JP2000162235A - Accelerometer and angular velocity sensor - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a sensor having simplified structure, is small-sized and whose efficiency is satisfactory. SOLUTION: Crossed finger-shaped electrodes X1, X2, Y1, Y2, Z1 to Z4 are formed on the surface of a disk-shaped piezoelectric element 500. Every crossed finger-shaped electrode is constituted in such a way that two kinds of electrode groups composed of a plurality of finger-shaped electrodes arranged at prescribed intervals are arranged alternately. A voltage at a prescribed polarity is applied across both electrode groups, and a polarization treatment is executed. A plumb-hob body 540 is bonded to the central part on the rear surface of the piezoelectric element 500. The circumferential part on the rear surface is fixed to a device enclosure via a pedestal 550. When an AC signal is given to the electrodes Z1 to Z4, the plumb bob 540 vibrates in the Z-axis direction. When an angular velocity ωx and an angular velocity ωy act in this state, the Coriolis force Fy and the Coriolis force Fx in the Y-axis direction or in the X-axis direction act on the plumb bob 540, a flexure is generated in the piezoelectric element 500, and the flexure is detected on the basis of electromagnetic forces which are generated in the electrodes Y1, Y2 or the electrodes X1, X2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an acceleration sensor and an angular velocity sensor, and more particularly to a sensor capable of detecting acceleration and angular velocity based on mechanical deformation of a piezoelectric element.

[0002]

2. Description of the Related Art In the automobile industry, the machinery industry, and the like, demands for acceleration sensors and angular velocity sensors capable of accurately detecting angular velocity around a predetermined axis and acceleration in a predetermined axial direction are increasing. In general, an object that moves freely in a three-dimensional space is affected by an acceleration in an arbitrary direction and an angular velocity in an arbitrary rotation direction. Therefore, in order to accurately grasp the motion of the object, it is necessary to detect the angular velocity around each coordinate axis together with the acceleration in each coordinate axis direction in the XYZ three-dimensional coordinate system. In particular, in order to accurately capture the three-dimensional movement of the object in the XYZ three-dimensional rectangular coordinate system, the angular velocity ωx around the X axis and the angular velocity ω around the Y axis
y, angular velocity ωz about the Z axis, acceleration αx in the X axis direction,
It is indispensable to detect angular velocity and acceleration components for a total of six axes, ie, the acceleration αy in the Y-axis direction and the acceleration αz in the Z-axis direction.

In order to meet such demands, the inventor of the present application has proposed, for example, International Publication No.
4/23272, JP-A-8-35981,
JP-A-8-68636, JP-A-8-94661, JP-A-8-226931, JP-A-8-28
No. 5608 and the like have proposed an angular velocity sensor and an acceleration sensor using a piezoelectric element. With these sensors,
By joining a weight to the piezoelectric element, or using a part of the piezoelectric element as a weight, and measuring the force based on acceleration or Coriolis force based on angular velocity acting on the weight, three-dimensional , The angular velocity around each axis and the acceleration in each axis direction can be detected. Here, as for the angular velocity, when an object is moved in the Z-axis direction in a state where an angular velocity ωx about the X axis is acting on a certain object,
Detection is performed using the principle that the Coriolis force Fy acts in the Y-axis direction. When the acceleration αx in the X-axis direction acts on a certain object, a force based on the acceleration in the X-axis direction (here, (Accelerated force)
Detection using the principle that fx acts is performed.

[0004]

Demand for angular velocity / acceleration detection of an object moving in a three-dimensional space is only increasing more and more. In the future, in particular, it is desired to reduce the size and cost of the sensor. However, the angular velocity sensor or acceleration sensor that has been put to practical use requires electrodes to be formed on the upper and lower surfaces of the piezoelectric element, and many structural parts are still complicated. There was a problem that was difficult.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a compact and efficient acceleration sensor and angular velocity sensor which are simplified in structure.

[0006]

According to a first aspect of the present invention, there is provided an acceleration sensor having a function of detecting acceleration acting in at least one axis direction in an XYZ three-dimensional coordinate system. A piezoelectric element that undergoes mechanical deformation when a force is applied to the displacement section with the fixed section fixed, an apparatus housing that accommodates the piezoelectric element and supports and fixes the fixed section, The weight body formed in the portion and the interdigital electrode formed at the position where the mechanical deformation of the piezoelectric element occurs are arranged at predetermined intervals so as to be substantially parallel to each other, and short-circuited to each other. A first electrode group consisting of a plurality of finger electrodes and a second electrode group consisting of a plurality of finger electrodes arranged at predetermined intervals so as to be substantially parallel to each other and short-circuited to each other form an interdigital finger. Constituting an electrode, a first electrode The finger electrodes forming the group and the finger electrodes forming the second electrode group are arranged so as to be alternately arranged, and the piezoelectric element includes a first electrode group and a second electrode group. Is applied by applying a voltage of a predetermined polarity to the piezoelectric element. When a force is applied to the displacement portion based on the acceleration applied to the weight body and the piezoelectric element is mechanically deformed, the first An electromotive force corresponding to the acceleration is generated between the electrode group and the second electrode group.

(2) A second aspect of the present invention is the above-mentioned first aspect.
In the acceleration sensor according to the aspect, a plate-shaped piezoelectric element having a flat upper surface is used, a peripheral portion thereof is fixed to the device housing as a fixing portion, and a weight portion is formed here as a center portion as a displacement portion. An XYZ three-dimensional coordinate system is defined such that the origin is at the center of the upper surface of the piezoelectric element and the upper surface is included in the XY plane. An interdigital electrode that is directed toward the interdigital electrode is arranged so that an X-axis component of the applied acceleration can be detected based on an electromotive force generated in the interdigital electrode.

(3) The third aspect of the present invention is the above-mentioned second aspect.
In the acceleration sensor according to the aspect, the first interdigital electrode in which each finger electrode is oriented substantially in the Y-axis direction is disposed on the positive portion of the upper surface of the piezoelectric element in the X-axis direction. X
A second interdigital electrode is arranged in the negative portion of the axis such that each of the interdigital electrodes is oriented substantially in the Y-axis direction, and an electromotive force generated in the first interdigital electrode and the second interdigital electrode are arranged. The X-axis direction component and the Z-axis direction component of the applied acceleration are detected based on the electromotive force generated in the above.

(4) The fourth aspect of the present invention relates to the above-described third aspect.
In the acceleration sensor according to the aspect, in addition to the first interdigital electrode and the second interdigital electrode, further, each of the finger electrodes is substantially connected to the X-axis on the positive portion of the Y-axis on the upper surface of the piezoelectric element. A third interdigital electrode is arranged so as to face in the direction, and a fourth interdigital electrode in which each finger electrode is oriented substantially in the X-axis direction is provided on the negative portion of the Y-axis on the upper surface of the piezoelectric element. An X-axis component of the applied acceleration is detected based on the electromotive force generated in the first interdigital electrode and the electromotive force generated in the second interdigital electrode, and the third interdigital electrode is arranged. The Y-axis component of the applied acceleration is detected based on the electromotive force generated in the first interdigital electrode and the electromotive force generated in the fourth interdigital electrode. Based on the electromotive force generated in the interdigital electrode, or based on the electromotive force generated in the third interdigital electrode and the fourth interdigital electrode.
Based on the electromotive force generated in the interdigital electrodes of
The Z-axis component of the applied acceleration is detected based on the electromotive force generated in all of the first to fourth interdigital electrodes.

(5) The fifth aspect of the present invention is the above-mentioned first aspect.
In the acceleration sensor according to the aspect, a plate-shaped piezoelectric element having a flat upper surface is used, a peripheral portion thereof is fixed to the device housing as a fixing portion, and a weight portion is formed here as a center portion as a displacement portion. An XYZ three-dimensional coordinate system having an origin at the center of the upper surface of the piezoelectric element and the upper surface included in the XY plane is defined. On the X axis of the upper surface of the piezoelectric element, each finger-shaped electrode is centered on the origin. An interdigital electrode that is oriented substantially along an arc is arranged, and an X-axis component of the applied acceleration can be detected based on an electromotive force generated in the interdigital electrode.

(6) The sixth aspect of the present invention is the above-mentioned fifth aspect.
In the acceleration sensor according to the aspect, the first interdigital electrode is disposed on the upper surface of the piezoelectric element on the positive portion of the X axis such that each finger electrode is oriented substantially along an arc centered on the origin. Then, on the negative portion of the X-axis on the upper surface of the piezoelectric element, a second intersecting finger-like electrode is arranged such that each finger-like electrode is oriented substantially along an arc centered on the origin, and The X-axis direction component and the Z-axis direction component of the applied acceleration are detected based on the electromotive force generated in the finger electrode and the electromotive force generated in the second interdigital electrode.

(7) The seventh aspect of the present invention is the above-described sixth aspect.
In the acceleration sensor according to the aspect, in addition to the first interdigital electrode and the second interdigital electrode, further, each finger electrode is centered on the origin on the positive portion of the Y-axis on the upper surface of the piezoelectric element. A third interdigital electrode is arranged so as to face a direction substantially along the circular arc, and each finger-shaped electrode substantially follows the circular arc centered on the origin on the negative portion of the Y-axis on the upper surface of the piezoelectric element. The fourth interdigital electrode is arranged so as to face in the direction indicated by the arrow, and based on the electromotive force generated in the first interdigital electrode and the electromotive force generated in the second interdigital electrode, X of the applied acceleration is obtained. Detecting an axial component, detecting a Y-axis component of the applied acceleration based on the electromotive force generated in the third interdigital electrode and the electromotive force generated in the fourth interdigital electrode, Based on the electromotive force generated in the interdigital electrode and the electromotive force generated in the second interdigital electrode,
Alternatively, based on the electromotive force generated in the third interdigital electrode and the electromotive force generated in the fourth interdigital electrode,
The Z-axis component of the applied acceleration is detected based on the electromotive force generated in all the fourth interdigital electrodes.

(8) An eighth aspect of the present invention is an angular velocity sensor having a function of detecting an angular velocity acting on at least one axis in an XYZ three-dimensional coordinate system, comprising: a fixed part and a displacement part; A piezoelectric element that undergoes mechanical deformation when a force is applied to the displacement section with the section fixed, a device housing that accommodates the piezoelectric element and supports and fixes the fixed section, and a weight formed on the displacement section. A weight, and a driving interdigital electrode and a detecting interdigital electrode formed at a position where mechanical deformation of the piezoelectric element occurs, are arranged at predetermined intervals so as to be substantially parallel to each other, A first electrode group consisting of a plurality of finger electrodes short-circuited to each other, and a second electrode group consisting of a plurality of finger electrodes short-circuited and arranged at predetermined intervals so as to be substantially parallel to each other. Each interdigital electrode The finger electrodes constituting the first electrode group and the finger electrodes constituting the second electrode group are arranged so as to be alternately arranged. A polarization process is performed by applying a voltage having a predetermined polarity between the first electrode group and the second electrode group to form a driving interdigital electrode. By supplying a signal, the weight body can be moved along a predetermined trajectory, and Coriolis force is generated based on the angular velocity acting during the movement of the weight body, and the piezoelectric element is mechanically deformed. Is generated, an electromotive force corresponding to the angular velocity is generated between the first electrode group and the second electrode group constituting the detection interdigital electrode.

(9) The ninth aspect of the present invention is the above-mentioned eighth aspect.
In the angular velocity sensor according to the aspect, a plate-shaped piezoelectric element having a flat upper surface is used, a peripheral portion thereof is fixed to the device housing as a fixing portion, and a weight body is formed here as a displacement portion at the center portion. An XYZ three-dimensional coordinate system having an origin at the center of the upper surface of the piezoelectric element and including the upper surface in the XY plane is defined. A first driving interdigital electrode that is oriented in the axial direction is arranged, and a second driving electrode in which each finger electrode is oriented substantially in the Y-axis direction is provided on the negative portion of the upper surface of the piezoelectric element on the X-axis. An interdigital electrode is arranged, and a third interdigital electrode for driving such that each finger electrode is oriented substantially in the X-axis direction is arranged on a positive portion of the Y-axis on the upper surface of the piezoelectric element. On the negative part of the Y axis on the top surface,
A fourth driving interdigital electrode is arranged such that each finger electrode is oriented substantially in the X-axis direction, and the first driving interdigital electrode and the second driving interdigital electrode are each provided with a weight. An AC signal for exciting in the X-axis direction capable of causing the body to vibrate in the X-axis direction is supplied, and the third driving interdigital electrode and the fourth driving interdigital electrode are connected to the weight body by Y. An AC signal for excitation in the Y-axis direction capable of causing a single oscillation in the axial direction is supplied, and the phase of the AC signal for excitation in the X-axis direction and the AC signal for excitation in the Y-axis direction are 90 °.
By displacing the weight, it is possible to cause the weight to perform a circular motion on the XY plane. When the weight performs the circular motion, the weight acts in a direction perpendicular to the tangential direction of the circular motion trajectory. By detecting the Coriolis force by the interdigital electrode for detection, the angular velocity about an axis orthogonal to both the tangential direction and the direction of the Coriolis force can be detected.

(10) According to a tenth aspect of the present invention, in the angular velocity sensor according to the eighth aspect described above, a plate-like piezoelectric element having a flat upper surface is used, and a peripheral portion of the piezoelectric element is used as a fixing portion. , A weight portion is formed here with a center portion thereof as a displacement portion, and an XYZ three-dimensional coordinate system having an origin at the center of the upper surface of the piezoelectric element and an upper surface included in the XY plane is defined. A first cross finger electrode for detection is arranged such that each finger-like electrode is oriented substantially in the Y-axis direction on the positive portion of the X-axis on the upper surface of the element, and on the negative portion of the X-axis on the upper surface of the piezoelectric element. By disposing a second detection interdigital electrode such that each finger electrode is oriented substantially in the Y-axis direction and supplying a predetermined AC signal to the driving interdigital electrode, the weight body is moved in the XY plane. To perform a circular motion on the top, and when the weight crosses the X-axis, the first detection Based on the electromotive force generated in the difference-digital electrodes and the second detection interdigital electrodes, in which to be able to detect the angular velocity around the Z-axis.

(11) According to an eleventh aspect of the present invention, in the angular velocity sensor according to the eighth aspect described above, a plate-like piezoelectric element having a flat upper surface is used, and a peripheral portion thereof is used as a fixing portion, and the housing of the device is used. , A weight portion is formed here with a center portion thereof as a displacement portion, and an XYZ three-dimensional coordinate system having an origin at the center of the upper surface of the piezoelectric element and an upper surface included in the XY plane is defined. By disposing a detection interdigital electrode capable of detecting the displacement of the weight body in the Z-axis direction on the upper surface of the element, and supplying a predetermined AC signal to the driving interdigital electrode, the weight body is obtained. Can be made to perform a circular motion on the XY plane, when the weight body crosses the X axis, based on the electromotive force generated in the detection interdigital electrode, to detect the angular velocity around the X axis, Electromotive force generated at the detection interdigital electrode when the weight crosses the Y axis Based on, in which to be able to detect the angular velocity around the Y-axis.

(12) A twelfth aspect of the present invention is the angular velocity sensor according to the eighth aspect described above, wherein a plate-like piezoelectric element having a flat upper surface is used, and a peripheral portion of the piezoelectric element is used as a fixing portion. And a weight portion is formed here with the center portion as a displacement portion. An XYZ three-dimensional coordinate system is defined in which the origin is at the center of the upper surface of the piezoelectric element and the upper surface is included in the XY plane. On the positive portion of the X-axis on the upper surface of the element, a first driving interdigital electrode is arranged such that each finger-shaped electrode is oriented substantially along an arc centered on the origin, On the negative portion of the X axis, a second driving interdigital electrode is arranged such that each finger electrode is oriented substantially along an arc centered on the origin, and the Y axis positive electrode on the upper surface of the piezoelectric element is arranged. The third drive for each finger-shaped electrode to point in the direction substantially along the arc centered on the origin A fourth driving interdigital electrode in which a forefinger electrode is arranged, and each finger electrode is oriented in a direction substantially along an arc centered on the origin on a negative portion of the Y-axis on the upper surface of the piezoelectric element. And an X-direction excitation AC signal capable of causing the weight body to vibrate in the X-direction in a simple manner is supplied to the first driving inter-digital electrode and the second driving inter-digital electrode. The third driving interdigital electrode and the fourth driving interdigital electrode are supplied with an AC signal for excitation in the Y-axis direction capable of making the weight body vibrate in the Y-axis direction, and the X-axis. 90 ° phase between AC signal for directional excitation and AC signal for Y-axis directional excitation
By displacing the weight, it is possible to cause the weight to perform a circular motion on the XY plane. When the weight performs the circular motion, the weight acts in a direction perpendicular to the tangential direction of the circular motion trajectory. By detecting the Coriolis force by the interdigital electrode for detection, the angular velocity about an axis orthogonal to both the tangential direction and the direction of the Coriolis force can be detected.

(13) According to a thirteenth aspect of the present invention, in the angular velocity sensor according to the eighth aspect, a plate-like piezoelectric element having a flat upper surface is used, and a peripheral portion of the piezoelectric element is used as a fixing portion. , A weight portion is formed here with a center portion thereof as a displacement portion, and an XYZ three-dimensional coordinate system having an origin at the center of the upper surface of the piezoelectric element and an upper surface included in the XY plane is defined. A first intersecting finger electrode for detection is arranged such that each finger electrode is oriented substantially along an arc centered on the origin on the positive portion of the X axis on the upper surface of the element, On the negative portion of the X-axis, a second detection interdigital electrode is disposed such that each finger electrode is oriented substantially along an arc centered on the origin, and a predetermined value is provided on the driving interdigital electrode. By supplying an AC signal, the weight body can make a circular motion on the XY plane. When the weight crosses the X-axis, the angular velocity around the Z-axis can be detected based on the electromotive force generated in the first detection interdigital electrode and the second detection interdigital electrode. It was done.

(14) According to a fourteenth aspect of the present invention, in the sensor according to the eighth to thirteenth aspects, the physically identical interdigital electrode is replaced with the driving interdigital electrode and the detecting interdigital electrode. This is used as an electrode that also serves as both a finger electrode.

(15) A fifteenth aspect of the present invention is the sensor according to any one of the first to fourteenth aspects, wherein the weight body is constituted by a part of the piezoelectric element.

(16) According to a sixteenth aspect of the present invention, in the sensor according to the first to fifteenth aspects, a plate-like piezoelectric element is used as the piezoelectric element, and crossed fingers are formed on both upper and lower surfaces of the piezoelectric element. An electrode is formed.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below based on an embodiment shown in the drawings.

§1. Piezoelectric element having interdigital electrodes As described above, various forms of acceleration sensors and angular velocity sensors using piezoelectric elements have already been proposed. A feature of the present invention is that an interdigital electrode is formed on a piezoelectric element, and based on an electromotive force generated in the interdigital electrode, an applied acceleration force or Coriolis force is detected. The point is that the piezoelectric element is caused to vibrate by applying a voltage. Therefore, here, the configuration of the piezoelectric element having the interdigital electrodes used in the present invention and its basic behavior will be described.

First, as shown in FIG.
An interdigital electrode constituted by the zero and second electrode groups 20 is formed on the upper surface of the plate-shaped piezoelectric element 30. The interdigital electrode in the specification of the present application is an electrode having a unique pattern formed by combining the first electrode group 10 and the second electrode group 20 as described above, and the first electrode group. Each of the electrode group 10 and the second electrode group 20 is composed of a plurality of short-circuited finger electrodes arranged at predetermined intervals so as to be substantially parallel to each other. Moreover, the finger-like electrodes constituting the first electrode group 10 and the finger-like electrodes constituting the second electrode group are arranged alternately.

In the specific example shown in FIG. 1, X
By defining the axis and the Y axis in the vertical direction of the drawing, the first electrode group 10
Are five finger-like electrodes 11 to 11 arranged in the Y-axis direction.
15, a wiring section 16 for connecting them, and a terminal section 17 for making electrical contact with the outside, while the second electrode group 20 is oriented in the Y-axis direction. It comprises five arranged finger-like electrodes 21 to 25, a wiring part 26 for connecting them, and a terminal part 27 for making electrical contact with the outside. Here, the finger electrodes 11 to 15 constituting the first electrode group 10 and the finger electrodes 21 to 25 constituting the second electrode group 20 alternately (alternately) along the X-axis direction. ) They are arranged side by side. In FIG. 1, each of the first electrode group 10 and the second electrode group 20 is shown in a hatched pattern so that the shapes of the first electrode group 10 and the second electrode group 20 can be easily grasped.
FIG. 1 is a top view of a plate-shaped piezoelectric element 30, and the hatching patterns applied to the first electrode group 10 and the second electrode group 20 are not intended to show cross sections.

FIG. 2 is a side sectional view of the plate-shaped piezoelectric element 30 shown in FIG. 1 cut along the X axis.
The axis and the Z axis are defined in the vertical direction (the Y axis is perpendicular to the paper surface). The individual finger electrodes 11 to 15 constituting the first electrode group 10 and the individual finger electrodes 21 to 25 constituting the second electrode group 20 are arranged on the upper surface of the plate-shaped piezoelectric element 30 in the X-axis direction. The state of being alternately arranged along is clearly shown.

Now, as shown in FIGS. 1 and 2,
An interdigital electrode (first electrode group 1) is placed on a plate-shaped piezoelectric element 30.
After the 0th and second electrode groups 20) are formed, a predetermined polarization process is performed on the piezoelectric element using the interdigital electrodes. Here, it is assumed that the polarization processing is performed by a method as shown in the side sectional view of FIG. That is, the second electrode group 20 is located between the first electrode group 10 and the second electrode group 20.
A predetermined polarization voltage Ep is applied so that the side becomes positive, and is left as it is for a while. When such a polarization voltage Ep is applied, an electric field having the polarity as shown in the drawing is generated between the adjacent finger electrodes near the upper surface of the plate-shaped piezoelectric element 30. The element 30 has a specific electric property as described later.

Various conditions for performing such a polarization treatment are as follows.
The determination is made in consideration of the type of the piezoelectric element to be used, the dimensions of each part, the distance between the finger electrodes, the sensitivity of the sensor to be created, and the like. For example, PZT (PbZr _x
On the upper surface of a plate-like piezoelectric element made of Ti _1-x O ₃ : lead zirconate titanate) having a thickness of 0.3 to 0.5 mm, cross fingers are arranged so that the interval between adjacent finger electrodes is 0.2 mm. When the electrode is formed, a state where a polarization voltage Ep = 200 V (an electric field of 1000 V / mm is generated between adjacent finger electrodes) is applied for 20 minutes is maintained. In addition, a polarization treatment suitable for use in the present invention could be performed. Of course, this condition is an example, and any condition for the polarization process may be set as long as the measurement principle described below can be implemented.

When the above-mentioned polarization processing is completed, the plate-shaped piezoelectric element 30 has the following specific electric properties. First, as shown in FIG.
And a predetermined driving voltage Ed between the second electrode group 20 and the second electrode group 20.
When (in this example, the second electrode group 20 side is positive), as shown by an arrow in the figure, a stress is generated such that the distance between the finger electrodes is extended, and the piezoelectric element 30 is extended in the horizontal direction in the figure. Such mechanical deformation will occur. Further, as shown in FIG. 5, when a driving voltage −Ed of the opposite polarity is applied, as shown by an arrow in the drawing, a stress is generated such that the space between the finger electrodes contracts, and the piezoelectric element 30 is moved in the horizontal direction in the drawing. Mechanical deformation such as shrinking occurs. That is, the piezoelectric element 30 can be expanded or contracted in the horizontal direction in the figure depending on the polarity of the driving voltage applied between the first electrode group 10 and the second electrode group 20. Moreover, the degree of the expansion and contraction can be adjusted according to the magnitude of the driving voltage.

However, the absolute value of the drive voltage Ed is set to be sufficiently smaller than the absolute value of the polarization voltage Ep, and care is taken so that the application of the drive voltage Ed does not perform the polarization process again. For example, in the above-described polarization processing, the polarization voltage Ep is set to 200 V. On the other hand, if the driving voltage Ed is set to about ± 5 V, the influence of the application of the driving voltage to the polarization processing again can be ignored. Further, here, the electrical characteristics are such that when a driving voltage Ed having the same polarity as the polarization voltage Ep is applied, the distance between the finger electrodes is increased, and when a driving voltage having the opposite polarity is applied, the distance between the finger electrodes is reduced. Although an example in which the electric characteristics are taken is shown, depending on the piezoelectric element used, electric characteristics opposite to this may be taken. In any case,
The first electrode group 10 and the second electrode group 10
When a drive voltage is applied with a first polarity between the electrode groups 20, the finger-like electrodes expand, and when a drive voltage is applied with a second polarity opposite to the first polarity, the finger-like electrodes shrink. Electrical characteristics will result.

In the above, the predetermined driving voltage E is applied to the interdigital electrode.
The characteristic that a predetermined mechanical deformation occurs when d is applied. On the contrary, the characteristic that a predetermined electromotive force is generated in the interdigital electrode when the piezoelectric element 30 is mechanically deformed. appear. For example, as shown in FIG. 6, a force F that pulls the right end of the piezoelectric element 30 rightward is applied to the piezoelectric element 30.
When a force FL that pulls the left end of the left end portion in the left direction is applied simultaneously with the application of R, a stress in the extending direction is applied between the finger electrodes. When such a stress is applied, as shown, a negative charge is generated on the first electrode group 10 side, and a positive charge is generated on the second electrode group side (depending on the piezoelectric element). And the polarity of the charge may be reversed), and an electromotive force is generated between the two. On the other hand, as shown in FIG. 7, when a force FL that pushes the right end of the piezoelectric element 30 to the left and a force FR that pushes the left end of the piezoelectric element 30 to the right act on the piezoelectric element 30, each finger-like shape is obtained. A compressive stress is applied between the electrodes. When such a stress is applied, as shown, a positive charge is generated on the first electrode group 10 side, and a negative charge is generated on the second electrode group 20 side (by the piezoelectric element). In some cases, the polarity of the charges may be reversed), and an electromotive force having a polarity opposite to that in the case described above is generated between the two.

The electromotive force generated in this way changes according to the magnitude of the applied force, and when a larger force is applied, a larger electromotive force is generated.
Therefore, the first electrode group 10 and the second electrode group 20
By measuring the electromotive force generated between them and its polarity, it is possible to detect the magnitude and direction (whether to expand or contract in the horizontal direction in the figure) of the force applied to the piezoelectric element 30.

§2. Basics of acceleration sensor according to the present invention
Structure and Principle of Operation Subsequently, the basic structure and operation principle of the acceleration sensor according to the present invention will be described. Here, first, a piezoelectric element 30 as shown in the top view of FIG. 8 is prepared. This piezoelectric element 30
It is a disk-shaped piezoelectric element, and two sets of interdigital electrodes X1 and X2 are formed on the upper surface thereof. These interdigital electrodes X1 and X2 are the interdigital electrodes described in §1, and are the first electrode group 10 and the second electrode group 2 respectively.
It is composed of 0 combinations. Here, the origin O is set at the center position of the piezoelectric element 30, and X is set in the horizontal direction of the drawing.
XYZ with axis, Y axis in vertical direction, and Z axis in vertical direction on paper
A three-dimensional coordinate system is defined (coordinate axes are indicated by dashed lines here). Focusing on the positional relationship on this coordinate system, as shown in the figure, the individual finger electrodes constituting each of the interdigital electrodes X1 and X2 are all oriented in the Y-axis direction, and along the X-axis. It will be arranged side by side. Further, the first interdigital electrode X1 is disposed at the positive portion of the X-axis, and the second interdigital electrode X2 is disposed at the negative portion of the X-axis. Are arranged at positions substantially symmetric with respect to the Y axis. In the illustrated example, focusing on the shapes of the interdigital electrodes X1 and X2, both shapes are completely the same, and are arranged point-symmetrically with respect to the origin O. Of course, the shapes of both interdigital electrodes X1 and X2 may be mirror images.

When such a piezoelectric element 30 is prepared, a polarization process is performed by the method described in §1. Then, as shown in the side sectional view of FIG. 9, the weight body 40 is joined to the lower surface of the central portion of the piezoelectric element 30 after the polarization processing, and the cylindrical pedestal 50 is attached to the lower surface of the peripheral portion of the piezoelectric element 30. To join. The pedestal 50 is a member that constitutes a part of the device housing. Actually, the piezoelectric element 30 is housed inside the device housing, but the illustration of the entire device housing is omitted here for convenience of explanation. As described above, the piezoelectric element 30 has a property of causing mechanical deformation. As shown, the periphery of the piezoelectric element 30 is
To the device housing. On the other hand, a weight body 40 is joined to the center of the piezoelectric element 30, and the weight body 40 is
Is suspended in the air. Therefore, when a force based on acceleration (acceleration force) or Coriolis force acts on the weight body 40, mechanical deformation occurs in the piezoelectric element 30, and the weight body 40 is displaced. Eventually, the peripheral portion of the piezoelectric element 30 functions as a fixed portion, and the piezoelectric element 30
Of the piezoelectric element 30 will be mechanically deformed when a force is applied to the displacement portion while the fixed portion is fixed. The interdigital electrodes X1 and X2 are formed at positions where mechanical deformation of the piezoelectric element 30 occurs. It will be indicated by a simple bold line).

First, the principle of detecting acceleration using a sensor as shown in FIG. 9 will be described. Now, assuming that the acceleration αx along the X-axis direction acts on the entire sensor, as shown in FIG. 10, the weight body 40 acts on the acceleration force fx along the X-axis direction based on the acceleration αx. Force) acts, and the position of the center of gravity G is X
It will move by + Δx in the axial direction. At this time, the piezoelectric element 30 undergoes mechanical deformation as shown in the drawing, and the interdigital electrode X1 extends in the X-axis direction, and the interdigital electrode X2 contracts in the X-axis direction. As a result, a predetermined electromotive force is generated in each of the interdigital electrodes X1 and X2, but the polarities of both electromotive forces are reversed. For example, when the first electrode group 10 side of each interdigital electrode is set to the ground level, the second electrode group 20 of the interdigital electrode X1 is set.
When a positive voltage is generated on the side, the second electrode X2
, A negative voltage is generated on the side of the electrode group 20. Therefore, the magnitude of the applied acceleration force fx can be obtained by taking the difference in consideration of the sign of both electromotive forces.

When the position of the center of gravity G of the weight body 40 moves by -Δx in the X-axis direction due to the action of the acceleration force -fx in the opposite direction, as shown in FIG.
Since the expansion and contraction state of 1 and X2 is reversed, the sign of the difference between the two electromotive forces is also reversed. Thus, by measuring the electromotive force generated in the interdigital electrodes X1 and X2, the direction and magnitude of the acceleration αx acting in the X-axis direction can be obtained. In the above example,
The acceleration αx in the X-axis direction is determined by the pair of interdigital electrodes X1 and X2.
Alternatively, it is possible to obtain the acceleration αx using only one of X2 and X2. However, in order to eliminate various measurement errors and disturbances and obtain a highly accurate detection value, it is preferable to use a method of obtaining a difference between electromotive forces generated in a pair of interdigital electrodes. As will be described later, when the acceleration αz acting in the Z-axis direction is also detected, a pair of interdigital electrodes as described here is used to remove a component caused by the acceleration αz. It is necessary to adopt a detection method based on the difference.

According to the same principle, the direction and magnitude of the acceleration acting in the Y-axis direction can be obtained. That is, in the example shown in the top view of FIG. 8, two interdigital electrodes X1 and X2 arranged on the X axis are used, but similarly, two interdigital electrodes arranged on the Y axis. Y1, Y2
The acceleration αy acting in the Y-axis direction can be detected by using (interdigital electrodes obtained by rotating the illustrated interdigital electrodes X1 and X2 by 90 ° about the origin O). become.

Next, for a sensor as shown in FIG.
Consider a case where an acceleration αz along the Z-axis direction acts.
For example, as shown in FIG. 12, when the acceleration force fz (force acting based on the acceleration αz) along the Z-axis direction acts on the weight body 40, the position of the center of gravity G moves in the Z-axis direction. Assume that it has moved by + Δz. Then, the piezoelectric element 3
0, mechanical deformation occurs as shown, and the interdigital electrode X
Both 1 and X2 extend in the X-axis direction. As a result, an electromotive force of the same polarity is generated in each of the interdigital electrodes X1 and X2. When the first electrode group 10 side of each interdigital electrode is set to the ground level, for example, a positive voltage is generated on the second electrode group 20 side of each interdigital electrode. Will be. Therefore, the magnitude of the applied acceleration force fz can be obtained by taking the sum of the two electromotive forces.

Also, consider a case where the position of the center of gravity G of the weight body 40 moves by -Δz in the Z-axis direction due to the action of the acceleration force -fz in the opposite direction. In this case, the piezoelectric element 30 undergoes mechanical deformation as shown in FIG. According to an experiment conducted by the inventor of the present application, in this case, an electromotive force having a polarity opposite to that shown in FIG. 12 was generated in the interdigital electrodes X1 and X2. These are the interdigital electrodes X1, X2
However, each of them means that they are deformed in the direction of shrinking in the X-axis direction. As far as the state shown in FIG. 13 is concerned, the phenomenon that the interdigital electrodes X1 and X2 are shrunk may seem somewhat unnatural, but in the sensor used by the present inventor in the experiment, the pedestal 50 has a certain degree. It is made of a flexible material (specifically, a metal).
It is considered that the deformation such that the upper part of the sword narrows inward is also occurring at the same time. That is, considering the deformation of the pedestal 50, as shown in FIG. 13, when the weight body 40 is displaced downward, most of the lower surface of the piezoelectric element 30 is subjected to stress in the extending direction. On the other hand, it is considered that a stress acts on most of the upper surface of the piezoelectric element 30 in the contracting direction.

Thus, by measuring the electromotive force generated in the interdigital electrodes X1 and X2, the sum of the two is obtained.
The direction and magnitude of the acceleration αz acting in the axial direction can be obtained. Of course, in principle, it is possible to obtain the acceleration αz with only one of the interdigital electrodes X1 or X2. However, when the acceleration αx acting in the X-axis direction is also detected, the acceleration α
In order to remove a component caused by x, it is necessary to adopt a detection method based on a sum using a pair of interdigital electrodes as described herein. As described above, the direction and magnitude of the acceleration αx acting in the X-axis direction depend on the interdigital electrodes X1, X2
Can be obtained from the difference between the electromotive forces generated in the above. Therefore, by measuring the electromotive force generated in the interdigital electrodes X1 and X2, the acceleration αz acting in the Z-axis direction can be detected from the sum of the two, and the acceleration αx acting in the X-axis direction can be detected based on the difference between the two. Can be detected.

Finally, if the piezoelectric element 30 as shown in the top view of FIG. 14 is used, it is possible to detect all of the acceleration αx in the X-axis direction, the acceleration αy in the Y-axis direction, and the acceleration αz in the Z-axis direction. is there. The piezoelectric element 30 shown in FIG.
The piezoelectric element 30 shown in FIG.
1 and Y2. This interdigital electrode Y
1 and Y2 are interdigital electrodes obtained by rotating the interdigital electrodes X1 and X2 by 90 ° counterclockwise around the origin O, and each of the interdigital electrodes is oriented in the X-axis direction. Are located. Such a pair of interdigital electrodes Y
As described above, the acceleration αy in the Y-axis direction can be detected by calculating the difference between the electromotive forces generated in Y1 and Y2. Also, a pair of interdigital electrodes X1, X2
As described above, it is possible to detect the acceleration αx in the X-axis direction by taking the difference between the electromotive forces generated in the above. On the other hand, the acceleration αz in the Z-axis direction can be obtained by taking the sum of the electromotive forces generated in the pair of interdigital electrodes X1 and X2, or can be obtained by summing the electromotive forces generated in the pair of interdigital electrodes Y1 and Y2.
And the sum of the electromotive forces generated in the four sets of interdigital electrodes X1, X2, Y1, Y
2 can also be obtained by taking the sum of all the electromotive forces that occur in 2.

§3. Basics of angular velocity sensor according to the present invention
The structure and operation principle will now be the basic structure of the angular velocity sensor according to the present invention and its operating principle. The basic structure of this angular velocity sensor is almost the same as the basic structure of the acceleration sensor described in §2. That is, the piezoelectric element 3 whose top view is shown in FIG.
0 (the polarization processing described in §1 has been performed)
The weight body 40 and the pedestal 50 are joined to the piezoelectric element 30 as shown in the side sectional view of FIG. As described above, the sensor having such a structure functions as an acceleration sensor capable of detecting the three-axis acceleration components αx, αy, and αz of X, Y, and Z, but has exactly the same structure. It is also possible to make the sensor function as an angular velocity sensor capable of detecting angular velocity components ωx, ωy, ωz around three axes of X, Y, Z. Hereinafter, the specific method will be described.

First, of the four sets of interdigital electrodes X1, X2, Y1 and Y2 shown in FIG. 14, the interdigital electrodes X1 and X2 arranged on the X axis are used as driving interdigital electrodes. , And the interdigital electrodes Y1 and Y2 arranged on the Y axis are used as interdigital electrodes for detection. here,
The driving interdigital electrodes X1 and X2 are used to vibrate the weight body 40 along the X axis, and the detecting interdigital electrodes Y1 and Y2 are used to detect the displacement of the weight body 40. Used.

Using the driving interdigital electrodes X1 and X2,
In order to vibrate the weight body 40 along the X axis, FIG.
Are prepared, the AC signal S1 is applied to the interdigital electrode X1, and the AC signal S2 is applied to the interdigital electrode X2. Each of the AC signals is a sine wave signal having the horizontal axis on the time axis t, but the phases of the AC signals S1 and S2 are reversed. That is, the driving interdigital electrodes X1 and X2 are supplied with AC signals S1 and S2 having opposite phases, respectively.
When a stress in the direction of extension is generated between one finger electrode, a stress in a contraction direction is generated between the other finger electrodes. As a result, if this sensor assumes a state as shown in FIG. 10 at time t = t1 in the graph of FIG. 15, for example, it will take a state as shown in FIG. 11 at time t = t3. Times t = 0, t = 2, t = 4
At this point, a neutral state as shown in FIG. 9 is taken (actually, the movement of the weight body 40 causes a phase delay with respect to the AC signal, but here, for convenience of explanation, An operation when there is no such phase delay will be described). this is,
The weight body 40 is a simple vibration along the X axis.

Now, at a certain moment when the weight body 40 is moving with the velocity component in the X-axis direction, the angular velocity ω about the Z-axis is ω.
When z acts, Coriolis force Fy acts on the weight body 40 in the Y-axis direction. The direction of the Coriolis force Fy is determined by the motion direction of the weight body 40, and the magnitude thereof is determined by the motion speed of the weight body 40 and the magnitude of the angular velocity ωz. As described above, when the Y-axis direction Coriolis force Fy is generated on the weight body 40, the weight body 40 is displaced in the Y-axis direction, and the piezoelectric element 30 is mechanically deformed. . The displacement of the weight body 40 in the Y-axis direction can be detected by a pair of interdigital electrodes Y1 and Y2 for detection (the principle is that the acceleration αy in the Y-axis direction described in §2 acts). Is the same as the detection principle).
Therefore, for example, the time t2 or t4 is defined as the time of detection, and at the time of this detection (when the center of gravity of the weight body 40 passes on the Y-axis at the maximum speed in the X-axis direction), a pair of detection intersections If the difference between the electromotive forces generated in the finger electrodes Y1 and Y2 is determined, the difference indicates the direction and magnitude of the angular velocity ωz around the Z axis (the sign of the difference indicates the direction, and the absolute value is the magnitude. Is shown). However, at times t2 and t4, the direction of motion of the weight body 40 is opposite, so that the angular velocity ωz
It is necessary to take into account whether the time of detection is time t2 or t4.

Similarly, when an angular velocity ωy about the Y axis acts at a certain moment when the weight body 40 is moving with a velocity component in the X axis direction, the Coriolis force Fz is applied to the weight body 40 in the Z axis direction. Acts. The direction of the Coriolis force Fz is determined by the motion direction of the weight body 40, and the magnitude thereof is determined by the motion speed of the weight body 40 and the magnitude of the angular velocity ωy. As described above, when the Coriolis force Fz in the Z-axis direction is generated in the weight body 40, the weight body 40 is displaced in the Z-axis direction, and the piezoelectric element 30 is mechanically deformed. . The displacement of the weight body 40 in the Z-axis direction can also be detected by the pair of detection interdigital electrodes Y1 and Y2 (the principle is that the acceleration αz in the Z-axis direction described in §2 acts. This is the same as the detection principle in the case). The displacement of the weight body 40 in the Z-axis direction can also be detected by using the pair of driving interdigital electrodes X1 and X2 as a detecting interdigital electrode (in this case, it will be described later). Therefore, it is necessary to separate the AC signals S1 and S2 used for driving from the signals to be detected). Therefore, for example, at time t2 or t4
Is defined as the time of detection, and at the time of this detection, if the sum of the electromotive forces generated in the pair of detection interdigital electrodes Y1 and Y2 is obtained, the sum indicates the direction and magnitude of the angular velocity ωy about the Y axis. (The sign of the sum indicates the direction, and the absolute value indicates the magnitude). However, since the movement direction of the weight body 40 is opposite between the times t2 and t4, when determining the direction of the angular velocity ωy, it is necessary to consider whether the detection time is the time t2 or t4.

In the examples described above, the pair of interdigital electrodes X1 and X2 arranged on the X axis is used as a driving interdigital electrode, and the weight body 40 is vibrated in the X axis direction in a simple vibration. In this state, a pair of interdigital electrodes Y1 and Y2 arranged on the Y axis are used as detecting interdigital electrodes, and the Coriolis force F acting on the weight body 40 in the Y axis direction is applied.
In this operation, the angular velocity ωz about the Z axis or the angular velocity ωy about the Y axis is obtained by detecting the Coriolis force Fz in the y or Z axis direction. On the other hand, an operation in which the roles of the driving interdigital electrode and the detecting interdigital electrode are completely interchanged is also possible. That is, a pair of interdigital electrodes Y1 and Y2 arranged on the Y axis is used as driving interdigital electrodes, and the weight body 40 is arranged on the X axis in a state where the weight body 40 is vibrated in the Y axis direction. Pair of interdigital electrodes X1,
By using X2 as a detection interdigital electrode and detecting the Coriolis force Fx in the X-axis direction or the Coriolis force Fz in the Z-axis direction acting on the weight body 40, the angular velocity ωz about the Z-axis or the X-axis The angular velocity ωx is determined.
By adopting these two detection operations alternately, it is possible to detect the angular velocities ωx, ωy, ωz around all the X, Y, and Z axes.

As another operation, the weight body 40 is
It is also possible to vibrate in the axial direction. For example, a pair of interdigital electrodes X1 and X2 arranged on the X-axis are
When the in-phase AC signals S1 and S2 are supplied as shown in FIG.
At t1, if a state as shown in FIG. 12 is taken,
At time t = t3, the state as shown in FIG. 13 is taken. At times t = 0, t = 2, and t = 4, a neutral state is established as shown in FIG. Occurs). This is nothing but that the weight body 40 makes a simple vibration along the Z axis.

As described above, in the state where the weight body 40 is vibrated in the Z-axis direction, the pair of interdigital electrodes Y1 and Y2 arranged on the Y-axis are used as the interdigital electrodes for detection.
By detecting the Coriolis force Fy acting on the weight body 40 in the Y-axis direction, the angular velocity ωx around the X-axis can be obtained,
In addition, a pair of interdigital electrodes X1, X arranged on the X axis
2 is also used as a detection interdigital electrode, the weight 4
By detecting the Coriolis force Fx in the X-axis direction acting on 0,
The angular velocity ωy about the Y axis can also be obtained. Alternatively, a pair of interdigital electrodes Y1 and Y2 arranged on the Y axis
Is used as a driving interdigital electrode, and by the same method,
It is also possible to obtain the angular velocities ωx and ωy.

In order to continuously detect the angular velocities ωx, ωy and ωz around all the X, Y and Z axes, it is preferable to adopt a method of rotating the weight body 40 in the XY plane. For example, four sets of interdigital electrodes X shown in FIG.
1, X2, Y1 and Y2 are supplied with AC signals S1, S2, S3 and S4 as shown in the graph of FIG. 17, respectively. Here, the AC signals S1 and S2 are sinusoidal signals having phases opposite to each other, and function as AC signals for exciting the weight body 40 in the X-axis direction for simple oscillation in the X-axis direction. Are also sinusoidal signals having phases opposite to each other, and function as AC signals for excitation in the Y-axis direction for causing the weight body 40 to vibrate in the Y-axis direction. Moreover, the phase of the AC signal for X-axis excitation and the AC signal for Y-axis excitation is 9
Due to the shift of 0 °, the weight body 40 performs a circular motion on the XY plane.

FIG. 18 is a top view showing the locus of the center of gravity G when the weight body 40 makes a circular motion on the XY plane.
Here, the points G (t1), G (t2), G (t3), G
(T4) indicates the positions of times t1, t2, t3, and t4 on the time axis shown in FIG. 17 (when the phase delay of the actual motion is ignored), and arrows V (t1), V
(T2), V (t3), and V (t4) indicate the velocity vectors of the weight 40 at the respective times t1, t2, t3, and t4 (facing in the tangential direction of the circular motion trajectory).

As described above, the four sets of interdigital electrodes X1, X
2, Y1 and Y2 function as interdigital electrodes for driving, but if they are used also as interdigital electrodes for detection, angular velocities ωx, ωy, ωz can be detected. For example, assuming that the times t1 and t3 are the times of the first detection, at the time of the first detection, the weight body 40 moves with the velocity vector in the Y-axis direction. If the Coriolis force Fx in the X-axis direction is detected using the X-axis direction, the angular velocity ωz about the Z-axis can be obtained, and the interdigital electrode X
If the Coriolis force Fz in the Z-axis direction is detected using 1, X2 or Y1, Y2, the angular velocity ωx around the X-axis can be obtained. On the other hand, assuming that times t2 and t4 are the times of the second detection, at the time of the second detection, the weight body 40 is moving with the velocity vector in the X-axis direction. Detecting the Coriolis force Fy in the Y-axis direction using the X-axis direction, the angular velocity ωz around the Z-axis can be obtained, and the Coriolis force Fz in the Z-axis direction using the interdigital electrodes X1, X2 or Y1, Y2. Then, the angular velocity ωy about the Y axis can be obtained.

After all, when the weight body 40 is performing a circular motion, the Coriolis force acting in a direction orthogonal to the tangential direction of the circular motion trajectory is detected by the interdigital electrode for detection, whereby the tangential direction is obtained. And the angular velocity about an axis orthogonal to both the directions of the Coriolis force can be detected. As described above, if the detection operation is performed at the time of the first detection and at the time of the second detection, Angular velocity ω around three axes
All of x, ωy, ωz can be detected continuously.

§4. Specific Embodiment (Part 1) FIG. 19 is a top view of a piezoelectric element 130 used for an acceleration sensor or an angular velocity sensor according to a more specific embodiment of the present invention. As described above, whether this sensor is used as an acceleration sensor or an angular velocity sensor depends on its operation mode, and the structure of the sensor body is the same for all sensors. In other words, if this sensor is used as an acceleration sensor, a circuit for detecting an electromotive force generated at each interdigital electrode formed on the piezoelectric element 130 shown in FIG. 19 may be prepared. If this sensor is used as an angular velocity sensor, it is necessary to prepare a circuit for detecting an electromotive force generated in each interdigital electrode and a circuit for supplying a driving AC signal to each interdigital electrode.

In the illustrated example, four pairs of interdigital electrodes are formed on the upper surface of the disc-shaped piezoelectric element 130. Here, too, let us consider an XYZ three-dimensional coordinate system in which the origin O is taken at the center of the upper surface of the piezoelectric element 130, the X axis is taken in the horizontal direction of the drawing, the Y axis is taken in the vertical direction, and the Z axis is taken in the direction perpendicular to the paper surface. An interdigital electrode X1 such that each finger electrode is oriented in the Y-axis direction is arranged on the positive portion of the X-axis on the upper surface of the piezoelectric element 130, and each finger electrode is connected to the Y-axis in a negative portion of the X-axis. The interdigital electrode X2 is arranged so as to face the direction, and the interdigital electrode Y1 such that each finger electrode is oriented in the X axis direction is arranged at the positive portion of the Y axis.
In the negative part of the Y-axis, the interdigital electrode Y2 is arranged such that each finger-shaped electrode faces the X-axis direction. The basic structure of these interdigital electrodes is substantially the same as the example shown in FIG. However, in order to increase the detection sensitivity, it is preferable that the individual finger electrodes are made as long as possible. Therefore, the upper surface of the piezoelectric element 130 is used as effectively as possible to form a long finger electrode.

One electrode group constituting each interdigital electrode is short-circuited as a common electrode group 110. FIG.
In FIG. 9, a line intersecting in an X shape on the origin O is a portion constituting a part of the common electrode group 110, and a total of 24 lines extending in a branch shape from the line intersecting in the X shape Constitute individual finger electrodes. The common electrode group 110 is connected to a ground terminal Eg, and the ground terminal Eg is grounded when the sensor operates. On the other hand, the other electrode group constituting each interdigital electrode has an electrode group 12
1, 122, 123, and 124 are electrically independent, and are respectively connected to terminal portions Ex1, Ex2, Ey1, and Ey2.

As in the case of the piezoelectric element 130 described above, the peripheral portion is used as a fixed portion and the central portion is used as a displacement portion. Therefore, for example, as in the example shown in FIG. 9, the weight body 40 is joined to the center portion of the lower surface, and the cylindrical pedestal 50 is joined to the periphery.

In this embodiment, four sets of interdigital electrodes X
1, X2, Y1, and Y2 are used not only as interdigital electrodes for driving but also as interdigital electrodes for detection. That is, the physically identical interdigital electrode is used as an electrode that is used as both the driving interdigital electrode and the detecting interdigital electrode. In order to use the electrode as a dual-purpose electrode in this manner, a circuit as shown in FIG. 20 may be used. Terminal E in this circuit
Are the terminal portions Ex1 and Ex in the embodiment shown in FIG.
2, Ey1 and Ey2. An AC power supply 1 is connected to the terminal E via a resistor R1, and a voltage detector 2 is connected via a resistor R2. Since the AC signal generated by the AC power supply 1 is supplied to the terminal E via the resistor R1, the interdigital electrode composed of the electrode group connected to the terminal E functions as a driving interdigital electrode. can do. On the other hand, the electromotive force generated in the interdigital electrode is detected by the voltage detection device 2 from the terminal E via the resistor R2. Of course, the AC signal generated by the AC power supply 1 is also supplied to the voltage detection device 2 via the resistor R2.
As a component superimposed on the AC signal, an electromotive force generated in the interdigital electrode is detected.

The principle of detecting the axial components αx, αy, αz of the acceleration and the axial components ωx, ωy, ωz of the angular velocity by the sensor having such a structure has already been described in §2 and §3. It is as stated. For example, if the AC signals S1, S2, S3, and S4 shown in FIG. 17 are supplied to the terminal portions Ex1, Ex2, Ey1, and Ey2, respectively, the weight body 40 can be made to circularly move on the XY plane. When the weight body 40 crosses the X-axis or the Y-axis, the terminal portions Ex1, Ex2,
By measuring the electromotive force generated at Ey1 and Ey2, the axial components ωx, ωy, ωz of the angular velocity can be detected.

In an environment where both the angular velocity and the acceleration are acting, the force acting on the weight becomes a superposition component of the Coriolis force based on the angular velocity and the acceleration force based on the acceleration. And acceleration force can be separated based on frequency components. That is, when the weight body is caused to perform a simple vibration or a rotational movement, the direction of the movement is reversed every half cycle of the vibration or the rotation. Therefore, the direction of the Coriolis force is also reversed every half cycle. Therefore, if the period of the simple vibration or the rotational movement of the weight body is set sufficiently higher than the fluctuation period of the acceleration or angular velocity to be detected, each terminal portion Ex
Among the fluctuating components of the electromotive force generated in Ex1, Ey2, Ey1, and Ey2, the frequency component corresponding to the motion cycle of the weight body can be recognized as Coriolis force, and the frequency components sufficiently lower than that are the acceleration force. Can be recognized. Therefore, if a frequency separation circuit is prepared in the detection circuit, it is possible to separately detect both the accelerations αx, αy, αz in the three axes and the angular velocities ωx, ωy, ωz around the three axes. .

FIG. 21 is a top view of a piezoelectric element 230 used in a sensor according to another embodiment of the present invention. This piezoelectric element 230 is also a disk-shaped piezoelectric element, and on its upper surface, the interdigital electrodes X1 to X4, Y1 to Y
4, Z1 to Z4 are arranged and subjected to the polarization processing as described in §1. In FIG. 21, in order to avoid complication of the figure, for each interdigital electrode, instead of drawing a pattern shape composed of individual finger electrodes, only the outline shape outside the pattern is shown. . That is, in FIG. 21, the interdigital electrodes X3, X4, Y3, Y4, Z3, which have an “I” -shaped contour shape, are shown.
In practice, Z4 is, as shown in FIG.
Interdigital finger electrodes X1, X2, Y1, Y2, each of which is formed by a first electrode group 210 and a second electrode group 220, and has a U-shaped contour. Z
Actually, 1 and Z2 are interdigital electrodes composed of a first electrode group 215 and a second electrode group 225, as shown in FIG. 22 (b). Each electrode portion is hatched to facilitate understanding of the shape of each electrode.)

The interdigital electrode shown in FIG. 22A has the same structure as the interdigital electrode shown in FIG. The interdigital electrode shown in FIG. 22 (b) is obtained by arranging two sets of interdigital electrodes shown in FIG. 22 (a) and connecting the corresponding electrode groups. This is the same as the interdigital electrode shown in FIG.

In the piezoelectric element 230 shown in FIG. 21, the peripheral portion is used as a fixed portion and the central portion is used as a displacement portion, as in the examples described above. The weight 240 shown by a broken line in FIG. 21 is a weight joined to the center of the lower surface of the piezoelectric element 230, and the pedestal 250 also shown by the broken line in FIG. A cylindrical pedestal joined to the periphery of the lower surface of 230.

In this embodiment, a total of 12 sets of interdigital electrodes X1 to X4, Y1 to Y4 and Z1 to Z4 are formed, each of which is used as a driving interdigital electrode or a detecting interdigital electrode. Will take on the role of. For example, the interdigital electrodes X1 and X2 are driven in the X-axis direction (weight 240
Is used to supply an AC signal for vibrating the X-axis along the X-axis), and for driving the interdigital electrodes Y1 and Y2 in the Y-axis direction (AC signal for vibrating the weight body 240 along the Y-axis). , The interdigital electrodes Z1, Z
2 is used for driving in the Z-axis direction (used to supply an AC signal for vibrating the weight body 240 along the Z-axis),
The interdigital electrodes X3 and X4 are used for detecting the X-axis direction (the weight 240 based on the action of the acceleration force and the Coriolis force in the X-axis direction).
For detecting the displacement of the X-axis in the X-axis direction), the interdigital electrode Y
3, Y4 for detecting in the Y-axis direction (used for detecting the displacement of the weight body 240 in the Y-axis direction based on the action of the acceleration force and Coriolis force in the Y-axis direction), and the interdigital electrodes Z3, Z4 in the Z-axis direction. For detection (used for detecting displacement of the weight body 240 in the Z-axis direction based on the action of the acceleration force and Coriolis force in the Z-axis direction), a predetermined AC signal is supplied to a predetermined driving interdigital electrode. By doing so, the weight body 240 is
Axis and Z axis can be driven in any direction.
By detecting an electromotive force generated in a predetermined detection interdigital electrode, the X-axis and Y-axis applied to the weight body 240 are detected.
Force in each direction of axis and Z axis (acceleration force and Coriolis force)
Can be detected. The driving principle and the detection principle are as described above. Needless to say, an embodiment in which the roles of driving and detection are exchanged with respect to the above-described example is also possible.

As described above, if the function of driving or detecting and which axis is assigned to each interdigital electrode is determined and used, the driving circuit and the detecting circuit can be more efficiently used. Can be simplified. Hereinafter, an example of the angular velocity detection operation using the sensor shown in this embodiment will be described. Of course, the detection operation described below is merely an example, and various other detection operations are possible using the detection principle described above. In addition, acceleration can be detected.

First, an example of a detecting operation for detecting only the angular velocity around one axis will be described. For example, in the case of using as a one-axis angular velocity sensor for detecting the angular velocity ωx around the X axis, AC signals S1 and S2 having the same phase as shown in FIG. 16 are supplied to the driving interdigital electrodes Z1 and Z2. Then, the weight body 240 is caused to make a simple vibration in the Z-axis direction. As described above, when the angular velocity ωx about the X axis acts while the weight body 240 is moving with the motion component in the Z axis direction, the weight body 240
An axial Coriolis force Fy acts, and the weight body 240 is displaced in the Y-axis direction. The Coriolis force Fy can be detected by the interdigital electrodes Y3 and Y4 for detection. For example, the time point at which the weight body 240 passes the center position (the position where the speed is the highest) of the amplitude of the simple vibration is defined as the detection time, and at this time point, the detection interdigital electrode Y is detected.
If the difference between the electromotive forces generated in 3, Y4 is obtained, this difference indicates the angular velocity ωx about the X axis.

Next, an example of a detection operation for detecting angular velocities around two axes will be described. For example, the angular velocity ωx around the X axis
And the angular velocity ωy around the Y-axis, the driving interdigital electrode Z1, as in the case of the angular velocity detection around one axis described above.
The AC signals S1 and S2 having the same phase are supplied to Z2 to cause the weight body 240 to vibrate in the Z-axis direction. In this state,
If the Coriolis force Fy is detected based on the difference between the electromotive forces generated in the detection interdigital electrodes Y3 and Y4, the angular velocity ωx about the X axis can be obtained as described above. If the Coriolis force Fx is detected based on the difference between the electromotive forces generated in the interdigital electrodes X3 and X4, the angular velocity ωy about the Y axis can be obtained.

Further, an example of a detection operation for detecting angular velocities around three axes will be described. In order to continuously detect the angular velocities around the three axes, it is most preferable to adopt a method of rotating the weight body as described in §3. For example, the rotating surface of the weight body may be any of the XY plane, the XZ plane, and the YZ plane, but here, as in the example described in §3, the weight body 240 is rotated along the XY plane. Let me give an example. To do so, the driving interdigital electrode X
AC signals S1, S2, S3, S4 as shown in FIG. 17 may be given to each of X1, Y2, Y1, and Y2. Thus, the center of gravity G of the weight body 240 performs a circular motion along a circular orbit as shown in FIG. Here, at time t1 or t3 (that is, at the time when the weight body 240 crosses the X-axis with the velocity component in the Y-axis direction), the Coriolis force Fx is generated by the difference between the electromotive forces generated in the detection interdigital electrodes X3 and X4. Is detected, the angular velocity ω about the Z axis
z can be obtained, and the detection interdigital electrodes Z3, Z4
If the Coriolis force Fz is detected based on the sum of the electromotive forces generated in the above, the angular velocity ωx around the X axis can be obtained. Also, at time t2 or t4 (that is, when the weight 240
If the Coriolis force Fy is detected based on the difference between the electromotive forces generated in the detection interdigital electrodes Y3 and Y4 at the time of crossing the Y axis with the velocity component in the X axis direction, the angular velocity ωz about the Z axis can be obtained. , Detection interdigital electrode Z
If the Coriolis force Fz is detected based on the sum of the electromotive forces generated in 3, 3 and 4, the angular velocity ωy about the Y axis can be obtained. Thus, the angular velocities ωx, ωy, ωz around each axis
Can be continuously detected.

§5. Specific Embodiment (Part 2) The embodiments described so far have a structure in which mechanical deformation occurs almost entirely in the plate-like piezoelectric element. In other words, the weight body is joined to a very small part of the center of the plate-shaped piezoelectric element, and when viewed from the top, the joint of the weight body with respect to the entire area of the plate-shaped piezoelectric element. This is an example of the case where the area is sufficiently small. In such an example, when the weight body is displaced in various directions, as shown in FIGS.
Each part of the upper surface of the weight body expands and contracts.

However, when the area of the joining portion of the weight body is increased to some extent with respect to the entire area of the plate-shaped piezoelectric element, mechanical deformation occurs only in a part of the plate-shaped piezoelectric element. When the weight body is displaced in various directions,
The form of expansion and contraction occurring at each part of the upper surface of the weight body is shown in FIGS.
It is slightly different from the embodiment shown in FIG.

For example, a piezoelectric element 300 whose side sectional view is shown in FIG. 23 is one in which a donut-shaped groove 335 is formed on the lower surface of a slightly thick disk-shaped piezoelectric element. A flexible portion 330 having a small thickness is formed on the upper portion of the groove portion 335, and substantial mechanical deformation occurs only in the flexible portion 330. A column-shaped weight body 340 is formed inside the groove 335, and a cylindrical pedestal 350 is formed outside the groove 335. Flexible part 3
Each of the weight 30, the weight 340, and the pedestal 350 is composed of a part of a thick piezoelectric element. It can be considered that no mechanical deformation occurs. Therefore, the mechanical deformation that contributes to the operation as the sensor occurs only in the flexible portion 330.

Now, in FIG. 23, X
Axis, Z axis in the vertical direction, Y axis in the direction perpendicular to the paper,
With the portion of the pedestal 350 fixed, the weight 34
Consider a case where a force in the X-axis direction is applied to zero. In this case, as shown in the side sectional view of FIG. 24, the weight body 340 generates a displacement + Δx in the X-axis direction, and
A mechanical deformation occurs at 0. In this case, the expansion and contraction of the upper surface of the flexible portion 330 in the X-axis direction is
It is as shown in the figure. That is, in the figure, the weight body 34
In the flexible portion 330 located on the right side of 0, the inside of the upper surface (the weight body 340 side) extends, while the outside of the upper surface (the pedestal 350) extends.
Side) will shrink. On the other hand, in FIG.
In the flexible portion 330 located on the left side of the upper side, the inside of the upper surface (side of the weight body 340) shrinks, whereas the outside of the upper surface (side of the pedestal 350) is shrunk.
Will grow. When a force in the Z-axis direction is applied to the weight body 340, the weight body 340 generates a displacement + Δz in the Z-axis direction as shown in the side sectional view of FIG. Mechanical deformation occurs in the bending portion 330. In this case, X on the upper surface of the flexible portion 330
The expansion and contraction in the axial direction is such that, on both the left and right sides of the weight body 340, the inside of the upper surface (weight body 340 side) extends,
The upper surface outside (the pedestal 350 side) will shrink. The above is
In both cases, the upper and lower sides of the flexible portion 330 are expanded and contracted, but the expanded and contracted states of the lower side of the flexible portion 330 are all opposite to the upper side.

After all, in the examples described up to §5, in the embodiment shown here, the size of the weight body 340 is sufficiently small, and the joint portion of the weight body can be treated as a point in practical use. You can say an example. In a structure in which the joint portion of the weight body occupies a certain area as in the embodiment shown here, the flexible portion where mechanical deformation occurs is divided into an inner portion (weight side) and an outer portion (pedestal side). It is understood that it is necessary to handle separately.

FIG. 26 is a top view showing the arrangement of the interdigital electrodes when the joints of the weights occupy an area that cannot be ignored. The piezoelectric element 400 includes the piezoelectric element 300
Similarly, the piezoelectric element is a thick disk-shaped piezoelectric element, and as shown by a broken line in FIG.
Are formed. The flexible portion 430 is a portion having a reduced thickness by forming a donut-shaped groove on the lower surface of the piezoelectric element 400, similarly to the above-described flexible portion 330, and contributes to the operation of the sensor. This is a portion having sufficient flexibility. The column-shaped weight body 440 is formed by the flexible portion 43.
0, which is a thick portion located inside
50 is a thick part located outside the flexible part 430. The pedestal 450 is used while being fixed to the sensor housing, and the weight body 440 is supported by the flexible portion 430 from the surroundings. When an acceleration force or a Coriolis force acts on the weight body 440, mechanical deformation occurs in the flexible portion 430, and partial expansion and contraction occurs.
The mode of the expansion and contraction is as described above.

In this embodiment, a total of 24 sets of interdigital electrodes are formed on the upper surface of the flexible portion 430. That is,
The interdigital electrodes X1 to X4 arranged on the X axis are driving interdigital electrodes for driving the weight body 440 in the X axis direction, and the interdigital electrodes Y1 arranged on the Y axis. ~ Y4
Is a driving interdigital electrode for driving the weight body 440 in the Y-axis direction, and the interdigital electrodes Z1 to Z4 arranged on the W axis drive the weight body 440 in the Z-axis direction. (The W axis is an axis inclined by 45 ° with respect to the Y axis in the illustrated example, but may be an arbitrary axis.) In addition, in FIG. 26, only the outer outline shape of each of the above-mentioned driving interdigital electrodes is shown.
It is an interdigital electrode composed of a first electrode group 215 and a second electrode group 225 as shown in FIG.

On the other hand, the interdigitated electrodes X arranged on the X axis
5-X8 are detection interdigital electrodes for detecting an acceleration force or a Coriolis force applied to the weight body 440 in the X-axis direction, and are interdigital electrodes Y5 arranged on the Y-axis.
Y8 to Y8 are detection interdigital electrodes for detecting the acceleration force or Coriolis force acting on the weight body 440 in the Y-axis direction, and the interdigital electrodes Z5 to Z5 arranged on the W axis.
Z8 is a detection interdigital electrode for detecting an acceleration force or a Coriolis force acting on the weight body 440 in the Z-axis direction. Each of these detection interdigital electrodes is also shown in FIG.
In FIG. 22, only the outline shape of the outside is shown, but in actuality, each of them is constituted by a first electrode group 210 and a second electrode group 220 as shown in FIG. Interdigital electrodes.

The basic principle of detecting the acceleration in each axial direction and the angular velocity around each axis by using each of these interdigital electrodes is almost the same as that of the embodiments described above. However, regarding the handling of the polarity of the AC signal applied to each driving interdigital electrode and the polarity of the electromotive force generated in each detecting interdigital electrode, the above-described embodiments need to be slightly modified. .

For example, in order to cause displacement + Δx in the weight body, it is necessary to cause each part of the flexible portion to expand and contract in a manner as shown in FIG. Therefore, in order to vibrate the weight body in the X-axis direction, as shown in FIG. 15, AC signals S1 and S2 having phases opposite to each other are prepared, and the AC signal S1 is supplied to the interdigital electrodes X1 and X3. Then, an AC signal S2 may be supplied to the interdigital electrodes X2 and X4.
Similarly, if the AC signal S1 is supplied to the interdigital electrodes Y1 and Y3 and the AC signal S2 is supplied to the interdigital electrodes Y2 and Y4, the weight body can be vibrated in the Y-axis direction.

In order to vibrate the weight body in the Z-axis direction, an AC signal is applied to the interdigital electrodes X1 and X4 (or Y1 and Y4) in consideration of the expansion and contraction as shown in FIG. S1 to supply the interdigital electrodes X2, X3 (or Y
2, Y3) to supply the AC signal S2. Further, in order to rotate the weight body on the XY plane, four types of AC signals S1, S2, S3, and S4 as shown in FIG. , And an AC signal S2 is supplied to the interdigital electrodes X2 and X4, an AC signal S3 is supplied to the interdigital electrodes Y1 and Y3, and an AC signal S4 is supplied to the interdigital electrodes Y2 and Y4. do it.

On the other hand, in order to detect the acceleration force or Coriolis force acting on the weight body in the X-axis direction, the interdigital electrode X
1, X3 and the interdigital electrodes X2, X3
The difference between the sum of the electromotive forces generated in No. 4 and the sum of the electromotive forces may be obtained. Similarly, in order to detect the acceleration force or the Coriolis force in the Y-axis direction acting on the weight, the sum of the electromotive forces generated in the interdigital electrodes Y1 and Y3 and the generated electromotive force in the interdigital electrodes Y2 and Y4 is used. What is necessary is just to obtain the difference between the sum of the electromotive forces. Further, to detect the Z-axis acceleration force or Coriolis force acting on the weight,
The difference between the sum of the electromotive forces generated in the interdigital electrodes Z1 and Z4 and the sum of the electromotive forces generated in the interdigital electrodes Z2 and Z3 may be obtained.

In order to enhance the detection accuracy, it is preferable to perform the detection operation using all 24 sets of interdigital electrodes shown in FIG. 26, but it is not always necessary to perform detection using all these interdigital electrodes. No need to do. For example, the weight body 44
0 in the X-axis direction, the driving interdigital electrode X
1, X4 alone or the driving interdigital electrode X
Alternatively, only X2 and X3 may be used. Similarly, when the weight body 440 is driven in the Y-axis direction, the driving interdigital electrodes Y1, Y
4 may be used, or the driving interdigital electrodes Y2, Y
Only three may be used. Further, when the weight body 440 is driven in the Z-axis direction, only the driving interdigital electrodes Z1 and Z4 may be used, or only the driving interdigital electrodes Z2 and Z3 may be used. The same applies to the detection interdigital electrodes. For example, when detecting the force in the X-axis direction on the weight body 440, only the detection interdigital electrodes X5 and X8 may be used, or the detection interdigital electrodes may be used. Only the electrodes X6 and X7 may be used. Similarly, when detecting the force in the Y-axis direction on the weight body 440, only the detection interdigital electrodes Y5 and Y8 may be used, or only the detection interdigital electrodes Y6 and Y7 may be used. . Further, when detecting the force in the Z-axis direction on the weight body 440, only the detection interdigital electrodes Z5 and Z8 may be used, or only the detection interdigital electrodes Z6 and Z7 may be used.

Therefore, when actually producing the sensors, the functions of the individual sensors (how many of the six axial components of the acceleration in the three axes and the angular velocity around the three axes need to be detected) and In consideration of the accuracy required for the measurement, etc., only the necessary one of the 24 sets of interdigital electrodes shown in FIG. 26 may be formed.

§6. Other Embodiments Finally, some modifications of the various embodiments described above will be described.

(1) The piezoelectric element 500 shown in FIG. 27 has the same structure as the piezoelectric element 400 shown in FIG. 26, and a donut-shaped groove is formed on the entire lower surface of the thick piezoelectric element. By doing so, a flexible portion 530 having flexibility,
It comprises a weight body 540 located inside the pedestal and a pedestal 550 located outside the flexible portion 530. However, the interdigital electrodes formed on the upper surface are greatly simplified. That is, two sets of interdigital electrodes X1 and X2 are arranged on the X axis, and two sets of interdigital electrodes Y1 and Y2 are also arranged on the Y axis. It is arranged inside 530 (on the weight body 540 side).
These interdigital electrodes X1, X2, Y1 and Y2 are shown in FIG.
6, the interdigital electrodes X2, X3, Y in the embodiment shown in FIG.
2, Y3. On the other hand, four sets of interdigital electrodes Z1 are arranged on an axis that forms 45 ° with respect to the X axis and the Y axis.
To Z4 are arranged. These interdigital electrodes Z1 to Z1
Z4 is arranged at a substantially central position in the radial direction of the flexible portion 530, and corresponds to the interdigital electrodes Z1 to Z4 in the embodiment shown in FIG.

As described above, the piezoelectric element 5 shown in FIG.
The electrode arrangement in the sensor using 00 is a compromise between the sensor described in §4 and the sensor described in §5.
Even such an electrode arrangement does not hinder the function as a sensor. For example, if this sensor is used as a two-axis angular velocity sensor, four sets of interdigital electrodes Z1 to Z1 are used.
The same AC signal is supplied to each of the weights Z4.
0 is oscillated in the Z-axis direction (perpendicular to the plane of FIG. 27), and the angular velocity ωy is determined from the difference between the electromotive forces generated in the interdigital electrodes X1 and X2. The angular velocity ωx may be obtained from the difference.

(2) In the embodiments described so far, the polarization process of the same polarity is applied to each interdigital electrode. However, the polarity of the polarization process is changed for each individual interdigital electrode. Then, the driving circuit and the detection circuit can be simplified. For example, in the polarization process shown in FIG. 3, a polarization voltage Ep is applied such that the second electrode group 20 side becomes positive. On the other hand, in the polarization processing as shown in FIG. 28, a polarization voltage -Ep is applied so that the second electrode group 20 side becomes negative, and the direction of the electric field generated between adjacent finger electrodes is reversed. Turn. Therefore, FIG.
FIG.
The electrical polarity of the interdigitated electrode subjected to the polarization treatment as shown in FIG.

As described above, if the electric polarity of the interdigital electrode can be freely selected, it becomes possible to form the interdigital electrode having a polarity suitable for each sensor, and the driving circuit And the detection circuit can be simplified. For example, in the case of the embodiment described so far, in order to vibrate the weight body in the X-axis direction, it is necessary to dispose the intersecting finger-shaped electrode disposed in the positive portion of the X-axis and the negative electrode disposed in the negative portion of the X-axis. AC signals having opposite phases (for example, AC signals S1 and S2 shown in FIG. 15)
However, if the polarity of the polarization process for both interdigital electrodes is reversed, only the same AC signal is supplied to both interdigital electrodes,
The weight body can be vibrated in the X-axis direction, and the driving circuit can be simplified. Also, when it is necessary to take the difference between the electromotive forces generated in the two interdigital electrodes, by inverting the polarity of the polarization processing for these two interdigital electrodes, a calculation is performed to take the sum instead of taking the difference. Can be performed, and the detection circuit can be simplified.

(3) In the embodiments described so far, each finger-like electrode constituting the interdigital electrode has a linear shape.
The individual finger electrodes need not necessarily be linear electrodes, but may be curved electrodes. In particular, when a disk-shaped piezoelectric element is used, it is preferable to use an interdigital electrode composed of a large number of arc-shaped finger electrodes as the interdigital electrode formed on the upper surface thereof. FIG.
The piezoelectric element 600 shown in FIG.
And a cylindrical weight element 640 formed on the inside thereof and a cylindrical pedestal 650 formed outside the flexible portion 630. FIG. 29 shows a state in which interdigital electrodes 660 composed of arc-shaped finger electrodes are formed on the flexible portion 630 of such a disk-shaped piezoelectric element 600 (here, only one set is used). Example) is shown. The function itself of the interdigital electrode 660 is exactly the same as that of the various interdigital electrodes described above, but along the arc around the origin O of the coordinate system defined at the center of the upper surface of the piezoelectric element 600. Since the finger-shaped electrodes are arranged, it is possible to form an electrode by efficiently using the space on the upper surface of the disk-shaped piezoelectric element 600.

For example, the piezoelectric element 700 whose upper surface is shown in FIG. 30 is a disk-shaped piezoelectric element, and eight pairs of interdigital electrodes X1 to X4, Y1 to Y4 are arranged on the upper surface. Well placed. These eight sets of interdigital electrodes
Each of them is composed of a first electrode group and a second electrode group, but one of the electrode groups is short-circuited to each other and connected to the ground terminal Eg. On the other hand, the other electrode group is electrically separated from each other and connected to the terminal portions Ex1 to Ex4 and Ey1 to Ey4, respectively.

If the sensor is constructed by fixing the peripheral portion of the piezoelectric element 700 to the housing of the device and joining the weight to the center, the acceleration and angular velocity can be detected by the following method. For example, if the interdigital electrodes X1, X4, Y1, and Y4 are used as driving interdigital electrodes and AC signals S1 to S4 as shown in FIG.
A circular motion can be made along a plane. On the other hand, if the interdigital electrodes X2, X3, Y2, and Y3 are used as the interdigital electrodes for detection, a difference in electromotive force generated in the interdigital electrodes X2 and X3 causes a force in the X-axis direction acting on the weight body. Can be detected, and the force in the Y-axis direction applied to the weight body can be detected based on the difference between the electromotive forces generated in the interdigital electrodes Y2 and Y3, and the interdigital electrodes X2, X3 and Y2 can be detected. The Z-axis direction force acting on the weight body can be detected from the sum of the electromotive forces generated in Y3. The method of detecting the acceleration in each axis direction and the angular velocity around each axis based on the force thus detected is as described above.

(4) In the embodiments described so far, the individual finger electrodes constituting each interdigital electrode face in the direction perpendicular to the radial direction of the disk-shaped piezoelectric element or in the circumferential direction. Had been arranged. However, in practicing the present invention, the orientation of each finger-like electrode need not necessarily be limited to such a direction. For example, in the interdigital electrode 670 shown in FIG.
00 in the radial direction. As described above, when the interdigital electrodes in which the finger electrodes are oriented in the radial direction are used, the direction of expansion and contraction of the piezoelectric element is considered to be not the radial direction but the circumferential direction. It was confirmed that the expansion and contraction phenomenon also occurred. This is probably because when a part of one disk-shaped piezoelectric element experiences expansion and contraction stress in the circumferential direction, the entire disk expands or contracts, resulting in radial expansion and contraction. It is thought to be caused.

(5) In the embodiments described above, the interdigital electrodes are formed on the upper surface of the piezoelectric element.
Interdigital electrodes may be formed on the lower surface of the piezoelectric element. Further, interdigital electrodes may be formed on both upper and lower surfaces of the piezoelectric element. However, when the interdigital electrodes are formed on both upper and lower surfaces, the polarity of the driving AC signal and the polarity of the detected AC signal are determined in consideration of the difference between the expansion and contraction on the upper surface of the piezoelectric element and the expansion and contraction on the lower surface. It is necessary to decide how to treat the sign of the electromotive force.

For example, in the cross-sectional side view of FIG. 31, the interdigital electrode X1, X
2 is formed, and interdigitated electrodes XX1 and XX2 are formed on the lower surface at positions facing these. In a state where the weight body 40 is joined to the center of the piezoelectric element 30 and the periphery is fixed by the pedestal 50, as shown in FIG.
When a displacement + Δx in the X-axis direction is applied to the weight body 40, the interdigital electrode X1 on the upper surface extends in the X-axis direction, while the interdigital electrode XX1 on the lower surface contracts in the X-axis direction. Become. The interdigital electrode X2 on the upper surface shrinks in the X-axis direction, while the interdigital electrode XX2 on the lower surface extends in the X-axis direction.

As shown in FIG. 32, when a displacement + Δz in the Z-axis direction is applied to the weight body 40, both the interdigital electrodes X1 and X2 on the upper surface extend in the X-axis direction. , Both of the interdigital electrodes XX1 and XX2 on the lower surface shrink in the X-axis direction. When the displacement −Δz in the opposite direction is applied, the state of expansion and contraction is reversed as shown in FIG.

As described above, since the expansion and contraction of the upper and lower surfaces of the piezoelectric element are generally reversed, it is necessary to take into consideration when forming the interdigital electrodes on both the upper and lower surfaces.

(6) In the embodiments described so far, the AC signals supplied to drive the weight are shown in FIGS.
Although a sine wave signal as shown in was used, a square wave signal can be used instead of such a sine wave signal.
Alternatively, a pulse signal can be used.

(7) Piezoelectric elements are generally vulnerable to impact and are easily damaged by cracks. Therefore, in a sensor using a flat piezoelectric element, it is preferable to provide a protective substrate on the back surface of the piezoelectric element in order to improve impact resistance. FIG.
The embodiment shown in FIG. 9 is a modification in which a protective substrate 60 is provided on the lower surface of the piezoelectric element 30 in the sensor shown in FIG. As the protective substrate 60, a plate made of a material having a certain degree of flexibility may be used. Specifically, a metal plate (for example, a phosphor bronze plate or a stainless steel plate) or a flexible ceramic substrate (for example, a zirconia plate) can be used. When a metal plate is used, the lower surface of the piezoelectric element 30 may be bonded using an adhesive. When a ceramic substrate is used, the lower surface of the piezoelectric element 30 may be joined by sintering.

[0098]

As described above, according to the acceleration sensor and the angular velocity sensor according to the present invention, the structure can be simplified,
It is possible to realize a small and efficient sensor.

[Brief description of the drawings]

FIG. 1 is a top view of a piezoelectric element on which interdigital electrodes used in a sensor according to the present invention are formed (hatching indicates an electrode pattern, not a cross section). .

FIG. 2 is a side sectional view of the piezoelectric element shown in FIG. 1 cut along an X axis.

FIG. 3 is a side sectional view illustrating the principle of polarization processing on the piezoelectric element shown in FIG.

FIG. 4 shows the piezoelectric element after the polarization treatment shown in FIG.
FIG. 4 is a side cross-sectional view illustrating one form of a characteristic in which mechanical deformation occurs when a voltage is applied.

FIG. 5 shows the piezoelectric element after the polarization process shown in FIG.
It is a sectional side view which shows another form of the characteristic which a mechanical deformation produces by applying a voltage.

FIG. 6 shows the piezoelectric element after the polarization processing shown in FIG.
It is a sectional side view which shows one form of the characteristic which an electromotive force produces by applying a mechanical deformation.

FIG. 7 shows the piezoelectric element after the polarization treatment shown in FIG.
It is a sectional side view which shows another form of the characteristic which electromotive force produces by applying a mechanical deformation.

FIG. 8 is a top view showing an example of a piezoelectric element constituting the sensor according to the present invention.

9 is a side sectional view showing an example of a sensor using the piezoelectric element shown in FIG.

10 is a diagram showing a weight 40 in the sensor shown in FIG.
FIG. 6 is a side sectional view showing a deformed state of the piezoelectric element 30 when a displacement + Δx occurs in the axial direction.

11 is a diagram showing a weight 40 in the sensor shown in FIG.
FIG. 6 is a side cross-sectional view illustrating a deformed state of the piezoelectric element 30 when a displacement −Δx occurs in the axial direction.

12 is a diagram illustrating the weight 40 in the sensor shown in FIG.
FIG. 5 is a side sectional view showing a deformed state of the piezoelectric element 30 when a displacement + Δz is generated in the axial direction.

FIG. 13 shows a weight body 40 in the sensor shown in FIG.
FIG. 6 is a side sectional view showing a deformed state of the piezoelectric element 30 when a displacement −Δz is generated in the axial direction.

FIG. 14 is a top view showing a piezoelectric element 30 used in a sensor according to a basic embodiment of the present invention.

FIG. 15 is a graph showing an example of an AC signal supplied to the interdigital electrode on the piezoelectric element 30 shown in FIG.

16 is a graph showing another example of the AC signal supplied to the interdigital electrode on the piezoelectric element 30 shown in FIG.

17 is a graph showing still another example of the AC signal supplied to the interdigital electrode on the piezoelectric element 30 shown in FIG.

FIG. 18 is a plan view showing a movement trajectory when the weight body in the sensor according to the present invention is circularly moved on the XY plane.

FIG. 19 is a top view of a piezoelectric element 130 used in a sensor according to one embodiment of the present invention.

20 is a circuit diagram showing an example of an electric circuit connected to each terminal on the piezoelectric element 130 shown in FIG.

FIG. 21 is a top view of a sensor according to another embodiment of the present invention.

FIG. 22 is a plan view showing a shape of an interdigital electrode used in the sensor shown in FIG. 21;

FIG. 23 is a side sectional view of a sensor according to one embodiment of the present invention, in which the weight body is constituted by a part of the piezoelectric element.

24 shows a weight body 340 in the sensor shown in FIG.
When the displacement + Δx occurs in the X-axis direction
It is a sectional side view which shows the deformation state of 0.

25 shows a weight body 340 in the sensor shown in FIG.
Is the piezoelectric element 30 when the displacement + Δz occurs in the Z-axis direction.
It is a sectional side view which shows the deformation state of 0.

26 is a top view of the sensor shown in FIG.

FIG. 27 is a top view of a sensor according to yet another embodiment of the present invention.

FIG. 28 is a side cross-sectional view illustrating another embodiment of the polarization processing on the piezoelectric element shown in FIG.

FIG. 29 is a top view showing a variation of the interdigital electrode used in the sensor according to the present invention.

FIG. 30 is a top view of a sensor according to an embodiment of the present invention using interdigitated electrodes formed of arc-shaped finger electrodes.

FIG. 31 is a side sectional view showing a deformed state of the piezoelectric element 30 when the weight body 40 of the sensor in which the interdigital electrodes are formed on the upper and lower surfaces of the piezoelectric element 30 generates displacement + Δx in the X-axis direction. .

32 is a side sectional view showing a deformed state of the piezoelectric element 30 when the weight body 40 of the sensor shown in FIG. 31 generates a displacement + Δz in the Z-axis direction.

FIG. 33 is a side sectional view showing a deformed state of the piezoelectric element 30 when the weight body 40 of the sensor shown in FIG. 31 generates a displacement −Δz in the Z-axis direction.

FIG. 34 is a side sectional view showing a modification of the sensor shown in FIG. 9 in which a protective substrate is provided on the lower surface of a piezoelectric element.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... AC power supply 2 ... Voltage detection device 10 ... 1st electrode group 11-15 ... Finger electrode 16 ... Wiring part 17 ... Terminal part 20 ... 2nd electrode group 21-25 ... Finger electrode 26 ... Wiring part 27 ... Terminal part 30. Piezoelectric element 40... Weight body 50... Pedestal 60... Protective substrate 110... Common electrode group 121 to 124 .. Individual electrode group 210, 215. ... piezoelectric element 240 ... weight body 250 ... pedestal 300 ... piezoelectric element 330 ... flexible part 335 ... groove part 340 ... weight body 350 ... pedestal 400 ... piezoelectric element 430 ... flexible part 440 ... weight body 450 ... pedestal 500 ... Piezoelectric element 530 Flexible part 540 Weight body 550 Pedestal 600 Piezoelectric element 630 Flexible part 650 Weight body 650 Pedestal 660 Cross finger electrode 670 Cross finger electrode 700 Piezoelectric element E Terminal portion Ed: drive voltage Eg: ground terminal portion Ep: polarization voltage Ex1, Ex2, Ey1, Ey2: terminal portion G (t1) to G (t4): position of the center of gravity G of the weight body at times t1 to t4 FR, FL: lateral force applied to the piezoelectric element R1, R2: resistive element S1 to S4: driving AC signal t0 to t4: time on time axis t V (t1) to V (t4): time t1 to t4 Speed vectors of the center of gravity G of the weight body X1 to X8... Intersecting electrodes XX1, XX2... Intersecting electrodes Y1 to Y8... Intersecting electrodes Z1 to Z8. Δx: displacement in the X-axis direction ± Δz: displacement in the Z-axis direction

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Kazuhiro Okada 4-73, Sugaya, Ageo-shi, Saitama F-term (reference) 2F105 BB12 BB13 CC11 CC14 CD02 CD06

Claims (16)

[Claims] 1. An acceleration sensor having a function of detecting acceleration acting in at least one axis direction in an XYZ three-dimensional coordinate system, comprising: a fixed portion and a displacement portion, wherein the displacement portion is fixed in a fixed state. A piezoelectric element that undergoes mechanical deformation when a force is applied thereto; a device housing that accommodates the piezoelectric element and supports and fixes the fixing portion; a weight body formed in the displacement portion; A first electrode comprising a plurality of finger-like electrodes arranged at predetermined intervals so as to be substantially parallel to each other and short-circuited to each other; And a second electrode group consisting of a plurality of finger electrodes arranged at predetermined intervals so as to be substantially parallel to each other and short-circuited with each other, thereby forming the interdigital electrodes, Group Finger electrodes constituting the second electrode group and the finger electrodes constituting the second electrode group are arranged alternately. The piezoelectric element includes the first electrode group and the second electrode group. The polarization process is performed by applying a voltage of a predetermined polarity during the period, and a force acts on the displacement portion based on the acceleration acting on the weight body, and the piezoelectric element is mechanically deformed. sometimes,
An acceleration sensor, wherein an electromotive force corresponding to the acceleration is generated between the first electrode group and the second electrode group. 2. The acceleration sensor according to claim 1, wherein a plate-shaped piezoelectric element having a flat upper surface is used, a peripheral portion thereof is fixed to a device housing as a fixing portion, and a central portion thereof is set as a displacement portion. A weight body is formed at the center of the piezoelectric element, and the origin is located at the center of the upper surface of the piezoelectric element.
An XYZ three-dimensional coordinate system that is included in a plane is defined, and interdigitated electrodes are arranged on the X-axis on the upper surface of the piezoelectric element such that each finger-shaped electrode is oriented substantially in the Y-axis direction. An acceleration sensor characterized in that an X-axis component of the applied acceleration can be detected based on an electromotive force generated in the electrode. 3. The acceleration sensor according to claim 2, wherein a first cross finger-like electrode is disposed on a positive portion of the upper surface of the piezoelectric element along the X-axis such that each finger-like electrode is oriented substantially in the Y-axis direction. A second interdigital electrode is disposed on the upper surface of the piezoelectric element on the negative portion of the X axis so that each finger electrode is oriented substantially in the Y-axis direction. An acceleration sensor, wherein an X-axis direction component and a Z-axis direction component of an applied acceleration are detected based on electric power and an electromotive force generated in the second interdigital electrode. 4. The acceleration sensor according to claim 3, wherein, in addition to the first interdigital electrode and the second interdigital electrode,
Further, a third interdigital electrode is disposed on the upper surface of the piezoelectric element on the positive portion of the Y axis so that each finger electrode is oriented substantially in the X-axis direction. A fourth interdigital electrode in which each finger electrode is oriented substantially in the X-axis direction, and an electromotive force generated in the first interdigital electrode and an electromotive force generated in the second interdigital electrode. The X-axis direction component of the applied acceleration is detected based on the electric power, and is applied based on the electromotive force generated in the third interdigital electrode and the electromotive force generated in the fourth interdigital electrode. Detecting a Y-axis direction component of the acceleration, based on an electromotive force generated in the first interdigital electrode and an electromotive force generated in the second interdigital electrode, or based on the third interdigital electrode. Based on the generated electromotive force and the electromotive force generated in the fourth interdigital electrode, or based on the first to fourth intersecting electrodes. Based on the electromotive force generated in all Jo electrode,
An acceleration sensor, wherein a Z-axis component of the applied acceleration is detected. 5. The acceleration sensor according to claim 1, wherein a plate-shaped piezoelectric element having a flat upper surface is used, and a peripheral portion thereof is fixed to a device housing as a fixed portion, and a central portion thereof is set as a displacement portion. A weight body is formed at the center of the piezoelectric element, and the origin is located at the center of the upper surface of the piezoelectric element.
An XYZ three-dimensional coordinate system that is included in a plane is defined. On the X axis of the upper surface of the piezoelectric element, each finger electrode is oriented in a direction substantially along an arc centered on the origin. An acceleration sensor in which electrodes are arranged, and an X-axis component of the applied acceleration can be detected based on an electromotive force generated in the interdigital electrode. 6. The acceleration sensor according to claim 5, wherein each finger-like electrode is oriented in a direction substantially along an arc centered on the origin on a positive portion of the upper surface of the piezoelectric element on the X axis. A second interdigital electrode in which a finger is oriented in a direction substantially along an arc centered on the origin on a negative portion of the upper surface of the piezoelectric element on the X-axis. An electrode is disposed, and an X-axis component and a Z-axis component of the applied acceleration are detected based on an electromotive force generated in the first interdigital electrode and an electromotive force generated in the second interdigital electrode. An acceleration sensor characterized in that: 7. The acceleration sensor according to claim 6, wherein in addition to the first interdigital electrode and the second interdigital electrode,
Further, a third interdigital electrode is disposed on the upper surface of the piezoelectric element on the positive portion of the Y-axis such that each finger-shaped electrode is oriented substantially along a circular arc centered on the origin. A fourth interdigital electrode is arranged on a negative portion of the Y-axis on the upper surface such that each finger electrode is oriented substantially along an arc centered on the origin, and wherein the first interdigital electrode is The X-axis component of the applied acceleration is detected based on the electromotive force generated in the third interdigital electrode and the electromotive force generated in the second interdigital electrode. The Y-axis component of the applied acceleration is detected based on the electromotive force generated in the interdigital electrode of the first and second interdigital electrodes, and the electromotive force generated in the first interdigital electrode and the electromotive force generated in the second interdigital electrode are detected. An electromotive force generated on the third interdigital electrode based on the electric power or the fourth interdigital electrode; Based on the electromotive force generated in, or on the basis of the electromotive force generated in all of the first to fourth interdigital electrode,
An acceleration sensor, wherein a Z-axis component of the applied acceleration is detected. 8. An angular velocity sensor having a function of detecting an angular velocity acting on at least one axis in an XYZ three-dimensional coordinate system, comprising: a fixed part and a displacement part, wherein the fixed part is fixed and the displacement part is fixed. A piezoelectric element that undergoes mechanical deformation when a force is applied thereto; a device housing that accommodates the piezoelectric element and supports and fixes the fixing portion; a weight body formed in the displacement portion; A driving interdigital electrode and a detecting interdigital electrode formed at positions where mechanical deformation of the element occurs, and a plurality of short-circuited mutually arranged at predetermined intervals so as to be substantially parallel to each other. A first electrode group consisting of finger electrodes and a second electrode group consisting of a plurality of finger electrodes arranged at predetermined intervals so as to be substantially parallel to each other and short-circuited with each other, and The finger-like electrodes constituting the first electrode group and the finger-like electrodes constituting the second electrode group are arranged alternately, and the piezoelectric element includes the first electrode group. A polarization process is performed by applying a voltage having a predetermined polarity between the first electrode group and the second electrode group, and the first electrode group and the second electrode group that constitute the driving interdigital electrode.
By supplying a predetermined AC signal between the electrodes, the weight can be moved along a predetermined trajectory, and based on the angular velocity acting during the movement of the weight. When the Coriolis force is generated and the piezoelectric element is mechanically deformed, the piezoelectric element is driven in accordance with the angular velocity between a first electrode group and a second electrode group constituting the detection interdigital electrode. An angular velocity sensor characterized in that an electromotive force is generated. 9. The angular velocity sensor according to claim 8, wherein a plate-shaped piezoelectric element having a flat upper surface is used, and a peripheral portion thereof is fixed to a device housing as a fixed portion, and a central portion thereof is set as a displacement portion. A weight body is formed at the center of the piezoelectric element, and the origin is located at the center of the upper surface of the piezoelectric element.
An XYZ three-dimensional coordinate system that is included in a plane is defined, and a first driving interdigital electrode in which each finger electrode is oriented substantially in the Y-axis direction on the positive portion of the X-axis on the upper surface of the piezoelectric element And a second driving interdigital electrode such that each finger-shaped electrode is oriented substantially in the Y-axis direction on a negative portion of the X-axis on the upper surface of the piezoelectric element. A third driving interdigital electrode such that each finger electrode is oriented substantially in the X-axis direction is disposed on the positive portion of the piezoelectric element, and each finger electrode is disposed on the negative portion of the Y-axis on the upper surface of the piezoelectric element. A fourth driving interdigital electrode that is oriented substantially in the X-axis direction is disposed, and the first driving interdigital electrode and the second driving interdigital electrode are each provided with a weight X. An AC signal for exciting in the X-axis direction capable of causing a single oscillation in the axial direction;
The driving interdigital electrode and the fourth driving interdigital electrode are supplied with a Y-axis direction excitation AC signal capable of causing the weight body to vibrate in the Y-axis direction in the X-axis direction. The phase of the AC signal for excitation and the AC signal for excitation in the Y-axis direction is 9
By shifting the weight by 0 °, the weight can be made to perform a circular motion on the XY plane. When the weight is performing the circular motion, the weight is orthogonal to the tangential direction of the circular motion trajectory. An angular velocity about an axis perpendicular to both the tangential direction and the direction of the Coriolis force by detecting the Coriolis force acting in the direction of the Coriolis force. Sensors. 10. The angular velocity sensor according to claim 8, wherein a plate-shaped piezoelectric element having a flat upper surface is used, and a peripheral portion thereof is fixed to a device housing as a fixed portion, and a central portion thereof is set as a displacement portion. A weight body is formed at the center of the piezoelectric element, and the origin is located at the center of the upper surface of the piezoelectric element.
An XYZ three-dimensional coordinate system that is included in a plane is defined, and a first detection interdigital electrode in which each finger electrode is oriented substantially in the Y-axis direction on the positive portion of the X-axis on the upper surface of the piezoelectric element. And a second detection interdigital electrode such that each finger electrode is oriented substantially in the Y-axis direction on a negative portion of the X-axis on the upper surface of the piezoelectric element. By supplying a predetermined AC signal, the weight body can be made to perform a circular motion on the XY plane. When the weight body crosses the X-axis, the first detection interdigital finger is formed. An angular velocity sensor characterized in that an angular velocity around the Z-axis can be detected based on an electromotive force generated in an electrode and the second detection interdigital electrode. 11. The angular velocity sensor according to claim 8, wherein a plate-like piezoelectric element having a flat upper surface is used, and a peripheral portion thereof is fixed to a device housing as a fixed portion, and a central portion thereof is set as a displacement portion. A weight body is formed at the center of the piezoelectric element, and the origin is located at the center of the upper surface of the piezoelectric element.
An XYZ three-dimensional coordinate system that is included in a plane is defined. A detection interdigital electrode capable of detecting the displacement of the weight body in the Z-axis direction is disposed on the upper surface of the piezoelectric element. By supplying a predetermined AC signal to the shape electrode, the weight body can be made to perform a circular motion on the XY plane, and when the weight body crosses the X axis, the detection interdigital finger is formed. An angular velocity around the X axis is detected based on an electromotive force generated at the electrode, and an angular velocity around the Y axis is detected based on the electromotive force generated at the detection interdigital electrode when the weight body crosses the Y axis. An angular velocity sensor characterized in that the angular velocity sensor can detect the angular velocity. 12. The angular velocity sensor according to claim 8, wherein a plate-shaped piezoelectric element having a flat upper surface is used, and a peripheral portion thereof is fixed to the device housing as a fixed portion, and a central portion thereof is set as a displacement portion. A weight body is formed at the center of the piezoelectric element, and the origin is located at the center of the upper surface of the piezoelectric element.
An XYZ three-dimensional coordinate system that is included in a plane is defined, and a positive part of the X-axis on the upper surface of the piezoelectric element is arranged such that each finger-like electrode is oriented substantially along an arc centered at the origin. A second driving method in which the driving interdigital electrodes are arranged on the negative portion of the X-axis on the upper surface of the piezoelectric element, and each finger electrode is oriented substantially along an arc centered on the origin. A third driving interdigital electrode in which a finger electrode is oriented in a direction substantially along an arc centered on the origin on a positive portion of the Y-axis on the upper surface of the piezoelectric element. And a fourth driving interdigital electrode such that each finger electrode is oriented substantially along an arc centered on the origin on a negative portion of the Y-axis on the upper surface of the piezoelectric element. The weight body is disposed in the X-axis direction on the first driving interdigital electrode and the second driving interdigital electrode. Supplying X-axis direction excitation AC signal can be vibrated, the third
The driving interdigital electrode and the fourth driving interdigital electrode are supplied with a Y-axis direction excitation AC signal capable of causing the weight body to vibrate in the Y-axis direction in the X-axis direction. The phase of the AC signal for excitation and the AC signal for excitation in the Y-axis direction are set to 9
By shifting the weight by 0 °, the weight can be made to perform a circular motion on the XY plane. When the weight is performing the circular motion, the weight is orthogonal to the tangential direction of the circular motion trajectory. An angular velocity about an axis perpendicular to both the tangential direction and the direction of the Coriolis force by detecting the Coriolis force acting in the direction of the Coriolis force. Sensors. 13. The angular velocity sensor according to claim 8, wherein a plate-shaped piezoelectric element having a flat upper surface is used, and a peripheral portion thereof is fixed to a device housing as a fixed portion, and a central portion thereof is set as a displacement portion. A weight body is formed at the center of the piezoelectric element, and the origin is located at the center of the upper surface of the piezoelectric element.
An XYZ three-dimensional coordinate system that is included in a plane is defined, and a positive part of the X-axis on the upper surface of the piezoelectric element is arranged such that each finger-like electrode is oriented substantially along an arc centered at the origin. 1st detection interdigital electrode is arranged, and a second detection in which each finger-shaped electrode is oriented in a direction substantially along an arc centered on the origin on a negative portion of the X-axis on the upper surface of the piezoelectric element. By disposing the interdigital electrode for driving and supplying a predetermined AC signal to the driving interdigital electrode, the weight body can be made to perform a circular motion on the XY plane, and the weight body is When crossing the X-axis, the angular velocity around the Z-axis can be detected based on the electromotive force generated in the first detection interdigital electrode and the second detection interdigital electrode. Angular velocity sensor. 14. The angular velocity sensor according to claim 8, wherein a physically identical interdigital electrode is used as both a driving interdigital electrode and a detecting interdigital electrode. An angular velocity sensor used as an electrode. 15. The sensor according to claim 1, wherein the weight body is constituted by a part of the piezoelectric element. 16. The sensor according to claim 1, wherein a plate-shaped piezoelectric element is used as the piezoelectric element, and interdigital electrodes are formed on both upper and lower surfaces of the piezoelectric element. .