JPH09184774A - Piezoelectric type physical quantity sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the cost by forming a sensor part of piezoelectric ceramics, providing a plurality of electrodes for detecting physical quantity on the upper surface of the sensor part and a facing electrode to the lower surface respectively, polarizing the piezoelectric ceramics with the upper and lower electrodes, and connecting respective electrodes as necessary. SOLUTION: A sensor 1 is constituted of a sensor part 1a, a sensor box 1b and a weight, and it is formed integrally with piezoelectric ceramics. The sensor part 1a is provided with electrodes 2 to 9 for detecting physical quantity on its upper surface and an electrode on its lower surface, and the piezoelectric ceramics is polarized by the upper and lower electrodes, then the respective electrodes are conencted with connecting electrodes 10 and 13, etc., as necessary, thereby constituting the sensor part 1a. The upper and lower electrodes forms a capacitor using a piezoelectric ceramics as a dielectric body. Then, when the sensor 1 is given any acceleration, the weight is moved and any deformation is generated in the sensor part 1a supporting the weight, so that the charges in the respective capacitors are changed thereby. The change in charge quantity is detected to detect the physical quantity working to the sensor 1.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric type physical quantity sensor.

Demands for measuring physical quantities such as force, speed, and acceleration exist in many fields, and measuring methods and measuring elements have been developed. In particular, in the field where the physical quantity is measured to control the object, stable and sensitive measurement and simultaneous miniaturization are desired.

In the piezoelectric type physical quantity sensor of the present invention, a piezoelectric ceramic is used for the sensor portion, a plurality of physical quantity detecting electrodes are provided at predetermined positions on the upper surface of the piezoelectric ceramic, and an electrode facing the physical quantity detecting electrode is provided on the lower surface. To provide. The piezoelectric ceramics are polarized by the upper and lower electrodes, and then the electrodes are connected as necessary to complete the sensor section. Reference numeral 12 is an extraction electrode. Reference numerals 16, 17, and 18 denote terminal electrodes for connecting the electrodes of the sensor section to external terminals or drive circuits and detection circuits, which are formed on the sensor housing 1b.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 is a perspective view of an essential part of a piezoelectric type physical quantity sensor according to the present invention. FIG. 2 is a front sectional view of the piezoelectric type physical quantity sensor of FIG. FIG. 3 is a top view of the piezoelectric type physical quantity sensor of FIG.

The sensor 1 includes a sensor portion 1a and a sensor housing 1b.
And the weight body 15 and are integrally formed of piezoelectric ceramics. A plurality of physical quantity detection electrodes 2, 3, 4, 5, 6, 7, 8 and 9 are provided at predetermined positions on the upper surface of the sensor unit 1a.
And an electrode 1 facing the physical quantity detection electrode on the lower surface.
4 is provided. The piezoelectric ceramics are polarized by the upper and lower electrodes, and then each electrode is connected to the connecting electrode 10 if necessary.
The sensor unit 1a is completed by connecting 11 and 13.

The use of the piezoelectric type physical quantity sensor for detecting and measuring acceleration will be described below. The upper surface electrode and the lower surface electrode form a capacitor having a piezoelectric ceramic as a dielectric. When acceleration acts on the sensor, the weight 15
Moves, and strain is generated in the sensor unit 1a supporting the weight body 15. When distortion occurs, the electric charge of each capacitor unit changes. The piezoelectric type physical quantity sensor of the present invention detects the physical quantity acting on the sensor by detecting the change in the charge quantity.

An origin is defined at a point on one surface of the piezoelectric ceramics element (sensor portion 1a), the X axis extends in a direction passing through the origin and parallel to the piezoelectric ceramics element surface, and the piezoelectric ceramics is orthogonal to the X axis at the origin. The Y axis is defined in the direction parallel to the element surface, and the two electrodes 2 and 6 are provided on the positive side of the X axis.
On the negative side, the two electrodes 3 and 7 are arranged concentrically, and Y
Two electrodes 4 and 8 are concentrically arranged on the positive side of the axis, two electrodes 5 and 9 are concentrically arranged on the negative side, and an electrode 14 facing the electrode group is arranged on the opposite surface of the piezoelectric ceramic element. A piezoelectric ceramic capacitor is formed as the sensor unit 1a. The outer periphery of the sensor portion 1a is fixed to the sensor housing 1b, the electrodes (2, 3, 4 and 5) facing each other at the origin are symmetrically formed, and after the electrodes are polarized to have different polarities, the inner electrode is placed on the piezoelectric ceramics. Connection electrode 13 on the piezoelectric ceramics connection electrode (10,
Connect in 11). Piezoelectric generated by the force generated in the acting body (weight body 15) by forming an acting body (weight body 15) having a function of transmitting a force generated based on a physical quantity acting from the outside to the origin. The distortion of the ceramics is detected by the electrode group as a change in the charge amount of the capacitor.

Next, the manufacture of the piezoelectric type physical quantity sensor will be described. Various piezoelectric ceramic materials have been developed, but for example, PZT (lead zirconate titanate), which is ferroelectric and piezoelectric, is used. The powder is molded with a mold (the sensor portion, the sensor housing portion, and the weight body portion are integrally molded) and fired. Electrodes are formed on the upper and lower surfaces of the sensor unit by a method such as vapor deposition, sputtering, and screen printing. The electrodes on the upper and lower surfaces are used to polarize the piezoelectric ceramic. Since there are two types of polarization directions, each electrode is classified and polarized. After the polarization, the upper electrodes polarized differently by the connecting electrodes are connected as described above. Reason

A description will be given below.

The electrodes are formed in two steps, but in the case of vapor deposition or sputtering, a metal mask is generally used,
A screen is used in screen printing, and heat treatment is performed after printing. 4 is a plan view of a mask shape for the first electrode formation by vapor deposition, and FIG. 5 is a plan view of a mask shape for the second connection electrode formation. The number of manufacturing steps is increased if the electrodes are set again after polarization to form overlapping electrodes.
FIG. 6 is a plan view of a mask shape for forming electrodes by a single vapor deposition. In the present invention, the mask shape as shown in FIG.
A part of the connection electrode was cut with a mask, and after polarization, connection was made with a conductive paste. As a result, the deterioration of the strength of the mask due to the opening of the window can be reinforced by the crosspiece for cutting a part of the connection electrode, and the electrode can be formed at once, and the number of manufacturing steps can be reduced.

Next, the theory of detecting and measuring a physical quantity with the piezoelectric type physical quantity sensor of the present invention will be described with reference to FIGS. 1, 7, and 8.

Consider a case where acceleration is applied to the piezoelectric physical quantity sensor of FIG. 1 in the X-axis direction. FIG. 7 is a front cross-sectional view showing a strain generation state of the sensor unit 1a when acceleration acts in the X-axis direction. When acceleration acts on the weight body 15, as shown in FIG.
As shown in, a force F in the X-axis direction is generated at the center of gravity G of the weight body 15. Due to this force F, a counterclockwise moment force in FIG. 7 is generated at the origin O, and the sensor unit 1a is distorted as shown in the figure. Due to this strain, the piezoelectric ceramic is deformed such that a certain portion is expanded and a certain portion is contracted, and accordingly, an internal stress is generated. Due to such changes, the electrodes 2,
The amount of electric charge of the capacitor composed of 3, 4, 5, 6, 7, 8, 9 and the electrode 14 changes. At the moment when the charge amount of the capacitor changes, a current flows through the capacitor and the weight 15
The current flows as if it were an alternating current until the vibration of is attenuated. The magnitude of the current is proportional to the change in the charge of the capacitor,
Unless other conditions change, it is proportional to the magnitude of the acceleration. The generation of strain and stress in the sensor unit 1a can be almost simulated by a circular plate, peripheral fixing, and concentrated load at the center, and the arrangement of electrodes is determined in consideration of the part where the stress + and- are reversed.

The electrodes 2 and 3 should have the same size and opposite directions, but if the polarization directions are reversed, currents will flow in the same direction, so connect the electrodes to each other. If so, the same current will flow even with the double electrode area. Although the detection sensitivity does not change, the frequency characteristic is improved. The connection electrode 10 is therefor. Electrodes 4, 5
Distortion is also generated in the capacitor portion due to, but since the electrodes are formed in line symmetry with respect to the Y axis which is orthogonal to the X axis, they are offset and no current flows. The same can be detected when acceleration acts in the Y-axis direction. The acceleration acting on the XY plane can detect and measure the magnitude and direction of the acceleration by combining the respective outputs.

Let us consider a case where the Z axis orthogonal to the XY plane is defined and acceleration acts in the Z axis direction. FIG. 8 is a front cross-sectional view showing a state in which the sensor unit 1a is distorted when acceleration acts in the Z-axis direction. The detection theory is the same as that described above, and the electrodes 6, 7, 8, 9 are connected by the connection electrode 13 (the ceramics of the electrodes 6, 7, 8, 9 are polarized in the same direction). It can be easily understood that the detection signal is reversed when the acceleration direction is reversed. In the case of acceleration parallel to the XY plane, the distortion of the capacitors of the four electrode portions, which are point-symmetrical, are canceled and the output disappears.

By detecting and synthesizing the accelerations in the X-axis, Y-axis and Z-axis directions, the direction and magnitude of the acceleration can be measured.

[0015]

According to the present invention, the following effects can be obtained by employing the above-described structure.

Since the sensor portion is made of piezoelectric ceramic and the electrodes are directly formed, the structure is simple and the manufacturing cost is low.

Since electrode connection after polarization is performed on the sensor section by screen printing, vapor deposition, sputtering, etc., the number of connections between the sensor section and external terminals or drive circuits can be reduced.

Since the pattern is cut with the mask used for forming the electrodes, the mask can be reinforced and the number of times the electrodes are formed is 1
Could be times.

By connecting the pattern cut portion with the conductive paste, the electrode connection can be made without requiring a special device.

[Brief description of the drawings]

FIG. 1 is a perspective view of a main part of a piezoelectric physical quantity sensor according to the present invention.

FIG. 2 is a front sectional view of a piezoelectric type physical quantity sensor according to the present invention.

FIG. 3 is a top view of a piezoelectric physical quantity sensor according to the present invention.

FIG. 4 is a plan view showing a mask shape for first electrode formation.

FIG. 5 is a plan view showing a mask shape for second electrode formation.

FIG. 6 is a plan view showing a mask shape.

FIG. 7 is a front cross-sectional view showing a strain generation state of the sensor unit when acceleration is applied in the X-axis direction.

FIG. 8 is a front cross-sectional view showing a strain generation state of the sensor unit when acceleration is applied in the Z-axis direction.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 sensor 1a sensor part 1b sensor housing 2 detection electrode 3 detection electrode 4 detection electrode 5 detection electrode 6 detection electrode 7 detection electrode 8 detection electrode 9 detection electrode 10 connection electrode 11 connection electrode 12 Lead-out electrode 13 Connection electrode 14 Electrode 15 Weight body 16 Terminal electrode 17 Terminal electrode 18 Terminal electrode

Claims (8)

[Claims] 1. A sensor unit comprising a plate-shaped piezoelectric ceramic element, an upper electrode formed on the upper surface of the piezoelectric ceramic element, and a lower electrode formed on the lower surface of the piezoelectric ceramic element. A piezoelectric type physical quantity sensor characterized in that each electrode is connected as needed after polarization processing of a piezoelectric ceramic element in a desired direction. 2. An origin is defined at one point on one surface of the piezoelectric ceramic element, and the X axis is in a direction passing through the origin and parallel to the surface of the piezoelectric ceramic element. The Y axis is defined in a parallel direction, one electrode is arranged on the positive side of the X axis, one electrode is arranged on the negative side, and one electrode is arranged on the positive side of the Y axis and one is arranged on the negative side. Two electrodes are arranged, electrodes facing the electrode group are arranged on the opposite surface of the piezoelectric ceramics element to form a capacitor, and the sensor part is formed, and the outer periphery of the sensor part is fixed to the sensor housing and faces the origin. An actuator having a function of transmitting the force generated based on the physical quantity acting from the outside to the origin by connecting the electrodes on the piezoelectric ceramics after the electrodes are symmetrically polarized and polarized to different polarities. Forming in the acting body Piezoelectric physical quantity sensor and detecting a change in the charge amount of the piezoelectric ceramic by the force by the electrode group. 3. An origin is defined at a point on one surface of the piezoelectric ceramic element, and the X axis is in a direction passing through this origin and parallel to the surface of the piezoelectric ceramic element. The Y axis is defined in a parallel direction, two electrodes are arranged concentrically on the positive side of the X axis, two electrodes are arranged concentrically on the negative side, and two electrodes are arranged on the positive side of the Y axis and 2 electrodes are concentrically arranged on the side, the electrodes facing the electrode group are arranged on the opposite surface of the piezoelectric ceramic element to form a capacitor to form a sensor portion, and the outer periphery of the sensor portion is fixed to the sensor housing. , The electrodes facing the origin are made symmetrical, and after polarization treatment with different polarities from each other, the inner electrodes are connected on the piezoelectric ceramics, the outer electrodes connect the coaxial electrodes on the piezoelectric ceramics, and It is generated based on the physical quantity that acts Force, said forming a working body having a function to transmit to the origin, piezoelectric physical quantity sensor, characterized in that a change in the charge amount of the piezoelectric ceramic by the force generated in the working body is detected by the electrode group. 4. The piezoelectric type physical quantity sensor according to claim 1, wherein the electrode connection after polarization is made by printing. 5. The piezoelectric physical quantity sensor according to claim 1, wherein the electrode connection after polarization is vapor deposition or sputtering. 6. The electrodes to be connected after polarization are connected by a thin connection pattern, but a part of the connection pattern is cut, and the cut portion is cut by a mask during electrode formation by vapor deposition or sputtering. The piezoelectric type physical quantity sensor according to claim 1, 2, or 3. 7. The piezoelectric type physical quantity sensor according to claim 6, wherein the connection of the cut portion is performed by applying a conductive paste. 8. The piezoelectric type physical quantity sensor according to claim 2, wherein the physical quantity is acceleration.