JP4062780B2 - Ultrasonic sensor - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an ultrasonic sensor. In particular, the present invention relates to a drip-proof ultrasonic sensor used for automobile back sonar and corner sonar.
[0002]
[Prior art]
An ultrasonic sensor performs sensing using ultrasonic waves, intermittently transmits an ultrasonic pulse signal from the piezoelectric vibration element, and receives a reflected wave from an object to be detected in the vicinity by the piezoelectric vibration element. By doing so, an object is detected. As this type of ultrasonic sensor, one having the structure shown in FIG. 1 has been conventionally used (registered gazette of Utility Model Registration No. 3014800). That is, in this ultrasonic sensor 1, the bottom surface of the bottomed cylindrical sensor case 2 made of metal is the diaphragm 3, and the element electrodes 4 a and 4 b are formed on both main surfaces inside the diaphragm 3. The piezoelectric vibration element 5 is joined. On the inner peripheral surface of the sensor case 2 and the inner surface of the connecting portion of the diaphragm 3, a step portion 6 is formed over the entire circumference. Further, both element electrodes 4 a and 4 b of the piezoelectric vibration element 5 are electrically connected to the terminal 8 via the lead wire 7 and the sensor case 2.
[0003]
The ultrasonic sensor 1 having such a configuration applies a driving voltage of a predetermined frequency to the piezoelectric vibration element 5, causes the vibration plate 3 to resonate with the piezoelectric vibration element 5, and emits ultrasonic waves forward from the vibration plate 3. When the ultrasonic wave reflected from the object to be detected causes the diaphragm 3 to resonate after the lapse of the required time, the vibration of the diaphragm 3 is converted into an electric signal by the piezoelectric vibrating element 5. Here, the distance of the detected object is calculated from the elapsed time from transmission (application of drive voltage) to reception (reflection signal detection).
[0004]
Since the ultrasonic sensor operates according to the principle as described above, in order to operate efficiently, the center frequency (hereinafter simply referred to as frequency) relating to the sensitivity and sound pressure of the ultrasonic sensor is determined in advance. Must match the frequency. However, in practice, the frequency of the diaphragm may deviate from the design frequency due to manufacturing variations of the sensor case.
[0005]
Therefore, in the ultrasonic sensor 1, a step 6 for adjusting the frequency is provided on the inner peripheral surface of the sensor case 2 and the inner surface of the connecting portion of the diaphragm 3, and this step 6 is shown by an arrow B in FIG. The frequency adjustment after the assembly of the ultrasonic sensor is made possible by cutting in the direction indicated by.
[0006]
[Problems to be solved by the invention]
However, since the step 6 for frequency adjustment is located in the vicinity of the stress concentration portion (inner corner) A of the sensor case 2, if the step 6 is cut for frequency adjustment, the case material, particularly the diaphragm 3 suffered fatigue deterioration, resulting in variations in sensor characteristics and changes over time, reducing the reliability of the ultrasonic sensor.
[0007]
Further, in order to cut the stepped portion 6 in the direction of arrow B in FIG. 2, it is necessary to support the front end surface of the sensor case 2, and the stepped portion 6 is cut by a cutting tool while the front end surface of the sensor case 2 is pressed. Is cut in the direction of arrow B. Therefore, when cutting the stepped portion 6, stress is generated in the thickness direction of the diaphragm 3, and in the worst case, the diaphragm 3 is deformed, and there is a possibility that the vibration mode of the ultrasonic sensor 1 is changed.
[0008]
In addition, the frequency of the ultrasonic sensor can be adjusted by polishing the outer surface of the diaphragm. However, in order to prevent the directivity of the ultrasonic sensor from being bent, the outer surface of the diaphragm is sufficiently flat. It was necessary to finish and advanced technology was necessary.
[0009]
The present invention has been made in view of the drawbacks of the above-described conventional examples, and the object of the present invention is to provide advanced technology without causing fatigue deterioration in the case material or deforming the diaphragm. It is to be able to adjust the frequency of the ultrasonic sensor without necessity.
[0010]
DISCLOSURE OF THE INVENTION
Ultrasonic sensor according to the present invention, the bottom of the case where the bottomed cylindrical diaphragm and without, in the ultrasonic sensor with bonding the piezoelectric vibrating element on the inner surface of the vibration plate, the bottom portion of the body portion of said casing On the other hand, a cutting portion for adjusting the frequency is provided in an intermediate portion between the opposite end portion and the bottom portion .
[0011]
In the present invention, since the frequency is adjusted by cutting an intermediate portion between the end opposite to the bottom of the case body and the bottom, the bottom of the case as in the conventional example. Compared with the case where the frequency adjustment is performed by cutting the inner corner portion of the tube, the case of the ultrasonic sensor is less likely to be fatigue-degraded due to the frequency adjustment, and the characteristics of the ultrasonic sensor and variations over time are less likely to occur. Therefore, the reliability of the ultrasonic sensor is not impaired by adjusting the frequency of the ultrasonic sensor.
[0012]
Further, as compared with the case where the frequency is adjusted by cutting the outer surface of the diaphragm as in the conventional example , stress is not applied to the diaphragm and the diaphragm is not deformed, and the vibration mode is not changed. In addition, unlike the method of cutting the diaphragm, there is no fear that the flatness of the diaphragm is impaired by the frequency adjustment, and the frequency adjustment can be performed without requiring a high level technique.
[0013]
Moreover, when providing the cutting part for frequency adjustment in the trunk | drum inner peripheral surface of a case, it is preferable to cut toward the outer peripheral direction from a trunk | drum internal peripheral surface. Or when providing a cutting part in the trunk | drum outer peripheral surface of a case, it is preferable to cut toward an inner peripheral direction from a trunk | drum outer peripheral surface. If the cutting part is machined in such a direction, the cutting part can be machined so that no stress is applied to the diaphragm, so that there is no possibility that the diaphragm deforms and changes the vibration mode.
[0014]
Moreover, if a cutting part for adjusting the frequency is provided on the outer peripheral surface of the case body, the frequency of the ultrasonic sensor can be obtained even after the ultrasonic sensor is completed by filling the case with a sound absorbing material or insulating resin. You can make adjustments.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
(First embodiment)
FIG. 3 is a cross-sectional view showing a structure during the manufacturing process of the ultrasonic sensor 11 according to the embodiment of the present invention. The structure of the ultrasonic sensor 11 and the frequency adjustment method will be described. The sensor case 13 that houses the piezoelectric vibration element 12 is formed of a metal material such as aluminum into a bottomed cylindrical shape having an open back surface. The sensor case 13 has a bottom surface at the front end of a substantially cylindrical body portion 14, and this bottom surface is a thin plate-shaped diaphragm 15 that generates vibration and receives reflected waves. A step portion 17 is provided around the inner peripheral surface of the rear end portion.
[0016]
The piezoelectric vibration element 12 has element electrodes 16a and 16b formed on both main surfaces of a piezoelectric plate made of a piezoelectric ceramic material. The piezoelectric vibration element 12 is attached to the center of the inner surface of the vibration plate 15, and one element electrode 16 a of the piezoelectric vibration element 12 is joined to the vibration plate 15 with a conductive adhesive. One lead wire 18 is connected to the step portion 17 of the sensor case 13, and is conducted to one element electrode 16 a of the piezoelectric vibration element 12 via the sensor case 13, and the other lead wire 18 is connected to the piezoelectric vibration element 12. It solders directly to the other element electrode 16b.
[0017]
Thus, as shown in FIG. 3, after attaching the piezoelectric vibrating element 12 to the inner surface of the diaphragm 15 of the sensor case 13 and wiring the lead wire 18, the frequency of the ultrasonic sensor 11 is measured. When the measured frequency is different from the design value, as shown in FIG. 4, the cutting part 19 having a groove shape is formed by cutting the inner peripheral surface of the body part 14 of the sensor case 13 using a cutting tool. Set up. At this time, since the inner corner portion of the stepped portion 17 of the sensor case 13 and the inner corner portion of the outer peripheral portion of the diaphragm 15 are the stress concentration portion C, the stress concentration portion C is cut to avoid the stress concentration portion C. Further, at the time of this cutting, for example, the outer peripheral surface of the body portion of the sensor case 13 is held by a chuck, and is directed from the inner peripheral surface of the body portion 14 to the outer peripheral surface by a cutting tool (direction indicated by arrow D in FIG. 4). Process as if carving. The frequency of the ultrasonic sensor 11 can be adjusted by changing the width and depth of the cutting portion 19.
[0018]
When the frequency adjustment of the ultrasonic sensor 11 is completed in this way, a sound absorbing material (not shown) such as felt is put in the sensor case 13 to cover the vicinity of the piezoelectric vibration element 12 with the sound absorbing material, and the sensor case 13 is placed after the sound absorbing material. The inside is filled with an insulating resin (not shown) having elasticity such as silicon rubber or urethane rubber and cured. As this insulating resin, a synthetic resin foam may be used.
[0019]
In the ultrasonic sensor 11 of the present invention, since the position away from the stress concentration portion C is cut on the inner peripheral surface of the body portion 14 of the sensor case 13, the sensor case 13 is cut for frequency adjustment. However, it is difficult for fatigue deterioration to occur in the sensor case 13, particularly the diaphragm 15, and variations in sensor characteristics and changes over time can be suppressed, and the reliability of the ultrasonic sensor 11 can be improved.
[0020]
Furthermore, since the cutting portion 19 is cut from the inner peripheral surface toward the outer peripheral direction, it is only necessary to hold the outer peripheral surface of the sensor case 13 and it is not necessary to apply stress to the diaphragm 15. Therefore, there is no possibility that the vibration plate 15 is deformed and the vibration mode of the ultrasonic sensor 11 is changed. Even if compared with the conventional method of polishing the outer surface of the diaphragm 15, the frequency of the ultrasonic sensor 11 can be adjusted without requiring advanced techniques.
[0021]
(Second Embodiment)
FIG. 5 is a sectional view showing the structure of an ultrasonic sensor 21 according to another embodiment of the present invention. In this ultrasonic sensor 21, the piezoelectric vibrating element 12 is joined to the diaphragm 15 of the sensor case 13 and the lead wire 18 is wired, and then the sound absorbing material 22 such as felt and silicon rubber, urethane rubber, or the like are placed in the sensor case 13. The insulating resin 23 having elasticity is filled.
[0022]
Next, a cutting portion 19 for adjusting the frequency is processed on the outer peripheral surface of the body portion 14 of the sensor case 13. Also in this case, cutting is performed from the outer peripheral surface of the sensor case 13 toward the inner periphery with the outer peripheral surface of the sensor case 13 held by the chuck.
[0023]
Even in this embodiment, the position away from the stress concentration portion of the outer peripheral surface of the sensor case 13 is cut. Therefore, even if the sensor case 13 is cut for frequency adjustment, the sensor case 13, particularly the diaphragm 15 is less susceptible to fatigue deterioration, can suppress variations in sensor characteristics and fluctuations over time, and can improve the reliability of the ultrasonic sensor 21.
[0024]
Furthermore, since the cutting part 19 is cut from the outer peripheral surface toward the inner peripheral surface, it is only necessary to hold the outer peripheral surface of the sensor case 13 and there is no need to apply stress to the diaphragm 15. Therefore, there is no possibility that the vibration plate 15 is deformed and the vibration mode of the ultrasonic sensor 21 is changed. Even if compared with the conventional method of polishing the outer surface of the diaphragm 15, the frequency of the ultrasonic sensor 21 can be adjusted by a simple operation without requiring a high level of technology.
[0025]
Further, when the first embodiment and the second embodiment are compared, in the first embodiment, even when the surface of the sensor case 13 is coated with a corrosion preventing paint or the like, the corrosion preventing paint on the outer surface. Is not cut, there is an advantage that it is not necessary to repaint the anticorrosion paint in the cutting part 19. On the other hand, in the second embodiment, since the frequency can be adjusted after filling the sound absorbing material or the insulating resin, there is an advantage that the frequency deviation hardly occurs after the frequency adjustment.
[0026]
(Third embodiment)
The present invention can also be applied to an ultrasonic sensor in which the body portion 14 and the diaphragm 15 of the sensor case 13 are separately formed. The structure of such an ultrasonic sensor 31 is shown in FIG. The structure of the ultrasonic sensor 31 will be described with reference to the assembly procedure. A sensor case 13 for housing the piezoelectric vibration element 12 is made of a substantially cylindrical body portion 14 made of an engineering resin such as an insulating resin such as polyphenylene sulfide (PPS) or a liquid crystal polymer, and a disk-like metal such as aluminum. And a diaphragm 15. An annular shallow recess 33 is provided in the inner periphery of the front end opening of the body portion 14, and an annular step 17 is formed on the inner periphery of the rear end opening of the body portion 14. 33 is configured with a bottomed cylindrical sensor case 13 fitted with a diaphragm 15 that generates vibration and receives reflected waves. A conductive member 32 made of a metal material such as white or 42 nickel is inserted into the body portion 14, and one of the conductive members 32 has a front end protruding from the inner peripheral surface of the body portion 14 and a rear end portion. Is exposed at the rear end surface of the body portion 14, and the other conductive member 32 is exposed at the front end portion in the shallow recess portion 33 and at the rear end portion at the stepped portion 17.
[0027]
The piezoelectric vibration element 12 has element electrodes 16a and 16b formed on both main surfaces, and one element electrode 16a of the piezoelectric vibration element 12 is bonded to the center of the inner surface of the vibration plate 15 by a conductive adhesive. In this way, the body portion 14 is integrally formed with the conductive member 32 and the piezoelectric vibration element 12 is integrated with the vibration plate 15, and then the outer peripheral portion of the vibration plate 15 to which the piezoelectric vibration element 12 is bonded is recessed in the body portion 14. The sensor case 13 is assembled by being fitted into the portion 33 and adhered with an adhesive, and the piezoelectric vibration element 12 is placed in the sensor case 13. Next, the tip of one conductive member 32 is soldered to the element electrode 16 b of the piezoelectric vibration element 12. The tip of the other conductive member 32 is in pressure contact with the vibration plate 15 and is electrically connected to the element electrode 16a of the piezoelectric vibration element 12 (the tip of the conductive member 32 and the vibration plate 15 may be joined with a conductive adhesive or the like. Therefore, the two conductive members 32 are electrically connected to both element electrodes 16a and 16b of the piezoelectric vibration element 12.
[0028]
Thereafter, the inner peripheral surface or the outer peripheral surface of the body portion 14 of the sensor case 13 is cut to provide the cutting portion 19, and the frequency of the ultrasonic sensor 31 is adjusted. Further, the end of a signal line (not shown) is soldered to the rear end of each conductive member 32. When the mounting and connection of each component are thus completed, the body portion 14 is filled with a sound absorbing material (not shown) such as felt, or an insulating resin (not shown) having elasticity such as silicon rubber or urethane rubber.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing the structure of a conventional ultrasonic sensor.
FIG. 2 is a partially enlarged cross-sectional view for explaining the frequency adjustment method of the ultrasonic sensor according to the above.
FIG. 3 is a cross-sectional view showing a state before the frequency adjustment of the ultrasonic sensor according to the embodiment of the present invention.
FIG. 4 is a cross-sectional view showing a state after frequency adjustment of the above ultrasonic sensor.
FIG. 5 is a cross-sectional view showing a state after frequency adjustment of an ultrasonic sensor according to another embodiment of the present invention.
FIG. 6 is a cross-sectional view showing a state after frequency adjustment of an ultrasonic sensor according to still another embodiment of the present invention.
[Explanation of symbols]
12 Piezoelectric Vibration Element 13 Sensor Case 14 Body 15 Diaphragm 19 Cutting Part C Stress Concentration Part

Claims (3)

In the ultrasonic sensor in which the bottom of the bottomed cylindrical case is a diaphragm, and a piezoelectric vibration element is bonded to the inner surface of the diaphragm,
An ultrasonic sensor, wherein a cutting portion for adjusting a frequency is provided in an intermediate portion between an end portion on the opposite side to the bottom portion of the body portion of the case and the bottom portion .   The ultrasonic sensor according to claim 1, wherein the cutting portion is cut from an inner peripheral surface of the case portion toward an outer peripheral direction.   The ultrasonic sensor according to claim 1, wherein the cutting portion is cut from an outer peripheral surface of the body portion of the case toward an inner peripheral direction.

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