JP3129963B2 - Piezoelectric sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] The present invention relates to a piezoelectric sensor.

[0002]

2. Description of the Related Art Piezoelectric sensors of this type are used for detecting acceleration and impact in, for example, hard disk drives, CD players, airbag systems, electronically controlled suspension systems, etc., and have a high degree of reliability. At the same time, it is extremely important that the number of parts is small and the size is small.

As examples of known documents that disclose technologies meeting such demands, Japanese Patent Application Laid-Open Nos. 7-202283 and 8-
No. 29447 can be mentioned. In these prior arts, a concave portion and an element mounting portion are provided in a base member, and a piezoelectric element is fixed to the element mounting portion. The piezoelectric element is arranged on the element mounting portion such that a gap is formed between the piezoelectric element and the bottom surface of the concave portion. The element mounting portion is constituted by a concave groove.

In this type of piezoelectric sensor, when it is necessary to detect both impacts in the horizontal and vertical directions of the sensor, the piezoelectric element is mounted at a certain angle with respect to the base member. In such a case, an angle is given to the piezoelectric element by inclining the side surface of the concave groove serving as the element mounting portion and arranging the piezoelectric element along the side surface.

As means for mounting a piezoelectric element at a certain angle with respect to a base member, Japanese Patent Laid-Open No. 8-29447 discloses a method in which only one side surface of a concave groove forming an element mounting portion is formed as an inclined surface. A structure is employed in which an angle according to the inclination angle of the inclined surface is given to the piezoelectric element. The other side opposite to the one side does not have an inclination angle and is a substantially vertical plane.
Due to the structure of the concave groove, the base member becomes left-right asymmetric, and in order to give the piezoelectric element a tilt in almost the same direction,
In the process, it is necessary to uniformly align the directions of the base members so that the inclined surfaces of the concave grooves are located on the left side, for example.

However, in this kind of piezoelectric sensor, miniaturization is an important issue in view of its application. In an actual product, the shape of the concave groove provided on the base member is visually recognized by the naked eye. It is a small part that is difficult to perform. The cross-sectional diameter of the piezoelectric element is about the same as that of the pencil lead.

For this reason, in the process, it is not easy to make the orientation of the base member uniform so that the inclined surface of the concave groove is positioned on the left side, for example.

[0008]

SUMMARY OF THE INVENTION An object of the present invention is to provide a piezoelectric sensor capable of reliably detecting acceleration or impact with a simple structure.

Another object of the present invention is to provide a piezoelectric sensor capable of detecting both impacts in the horizontal and vertical directions of the sensor.

Another object of the present invention is to provide a piezoelectric sensor having no directivity with respect to the inclination of the piezoelectric element with respect to the base member.

[0011]

In order to solve the above-mentioned problems, a piezoelectric sensor according to the present invention includes a base member and a piezoelectric element. The base member has a concave portion and a concave groove serving as an element mounting portion. The recess is provided on one surface of the base member. The concave groove has a bottom surface slightly higher than a bottom portion of the concave portion and a position lower than the one surface of the base member. The concave groove further has both side surfaces rising from the bottom surface inclined at substantially the same obtuse angle with respect to the bottom surface. The piezoelectric element is received by one of the side surfaces in the concave groove, and is arranged to extend above the concave portion.

Preferably, the concave groove has a gouge at a corner where the bottom surface and the both side surfaces intersect.

[0013] As described above, the base member has a groove on one surface side as an element mounting portion, and the groove has a bottom surface slightly higher than the bottom of the concave portion provided on the base member, and
It is at a position lower than one surface of the base member. The piezoelectric element is
It is received in the groove and extends above the recess. According to this structure, when an acceleration or an impact is received, the piezoelectric element operates on the concave portion without receiving any interference from the base member, and the applied acceleration or the impact is detected.

[0014] Further, both side surfaces rising from the bottom surface of the groove are inclined at substantially the same obtuse angle with respect to the bottom surface, and the piezoelectric element is received by one of the two side surfaces in the groove. According to this structure, it is possible to detect both impacts from the horizontal axis direction and the vertical axis direction of the sensor.

Since both side surfaces are inclined at substantially the same obtuse angle with respect to the bottom surface, the piezoelectric element is fixed at substantially the same angle, regardless of which side of the groove is provided with the piezoelectric element. . Therefore, a piezoelectric sensor having no directionality can be obtained with respect to the inclination of the piezoelectric element with respect to the base member.

In a preferred embodiment, the concave groove has a gouge at a corner where the bottom surface and both side surfaces intersect. In the preferred embodiment, when the gouge fixes the piezoelectric element with an adhesive, the adhesive receives an extra adhesive. Functions as a pool. For this reason, the piezoelectric element does not float due to the adhesive, and the piezoelectric element can be securely fixed at a correct position.

[0017]

FIG. 1 is a perspective view showing the appearance of a piezoelectric sensor according to the present invention, FIG. 2 is a perspective view of the piezoelectric sensor shown in FIG. 1 with a part of a lid removed, and FIG. FIG. 4 is an exploded perspective view showing a combination with an element, FIG. 4 is a plan view of the piezoelectric sensor shown in FIGS. 1 to 3 with a lid removed, FIG. 5 is a cross-sectional view taken along line A5-A5 in FIG.
4 is a cross-sectional view taken along line A6-A6 in FIG. 4, and FIG. 7 is a cross-sectional view taken along line A7-A7 in FIG.

The piezoelectric sensor according to the present invention has a base member 1
And a piezoelectric element 2. Reference numeral 3 is a lid.

The base member 1 has a concave portion 11 and a concave groove 12 serving as an element mounting portion. The recess 11 is provided on one surface of the base member 1. The concave groove 12 has a bottom surface 121.
Is slightly higher than the bottom 111 of the concave portion 11 and lower than one surface of the base member 1.

Further, both side surfaces 122 and 123 rising from the bottom surface 121 of the concave groove 12 are inclined at substantially the same obtuse angle with respect to the bottom surface 121. The piezoelectric element 2 is received by one of the side surfaces 122 and 123 in the concave groove 12 and is arranged to extend above the concave portion 11.

As described above, the base member 1 has, on one surface side, the concave groove 12 serving as an element mounting portion. The concave groove 12 has a bottom surface 121 larger than a bottom portion 111 of the concave portion 11 provided in the base member 1. It is slightly higher and lower than one surface of the base member 1. The piezoelectric element 2 is received in the concave groove 12 and is arranged to extend above the concave part 11. According to this structure, when receiving an acceleration or a shock, the piezoelectric element 2 responds on the concave portion 11 without receiving any interference from the base member 1, and the acceleration or the shock applied thereby is detected.

The concave groove 12 further has both side surfaces 122 and 123 rising from the bottom surface 121 inclined at substantially the same obtuse angle with respect to the bottom surface 121. , 123 is received by the side surface 122. According to this structure, it is possible to detect both impacts from the horizontal axis direction and the vertical axis direction of the sensor.

Both side surfaces 122 and 123 are inclined at substantially the same obtuse angle with respect to the bottom surface 121. According to this structure, the piezoelectric element 2 is fixed at substantially the same angle regardless of which side of the side face 122 or 123 of the groove 12 is mounted. For this reason, the piezoelectric element 2 with respect to the base member 1
With respect to the inclination of the piezoelectric sensor, a piezoelectric sensor having no directionality can be obtained.

Between the piezoelectric element 2 and the concave groove 12, for example,
It is desirable to use an insulating adhesive 5 for joining. By doing so, the impact resistance can be further improved.

Further, in the embodiment, the concave groove 12 has a gouge 124 at a corner where the bottom surface 121 and the side surfaces 122 and 123 intersect. The hollow portion 124 is formed by the piezoelectric element 2
When fixing with the adhesive 5, it functions as an adhesive pool that receives the surplus. For this reason, the piezoelectric element 2 does not float due to the buoyancy of the adhesive 5, and the piezoelectric element 2 can be reliably fixed at a correct position.

Further, the concave groove 12 has a convex
Five. This convex portion 125 has both side surfaces 122-12.
It is provided substantially at the center between the three. The bottom of the piezoelectric element 2 is received by the projection 125. Therefore, the support stability of the piezoelectric element 2 is improved.

In the embodiment, when the width direction W and the length direction L are imagined on one surface of the base member 1,
The recess 11 is provided at or near the center in the length direction L. The piezoelectric element 2 has a central portion, a central portion, or one side portion fixed to the concave groove 12, is disposed on the concave portion 11 along the length direction L, and has a gap g with the bottom portion 111 of the concave portion 11. ing.

The base member 1 has at least two terminal conductors 13 and 14. The first terminal conductor 13 is provided on one end side in the length direction L of the base member 1, and the second terminal conductor 14 is provided on the other end side in the length direction L. The piezoelectric element 2 is provided with conductive adhesives 41 and 42 on the terminal conductors 13 and 14.
It is conducting by. With such a structure, the first terminal conductor 13 and the second terminal conductor 1 at both ends in the length direction L are required for mounting on a circuit board or other external device.
4, a strong and stable mounting structure can be realized by surface mounting.

Further, the first terminal conductor 13 has its lead conductor 131 guided to one side of the concave groove 12, and the second terminal conductor 14 has its lead conductor 141 connected to the other side of the concave groove 12. You are being led. The piezoelectric element 2 has its electrodes 21, 21
Are connected and fixed to the lead conductors 131 and 141, respectively. With such a structure, the piezoelectric element 2 can be connected to the terminal conductors 13 and 14 via the lead conductors 131 and 141 arranged on both sides.

The concave groove 12 for mounting the piezoelectric element 2 is W-shaped in the embodiment. The bottom surface 121 of the W-shaped concave groove 12 is slightly higher than the bottom 111 of the concave portion 11, and
An offset is provided so as to be lower than one surface of the base member 1. With the above structure, the piezoelectric element 2 is
, The necessary gap g is secured between the piezoelectric element 2 and the bottom 111 of the recess 11 by utilizing the step between the bottom 121 of the recess 12 and the bottom 111 of the recess 11. The piezoelectric element 2 can be positioned or fixed using a step between the bottom surface of the concave groove 12 and one surface of the base member 1.
Further, by placing the piezoelectric element 2 along the wall of the W-shaped concave groove 12, a constant angle is maintained.

Furthermore, since the W-shaped concave groove 12 is necessarily symmetrical, the piezoelectric element 2 can be mounted at substantially the same angle on either side of the both side surfaces 122 and 123. Therefore, in the process of incorporating the piezoelectric element 2 into the base member 1, it is not necessary to align the directions of the base member 1.

When the concave groove 12 is W-shaped, a gouge 124 which becomes a pool of the adhesive is inevitably generated, so that the excess adhesive 4 is absorbed inside the gouge 124. Therefore, the piezoelectric element 2 can be reliably fixed.

The base member 1 is formed of an electrically insulating ceramic or plastic. Ceramic materials that can be used include alumina, forsterite, steatite and the like. When using plastic materials,
It is desirable to use one having high heat resistance.

First terminal conductor 13 and second terminal conductor 14
Is formed by printing, sputtering, vapor deposition, or a combination of these with plating. The first terminal conductor 13 and the second terminal conductor 14 are formed to extend from one surface side of the base member 1, pass through the side surface, and further reach the back surface.

A preferred example of the piezoelectric element 2 is a bimorph piezoelectric element. The figure shows a bimorph piezoelectric element, which has a pair of piezoelectric elements 20. A pair of piezoelectric elements 2
Nos. 0 and 20 have electrodes 21 and 22 on both surfaces of the piezoelectric element, and are overlapped so that the electrode 22 of one piezoelectric element 20 and the electrode 22 of the other piezoelectric element 20 are in surface contact with each other. Are joined. A pair of piezoelectric elements 20, 20
Are superimposed so that the polarization directions are opposite to each other in order to cancel noise due to temperature fluctuation. In another example, the pair of piezoelectric elements 20 may be overlapped and coupled so that the polarization directions are substantially the same. In this case, the commonly connected electrodes are connected, for example, to ground. A configuration is often adopted in which a diaphragm made of a conductive metal elastic plate is interposed between commonly connected electrodes, and the diaphragm is connected to the ground. A piezoelectric sensor using a bimorph piezoelectric element is disclosed in JP-A-64-72012,
It is known in U.S. Pat.

The cover 3 is made of an electrically insulating ceramic or plastic. Ceramic materials that can be used include alumina, forsterite, steatite and the like. When using a plastic material, it is desirable to use a high heat-resistant material. The lid 3 is arranged on one surface side of the base member 1 so as to surround the piezoelectric element 2, and the contact end surface is joined to the base member 1 by bonding or other means. It is desirable to seal the periphery of the joining surface with resin.

Next, a modification of the present invention will be described. In the embodiment shown in FIG. 8, the bottom surface 121 of the concave groove 12 is substantially flat, and both side surfaces 122 and 123 are inclined at substantially the same obtuse angle with respect to the flat bottom surface 121.

The embodiment shown in FIG. 9 shows an example in which a projection 125 is added to a substantially central portion of the bottom surface 121 with respect to the embodiment shown in FIG.

In the embodiment shown in FIG. 10, the concave groove 12 is arranged to be offset from one end of the base member 1.

In the embodiment shown in FIG. 11, the grooves 12 are arranged on both sides of the recess 11 provided in the base member 1.

In the embodiment shown in FIG.
Are arranged with the recess 11 therebetween, and the recess 1 is
1 is provided.

FIG. 13 is an electric circuit diagram in a use state of the piezoelectric sensor according to the present invention. As shown, a resistor 6 is electrically connected in parallel with the piezoelectric element 2. According to this configuration, a high-pass filter is formed by the capacitance C of the piezoelectric element 2 and the resistor 6, whereby unnecessary low-frequency noise can be cut off. The resistor 6 may be provided on, for example, the base member 1 of the piezoelectric sensor. This eliminates the need to provide the resistor 6 externally. FIG. 14 shows a specific example. In FIG. 14, the resistor 6 is provided on the surface of the base member 1.

[0043]

As described above, according to the present invention, the following effects can be obtained. (A) It is possible to provide a piezoelectric sensor capable of reliably detecting acceleration or impact with a simple structure. (B) It is possible to provide a piezoelectric sensor capable of detecting both impacts from the horizontal axis direction and the vertical axis direction of the sensor. (C) It is possible to provide a piezoelectric sensor having no directionality with respect to the inclination of the piezoelectric element with respect to the base member.

[Brief description of the drawings]

FIG. 1 is an external perspective view of a piezoelectric sensor according to the present invention.

FIG. 2 is a perspective view of the piezoelectric sensor shown in FIG. 1 with a part of a lid removed.

FIG. 3 is an exploded perspective view showing a combination of a base member and a piezoelectric element.

FIG. 4 is a plan view of the piezoelectric sensor shown in FIGS. 1 to 3 with a part of a lid removed.

FIG. 5 is a sectional view taken on line A5-A5 of FIG. 4;

FIG. 6 is a cross-sectional view taken along line A6-A6 of FIG.

FIG. 7 is a sectional view taken along line A7-A7 in FIG. 4;

FIG. 8 is a sectional view of a base member showing another embodiment of the piezoelectric sensor according to the present invention.

FIG. 9 is a cross-sectional view of a base member showing another embodiment of the piezoelectric sensor according to the present invention.

FIG. 10 is a plan view of a base member showing another embodiment of the piezoelectric sensor according to the present invention.

FIG. 11 is a plan view of a base member showing another embodiment of the piezoelectric sensor according to the present invention.

FIG. 12 is a plan view of a base member showing another embodiment of the piezoelectric sensor according to the present invention.

FIG. 13 is an electric circuit diagram in a use state of the piezoelectric sensor according to the present invention.

FIG. 14 is a plan view of a base member showing still another embodiment of the piezoelectric sensor according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 base member 11 concave portion 12 concave groove serving as element mounting portion 121 bottom surface of concave groove 122 side surface of concave groove 123 side surface of concave groove 124 recessed portion 125 convex portion 2 piezoelectric element

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-9-113533 (JP, A) JP-A-8-166307 (JP, A) JP-A-9-203745 (JP, A) JP-A 9-113 243447 (JP, A) JP-A-8-29447 (JP, A) JP-A-7-202283 (JP, A) JP-A-5-133974 (JP, A) JP-A-57-139664 (JP, A) JP-A-2-45430 (JP, U) JP-A 63-228 (JP, U) (58) Fields investigated (Int. Cl. ⁷ , DB name) G01P 15/00 G01P 15/09 G01H 11/08 G01L 1/16 G11B 33/08

Claims (5)

(57) [Claims] 1. A piezoelectric sensor including a base member and a piezoelectric element, wherein the base member has a concave portion and a concave groove serving as an element mounting portion, and the concave portion is a surface of the base member. The concave groove is provided at a position where the bottom surface is slightly higher than the bottom of the concave portion and lower than the one surface of the base member,
Both side surfaces rising from the bottom surface are inclined at substantially the same obtuse angle with respect to the bottom surface, and the piezoelectric element is received by one of the both side surfaces in the concave groove, and is arranged to extend above the concave portion. Piezoelectric sensor. 2. The piezoelectric sensor according to claim 1, wherein the concave groove has a gouge at a corner where the bottom surface and the both side surfaces intersect. 3. The piezoelectric sensor according to claim 1, wherein the concave groove has a convex portion on the bottom surface, and the convex portion is provided at a substantially central portion between the two side surfaces. Piezoelectric sensor. 4. The piezoelectric sensor according to claim 1, 2 or 3, wherein the element mounting portion is configured such that when the width direction and the length direction are imagined on the one surface, the length of the concave portion is in the length direction. A piezoelectric sensor provided near the center or on one side in the length direction. 5. The piezoelectric sensor according to claim 1, wherein the base member has at least two terminal conductors, and the first terminal conductor has a lead conductor of the element. The lead terminal of the second terminal conductor is led to the other side of the element mounting portion, and the electrode of the piezoelectric element is connected to each of the lead conductors. A piezoelectric sensor that is connected and fixed.