JPS62153766A - Laminated type piezoelectric ceramic element - Google Patents

Abstract

PURPOSE:To make it possible to measure an acceleration component in one direction, by stacking a plurality of piezoelectric ceramics having the same shape, forming each of inner electrodes to each junction surface, and connecting those different from each other of the inner electrodes every other one to form outer electrodes. CONSTITUTION:A plurality of piezoelectric ceramics 10 having the same shape are stacked and inner electrodes 16 are formed to the junction surfaces of said piezoelectric ceramics 10. Those different from each other of said inner electrodes 16 are connected every other one to form a pair of outer electrodes N, Q. A pair of these outer electrodes N, Q are provided to be close to each other as much as possible.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a laminated piezoelectric ceramic element suitable for use in an acceleration sensor.

[Conventional technology]

FIG. 7 is a partial cross-sectional view showing an example of a conventional piezoelectric acceleration sensor. Assuming that the bottom surface of the sensor is parallel to the Xy plane, when vibration (acceleration) in two directions is applied to the sensor, compressive stress due to the weight (2) acts on the piezoelectric ceramic element (1), causing the piezoelectric ceramic element to A charge is generated on the surface of +11.0 The generated charge is carried to the connector (7) through an electrode (not shown) and a lead wire (5).
It is extracted externally as an electrical signal. Preload bolt (4)
is used to fix the weight (2) and the element (11) so that they do not come apart, and a spring washer (3) is installed between the preload bolt (4) and the weight (2).
), but between the inner wall of element +11 and the base (8) there is an insulating ring (9). The cover (6) cushions the effects of sudden environmental changes and protects the sensing section. The acceleration sensor with this structure can use piezoelectric ceramic elements from a single layer type to a laminated type.

Figure 6 shows various examples of piezoelectric ceramic elements used in the acceleration sensor. Figure A is a single layer type, Figure B is a 2N type, and Figures C-E are perspective views of a laminated type. be. The one in FIG. 6A has electrodes (11) at both ends of the piezoelectric ceramic αω and an insulator (12) on the outside thereof.

If a material (step 3) such as a conductive paste is used to connect the lead wire (5) and the electrode (11), and this material (13) protrudes and adheres to the side surface of the element, this becomes an external electrode in a broad sense. In the case of FIG. 6B, a metal plate (14) is interposed between two piezoelectric ceramics α, and both piezoelectric ceramics 0ω
Obtain electrical output from. These single-layer type and two-layer type elements have lower output sensitivity than the laminated type elements described later.

There is a way to increase the sensitivity by increasing the weight of the weight (2) and increasing the stress applied to the element (1), but this results in an increase in the weight of the acceleration sensor, a decrease in the resonance frequency, and a decrease in acceleration impact resistance. The usage range of the acceleration sensor becomes narrower.

In the case of C-H in Fig. 6, since a plurality of piezoelectric ceramics are stacked, a charge proportional to the number of layers is generated.
Higher sensitivity can be obtained than the acceleration sensor using the H type. 6C is a laminated version of FIG. 6A, and FIG. 6B is a laminated version of FIG. Items C and D in Figure 6 have poor work efficiency because the lead wires (5) must be connected one by one.Especially in the item shown in Figure 6, the metal plate (14) must be held between each eyebrow. Therefore, the reproducibility of the device manufacturing is poor due to variations in the precision of device dimensions, etc., and the cost is high. Moreover, since both have many connection points for lead wires (5), there are drawbacks such as restrictions on element size and reduction in element strength. On the other hand, the one in FIG. 6E uses an external electrode (15) and does not have the above-mentioned drawback. Laminated piezoelectric ceramic elements having external electrodes can be mass-produced using the green sheet method and are inexpensive, and have advantages such as small size, light weight, high sensitivity, and high resonant frequency when used in acceleration sensors.

[Problem that the invention seeks to solve]

However, conventional multilayer piezoelectric ceramic elements have been mainly used as elements for converting electrical signals into mechanical imaging or acoustic vibrations, and have rarely been used in acceleration sensors. Therefore, the influence of external electrodes is not clear;
In conventional laminated piezoelectric ceramic elements, the positions of the external electrodes are not defined. For this reason, acceleration sensors using conventional laminated piezoelectric ceramic elements have high lateral sensitivity, which is one of their basic characteristics due to the influence of external electrodes, and therefore have to strictly measure acceleration in only one direction component. The problem was that it was difficult to measure. Here, the lateral sensitivity is the electrical output generated when acceleration parallel to the xy plane in FIG. 7 is applied, for example.

[Means for solving problems]

The acceleration sensor normally measures acceleration in the two directions shown in FIG. 7, and due to this acceleration, the weight (2) exerts expansion and contraction stress on the piezoelectric ceramic element (1).

If this is schematically shown using a rectangular parallelepiped element, it will be as shown in FIG. The polarization direction P is perpendicular to the xy plane, and tensile stress from the weight acts in the direction Fl due to the acceleration α1, generating charges on the bottom and top surfaces of the element (planes parallel to the xy plane). Therefore, electrodes are provided on this surface to obtain electrical output. In FIG. 7, when an acceleration component parallel to the xy plane is applied, the weight (2) exerts a shear stress on the piezoelectric ceramic element (1).

If this is schematically shown using a rectangular parallelepiped element, it will be as shown in FIG. 5B. The polarization direction P is the same as that shown in FIG.

A shear stress from the weight acts in the F2 direction due to the acceleration α2, and charges with mutually different polarities are generated on the side surfaces β and γ of the element. Providing electrodes on the planes corresponding to β and T generates electrical output, which is one of the causes of increased lateral sensitivity. In a piezoelectric ceramic element having an external electrode, since the external electrode is located on the side surface, the piezoelectric ceramic element cannot avoid the influence of electric charge generated on the side surface of the element due to lateral vibration.

Therefore, consider the above-mentioned phenomenon regarding a piezoelectric ceramic element having an external electrode. FIG. 3 is a top view of the ring (or short tube) shaped piezoelectric ceramic element. A and B indicate the external electrodes (Fig. 6 C-H), and X and the X direction are x in Fig. 7.
, corresponds to the X direction, and θ indicates the angle between the external electrodes A and B when viewed from the center of the device with reference to the straight line connecting the external electrode A and the center of the device. Indirectly, θ indicates the facing angle of both electrode surfaces. For simplicity, the straight line connecting external electrode A and the element center is made parallel to the X direction, and
Consider the case of applying directional vibration. Assuming that the magnitude of acceleration parallel to the Xy plane is α, in lateral vibration, electric output is generated by the acceleration component perpendicular to the electrode surface as shown in Figure 5B. When is in the X direction, it receives the maximum electrical output, and when it is in the X direction, it receives the minimum electrical output. Regarding external electrode B, considering the acceleration component perpendicular to the electrode surface as described above, for the X direction and the magnitude α of the acceleration in the X direction, the acceleration component related to the electrical output of the acceleration in each direction is , When applying acceleration in the X direction, αy = α・ from Figure 4A.
sin θ When applying acceleration in the X direction, αX −α from Figure 4B
” cosθ In Figure 3, the positional relationship between external electrodes A and B is θ=0°
, 45°, 90°, 135", 180°,
Taking the case of 270' as an example, Table 1 shows the electrical output of the external electrode due to the charges generated on the side surface of the element.

However, the external electrode A is at the position described above, and the acceleration α is
Table 1 shows the electrical output of external electrode B based on external electrode A, assuming that the electrical output of external electrode A in the direction is +100 and the electrical output of external electrode A when acceleration α is in the X direction is 0.
It was shown to. In addition, the electrical polarity (symbol) is also shown in the table.

Table 1 Since the positional angle θ of the conventional external electrodes was not fixed, the lateral sensitivity characteristics varied depending on the individual elements, and it was not possible to compensate for this. In the present invention, the position of the external electrode that allows compensation is determined and the external electrode is provided at that position.

Next, an example of a compensation method will be shown.

(a) Method of compensating between two external electrodes This is a method of correcting the electrical output of a local external electrode using one external electrode as a reference. To use this method, it is necessary that the electrical outputs generated from the two external electrodes be equivalent in response to acceleration in the lateral direction. It can be seen from Table 1 that in order to obtain equivalent electrical output, the positional relationship between the two external electrodes should be set to θ-0°. The structure with θ=0′ can be approximately obtained by providing two external electrodes adjacent to each other (or as close as possible).

(b) Method of obtaining electrical output after correcting each external electrode This method involves attaching a compensation electrode to each of the two external electrodes,
This is a method of obtaining electrical output from each external electrode after canceling out the effects of charges generated on the side surfaces of the element. To use this method,
The values of the electrical output of the external electrode and the electrical output of the compensation electrode for lateral acceleration must have opposite polarities and the same absolute value. To obtain electrical outputs with opposite polarity and the same absolute value, 1, the positional relationship between the external electrode and the compensation electrode is θ-
It turns out that the angle should be 180°. In the θ-180° structure, the external electrode and the compensation electrode are provided at opposing positions on the element center line (opposite positions to each other).

The present invention can be divided into two inventions depending on the above-mentioned difference in compensation method. Below, the first method uses the compensation method (a).
The invention using the compensation method (b) will be referred to as the second invention.

[Effect]

According to the present invention, when a piezoelectric ceramic element having an external electrode is used as an acceleration sensor, charges generated on the side surfaces of the element are electrically compensated for, and the lateral sensitivity is significantly reduced.

〔Example〕

Fig. 1 shows an embodiment of the first invention, in which Fig. 1A is a top view and Fig. 1B is a partially cutaway perspective view. In these figures, CIQI is a polarized piezoelectric ceramic, N and Q are external electrodes, (16) is an internal electrode, and (F) is an insulating protective film. The external electrodes N and Q are formed by applying a conductive material such as silver paste to every other end surface of different internal electrodes (16) and connecting them, and the end surfaces of the internal electrodes (16) that are not connected are For example, an insulating protective film (17) is formed using an insulator such as glass. The two external electrodes N and Q are connected to different internal electrodes (16), the external electrode Q is connected to the output terminal, and the external electrode N is connected to the ground. By arranging the external electrodes N and Q to be adjacent to each other in this manner, the electrical output due to the charges generated on the side surface of the element becomes almost the same regardless of the acceleration from the lateral direction, and its influence is compensated for.

Fig. 2 shows an embodiment of the second invention, in which Fig. A is a top view, Fig. B is a perspective view taken along the straight line l of Fig. A;
Figure C is a perspective view taken along the straight line m in figure A. In these figures, parts corresponding to those in FIG. 1 are given the same reference numerals.

The external electrodes S and T, and R and U are located at opposite positions on the element center line, respectively, and are connected to the internal electrode (16) of the same eyebrow.
Connected every second. The end surfaces of the internal electrodes (16) that are not connected are similarly covered with an insulating protective film (17). External electrodes located at positions that do not face each other on the element center line, for example, R and S
are connected to mutually different internal electrodes (16).

Then, the external electrodes S and T connected to the same internal electrode (work 6) are connected to each other and the external electrodes R and U are connected to the output terminal.
are wired together and connected to ground. With the above configuration, when subjected to lateral acceleration, the electrical output is canceled out between the opposing electrodes due to the charge generated on the side surface of the element, and the electrical output from the output lead wire (18) is also offset by the ground lead wire (19).
) will also be zero.

Note that the present invention is not limited to the ring (or short tube)-shaped element shown in the above-described embodiment, but may also be a rectangular parallelepiped or polygonal column-shaped element.

〔Effect of the invention〕

As explained above, according to the present invention, the following remarkable effects can be obtained.

(a) The acceleration sensor using the piezoelectric element according to the present invention has lower lateral sensitivity without affecting the electrical output of the acceleration component in the longitudinal direction, so it is better than the conventional acceleration sensor using the piezoelectric element having an external electrode. It becomes possible to measure acceleration components in exactly one direction.

(b) The acceleration sensor using the piezoelectric element according to the present invention has the characteristics of the laminated piezoelectric element, such as small size, light weight, and high sensitivity, and is therefore optimal for vibration measurement.

[Brief explanation of drawings]

Figure 1 is a diagram showing an embodiment of the first invention, Figure 2 is a diagram showing an embodiment of the second invention, Figures 3 and 4 are diagrams for explaining the invention, and Figure 5 is lateral sensitivity. FIG. 6 is a perspective view showing an example of a conventional piezoelectric ceramic element, and FIG. 7 is a partial sectional view showing an example of a conventional piezoelectric acceleration sensor. 0φ...Piezoelectric ceramics, (16)...Internal electrode, (N, Q), (S, R)...External electrode, (T, U)...Compensation electrode.

Claims (1)

[Claims] 1. A plurality of piezoelectric ceramics having the same shape are stacked, internal electrodes are formed on the joint surfaces of these piezoelectric ceramics, and different internal electrodes are connected every other time to form a pair of piezoelectric ceramics. A laminated piezoelectric ceramic element characterized in that external electrodes are formed and a pair of external electrodes are provided as close as possible. 2. Pile up a plurality of piezoelectric ceramics of the same shape, form internal electrodes on the joint surfaces of these piezoelectric ceramics, and connect every other internal electrode that is different from each other to form a pair of external electrodes, A laminated piezoelectric ceramic element characterized in that compensation electrodes are provided at opposing positions on opposite sides of the pair of external electrodes, and the corresponding external electrodes and compensation electrodes are connected to each other.