JPS62153767A - Laminated type piezoelectric ceramic element - Google Patents

Abstract

PURPOSE:To attain miniaturization and to enhance electric output sensitivity, by making the junction surface of piezoelectric ceramics vertical to the direction of a shearing force generated by acceleration. CONSTITUTION:Piezoelectric ceramics 11 radially polarized from the center of the shape of each piezoelectric ceramic to the outside and piezoelectric ceramics 11 polarized to the direction opposite thereto are alternately stacked to form inner electrodes 12 to the junction surfaces of said piezoelectric ceramics 11, those different from each other of the inner electrodes 12 being connected every other one to constitute output electrodes. A wt. 2 is mounted to thus constituted piezoelectric ceramic element and fixed to a base 8 by a support 10.

Description

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

[Prior Art] When a shear force is applied to a piezoelectric ceramic, a phenomenon in which an electric charge is generated on the surface of the piezoelectric ceramic is called a shear effect, and the direction of the shear force, electric output direction, and polarization direction are specific directions. Figure 7A.

In these figures, B shows the relationship between the three directions above, P
is the polarization direction, F is the direction of the electric force, B is the electric output direction,
α and β (shaded areas) indicate the surface on which the electrode is to be attached to obtain electrical output (the surface in the direction in which electric charge is generated), and the seventh
In FIG. A, the force F causes an in-plane displacement strain parallel to the polarization direction P and perpendicular to the electric output direction E, and charges of different polarities are generated on the side surfaces α and β. In FIG. 7B, the shear force F causes an in-plane displacement strain perpendicular to the polarization direction P and parallel to the electrical output direction E, and the side surfaces α and β have different polarities.
! ! Generate load.

The above-mentioned shearing effect can be used in acceleration sensors, and by attaching a weight at a position where shearing force acts on the piezoelectric ceramic element when acceleration is applied, an electrical signal corresponding to acceleration can be obtained. Such an acceleration sensor is called a shear type acceleration sensor.

On the other hand, an acceleration sensor that uses the longitudinal effect attaches a weight at a position where expansion and contraction stress acts on the piezoelectric ceramic element, and obtains an electrical output due to expansion and contraction strain of the piezoelectric ceramic element. It is called a type acceleration sensor.

FIG. 8 is a partial sectional view showing an example of a compression type acceleration sensor. In this type of acceleration sensor, the piezoelectric ceramic element (1) is placed directly on the top surface of the base (8), and the bottom surface of the base (8) is in contact with the object to be measured, so if the surface of the object to be measured is uneven, In Fig. 8, when acceleration in each direction is applied, the weight becomes distorted. Due to the inertial force of (2), expansion and contraction stress in the Z direction acts on the piezoelectric ceramic element (1), which distorts the piezoelectric ceramic and generates charges on the top and bottom surfaces of the element (1). Connector (7) via the electrodes (not shown) on the top and bottom surfaces of the
) and extracted externally as an electrical signal. The preload bolt (4) is used to fix the element (1) and the weight (2).
The cover (6) is used to soften the effects of sudden environmental changes and to protect the sensing section. A spring washer (3) is placed between the preload bolt (4) and the weight (2).
Between the inner wall of the piezoceramic element (1) and the base (8) there is an insulating ring (9).

When the external temperature changes, pyroelectricity is generated in the piezoelectric ceramic element (1), which affects the output signal of the acceleration sensor.Pyroelectricity is the spontaneous generation of piezoelectric ceramics such as lead zirconate titanate as the ambient temperature changes. When polarization changes, does it occur in a plane perpendicular to the polarization direction? ! It refers to cargo. In the compression type sensor shown in Fig. 8, which measures acceleration using electrical output due to the longitudinal effect, the positions of the electrode surfaces are in planes α and β perpendicular to the polarization direction P, as shown in Fig. 9.
In FIG. 9, E indicates the direction of electrical output, and F indicates the direction of expansion and contraction stress.

In the shear type acceleration sensor that uses shear effect to measure acceleration, as shown in Figure 7A and B, the electrode surfaces α and β are not perpendicular to the polarization direction P but parallel to it, so pyroelectricity is reduced. The impact is small.

FIG. 5 shows an example of a conventional sliding type acceleration sensor, in which FIG. 5A is a top view and FIG. 5B is a partially sectional 1-piece view. As shown in these figures, piezoelectric ceramic element +1
) is a single-layer element that is ring- or short-tubular and has electrodes on the inner and outer sides of the ring, and the element (1), weight (2), and support (10) are arranged concentrically, and the polarization is determined by the height of the element. When acceleration is applied in the Z direction (two directions in the figure), a force is applied to the element (1), generating electric charges on the inner and outer sides of the element (1), which causes the electrodes and lead wires (5) to The signal is then transferred to the connector (7) and taken out as an electrical signal to the outside. Since the element (1) and the weight (2), and the element (11 and the support (10)) are fixed by adhesive, the acceleration impact resistance is lower than that of the compression type acceleration sensor. ,
Although it would be possible to reduce the weight of the weight (2), this would inevitably lead to a decrease in sensitivity.

Fig. 6 shows a new type of acceleration sensor in which sensitivity is improved by stacking a plurality of plate-shaped piezoelectric ceramics. Fig. 6A is a top view, and Fig. 6B is a front view. As shown in these figures, piezoelectric ceramic elements (11 and 1 (1111) with weights (2) each laminated with a plurality of piezoelectric ceramics (11) are arranged on the left and right sides of a support (10), and these are connected with bolts ( 13) to the support (10), and the electrode (12
) is provided on the bonding surface of each piezoelectric ceramic (11). The interface between each piezoelectric ceramic (11) is a space when viewed microscopically (in the case of adhesive fixing, there is an adhesive), and these interfaces are more sensitive to stress than the inside of the piezoelectric ceramic (11). In the case shown in Fig. 6, where misalignment is likely to occur, the direction of acceleration to be measured and the interface between the piezoelectric ceramics (11) are parallel, so the stress caused by the acceleration will cause a large in-plane misalignment strain at the interface. In order to reduce the strain inside the piezoelectric ceramic (11) by 1°, there is a distortion that causes a decrease in the common Di frequency and sensitivity. In addition, compared to an acceleration sensor using a ring-shaped piezoelectric ceramic element (11) as shown in Fig. 5, not only is there a waste of space and it is difficult to downsize, but also the left and right C piezoelectric ceramic elements (1) and weights ( 2), if the dimensions of the piezoelectric ceramic element and the weight of the weight are different between the left and right sides, different vibration states will occur between the left and right sides, which will affect the wave number characteristics of the acceleration sensor as a whole.

However, the acceleration sensor shown in Figures 5 and 6 uses the shear effect in Figure 7 to reduce the influence of pyroelectricity, and at the same time, the piezoelectric ceramic element 11) itself does not come into contact with the base 18). There is an advantage that the influence of distortion propagating from the base (8) is also small.

[Problem that the invention seeks to solve]

As mentioned above, the spiral type acceleration sensor can be easily miniaturized by arranging the piezoelectric ceramic element (1) and the weight (2) concentrically as shown in Fig. 5, since space can be effectively utilized.
If the weight of @(2) is increased to increase the electrical output, problems such as a decrease in the resonant frequency and a decrease in acceleration impact resistance will occur. In order to increase sensitivity, it is better to use a multilayer piezoelectric ceramic element. However, as shown in FIG. 6, the conventional stacked acceleration sensor is 1! in FIG. The layer type could not be made smaller.

Therefore, the present invention aims to provide a laminated piezoelectric ceramic element that can be used to obtain a compact and highly sensitive folding type acceleration sensor that does not have the above-mentioned drawbacks. but,
When ring-shaped piezoelectric ceramics (11) are stacked using the same electrical output extraction method as shown in FIGS. 5 and 6, that is, the principle shown in FIG. 7IA, a concentric +? ! iN type piezoelectric cell type piezoceramic element Figure A is a top view, and Figure B is a front view. The electrode (12) is attached to the joint surface of each piezoelectric ceramic Wl (11). In this element, the joint surfaces between the piezoelectric ceramics (11) are parallel to the direction of the shear force generated by acceleration, so in-plane shear strain of the element is applied to the weak joint surfaces, which reduces the frequency characteristics and acceleration resistance of the acceleration sensor. Not only does the i% impact resistance deteriorate, but since the dimensions and shapes of the piezoelectric ceramics (11) in each layer are different, there are problems such as requiring many types of jigs and increasing the number of man-hours during manufacturing.

[Means for solving problems]

Therefore, the present invention provides the 78th U as an electric output extraction method.
Using the principle of B, a laminated structure as shown in FIG. 2 is formed.

Figure A is a top view, and Figure B is a front view. This structure is
Piezoelectric ceramics (11) of the same shape are stacked in the height direction (Z direction in the figure), and the bonding surface is perpendicular to the direction of the shearing force generated by acceleration. The internal electrode (12) is provided on the bonding surface of the piezoelectric ceramic (11), and the polarization is determined by the seventh
I! This is done as follows, taking into account the relationships shown in IB.
Figure 3.

indicates the polarization direction of the piezoelectric ceramic element in Figure 2 (), so Figure A shows the piezoelectric ceramic (11) polarized radially outward from the center of the piezoelectric ceramic (11), and Figure B shows the piezoelectric ceramic polarized in the opposite direction. Figure C shows a piezoelectric ceramic element in which piezoelectric ceramics polarized in opposite directions (represented by A and B) are stacked alternately. Connect every other electrode (12) to form a pair of output electrodes (1,1),
(15), so as to obtain a weight 1η proportional to the product If the number of sheets. Although FIG. 5C shows, as an example, a case in which the connection is made by a lead wire (5), other methods may be used.

[Effect]

With the above structure, the bonding surface of the piezoelectric ceramic (11) is perpendicular to the direction of the shearing force generated by acceleration, so the problem of the structure shown in FIG. 4 is solved.

〔Example〕

FIG. 1 shows an example in which the multilayer piezoelectric ceramic element according to the present invention is applied to a new type of acceleration sensor. FIG. 1A is a top view, FIG. B is a front view, and IMIC is a partially enlarged sectional view. In these figures, the same reference numerals are given to parts corresponding to those already explained, and redundant explanation will be omitted. (16) in Fig. 1 is a piezoelectric ceramic element (1)
A hole is provided between the lead wire (5) and a part of the weight (2).
). In addition, (17) in the 11th MIC is an insulating adhesive, and (η; group electrode 1
Care was taken so that the end face of 2) did not come into contact with the weight (2) and the support (lO).

In the above example, a ring-shaped J-type piezoelectric ceramic element is shown, but a laminated piezoelectric ceramic element in the shape of a rectangular parallelepiped or a polygonal column may also be used.

〔Effect of the invention〕

As explained above, by using the J-type piezoelectric ceramic element according to the present invention, it is possible to realize an acceleration sensor that simultaneously satisfies the following conditions, which have been difficult to manufacture in the past.

(a) @ High load sensitivity and capacitance.

(b) The influence of pyroelectricity and base distortion is small.

(c) Capable of being made smaller and lighter.

Furthermore, it has little effect on the frequency characteristics of the joint between piezoelectric ceramics, making it ideal for recessed acceleration sensors.

[Brief explanation of drawings]

FIG. 1 is a diagram showing an example in which the present invention is applied to a concave type acceleration sensor, FIG. 2 is a diagram showing an example of a laminated piezoelectric ceramic element according to the present invention, and FIG. 3 is a diagram showing the polarization method of the one in FIG. FIG. 4 is a diagram showing another multilayer J-type piezoelectric ceramic element not according to the present invention, FIG. 5 is a diagram showing an example of a recessed acceleration sensor using a single-layer piezoelectric ceramic element, and FIG. The figure shows an example of a new type of shear acceleration sensor using a laminated piezoelectric ceramic element that is not based on the present invention, Figure 7 is an explanatory diagram of the shear effect, and Figure 8 is an example of a conventional compression type acceleration sensor. FIG. 9 is an explanatory diagram of the longitudinal effect. (11) Piezoelectric ceramics, (12) Internal electrodes, (14), (15) A pair of output electrodes.

Claims (1)

[Claims] A laminated piezoelectric ceramic element in which a plurality of piezoelectric ceramics of the same shape are stacked, and piezoelectric ceramics polarized radially outward from the center of the shape of the piezoelectric ceramics and piezoelectric ceramics polarized in the opposite direction are alternately arranged. A laminated piezoelectric ceramic characterized in that internal electrodes are formed on the joining surfaces of these piezoelectric ceramics, and every other internal electrode that is different from each other is connected to form a pair of output electrodes. element.