JP2004128813

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DESCRIPTION JP2004128813
An object of the present invention is to prevent the occurrence of reverberation characteristic
variation of an ultrasonic sensor and the temporal change of the reverberation characteristic. An
ultrasonic sensor (10) comprises a piezoelectric vibrator (3) and a housing for housing the same.
The housing is composed of a terminal 5 and a cover 6. The piezoelectric vibrator 3 is formed by
sticking the piezoelectric element 1 on one surface of the metal plate 2. An additional resonator 4
is fixed to the other surface of the metal plate 2 of the piezoelectric vibrator 3. The terminal
portion 5 is provided with a protruding annular joint 5 a. The piezoelectric vibrator 3 is bonded
to the annular bonding portion 5 a by a silicon adhesive 9 via a resin-molded elastic body 8 in
the vicinity of the node line. Here, as the resin-molded elastic body 8, silicone rubber having a
ring shape with a predetermined thickness is used. [Selected figure] Figure 1
Ultrasonic sensor
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
ultrasonic sensor using a piezoelectric vibrator. [0002] In recent years, ultrasonic sensors have
been used for security sensors and for detecting human objects in automatic doors. FIG. 2 is a
cross-sectional view showing an example of this ultrasonic sensor. The ultrasonic sensor 20 is
composed of the piezoelectric vibrator 13 and a case for housing the same. The housing is
composed of a terminal portion 15 and a cover portion 16. The piezoelectric vibrator 13 is
formed, for example, by adhering a substantially circular piezoelectric element 11 made of, for
example, piezoelectric ceramic on one surface of a metal plate 12 having a substantially circular
shape in plan view. Electrodes (not shown) are provided on both sides of the piezoelectric
element 11. A substantially conical additional resonator 14 for transmitting and receiving
ultrasonic waves is fixed to the other surface of the metal plate 12 of the piezoelectric vibrator
13. The piezoelectric vibrator 13 bends and vibrates with a node line on the circumference at a
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predetermined distance from the center thereof. The terminal portion 15 is provided with a
protruding annular joint portion 15 a so as to substantially match the node line position. The
piezoelectric vibrator 13 is joined to the annular joint 15 a via the elastic body 19 near the node
line. The elastic body 19 is for preventing the vibration of the piezoelectric vibrator 13 from
being transmitted to the terminal portion 15, and, for example, a silicon adhesive is used.
Furthermore, a pair of external terminals 17 are fixed to the terminal portion 15 as input /
output terminals. One of the pair of external terminals 17 and the electrodes on both sides of the
piezoelectric element 11 is electrically connected by a lead wire and the other is connected by a
lead wire and the metal plate 12. Further, a cover portion 16 having an ultrasonic wave
transmission / reception opening 16 a is fixed to the terminal portion 15 so as to cover the
piezoelectric vibrator 13 and the additional resonator 14. Conventionally, various related
techniques of this type have been proposed (see Patent Document 1 and Patent Document 2).
[Patent Document 1] Japanese Patent Application Laid-Open No. 2-301398 [Patent Document 2]
Japanese Patent Application Laid-Open No. 9-18995 As stated above, in the conventional
ultrasonic sensor, A silicon adhesive has been used to bond the piezoelectric vibrator to the
protruding annular joint. At the time of this bonding, bonding processing had to be performed
while securing a silicon layer between the piezoelectric vibrator and the annular bonding portion.
However, due to processing variations and the like, it has not been possible to reliably form a
silicon layer of a sufficient thickness.
Therefore, the piezoelectric vibrator and the annular joint may be in contact with each other or in
a state close to the contact, and the vibration of the piezoelectric vibrator 13 is transmitted to the
terminal portion 15. As a result, there has been a problem that products having inferior
reverberation characteristics become important, which is important when detecting an object at a
short distance. In addition, even in the case of a product having good initial stage characteristics
and reverberation characteristics, external stress is applied to terminals and the like at the time
of use, and the contact condition is changed, resulting in the occurrence of reverberation
characteristic failure. The present invention has been made in view of the above-mentioned
problems, and a piezoelectric vibrator of an ultrasonic sensor is joined to an annular joint with an
elastic body surely, and occurrence of reverberation characteristic variation and reverberation
characteristic The purpose is to prevent the temporal change of In order to achieve the above
object, an ultrasonic sensor according to the present invention is an ultrasonic sensor comprising
a piezoelectric vibrator and a case for housing the piezoelectric vibrator. The housing is
composed of a terminal portion and a cover portion, and the terminal portion has a projecting
annular joint portion for joining with the piezoelectric vibrator, and the piezoelectric vibrator is
resin-molded in advance It is characterized in that it is joined to the annular joint by an adhesive
through an elastic body. As a result, it is possible to prevent the occurrence of reverberation
characteristic variation and the temporal change of the reverberation characteristic. BEST MODE
FOR CARRYING OUT THE INVENTION An embodiment of the present invention will be described
below with reference to FIG. As shown in FIG. 1A, the ultrasonic sensor 10 is composed of the
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piezoelectric vibrator 3 and a case for housing the same. The housing is composed of a terminal
5 and a cover 6. The piezoelectric vibrator 3 is formed, for example, by sticking a substantially
circular piezoelectric element 1 made of, for example, a piezoelectric ceramic on one surface of a
metal plate 2 having a substantially circular shape in plan view. Electrodes (not shown) are
provided on both sides of the piezoelectric element 1. A substantially conical additional resonator
4 for transmitting and receiving ultrasonic waves is fixed to the other surface of the metal plate 2
of the piezoelectric vibrator 3. The piezoelectric vibrator 3 bends and vibrates with a node line on
a circumference at a predetermined distance from the center thereof. The terminal portion 5 is
provided with a projecting annular joint 5 a so as to substantially match the node line position.
The piezoelectric vibrator 3 is bonded to the annular bonding portion 5a by, for example, a
silicon adhesive 9 via an elastic body 8 which is previously molded with a resin as shown in FIG.
1B in the vicinity of the node line. Here, the resin-molded elastic body 8 is for preventing the
vibration of the piezoelectric vibrator 3 from being transmitted to the terminal portion 5, and for
example, silicon rubber or the like having a ring shape with a predetermined thickness is used.
There is.
The silicone adhesive 9 is formed to cover the resin-molded elastic body 8 and the annular joint
5a. Furthermore, a pair of external terminals 7 are fixed to the terminal portion 5 as input /
output terminals. One of the pair of external terminals 7 and the electrodes on both sides of the
piezoelectric element 1 are electrically connected by lead wires and the other by lead wires and
the metal plate 12. Further, a cover 6 having an ultrasonic wave transmission / reception
opening 6 a is fixed to the terminal 5 so as to cover the piezoelectric vibrator 3 and the
additional resonator 4. According to the configuration of one embodiment of the present
invention, since the piezoelectric vibrator of the ultrasonic sensor is joined to the annular joint
projecting through the resin-molded elastic body, the piezoelectric vibrator and the annular joint
are joined The parts never come into contact or near contact. For this reason, generation ¦
occurrence ¦ production of reverberation characteristic dispersion ¦ variation and the timedependent change of reverberation characteristics can be prevented. In addition, since the
thickness of the elastic body is constant, the piezoelectric vibrator can be attached obliquely, and
the directivity can be suppressed from becoming asymmetric. Furthermore, the workability is
better than that of forming an elastic body having the same function in coating and printing. In
addition, since there is no resin curing failure such as an adhesive, the supported piezoelectric
vibrator can be stabilized, and variations in sound pressure and sensitivity and deterioration can
be suppressed. In the present invention, an example in which the silicone adhesive is formed to
cover the resin-molded elastic body is described. However, the elastic body is disposed between
the piezoelectric vibrator and the annular joint, and the silicon bonding is performed. An agent
may be formed on the outer peripheral surface of the elastic body to bond the piezoelectric
vibrator and the annular joint. As described above, according to the present invention, since the
piezoelectric vibrator of the ultrasonic sensor is joined to the annular joint through the resinmolded elastic body, generation of reverberation characteristic variation occurs. It is possible to
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prevent the time-lapse change of the reverberation characteristics. In addition, it is possible to
suppress the asymmetry of the directivity, and to suppress the variation and the reduction of the
sound pressure and the sensitivity. As a result, an ultrasonic sensor with good characteristics can
be provided. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional view showing a
schematic configuration of an ultrasonic sensor according to an embodiment of the present
invention, and a perspective view showing a resin-molded elastic body. FIG. 2 is a cross-sectional
view showing a schematic configuration of a conventional ultrasonic sensor. Explanation of
symbols 1-----Piezoelectric element 3----Piezoelectric vibrator 5----Terminal 5a----Protruding
annular joint 6-----Cover 8 --- --- Resin-molded elastic body 9 --- --- Silicon adhesive 10 --- --Ultrasonic sensor
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