WO2014132492A1

WO2014132492A1 - Ultrasonic sensor

Info

Publication number: WO2014132492A1
Application number: PCT/JP2013/080185
Authority: WO
Inventors: 佐藤健宏; カンライスパナン
Original assignee: 株式会社村田製作所
Priority date: 2013-02-28
Filing date: 2013-11-08
Publication date: 2014-09-04

Abstract

This ultrasonic sensor is provided with: a bottomed cylindrical case (51) having an opening, a bottom portion, and a side wall portion; a piezoelectric element (52), bonded to the inner surface of a bottom portion (51b) of the case (51); and filling materials (55, 56) that are applied to the inside of the case (51). A vibration region including a bonding position of the piezoelectric element (52), and a thick portion (51r), which is disposed on the outer circumference of the vibration region, and which is thicker than the vibration region, are provided on the inner side of the bottom portion of the case (51). A reinforcing material (57) having higher rigidity than the bottom portion of the case is disposed on the thick portion (51r). The thick portion (51r) is continuous over the whole circumference in the circumferential direction of the bottom portion of the case (51). With such structure, vibration amplitude of the vibration region is increased, and sensitivity of the ultrasonic sensor is improved.

Description

Ultrasonic sensor

The present invention relates to an ultrasonic sensor that detects an object by transmitting and receiving ultrasonic waves.

Patent Document 1 discloses an ultrasonic sensor having a bottomed cylindrical case having a bottom portion and a side portion, a piezoelectric element attached to the inner bottom portion of the case, and a filler filled in the case. Has been. This ultrasonic sensor has a thin portion that becomes a main vibration region at the center of the inner bottom portion of the case, and is thicker on both sides of the thin portion at the inner bottom portion of the case than the thin portion, and serves as a vibration suppression region. Thick part is provided. The case is provided with an elliptical vibration region so that the directivity of the ultrasonic sensor has anisotropy in the horizontal direction and the vertical direction. The vibration suppression region does not extend over the entire periphery of the bottom portion of the case, but is separated on both sides of the vibration region and is arranged side by side in the short side direction of the vibration region.

In the ultrasonic sensor shown in Patent Document 1, since a reinforcing material for reinforcing the vibration suppression region is placed on the thick part of the case, the rigidity of the thick part of the case bottom and the case side part is increased. It can suppress more that the vibration of a case bottom part is transmitted to a case side part. In addition, it is possible to form a vibration surface for transmitting / receiving necessary ultrasonic waves.

International Publication No. 2011/090201 Pamphlet

In an ultrasonic sensor that detects the presence or absence of an object and measures the distance to the object using ultrasonic waves, it is generally necessary to increase the vibration amplitude in the vibration region in order to increase the sensitivity of the sensor. The inventor of the present application has conducted experiments and simulations and found that it is important to increase the rigidity or mass around the vibration region at the bottom of the case in order to increase the amplitude when the vibration region vibrates. For this purpose, it is effective to increase the thickness of the thick part (vibration suppression region) or increase the thickness of the reinforcing material. However, if the thickness of the thick part or the reinforcing material increases, the thickness increases. This reduces the amount of the filled resin, leading to insufficient damping and worsening reverberation characteristics. In addition, since the space for other internal materials is reduced, there is a further problem that the case becomes taller to secure the space for other members. Therefore, it is difficult to increase sensitivity with the above structure.

Therefore, an object of the present invention is to provide an ultrasonic sensor capable of obtaining higher sensitivity than before without increasing the size of the case.

An ultrasonic sensor of the present invention includes a bottomed cylindrical case having a bottom portion provided at one end in the axial direction, an opening portion provided at the other end in the axial direction, and a side wall portion, and a bottom portion of the case. A piezoelectric element provided at the center of the inner surface, and a filler (elastic resin) filled in the case,
The case is disposed at a central portion of the inner surface of the bottom portion at a thin portion (vibration region) including the placement position of the piezoelectric element, and at an outer periphery of the thin portion of the inner surface of the bottom portion, and has a thickness compared to the thin portion. A thick wall portion (vibration suppression region),
A reinforcing material having rigidity higher than that of the bottom portion of the case is disposed (joined) on the thick portion,
The thick portion is characterized in that it is continuous over one circumference in the circumferential direction of the bottom of the case.

With the above configuration, since there is no thin portion in the circumferential range along the inner surface of the side wall portion of the case, and the thick portion continuously surrounds the vibration region in the circumferential direction, vibration from the vibration region to the side wall portion of the case There is less energy leakage than before. For this reason, the vibration amplitude in the vibration region increases. That is, higher sensitivity can be obtained without increasing the size of the case. In addition, since the joint area between the reinforcing part at the top of the thick part and the thick part increases, the rigidity or mass around the vibration area at the bottom of the case can be effectively increased, and high-order spurious vibrations are suppressed. it can.

It is preferable that the reinforcing material has a size that covers the entire thick portion as viewed from the opening of the case. This enhances the mass addition effect and rigidity improvement effect of the reinforcing material.

According to the present invention, since leakage of vibration energy from the vibration region to the outer periphery at the bottom of the case can be suppressed, the vibration amplitude in the vibration region is increased, and higher sensitivity can be obtained without increasing the size of the case. it can.

FIG. 1A is a plan view of some members of the ultrasonic sensor according to the embodiment of the present invention, and FIG. 1B is a cross-sectional view of the ultrasonic sensor. FIG. 2 is a plan view showing an example of the shape of the side wall 51a and the thick part 51r of the case of the ultrasonic sensor 101 shown in FIGS. 1 (A) and 1 (B). FIG. 3 is a plan view showing an example of the shapes of the side wall 51a and the thick part 51r of the case of the ultrasonic sensor according to the first modification of the embodiment of the present invention. FIG. 4 is a plan view of a simulation model showing the shapes of the thick portions of the three ultrasonic sensors according to the embodiment of the present invention, Modification 1 thereof, and Comparative Example. FIG. 5 shows the result of the simulation. The horizontal axis represents the bonding area [mm ² ] between the thick part 51r and the reinforcing member 57, and the vertical axis represents the vibration amplitude [μm] of the vibration region. It is a top view of some members of an ultrasonic sensor concerning modification 2 of an embodiment of the present invention. It is a top view of some members of an ultrasonic sensor concerning modification 3 of an embodiment of the present invention.

FIG. 1A is a plan view of some members of an ultrasonic sensor according to an embodiment of the present invention, and FIG. 1B is a cross-sectional view of the ultrasonic sensor. The ultrasonic sensor 101 includes a bottomed cylindrical case 51 having a bottom portion 51b and a side wall portion 51a, and a plurality of members provided in the case 51. The case 51 is a molded body formed by forging an aluminum material, for example. The case 51 includes a side wall 51a and a bottom 51b.

A piezoelectric element 52 is bonded to the center of the bottom 51b of the case 51. The bottom 51b includes a thin portion (vibration region) 51t including the bonding position of the piezoelectric element 52, and a thick portion (vibration suppression region) 51r that is disposed outside the thin portion 51t and is thicker than the thin portion 51t. I have.

On the thick part 51r, a reinforcing material (weight) 57 having a rigidity higher than that of the bottom part 51b of the case is disposed. Specifically, a ring-shaped reinforcing material (weight) 57 is provided at a position on the thick part 51r of the case 51 and not in contact with the inner peripheral surface of the side wall part 51a. The reinforcing material (weight) 57 may be a member having higher acoustic impedance than the case 51. For example, it may be a molded body made of the same material (aluminum) as the case 51 so that the acoustic impedance is higher than that of the case 51 by adjusting the thickness and shape. Further, for example, a material having a higher density than the case 51, such as SUS or zinc, may be used to increase the acoustic impedance. The reinforcing member 57 is preferably large enough to cover the thick portion 51r in plan view from the opening side of the case. The structure increases the joint area between the reinforcing member 57 and the thick part 51r, so that the rigidity or mass around the vibration region in the case bottom 51b can be effectively increased, and higher-order spurious vibrations can be suppressed. .

The thick part 51r of the bottom part 51b of the case is continuous over one circumference in the circumferential direction of the bottom part 51b of the case 51.

An elastic member 53 is provided on the upper portion of the reinforcing member 57. A gap between the elastic member 53 and the inner peripheral surface of the case 51 is filled with a first filler 55.

The terminal holding member 61 holds two pins. One end of the two pins held by the terminal holding member 61 is an external terminal 63, and the other end is an internal terminal 62. A wiring material (conductive member) 54 is connected between the internal terminal 62 and the electrode of the piezoelectric element 52. The terminal holding member 61 is placed on top of the elastic member 53, and the second holding material 56 is filled around the terminal holding member 61. In this way, a part of the terminal holding member 61 is embedded in the second filler 56, whereby the terminal holding member 61 is fixed in the case 51 by the second filler 56.

A sound absorbing material 58 is provided on the surface of the elastic member 53 on the piezoelectric element side. The sound absorbing material 58 is, for example, polyester felt, and is bonded to the elastic member 53 with an adhesive.

The first filler 55 is configured to contact the side wall 51a of the case 51, and the second filler 56 is configured to contact the periphery of the terminal holding member 61. The elastic modulus of the first filler 55 is an elastic material higher than the elastic modulus of the second filler 56. For example, the first filler 55 is a urethane resin, and the second filler 56 is a silicone resin. Further, if the elastic modulus is different, both may be urethane resins. The first filler 55 is an elastic material having a high vibration damping property with respect to the side wall 51 a of the case, and the second filler 56 is an elastic material that hardly propagates the vibration of the side wall to the terminal holding member 61. Good.

FIG. 2 is a plan view showing an example of the shape of the side wall 51a and the thick part 51r of the case of the ultrasonic sensor 101 according to the embodiment. FIG. 3 is a plan view showing an example of the shape of the thick portion 51r according to the first modification of the embodiment. Both are plan views of the state before the reinforcing member 57 is placed. However, the illustration of the piezoelectric element 52 is omitted. In the example of FIG. 2, the thick part 51r is a concentric ring shape with the case bottom (51b in FIG. 1). In the example of FIG. 3, the thick portion 51r has different inner diameters in the horizontal direction and the vertical direction. That is, it has a major axis Da and a minor axis Db.

As shown in FIG. 2, if the thick portion 51r is concentric with the case bottom 51b, that is, if it is rotationally symmetric, vertical and horizontal isotropic directivity can be obtained. As shown in FIG. 3, if the thick portion 51r has anisotropy in the vertical and horizontal directions, the directivity is narrow in the long axis direction (the horizontal direction in the direction of FIG. 3) and short axis direction (the direction in FIG. 3). In the vertical direction).

Here, the result of obtaining the vibration characteristics when the shape of the thick part 51r and the dimensions of each part are changed is shown.

FIG. 4 is a plan view of a simulation model showing the shapes of the thick portions of the three ultrasonic sensors. FIG. 4A shows an embodiment of the present invention, which is an example in which the thick portion 51r is formed in a ring shape concentric with the case bottom. FIG. 4B is a first modification of the embodiment, and an example in which the directivity of the ultrasonic sensor has anisotropy between the horizontal direction and the vertical direction by providing the thick part 51r with the long diameter Da and the short diameter Db. It is. FIG. 4C is a comparative example, which is an example of a conventional structure in which the directivity of the ultrasonic sensor has anisotropy in the horizontal direction and the vertical direction by arranging the thick portion 51r in two places. . 4A to 4C, the configuration other than the thick portion is the same.

First, by changing the diameter D of the vibration region of the ultrasonic sensor provided with the case shown in FIG. 4A, the vibration of the vibration region when the joining area between the thick portion 51r and the reinforcing member 57 is changed. The change of amplitude was investigated by simulation. The inner diameter of the side wall portion 51a of the case was 12.8 mm, and the vibration amplitude in the vibration region when the diameter D of the vibration region was 6.0, 7.0, 8.0, 9.1, and 9.9 mm was obtained.

In the structure shown in FIG. 4B, the vibration in the vibration region when the long diameter Da is fixed at 10.8 mm and the short diameter Db is 5.0, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, 9.5 mm. The amplitude was determined.

For the structure shown in FIG. 4C, the vibration amplitude in the vibration region was determined when the major axis Da was fixed at 12.8 mm and the minor axis Db was 5.0, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5 mm. .

FIG. 5 shows the result of the simulation. The horizontal axis represents the area [mm ² ] of the thick part 51r, and the vertical axis represents the vibration amplitude [μm] of the vibration region. In FIG. 5, a curve A is a characteristic of the structure shown in FIG. 4A, a curve B is a characteristic of the structure shown in FIG. 4B, and a curve C is a characteristic of the structure shown in FIG. . All of these are the characteristics when the same reinforcing material is joined.

As shown in FIGS. 4 (A) and 4 (B), the thick portion 51r has the same area as long as the thick portion is continuous over the circumference of the bottom of the case in the circumferential direction. When compared under certain conditions, it can be seen that a larger amplitude can be obtained compared to the conventional structure. This is because the thick portion continuously surrounds the vibration region in the circumferential direction, and therefore leakage of vibration energy from the thin portion to the side wall portion of the case is reduced as compared with the conventional structure. The vibration amplitude is increased.

When the thick part is separated as shown in FIG. 4C, the amplitude when the area of the thick part 51r is about 30 mm ² is about 2.33 μm. On the other hand, when the shape of the thick part has anisotropy as shown in FIG. 4B, the amplitude of the vibration region in the ultrasonic sensor becomes 2.33 μm because the area of the thick part 51r is about is the time of 60mm ^2. That is, if the short diameter Db shown in FIG. 4B is reduced within a range where the area of the thick part 51r is less than twice that of FIG. 4C, the directivity is not deteriorated without degrading the amplitude of the vibration region. Can have anisotropy.

In the example shown in FIG. 3 and FIG. 4 (B), the thick portion 51r is formed in which the planar shape of the inner diameter is an arc and a straight line, but the boundary between the arc and the straight line is continuous with a curve (curved surface). May be. Further, as shown in FIG. 6, the thick portion 51r may have an elliptical shape having a major axis Da and a minor axis Db.

Further, in the example shown in FIG. 3 and FIG. 4B, the thick portion 51r is formed in which the planar shape of the inner diameter is constituted by an arc and a straight line, but the planar shape of the inner diameter may be constituted only by a straight line. Good. For example, as shown in FIG. 7, the thick part 51r may have a rectangular shape having a long side Sa and a short side Sb.

D ... Diameter Da ... Long diameter Db ... Short diameter Sa ... Long side Sb ... Short side
51 ... Case 51a ... Side wall 51b ... Bottom 51r ... Thick part 51t ... Thin part 52 ... Piezoelectric element 53 ... Elastic member 55 ... First filler 56 ... Second filler 57 ... Reinforcing material 58 ... Sound absorbing material 61 ... Terminal holding member 62 ... Internal terminal 63 ... External terminal 101 ... Ultrasonic sensor

Claims

A bottomed cylindrical case having a bottom provided at one end in the axial direction, an opening provided at the other end, and a side wall; and a piezoelectric element provided at the center of the inner surface of the bottom of the case; And a filler filled in the case,
The case is disposed at a central portion of the inner surface of the bottom portion at a thin portion including the arrangement position of the piezoelectric element, and at a peripheral portion of the thin portion of the inner surface of the bottom portion, and a thick portion having a thickness larger than that of the thin portion. And comprising
A stiffener higher than the bottom of the case is disposed on the thick part,
The said thick part is an ultrasonic sensor which continues over the circumference of the circumferential direction of the bottom part of the said case.
2. The ultrasonic sensor according to claim 1, wherein the reinforcing material has a size that covers the entire thick portion as viewed from the opening of the case.