JPH10170539A - Acceleration sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To miniaturize an acceleration sensor and reduce its weight, by forming a detection electrode by avoiding a part, where a stress generated at a piezoelectric element becomes zero when an acceleration in the direction of X axis is applied to the acceleration sensor, and its vicinity, and a part, where a stress generated when an acceleration in a direction that is parallel to X and Y planes is applied becomes zero, and its vicinity. SOLUTION: Four detection electrodes 26 are formed on the upper surface of a piezoelectric element 23. The periphery part of the detection electrodes 26 is provided apart a specific distance from a line 27 inside the line 27 where a stress becomes zero when an acceleration in the direction of Z axis is applied to an acceleration sensor. Further, a ring-shaped detection electrode 28 is provided apart, by a specific distance, from a line 30 outside the line 30, where the stress becomes zero when an acceleration in the directions of X and Y axes is applied. The electrodes 26 with a high stress value and a small area are arranged at an inner periphery, an acceleration in the directions of X and Y axes is detected, and a detection electrode 28, where a stress value is low but an area is large is arranged at an outer-periphery side for detecting an acceleration in the direction of Z axis, thus generating more electric charges efficiently.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

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

[0002]

2. Description of the Related Art Acceleration sensors are used in the automobile industry as sensors for controlling air bags. Although various detection methods have been developed, the present invention provides a weight that generates inertial force due to acceleration at the center of a flexible member to which a piezoelectric element with an electrode formed on the surface is attached. The present invention relates to a method for detecting an acceleration by deforming a flexible member by force (the piezoelectric element attached to the surface at this time also deforms and generates an electric charge proportional to the amount of distortion).

As a prior art relating to the present invention, there is JP-A-5-26744. FIG. 1 is a front cross-sectional view showing a typical example of a conventional acceleration sensor. FIG. 2 is a plan view seen from the piezoelectric element side. A piezoelectric element 2 having detection electrodes 3, 4, 5, and 6 formed on both sides is attached to the upper surface of a flexible disk-shaped substrate 1, and the center of the lower surface is used to control the movement of the sensor. The weight body 7 for replacing the distortion of the disk-shaped substrate having the above is attached.

[0004] When the relative position between the weight and the flexible member is shifted by the acceleration, the piezoelectric element attached to the flexible member is distorted, and electric charges are generated. Electric charges are collected by electrodes formed on the surface and measured as a certain potential (voltage). In this specification, it is expressed as electric charge generated in an electrode. The amount of electric charge generated in the piezoelectric element changes depending on the amount of distortion. In addition, the amount of generated charges varies depending on the area and volume of the piezoelectric element.

Japanese Patent Application Laid-Open No. 5-25744 discloses a force sensor using a piezoelectric element, a plate-like piezoelectric element, an upper electrode formed on the upper surface of the piezoelectric element, and a lower electrode formed on the lower surface of the piezoelectric element. And four pairs of detectors composed of the lower electrode and the origin are defined at one point in the flexible substrate, and X is set in a direction passing through the origin and parallel to the substrate surface.
An axis is defined, two of the prepared four detectors are arranged on the positive side of the X-axis, and the other two are disposed on the negative side along the X-axis, respectively. One electrode is fixed to the substrate, the outer peripheral part of the substrate is fixed to the sensor housing, and an acting body having a function of transmitting a force generated based on a physical quantity acting from the outside to the origin is formed. The force generated in the body is detected based on the charge generated in each electrode of the four sets of detectors. The acceleration is detected by generating a force on the working body based on the acceleration given from the outside. it can. FIG. 2 shows four sets in the X axis direction and four sets in the Y axis direction.
It is an example in which sets of detectors are arranged. By arranging the electrodes in this manner, accelerations in three directions of the X axis, the Y axis, and the Z axis can be detected.

[0006]

In order to detect acceleration in three axial directions, for example, the shape of the detection electrode must be complicated as in the prior art. Therefore, processing accuracy,
It is difficult to increase the detection sensitivity because it is easily affected by the assembling accuracy and it is difficult to form a large area for each detection electrode. Furthermore, the distribution of stress generated on the piezoelectric element when acceleration is applied to the acceleration sensor is complicated, and unless the detection electrodes are arranged at appropriate positions, it is impossible to efficiently extract electric charges. The present invention is to solve the problem by devising the arrangement of the detection electrodes.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the conventional acceleration sensor, and is compact and lightweight.
Provided is an acceleration sensor capable of detecting acceleration in three axial directions with high sensitivity and high accuracy.

A plate-like flexible member, a piezoelectric element provided with an electrode attached to the surface of the flexible member, a weight body directly or indirectly attached to the flexible member, In an acceleration sensor having a support member that directly or indirectly supports the outer periphery of the member, an origin is defined inside a plate-shaped flexible member,
The X axis passes through the origin in a direction parallel to the plane of the flexible member, the X axis at the origin is orthogonal to the X axis, and the Y axis passes in a direction parallel to the plane of the flexible member, passes through the origin, and When the Z axis is defined in a direction perpendicular to the plane of the flexible member,
A portion where the stress generated in the piezoelectric element becomes zero when the acceleration sensor is applied with an acceleration in the Z-axis direction and its vicinity, and a piezoelectric element which is obtained by applying an acceleration to the acceleration sensor in a direction parallel to the X and Y planes. The detection electrode is formed so as to avoid the portion where the stress generated in the step becomes zero and its vicinity.

The electrodes for detecting acceleration in the X-axis and Y-axis directions include a portion where the stress generated in the piezoelectric element becomes zero when acceleration in the Z-axis direction is applied to the acceleration sensor, the vicinity thereof, and the acceleration sensor. An electrode for detecting acceleration in the Z-axis direction, formed on the inside of the surface of the piezoelectric element while avoiding a portion where the stress generated in the piezoelectric element becomes zero when acceleration is applied in a direction parallel to the X and Y planes and in the vicinity thereof, When acceleration is applied to the acceleration sensor in the direction parallel to the X and Y planes, and in the vicinity of the portion where the stress generated in the piezoelectric element becomes zero when acceleration in the Z-axis direction is applied, It is formed outside the surface of the piezoelectric element while avoiding the part where the stress generated in the element becomes zero and its vicinity.

Further, the detection electrodes for acceleration in the X-axis and Y-axis directions are formed on the X-axis and Y-axis and symmetrically with respect to the X-axis and Y-axis. , X axis, Y
Formed symmetrically about the axis. Then, a lead electrode is provided on the outer peripheral portion.

In the acceleration sensor configured as described above, when acceleration is applied to the acceleration sensor, the absolute value of the stress generated in the piezoelectric element becomes smaller toward the outer periphery in the radial direction, and eventually becomes zero. Further toward the outer periphery in the radial direction, the sign of the stress is reversed this time. That is, when the inner peripheral side is positive, the outer peripheral side is negative, and conversely, when the inner peripheral side is negative, the outer peripheral side is positive. Therefore, if the detection electrode is formed across the line where the stress becomes zero, the sign of the charge generated in the same detection electrode generates both positive and negative charges,
Since they cancel each other, the output voltage decreases as a result. Also, if the detection electrode is formed up to and near the part where the stress is zero, the stress distribution will be slightly shifted due to processing and assembly errors, and both positive and negative charges will be generated in the same detection electrode. In some cases. Therefore, by forming the detection electrodes as described above, the X-axis, Y-axis
Electric charges can be efficiently generated when acceleration is applied in the axial and Z-axis directions, and the detection sensitivity can be increased. The stress distribution will be described in detail in the embodiments of the present invention.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail with reference to the drawings. FIG. 3 is a top view of the first embodiment of the present invention. FIG.
1 is a front sectional view of a first embodiment of the present invention. An origin 22 is defined inside a disk-shaped flexible member 21 as shown in FIG.
2, the X axis in a direction parallel to the plane of the flexible member 21, the Y axis orthogonal to the X axis at the origin 22, and the Y axis in a direction parallel to the plane of the flexible member 21, passing through the origin 22, and , A Z axis is defined in a direction perpendicular to the plane of the flexible member 21.

A piezoelectric element 23 is attached to the upper surface of the disk-shaped flexible member 21 so that the center on the surface and the Z axis coincide with each other. A cylindrical weight 24 is attached to the lower surface of the flexible member 21 so that the central axis thereof coincides with the Z axis. The flexible member 21, the piezoelectric element 23, and the weight 24 constitute the sensor unit 20. The outer periphery of the flexible member 21 is supported by a support member 25. The support member 25 is provided with a circular through hole 25a and a sunken portion 25b having a large radius concentric with the through hole 25a. Here, the central axes of the through hole 25a and the sinking portion 25b coincide with the Z axis.
The flexible member 21 is positioned and supported by the sunken part 25b.

The flexible member 21 uses an elinvar material. The weight body 24 was made of stainless steel (SUS303). The support member 25 was made of a metal material. The piezoelectric element 23 is made of PZT which is a piezoelectric ceramic, and the electrode is made of Ag-
It was formed of a Cr alloy. The electrodes may be formed by a method such as sputtering or screen printing. The arrangement of the electrodes will be described later in detail. The flexible member 21 and the piezoelectric element 23 were joined with an epoxy adhesive. The flexible member 21 and the weight body 24 are also fixed by an epoxy adhesive, but may be fixed by a method such as welding. The flexible member 21 and the support member 25 were fixed with an adhesive. The material of the member is not limited to these as long as it satisfies a predetermined function. Preferably, materials having close thermal expansion coefficients are selected.

Next, the arrangement of the detection electrodes will be described. In determining the positions where the detection electrodes are to be arranged, a finite element method analysis was performed, and the distribution of the stress generated on the surface of the piezoelectric element 23 was examined in detail. FIG. 5 is a cross-sectional view showing a state where acceleration in the X-axis plus direction is applied to the acceleration sensor. (Electrode is omitted.) FIG. 6 is a cross-sectional view showing a state where acceleration in the X-axis minus direction is applied to the acceleration sensor. (The electrodes are omitted.) When acceleration in the negative X-axis direction is applied to the acceleration sensor, the direction in which the weight body 24 swings is opposite to that in FIG. FIG. 7 is a cross-sectional view showing a state in which acceleration in the Z-axis plus direction is applied to the acceleration sensor. (Electrodes are omitted.) FIG. 8 is a cross-sectional view showing a state in which acceleration in the Z-axis minus direction is applied to the acceleration sensor.
(The electrodes are omitted.) When acceleration in the negative Z-axis direction is applied to the acceleration sensor, the direction in which the weight body 24 swings is opposite to that in FIG.

FIG. 9 is a graph showing a stress distribution appearing on the X-axis when an acceleration in the Z-axis minus direction is applied to the acceleration sensor. FIG. 10 is a graph showing a stress distribution appearing on the X-axis when an acceleration in the X-axis plus direction is applied to the acceleration sensor. The horizontal axis represents the radial distance (mm) from the origin 22 and the vertical axis represents the stress value (Kgf / mm2). The graphs are shown on the plus side in the radial direction. Referring to FIGS. 5 to 8, the stress distribution on the minus side in the radial direction is line-symmetric with respect to the vertical axis in FIG. 9, and with respect to the origin in FIG. Point symmetry.

The following dimensions and materials were used in the finite element analysis. The flexible member 21 has a diameter of 20 mm and a thickness of 0.1 mm, and the piezoelectric element 23 has a diameter of 20 mm.
PZT having a thickness of 0.12 mm and a weight body 24 having a diameter of 4
The supporting member 25 was SUS303 having an outer diameter of 25 mm, an inner diameter (through hole 25a) of 19 mm, and a thickness of 4 mm. The sunken part 25b of the support member 25 had a diameter of 20.02 mm and a depth of 0.5 mm. The flexible member 21 and the piezoelectric element 23 are fixed to the sunken portion 25b with an adhesive at the outer peripheral plane portion and the circumferential portion. As for the constraint condition, the support member 25 was constrained in all directions on the end face opposite to the fixed end face of the flexible member 21. The analysis was performed by applying an acceleration of 10 G to the acceleration sensor in the Z-axis minus direction and 10 G in the X-axis plus direction. Here, G represents the gravitational acceleration.

According to the graphs of FIGS. 9 and 10, when acceleration is applied to the acceleration sensor, the absolute value of the stress generated in the piezoelectric element becomes smaller toward the outer periphery in the radial direction, and eventually becomes zero. Further toward the outer periphery in the radial direction, the sign of the stress is reversed this time. That is, when the inner peripheral side is positive, the outer peripheral side becomes negative, and conversely, when the inner peripheral side is negative, the outer peripheral side becomes positive. It was also found that the location where the stress value became zero was different between the case where acceleration in the Z-axis direction was applied to the acceleration sensor and the case where acceleration was applied in the X-axis and Y-axis directions. Therefore, if the detection electrode is formed across a line where the stress becomes zero, both positive and negative charges are generated in the same detection electrode and cancel each other, resulting in a small output voltage. If the detection electrode is formed near the portion where the stress becomes zero, the stress distribution may be slightly shifted due to processing and assembly errors, and both positive and negative charges may be generated in the same detection electrode. The stress value is substantially zero in the inner peripheral portion, which is a portion where the weight body 24 is fixed and where the deformation of the piezoelectric element 23 hardly occurs.

A detection electrode was formed based on the result of the finite element analysis. Four fan-shaped detection electrodes 26 are formed on the upper surface of the piezoelectric element 23 on the X-axis and the Y-axis and symmetrically with respect to the X-axis and the Y-axis. The circumferential portion of the detection electrode 26 is provided at a predetermined distance from the line 27 inside the line 27 where the stress becomes zero when an acceleration in the Z-axis direction is applied to the acceleration sensor. Further, the piezoelectric element 23
An annular detection electrode 28 is formed on the upper surface of the acceleration sensor 28 so as to be axially symmetrical with respect to the X axis and the Y axis. On the outside, it is provided at a predetermined distance from the line 30. On the piezoelectric element 23, the detection electrode 26 is disposed on the inner side, and the detection electrode 28 is disposed on the outer side. It is also possible to arrange the detection electrode 26 on the outer periphery and the detection electrode 28 on the inner periphery. However, in FIG. 10, when acceleration is applied in the X-axis and Y-axis directions, the inner peripheral side shows a higher stress value. Also in FIG. 9, the stress value on the inner circumference side is slightly larger than that on the outer circumference side. The amount of generated charge is proportional to the product of the stress value and the area. Therefore, a detection electrode 26 having a high stress value and a small area is arranged on the inner peripheral side to detect accelerations in two X-axis and Y-axis directions, and a detection electrode 28 having a low stress value but a large area can be obtained. It is preferable to detect the acceleration in the Z-axis direction by arranging it on the outer peripheral side because more charges can be efficiently generated.

Further, the detection electrodes were formed such that the amounts of charges generated in the detection electrodes in the X-axis, Y-axis, and Z-axis directions were substantially equal. The shape of the detection electrode was set by calculating the product of the stress value generated in the piezoelectric element 23 obtained by the finite element analysis and the distribution area where the stress value is distributed, and calculating the sum of the products. This calculation is performed for the detection electrodes 26a to 26d and the detection electrode 28. The sum of the charge amounts of the detection electrodes 26a and 26c related to the detection of the acceleration in the X-axis direction, the sum of the charge amounts of the detection electrodes 26b and 26d related to the detection of the acceleration in the Y-axis direction, and the acceleration of the Z-axis direction. The shape was determined so that the electric charges of the detection electrodes 28 related to the detection become equal. By forming the detection electrodes in this manner, electric charges can be efficiently generated when acceleration is applied in the X-axis, Y-axis, and Z-axis directions, and the detection sensitivity can be increased. Further, the detection sensitivities in the X-axis, Y-axis, and Z-axis directions become substantially equal. An electrode 29 is formed on almost the entire lower surface of the piezoelectric element 23. Four extraction electrodes 29 a are extended from the electrode 29 to the upper surface of the piezoelectric element 23.

The operation of detecting the acceleration will be described. When acceleration acts on the acceleration sensor, the weight 24
Is moved, the sensor section 20 is deformed, and the detection electrode 26,
A charge is generated at 28. Since the detection circuit (not shown) is connected to the detection electrodes 26 and 28 and the electrode 29 serving as the reference potential (lead electrode 29a) by lead wires, the four detection electrodes 26 and the charge generated in the detection electrodes 28 are connected. The direction and magnitude of the acceleration can be detected from the amount.

In the first embodiment, the direction of polarization of the electrodes formed on the upper surface of the piezoelectric element 23 is the same in the Z-axis direction. As described above, FIG. 5 is a cross-sectional view showing a state where acceleration in the X-axis plus direction is applied to the acceleration sensor.
(Electrode is omitted.) FIG. 6 is a cross-sectional view showing a state where acceleration in the X-axis minus direction is applied to the acceleration sensor. (The electrodes are omitted.) When acceleration in the negative X-axis direction is applied to the acceleration sensor, the direction in which the weight body 24 swings is opposite to that in FIG. When an acceleration in the positive direction of the X-axis is applied to the acceleration sensor, the charge generated on the detection electrode 26a is positive, and the charge generated on the detection electrode 26b is canceled by plus and minus to zero (hereinafter, generated on each detection electrode). This is the reason why the charge is zero), the charge generated on the detection electrode 26c is minus, the charge generated on the detection electrode 26d is zero, and the charge generated on the detection electrode 28 is zero. Here, the detection electrode 26 has an X-axis,
Since it is symmetric on the Y axis and about the X axis and the Y axis,
The charges generated at 26a and 26c have the opposite signs and the same magnitude. The magnitude and direction of the acceleration in the X-axis direction are detected by differentially amplifying the charges generated on the detection electrodes 26a and 26c. Regarding the detection electrode 28, a negative charge is generated in a region extending on the positive side of the X-axis, and a positive charge is generated in a region expanding on the negative side of the X-axis. The total charges generated in the detection electrodes 28 cancel each other to become zero. When an acceleration in the negative direction of the X-axis is applied to the acceleration sensor, the charge generated at the detection electrode 26a is negative, the charge generated at the detection electrode 26b is zero, the charge generated at the detection electrode 26c is positive, and the charge generated at the detection electrode 26d is generated. The charge generated is zero, and the charge generated on the detection electrode 28 is zero. The sign of the result of differentially amplifying the charges generated on the detection electrode 26a and the detection electrode 26c is opposite to that in the case where acceleration in the X-axis plus direction is applied to the acceleration sensor, and the direction of the applied acceleration can be specified.

A case where acceleration in the Y-axis direction is applied to the acceleration sensor will be described. When acceleration is applied to the acceleration sensor in the positive Y-axis direction, the charge generated on the detection electrode 26a is zero, the charge generated on the detection electrode 26b is positive,
The electric charge generated in the detection electrode 26c is zero, and the detection electrode 26d
Is negative, and the charge generated on the detection electrode 28 is zero. Here, since the detection electrode 26 is symmetric on the X axis and the Y axis and with respect to the X axis and the Y axis,
And 26d have the opposite sign and the same magnitude. The magnitude and direction of the acceleration in the Y-axis direction are detected by differentially amplifying the charges generated on the detection electrodes 26b and 26d. Regarding the detection electrode 28, a negative charge is generated in a region extending on the positive side of the Y axis and a positive charge is generated in a region extending on the negative side of the Y axis. However, since the detection electrode 28 is formed line-symmetrically with respect to the X and Y axes, The total charges generated in the detection electrodes 28 cancel each other to become zero. When acceleration in the negative Y-axis direction is applied to the acceleration sensor, the electric charge generated at the detection electrode 26a is zero, the electric charge generated at the detection electrode 26b is negative, the electric charge generated at the detection electrode 26c is zero, and the electric charge generated at the detection electrode 26d is generated. The generated charge is positive, and the charge generated on the detection electrode 28 is zero. Detection electrode 26
The sign of the result of differentially amplifying the electric charge generated at a and the detection electrode 26c is opposite to that in the case where acceleration in the Y-axis plus direction is applied to the acceleration sensor, and the direction of the applied acceleration can be specified.

As described above, FIG. 7 is a sectional view showing a state in which acceleration in the Z-axis plus direction is applied to the acceleration sensor.
(Electrodes are omitted.) FIG. 8 is a cross-sectional view showing a state in which acceleration in the Z-axis minus direction is applied to the acceleration sensor. (The electrodes are omitted.) When acceleration in the negative Z-axis direction is applied to the acceleration sensor, the direction in which the weight body swings is opposite to that in FIG. When an acceleration in the Z-axis plus direction is applied to the acceleration sensor, the charge generated on the detection electrodes 26a to 26d is positive, and the charge generated on the detection electrode 28 is negative. Here, the detection electrode 26 is on the X axis and the Y axis and is symmetric with respect to the X axis and the Y axis.
The electric charges generated at .about.26d have the same sign and the same magnitude. In order to differentially amplify the electric charges generated on the detection electrodes 26a and 26c and the detection electrodes 26b and 26d, the detection outputs in the X-axis and Y-axis directions become zero. When acceleration in the negative Z-axis direction is applied to the acceleration sensor, the charge generated on the detection electrodes 26a to 26d is negative, and the charge generated on the detection electrode 28 is positive. In order to differentially amplify the electric charges generated on the detection electrodes 26a and 26c and the detection electrodes 26b and 26d, the detection outputs in the X-axis and Y-axis directions become zero. The direction and magnitude of the acceleration in the Z-axis direction can be detected from the sign and magnitude of the charge generated on the detection electrode 28.

FIG. 11 is a top view of the second embodiment of the present invention. The configuration of the second embodiment is exactly the same as that of the first embodiment, and the shape of the electrodes formed on the top view of the piezoelectric element 23 is different. The different parts will be described. The annular detection electrode 28 formed in the first embodiment is divided into four parts as shown in FIG. The four divided detection electrodes 28 are formed line-symmetrically with respect to the X axis and the Y axis. Detection electrodes 26a to 26d
Thus, the extraction electrode 26e is drawn to the outer peripheral side through the divided portion of the detection electrode 28 (portion where no electrode is formed). The divided detection electrode 28 is the detection electrode 2
A cross-shaped electrode 28a is formed so as to pass through the portion where the electrode 6 is not formed, so that electrical continuity can be obtained. From one of the divided detection electrodes 28, an extraction electrode 28b is extended to the outer peripheral side. Electrode 2
Nine extraction electrodes 29a are provided at three places and are formed at positions of ± 45 ° with respect to the X axis. In the second embodiment, the extraction electrode is formed on the outer peripheral side of the piezoelectric element 23,
The position where the lead wire is fixed can be a position where deformation of the piezoelectric element 23 is small, that is, a position where generation of electric charge is small. If the extraction electrode is formed after polarization, no charge is generated from the extraction electrode even if the piezoelectric element 23 is deformed. Therefore, it is preferable that the charge generated in the detection electrode is not canceled.

[0026]

According to the present invention, the following effects can be obtained by employing the above-described structure. 14 detection electrodes 26 are arranged on the X axis and the Y axis, and
A predetermined distance from the line 27 is formed inside the line 27, which is formed axially symmetric with respect to the axis and the Y axis, and has a circumferential portion whose stress becomes zero when acceleration in the Z-axis direction is applied to the acceleration sensor. The detection electrode 28 having a circular shape is provided on the X-axis,
The X-axis and Y-axis are formed on the acceleration sensor
By providing a predetermined distance from the line 30 outside the line 30 where the stress becomes zero when the axial acceleration is applied, the charge can be efficiently collected and the detection sensitivity increases. 2 Forming the detection electrode so that the amount of electric charge generated in the detection electrode is equal by obtaining the product of the stress value generated in the piezoelectric element and the distribution area where the stress value is distributed, and obtaining the sum of the products. Thus, the detection sensitivities in the X-axis, Y-axis, and Z-axis directions become substantially equal. (3) Since the detection sensitivity between the axes is equal, the detection circuit is simplified. (4) The time required for circuit adjustment is shortened and the circuit can be manufactured at low cost. 5 The size of the circuit can be reduced because the circuit configuration is simplified.

[Brief description of the drawings]

FIG. 1 is a front sectional view of a conventional acceleration sensor.

FIG. 2 is a plan view of a conventional acceleration sensor viewed from a piezoelectric element side.

FIG. 3 is a top view of the acceleration sensor according to the first embodiment of the present invention.

FIG. 4 is a front sectional view of the acceleration sensor according to the first embodiment of the present invention.

FIG. 5 is a front view, partially in section, showing a state in which acceleration in the X-axis plus direction is applied to the acceleration sensor in the first embodiment of the acceleration sensor according to the present invention.

FIG. 6 is a front view of the acceleration sensor according to the first embodiment of the present invention, with a partial cross section showing a state in which acceleration in the X-axis negative direction is applied to the acceleration sensor;

FIG. 7 is a partial front view showing a state in which acceleration in the Z-axis plus direction is applied to the acceleration sensor in the first embodiment of the acceleration sensor according to the present invention.

FIG. 8 is a front view of the acceleration sensor according to the first embodiment of the present invention, with a partial cross section showing a state in which acceleration in the negative Z-axis direction is applied to the acceleration sensor.

FIG. 9 is a graph showing a stress distribution when acceleration in the negative Z-axis direction is applied to the acceleration sensor in the first embodiment of the acceleration sensor according to the present invention.

FIG. 10 is a graph showing a stress distribution when an acceleration in the X-axis plus direction is applied to the acceleration sensor in the first embodiment of the acceleration sensor according to the present invention.

FIG. 11 is a top view of a second embodiment of the acceleration sensor according to the present invention.

[Explanation of symbols]

 Reference Signs List 1 substrate 2 piezoelectric element 3 detection electrode 4 detection electrode 5 detection electrode 6 detection electrode 7 weight body 20 sensor unit 21 flexible member 22 origin 23 piezoelectric element 24 weight body 25 support member 25a through hole 25b sunken part 26 detection electrode 26a Detection electrode 26b Detection electrode 26c Detection electrode 26d Detection electrode 26e Extraction electrode 27 line 28 Detection electrode 28a electrode 28b Extraction electrode 29 electrode 29a Extraction electrode 30 line

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Minoru Hatakeyama 4107 Miyoshida, Miyoshida-cho, Kitasaku-gun, Nagano Prefecture Inside Miyota Co., Ltd. (72) Inventor Keiya Okada 4107 Miyoshida, Miyoshida-cho, Kitasaku-gun, Nagano Pref.

Claims (4)

[Claims] A piezoelectric element provided with an electrode attached to a surface of the flexible member; a weight directly or indirectly attached to the flexible member; In an acceleration sensor having a support member that directly or indirectly supports the outer periphery of a flexible member, an origin is defined inside the plate-like flexible member, and the origin is defined in a direction parallel to a plane of the flexible member through the origin. X
The axis is defined as a Y axis in a direction orthogonal to the X axis at the origin and parallel to the plane of the flexible member, and a Z axis in a direction passing through the origin and perpendicular to the plane of the flexible member. When acceleration is applied to the acceleration sensor in a direction parallel to the X and Y planes, and in the vicinity of the portion where the stress generated in the piezoelectric element becomes zero when acceleration in the Z-axis direction is applied to the acceleration sensor, An acceleration sensor, wherein a detection electrode is formed so as to avoid a portion where stress generated in the piezoelectric element becomes zero and its vicinity. 2. An electrode for detecting acceleration in the X-axis and Y-axis directions,
A portion where the stress generated in the piezoelectric element becomes zero when the acceleration in the Z-axis direction is applied to the acceleration sensor and its vicinity, and a portion in which the acceleration is applied to the piezoelectric element in a direction parallel to the X and Y planes. A portion where the generated stress is zero and its vicinity are avoided, and formed on the inner peripheral side of a portion where the stress generated in the piezoelectric element is zero on the surface of the piezoelectric element, and the detection electrode for acceleration in the Z-axis direction is the acceleration sensor. When the acceleration in the Z-axis direction is applied to the piezoelectric sensor, the stress generated in the piezoelectric element becomes zero when the acceleration is applied in a direction parallel to the X and Y planes, and in the vicinity of the portion where the stress generated in the piezoelectric element becomes zero. 2. The acceleration sensor according to claim 1, wherein the acceleration sensor is formed on an outer peripheral side of a portion where a stress generated in the piezoelectric element is zero on a surface of the piezoelectric element while avoiding a portion where the zero is present and its vicinity. 3. An electrode for detecting acceleration in the X-axis and Y-axis directions,
It is formed on the X axis and the Y axis and symmetrically with respect to the X axis and the Y axis, and the acceleration detection electrode in the Z axis direction is formed symmetrically with respect to the X axis and the Y axis. The acceleration sensor according to claim 1 or 2, wherein 4. The acceleration sensor according to claim 1, wherein a lead electrode is provided on an outer peripheral portion.