JP2012114540A - Ultrasonic sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ultrasonic sensor that has solved problems with constraint of a piezoelectric element by a resin case.SOLUTION: An ultrasonic sensor 101 includes a piezoelectric element 30 capable of ultrasonic vibration by application of a driving voltage, and a resin case 11 holding the piezoelectric element 30 indirectly. The resin case 11 has two terminals 12, 13 formed integrally. The terminals 12, 13 project out from a bottom of the resin case 11. The piezoelectric element 30 is mounted on internal tips of the terminals 12, 13 in an opening of the resin case 11. The resin case 11 has resin-recessed portions H for holding a part of the terminals 12, 13 during insert molding. The resin-recessed portions H reach the terminal 12 from two opposite points on outer surfaces of the resin case 11. The resin-recessed portions H relieve the piezoelectric element 30 from constraint to provide improved overall sensitivity.

Description

  The present invention relates to an ultrasonic sensor used to detect the presence / absence and size of an object or a distance to the object, and more particularly to an ultrasonic sensor using a piezoelectric element.

A sensor for detecting the presence / absence and size of an object or a distance to the object includes a piezoelectric element that vibrates ultrasonically when a driving voltage is applied, and a case that houses the piezoelectric element. In particular, an ultrasonic sensor in which a piezoelectric element is directly held with respect to a resin case is disclosed in Patent Document 1, for example.
Here, the structure of the ultrasonic sensor described in Patent Document 1 is shown in FIG.

  In the ultrasonic sensor shown in FIG. 1, a ground electrode 2 is formed on the front and side surfaces of the piezoelectric element 1, and a signal electrode 3 is formed on the back surface. A signal terminal 4 is connected to the right end of the signal electrode 3, and a ground terminal 5 is connected to the lower left end of the ground electrode 2. On the back side of the signal electrode 3, there is provided a back load material 6 that mechanically holds the piezoelectric element 1 and has a function of attenuating unnecessary ultrasonic signals. A heat conducting material 7 is provided between the signal electrode 3 and the back load material 6. A heat dissipating material 9 for dissipating the heat of the heat conducting material 7 is provided around the back surface load material 6. An acoustic matching layer 8 is provided on the front surface of the piezoelectric element 1.

JP 2000-184497 A

  In the ultrasonic sensor having the structure shown in FIG. 1, the piezoelectric element is directly held by the heat conducting material 7 that is a part of the resin case, so that the piezoelectric element is restrained by the resin case. . Therefore, there is a problem that it is difficult to increase the sensitivity of the ultrasonic sensor by suppressing the vibration of the piezoelectric element.

  Further, in the ultrasonic sensor shown in FIG. 1, since the piezoelectric element is directly connected to the terminal, there is a problem that the piezoelectric element also receives a binding force by the terminal.

  Accordingly, an object of the present invention is to provide an ultrasonic sensor that solves the problem caused by a structure in which a piezoelectric element is directly or indirectly held by a resin case.

The ultrasonic sensor of the present invention is an ultrasonic sensor comprising a piezoelectric element that vibrates ultrasonically by application of a drive voltage, and a resin case that houses the piezoelectric element.
The resin case has a bottom and is a molded body with an open top,
The piezoelectric element is directly or indirectly held at the bottom of the resin case so as to emit ultrasonic waves in the opening direction of the resin case,
A resin removal shape portion (through hole or blocking hole) is formed in the bottom portion of the resin case.

  For example, the resin case is integrally molded with a terminal protruding from the bottom to the outside, and the resin removal shape portion is a through-hole or a blocking hole for holding a terminal when the terminal is insert-molded into the resin case. is there.

  In addition, for example, the resin removal shape portion is a through hole, and a space is formed between the surface opposite to the ultrasonic radiation surface of the piezoelectric element and the bottom portion of the resin case, and the space and the through hole communicate with each other. A vertical hole is formed in the bottom of the resin case.

  According to the present invention, although the piezoelectric element is directly or indirectly held by the resin case, the vibration of the piezoelectric element is not strongly restrained by the resin case. Therefore, it is possible to reduce the cost with a simple structure and to obtain a highly sensitive ultrasonic sensor.

FIG. 1 is a cross-sectional view of an ultrasonic sensor described in Patent Document 1. FIG. 2A is a front view of the ultrasonic sensor 101 according to the first embodiment. 2 (B) and 2 (C) are diagrams showing the internal structure, FIG. 2 (B) is a front sectional view, and FIG. 2 (C) is a left sectional view. FIG. 3 is a front view and a left side view of the terminal 12 manufactured by punching and bending a metal plate. 4A is a perspective view of the piezoelectric element 30, and FIG. 4B is a cross-sectional view of the piezoelectric element 30 attached to a terminal. FIG. 5 is a diagram showing a manufacturing process of the ultrasonic sensor 101. FIG. 6 is a diagram showing the difference in the overall sensitivity characteristics depending on the presence or absence of the resin removal shape portion H. FIG. FIG. 7 is a diagram showing an internal structure of the ultrasonic sensor 102 according to the second embodiment.

<< First Embodiment >>
A first embodiment will be described with reference to FIGS.
FIG. 2A is a front view of the ultrasonic sensor 101 according to the first embodiment. 2 (B) and 2 (C) are views showing the internal structure, FIG. 2 (B) is a front sectional view, and FIG. 2 (C) is a left sectional view. The ultrasonic sensor 101 includes a piezoelectric element 30 that vibrates ultrasonically when a driving voltage is applied, and a resin case 11 that indirectly holds the piezoelectric element 30. The resin case 11 has a bottom part BP and is a molded body in which the top part AP is opened. Two terminals 12 and 13 are integrally formed in the resin case 11. The terminals 12 and 13 protrude from the bottom BP of the resin case 11 to the outside. The piezoelectric element 30 is attached to the tip of the terminals 12 and 13 inside the opening of the resin case 11. The terminals 12 and 13 are formed of a metal flat plate and are bent. Bending here refers to a structure obtained by bending a planar structure. In addition, although the propagation direction of the vibration transmitted through the terminals 12 and 13 is varied by bending the metal flat plate, the propagation direction of the vibration may be varied by forming a twist or the like without being bent.

  The resin case 11 has a resin removal shape portion H for holding the terminals 12 and 13 during insert molding of a part of the terminals 12 and 13. As shown in FIG. 2C, the resin removal shape portion H reaches the terminal 12 from two opposing locations on the outer surface of the resin case 11. The same applies to the terminal 13 side. Therefore, the resin removal shape portion H is four closed holes reaching the terminals 12 and 13 inside the resin case 11. When the terminals 12 and 13 are not completely closed, the resin removal shape portion H is two through holes.

An acoustic matching layer 17 made of a resin containing, for example, a glass balloon or the like is disposed on the ultrasonic radiation surface side of the piezoelectric element 30, and a lower space 18 is formed on the opposite side of the piezoelectric element 30 from the ultrasonic radiation surface. . A surrounding space 19 is formed around the piezoelectric element 30. The tips (piezoelectric element mounting portions) of the terminals 12 and 13 are exposed in the surrounding space 19.
In the ultrasonic sensor 101, the piezoelectric element 30 vibrates by application of a driving voltage, and the upper surface of the piezoelectric element 30, that is, the surface on which the acoustic matching layer 17 is disposed serves as an ultrasonic transmission or reception surface. The piezoelectric element 30 has electrodes 32 and 33 formed on the front and back surfaces of a disk-shaped piezoelectric substrate 31. The piezoelectric element 30 is placed on the support part 20 protruding from the inner bottom surface of the opening of the top part AP of the resin case 11, and the electrodes 32 and 33 of the piezoelectric element 30 are electrically connected to the tips of the terminals 12 and 13. Yes. Therefore, the piezoelectric element 30 is indirectly held with respect to the resin case 11 via the distal end portions of the terminals 12 and 13, and is directly held on the support portion 20 of the resin case 11.

  A lower space 18 is formed on the opposite side of the piezoelectric element 30 from the ultrasonic radiation surface. A surrounding space 19 is formed around the piezoelectric element 30, and the piezoelectric element mounting portions of the terminals 12 and 13 are exposed in the surrounding space 19. With this structure, the vibration of the piezoelectric element 30 is not inhibited. Further, since the space 19 is provided around the tips (piezoelectric element mounting portions) of the terminals 12 and 13, that is, because the space 19 is hollow, the piezoelectric element is caused by the difference in the linear expansion coefficient between the resin case 11 and the terminals 12 and 13. The thermal stress applied to 30 is relaxed.

FIG. 3 is a front view and a left side view of the terminal 12 manufactured by punching and bending a metal plate. The terminal 12 is a molded metal plate, and includes a column part 12a, an engaging part 12b, a relay part 12c, a beam part 12d, and a bundle part 12e. Broken lines in the figure are folding lines (valley folds), and these folding lines are bent at a right angle with a predetermined R (round).
The other terminal 13 is symmetrical with respect to the terminal 12.

  4A is a perspective view of the piezoelectric element 30, and FIG. 4B is a cross-sectional view of the piezoelectric element 30 attached to a terminal. The piezoelectric element 30 has electrodes 32 and 33 formed on the front and back surfaces of a disk-shaped piezoelectric substrate 31. Moreover, semicylindrical cutouts are formed at two locations on the edge, and terminal electrodes 32t and 33t of the cutouts are formed.

  As shown in FIG. 4B, the terminal electrodes 32t and 33t are electrically and mechanically joined to the tips of the bundle portions 12e and 13e, which are the tip portions inside the terminals 12 and 13, by solder SO. .

FIG. 5 is a diagram showing a manufacturing process of the ultrasonic sensor 101. Although the terminals 12 and 13 are actually connected by a hoop, the illustration of the hoop is omitted in FIG.
FIG. 5A shows a state after the resin case 11 is insert-molded (hoop insert mold-molded) at the ends of the terminals 12 and 13. In the resin case 11, the resin removal shape portion H is generated by holding a part of the terminals 12 and 13 at the time of insert molding.

  As the material of the resin case, a thermoplastic resin such as a liquid crystal polymer (LCP) is used. Since the liquid crystal polymer (LCP) has high vibration absorption, a high vibration damping effect can be obtained. Although generally inferior to LCP in terms of heat resistance, a good vibration damping effect can be obtained even when polybutylene terephthalate (PBT) is used. As a material for the terminals 12 and 13, copper, phosphor bronze, or the like can be used.

  In the next step, as shown in FIG. 5B, the piezoelectric element 30 is soldered to the tips of the bundle portions 12e and 13e that are the ends of the terminals 12 and 13. Specifically, the piezoelectric element 30 is inserted from the top opening AP of the resin case 11 and placed on the support portion 20 protruding from the inner bottom surface of the opening AP of the resin case 11. In this state, the piezoelectric element 30 is soldered to the tips of the bundle portions 12e and 13e.

  Thereafter, as shown in FIG. 5C, the acoustic matching layer 17 is formed in the opening of the top part AP of the resin case 11 on the upper side of the piezoelectric element 30. Specifically, a resin material that acts as an acoustic matching layer is filled.

  FIG. 6 is a diagram showing the difference in the overall sensitivity characteristics depending on the presence or absence of the resin removal shape portion H. FIG. The horizontal axis is frequency and the vertical axis is total sensitivity. The total sensitivity here is input sensitivity / output sensitivity when one ultrasonic sensor transmits ultrasonic waves and receives reflected ultrasonic waves.

The reflective target used for the measurement was a metal plate having a diameter of 85 mm, and an ultrasonic sensor was placed at a distance of 10 cm from the reflective target. The resin case 11 had a diameter of 9 mm and the piezoelectric element had a diameter of 8 mm, and the resin removal forming portion H formed a cavity having a cross section of 1.3 × 1.3 mm.

  A curve A in FIG. 6 is a characteristic of the ultrasonic sensor 101 of the first embodiment, and a curve B is a characteristic of the ultrasonic sensor 101 in which the resin removal shape portion H is filled with resin. Thus, higher total sensitivity is obtained when the resin removal shape portion H is provided. Moreover, it turns out that a peak sensitivity frequency becomes high. The increase in the peak sensitivity frequency is presumed to be due to the fact that the mass that restrains the vibration of the piezoelectric element is reduced, that is, the restraining force on the piezoelectric element is reduced. Therefore, it can be considered that the resin removal shape portion H relaxes the binding force on the piezoelectric element and improves the overall sensitivity.

  In addition, although the shape of the resin removal shape part of 1st Embodiment is a cross-sectional rectangular shape, you may be comprised by other cross-sectional shapes, such as cross-sectional circular shape and cross-sectional elliptical shape, for example. The resin removal shape portion H is not necessarily required to hold the terminals 12 and 13, and the resin removal shape portion H may be formed in a region where the terminals 12 and 13 are not formed. In particular, when the resin removal shape portion H is formed in the vicinity of the lower space 18 and the surrounding space 19, the restraining force on the element is more easily relaxed, and the overall sensitivity is improved.

<< Second Embodiment >>
FIG. 7 is a diagram showing an internal structure of the ultrasonic sensor 102 according to the second embodiment.
A vertical hole V is provided between the lower space 18 opposite to the ultrasonic radiation surface of the piezoelectric element 30 and the resin removal shape portion H. This vertical hole is formed at the time of insert molding. The vertical hole V allows the lower space 18 and the resin removal shape portion H to communicate with each other. Therefore, when the acoustic matching layer 17 is filled, the air in the opening at the top of the resin case 11 escapes, and no voids are generated in the acoustic matching layer 17, thereby acting as an acoustic matching layer having desired characteristics.

  The configuration other than the vertical hole V is the same as that shown in the first embodiment. Since the vertical hole V also acts to reduce the rigidity of the resin case 11, the restraining force of the piezoelectric element 30 is relaxed, and a more sensitive ultrasonic sensor can be obtained.

  As described above, the ultrasonic sensor of the present invention has a structure in which the piezoelectric element is directly or indirectly held by the resin case, but the vibration of the piezoelectric element is not strongly restrained by the resin case. Therefore, it is possible to reduce the cost with a simple structure and to obtain a highly sensitive ultrasonic sensor.

AP ... Top part BP ... Bottom part H ... Resin removal shape part V ... Vertical hole 11 ... Resin case 12, 13 ... Terminal 12a ... Column part 12b ... Engagement part 12c ... Relay part 12d ... Beam parts 12e, 13e ... Bundle part 17 ... Acoustic matching layer 18 ... lower space 19 ... surrounding space 20 ... support part 30 ... piezoelectric element 31 ... piezoelectric substrate 32, 33 ... electrodes 101, 102 ... ultrasonic sensor

Claims (3)

In an ultrasonic sensor comprising a piezoelectric element that vibrates ultrasonically by application of a drive voltage, and a resin case that houses the piezoelectric element,
The resin case has a bottom and is a molded body with an open top,
The piezoelectric element is directly or indirectly held at the bottom of the resin case so as to emit ultrasonic waves in the opening direction of the resin case,
An ultrasonic sensor, wherein a resin removal shape portion is formed in a bottom portion of the resin case.   A terminal projecting from the bottom of the resin case to the outside is integrally formed in the resin case, and the resin removal shape part is a through hole for holding a terminal when the terminal is insert-molded into the resin case or The ultrasonic sensor according to claim 1, wherein the ultrasonic sensor is a blocking hole. The resin removal shape portion is a through hole,
A space is formed between the surface of the piezoelectric element opposite to the ultrasonic radiation surface and the bottom of the resin case, and a vertical hole communicating the space with the through hole is formed in the bottom of the resin case. The ultrasonic sensor according to claim 1 or 2.

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