JP4304556B2 - Ultrasonic sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic sensor, and more particularly to a drip-proof ultrasonic sensor.
[0002]
[Prior art]
An ultrasonic sensor performs sensing using ultrasonic waves, intermittently transmits an ultrasonic pulse signal from a piezoelectric vibration element, and receives a reflected wave from a detected object existing in front by the piezoelectric vibration element. By doing so, an object is detected. As this type of ultrasonic sensor, one having a structure shown in FIG. 1 has been conventionally used. That is, the ultrasonic sensor 1 has a structure in which the bottom surface of the bottomed cylindrical case 2 made of metal is the vibration plate 3 and the piezoelectric vibration element 4 is attached to the inner surface of the vibration plate 3. Yes. Electrical extraction from the piezoelectric vibration element 4 is performed by lead wires 5 and 6. One lead wire 5 is connected to one element electrode of the piezoelectric vibration element 4 by soldering. The other lead wire 6 is soldered to a predetermined position of the metal case 2 and is electrically connected to the other element electrode of the piezoelectric vibration element 4 through the case 2.
[0003]
A felt 7 is housed in the bottom of the case 2, a resin 8 is filled into the case 2 from above the felt 7, and has a drip-proof structure in which raindrops and the like do not enter. In addition, a relay board 9 is enclosed in the resin 8 so as to float from the case 2, and the lead wires 5 and 6 are connected to the input / output signal lines 10 and 11 via the relay board 9. .
[0004]
The ultrasonic sensor 1 having such a configuration operates as follows. That is, when a driving voltage is applied from the signal lines 10 and 11 to the piezoelectric vibration element 4 to vibrate the piezoelectric vibration element 4 , the diaphragm 3 of the case 2 vibrates and emits ultrasonic waves forward from the diaphragm 3. . When the ultrasonic wave reflected from the object to be detected reaches the piezoelectric vibration element 4 via the diaphragm 3 after a predetermined time has elapsed, the received ultrasonic wave is converted into a reflected signal and output from the signal lines 10 and 11. Is done. Here, the elapsed time from transmission (application of the drive voltage) to reception (detection of the reflected signal) is measured, and the distance to the detected object can be measured from the detection result. Alternatively, it is possible to determine the presence or absence of an object to be detected within a detection area or a predetermined distance range.
[0005]
[Problems to be solved by the invention]
One of the characteristics of the ultrasonic sensor is a directivity characteristic (the detection area is wide or narrow). When the vibration area (area of the diaphragm 3) S is increased, the directivity characteristic of the ultrasonic sensor is narrowed, and when the vibration area S is decreased, it is super. It is known that the directivity characteristics of a sound wave sensor are widened.
[0006]
Such an ultrasonic sensor has various uses such as detection of a preceding vehicle and an obstacle, and security, but depending on the use, a sensor having a narrow directivity may be required. For example, when it is installed on the ceiling of a vehicle and it is desired to determine the presence or absence of a passenger at each boarding position, it is necessary to narrow the directivity.
[0007]
On the other hand, since the ultrasonic sensor is required to be downsized, if an attempt is made to increase the area of the diaphragm while keeping the outer shape small, the inner diameter of the outer peripheral portion of the case is increased within the range allowed by the size of the case. . When the inner diameter of the case 2 is increased while keeping the outer diameter of the case 2 in this way, the wall thickness T of the case outer peripheral portion 2a is reduced as shown in FIG. When the thickness T of the case outer peripheral portion 2a is reduced, the leakage of vibration from the diaphragm 3 to the case outer peripheral portion 2a increases, so that the vicinity of the diaphragm 3 of the case outer peripheral portion 2a vibrates, and the vibration node point ( Node) becomes unclear. Further, since the ultrasonic sensor is attached while holding the case outer peripheral portion 2a, if vibration leaks to the case outer peripheral portion 2a, the sensor characteristics are easily affected by the holding position of the ultrasonic sensor, and the sensor characteristics are stabilized. It becomes impractical.
[0008]
Further, when the thickness T of the case outer peripheral portion 2a is reduced, the mechanical strength of the case 2 is reduced, so that a large external force is applied when the case 2 is processed or an ultrasonic sensor is attached, and the case 2 may be deformed. There is.
[0009]
Therefore, in the conventional ultrasonic sensor 1, as shown in FIG. 1, in order to prevent the vibration of the diaphragm 3 from being transmitted to the case outer peripheral portion 2 a, the case outer peripheral portion 2 a has a thickness t of the diaphragm 3. It is necessary to make the wall thickness T three times or more (in the ultrasonic sensor 1 as shown in FIG. 1, the outer diameter of the case 2 is 14 mm, the inner diameter is 1 mm, the outer wall 2 a has a wall thickness T of 2 mm, and the diaphragm The thickness t of the ultrasonic sensor is 0.6 mm.) The narrowness of the directivity of the ultrasonic sensor and the thin thickness of the outer periphery of the case (the outer diameter of the ultrasonic sensor) are in a trade-off relationship. There was no choice but to sacrifice one.
[0010]
The present invention has been made in view of the above-described conventional problems, and an object of the present invention is to provide an ultrasonic sensor capable of widening the area of the vibration surface without reducing the thickness of the outer peripheral portion of the case. Is to provide.
[0011]
[Means for Solving the Problems]
The ultrasonic sensor according to claim 1, wherein a vibration plate is formed at a bottom portion of a case having a cavity inside, and a piezoelectric vibration element is bonded to an inner surface of the vibration plate . By providing a recess along the direction parallel to the inner surface of the diaphragm in at least a part of the inner peripheral surface in contact with the diaphragm, the diaphragm is not fixed to the outer periphery of the case. The thickness of the region is made uniform, and the diameter of the region of the diaphragm that is not fixed to the outer periphery of the case in the direction in which the recess is provided is larger than the inner diameter of the outer periphery of the case. It is said.
[0012]
The ultrasonic sensor according to claim 2 is characterized in that, in the ultrasonic sensor according to claim 1, the height of the concave section gradually decreases toward the outer peripheral surface of the case .
The ultrasonic sensor according to claim 3 is the ultrasonic sensor according to claim 1 or 2, wherein a region of the diaphragm that is not fixed to the outer peripheral portion of the case has a maximum diameter in a certain direction. The minimum diameter is the direction perpendicular to the direction of the maximum diameter.
The ultrasonic sensor according to a fourth aspect is the ultrasonic sensor according to the third aspect, wherein the minimum diameter is equal to an inner diameter of an outer peripheral portion of the case.
[0013]
[Action]
In the ultrasonic sensor according to claim 1, a recess is provided along a direction parallel to the inner surface of the diaphragm in at least a part of a region in contact with the diaphragm on the inner peripheral surface of the outer peripheral portion of the case. Accordingly, the thickness of the region of the diaphragm that is not fixed to the outer periphery of the case is made uniform, and the diameter of the region of the diaphragm that is not fixed to the outer periphery of the case in the direction in which the recess is provided Since the diameter of the diaphragm is larger than the inner diameter of the case in at least one of the cross sections, even if the diameter of the diaphragm is increased (for example, the diaphragm The diameter of the outer periphery of the case does not need to be reduced.
[0014]
Therefore, according to the ultrasonic sensor of the first aspect, the size of the diaphragm can be increased without increasing the size of the case and without reducing the thickness of the outer peripheral portion of the case, and the sensor characteristics can be improved. The directivity characteristics of the ultrasonic sensor can be narrowed without deteriorating or making the handling difficult.
[0015]
In the ultrasonic sensor according to the second aspect, since the height of the concave portion gradually decreases as the cross section of the concave portion moves toward the outer peripheral surface of the case and the taper is provided, the boring of the concave portion is facilitated.
[0016]
In the ultrasonic sensor according to claim 3, a region of the diaphragm that is not fixed to the outer peripheral portion of the case has a maximum diameter in a certain direction and a minimum diameter in a direction orthogonal to the direction of the maximum diameter ( In claim 4, since it is equal to the inner diameter of the outer peripheral portion of the case, the directivity of the ultrasonic sensor can be made anisotropic.
[0017]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 3 is a cross-sectional view showing the structure of the ultrasonic sensor 21 according to an embodiment of the present invention, and FIG. 4 is a plan view of a case 22 used in the ultrasonic sensor 21. The structure of the ultrasonic sensor 21 will be described. The case 22 that houses the piezoelectric vibration element 25 has a bottomed cylindrical shape, and a disc-shaped diaphragm that generates vibration and receives reflected waves at the tip (bottom) of the cylindrical case outer peripheral portion 22a. 23 is provided integrally. In addition, a concave portion 24 having a tapered cross section by boring is provided in an annular shape at a position in contact with the diaphragm 23 on the inner peripheral surface of the case 22, that is, the inner periphery of the tip end portion of the case outer peripheral portion 22a. The case 22 is formed of a metal material, and is preferably formed of, for example, aluminum or aluminum alloy that is lightweight, has good workability, and does not easily rust.
[0018]
The piezoelectric vibration element 25 has element electrodes 26 a and 26 b formed on both main surfaces of a piezoelectric substrate. The piezoelectric vibration element 25 is bonded to the center of the inner surface of the vibration plate 23 with one element electrode 26 b by a conductive adhesive. . One end of a lead wire 27 is soldered to the other element electrode 26 a of the piezoelectric vibration element 25 housed in the case 22. In addition, an elastic material 28 such as silicon rubber, urethane rubber, or elastic adhesive is filled in the outer region of the piezoelectric vibration element 25 and the recess 24 on the inner surface of the vibration plate 23.
[0019]
Further, a sound absorbing material 29 such as felt is placed inside the case 22 to cover the vicinity of the piezoelectric vibration element 25 with the sound absorbing material 29, and after the sound absorbing material 29, silicon rubber, urethane rubber, synthetic resin foam ( An insulating resin 30 having elasticity such as a closed cell foam) is filled, and the inside of the case 22 is sealed. A relay substrate 31 is embedded in the insulating resin 30, and the other end of the lead wire 27 connected to the element electrode 26 a of the piezoelectric vibration element 25 is soldered onto the relay substrate 31. The signal line 34 connected to is electrically connected.
[0020]
In addition, one end of a lead wire 33 is inserted into a recessed hole 32 provided in the inner peripheral surface of the case 22 and is fixed by a conductive adhesive 32a. The element 25 is electrically connected to the other element electrode 26b. The other end of the lead wire 33 is also soldered on the relay board 31 and is electrically connected to the signal line 35 connected to the relay board 31. Thus, the signal lines 34 and 35 and the lead wires 27 and 33 are connected via the relay substrate 31 because the external force applied to the signal lines 34 and 35 is connected to the lead wires 27 and 33 and the lead wire 27 and piezoelectric. This is to prevent transmission to a connection portion with the vibration element 25 or the like. Note that a chip capacitor for temperature compensation or the like may be mounted on the relay substrate 31 as necessary.
[0021]
In the ultrasonic sensor 21, sound waves are generated when an AC voltage is applied to the piezoelectric vibration element 25 through the signal wires 34 and 35, the lead wires 27 and 33 and the case 22 to vibrate the diaphragm 23. Is emitted forward. On the contrary, the distortion generated when the diaphragm 23 is vibrated by the received reflected sound wave is converted into an electric signal by the piezoelectric vibration element 25, and the signal is taken out via the lead wires 27 and 33, the signal lines 34 and 35, and the like. Detects detected objects such as obstacles.
[0022]
Furthermore, since the recess 24 is filled with the elastic material 28, the mechanical Q of the case 22 is reduced, the reverberation vibration is suppressed, the reverberation time during reception is shortened, and the reverberation characteristics can be improved. . On the other hand, since the elastic material 28 is not attached to the piezoelectric vibration element 25, it does not affect the excitation vibration of the diaphragm 23, and reverberation vibration is hardly caused without changing the resonance frequency or sensitivity of the ultrasonic sensor 21. Can be suppressed.
[0023]
In the ultrasonic sensor 21, the recess 24 is formed at the tip of the inner peripheral surface of the case 22, so that the diameter A of the diaphragm 23 is larger than the inner diameter D <b> 2 of the case 22. Therefore, the diameter A of the diaphragm 23 can be increased without increasing the outer diameter D1 of the case 22 and maintaining the thickness (D1-D2) / 2 of the case outer peripheral portion 22a at a necessary thickness. The directivity characteristic of the ultrasonic sensor 21 can be narrowed. For example, considering a case 22 with an outer diameter D1 = 14 mm, an inner diameter D2 = 10 mm, and a height H = 10 mm, the diameter A of the diaphragm 23 is changed between 10 mm and 14 mm by changing the depth of the recess 24. Can do.
[0024]
When the diameter A of the diaphragm 23 is 10 mm (conventional example), the directional half-value angle is approximately 45 ° as shown in FIG. 5, but the directional half-value angle is set by setting the diameter of the diaphragm 23 to A = 14 mm. Is approximately 30 °, and a very narrow directivity can be obtained. In the ultrasonic sensor 21 having the outer diameter D1 of 14 mm, the diameter of the diaphragm 23 cannot be 14 mm, but the depth of the recess 24 is increased to such an extent that a necessary strength can be obtained at the position of the recess 24. By bringing the diameter A close to 14 mm, the directivity can be made close to that shown in FIG. 5, and the directivity can be narrowed without increasing the outer diameter of the ultrasonic sensor 21. Therefore, for example, pinpoint sensing such as whether there is a person in each passenger seat installed on the ceiling in the vehicle is also possible. In addition, since it is not necessary to reduce the thickness of the case 22, the node point is not obscured, and the case 22 can be provided with the strength necessary for processing and mounting.
[0025]
The concave portion 24 of the case 22 may have a U-shaped cross section without being tapered as in the ultrasonic sensor 41 shown in FIG. 6, but the concave portion 24 of the ultrasonic sensor 21 shown in FIG. It is easier to bore the recess 24 by tapering the one side.
[0026]
FIG. 7 is a sectional view showing the structure of an ultrasonic sensor 42 according to still another embodiment of the present invention. In this ultrasonic sensor 42, the stepped portion 43 is provided by scraping the tip of the outer peripheral surface of the case 22 to make it a little thinner. The ultrasonic sensor 42 may be covered with an anti-vibration cover 44 made of rubber or the like in order to block vibrations from the outside. If the convex portion 45 provided on the inner periphery of the tip end portion of the cylindrical anti-vibration cover 44 is fitted to the step portion 43, the anti-vibration cover 44 can be positioned.
[0027]
FIG. 8 is a sectional view showing the structure of an ultrasonic sensor 46 according to still another embodiment of the present invention. In the ultrasonic sensor 46, a continuous or discontinuous groove 47 is provided on the inner peripheral surface of the diaphragm 23 so as to surround the piezoelectric vibration element 25. In the ultrasonic sensor 46, the resonance frequency of the ultrasonic sensor 46 can be adjusted by the position and depth of the groove 47. In particular, even after the piezoelectric vibration element 25 is attached to the case 22, the resonance frequency can be finely adjusted. In place of the groove 47, a convex for adjusting the resonance frequency may be provided.
[0028]
FIG. 9 is a plan view of a case 22 used in an ultrasonic sensor according to still another embodiment of the present invention. In this embodiment, the concave portion 24 is deep in one cross section (XX cross section), and the concave portion 24 is shallow in the other cross section (YY cross section) (or the concave portion 24 may not be provided). It has become. For example, in FIG. 9, a recess 24 having an elliptical outline in plan view is provided on the circular inner periphery of the case 22. In this way, if the diameter of the diaphragm 23 varies depending on the cross section, the directivity can be made anisotropic.
[0029]
【The invention's effect】
According to the present invention, the size of the diaphragm can be increased without increasing the outer dimensions of the case and while maintaining the thickness of the outer peripheral portion of the case, thereby deteriorating sensor characteristics and making handling difficult. Therefore, an ultrasonic sensor with narrow directivity can be manufactured.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view showing the structure of a conventional ultrasonic sensor.
FIG. 2 is a diagram illustrating a method for narrowing the directivity characteristics of an ultrasonic sensor.
FIG. 3 is a cross-sectional view showing a structure of an ultrasonic sensor according to an embodiment of the present invention.
FIG. 4 is a plan view of a case used in the above ultrasonic sensor.
FIG. 5 is a diagram for explaining directivity characteristics of the above ultrasonic sensor.
FIG. 6 is a cross-sectional view showing the structure of an ultrasonic sensor according to another embodiment of the present invention.
FIG. 7 is a cross-sectional view showing the structure of an ultrasonic sensor according to still another embodiment of the present invention.
FIG. 8 is a cross-sectional view showing the structure of an ultrasonic sensor according to still another embodiment of the present invention.
FIG. 9 is a plan view of a case used in an ultrasonic sensor according to still another embodiment of the present invention.
[Explanation of symbols]
22 Case 22a Case outer periphery 23 Diaphragm 24 Recess 25 Piezoelectric vibration element 28 Elastic material

Claims (4)

In an ultrasonic sensor in which a diaphragm is formed at the bottom of a case having a cavity inside, and a piezoelectric vibration element is bonded to the inner surface of the diaphragm,
An outer periphery of the case of the diaphragm is provided by providing a recess along a direction parallel to the inner surface of the diaphragm in at least a part of the inner peripheral surface of the outer periphery of the case in contact with the diaphragm. The thickness of the region not fixed to the part is made uniform, and the diameter of the region of the diaphragm not fixed to the outer peripheral part of the case in the direction in which the concave portion is provided is larger than the inner diameter of the outer peripheral part of the case Ultrasonic sensor characterized by the fact that 2. The ultrasonic sensor according to claim 1, wherein a height of the cross section of the recess gradually decreases toward the outer peripheral surface of the case . The region of the diaphragm that is not fixed to the outer periphery of the case has a maximum diameter in a certain direction and a minimum diameter in a direction orthogonal to the direction of the maximum diameter. The ultrasonic sensor as described in. The ultrasonic sensor according to claim 3, wherein the minimum diameter is equal to an inner diameter of an outer peripheral portion of the case.

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