JPH11281664A - Holding structure for piezoelectric element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce generation frequency of noise due to cracking of a piezoelectric element caused by concentration of stress through tightening of a bolt or outer temperature fluctuation. SOLUTION: Piezoelectric elements 3, 3 are clamped by a support 1 and mass bodies 4, 4 and secured by insertion a bolt 5 into through holes 1a, 4a. In such a holding structure for piezoelectric element, deformation clearances 1b, 4b are provided at the opening fringe of the through holes 1a, 4a in the support 1 and mass bodies 4, 4 where the piezoelectric elements 3, 3 face each other. Concentration of stress to the piezoelectric elements 3, 3 due to deformation of first and second holding members caused by tightening of the bolt can thereby be avoided and since cracking can be prevented on the periphery of the opening fringe of the piezoelectric element 3, generation frequency of noise can be suppressed when the holding structure is applied to an acceleration sensor, or the like.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric element holding structure applied to an acceleration sensor or the like.

[0002]

2. Description of the Related Art Conventionally, as a piezoelectric element holding structure of this kind, as shown in FIG. 5, a shear-type piezoelectric element 100 is disposed so as to be sandwiched between a support body 101 and a mass body 102, and respective through holes 100a, 100a. It is known that a bolt 103 is inserted through 101a and 102a and fastened with a nut to an end of the bolt 103 to hold the shear-type piezoelectric element 100 with a support body 101 and a mass body 102 (for example, Jiko Shoji). 61-165
No. 28).

[0003]

However, when a weak acceleration such as an earthquake is continuously observed for a long period of time by using a shearing type acceleration pickup to which such a piezoelectric element holding structure is applied, the outside air temperature may be reduced. There has been a problem that the frequency of noise generated by the acceleration pickup due to the fluctuation cannot be ignored.

That is, as shown in FIG. 5, when the mass body 102, the piezoelectric element 100, and the support body 101 are fastened with the bolt 103, the support body 101 or the mass body 102 is deformed. Through hole 100a of element 100
Stress acts intensively around the edge of the opening. Piezoelectric element 1
When stress concentrates on the periphery of the opening edge of the through-hole 100a, this portion is locally broken and a fine crack occurs. If the outside air temperature changes when such a crack occurs, the state of the crack changes, and noise is generated in accordance with the change.

When the mass body 102, the piezoelectric element 100, and the support 101 are fastened with bolts 103, the piezoelectric element 1
One side surface of the piezoelectric element 100 is in close contact with the mass body 102 over the entire surface, and the other side surface of the piezoelectric element 100 is in close contact with the support body 101 over the entire surface. In such a state, when the outside air temperature changes, the linear expansion coefficient of the mass body 102 is about ten times larger than the linear expansion coefficient of the piezoelectric element 100.
Is exerted by the mass body 102. When the stretching force is larger than the frictional force between the mass body 102 and the piezoelectric element 100, the piezoelectric element 100 extends beyond its own breaking limit, and cracks occur partially. Similarly, cracks occur in the piezoelectric element 100 also in relation to the support 101. Once a crack occurs in a part of the piezoelectric element 100, the state of the crack changes depending on the temperature, so that if the temperature changes, noise will occur.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to prevent stress concentration on a piezoelectric element due to tightening of bolts and fluctuations in the outside temperature. It is another object of the present invention to provide a piezoelectric element holding structure that can reduce the frequency of occurrence of noise caused by cracks generated in a piezoelectric element.

[0007]

According to a first aspect of the present invention, a piezoelectric element is sandwiched between a first holding member and a second holding member, and bolts are inserted through these through holes and fixed. In the piezoelectric element holding structure, a deformation relief portion is provided at an opening edge of a through hole of the first holding member and the second holding member facing the piezoelectric element.

According to a second aspect of the present invention, there is provided a piezoelectric element holding structure in which a piezoelectric element is sandwiched between a first holding member and a second holding member and bolts are inserted into these through holes and fixed. It is sandwiched between the first holding member and the second holding member via a spacer smaller than the outer shape.

[0009]

Embodiments of the present invention will be described below with reference to the accompanying drawings. Here, FIG. 1 is a cross-sectional view of a shearing type acceleration sensor to which the piezoelectric element holding structure according to claim 1 is applied, FIG. 2 is a perspective view of a shearing type piezoelectric element, and FIG.
FIG. 4 is a cross-sectional view of a shear-type acceleration sensor to which the piezoelectric element holding structure according to the first embodiment is applied, and FIG. 4 is a cross-sectional view of a compression-type acceleration sensor to which the piezoelectric element holding structure according to the first embodiment is applied.

As shown in FIG. 1, a shearing type acceleration sensor to which the piezoelectric element holding structure according to claim 1 is applied has a support 1, an insulating tube 2, a pair of piezoelectric elements 3, 3, a pair of masses 4, 4, a bolt 5, a nut 6, and an output terminal 7.

The piezoelectric elements 3 and 3 are respectively disposed on the side surfaces of the support 1, and the mass bodies 4 and 4 are disposed on the outer side surfaces of the piezoelectric elements 3 and 3. The bolt 5 penetrates through the support 1, the piezoelectric elements 3, 3, and the masses 4, 4. The nuts 6 are screwed onto the ends of the bolts 5 and tightened, whereby the piezoelectric elements 3 and 3 and the mass bodies 4 and 4 are fixed to the support 1.

The support 1 is made of a metal member and has a T-shaped cross section. In the upright portion, a through hole 1a for inserting the insulating tube 2 and the bolt 5 is formed.
Further, the support 1 expands due to the fluctuation of the outside air temperature at both opening edges of the through hole 1a, and the opening edge of the support 1
In order not to squeeze the opening edge of the through hole 3a,
Deformation relief portions 1b, 1b having a predetermined inner diameter and a predetermined depth are formed.

The insulating tube 2 comprises a bolt 5 and a mass body 4,
4 for maintaining insulation from the substrate 4 and made of a polymer material such as Teflon. As shown in FIG. 2, the piezoelectric element 3 is a shear-type piezoelectric element having a square plate shape. A through hole 3a is formed in the center of the piezoelectric element 3, and electrodes 3b and 3c are provided on both sides in the thickness direction. Here, the arrow a indicates the polarization direction.

As shown in FIG. 1, the mass members 4 and 4 are made of a metal member, have a substantially cylindrical shape, and have a through hole 4a for inserting a bolt 5 at the center. Also, at the opening edge of the through hole 4a where the masses 4 and 4 abut on the piezoelectric elements 3 and 3, the masses 4 and 4 expand due to the fluctuation of the outside air temperature, and the opening edges of the masses 4 and 4 In order to prevent the opening edge of the through hole 3a of the element 3 from being pressed, deformation relief portions 4b, 4b having a predetermined inner diameter and a predetermined depth are formed.

The operation of the piezoelectric element holding structure according to the first aspect will be described. In the piezoelectric element holding structure according to the first aspect, the support body 1 has the deformation relief portions 1b, 1b.
And the mass escapers 4b, 4 are also provided on the mass bodies 4, 4.
Since the b is provided, even if the periphery of the opening of the support 1 and the masses 4 and 4 is deformed by tightening the bolt 5, the vicinity of the opening of the through hole 3a of the piezoelectric element 3 is locally localized. There is no pressure.

Therefore, stress is not concentrated on the periphery of the opening of the through hole 3a of the piezoelectric elements 3 and 3 due to deformation of the support 1 and the masses 4 and 4.
The generation of cracks around the edge of the opening 3 can be prevented. Therefore, the frequency of occurrence of noise of the acceleration sensor can be suppressed.

As shown in FIG. 3, the acceleration sensor to which the piezoelectric element holding structure according to claim 2 is applied has a support 11, an insulating tube 2, four spacers 12, a pair of piezoelectric elements 3, 3, and a pair of piezoelectric elements. Masses 14, 14, Bolt 5, Nut 6
And an output terminal 7.

On the outer side surfaces of the piezoelectric elements 3, 3, a mass body 1 is provided.
4, 14 are arranged. The bolt 5 is attached to the support 11,
The piezoelectric elements 3, 3 penetrate the mass bodies 14, 14. The nuts 6 are screwed onto the ends of the bolts 5 and tightened, so that the piezoelectric elements 3 and 3 and the mass bodies 14 and 14
Fixed to 1.

The support 11 is made of a metal member and has a T-shaped cross section. The upright portion is provided with a through hole 11a for inserting the insulating tube 2 and the bolt 5. The spacer 12 is a disk-shaped thin metal plate having a smaller outer diameter than the piezoelectric elements 3 and 3 and a through hole formed in the center, for example, a thin phosphor bronze plate.

The spacers 12 are arranged between the support 11 and the piezoelectric elements 3 and between the piezoelectric elements 3 and the masses 14. The mass bodies 14, 14 are made of a metal member,
It has a substantially columnar shape, and has a through hole 14b for inserting the bolt 5 in the center.

The operation of the above-structured piezoelectric element holding structure according to claim 2 will be described. In the case of an acceleration sensor to which the piezoelectric element holding structure according to claim 2 is applied,
Since the spacers 12 are disposed on both sides of the piezoelectric elements 3, both sides of the piezoelectric elements 3 are in close contact with the spacer 12.

Since the piezoelectric elements 3 and 3 are in close contact with the spacer 12, the support 11 is directly provided without the spacer 12.
And the contact area of the piezoelectric elements 3, 3 is smaller than that in the case where the piezoelectric elements 3, 3 are held in contact with the mass bodies 14, 14, and even when the outside air temperature changes, the absolute force of extending the piezoelectric elements 3, 3 is increased. The value decreases. Therefore, the occurrence of cracks in the piezoelectric elements 3 can be prevented beforehand, and the frequency of occurrence of noise in the acceleration sensor can be suppressed.

In the above embodiment, the case where the present invention is applied to the shear type acceleration sensor using the shear type piezoelectric elements 3 and 3 has been described. However, the piezoelectric element holding structure according to the present invention is not limited to this. It can be applied to other piezoelectric elements.

For example, as shown in FIG. 4, a compression type acceleration sensor using a compression type piezoelectric element may be used. Here, reference numeral 21 denotes a support having a screw hole 21a at the center thereof. A deformation relief portion 21b is provided at the opening edge of the screw hole 21a.
Is formed.

The pair of compression-type piezoelectric elements 22, 22 are arranged so that the polarization directions thereof are opposite to each other.
Further, a common electrode plate 23 is provided between the two compression type piezoelectric elements 22 and 22.

The mass body 24 and the support body 21 are arranged so as to sandwich the two compression-type piezoelectric elements 22 and 22 therebetween.
The bolt 25 passes through a through hole 24 a formed in the mass body 24, the pair of compression piezoelectric elements 22, 22 and the common electrode plate 23 and is screwed into the screw hole 21 a of the support 21. 26 is an insulating tube. The piezoelectric element holding structure shown in FIG. 4 also has the same function and effect as the shearing type acceleration sensor shown in FIG.

Further, in the above-described embodiment, the countermeasure-shaped portions of the deformation relief portions 1b and 4b of the piezoelectric element holding structure according to the first aspect have been described. Other shapes may be used according to the size and shape. For example, it may be hollowed out in a conical shape, or may be rounded in two steps.

Further, in the above embodiment, the case where the piezoelectric element holding structure according to claim 1 or 2 is applied to an acceleration sensor has been described. However, the piezoelectric element holding structure according to the present invention is not limited to this.
As long as the structure is sandwiched between two holding members and bolts are penetrated and fixed thereto, the present invention can be applied to a device having another piezoelectric element, for example, a force sensor used for an impulse hammer.

[0029]

As described above, according to the piezoelectric element holding structure of the first aspect, the first holding member and the second holding member are provided with the deformation relief portions, so that the first holding member accompanying the bolt tightening is provided. In addition, since stress concentration on the piezoelectric element due to deformation of the second holding member is avoided, and generation of cracks around the opening edge of the piezoelectric element can be prevented, the frequency of occurrence of noise when applied to an acceleration sensor or the like can be suppressed.

According to the piezoelectric element holding structure according to the second aspect, cracks in the piezoelectric element caused by elongation of the first holding member and the second holding member due to a change in the outside air temperature can be prevented. In this case, the frequency of occurrence of noise can be suppressed.

[Brief description of the drawings]

FIG. 1 is a sectional view of a shearing type acceleration sensor to which a piezoelectric element holding structure according to claim 1 is applied.

FIG. 2 is a perspective view of a shear-type piezoelectric element.

FIG. 3 is a sectional view of a shearing type acceleration sensor to which the piezoelectric element holding structure according to claim 2 is applied.

FIG. 4 is a sectional view of a compression-type acceleration sensor to which the piezoelectric element holding structure according to claim 1 is applied.

FIG. 5 is a sectional view of a main part of a conventional piezoelectric element holding structure.

[Explanation of symbols]

1,11,21 ... Support (first holding member), 1a, 3
a, 4a, 11a, 14a, 24a ... through-hole, 1b, 4
b, 21b: deformation escape portion, 2, 26: insulating tube, 3
... Shear type piezoelectric element, 3b, 3c ... Electrodes, 4, 14, 24
... Mass (second holding member), 5, 25 bolt, 6 nut, 7 output terminal, 12 spacer, 22 compression piezoelectric element, 23 electrode plate.

Claims (2)

[Claims] In a piezoelectric element holding structure in which a piezoelectric element is sandwiched between a first holding member and a second holding member and bolts are inserted through these through holes and fixed, the first holding member and the piezoelectric element facing each other are connected to each other. A piezoelectric element holding structure, wherein a deformation relief portion is provided at an opening edge of a through hole of a second holding member. 2. A piezoelectric element holding structure in which a piezoelectric element is sandwiched between a first holding member and a second holding member and bolts are inserted through these through holes and fixed, wherein the piezoelectric element is interposed by a spacer smaller than its outer shape. A piezoelectric element holding structure sandwiched between the first holding member and the second holding member.