JP3114480B2 - 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 includes a pair of piezoelectric ceramic plates 14 and 15 each having a strip shape and having signal electrodes 11 and 12 and an intermediate electrode 13 formed on a main surface thereof, respectively. The two piezoelectric ceramic plates 14 and 15 are integrated by face-to-face joining, and each of the piezoelectric ceramic plates 14 and 15 is oriented in the direction of the thickness of each plate and opposite to the other side (in FIG. , Arrow X,
(Indicated by Y).

[0003] Both ends along the longitudinal direction of the detecting element 10 are fixedly supported by a pair of holding parts 16 and 17 each having a U-shape in a side view. Each of the signal electrodes 11 and 12 formed on the side main surface includes external components 18 and 17 formed on different end faces of the holding components 16 and 17 and a case component (not shown) attached to these upper and lower positions. 1
9 are electrically connected to each other. It is to be noted that the holding parts 16 and 17 are formed in the above-described shape when the acceleration G acts on these and the case parts.
This is to ensure a deflection allowance of the detection element 10 that is deformed by the inertial force due to the action of (1).

[0004]

Incidentally, in recent years, there has been a demand for further downsizing of the acceleration sensor, and there is an increasing need to reduce the size of the detecting element incorporated therein. However, simply reducing the size of the detection element 10 having the conventional configuration reduces the amount of electric charge generated when the acceleration G is applied.
The disadvantage is that the detection sensitivity is greatly reduced.

The present invention has been made in view of such inconveniences, and an object of the present invention is to provide an acceleration sensor capable of realizing miniaturization and improvement of detection sensitivity collectively.

[0006]

SUMMARY OF THE INVENTION An acceleration sensor according to the present invention comprises a pair of piezoelectric ceramic plates each having a strip shape and a signal electrode and an intermediate electrode formed on a main surface, respectively. An acceleration sensor having a structure in which both ends along the longitudinal direction of a bimorph-type detection element in which intermediate electrodes of a piezoelectric ceramic plate are joined face-to-face are fixed and supported, and each of the piezoelectric ceramic plates extends in the longitudinal direction. At least a central portion along the plate is polarized according to directions opposite to each other along each plate thickness direction, and one signal electrode is formed from the central portion of one piezoelectric ceramic plate to one side of an end portion, Further, the other signal electrode is formed from the center portion of the other piezoelectric ceramic plate to the other side of the end portion. Are those formed only in the central portion of the conductive ceramic plate and the central portion, the acceleration
Is divided into tension and compression by the stress generated by the action of
It is characterized in that it is set on the center side of the boundary of the change to be made.

[0007]

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, and FIG. 2 is a diagram schematically showing a deformed 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,
1 and 2 which are the same as those in FIG. 3 showing the conventional example are denoted by the same reference numerals.

The detecting element 1 according to the present embodiment includes a pair of piezoelectric ceramic plates 2 and 3 formed in a strip shape having substantially the same size, and each of the piezoelectric ceramic plates 2 and 3 has a longitudinal direction. The area is divided into three parts, that is, central parts 2a and 2b and end parts 3a and 3b via a preset boundary line L (described later). The central portions 2a, 3a of the piezoelectric ceramic plates 2, 3 sandwiched by a pair of boundary lines L set at predetermined positions along the longitudinal direction are opposite to each other along the respective plate thickness directions ( In the figure, arrows X and Y
), While each of the end portions 2b and 3b located outside each boundary line L remains unpolarized. At this time, as in the conventional example, the entirety of the piezoelectric ceramic plates 2 and 3 including these end portions 2b and 3b are polarized according to directions X and Y which are opposite to each other along the respective plate thickness directions. Needless to say, in the present invention, at least the central portions 2a, 3a along the longitudinal direction of the piezoelectric ceramic plates 2, 3 are used.
Must be polarized.

A signal electrode 4 and an intermediate electrode 5 are formed on each of the main surfaces of one of the piezoelectric ceramic plates 2, while an intermediate electrode 5 and an intermediate electrode 5 are formed on each of the main surfaces of the other piezoelectric ceramic plate 3. A signal electrode 6 is formed, and one signal electrode 4 is formed from the central portion 2a of the piezoelectric ceramic plate 2 to one side (the left side in the figure) of the end portion 2b. At this time, the intermediate electrode 5
Are central portions 2a of the piezoelectric ceramic plates 2, 3, respectively.
On the other hand, the other signal electrode 6 is formed on the other side (the right side in the figure) of the end portion 3b of the piezoelectric ceramic plate 3 while the other signal electrode 6 is formed on the other side. ing.

Further, the detecting element 1 is formed by joining the intermediate electrodes 5 face to face with each other and by connecting the two piezoelectric ceramic plates 2, 3.
As in the case of the detection element 10 in the conventional example, both ends along the longitudinal direction of the detection element 1 have a pair of pinches formed in a "U" shape in side view. Parts 16 and 17 are fixedly supported by inwardly protruding ends. The signal electrodes 4 and 6 of the piezoelectric ceramic plates 2 and 3 constituting the detection element 1 are respectively provided for different end faces of the sandwiching parts 16 and 17 and case parts (not shown) attached to the upper and lower positions thereof. External electrodes 18 and 19 formed
Are electrically connected to each other.

In this embodiment, it is assumed that the center portions 2a, 2b and the end portions 3a, 3b in the longitudinal regions of the piezoelectric ceramic plates 2, 3 are separated from each other via a boundary line L. However, these boundary lines L are set in order to determine the execution range of the polarization process for the piezoelectric ceramic plates 2 and 3 and the formation range of the intermediate electrode 5. However, by adopting the configuration as described above, these boundary lines L also indicate boundaries of change in which the stress generated by the action of the acceleration G is divided into “tensile” and “compressive”. Will be. Less than,
The operation and operation of the detection element 1 when the acceleration G acts on the acceleration sensor configured by incorporating the detection element 1 having the structure of the present embodiment will be described with reference to FIG.

First, when the acceleration G acts on the entire acceleration sensor, the acceleration G directly acts on the holding parts 16, 17 and the case parts which fixedly support the detecting element 1. , These holding parts 16, 17
Both the case component and the case component tend 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 detecting element 1, the detecting element 1 tries to keep the state before the acceleration G acts, and this detecting element 1 1, the inertial force generated by the action of the acceleration G acts. Therefore, the end portions 2b and 3b of the piezoelectric ceramic plates 2 and 3 constituting the detecting element 1 try to move together with the holding parts 16 and 17 for fixing and supporting them.
As a result of the respective central portions 2a and 3a maintaining their initial positions, this detecting element 1 is deformed to have a curved shape (upward convex shape in the figure) bent toward the side where the acceleration G acts. Will do.

Therefore, as shown in FIG. 2, a tensile stress Pt is applied to the central portion 2a of the piezoelectric ceramic plate 2 located on the outer side in the bending direction (upper side in the drawing), and a compressive stress Pc is applied to the end portion 2b. On the other hand, the compressive stress Pc appears at the central portion 3a of the piezoelectric ceramic plate 3 located on the inner side in the bending direction (the lower side in the drawing), and the tensile stress Pt appears at the end portion 3b. That is, in the detecting element 1 according to the present embodiment, the stress appearing along the longitudinal direction region of each of the piezoelectric ceramic plates 2 and 3 changes from “tensile” to “compressed” with the boundary L as a boundary, and “compression”. "To" pull ". Note that the boundary line L indicating such a stress change is
For example, it is possible to know by an experiment using a finite element method which is one of numerical analysis methods.

When such a deformation occurs, the signal electrode 4 which constitutes the detecting element 1 and covers the central portion 2a and one side of the end portion 2b on the piezoelectric ceramic plate 2 located on the outer side in the bending direction. Is formed, a large positive (+) charge is generated on the outer main surface of the central portion 2a based on the relationship between the polarization direction X and the tensile stress Pt, and the end portion 2b , A negative (-) charge is generated on the outer main surface due to the relationship between the polarization direction X and the compressive stress Pc. However, in this end portion 2b,
Since no electrode is formed so as to sandwich the piezoelectric ceramic plate 2 and the generated charge is not taken out as an output, the negative charge does not cancel out the positive charge.

At the same time, the signal electrode 6 which covers the central portion 3a and the other side of the end portion 2b is formed on the piezoelectric ceramic plate 3 located on the inner side in the bending direction. A large negative charge is generated on the outer main surface due to the relationship between the direction Y of polarization and the compressive stress Pc, while a positive charge is generated on the outer main surface at the end portion 3b based on the relationship between the direction Y of polarization and the tensile stress Pt. Occurs. However, even at the end portion 2b, the generated charge is not taken out as an output, so that the negative charge cannot be canceled by the positive charge.

Therefore, the detecting element 1 having the above-described structure is used.
According to this, despite the fact that it has a doubly supported structure similar to that of the detection element 10 of the conventional example, the amount of electric charge generated when the acceleration G acts is increased. No reduction in detection sensitivity will occur. In addition,
Piezoelectric ceramic plates 2 and 3 when acceleration G acts
Positive or negative charges different from each outer main surface are generated on each inner main surface, and these charges are canceled out through the intermediate electrode 5. That is, in the detection element 1 according to the present embodiment described above,
As a result, no electric charge is generated on one side or the other side of the end portions 2b, 3b of the piezoelectric ceramic plates 2, 3 which are not opposed to the intermediate electrode 5, so that only the signal electrode 4 is used. , 6 are not reduced, and a large signal appears.

[0018]

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, there is an effect that the miniaturization and the improvement of the detection sensitivity can be realized collectively.

[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 view schematically showing a deformed state of a detection element during acceleration.

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

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Detection element (bimorph type detection element) 2 Piezoelectric ceramic plate 2a Central part 2b End part 3 Piezoelectric ceramic plate 3a Central part 3b End part 4 Signal electrode 5 Intermediate electrode 6 Signal electrode L Boundary line G Acceleration X Polarization direction Y Polarization direction

Claims (1)

(57) [Claims] 1. A pair of piezoelectric ceramic plates (2, 3) each having a strip shape and a signal electrode (4, 6) and an intermediate electrode (5) formed on a main surface, respectively.
This is an acceleration sensor having a structure in which both ends along the longitudinal direction of a bimorph-type detection element (1) integrated by joining the intermediate electrodes (5) of the piezoelectric ceramic plates (2, 3) face to face are fixed. Each of the piezoelectric ceramic plates (2, 3) is subjected to a polarization process in accordance with directions (X, Y) in which at least a central portion (2a, 3a) along the longitudinal direction is along the respective plate thickness direction and opposite to each other. One signal electrode (4) is one piezoelectric ceramic plate (2)
Is formed from the central part (2a) to one side of the end part (2b), and the other signal electrode (6) is formed from the central part (3a) to the end part (3) of the other piezoelectric ceramic plate (3).
b), and the intermediate electrode (5) is formed only on the central portion (2a, 3a) of each piezoelectric ceramic plate (2, 3).
It is intended, and, said central portion (2a, 3a) is the action of the acceleration
Is divided into tension and compression by the stress generated by
An acceleration sensor set at a center side of a boundary line (L) of the change .