JP2780594B2 - Acceleration sensor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor, and more particularly, to a structure of a bimorph detecting element used for constructing the acceleration sensor.

[0002]

2. Description of the Related Art Hitherto, some acceleration sensors have been constructed by incorporating a piezoelectric element. As this kind of piezoelectric element, a bimorph type so-called double-ended beam structure as shown in FIG. Detection element (hereinafter referred to as detection element)
It is common to use ten. That is, the detection element 10 is provided with a pair of piezoelectric ceramic plates 13 each having a strip shape and a signal extraction electrode 11 and an intermediate electrode 12 formed on each of the main surfaces thereof. , And each of the piezoelectric ceramic plates 13 is polarized in a direction (indicated by arrows X and Y in the drawing) opposite to the other side along the plate thickness direction. .

[0003] Both ends along the longitudinal direction of the detection element 10 are fixed and supported by a pair of holding parts 14 having a U-shape in a side view, and a signal formed on each piezoelectric ceramic plate 13 is formed. Each of the extraction electrodes 11 is connected to each of the external extraction electrodes 15 and 16 formed at different end faces of the sandwiching parts 14 and the case parts (not shown) attached to these upper and lower positions. . The shape of the holding component 14 is such that when the acceleration G acts on the whole of the holding component 14 and the case component, the detection element 10 that is deformed by the inertial force accompanying the action of the acceleration G This is to secure the allowance for the bending.

On the other hand, in recent years, there has been a demand for further downsizing of the acceleration sensor, and thus it is necessary to reduce the size of the detection element itself. However,
If the detection element 10 having the double-supported beam structure is directly reduced in size, the deformation during the action of the acceleration G becomes small, and the amount of generated charges due to this deformation becomes too small. As a result, the detection sensitivity is greatly reduced. . Therefore, an acceleration sensor having a high detection sensitivity using a cantilever structure that can be more greatly deformed when the acceleration G having the same magnitude acts, for example, a detection element 20 having a structure as shown in FIG. Configuration has begun to take place.

That is, the detecting element 20 has a pair of piezoelectric ceramic plates 21 having the same structure as the detecting element 10 but having a shorter dimension along the longitudinal direction. Are fixedly supported by a pair of holding parts 14. Each of the signal extraction electrodes 11 formed on each piezoelectric ceramic plate 21 of the detection element 20 is connected to the external extraction electrodes 15 and 16 formed separately on the same end face of the holding component 14 and the case component. Connected to each. Since the entire structure of the detection element 20 is not basically different from that of the detection element 10, parts that are the same as those in FIG. 3 are denoted by the same reference numerals in FIG. 4, and the description thereof is omitted.

[0006]

By the way, when manufacturing the detection element 10 having the double-supported beam structure, as shown in FIG. 5, the electrode patterns (signals shown in FIG. (Not shown) are formed on each of the main surfaces in advance, a ceramic parent substrate 17 for the piezoelectric ceramic plate 13, and a clamping component parent substrate 18 in which a concave groove having a predetermined width is formed at each predetermined position on the inner surface side. After each of them is prepared, and each of the sandwiched component parent substrates 18 is applied from the outside of each of the ceramic parent substrates 17 disposed opposite to each other with the electrode pattern serving as the intermediate electrode 12 therebetween, and joined together,
Generally, these are cut along a predetermined cutting line S.

When manufacturing the cantilevered detector element 20, the same manufacturing procedure as that of the cantilevered beam structure is followed. In this case, as shown by a virtual line in FIG. A through-groove 2 having a predetermined width for making the size of the piezoelectric ceramic plate 21 shorter than that of the piezoelectric ceramic plate 13.
2 must be formed in advance for each predetermined position of the ceramic parent substrate 23. Therefore, it takes a lot of trouble to prepare the ceramic parent substrate 23 in which the through groove 22 is formed. Also, unless the ceramic parent substrates 23 having the through-grooves 22 formed therein and the sandwiching component parent substrate 18 with respect to the ceramic parent substrates 23 are accurately positioned, a cantilever structure may not be possible. In terms of point, it was also troublesome.

Furthermore, when the cantilever structure is employed, the impact resistance is inferior to that of the double-support structure, and it is inevitable that the strength becomes weak. In addition, in the detection element 20 having a cantilever structure,
Each of the signal extraction electrodes 11 is intensively drawn out on the same end face of the holding component 14 and the case component,
As a result of being different from ordinary electronic components, there has been an inconvenience that a wiring pattern needs to be changed on the wiring board side on which the acceleration sensor is mounted.

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and an object of the present invention is to provide an acceleration sensor capable of realizing a great improvement in production efficiency while improving detection sensitivity and miniaturization. And

[0010]

SUMMARY OF THE INVENTION An acceleration sensor according to the present invention comprises a pair of piezoelectric ceramic plates, each of which has a strip shape, and on which a signal extraction electrode and an intermediate electrode are formed on respective main surfaces, and The detection element is formed by fixing both ends along the longitudinal direction of a detection element in which the intermediate electrodes on the piezoelectric ceramic plate are joined face-to-face with each other and integrated. Is divided into three parts separated by a boundary line in which the stress generated by the piezoelectric element changes, and the central part and the end part are polarized in the directions opposite to each other along the thickness direction, while both piezoelectric ceramics are polarized. The directions of polarization in the central portion and the end portions of the plate are different from each other.

[0011]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is an external perspective view showing only a detection element used when constructing the acceleration sensor according to the present embodiment. FIG. 2 is a diagram schematically showing a deformation state of the detection element when an acceleration is applied. It is a figure, and the code | symbol 1 in these figures is a detection element made into the doubly supported structure. In addition,
In FIGS. 1 and 2, parts which are the same as those in FIGS. 3 and 4 are denoted by the same reference numerals. In addition, since the manufacturing procedure of the detection element 1 is the same as that of the detection element 10 according to the conventional example, the description is omitted here.

The detecting element 1 according to the present embodiment is provided with a pair of piezoelectric ceramic plates 4 each having a strip shape and a thin film signal extracting electrode 2 and an intermediate electrode 3 formed on each of the main surfaces. The two piezoelectric ceramic plates 4 are integrated by joining the intermediate electrodes 3 face-to-face, and along the longitudinal direction of the detection element 1 like the detection element 10 having a double-supported beam structure in the conventional example. Both end edges are fixed and supported by a pair of holding parts 14 having a “U” shape in side view. The longitudinal region of each of the piezoelectric ceramic plates 4 constituting the detection element 1 is the acceleration G
Are divided into three parts 4a and 4b divided by a boundary line L (described later) in which the stress generated by the action of the center part 4a and the end part 4 are divided.
b are opposite to each other along the thickness direction of each piezoelectric ceramic plate 4 (in the figure, arrows A, B and C, D
).

At this time, the central portions 4a of the two piezoelectric ceramic plates 4 which are integrated with each other to form the detecting element 1 are formed.
And polarization directions A, B and C between the end portions 4b,
Each of D is different from each other. That is, for example, the polarization directions A and C at the central portion 4a of each piezoelectric ceramic plate 4 are inwardly approaching each other, while the polarization directions B and D at both end portions 4b are outwardly away from each other. Orientation. Each of the signal extraction electrodes 2 formed on each of the piezoelectric ceramic plates 4 has an external component formed for a different end face of the holding component 14 and a case component (not shown) attached to the upper and lower positions thereof. It is connected to each of the extraction electrodes 15 and 16.

Here, the boundary line L of the stress change which divides the longitudinal region of each piezoelectric ceramic plate 4 into three portions 4a and 4b, that is, the stress generated in each piezoelectric ceramic plate 4 by the action of the acceleration G. Referring to FIG. 2, a description will be given of a boundary line L of change classified into “pull” and “compression”.

First, when an acceleration G acts on the entire acceleration sensor, a holding component 1 for fixing and supporting the detection element 1 is provided.
The acceleration G directly acts on the case 4 and the case component, and both the holding component 14 and the case component try to move along the direction of action of the acceleration G. However, even in this case, since the acceleration G does not directly act on the detection element 1, the detection element 1 tries to keep the state before the acceleration G acts, and this detection element 1 , An inertial force generated due to the action of the acceleration G acts. Therefore, while each end portion 4b of each piezoelectric ceramic plate 4 constituting the detection element 1 tries to move together with the holding parts 14 for fixing and supporting them, each center portion 4a tries to remain at the initial position, The detection element 1 is deformed so as to have a curved shape (upward convex shape in the figure) bent toward the side of the action of the acceleration G.

Therefore, as shown in FIG. 2, the central portion 4a of the piezoelectric ceramic plate 4 located on the outer side in the bending direction (upper side in the figure) has a tensile stress Pt and an end portion 4a.
b, the compressive stress Pc appears on the center portion 4a of the piezoelectric ceramic plate 4 located on the inner side (lower side in the drawing) in the bending direction.
, A tensile stress Pt appears. That is,
In the detection element 1 according to the present embodiment, the stress appearing along the longitudinal region of each piezoelectric ceramic plate 4 changes from “tensile” to “compressed” and from “compressed” to “tensile”.
The boundary that changes to is the boundary line L where the stress changes,
The central portion 4a and the end portion 4b of each piezoelectric ceramic plate 4 divided by these boundary lines L are polarized according to directions A, B and C, D opposite to each other. Note that the boundary line L can be known by an experiment using a finite element method, which is one of numerical analysis methods, for example.

Next, the operation and action of the detection element 1 having the above structure will be described.

The acceleration G acts on the acceleration sensor,
When the deformation as shown in FIG. 2 occurs in the detecting element 1, the direction A of the polarization and the tensile stress Pt are applied to the outer main surface of the central portion 4a of the piezoelectric ceramic plate 4 located on the outer side in the bending direction of the detecting element 1. And a positive (+) charge is generated on the outer main surface of the end portion 4b from the relationship between the polarization direction B and the compressive stress Pc. Therefore, the positive charges generated on the outer main surfaces of the central portion 4a and the end portion 4b of the piezoelectric ceramic plate 4 are transmitted from the signal extraction electrode 2 to the external extraction electrode 15 while strengthening each other. Further, at this time, a negative (-) charge is generated on the outer main surface of the central portion 4a of the piezoelectric ceramic plate 4 located on the inner side in the bending direction of the detection element 1 due to the relationship between the direction of polarization C and the compressive stress Pc. Negative charges are also generated on the outer main surface of the end portion 4b due to the relationship between the direction of polarization D and the tensile stress Pt.
To the external extraction electrode 16.

Therefore, according to the detecting element 1, the amount of electric charge generated when the acceleration G acts is increased despite the fact that the detecting element 1 has the same doubly supported structure as the conventional detecting element 10. As a result, even if the size is reduced, the detection sensitivity does not decrease. When the acceleration G is applied, positive or negative charges different from those of the outer main surfaces are generated on the inner main surfaces of the respective piezoelectric ceramic plates 4, but these charges are canceled each other through the intermediate electrode 3. In other words, it has no external effect.

Incidentally, in each of the piezoelectric ceramic plates 13 constituting the detection element 10 having the conventional double-supported beam structure, the polarization directions X and Y over the entire longitudinal direction region are the same as shown in FIG. Therefore, inconvenience has arisen. That is, although not shown, the acceleration G
In the case where acts, the stress state as shown in FIG. 2 appears also in the piezoelectric ceramic plate 13 constituting the detecting element 10 as in the case of this embodiment. However, since the directions X and Y of polarization of each piezoelectric ceramic plate 13 of the detection element 10 are the same, a positive charge is applied to the central portion of the piezoelectric ceramic plate 4 located outside the deformed detection element 1 in the bending direction. When a negative charge is generated at the end portion of the piezoelectric ceramic plate 4 located at the inner side in the bending direction, a negative charge is generated at the end portion of the piezoelectric ceramic plate 4. Respectively occur. For this reason, the positive and negative charges generated on the same main surface of each piezoelectric ceramic plate 13 cancel each other, and as a result, the detection sensitivity is reduced.

[0022]

As described above, according to the detection element of the acceleration sensor according to the present invention, the amount of electric charge generated during the operation of acceleration increases despite the fact that the detection element has a doubly supported structure. Even if the size is reduced, the detection sensitivity does not decrease. Therefore, it is not necessary to incorporate the detecting element having the cantilever structure into the acceleration sensor after employing the detecting element having the cantilever structure, and it is possible to avoid various problems caused when the detecting element having the cantilever structure is employed. as a result,
The effect of achieving a significant improvement in production efficiency while improving the detection sensitivity and reducing the size can be obtained.

[Brief description of the drawings]

FIG. 1 is an external perspective view illustrating a detection element of an acceleration sensor according to an embodiment.

FIG. 2 is an explanatory diagram schematically showing a deformation state of a detection element when an acceleration is applied.

FIG. 3 is an external perspective view showing a detection element having a doubly supported structure according to a conventional example.

FIG. 4 is an external perspective view showing a detection element having a cantilever structure according to a conventional example.

FIG. 5 is an exploded perspective view showing a procedure for manufacturing the detection element.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Detection element (bimorph type detection element) 2 Signal extraction electrode 3 Intermediate electrode 4 Piezoelectric ceramic plate 4a Central part 4b End part L Boundary line G Acceleration

Claims (1)

(57) [Claims] 1. A pair of piezoelectric ceramic plates (4) each having a strip shape and a signal extraction electrode (2) and an intermediate electrode (3) formed on each of the main surfaces, and
Bimorph-type detection element (1) in which intermediate electrodes (3) on these piezoelectric ceramic plates (4) are joined face-to-face and integrated.
An acceleration sensor having a structure in which both end edges along a longitudinal direction of the piezoelectric sensor are fixedly supported, wherein a boundary line in which a stress generated by the action of the acceleration (G) changes in each longitudinal region of the piezoelectric ceramic plate (4). Three parts (4a, 4b) divided by (L)
And the central portion (4a) and the end portion (4b) are polarized in directions opposite to each other (A, B and C, D) along the plate thickness direction, while both piezoelectric ceramic plates (4 ), The directions of polarization (A, C and B, D) between the central part (4a) and the end part (4b).
Are different from each other.