JP2000298137A - Acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent an X-, Y-axis direction acceleration error caused by Z-axis direction acceleration by forming spaced annular electrode rows straddling a weight-opposed region and an intermediate region of a piezoelectric ceramic board so as to surround the weight-opposed region in each pair of X-axis and Y-axis direction acceleration detecting electrodes. SOLUTION: A stress generating region 8B has annular shape surrounding a weight-opposed region 8A, and a stress generating region 8C has annular shape surrounding the stress generating region 8B. Each pair of X-axis and Y-axis direction acceleration detecting electrodes EX1, EX2 and EY1, EY2 are in line symmetry with respect to X-axis and Y-axis imaginary lines XL, YL. These electrodes as well as Z-axis direction acceleration detecting electrodes EZ1-EZ4, are of rectangular shape straddling the weight-opposed region 8A and stress generating region 8B. Spontaneous polarization charges generated to the X-axis and Y-axis direction acceleration detecting electrodes EX1, EX2 and EY1, EY2 when Z-axis direction acceleration is applied to a weight, are equal to each other and offset each other because of reverse polarity so as to cause no error.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor for detecting acceleration using piezoelectric ceramics.

[0002]

2. Description of the Related Art A pair of electrodes for detecting acceleration in an X-axis direction arranged on an imaginary line in the X-axis assumed on one surface and a pair of electrodes arranged on an imaginary line in the Y-axis direction orthogonal to the imaginary line in the X-axis direction. A piezoelectric ceramic substrate on which a detection electrode pattern including a Y-axis direction acceleration detection electrode is formed, and a counter electrode pattern facing the detection electrode pattern is formed on the other surface, is subjected to polarization processing, and is subjected to acceleration to receive the piezoelectric ceramic. 2. Description of the Related Art There is known an acceleration sensor which outputs signals corresponding to acceleration components in an X-axis direction and a Y-axis direction based on spontaneous polarization charges generated in an acceleration detecting electrode in each direction due to stress generated therein. The basic principle and technology of this acceleration sensor are described in International Publication WO93 / 02342 (PCT / JP92 / 008).
82). In this acceleration sensor, a weight is bonded to the back surface of the piezoelectric ceramic substrate via a diaphragm, and a pair of X-axis direction acceleration detecting electrodes and a pair of Y-axis direction acceleration detecting electrodes Formed so as to form a ring-shaped electrode array that straddles the weight-facing region of the ceramic substrate and the intermediate region located between the weight-facing region and the outer peripheral portion and surrounds the weight-facing region at an interval from each other Have been. When the acceleration in the Z-axis direction orthogonal to the X-axis direction and the Y-axis direction acts on the weight, the polarization process is performed for each of the pair of X-axis acceleration detection electrodes or the pair of Y-axis acceleration detection. The electrodes are provided such that spontaneous polarization charges of different polarities are generated in each of the electrodes. Thereby, when the acceleration in the Z-axis direction acts on the weight, the spontaneously polarized charges generated at the respective electrodes of the pair of X-axis direction acceleration detection electrodes or the respective electrodes of the pair of Y-axis direction acceleration detection electrodes are applied. Since the generated spontaneous polarization charges cancel each other out, when an acceleration acting only in the Z-axis direction acts on the weight, an erroneous detection is not made as if the acceleration acts in the X-axis direction or the Y-axis direction. It has become.

[0003]

In order to obtain such an effect completely, it is necessary to intersect an imaginary line in the X-axis direction with an imaginary line in the Y-axis direction (hereinafter simply referred to as an intersection of the imaginary lines) and the center of the weight. This is the case where the piezoelectric ceramic substrate is bonded to the diaphragm so that the two completely match, and the mutual positional relationship between the piezoelectric ceramic substrate and the weight is accurately set. However, it is not technically easy to always fix the piezoelectric ceramic substrate at an accurate position with respect to the weight, and an error occurs at this fixing position due to an error in processing accuracy. In the conventional acceleration sensor, a pair of sides of the detection electrode are formed so as to radially expand from the intersection of the virtual line toward the peripheral direction. A imaginary boundary line (hereinafter, referred to as a boundary between the weight facing region and the intermediate region)
The length across which each of the detection electrodes intersects is simply different. For this reason, there is a problem that the dispersion of the peak value of the spontaneous polarization charge appearing on each detection electrode becomes large, and the accuracy of detecting the acceleration decreases. When acceleration is applied only in the Z-axis direction in a state where the intersection of the virtual line and the center of the weight are displaced in this way, a pair of X-axis direction acceleration detecting electrodes or a pair of Y-axis direction acceleration detecting electrodes A large spontaneous polarization charge appears at one of the electrodes, and a small spontaneous polarization charge appears at the other electrode. Therefore, even when acceleration occurs only in the Z-axis direction, an X-axis direction acceleration signal or a Y-axis direction acceleration signal indicating that acceleration is occurring in the X-axis direction or the Y-axis direction is generated. was there.

An object of the present invention is to provide an acceleration sensor and a three-axis acceleration sensor capable of suppressing a decrease in measurement accuracy due to a positioning error of a piezoelectric ceramic substrate.

Another object of the present invention is to provide an X-axis acceleration signal or Y-axis acceleration signal generated when acceleration is applied only in the Z-axis direction.
An object of the present invention is to provide an acceleration sensor and a three-axis acceleration sensor capable of minimizing an axial acceleration signal.

[0006]

An acceleration sensor according to the present invention comprises a pair of electrodes for detecting acceleration in the X-axis direction arranged on a virtual line in the X-axis direction assumed on the surface, and a pair of electrodes for detecting acceleration in the X-axis direction. An electrode pattern including a pair of Y-axis direction acceleration detection electrodes arranged on a Y-axis direction imaginary line is formed on the front surface, and a counter electrode pattern facing at least each detection electrode is formed on the back surface. A piezoelectric ceramics substrate in which portions between the X-axis direction acceleration detecting electrode and the pair of Y-axis direction acceleration detecting electrodes and the counter electrode pattern are polarized, and a diaphragm having the front surface joined to the back surface of the piezoelectric ceramic substrate And a column-shaped weight fixed to the diaphragm so as to protrude to the rear surface side of the diaphragm, and a base for supporting an outer peripheral portion of the diaphragm so as to allow displacement of the weight. ; And a nest. And a pair of X
The axial acceleration detection electrode and the pair of Y-axis acceleration detection electrodes are provided in a weight facing region of the piezoelectric ceramic substrate facing the weight and an intermediate region located between the weight facing region and the outer peripheral portion. It is formed so as to straddle and to form a ring-shaped electrode row surrounding the weight opposing region with an interval therebetween.
More specifically, each of the pair of X-axis direction acceleration detection electrodes is arranged at a target position around the intersection and has a shape symmetrical with the X-axis direction virtual line as a center line. . Further, each of the pair of Y-axis direction acceleration detecting electrodes is arranged at a symmetrical position with the intersection point as a center, and has a shape symmetric with respect to the Y-axis direction virtual line as a center line.

According to the present invention, a pair of sides located in the direction in which the annular electrode row of the X-axis direction acceleration detecting electrode extends is substantially equally spaced on both sides of the X-axis direction virtual line and substantially parallel to the X-axis direction virtual line. The pair of sides located in the direction in which the annular electrode row of the Y-axis direction acceleration detecting electrode extends is made substantially parallel to the Y-axis direction virtual line at substantially equal intervals on both sides of the Y-axis direction virtual line. In this way, the virtual region boundary line at the boundary between the weight-facing region and the intermediate region crosses over a pair of parallel sides of each detection electrode. Therefore, even if the fixing position of the piezoelectric ceramic substrate is slightly shifted, the length of the region boundary line crossing each detection electrode does not change significantly. Therefore, even if the fixed position of the piezoelectric ceramic substrate is displaced within the manufacturing error range, the fluctuation or variation of the peak value of the spontaneous polarization charge appearing on each detection electrode is reduced, and the accuracy of acceleration detection is prevented from deteriorating. be able to.
Further, when the fixed position of the piezoelectric ceramic substrate is shifted, X
Even if acceleration is applied only in the Z-axis direction orthogonal to the axial direction and the Y-axis direction, the polarity appearing on each electrode of the pair of X-axis acceleration detection electrodes or each electrode of the pair of Y-axis acceleration detection electrodes. Are approximately equal. Therefore, an X-axis direction acceleration signal or a Y-axis direction acceleration signal generated when an acceleration acts only in the Z-axis direction is reduced.

However, even if each detection electrode is formed in this manner, there is a limit to reducing the X-axis or Y-axis acceleration signal generated when acceleration is applied only in the Z-axis direction. there were. The present inventor who has investigated the cause has found that there is also a region (stress generating region) in which stress is generated in the region of the piezoelectric ceramic substrate facing the weight when the weight is displaced by the acceleration. In this stress generating region, the stress gradually decreases from the region boundary line toward the center of the counterweight region. When such a stress generation region exists in the weight-facing region, when the center of the weight and the intersection of the imaginary line deviate, a pair of X-axis direction acceleration detection electrodes or a pair of Y-axis direction acceleration detection The area of the portion of the electrode located on the stress generating region in the weight facing region differs.
For example, the inner end of one electrode of the pair of acceleration detecting electrodes is located at the center of the stress generating region, and the inner end of the other electrode is located at the center of the counterweight region beyond the stress generating region. Then, the area of each electrode facing the stress generating region in the weight-facing region is different, and the spontaneous polarization charge or voltage generated at each electrode is different. As a result, when acceleration acts only in the Z-axis direction, a spontaneous polarization charge generated in each electrode is not canceled out, and a slight X-axis direction acceleration signal or a small Y-axis direction acceleration signal is output. Therefore, in the present invention, a pair of X-axis direction acceleration detecting electrodes and a pair of Y-axis direction acceleration detecting electrodes are connected to the intersection of the center of the weight and the imaginary line generated when the piezoelectric ceramic substrate is joined to the diaphragm. When the amount of displacement is maximized, a region where stress is generated in the weight-facing region due to the displacement of the weight in the Z-axis direction is defined by a pair of X-axis acceleration detection electrodes and a pair of Y-axis acceleration detection electrodes. Is formed so as to exceed the inner end. In other words, the inner end of each of the pair of X-axis direction acceleration detecting electrodes and the inner side of each of the pair of Y-axis direction acceleration detecting electrodes are defined by the intersection of the center of the weight and the virtual line. Is located on the center side of the weight opposing region beyond the stress generating region in the weight opposing region when the amount of deviation from the maximum becomes the maximum. In this way, even if the center of the weight and the intersection of the imaginary line are maximally shifted, a pair of X
Each of the electrodes for detecting the axial acceleration or each of the pair of electrodes for detecting the acceleration in the Y-axis direction is located on the stress generating region in the weight facing region. Therefore, even if the acceleration only in the Z-axis direction acts on the weight, spontaneous polarization charges having different polarities generated in the respective electrodes of the pair of X-axis direction acceleration detection electrodes or the pair of Y-axis direction acceleration detection electrodes are generated. The spontaneous polarization charges having different polarities generated at the respective electrodes are substantially equal, and the spontaneous polarization charges generated at the respective electrodes substantially cancel each other. As a result, X that occurs when acceleration acts only in the Z-axis direction
The axial acceleration signal or the Y-axis acceleration signal can be made much smaller than in the past, and the measurement accuracy can be increased.

As in the present invention, even when the amount of deviation between the center of the weight and the intersection of the imaginary line is maximized, a pair of X-axis direction acceleration detection To locate the electrodes and the pair of Y-axis direction acceleration detection electrodes, a virtual circle drawn with the same radius R as the radius of the weight is set around the intersection of the X-axis virtual line and the Y-axis virtual line. Assuming that the length of the portion extending beyond the virtual circle of the pair of X-axis direction acceleration detecting electrodes is set to 25% or more of the radius dimension R and exceeding the virtual circle of the pair of Y-axis direction acceleration detecting electrodes. The length of the extending portion may be set to 25% or more of the radius dimension R. Then, the pair of X-axis direction acceleration detecting electrodes and the pair of Y-axis direction acceleration detecting electrodes may be prevented from being in contact with each other.

The weight, the diaphragm and the base can be formed in various shapes, and they can be formed as a single unit integrally formed of a metal material. In this case, the single unit can be used as an insert for resin injection molding. Further, by using the single unit as described above, the attachment position of the weight to the diaphragm can be made constant, and not only the assembling accuracy of the acceleration detecting device can be increased, but also the decrease in the measuring accuracy can be suppressed. In addition, this reduces the number of parts of the acceleration sensor, and facilitates the manufacture of the acceleration sensor.

A three-axis acceleration sensor to which the present invention is applied has a pair of X-axis sensors arranged on an imaginary line in the X-axis direction assumed on the surface.
An axial acceleration detection electrode, a pair of Y-axis acceleration detection electrodes disposed on a Y-axis virtual line orthogonal to the X-axis virtual line, a pair of X-axis acceleration detection electrodes, and a pair of Y-axes. An electrode pattern including a plurality of Z-axis direction acceleration detection electrodes disposed between two adjacent electrodes of the direction acceleration detection electrode is formed on a front surface, and a counter electrode pattern facing at least each detection electrode on a back surface. Is formed, and a portion between a pair of X-axis direction acceleration detecting electrodes, a pair of Y-axis direction acceleration detecting electrodes, a plurality of Z-axis direction acceleration detecting electrodes, and a counter electrode pattern is subjected to polarization processing. A substrate, a diaphragm having a back surface joined to a piezoelectric ceramic substrate, a cylindrical weight fixed to the diaphragm so as to protrude toward the back surface of the diaphragm, and a weight change. And comprising a base for supporting the outer peripheral portion of the diaphragm to permit. In the polarization processing, when the acceleration in the Z-axis direction acts on the weight, the respective electrodes of the pair of X-axis direction acceleration detecting electrodes or the pair of Y-axis direction acceleration detecting electrodes have spontaneous spontaneous polarities different from each other. The piezoelectric ceramics are generated so that polarized charges are generated, and a pair of X-axis direction acceleration detection electrodes, a pair of Y-axis direction acceleration detection electrodes, and a plurality of Z-axis direction acceleration detection electrodes are opposed to the weight. In order to form a ring-shaped electrode array that straddles a circular counterweight region of the substrate and an intermediate region located between the counterweight region and the outer peripheral portion and surrounds the counterweight region at an interval from each other. Is formed. In such a three-axis acceleration sensor, a pair of sides located in the direction in which the annular electrode row of the X-axis direction acceleration detection electrode extends extends at substantially equal intervals on both sides of the X-axis direction virtual line, and the X-axis direction virtual line is formed. And a pair of sides positioned in a direction in which the annular electrode row of the Y-axis direction acceleration detecting electrode extends is substantially parallel to the Y-axis direction virtual line at substantially equal intervals on both sides of the Y-axis direction virtual line. I do. The pair of electrodes for detecting the acceleration in the X-axis direction and the pair of electrodes for detecting the acceleration in the Y-axis are formed by the center of the weight, the virtual line in the X-axis direction, and the virtual line in the Y-axis direction generated when the piezoelectric ceramic substrate is joined to the diaphragm. When the amount of deviation from the intersection of the lines is at a maximum, a pair of electrodes for a pair of X-axis acceleration detection or a pair of Y-axis acceleration detection is performed when acceleration in the Z-axis direction acts on the weight. The electrodes are formed such that the sum of the voltages due to the spontaneously polarized charges having different polarities generated at each of the electrodes is 10% or less of the maximum voltage appearing at the plurality of Z-axis direction acceleration detecting electrodes. With this configuration, even if the center of the weight and the intersection of the imaginary line are maximally shifted, even if the acceleration only in the Z-axis direction acts on the weight,
Spontaneous polarization charges having different polarities generated at respective electrodes of the pair of X-axis direction acceleration detection electrodes or spontaneous polarization charges having different polarities generated at respective electrodes of the pair of Y-axis direction acceleration detection electrodes are substantially equal to each other, The spontaneous polarization charges generated in the respective electrodes almost cancel each other. As a result, Z
The X-axis direction acceleration signal or the Y-axis direction acceleration signal generated when the acceleration acts only in the axial direction can be made much smaller than in the past, and the measurement accuracy can be improved.

In order to concretely carry out such a configuration, an imaginary circle drawn with the same radius R as the radius of the weight is assumed around the intersection of the imaginary line in the X-axis and the imaginary line in the Y-axis. Sometimes, the length of the portion extending beyond the virtual circle of the pair of X-axis direction acceleration detecting electrodes is set to 25% or more of the radius dimension R, and the portion extending beyond the virtual circle of the pair of Y-axis direction acceleration detecting electrodes. Is 25% or more of the radius dimension R. And
It is sufficient that the pair of X-axis acceleration detection electrodes, the pair of Y-axis acceleration detection electrodes, and the plurality of Z-axis acceleration detection electrodes do not contact each other.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a schematic sectional view of an acceleration sensor according to an embodiment of the present invention applied to a three-axis acceleration sensor. As shown in the figure, the three-axis acceleration sensor is fixed on the surface of the diaphragm 1, the weight 3, the base 5, and the surface of the diaphragm 1 opposite to the surface on which the weight 3 is mounted. And a sensor element 7. In this figure, the thickness of each part of the sensor element 7 is exaggerated for easy understanding. These members are housed in a case 9 made of insulating resin, and the case 9 made of insulating resin has output electrodes OZ, OE0.
And two metal terminal members 11 having terminal fittings 25.

The diaphragm 1, the weight 3 and the base 5
As shown in FIG. 1, FIG. 2 (A) and FIG. 2 (B), a single unit 1 integrally formed of a metal material made of brass.
It is configured as 0. FIG. 2A is a bottom view of the single unit 10, and FIG.
FIG. 4 is a cross-sectional view taken along line B. Diaphragm 1 has a disk shape and has a thickness of about 0.1 mm. Weight 3
Has a cylindrical shape with a diameter of 40 mm, and is integrated with the diaphragm 1 so that an extension of the axis passes through the center of the diaphragm 1. The base 5 has a cylindrical shape and supports the outer peripheral portion of the diaphragm 1. A V-shaped groove 5 continuous in the circumferential direction is provided on the outer peripheral portion of the base 5.
a is formed. In the present embodiment, a cylindrical metal material made of brass is prepared, and the cylindrical metal material is subjected to a cutting process so as to cut out the weight 3 to form a hollow portion of the annular portion C. To V-groove 5
a was formed and the single unit 10 was integrally molded.

In this example, the piezoelectric ceramic substrate 7a is used as the sensor element 7 as shown in the plan views of FIGS.
A piezoelectric type three-axis sensor element having a triangular acceleration detecting electrode pattern E1 formed on the front surface and an annular counter electrode pattern E0 opposing the main part of the detecting electrode pattern E1 formed on the back surface is used. ing. The back surface of the piezoelectric ceramic substrate 7a and the counter electrode pattern E0 are joined to the surface of the diaphragm 1 with an epoxy-based adhesive, and the sensor element 7 is mounted on the diaphragm 1. The surface of the counter electrode pattern E0 on the side of the diaphragm 1 has irregularities, and an adhesive is filled between the concave part of the irregularities and the diaphragm 1 so that the convex part comes into contact with the diaphragm 1. Are joined to the diaphragm 1. Therefore, the opposing electrode pattern E0 is electrically connected to the base 5 via the diaphragm 1. The piezoelectric ceramic substrate 7a has a quadrangular contour, and a portion corresponding to the electrodes is subjected to polarization processing so that spontaneous polarization is generated when stress is applied to the inside. The polarization process will be described later in detail.

As shown in FIG. 3, the piezoelectric ceramic substrate 7a has a weight facing region 8A, a first stress generating region 8B, and a second stress generating region 8C. A region boundary line 8D is formed between the weight facing region 8A and the first stress generation region 8B. The weight facing region 8 </ b> A has a circular shape at the center of the piezoelectric ceramic substrate 1. In the portion corresponding to the weight facing region 8A,
The weight 3 is located. In this example, an intermediate region is formed by the first stress generation region 8B and the second stress generation region 8C.

The first stress generation region 8B has an annular shape surrounding the weight facing region 8A. When acceleration acts on the weight 3 in a direction parallel to the piezoelectric ceramic substrate 7a (X-axis direction or Y-axis direction), the first stress generation region 8B differs point-symmetrically about the center of gravity of the weight 3. (A state in which a tensile stress is applied and a state in which a compressive stress is applied). When acceleration acts on the weight 3 in a direction (Z-axis direction) orthogonal to the piezoelectric ceramic substrate 7a, each part of the first stress generation region 8B is deformed to the same state.

The second stress generating region 8C has an annular shape surrounding the first stress generating region 8B. Direction perpendicular to the piezoelectric ceramic substrate 1 with respect to the weight 3 (Z-axis direction)
When an acceleration acts on each portion of the second stress generating region 8C, the respective portions are deformed in a state different from that of the first stress generating region 8B.

The detection electrode pattern E1 and the counter electrode pattern E0 formed on the front and back surfaces of the piezoelectric ceramic substrate 7a are both formed by screen printing. When the diaphragm 1 is deformed based on the acceleration acting on the weight 3, the piezoelectric ceramic substrate 7a bends, and the spontaneous polarization charge generated between the detection electrode pattern E1 and the counter electrode pattern E0 changes. The applied acceleration in the directions of the three axes (X axis, Y axis, Z axis) is measured as a change in current or voltage. Note that the X axis, Y axis,
The Z axis is an axis extending in directions orthogonal to each other. X axis is X
It extends in the direction of the imaginary line XL in the axial direction, the Y axis extends in the direction of the imaginary line YL in the Y axis direction, and the Z axis extends in a direction orthogonal to the surface direction of the piezoelectric ceramic substrate 7a.

The detection electrode pattern E1 has an X-axis direction detection electrode pattern 13, a Y-axis direction detection electrode pattern 15, and a Z-axis direction detection electrode pattern 17. The X-axis direction detecting electrode pattern 13 includes a pair of X-axis direction acceleration detecting electrodes EX1 and EX2 and an X-axis output electrode OX connected to a connection line L1.
It has a structure connected in series by L2. The pair of X-axis direction acceleration detection electrodes EX1 and EX2 are a pair of Y-axis direction acceleration detection electrodes EY1 and EY2 of the Y-axis direction detection electrode pattern 15 and the Z-axis direction acceleration of the Z-axis direction detection electrode pattern 17, which will be described later. Detection electrodes EZ1 to EZ4
At the same time, an annular row surrounding the weight facing region 8A is formed. The electrodes EX1 and EX2 of the pair of X-axis direction acceleration detecting electrodes are line-symmetric with respect to the X-axis direction virtual line XL, and the weight facing region 8A and the first stress generating region 8B
(Spans the region boundary line 8D). The acceleration detection electrodes EX1 and EX2
A pair of sides EXa, EXa located in the direction in which the annular detection electrode row extends are substantially parallel to each other. Note that the acceleration detection electrodes EX1 and EX2 are connected to the weight facing region 8.
The dimensions entering A will be described later in detail.

Electrode pattern 15 for detecting acceleration in the Y-axis direction
Has a structure in which two Y-axis direction acceleration detecting electrodes EY1 and EY2 and a Y-axis output electrode OY are connected in series by connection lines L3 to L5. Each of the acceleration detection electrodes EY1 and EY2 of the pair of Y-axis direction acceleration detection electrodes has the same shape as the X-axis direction acceleration detection electrodes EX1 and EX2, and corresponds to the Y-axis direction virtual line YL. It has a shape close to a rectangle which is an object and straddles the weight facing region 8A and the first stress generating region 8B (strides over the region boundary line 8D). Further, a pair of sides E located in a direction in which the annular detection electrode rows of the acceleration detection electrodes EY1 and EY2 extend.
Ya and EYa are substantially parallel to each other. In addition,
The dimensions of the acceleration detection electrodes EY1 and EY2 entering the weight facing region 8A will be described later in detail. Since the Y-axis direction virtual line YL and the X-axis direction virtual line XL are orthogonal to each other, the X-axis direction acceleration detection electrode EX1, the Y-axis direction acceleration detection electrode EY1, and the X-axis direction acceleration detection electrode EX2
And the Y-axis direction acceleration detecting electrode EY2 are arranged at intervals of 90 degrees. Y-axis output electrode O
Y has a substantially square shape similar to the X-axis output electrode OX, and the X-axis output electrode OX is located at the outer peripheral edge of the piezoelectric ceramic substrate 7a outside the second stress generation region 8C. They are formed side by side.

Electrode pattern 17 for detecting acceleration in the Z-axis direction
Are Z-axis direction acceleration detecting electrode EZ1, Z-axis direction acceleration detecting electrode EZ2, Z-axis direction acceleration detecting electrode EZ3.
Z-axis direction acceleration detection electrode EZ4, Z-axis output electrode OZ
Have a structure in which they are connected in series in this order by connection lines L6 to L9. The four Z-axis direction acceleration detecting electrodes EZ1 to EZ4 have a shape close to a rectangle.
The Z-axis direction acceleration detection electrodes EZ1 to EZ4 are also formed so as to straddle the weight facing region 8A and the first stress generation region 8B, similarly to the X-axis direction acceleration detection electrodes EX1 and EX2. Also, the Z-axis direction acceleration detecting electrodes EZ1 to EZ4
Represents an electrode E2 between the X-axis direction acceleration detecting electrode EX2 and the Y-axis direction acceleration detecting electrode EY1;
Y1 and X-axis acceleration detection electrode EX1, X-axis acceleration detection electrode EX1 and Y-axis acceleration detection electrode EY2, Y-axis acceleration detection electrode EY2 and X-axis acceleration detection It is arranged at each central portion between the electrodes EX2. Therefore, the Z-axis direction acceleration detecting electrodes EZ1 to EZ4 are arranged at intervals of 90 degrees. The Z-axis output electrode OZ also has a substantially square shape similarly to the X-axis output electrode OX, and the piezoelectric ceramic substrate 7 outside the second stress generation region 8C.
X-axis output electrodes OX and Y
It is formed alongside the shaft output electrode OY.

On the outer peripheral edge of the piezoelectric ceramic substrate 7a, which is located symmetrically to the outer peripheral edge where the output electrodes OX, OY, OZ are arranged, three earth electrodes OE0.
They are formed side by side so as to be parallel to Y and OZ. The ground electrode OE0 is connected to the counter electrode pattern E0 via a through-hole conductive portion penetrating the piezoelectric ceramic substrate 7a and a connection line (not shown). The ground electrode OE0 and the base 5 may be positively connected using a conductive adhesive. Further, the output electrodes included in the sensor element 7 are divided into two groups of OX, OY, OZ, OE0, and so on. In addition,
In this example, all three electrodes located on the outer peripheral edge of the piezoelectric ceramic substrate 7a are earth electrodes OE0.
At least one of the three electrodes is a ground electrode OE0,
The remaining electrodes may be used as dummy electrodes only for connecting terminals.

X-axis direction acceleration detecting electrodes EX1, EX2
Is located on one side of the weight opposing area 8A when the same type of stress is generated in each part of the piezoelectric ceramic substrate 7a by applying acceleration in the Z-axis direction to the weight 3 at each part. The polarization processing is performed so that spontaneous polarization charges of opposite polarities appear on the acceleration detection electrode EX1 and the acceleration detection electrode EX2 located on the other side. In this example,
When a tensile stress is generated in each portion of the piezoelectric ceramic substrate 7a corresponding to the X-axis direction acceleration detecting electrodes EX1 and EX2, a negative spontaneous polarization charge appears on one X-axis direction acceleration detecting electrode EX1 and the other ends. The polarization processing is performed so that a positive spontaneous polarization charge appears on the X-axis direction acceleration detection electrode EX2.

The Y-axis direction acceleration detecting electrodes EY1,
Similarly to the respective portions of the piezoelectric ceramic substrate 7a corresponding to the X-axis direction acceleration detection electrodes EX1 and EX2, the weight 3 has a Z portion on the piezoelectric ceramic substrate 7a corresponding to the EY2.
When the same type of stress is generated in each part by the acceleration in the axial direction, the Y-axis direction acceleration detection electrode EY1 located on one side of the weight facing region 8A and the Y-axis direction located on the other side Polarization processing is performed so that spontaneous polarization charges of opposite polarities appear on the acceleration detection electrode EY2. In this example, when a tensile stress is generated in each portion of the piezoelectric ceramic substrate 7a corresponding to the Y-axis direction acceleration detection electrodes EY1 and EY2, a negative spontaneous polarization charge is applied to one Y-axis direction acceleration detection electrode EY1. The polarization processing is performed so that the positive spontaneous polarization charge appears on the other Y-axis direction acceleration detection electrode EY2.

The Z-axis direction acceleration detecting electrodes EZ1 to EZ1
Each part of the piezoelectric ceramic substrate 7a corresponding to the EZ4 is provided with all the Z-axis direction acceleration detecting electrodes EZ1 to EZ4 when the same type of stress is generated in the respective parts by the acceleration in the Z-axis direction acting on the weight 3. Has been subjected to a polarization treatment so that spontaneous polarization charges of the same polarity appear in FIG. In this example, when a tensile stress is generated in the portion of the piezoelectric ceramic substrate 7a corresponding to the Z-axis direction acceleration detecting electrodes EZ1 to EZ4, Z
Polarization processing is performed so that positive spontaneous polarization charges appear on the axial acceleration detection electrodes EZ1 to EZ4. These polarization processes are performed on the piezoelectric ceramic substrate 7a before the detection electrode pattern E1 and the counter electrode pattern E0 are formed.
By applying a DC voltage.

In this embodiment, the electrodes EX1 and EX2 for X-axis direction acceleration detection and the electrodes EY1 and E for Y-axis direction acceleration detection are provided.
The electrodes EZ1 to EZ4 for Y2 and Z-axis direction acceleration detection were formed to a thickness of 5 μm by screen printing using a silver paste, and then the connection lines L1 to L9 were formed by screen printing using a silver paste.

FIGS. 4A to 4C show diaphragms 1 and 2.
Single unit 1 in which weight 3 and base 5 are integrally formed
FIG. 5 is a plan view, a partially cutaway sectional view seen from a side, and a half cutaway sectional view seen from a front side of an insulating resin case 9 molded by resin injection molding with 0 as an insert. 4 (B) and 4 (C) show a state where the lid member 6 is attached, and FIG. 4 (A) shows a state where the lid member 6 is not attached. As can be seen from FIG. 4A, the contour of the insulating resin case 9 has a substantially rectangular shape, and has a concave portion 9a on the side where the diaphragm 1 is located. As a result, the insulating resin case 9 has the side wall 9j so as to surround the recess 9a. Note that the side wall portion 9j has a notch-shaped portion formed by a groove portion 19a, 19b and a part of the window portion 9i described later, and is constituted by three side wall portions separated by these notch-shaped portions. ing. Diaphragm 1
Are exposed on the bottom surface 9a1 of the recess 9a. Recess 9
In the inside of the single-unit storage portion 9b formed below the a, a V formed on the outer peripheral portion of the base 5 of the single unit 10 is provided.
The protrusion 9b1 is formed by the resin entering the groove 5a. A projection 9b2 is formed so as to be in contact with the end face 5b of the base 5 opposite to the diaphragm 1.
In this example, since the insulating resin case 9 is integrally formed by injection molding using the single unit 10 as an insert,
The protrusions 9b1 and 9b2 function as retaining members. On the bottom surface 9a1 of the concave portion 9a, four positioning projections 9c... Constituting a positioning portion of the piezoelectric ceramic substrate 7a and five lid member mounting ribs 9d to 9h are integrally formed. The positioning projections 9c are provided in the concave portions 9a of the insulating resin case 9 in the piezoelectric ceramic substrate 7a.
When arranging the piezoelectric ceramic substrate 7a, the center of the diaphragm 1 or the center of the weight is brought into contact with the center of the piezoelectric ceramic substrate 7a by contacting two adjacent sides of the piezoelectric ceramic substrate 7a. In this example, positioning projections 9c are arranged such that two positioning projections 9c abut on two orthogonal sides 7a1 of the piezoelectric ceramic substrate 7a (see FIG. 3). Rib 9 for placing lid member
d to 9h are formed such that the height dimension protruding from the bottom face 9a1 exceeds the height dimension protruding from the bottom face 9a1 of the positioning projections 9c. Then, the lid member 6 is placed on a surface of the lid member placing ribs 9d to 9h opposite to the bottom surface 9a1. Of the lid member mounting ribs 9d to 9h, the four lid member mounting ribs 9d to 9g are formed so as to be connected to the side wall 9j and the bottom surface 9a1 at the four corners of the bottom surface 9a1, respectively. Mounting rib 9h
Are formed so as to be connected to the side wall portion 9j and the bottom surface 9a1 between the lid member mounting ribs 9g and 9d, respectively. A window 9 for exposing a portion (exposed portion) 5c of the outer peripheral surface of the base 5 is provided on a portion of the insulating resin case 9 on the bottom surface 9a1 side and a portion of the side wall 9j continuous with the portion.
i is formed. The terminal support members 21 and 21 of the terminal units 11 and 11 shown in FIG. 1 are fitted and fixed to a pair of side wall portions of the insulating resin case 9 opposed to each other with the unit unit 10 interposed therebetween. Mating grooves 19, 19 are formed. The end of the terminal fitting of one of the terminal units 11 is connected to the output electrode OX, OY, OZ of one group by solder conductive bonding, respectively, and the end of the terminal fitting of the other terminal unit. Are connected to the ground electrodes OEO of the other group by solder conductive bonding.

Next, the acceleration detection electrodes EX1, EX2, E
The dimension in which Y1 and EY2 enter the weight facing region 8A will be described. Acceleration detection electrodes EX1, EX2, EY
Each of the acceleration detection electrodes EY1 and EY2 has the same shape, and the dimensions of each acceleration detection electrode entering the counterweight region 8A are the same. Will be described. FIG. 5 (A)
The state of a portion of the acceleration detection electrodes EY1 and EY2 located in the weight facing region 8A when the center C0 of the weight 3 and the intersection C1 of the virtual line coincide with each other is shown. In FIG. 5A, for easy understanding, the piezoelectric ceramic substrate 7a and the acceleration detection electrodes EY1, EY are used.
The members other than 2 are not shown. As shown in FIG. 5 (A), a radius R (the present example) which is the same as the radius of the weight 3 around an intersection (intersection of the imaginary line) C0 of the imaginary line XL in the X-axis direction and the imaginary line YL in the Y-axis direction. Assuming a first virtual circle 30 drawn in 2 mm), the respective acceleration detection electrodes EY1 and EY2 of the pair of Y-axis direction acceleration detection electrodes
Of the extension S0 extending beyond the first imaginary circle 30
Is 25% or more of the radius dimension R (29% in this example). The widths of the acceleration detection electrodes EY1 and EY2 are different from those of the other acceleration detection electrodes EX1, EX2, EZ1 to EZ.
The size is set so as not to contact with No. 4. In other words, the inner ends EY of the acceleration detection electrodes EY1 and EY2
b, EYb are located on the intersection C1 side of the imaginary line beyond the second imaginary circle 31 having a diameter of 25% of the radius dimension R. In this example, since the center C0 of the weight 3 and the intersection C1 of the imaginary line coincide with each other, the first imaginary circle 30 overlaps with the area boundary line 8D shown in FIG. The third imaginary circle 32 located between the region boundary 8D and the second imaginary circle 31 shown in FIG. 5A and the annular portion sandwiched between the region boundary 8D are the weight 3 33 in which a stress is generated in the weight facing region 8A due to the displacement in the Z-axis direction (stress generating region) 33
It has become. Therefore, the acceleration detection electrodes EY1,
Both the inner ends EYb and EYb of the EY2 exceed the stress generation region 33.

On the other hand, FIG. 5B shows a case where the displacement between the center C0 of the weight 3 and the intersection C1 of the imaginary line, which occurs when the piezoelectric ceramic substrate 7a is joined to the diaphragm 1, is maximized. The state of is shown. Note that FIG. 3 shows an example in which the center C0 of the weight 3 is shifted to the maximum toward the acceleration detection electrode EY2. Such a shift is caused by the dimensional accuracy of the positioning projections 9c of the insulating resin case 9 or the piezoelectric ceramic substrate 7a. When the lengths of the extended portions of the acceleration detection electrodes EY1 and EY2 are set as in this example, the deviation between the center C0 of the weight and the intersection C1 of the imaginary line becomes maximum as shown in FIG. 5B. , The inner ends EYb and EYb of the acceleration detection electrodes EY1 and EY2 are
Both are located on the virtual intersection C1 side beyond the stress generation region 33. As a result, the acceleration detection electrodes EY1,
Each of the EY2s is located on the stress generating region 33 in the weight facing region 8A. When the acceleration only in the Z-axis direction acts on the weight 3, the acceleration detection electrode EY
1 and EY2 are substantially equal in spontaneous polarization charges having different polarities, and the acceleration detection electrodes EY1 and EY2
2, the spontaneous polarization charges almost cancel each other. Therefore, the Y-axis direction acceleration signal generated when the acceleration only in the Z-axis direction acts on the weight can be made much smaller than in the related art. Similarly, the acceleration signal in the X-axis direction generated when the acceleration only in the Z-axis direction acts on the weight can be made much smaller than in the related art.

In each of the above drawings, an example is shown in which the ratio of the length of the extended portion to the radial dimension R is 29%, but when this ratio is 25%, FIG. As shown, when the center C0 of the weight and the intersection C1 of the virtual line are shifted,
The inner end EYb of the acceleration detection electrode EY1 overlaps the second virtual circle 31 (the end of the stress generation region 33).

Next, using the test electrode pattern shown in FIG. 6, a plurality of types of test three-axis acceleration sensors having different electrode dimensions were prepared and subjected to various tests. The three-axis acceleration sensor for testing has the same structure as the three-axis acceleration sensor of the above example except for the electrode pattern on the piezoelectric ceramic substrate 47a. Table 1 below shows the dimensions of the test triaxial acceleration sensors 1 to 10. Each dimension in Table 1 is a dimension of each part corresponding to FIG. More specifically, S1 is the dimension between the inner ends of the acceleration detection electrode Y1 and the acceleration detection electrode Y2, and S2 is the distance between the outer ends of the acceleration detection electrode Y1 and the acceleration detection electrode Y2. S3 is a width dimension of the acceleration detecting electrode Y1 or the acceleration detecting electrode Y2 extending in a direction parallel to the X-axis virtual line XL. S0 / R in Table 1 is the intersection C of the imaginary line.
1 with the same radius dimension R (2 m
m), the virtual circle 40 drawn by the acceleration detection electrodes Y1 and Y2
Is the ratio of the length S0 of the extension extending beyond the radius R to the radius R.

[0033]

[Table 1] Next, the acceleration detection electrodes Y1 and Y2 corresponding to the maximum voltage Vz obtained from the Z-axis direction acceleration detection electrodes Z1 to Z4 when only the Z-axis direction acceleration is applied to the test three-axis acceleration sensors 1 to 10 are applied. Ratio of sum of voltages Vy1 and Vy2 due to generated spontaneous polarization charges of opposite polarity [other axis sensitivity (%):
(Vy1 + Vy2) / Vz] and the deviation (μm) between the center C0 of the weight 3 and the intersection C1 of the virtual line were examined. FIG.
16 to 16 indicate data of the test triaxial acceleration sensors 1 to 10, respectively. The amount of displacement here is defined as the amount by which the center C0 of the weight is shifted toward the acceleration detection electrode Y2, and the amount by which the center C0 of the weight is shifted toward the acceleration detection electrode Y1 is negative. Is the amount of deviation. 7 to 16, in the acceleration sensors 5 to 10 (FIGS. 11 to 16) having S0 / R of 25% or more, the change in the sensitivity of the other axis with respect to the deviation amount can be reduced, and the sensitivity of the other axis is reduced to 0%. It can be seen that the value can be close to. Therefore, it can be seen that the absolute value of the sensitivity to the other axis can be reduced to 10% or less when the amount of displacement generated when the piezoelectric ceramic substrate is joined to the diaphragm becomes maximum (−300 μm to 300 μm in this example). Especially S
Acceleration sensors 8 to 10 with 0 / R of 42.5% (FIGS.
In FIG. 16), it can be seen that the change in the sensitivity of the other axis with respect to the shift amount can be significantly reduced.

Next, the test three-axis acceleration sensors 1 to 10
Sum of the voltages Vy1 and Vy2 due to the spontaneously polarized charges of the opposite polarities generated on the acceleration detecting electrodes Y1 and Y2 when only the acceleration in the Z-axis direction is applied [output difference (mV / G): (Vy1
+ Vy2)] and the amount of deviation (μm) between the center C0 of the weight 3 and the intersection C1 of the virtual line was examined. 17 to 26
Shows data of each of the test triaxial acceleration sensors 1 to 10. 17 to 26, S0 / R is 25.
It can be seen that in the acceleration sensors 5 to 10 (FIGS. 21 to 26) of not less than%, the change of the output difference with respect to the deviation amount can be made small, and the sensitivity of the other axis can be made close to 0%. Especially S0 / R is 4
It can be seen that in the 2.5% acceleration sensors 8 to 10 (FIGS. 24 to 26), the change in the output difference with respect to the shift amount can be significantly reduced.

Next, the test three-axis acceleration sensors 1 to 10
Sum of voltages Vy1 and Vy2 due to spontaneous polarization charges of the same polarity generated on acceleration detecting electrodes Y1 and Y2 when an acceleration in the Y-axis direction is applied to the main axis [principal axis sensitivity (mV / G): (Vy1 +
Vy2)] and the amount of displacement (μm) between the center C0 of the weight 3 and the intersection C1 of the imaginary line was examined. FIG. 27 to FIG.
The data of each of the test triaxial acceleration sensors 1 to 10 is shown. 27 to 36, it can be seen that in the acceleration sensors 5 to 10 (FIGS. 31 to 36) having S0 / R of 25% or more, it is possible to reduce the variation of the spindle sensitivity to the deviation amount. In particular, acceleration sensors 8 to 10 having S0 / R of 42.5%
In FIGS. 34 and 36, it can be seen that the variation in the spindle sensitivity with respect to the amount of displacement can be significantly reduced.

In the present embodiment, an example is shown in which the present invention is applied to a three-axis acceleration sensor. However, the present invention can also be applied to a two-axis acceleration sensor that detects two-axis accelerations in the X-axis direction and the Y-axis direction. Of course.

[0037]

According to the present invention, even if the center of the weight and the intersection of the imaginary line deviate to the maximum, each of the pair of electrodes for detecting the acceleration in the X-axis direction or the pair of electrodes for detecting the acceleration in the Y-axis direction. Each of the electrodes is located on the stress generating region in the weight facing region. Therefore, even if the acceleration only in the Z-axis direction acts on the weight, spontaneous polarization charges having different polarities generated in the respective electrodes of the pair of X-axis direction acceleration detection electrodes or the pair of Y-axis direction acceleration detection electrodes are generated. The spontaneous polarization charges having different polarities generated at the respective electrodes are substantially equal, and the spontaneous polarization charges generated at the respective electrodes substantially cancel each other. As a result, the X-axis direction acceleration signal or the Y-axis direction acceleration signal generated when the acceleration acts only in the Z-axis direction can be made much smaller than before, and the measurement accuracy can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic sectional view of a three-axis acceleration sensor according to an embodiment of the present invention.

FIG. 2A is a bottom view of a single unit used in the three-axis acceleration sensor according to the embodiment of the present invention, and FIG.
It is a BB sectional view taken on the line of (A).

FIG. 3 is a plan view of a sensor element used in the three-axis acceleration sensor according to the embodiment of the present invention.

FIGS. 4A to 4C are plan views of an insulating resin case molded by resin injection molding using a single unit as an insert,
It is the partially broken sectional view seen from the side, and the half broken sectional view seen from the front side.

FIGS. 5A and 5B are diagrams used to describe aspects of an acceleration detection electrode of the three-axis acceleration sensor according to the embodiment of the present invention.

FIG. 6 is a plan view of a sensor element used in a three-axis acceleration sensor used for a test.

FIG. 7 shows another axis sensitivity [(Vy1 +
[Vy2) / Vz] and the amount of deviation between the center of the weight and the intersection of the imaginary line.

FIG. 8 shows another axis sensitivity [(Vy1 +
[Vy2) / Vz] and the amount of deviation between the center of the weight and the intersection of the imaginary line.

FIG. 9 shows another axis sensitivity [(Vy1 +
[Vy2) / Vz] and the amount of deviation between the center of the weight and the intersection of the imaginary line.

FIG. 10 shows another axis sensitivity [(Vy1) of the test three-axis acceleration sensor.
+ Vy2) / Vz] and the amount of deviation between the center of the weight and the intersection of the virtual line.

FIG. 11 shows another axis sensitivity [(Vy1) of the test three-axis acceleration sensor.
+ Vy2) / Vz] and the amount of deviation between the center of the weight and the intersection of the virtual line.

FIG. 12 shows another axis sensitivity [(Vy1) of the test three-axis acceleration sensor.
+ Vy2) / Vz] and the amount of deviation between the center of the weight and the intersection of the virtual line.

FIG. 13 shows the sensitivity of another axis of the test three-axis acceleration sensor [(Vy1
+ Vy2) / Vz] and the amount of deviation between the center of the weight and the intersection of the virtual line.

FIG. 14 shows another axis sensitivity [(Vy1) of the test three-axis acceleration sensor.
+ Vy2) / Vz] and the amount of deviation between the center of the weight and the intersection of the virtual line.

FIG. 15 shows another axis sensitivity [(Vy1) of the test three-axis acceleration sensor.
+ Vy2) / Vz] and the amount of deviation between the center of the weight and the intersection of the virtual line.

FIG. 16 shows another axis sensitivity of the test three-axis acceleration sensor [(Vy1
+ Vy2) / Vz] and the amount of deviation between the center of the weight and the intersection of the virtual line.

FIG. 17 shows an output difference [(Vy1 +
Vy2)] and the amount of deviation between the center of the weight and the intersection of the virtual line.

FIG. 18 shows an output difference [(Vy1 +
Vy2)] and the amount of deviation between the center of the weight and the intersection of the virtual line.

FIG. 19 shows the output difference [(Vy1 +
Vy2)] and the amount of deviation between the center of the weight and the intersection of the virtual line.

FIG. 20 shows an output difference [(Vy1 +
Vy2)] and the amount of deviation between the center of the weight and the intersection of the virtual line.

FIG. 21 shows an output difference [(Vy1 +
Vy2)] and the amount of deviation between the center of the weight and the intersection of the virtual line.

FIG. 22 shows an output difference [(Vy1 +
Vy2)] and the amount of deviation between the center of the weight and the intersection of the virtual line.

FIG. 23 shows an output difference [(Vy1 +
Vy2)] and the amount of deviation between the center of the weight and the intersection of the virtual line.

FIG. 24 shows an output difference [(Vy1 +
Vy2)] and the amount of deviation between the center of the weight and the intersection of the virtual line.

FIG. 25 shows an output difference [(Vy1 +
Vy2)] and the amount of deviation between the center of the weight and the intersection of the virtual line.

FIG. 26 shows an output difference [(Vy1 +
Vy2)] and the amount of deviation between the center of the weight and the intersection of the virtual line.

FIG. 27 shows a main axis sensitivity of a test three-axis acceleration sensor [(Vy1
+ Vy2)] and the amount of deviation between the center of the weight and the intersection of the virtual line.

FIG. 28 shows a main axis sensitivity of a test three-axis acceleration sensor [(Vy1
+ Vy2)] and the amount of deviation between the center of the weight and the intersection of the virtual line.

FIG. 29 shows a main axis sensitivity of a test three-axis acceleration sensor [(Vy1
+ Vy2)] and the amount of deviation between the center of the weight and the intersection of the virtual line.

FIG. 30 shows a main axis sensitivity of a test three-axis acceleration sensor [(Vy1
+ Vy2)] and the amount of deviation between the center of the weight and the intersection of the virtual line.

FIG. 31 shows the spindle sensitivity [(Vy1) of the test three-axis acceleration sensor.
+ Vy2)] and the amount of deviation between the center of the weight and the intersection of the virtual line.

FIG. 32 shows the main axis sensitivity of the test three-axis acceleration sensor [(Vy1
+ Vy2)] and the amount of deviation between the center of the weight and the intersection of the virtual line.

FIG. 33 shows the main axis sensitivity of the test three-axis acceleration sensor [(Vy1
+ Vy2)] and the amount of deviation between the center of the weight and the intersection of the virtual line.

FIG. 34 shows the main axis sensitivity of the test three-axis acceleration sensor [(Vy1
+ Vy2)] and the amount of deviation between the center of the weight and the intersection of the virtual line.

FIG. 35 shows a spindle sensitivity [(Vy1) of a test three-axis acceleration sensor.
+ Vy2)] and the amount of deviation between the center of the weight and the intersection of the virtual line.

FIG. 36 shows a spindle sensitivity [(Vy1) of a test three-axis acceleration sensor.
+ Vy2)] and the amount of deviation between the center of the weight and the intersection of the virtual line.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Diaphragm 3 Weight 5 Base 8A Weight facing area 8D Area boundary line 9 Insulating resin case 10 Single unit C0 Center of weight C1 Intersection of virtual line 30 Virtual circle 33 Stress generating area in weight facing area EX1, EX2 A pair of electrodes for detecting acceleration in the X-axis direction EY1, EY2 A pair of electrodes for detecting acceleration in the Y-axis direction

Claims (5)

[Claims] 1. A pair of electrodes for detecting acceleration in the X-axis direction arranged on an imaginary line in the X-axis direction assumed on the surface and a pair of Y electrodes arranged on an imaginary line in the Y-axis direction orthogonal to the imaginary line in the X-axis direction. An electrode pattern including an axial acceleration detection electrode is formed on the front surface, and a counter electrode pattern facing at least each of the detection electrodes is formed on the back surface, and the pair of Xs
A piezoelectric ceramics substrate in which a portion between the electrode for axial acceleration detection and the pair of electrodes for acceleration detection in the Y-axis direction and the counter electrode pattern is polarized, and the back surface of the piezoelectric ceramics substrate is joined to a front surface; A diaphragm, a column-shaped weight fixed to the diaphragm so as to protrude to the back side of the diaphragm, and a base supporting an outer peripheral portion of the diaphragm so as to allow displacement of the weight. The pair of X-axis direction acceleration detecting electrodes and the pair of Y
An electrode for detecting an acceleration in an axial direction extends over a weight-facing region of the piezoelectric ceramic substrate facing the weight and an intermediate region located between the weight-facing region and the outer peripheral portion and is spaced apart from each other. In the acceleration sensor formed so as to form an annular electrode row surrounding the weight-facing area, a pair of sides of the X-axis direction acceleration detecting electrode located in a direction in which the annular electrode row extends are formed by a pair of sides. A pair of the X-axis direction imaginary lines are substantially parallel to the X-axis direction imaginary line at substantially equal intervals on both sides of the X-axis direction imaginary line, and are located in a direction in which the annular electrode row of the Y-axis direction acceleration detection electrode extends. The sides are substantially parallel to the Y-axis direction virtual line at substantially equal intervals on both sides of the Y-axis direction virtual line, and the pair of X-axis direction acceleration detection electrodes and the pair of Y
The electrode for axial acceleration detection has a maximum deviation amount between the center of the weight and the intersection of the virtual line in the X-axis direction and the virtual line in the Y-axis direction generated when the piezoelectric ceramic substrate is bonded to the diaphragm. When the stress is generated in the weight-facing area by the displacement of the weight in the Z-axis direction orthogonal to the X-axis virtual line and the Y-axis virtual line, the pair of X-axis directions Acceleration detecting electrode and the pair of Y
An acceleration sensor, wherein the acceleration sensor is formed so as to extend beyond an inner end of the axial acceleration detecting electrode. 2. Each of the pair of X-axis direction acceleration detection electrodes is arranged at a symmetrical position with the intersection as a center and has a shape symmetric with respect to the X-axis imaginary line as a center line. Each of the pair of Y-axis direction acceleration detecting electrodes is arranged at a symmetrical position around the intersection and has a shape that is symmetrical with the Y-axis direction virtual line as a center line. A pair of X-axis direction accelerations when assuming a virtual circle drawn with the same radius dimension R as the radius dimension of the weight around an intersection of the X-axis direction virtual line and the Y-axis direction virtual line. The length of the portion of the detection electrode extending beyond the virtual circle is at least 25% of the radius dimension R, and the length of the portion of the pair of Y-axis direction acceleration detection electrodes extending beyond the virtual circle is At least 25% of the radius dimension R; The acceleration sensor according to claim 1, characterized in that it also and the pair of X-axis direction acceleration detecting electrodes and the pair of Y-axis direction acceleration detecting electrodes are not in contact. 3. The acceleration sensor according to claim 1, wherein the weight, the diaphragm, and the base are configured as a single unit integrally formed of a metal material. 4. A pair of X-axis direction acceleration detecting electrodes arranged on a virtual X-axis direction assumed on the surface, and a pair of electrodes arranged on a Y-axis virtual line orthogonal to the X-axis virtual line. A Y-axis direction acceleration detecting electrode, and a plurality of Z-axis direction acceleration detecting electrodes disposed between two adjacent electrodes of the pair of X-axis direction acceleration detecting electrodes and the pair of Y-axis direction acceleration detecting electrodes. Are formed on the front surface, and a counter electrode pattern facing at least the respective detection electrodes is formed on the back surface, and the pair of X-axis direction acceleration detection electrodes and the pair of Y-axis direction acceleration detection A piezoelectric ceramics substrate in which electrodes and portions between the plurality of Z-axis direction acceleration detecting electrodes and the counter electrode pattern are polarized; and the back surface of the piezoelectric ceramics substrate is joined to a front surface An ear diaphragm; a column-shaped weight fixed to the diaphragm so as to protrude to the rear surface side of the diaphragm; and a base supporting an outer peripheral portion of the diaphragm so as to allow displacement of the weight. The pair of X-axis direction acceleration detecting electrodes, the pair of Y-axis direction acceleration detecting electrodes, and the plurality of Z-axis direction acceleration detecting electrodes are circular weights of the piezoelectric ceramic substrate facing the weight. Formed so as to form a ring-shaped electrode row that straddles the weight facing region and the intermediate region located between the weight facing region and the outer peripheral portion and surrounds the weight facing region at intervals. The polarization process is performed when the acceleration in the Z-axis direction acts on the weight, and the respective electrodes of the pair of X-axis direction acceleration detection electrodes or the respective pairs of the Y-axis direction acceleration detection electrodes. In a three-axis acceleration sensor in which spontaneous polarization charges having different polarities are generated at the poles, a pair of sides of the X-axis direction acceleration detection electrode, which are located in a direction in which the annular electrode row extends, are formed along the X-axis. A pair of sides located in a direction in which the annular electrode row of the Y-axis direction acceleration detecting electrode extends in a direction substantially parallel to the X-axis direction virtual line at substantially equal intervals on both sides of the direction virtual line. The pair of electrodes for detecting acceleration in the X-axis direction and the pair of Y electrodes are substantially parallel to the virtual line in the Y-axis direction at substantially equal intervals on both sides of the virtual line in the Y-axis direction.
The electrode for axial acceleration detection has a maximum deviation amount between the center of the weight and the intersection of the virtual line in the X-axis direction and the virtual line in the Y-axis direction generated when the piezoelectric ceramic substrate is bonded to the diaphragm. When the acceleration in the Z-axis direction acts on the weight, a voltage is generated on each electrode of the pair of X-axis acceleration detection electrodes and on each of the pair of Y-axis acceleration detection electrodes. Characterized in that the sum of voltages due to spontaneously polarized charges of different polarities is 10% or less of the maximum voltage appearing at the plurality of Z-axis direction acceleration detecting electrodes. . 5. Each of the pair of X-axis direction acceleration detecting electrodes is arranged at a symmetrical position with respect to the intersection, and has a shape symmetric with respect to the X-axis imaginary line as a center line. Each of the pair of Y-axis direction acceleration detecting electrodes is arranged at a symmetrical position around the intersection and has a shape that is symmetrical with the Y-axis direction virtual line as a center line. A pair of X-axis direction accelerations when assuming a virtual circle drawn with the same radius dimension R as the radius dimension of the weight around an intersection of the X-axis direction virtual line and the Y-axis direction virtual line. The length of the portion of the detection electrode extending beyond the virtual circle is at least 25% of the radius dimension R, and the length of the portion of the pair of Y-axis direction acceleration detection electrodes extending beyond the virtual circle is At least 25% of the radius dimension R; 5. The acceleration sensor according to claim 4, wherein the pair of X-axis direction acceleration detection electrodes, the pair of Y-axis direction acceleration detection electrodes, and the plurality of Z-axis direction acceleration detection electrodes do not contact each other. .