultrasonic sensor according to the present embodiment enables stable distance detection from a short distance regardless of the ambient temperature.

As described above, in this embodiment, by incorporating the control board for correcting the range of the rate of change of the reverberation amount due to the temperature change, the configuration of the external drive circuit can be further simplified, and the cost can be reduced. In addition to faster processing speed and faster detection of the distance to the object, the cost of at least three types of interkances for low temperature, normal temperature, and high temperature and a switch for changing the resistance is also reduced. did it.).

The reverberation temperature correction section can be realized by simple chip components including only a thermistor and a capacitor, and the circuit mounting space can be reduced by about 10% of the conventional type, so that the entire module can be reduced in size. Become. Furthermore, by performing a correction process using a thermistor provided in the sensor head portion in the case together with a microcomputer for temperature monitoring, more accurate and stable distance measurement can be realized.

Even in the case of a sensor having a large variation in the resonance point frequency due to a change in the ambient temperature, stable reflection sensitivity characteristics and a low reflection sensitivity can be obtained by selecting and combining values of the thermistor and the capacitor in accordance with the temperature change rate. Since reverberation characteristics can be expected, an ultrasonic sensor that can perform high-accuracy and wide-area detection can be realized.

Although the above-described embodiment of the ultrasonic sensor has been described with respect to the airborne ultrasonic sensor, the incorporation of the temperature correction function is not particularly limited to this. In other words, even in underwater ultrasonic sensors and sensors for vibration and deep wounds in solids, such simple correction circuit parts are built in the sensor head and combined with an external circuit, it is possible to detect a wide range with high accuracy Becomes

[0050]

As described above in detail, according to the present invention, reverberation vibration of vibration generated by applying a voltage to a piezoelectric vibrator can be effectively absorbed. Even in position detection, the reflected wave reflected by the detected object will not be buried in reverberation vibration,
It is possible to detect a wide range of objects without complicating the drive circuit. Further, according to the present invention, since a change in the characteristics of the ultrasonic sensor due to a temperature change can be corrected on the sensor side, it is possible to provide an ultrasonic sensor with a small error due to the temperature change without complicating the drive circuit.

[Brief description of the drawings]

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

FIG. 2 is a cross-sectional view showing the structure of a conventional ultrasonic sensor.

FIG. 3 is a perspective view showing the appearance of the ultrasonic sensor shown in FIG. 1;

FIG. 4 is a sectional view showing a second embodiment of the ultrasonic sensor according to the present invention.

FIG. 5 is a cross-sectional view showing a third embodiment of the ultrasonic sensor according to the present invention.

FIG. 6 is a cross-sectional view showing a fourth embodiment of the ultrasonic sensor according to the present invention.

FIG. 7 is a graph showing a comparison of reverberation temperature characteristics between the embodiment of the ultrasonic sensor according to the present invention and a conventional ultrasonic sensor.

[Explanation of symbols]

 1, 40 Case 1a Main body 1b Sensor head 1b1 Acoustic matching section 1b2 Vibration resonance section 1d Step 2 Piezoelectric terminal 4 Silicon elastic body 6 Glass fiber sound absorbing material 10 Silicon plate 12 Control board 18 Lead wire 20 External lead wire 22 Silicon material 24 Absorption damper 30, 50, 60 Lid 30a Screw 30b, 50b Flange 30c Noise damper

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Seiichi Furusawa 3344-1, Iyohisa, Sakai-cho, Sawa-gun, Gunma Prefecture

Claims (5)

[Claims] 1. A transmitting / receiving piezoelectric vibrator for transmitting an ultrasonic wave by an applied voltage and receiving a reflected wave of the ultrasonic wave, and a case to which the piezoelectric vibrator is fixed, the case comprising: Comprises a body portion, a sensor head portion including an acoustic matching portion to which the piezoelectric vibrator is fixed, and a vibration resonance portion formed between the acoustic matching portion and the main body portion. The thickness of the resonance section is made smaller than the thickness of the main body section to enhance the resilience of the sensor head section, and the piezoelectric vibrator shortens the time of reverberation vibration generated at the time of transmitting the ultrasonic wave. Ultrasonic sensor. 2. The ultrasonic sensor according to claim 1, wherein said sensor head has a cylindrical shape. 3. The ultrasonic sensor according to claim 1, wherein at least a joining portion of the vibration resonance portion with the main body portion is tapered. 4. A transmitting / receiving piezoelectric vibrator for transmitting an ultrasonic wave by an applied voltage and receiving a reflected wave of the ultrasonic wave, and a case to which the piezoelectric vibrator is fixed, wherein the case A main body in which a control circuit for performing temperature correction of the piezoelectric vibrator is provided; an acoustic matching section to which the piezoelectric vibrator is fixed; and a vibration formed between the acoustic matching section and the main body. An ultrasonic sensor, comprising: a resonance section; and a sensor head section. 5. The ultrasonic sensor according to claim 4, wherein the control circuit for performing the temperature correction includes a thermistor for detecting a temperature change of the piezoelectric vibrator, and a capacitor having a predetermined temperature characteristic and a capacitance value. An ultrasonic sensor comprising: a circuit in which are connected in series.