JP2006203423A - Ultrasonic sensor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide, at a low cost, an ultrasonic sensor capable of measuring the position and distance of an object to be detected with high precision while avoiding influence of a reverberation sound and an attenuated sound. <P>SOLUTION: A reception section 10 comprises a pedestal 11 and receiving elements 12a to 12d which are in the same size shape and have the same constitution. The receiving elements 12a to 12d which are in the flat plate rectangular shape are arranged radially at equal angles of 45° around the center axis C of the pedestal 11 when the disk-like pedestal 11 is viewed from above. Further, the receiving elements 12a to 12d have their lengthwise one-end portions fitted and fixed on the top surface of the pedestal along the peripheral edge of the pedestal 11 at equal angles of 45° with respect to the top surface of the pedestal 11 while normals (n) of reception surfaces S of the receiving elements 12a to 12d cross one another at one point P on the center axis C of the pedestal 11 when the pedestal 11 is laterally viewed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an ultrasonic sensor, and more particularly to an ultrasonic sensor that converts a received ultrasonic wave into an electric signal or converts an electric signal into an ultrasonic wave and transmits the ultrasonic signal.

  Conventionally, vertical sonar such as acoustic sounding instrument and fish finder, horizontal sonar for measuring the direction of the target and distance from the ship, ultrasonic diagnostic equipment for imaging and diagnosing organs, etc. Ultrasonic sensors are widely used in various fields.

In recent years, an ultrasonic sensor is mounted on an automobile (vehicle), and the reflection of ultrasonic waves that are harmless to the human body transmitted from the ultrasonic sensor is received. The development of technologies that measure position and distance, monitor the surroundings of automobiles, and use them for safe driving has been promoted.
For example, an ultrasonic sensor is installed at the rear of the car, and a device (generally called “back sonar”) that detects objects (humans, obstacles, etc.) located behind the car is used to avoid collision with the object. An automatic parking assistance system that supports parking in the back has been put into practical use.

As an ultrasonic sensor (ultrasonic probe) used for position measurement and distance measurement of such a detection target, for example, a composite piezoelectric body composed of a plurality of piezoelectric elements connected via an organic polymer, and A plurality of array electrodes arranged on one surface of the composite piezoelectric body with a gap between each other, and the portion of the composite piezoelectric material corresponding to the gap portion of the array electrode has a sound wave attenuation coefficient from the organic polymer. A material filled with a large filler is disclosed (see Patent Document 1).
JP-A-5-347797 (pages 2 to 4 and FIGS. 1 to 3)

In a conventional ultrasonic sensor including the technique of Patent Document 1, a receiving unit that converts received (sound received) ultrasonic waves into an electric signal includes a plurality of diaphragms having the same size and shape (array electrodes of Patent Document 1). Either a one-dimensional arrangement in which the diaphragms are arranged in one direction on the same plane, or a two-dimensional arrangement in which a plurality of diaphragms having the same size are arranged in two vertical and horizontal directions on the same plane. Take.
And the transmission part of the ultrasonic sensor which converts the electric signal inputted from the outside into the ultrasonic wave and transmits (sounds) transmits the ultrasonic wave to the detection object, and the ultrasonic wave is reflected on the detection object. The reflected sound is received by each diaphragm of the receiving unit.

  Therefore, the reception unit detects a difference in timing of ultrasonic waves received by a plurality of diaphragms (sound receiving plates), and compares the received ultrasonic wave timing difference with the ultrasonic waves emitted by the transmission unit. Thus, it is possible to perform two-dimensional or three-dimensional position measurement of the detection target, distance measurement between the ultrasonic sensor and the detection target, and the like.

Moreover, the transmission part of the conventional ultrasonic sensor normally transmits an ultrasonic wave from a single diaphragm (sound generating plate) to the detection target.
A type of transmitting ultrasonic waves from a plurality of diaphragms has also been proposed, but the type of transmitting unit is similar to the receiving unit in that a plurality of diaphragms of the same size and shape are arranged in one dimension on the same plane. It takes an arrangement or a two-dimensional arrangement.
The reason why the transmission unit includes a plurality of diaphragms is to increase the transmission output of ultrasonic waves.

By the way, the ultrasonic wave reflected from the detection target may bounce back to surrounding objects many times and remain in the space, and a reverberant sound (reflected sound) composed of the sound remaining in the space may be generated.
In addition, it is difficult to stop the vibration of the diaphragm of the transmitter simultaneously with the stop of the input electric signal. Since the vibration of the diaphragm stops while attenuating, the ultrasonic wave transmitted from the transmitter has a damped sound. Arise.

Due to the reverberant sound and the attenuated sound, it is difficult to accurately detect the deviation in the timing of the ultrasonic waves. Therefore, it is necessary to take the following measures in the conventional ultrasonic sensor.
(A) In order to remove reverberation sound and attenuation sound from the ultrasonic wave received by the receiving unit, a complicated signal processing circuit for processing the electrical signal generated by the receiving unit is provided.
(B) Since the resonating sound and the attenuation sound disappear and the ultrasonic wave consisting of a long-period pulse wave or continuous wave that can avoid the influence is transmitted from the transmitting unit, the electrical signal input by the transmitting unit is complicated. A signal processing circuit is provided.
(C) A special damping structure is provided in the transmission unit in order to quickly reduce the attenuation sound.

However, if a complicated signal processing circuit or a special damping structure is provided, there is a problem that the product cost of the ultrasonic sensor increases.
In recent years, in order to avoid the effects of reverberant sound and attenuated sound and to improve the accuracy of measurement of the position and distance of the detection target, it is required to arbitrarily control the directivity of the ultrasonic waves transmitted from the transmitter. Has been.

The present invention has been made to solve the above-described problems or to satisfy the above-described requirements, and has the following objects.
(1) An ultrasonic sensor capable of measuring the position and distance of a detection target object with high accuracy while avoiding the influence of reverberant sound and attenuated sound is provided at low cost.
(2) An ultrasonic sensor capable of arbitrarily controlling the directivity of transmitted ultrasonic waves is provided at a low cost.

  The invention according to claim 1 is provided with a plurality of conversion means for converting received ultrasonic waves into electric signals or converting electric signals into ultrasonic waves and transmitting the three-dimensional conversion means. This is a technical feature.

The invention described in claim 2 is the ultrasonic sensor according to claim 1,
Each of the conversion means includes a plurality of three or more conversion means, and each conversion means has a receiving surface for receiving ultrasonic waves or a transmitting surface for transmitting ultrasonic waves arranged radially at equal angles. Technical features.

The invention according to claim 3 is the ultrasonic sensor according to claim 2,
Each of the converting means is technically characterized in that the receiving surface or the transmitting surface is disposed at an angle of 45 ° with respect to a plane including one end of each converting means.

The invention according to claim 4 is the ultrasonic sensor according to any one of claims 1 to 3,
A technical feature is that a protective cover for covering each of the conversion means is provided.

The invention according to claim 5 is the ultrasonic sensor according to claim 4,
A technical feature is that the back side of the protective cover is in close contact with each of the converting means.

The invention according to claim 6 is the ultrasonic sensor according to claim 4,
A technical feature is that a gap is provided between the back surface side of the protective cover and each of the conversion means.

The invention according to claim 7 is the ultrasonic sensor according to any one of claims 1 to 6,
The conversion means is technically characterized by being of a piezoelectric type or a capacitance type.

(Claim 1)
According to the first aspect of the present invention, in a case where each converting means is made to function as a receiving element for converting the received ultrasonic wave into an electric signal, and the receiving section is constituted by each converting means, an ultrasonic sensor provided separately from the receiving section The transmitting unit transmits ultrasonic waves to the detection target, and the reflected sound reflected by the detection target is received by each receiving element (conversion unit) of the receiving unit.
The receiving unit detects the sound pressure difference between the ultrasonic waves received by each receiving element (conversion means), and compares the received sound pressure difference between the received ultrasonic waves and the ultrasonic wave emitted by the transmitting unit, thereby detecting the object to be detected. 2D or 3D position measurement, distance measurement between an ultrasonic sensor and a detection target can be performed.

By the way, the longitudinal wave has a characteristic that pressure is generated in the same direction as the traveling direction and no pressure is generated in the direction perpendicular to the traveling direction.
Since the ultrasonic wave is a longitudinal wave, when the incident angle of the ultrasonic wave with respect to the receiving surface for receiving the ultrasonic wave by the converting means is 0 °, the sound pressure received by the receiving surface becomes maximum, and the incident angle approaches 90 °. The sound pressure decreases so that the sound pressure becomes zero when the incident angle is 90 °.

The level of the electric signal generated by the conversion means increases as the sound pressure received by the receiving surface increases. That is, the level of the electric signal generated by converting the ultrasonic wave received by the converting means depends on the incident angle of the ultrasonic wave with respect to the receiving surface of each converting means.
Here, the level of the electric signal generated by the conversion means corresponds to the reception sensitivity of the conversion means, and the higher the electric signal level, the higher the reception sensitivity. In other words, the ultrasonic wave reception sensitivity in the conversion means corresponds to the sound pressure received by the reception surface and depends on the incident angle of the ultrasonic wave with respect to the reception surface.

  Therefore, in the first aspect of the invention, when each converting means functions as a receiving element, the receiving sensitivity of each receiving element depends on the incident angle by arranging each receiving element (converting means) in a three-dimensional manner. The position measurement and the distance measurement of the detection target can be accurately performed based on the sound pressure difference between the ultrasonic waves received by the receiving elements.

  In the first aspect of the invention, ultrasonic waves received by a plurality of diaphragms as in the prior art (a structure in which a plurality of diaphragms having the same size and shape are arranged one-dimensionally or two-dimensionally on the same plane). The measurement is performed based on the difference in sound pressure between the ultrasonic waves received by each receiving element (conversion means), instead of performing the measurement based on the timing difference of Measurement accuracy can be improved.

Furthermore, according to the invention of claim 1, since it is not necessary to provide a complicated signal processing circuit or a special damping structure as in the prior art, the product cost of the ultrasonic sensor can be reduced.
Here, each receiving element (conversion means) constituting the receiving unit may be arranged three-dimensionally according to the required measurement accuracy and directivity, and the number and arrangement of the receiving elements are cut and tried. Find and set the optimal value experimentally.

  Further, in the first aspect of the present invention, when each converting means is made to function as a transmitting element that converts an electrical signal inputted from the outside into an ultrasonic wave and transmits the ultrasonic signal, The number of transmitting elements to be configured corresponds to the transmission output (acoustic output) of ultrasonic waves, and the transmission output can be increased as the number of transmitting elements is increased.

And the directivity of the transmission direction of an ultrasonic wave can be set suitably by setting suitably the arrangement state of the transmitting element (conversion means) which constitutes a transmitting part.
Here, each transmitting element (conversion means) constituting the transmitting unit may be three-dimensionally arranged according to the required transmitting output and directivity, and the number and arrangement of the transmitting elements are cut and tried. Find and set the optimal value experimentally.

(Claim 2)
According to the invention of claim 2, the operation and effect of the invention of claim 1 is provided by providing a plurality of three or more conversion means, and arranging the reception surface or the transmission surface of each conversion means radially at an equal angle. Can be obtained reliably.

(Claim 3)
According to the invention of claim 3, the operation and effect of the invention of claim 2 can be achieved by arranging the receiving surface or the transmitting surface at an angle of 45 ° with respect to the plane including one end of each converting means. Furthermore, it becomes possible to obtain reliably.

(Claim 4: corresponds to the second embodiment)
According to the invention of claim 4, by providing the protective cover for covering each conversion means, each conversion means can be protected from the surrounding environment and the weather resistance of the ultrasonic sensor can be improved, and each conversion means can be prevented from being damaged.

(Claim 5: corresponds to the first structural example of the second embodiment)
According to the invention of claim 5, since the vibration is directly transmitted between the protective cover and each converting means by bringing the back side of the protective cover into close contact with each converting means, each conversion by providing the protective cover. A decrease in the reception sensitivity or transmission sensitivity of the means can be avoided.

  Here, in addition to high weather resistance that does not allow air, dust, liquid, or the like to pass through, the protective cover is required to have high ultrasonic transmission and low rigidity that does not impede vibration of each conversion means. Examples of materials that satisfy such requirements include thin films of various metals (such as aluminum alloys), various synthetic resin films, and rubber films.

(Claim 6: corresponds to the second structural example of the second embodiment)
According to the invention of claim 6, by providing a gap between the back side of the protective cover and each conversion means, even if an external force is applied to the ultrasonic sensor, the external force is only applied to the protective cover, Since no external force is directly applied to each conversion means, it is possible to reliably prevent damage to each conversion means.

Here, in addition to high weather resistance that does not allow air, dust, liquid, or the like to pass through, the protective cover is required to have a property of being easily vibrated by ultrasonic waves and allowing ultrasonic waves to pass through without being refracted.
When the gap between the protective cover and each conversion means is filled with a filling material of liquid, sol, or gel, the acoustic impedance of the filling material is brought close to the acoustic impedance of the protective cover, It becomes possible to reliably transmit vibration between the respective conversion means, and it is possible to avoid a decrease in reception sensitivity or transmission sensitivity of each conversion means.

(Claim 7)
According to the seventh aspect of the present invention, a piezoelectric or capacitive ultrasonic sensor can be obtained.

(Explanation of terms)
The correspondence between the constituent elements described in [Means for Solving the Problems] described above and the constituent members described in [Best Mode for Carrying Out the Invention] described below is as follows. .
“Conversion means” corresponds to the receiving elements (transmitting elements) 12a to 12f.
The “plane including one end of each conversion means” in claim 3 corresponds to the surface of the base 11.

Hereinafter, embodiments embodying the present invention will be described with reference to the drawings.
In each embodiment, the same constituent members as those in the first embodiment are denoted by the same reference numerals, and duplicate descriptions are omitted for portions having the same contents.

(First embodiment)
FIG. 1 is a perspective view of the receiving unit 10 of the ultrasonic sensor according to the first embodiment.
FIG. 2A is a plan view of the receiving unit 10. FIG. 2B is a front view of the receiving unit 10.

The receiving unit 10 includes a pedestal 11 and four receiving elements (conversion means) 12a to 12d having the same size and the same configuration.
The flat rectangular receiving elements 12 a to 12 d are arranged radially at an equal angle of 45 ° from the central axis C of the base 11 when the disk-shaped base 11 is viewed from above.

In each receiving element 12a to 12d, the normal n of the receiving surface S of each receiving element 12a to 12d is 1 on the center axis C (the radial center axis) of the base 11 when the base 11 is viewed from the lateral direction. And intersecting at two points P, and the receiving surfaces S of the receiving elements 12a to 12d form an equiangular angle of 45 ° with respect to the surface of the base 11 (a plane including one end of each receiving element 12a to 12d). One end in the longitudinal direction of each receiving element 12 a to 12 d is fixedly mounted on the surface of the base 11 along the periphery of the base 11.
That is, each of the receiving elements 12a to 12d has the receiving surface 12 of each receiving element 12a, 12d and each receiving element 12b, 12c arranged in a straight line when the disk-shaped pedestal 11 is viewed from above, and so on. They are arranged at an angle.

[Receiver structure]
3 to 5 are schematic longitudinal sectional views showing first to third structural examples of the receiving elements 12a to 12d. 3 to 5 exaggerate the height direction (plate thickness direction).

<First structure example>
In the first structural example shown in FIG. 3, each of the piezoelectric receiving elements 12a to 12d includes a lower electrode 21, a receiving electrode 22, a composite piezoelectric body 23, and the like.
The flat rectangular electrodes 21 and 22 are arranged in parallel, and a composite piezoelectric body 23 is sandwiched between the electrodes 21 and 22.
The composite piezoelectric body 23 includes a plurality of columnar piezoelectric elements 24 and an organic polymer layer 25.

Each piezoelectric element 24 has upper and lower ends connected to the electrodes 21 and 22.
The organic polymer layer 25 is filled in the gaps between the piezoelectric elements 24 and couples the piezoelectric elements 24 to each other. That is, each piezoelectric element 24 is embedded in the organic polymer layer 25.
Each piezoelectric element 24 is made of a ferroelectric material (for example, PZT).
The organic polymer layer 25 is made of, for example, silicon rubber, epoxy resin, polyurethane resin, or the like.

Then, the surface of the reception electrode 22 becomes an ultrasonic reception surface S, and when the reception electrode 22 vibrates due to the ultrasonic wave, the vibration is transmitted to the composite piezoelectric body 23, and when the composite piezoelectric body 23 vibrates, an electrical signal is generated due to the piezoelectric effect. The generated electrical signal is output via wiring (not shown) connected to the electrodes 21 and 22.
That is, in each of the receiving elements 12a to 12d of the first structure example, a diaphragm (sound receiving plate) is configured from the laminated structure of the electrodes 21 and 22 and the composite piezoelectric body 23, and the ultrasonic waves received by the diaphragm are electrically Converted to a signal.

<Second structure example>
In the second structural example shown in FIG. 4, each of the piezoelectric receiving elements 12 a to 12 d includes a lower electrode 21, a receiving electrode 22, a dielectric layer 31, and the like.
A dielectric layer 31 made of a ferroelectric material (for example, PZT) is sandwiched between the electrodes 21 and 22.

The surface of the receiving electrode 22 becomes an ultrasonic receiving surface S. When the receiving electrode 22 vibrates due to the ultrasonic wave, the vibration is transmitted to the dielectric layer 31, and when the dielectric layer 31 vibrates, an electric signal is generated by the piezoelectric effect. The generated electrical signal is output via wiring (not shown) connected to the electrodes 21 and 22.
In other words, in each of the receiving elements 12a to 12d of the second structure example, a diaphragm (sound receiving plate) is configured from the laminated structure of the electrodes 21 and 22 and the dielectric layer 31, and the ultrasonic waves received by the diaphragm are electrically Converted to a signal.

<Third structure example>
In the third structural example shown in FIG. 5, each of the capacitance type (capacitor type) receiving elements 12 a to 12 d includes a lower electrode 21, a receiving electrode 22, a holding member 41, and the like.
A holding member 41 is sandwiched between both ends of each electrode 21, 22, and each electrode 21, 22 is opposed with a gap K therebetween.
The lower electrode 21 is fixed so as not to vibrate to constitute a fixed electrode, and the receiving electrode 22 is capable of vibrating to constitute a movable electrode.

When the surface of the reception electrode 22 becomes an ultrasonic reception surface S and the reception electrode 22 vibrates due to the ultrasonic wave, the distance between the electrodes 21 and 22 changes, and the capacitance between the electrodes 21 and 22 also changes. To do. Therefore, a change in capacitance between the electrodes 21 and 22 is converted into an electrical signal using a conversion circuit (not shown) connected to the electrodes 21 and 22 via wiring (not shown).
That is, in each of the receiving elements 12a to 12d of the third structural example, a diaphragm (sound receiving plate) is configured from the receiving electrode 22, and ultrasonic waves received by the diaphragm are converted into an electric signal.

[Operations and effects of the first embodiment]
According to the first embodiment, the following actions and effects can be obtained.

[1]
A transmitting unit (not shown) of an ultrasonic sensor provided separately from the receiving unit 10 transmits an ultrasonic wave to the detection target, and the reflected sound reflected from the detection target by the ultrasonic wave is received by the receiving unit 10. The signals are received by the receiving elements 12a to 12d.

And the receiving part 10 detects the sound pressure difference of the ultrasonic wave which each receiving element 12a-12d received, and compares the sound pressure difference of the received ultrasonic wave with the ultrasonic wave which the transmission part emitted, and a detection target object 2D or 3D position measurement, distance measurement between an ultrasonic sensor and a detection target can be performed.
Note that any type (for example, a piezoelectric type or a capacitance type) may be used for the transmitter of the ultrasonic sensor.

[2]
FIG. 6 is an explanatory diagram for explaining the incident angle θ of the ultrasonic wave with respect to the receiving surface S of the receiving elements 12a to 12d.
The incident angle θ of the ultrasonic wave with respect to the receiving surface S is an angle formed by the normal line n of the receiving surface S and the direction in which the ultrasonic wave enters.

FIG. 7 is a characteristic diagram showing the relationship between the incident angle θ of the ultrasonic wave with respect to the receiving surface S of the receiving elements 12a to 12d and the sound pressure received by the receiving surface S. Note that the maximum value of the sound pressure is displayed as “1”.
The longitudinal wave has a characteristic that pressure is generated in the same direction as the traveling direction, and no pressure is generated in the direction perpendicular to the traveling direction.
Since the ultrasonic wave is a longitudinal wave, when the incident angle θ of the ultrasonic wave with respect to the receiving surface S of the receiving elements 12a to 12d is 0 °, the sound pressure received by the receiving surface S becomes the maximum, and the incident angle θ approaches 90 °. As the sound pressure decreases, the sound pressure becomes zero when the incident angle θ is 90 °.

In each of the receiving elements 12a to 12d, the greater the sound pressure received by the receiving surface S, the greater the bending of the receiving electrode 22, so that the level of the electric signal to be generated increases.
That is, the level of the electric signal generated by converting the ultrasonic wave received by each receiving element 12a to 12d depends on the incident angle θ of the ultrasonic wave with respect to the receiving surface S of each receiving element 12a to 12d.

Here, the level of the electric signal generated by each of the receiving elements 12a to 12d corresponds to the receiving sensitivity of each of the receiving elements 12a to 12d. The higher the level of the electric signal, the higher the receiving sensitivity.
In other words, the reception sensitivity of the ultrasonic waves in each of the receiving elements 12a to 12d corresponds to the sound pressure received by the reception surface S and depends on the incident angle θ of the ultrasonic waves with respect to the reception surface S.

[3]
As shown in FIG. 1 and FIG. 2, by arranging the receiving elements 12a to 12d, the ultrasonic waves received by the receiving elements 12a to 12d using the incident angle dependency of the receiving sensitivity of the receiving elements 12a to 12d are used. Based on the sound pressure difference, the position measurement and distance measurement of the detection object can be accurately performed.

By the way, the ultrasonic wave reflected from the detection target may bounce back to surrounding objects many times and remain in the space, and a reverberant sound (reflected sound) composed of the sound remaining in the space may be generated.
In addition, it is difficult to stop the vibration of the diaphragm of the transmitter simultaneously with the stop of the input electric signal. Since the vibration of the diaphragm stops while attenuating, the ultrasonic wave transmitted from the transmitter has a damped sound. Arise.

However, the receiving unit 10 of the first embodiment receives signals with a plurality of diaphragms as in the prior art (a structure in which a plurality of diaphragms having the same size and shape are arranged one-dimensionally or two-dimensionally on the same plane). The measurement is not performed based on the difference in the timing of the ultrasonic waves, but the measurement is performed based on the sound pressure difference between the ultrasonic waves received by the receiving elements 12a to 12d, thereby avoiding the influence of reverberation sound and attenuation sound. Thus, the measurement accuracy can be improved.
And according to 1st Embodiment, since it is not necessary to provide a complicated signal processing circuit and a special damping structure like the prior art, the product cost of an ultrasonic sensor can be reduced.

(Second Embodiment)
FIG. 8 is a perspective view of the receiving unit 50 of the ultrasonic sensor according to the second embodiment.
The receiving unit 50 is different from the receiving unit 10 of the first embodiment only in that a substantially conical protective cover 51 that covers the receiving elements 12 a to 12 d is attached and fixed on the surface of the base 11.
As described above, by providing the protective cover 51 that covers the receiving elements 12a to 12d, the receiving elements 12a to 12d are protected from the surrounding environment to improve the weather resistance of the receiving unit 50, and the receiving elements 12a to 12d Damage can be prevented.

FIG. 9 is a partial longitudinal sectional view for explaining a first structural example of the protective cover 51.
The back side of the protective cover 51 is in close contact with the receiving elements 12a to 12d.
Therefore, when the protective cover 51 is vibrated by ultrasonic waves, the vibration of the protective cover 51 is directly transmitted to the receiving elements 12a to 12d. Therefore, the reception sensitivity of the receiving elements 12a to 12d by providing the protective cover 51 is improved. Decrease can be avoided.

  Here, in addition to high weather resistance that does not allow air, dust, liquid, or the like to pass through, the protective cover 51 has high ultrasonic transmission and low rigidity that does not hinder the vibration of each of the receiving elements 12a to 12d. Required. Examples of materials that satisfy such requirements include thin films of various metals (such as aluminum alloys), various synthetic resin films, and rubber films.

FIG. 10 is a partial longitudinal sectional view for explaining a second structure example of the protective cover 51.
A gap L is provided between the back surface side of the protective cover 51 and each of the receiving elements 12a to 12d.
Therefore, even if an external force is applied to the receiving unit 50, the external force is only applied to the protective cover 51, and the external force is not directly applied to the receiving elements 12a to 12d. Therefore, the receiving elements 12a to 12d are reliably damaged. Can be prevented.
Here, in addition to high weather resistance that does not allow air, dust, liquid, or the like to pass through, the protective cover 51 is required to have a property of being easily vibrated by ultrasonic waves and transmitting ultrasonic waves without being refracted.

  Further, when the gap L between the protective cover 51 and each of the receiving elements 12a to 12d is filled with any filling material of liquid, sol, or gel, the acoustic impedance of the filling material is brought close to the acoustic impedance of the protective cover 51. Thus, it is possible to reliably transmit the vibration of the protective cover 51 to the receiving elements 12a to 12d through the filling material, and it is possible to avoid a decrease in receiving sensitivity of the receiving elements 12a to 12d.

  The acoustic impedance of a substance is the product of the density of the substance and the propagation sound velocity. And as the acoustic impedance between substances differs, the propagation characteristic of the sound wave between the substances deteriorates. That is, as the acoustic impedance between the filling material of the gap L and the protective cover 51 is different, the ultrasonic wave is more likely to be reflected by the protective cover 51 and propagate to the filling material.

  Therefore, when a synthetic resin film is used as the protective cover 51, a sol in which fine particles of the synthetic resin are dispersed in a liquid or a polymer gel made of the synthetic resin may be used as a filling material. Further, the filling material needs to be a material that does not attack the receiving elements 12a to 12d. Examples of the filling material that satisfies such requirements include silicon gel and fluorine gel.

(Third embodiment)
FIG. 11 is a perspective view of the receiving unit 60 of the ultrasonic sensor according to the third embodiment.
FIG. 12A is a plan view of the receiving unit 60. FIG. 12B is a front view of the receiving unit 60.

The receiving unit 60 includes a base 11 and six receiving elements 12a to 12f having the same configuration with the same size and shape.
The flat rectangular receiving elements 12a to 12f are arranged radially at an equal angle of 30 ° from the central axis C of the pedestal 11 when the disk-shaped pedestal 11 is viewed from above.

In addition, each receiving element 12a to 12f sees the pedestal 11 from the lateral direction, and the normal line n of the receiving surface S of each receiving element 12a to 12f intersects at one point P on the central axis C of the pedestal 11. The longitudinal ends of the receiving elements 12a to 12f extend along the periphery of the pedestal 11 so that the receiving surfaces S of the receiving elements 12a to 12f form an equal angle of 45 ° with respect to the surface of the pedestal 11. 11 is fixedly mounted on the surface.
That is, each of the receiving elements 12a to 12f is received by each of the receiving elements 12a and 12e, each of the receiving elements 12b and 12f, and each of the receiving elements 12c and 12d arranged in a straight line when the disk-shaped base 11 is viewed from above. The surfaces S are arranged so as to form an equal angle of 90 °.

As described above, the receiving unit 60 of the third embodiment is different from the receiving unit 10 of the first embodiment in that two receiving elements 12e and 12f are added and the planar arrangement of the receiving elements 12a to 12d is increased. Only the changes.
According to the third embodiment, the directivity in the reception direction of the ultrasonic wave is widened by the addition of the receiving elements 12e and 12f, and the incident angle dependence of the receiving sensitivity of the receiving elements 12a to 12f is used. Since it becomes possible to improve the measurement accuracy of the position and distance of the detection object, the above-mentioned operation and effect of the first embodiment can be further enhanced.

(Fourth embodiment)
FIG. 13 is a perspective view of the receiving unit 70 of the ultrasonic sensor according to the fourth embodiment.
FIG. 14A is a plan view of the receiving unit 70. FIG. 14B is a front view of the receiving unit 70.

The receiving unit 70 includes a base 11 and three receiving elements 12a to 12c having the same configuration with the same size and shape.
The flat rectangular receiving elements 12 a to 12 c are arranged radially at an equal angle of 60 ° from the central axis C of the pedestal 11 when the disk-shaped pedestal 11 is viewed from above.

  Each receiving element 12a to 12c sees the pedestal 11 from the lateral direction, and the normal line n of the receiving surface S of each receiving element 12a to 12c intersects at one point P on the central axis C of the pedestal 11. The longitudinal ends of the receiving elements 12 a to 12 c extend along the periphery of the pedestal 11 so that the receiving surfaces S of the receiving elements 12 a to 12 c form an equal angle of 45 ° with the surface of the pedestal 11. 11 is fixedly mounted on the surface.

Thus, the receiving unit 70 of the fourth embodiment differs from the receiving unit 10 of the first embodiment in that one receiving element 12d is omitted and the planar arrangement of each receiving element 12a to 12c is changed. Only.
According to the fourth embodiment, the product cost of the ultrasonic sensor can be reduced, although the operation and effect of the first embodiment are slightly reduced by the amount that the receiving element 12d is omitted.

[Another embodiment]
By the way, the present invention is not limited to the above-described embodiments, and may be embodied as follows. Even in this case, operations and effects equivalent to or more than those of the above-described embodiments can be obtained.

[Example 1]
Each of the receiving elements 12a to 12f may be arranged radially at an appropriate angle from the center axis C of the pedestal 11 when the pedestal 11 is viewed from above, or arranged in an appropriate shape (for example, a spiral shape). May be.
Each of the receiving elements 12a to 12f may be disposed so as to form an appropriate equiangular angle with respect to the surface of the pedestal 11 when the pedestal 11 is viewed from the lateral direction. You may arrange | position so that 12a-12f may form a separate angle.
The number of receiving elements is not limited to four (first embodiment), six (third embodiment), and three (fourth embodiment), but may be an appropriate number of three or more.

  That is, each receiving element constituting the receiving unit may be arranged three-dimensionally according to the required measurement accuracy and directivity, and the number and arrangement state of the receiving elements are experimentally optimal by cut-and-try. Find and set the value.

[Example 2]
Although each said embodiment is applied to the receiving part of an ultrasonic sensor, you may apply this invention to the transmission part of the ultrasonic sensor which converts an electric signal into an ultrasonic wave and transmits.
That is, the receiving elements 12a to 12f of the receiving units 10, 50, 60, and 70 may function as the transmitting elements of the transmitting unit. In this case, the receiving surface S of each receiving element 12a-12f becomes a transmitting surface which transmits an ultrasonic wave from a transmitting element.

For example, when each transmitting element is the first structural example (piezoelectric type) shown in FIG. 3, the composite piezoelectric body 23 vibrates due to the piezoelectric effect according to the electric signal applied to each electrode 21, 22. Ultrasound is transmitted from the electrode 22.
When each transmitting element is the second structural example (piezoelectric type) shown in FIG. 4, the dielectric layer 31 vibrates due to the piezoelectric effect according to the electric signal applied to each electrode 21, 22. Ultrasound is transmitted from the electrode 22.
When each transmitting element is the third structural example (capacitor type) shown in FIG. 5, an electrostatic attractive force is generated between the electrodes 21 and 22 in accordance with an electric signal applied to the electrodes 21 and 22. The electrode 22 is vibrated by the electrostatic attractive force, and an ultrasonic wave is generated.

By the way, the number of transmitting elements constituting the transmitting unit corresponds to the transmission output (acoustic output) of ultrasonic waves, and the transmission output can be increased as the number of transmitting elements is increased.
Moreover, the directivity of the transmission direction of an ultrasonic wave can be appropriately set by appropriately setting the arrangement state of the transmitting elements constituting the transmitting unit.

  Therefore, when each receiving element 12a-12f is functioned as each transmitting element of the transmitting unit, each transmitting element constituting the transmitting unit has the necessary transmitting output and directivity as in [Another Example 1]. Accordingly, the three-dimensional arrangement may be performed, and the number and arrangement state of the transmitting elements may be set by experimentally finding an optimum value by cut-and-try.

For example, when the transmitting elements of the transmitting unit are arranged in the same manner as the receiving elements 12a to 12f of the receiving units 10, 60, 70, wide hemispherical directivity with the base 11 as the bottom surface is obtained.
Further, if two transmitters having the same configuration as each of the receivers 10, 60, 70 are used and the bases 11 of the transmitters are bonded to each other and assembled together, a complete spherical omnidirectionality can be obtained.
FIG. 15 is a perspective view illustrating a configuration example in which two transmitting units 80a and 80b having the same configuration as the receiving unit 10 are used and the bases 11 of the transmitting units 80a and 80b are bonded to each other on the back side.

The perspective view of the receiving part 10 of the ultrasonic sensor in 1st Embodiment which actualized this invention. FIG. 2A is a plan view of the receiving unit 10. FIG. 2B is a front view of the receiving unit 10. FIG. 2 is a schematic longitudinal sectional view showing a first structural example of receiving elements 12a to 12d constituting the receiving unit 10. FIG. 4 is a schematic longitudinal sectional view showing a second structure example of receiving elements 12a to 12d constituting the receiving unit 10. FIG. 4 is a schematic longitudinal sectional view showing a third structure example of receiving elements 12a to 12d constituting the receiving unit 10. Explanatory drawing for demonstrating the incident angle (theta) of the ultrasonic wave with respect to the receiving surface S of receiving element 12a-12d. The characteristic view which shows the relationship between the incident angle (theta) of the ultrasonic wave with respect to the receiving surface S of the receiving elements 12a-12d, and the sound pressure which the receiving surface S receives. The perspective view of the receiving part 50 of the ultrasonic sensor in 2nd Embodiment which actualized this invention. The partial longitudinal cross-sectional view for demonstrating the 1st structural example of the protective cover 51 of 2nd Embodiment. The partial longitudinal cross-sectional view for demonstrating the 2nd structural example of the protective cover 51 of 2nd Embodiment. The perspective view of the receiving part 60 of the ultrasonic sensor in 3rd Embodiment which actualized this invention. FIG. 12A is a plan view of the receiving unit 60. FIG. 12B is a front view of the receiving unit 60. The perspective view of the receiving part 70 of the ultrasonic sensor in 4th Embodiment which actualized this invention. FIG. 14A is a plan view of the receiving unit 70. FIG. 14B is a front view of the receiving unit 70. The perspective view of the transmission parts 80a and 80b of the ultrasonic sensor in the another example 2 which actualized this invention.

Explanation of symbols

10, 50, 60, 70... Ultrasonic sensor receiver (transmitter)
11. Pedestal 12a-12f. Receiving element (transmitting element)
S ... Receiving surface (transmitting surface)
51 ... Protective cover L ... Gap

Claims (7)

  An ultrasonic sensor comprising a plurality of conversion means for converting received ultrasonic waves into electric signals or converting electric signals into ultrasonic waves for transmission, and each conversion means is arranged three-dimensionally. The ultrasonic sensor according to claim 1,
A plurality of three or more conversion means,
An ultrasonic sensor characterized in that each conversion means has a receiving surface for receiving ultrasonic waves or a transmitting surface for transmitting ultrasonic waves arranged radially at equal angles. The ultrasonic sensor according to claim 2,
The ultrasonic sensor, wherein each of the conversion means is arranged such that the reception surface or the transmission surface forms an angle of 45 ° with respect to a plane including one end of each conversion means. The ultrasonic sensor according to any one of claims 1 to 3,
An ultrasonic sensor comprising a protective cover for covering each of the conversion means. The ultrasonic sensor according to claim 4,
The ultrasonic sensor according to claim 1, wherein the back surface side of the protective cover is in close contact with the conversion means. The ultrasonic sensor according to claim 4,
An ultrasonic sensor, wherein a gap is provided between a back surface side of the protective cover and each of the conversion means. The ultrasonic sensor according to any one of claims 1 to 6,
The ultrasonic sensor is characterized in that the conversion means is a piezoelectric type or a capacitance type.

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