JP2014238373A - External force detection device - Google Patents

Abstract

An external force detection device capable of detecting an external force applied to a piezoelectric plate with a simple structure with high accuracy and having impact resistance. A crystal piece 2 is supported in a cantilever in a container 1. Excitation electrodes 31 and 33 are formed on the upper and lower surfaces, for example, at the center of the crystal piece 2. A movable electrode 41 and a posture adjusting electrode 43 are formed on the lower surface and the upper surface, respectively, at the tip of the crystal piece 2. A fixed electrode 51 and a posture adjusting electrode 52 are provided on the bottom and the ceiling inside the container 1 so as to face the movable electrode 41 and the posture adjusting electrode 43, respectively. The excitation electrode 31 and the fixed electrode 51 on the upper surface side are connected to the oscillation circuit 16. When an external force is applied to the crystal piece 2 to bend, the capacitance between the movable electrode 41 and the fixed electrode 51 changes, and this capacitance change is regarded as a change in the oscillation frequency of the crystal piece 2. Further, a voltage is applied to the fixed electrode 51 or the posture adjusting electrode 52 to apply electric charges to the movable electrode 41 or the posture adjusting electrode 43 to adjust the bending of the crystal piece 2 and suppress the breakage of the tip portion of the crystal piece 2. . [Selection] Figure 1

Description

  The present invention detects an external force such as acceleration, pressure, fluid flow velocity, magnetic force or electrostatic force by detecting the magnitude of an external force acting on the piezoelectric plate based on the oscillation frequency using a piezoelectric plate such as a quartz piece. Technical field.

  As external forces acting on the system, there are forces based on acceleration acting on an object, pressure, flow velocity, electrostatic force, magnetic force, etc., but it is often necessary to accurately measure these external forces. For example, in the stage of developing a car, the impact force on a seat at the time of a car collision is measured. In addition, there is a request to investigate the acceleration of shaking as precisely as possible in order to investigate the vibration energy and amplitude in an earthquake.

  Furthermore, a case where the flow rate of a liquid or fluid is accurately measured and the detected value is reflected in a control system or the performance of a magnet is measured can be cited as an example of measuring external force. In carrying out such a measurement, the measuring apparatus is required to have a structure as simple as possible and to be able to measure with high accuracy.

  Therefore, the present inventors, for example, as disclosed in Patent Document 1, provide a movable electrode together with an excitation electrode on a quartz plate, and also detect an external force by providing a fixed electrode on the container so as to face the movable electrode. Has proposed. Specifically, by supporting the quartz plate in a cantilever manner and providing a movable electrode at the other end, the capacitance between the movable electrode and the fixed electrode changes when the quartz plate is bent by an external force. This change in capacitance is converted into a change in frequency, and the change in frequency is measured. According to this technique, it is possible to perform external force measurement with high accuracy with a simple structure.

  By the way, when an impact is applied to the external force measuring device described above, there is a risk that the quartz plate will shake greatly and collide with the inner wall of the container and be damaged. Therefore, a countermeasure for enhancing the impact resistance of the external force detecting device is required. Yes. Also in Patent Document 1, a technique is provided in which a protrusion is provided at a portion corresponding to the center portion of the crystal plate in the external force detection device, and the impact is enhanced by receiving the crystal plate and preventing the tip from colliding at the time of impact. However, there is a need for further measures to enhance impact resistance.

JP 2013-7734 A

  The present invention has been made under such circumstances, and its purpose is to adjust the relationship between the external force applied to the piezoelectric plate and the amount of bending of the piezoelectric plate, and to suppress damage due to the collision of the piezoelectric plate. An object of the present invention is to provide an external force detection device capable of performing the above.

The present invention
In the external force detection device that detects external force,
A cantilever piezoelectric plate whose one end is supported by a support in the container;
One excitation electrode and the other excitation electrode provided respectively on one side and the other side of the piezoelectric plate;
A movable electrode for variable capacitance formation provided on the other end of the piezoelectric plate and electrically connected to the other excitation electrode;
An oscillation circuit electrically connected to the one excitation electrode;
A fixed electrode provided in the container so as to face the movable electrode, and for forming a variable capacitance with the movable electrode;
The other end of the piezoelectric plate and the container are provided so as to face each other, and one posture adjustment electrode and the other posture adjustment for adjusting the degree of bending of the piezoelectric plate according to the amount of electric charge of the capacitance therebetween Electrodes for
A DC power supply unit for applying a DC electrode between the posture adjusting electrodes;
A frequency information detection unit for detecting a signal that is frequency information corresponding to the oscillation frequency of the oscillation circuit;
The oscillation loop of the oscillation circuit includes the variable capacitor, one excitation electrode and the other excitation electrode,
The frequency information detected by the frequency information detector is for evaluating an external force acting on the piezoelectric plate.

  According to the present invention, in a device that detects an external force by capturing a change in variable capacitance caused by bending of a cantilever piezoelectric plate as a change in frequency, the tip (other end) of the piezoelectric plate and the container are opposed to each other. Each is provided with a posture adjusting electrode, and a DC voltage is applied between the posture adjusting electrodes to adjust the distance between the two electrodes to adjust the posture of the piezoelectric plate. As a result, the distance between the variable electrode and the fixed electrode can be adjusted, so the relationship between the external force and the amount of change in frequency can be adjusted, and the linearity of the orientation of the piezoelectric plate can be increased. It can suppress that a board collides with a container and is damaged.

It is a vertical side view which shows the principal part of 1st Embodiment of the external force detection apparatus which concerns on this invention. It is a top view which shows the upper surface and lower surface of the crystal piece used for 1st Embodiment. It is an external view which shows the external appearance of a part of external force detection apparatus. It is a block diagram which shows an external force detection apparatus. It is a circuit diagram which shows the equivalent circuit of the circuit containing a crystal oscillator. It is a vertical side view which shows a mode that a crystal piece bends with external force, and the dimension of each part. It is a cross-sectional top view which shows 2nd Embodiment of the external force detection apparatus which concerns on this invention. It is a block circuit diagram which shows the external force detection apparatus which concerns on 2nd Embodiment. It is a vertical side view which shows the principal part of the external force detection apparatus which concerns on 3rd Embodiment. 3 is a graph illustrating the effect of the present invention.

[First Embodiment]
A first embodiment of an external force detection device according to the present invention will be described with reference to FIGS. 1 to 6 by taking as an example a case where acceleration is detected as an external force.
In FIG. 1, reference numeral 1 denotes a sealed container made of, for example, quartz having a rectangular parallelepiped shape, and an inert gas such as nitrogen gas is sealed therein. The container 1 includes a lower portion 12 that forms a base and an upper portion 13 that is joined to the lower portion 12 at a peripheral portion, and is provided on an insulating substrate 11. The container 1 is not necessarily limited to a sealed container. A base 7 is provided in the container 1, and a base end (one end) of the crystal piece 2 that is a piezoelectric plate is fixed to the upper surface of the base 7 by a conductive adhesive 6. That is, the crystal piece 2 is cantilevered by the base 7, and the base 7 corresponds to a support portion that supports one end of the crystal piece 2.

  The quartz piece 2 is formed by, for example, AT-cut quartz in a strip shape, and has a thickness of the order of several tens of μm, for example, 0.03 mm. Therefore, by applying acceleration in a direction crossing the surface of the crystal piece 2, the tip of the crystal piece 2 is bent.

  As shown in FIG. 2A, the crystal piece 2 is provided with one excitation electrode 31 at the center of the upper surface of the crystal piece 2, and as shown in FIG. The other excitation electrode 33 is provided in the central portion and corresponding to the excitation electrode 31 to form the crystal resonator 20 forming the piezoelectric vibration portion. From the excitation electrode 31, the extraction electrode 32 is extracted to the base end side along the center in the long side direction of the crystal piece 2, and extended to the adhesion portion by the conductive adhesive 6. Further, from the excitation electrode 33, the extraction electrode 34 is extracted along one side of the long side of the crystal piece 2, and is extended to a bonded portion by the conductive adhesive 6. In FIG. 1, the extraction electrodes 32 and 34 are not shown.

  As shown in FIG. 2B, a movable electrode 41 electrically connected to the other excitation electrode 33 via a lead electrode 42 made of a metal film is provided on the lower surface of the tip of the crystal piece 2. A fixed electrode 51 is provided on the inner wall of the container 1 so as to face the movable electrode 41.

  The present invention requires that the tip of the crystal piece 2 and the container 1 are each provided with a posture adjusting electrode for adjusting the posture of the crystal piece 2. In this embodiment, the upper surface of the crystal piece 2 is provided. Posture adjustment electrodes are provided on the side and the lower surface side, and the lower surface side posture adjustment electrode is shared by the movable electrode 41 and the fixed electrode 51. As shown in FIG. 2A, the posture adjusting electrode 43 on the upper surface side of the crystal piece 2 is drawn out to the base end side of the crystal piece 2 by the extraction electrode 44 formed along the edge of the crystal piece 2. ing. In FIG. 4, reference numeral 52 denotes an attitude adjustment electrode provided on the container 1 side, which is paired with the attitude adjustment electrode 43 on the upper surface side of the crystal piece 2. In FIG. 1, the extraction electrodes 42 and 44 are not shown.

  One excitation electrode 31 is connected to the oscillation circuit 16 via the extraction electrode 32 and the conductive path 15, and the other excitation electrode 33 is electrically connected to the movable electrode 41 by the extraction electrode 42 as described above.

  Since the present invention detects an external force through a change in capacitance between the movable electrode 41 and the fixed electrode 51 that occurs based on deformation of the quartz crystal piece 2, the movable electrode 41 can also be referred to as a detection electrode.

  The fixed electrode 51 is connected to one end side of the conductive path 14 wired through the insulating substrate 11, and the other end side of the conductive path 14 is branched and connected to the oscillation circuit 16 and the power supply unit 17. Further, another conductive path 15 is extended from the power supply unit 17 and branched, and one is connected to the oscillation circuit 16 and the other is connected to the bonded portion by the conductive adhesive 6. Further, the posture adjustment electrode 52 is electrically connected to the power supply unit 17 and the posture adjustment electrode 43.

  FIG. 3 shows a partial appearance of the external force detection device, FIG. 4 shows a connection state of wiring of the external force detection device, and FIG. 5 shows a circuit diagram of an equivalent circuit of the circuit including the crystal resonator 20. In FIG. 5, C0 is an effective parallel capacitance including interelectrode capacitance, C1 is a series capacitance, CL is a load capacitance of the oscillation circuit 16, L1 is a series inductance corresponding to the mass of the crystal resonator, and R1 is a series resistance. . 4 and 5, the variable capacitance interposed between the movable electrode 41 and the fixed electrode 51 is Cv.

Here, according to the international standard IEC 60122-1, the general formula of the crystal oscillation circuit is expressed as the following formula (1).
FL = Fr × (1 + x)
x = (C1 / 2) × 1 / (C0 + CL) (1)
FL is an oscillation frequency when a load is applied to the crystal resonator, and Fr is a resonance frequency of the crystal resonator itself.
In the present embodiment, as shown in FIGS. 4 and 5, the load capacity of the crystal piece 2 is obtained by adding Cv to CL. Therefore, y represented by equation (2) is substituted in place of CL in equation (1).
y = 1 / (1 / Cv + 1 / CL) (2)
Therefore, assuming that the amount of bending of the crystal piece 2 changes from the state 1 to the state 2 and thereby the variable capacitor Cv changes from Cv1 to Cv2, the frequency change dFL is expressed by the equation (3).
dFL = FL1-FL2 = A × CL 2 × (Cv2-Cv1) / (B × C) ...... (3)
here,
A = C1 × Fr / 2
B = C0 × CL + (C0 + CL) × Cv1
C = C0 × CL + (C0 + CL) × Cv2
It is.

In addition, when the external force is not applied to the crystal piece 2, the distance between the movable electrode 41 and the fixed electrode 51 in the reference state is d1, and the distance when the external force is applied to the crystal piece 2 is d2. Then, equation (4) is established.
Cv1 = S × ε / d1
Cv2 = S × ε / d2 (4)
However, S is the area of the opposing area | region of the movable electrode 41 and the fixed electrode 51, and (epsilon) is a dielectric constant. Since d1 is known, it can be seen that dFL and d2 are in a correspondence relationship.

  An example of the dimensions of each part will be described with reference to FIG. The length dimension L1 and the width dimension of the crystal piece 2 are 20 mm and 1.6 mm, respectively. The thickness of the crystal piece 2 is, for example, 30 μm. Assuming that the support surface on one end side of the crystal piece 2 is set parallel to the horizontal plane, the crystal piece 2 is horizontal by applying a voltage from the fixed electrode 51 or the posture adjusting electrode 52 in a state where no external force is applied, as will be described later. It is.

Next, the operation of the above embodiment will be described.
As for the external force detection device, when the crystal piece 2 touches excessively and the tip collides with the ceiling or bottom of the container 1, there is a property that even a lump of crystal is easily chipped due to the phenomenon of “cleavage”. When no external force or electric charge other than gravity is applied to the crystal piece 2, the crystal piece 2 bends due to its own weight. Therefore, a voltage that keeps the crystal piece 2 horizontal is always applied to the fixed electrode 51 or the posture adjusting electrode 52 when no external force other than gravity is applied. For example, by applying a voltage of about 0.3 V to the attitude adjustment electrode 52, an electric charge is applied to the attitude adjustment electrode 43.

  When an earthquake or simulated vibration is applied to the external force detection device, the crystal piece 2 bends as shown by the dotted line in FIG. As described above, a state when the crystal piece 2 is parallel by applying a charge to the posture adjusting electrode 52 is set as a reference state, and the capacitance between the movable electrode 41 and the fixed electrode 51 at this time is expressed as Cv1. far. In a state where an external force is applied to the crystal piece 2 and the crystal piece 2 is bent, the distance between the electrodes 41 and 51 changes, whereby the capacitance changes from Cv1. For this reason, the oscillation frequency output from the oscillation circuit 16 changes.

  When the frequency detected by the frequency measuring unit 101, which is the frequency information detecting unit, is FL1, and the frequency when an external force (acceleration) is applied is FL2, the frequency difference FL1-FL2 is expressed by the following equation (3). expressed. The present inventor calculates the frequency change rate in the state where the external force is applied from the reference state from the frequency difference FL1-FL2, investigates the relationship between the frequency change rate {(FL1-FL2) / FL1} and the external force, A straight line relationship is obtained. Therefore, it is possible to obtain the external force by measuring the frequency difference. The value of FL1 is a frequency value at a reference temperature, for example, 25 ° C., when a certain temperature is determined as the reference temperature.

Next, the effect of the above embodiment will be described.
By applying a voltage to the posture adjusting electrode 52, a charge is applied to the posture adjusting electrode 43, and an upward attractive force acts on the tip of the crystal piece 2 in FIG. Further, by applying a voltage to the fixed electrode 51, a charge is applied to the movable electrode 41, and a downward attractive force acts on the tip of the crystal piece 2 in FIG. By combining these two effects, the posture of the crystal piece 2 can be kept horizontal, and therefore the crystal piece 2 is less likely to collide with the container 1. Moreover, since the attitude | position of the crystal piece 2 can be adjusted by applying a voltage to the fixed electrode 51 or the attitude | position adjustment electrode 52, the correspondence between an external force and a fixed electrode can be changed. That is, it is possible to change the range of external force that can be measured.

  In the embodiment, there are two sets of electrodes for adjusting the attitude of the crystal blank 2, that is, the movable electrode 41 and the fixed electrode 51, and the attitude adjustment electrodes 43 and 52. . However, even if only one set of the posture adjusting electrodes 43 and 52 is taken into consideration, by applying a voltage to the posture adjusting electrode 52 so that the crystal piece 2 is horizontal in consideration of the force derived from the relative dielectric constant ε. It is clear that the impact resistance effect can be obtained.

  Further, for example, the movable electrode 41 and the fixed electrode 51 may be provided on the upper surface side of the crystal piece 2, and the combination of the movable electrode 41 and the fixed electrode 51 may also serve as the posture adjusting electrode. In this case, by applying a voltage to the fixed electrode 51, a charge is given to the movable electrode 41, and the posture of the crystal piece 2 is adjusted.

[Second Embodiment]
FIG. 7 shows another example of the external force measuring device. This embodiment is characterized in that two sets of the crystal piece 2, the excitation electrodes 31 and 33, the movable electrode 41, the fixed electrode 51, the attitude adjustment electrodes 43 and 52, and the oscillation circuit 16 described above are provided. Different from the embodiment. Regarding the crystal piece 2 and the oscillation circuit 16, one set of parts is given a symbol “A”, and the other set of parts is given a symbol “B”. When the inside of the external force measurement device is viewed in plan, the first crystal piece 2A and the second crystal piece 2B are arranged in parallel in the horizontal direction as shown in FIG. The structure of these crystal pieces 2A and 2B is substantially the same as that of the crystal piece 2 in the external force measuring device of the first embodiment.

  FIG. 8 shows a circuit diagram of the external force measuring device in this embodiment. The difference from the first embodiment is that the first oscillation circuit 16A and the second oscillation circuit 16B are connected to correspond to the first crystal piece 2A and the second crystal piece 2B, respectively. An oscillation loop including the oscillation circuit 16A (16B), the excitation electrodes 31, 33, the movable electrode 41, the fixed electrode 51, and the attitude adjustment electrodes 43 and 52 is formed for each of the one crystal piece 2A and the second crystal piece 2B. It is that. Outputs from these oscillation circuits 16A and 16B are sent to the frequency measurement unit 102, where the difference in oscillation frequency from each oscillation circuit 16A and 16B or the difference in frequency change rate is detected.

  The frequency change rate has the following meaning. That is, in the oscillation circuit 16A, when the frequency in the reference state in which the crystal piece 2A is parallel is called a reference frequency, when the frequency changes due to the crystal piece 2A being bent by an external force, the frequency change / reference frequency is expressed. For example, expressed in units of ppb. Similarly, the frequency change rate is calculated for the crystal piece 2B, and the difference between the change rates is output to the data processing unit 102 as information corresponding to the frequency. In the data processing unit 102, for example, data in which a frequency difference is associated with a magnitude of acceleration is stored in a memory, and acceleration can be detected based on the difference between the data and the change rate.

An example of the relationship between the amount of deflection of the crystal piece 2A (2B) (the difference in height level of the tip portion between the state in which the crystal piece 2A extends horizontally and the state in which the crystal piece 2A is bent) and the amount of change in frequency is given. When the tip of the crystal piece 2A (2B) changes on the order of 10 ⁻⁵ μm, when the oscillation frequency is 70 MHz, the change in frequency is 0.65 ppb. Accordingly, even a very small external force such as acceleration can be accurately detected.

  According to the second embodiment described above, since the crystal pieces 2A and 2B are arranged in the same temperature environment in addition to the effects of the first embodiment, the frequency of each of the crystal pieces 2A and 2B is the temperature. This change is canceled, and as a result, only the change in frequency based on the bending of the crystal pieces 2A and 2B can be detected, so that the detection accuracy is high.

[Third Embodiment]
Next, an apparatus according to a third embodiment will be described with reference to FIG. In addition, illustration is abbreviate | omitted about parts other than the container 1, for example, the insulated substrate 11, the conductive path 14, etc. FIG.
In the third embodiment, the crystal piece 2 is bonded at two places on the upper surface of the base 7 of the first embodiment. One of the bonded portions is the base end portion of the crystal piece 2 and is bonded by the conductive adhesive 6, and the other bonded portion is the other end (front end) side of the upper surface of the base 7 and is bonded by the adhesive 9, They are separated from each other.

  For the crystal piece 2, as shown in FIG. 9, the crystal piece 2 is excited on the upper surface of the base 7 between the adhesion site by the conductive adhesive 6 and the adhesion site by the adhesive 9. An excitation electrode 33 a is provided, and an excitation electrode 31 a is provided on the inner surface of the upper portion 13 of the container 1 facing the upper surface of the crystal piece 2. The excitation electrodes 31a and 33a are disposed at positions facing each other with the crystal piece 2 interposed therebetween. These excitation electrodes 31 a and 33 a exist as space electrodes with respect to the crystal piece 2. One excitation electrode 31a is connected to the oscillation circuit 16 (not shown) via a conductive path, and the other excitation electrode 33a is a movable electrode at the tip of the crystal piece 2 via a conductive path and a lead electrode (not shown). 4 is electrically connected.

  On the other hand, a fixed electrode 5 for forming a variable capacitance is provided on the bottom surface of the container 1. On the bottom of the container 1 is provided a protrusion 8 made of a convex crystal. The protrusion 8 is quadrangular when viewed in plan view. The fixed electrode 5 is provided at the protrusion 8 so as to face the movable electrode 4 substantially. For example, when an impact is applied to the container 1 by the protrusion 8, the crystal piece 2 can be received by the protrusion 8 and the tip of the crystal piece 2 can be prevented from colliding with the container 1.

  In addition, a voltage is applied to the fixed electrode 5 in order to prevent the movable electrode 4 from contacting the inside of the container 1, for example, the fixed electrode 5. As a result, electric charge is given to the movable electrode 4. Therefore, when the crystal piece 2 is bent before the measurement, the deformation of the crystal piece 2 can be adjusted.

[Comparison with conventional external force measuring device]
The external force measuring device according to the embodiment of the present invention was tested under the following conditions.
As an example, an impact test was performed on the same external force detection device as that of the first embodiment described above. Specifically, the conditions are as follows.
Crystal piece: Nominal frequency: 73 MHz
Cutting orientation: AT cut
Vibration mode: Basic vibration mode Container 1 external dimensions: 27.0 mm × 12.0 mm × 1.0 mm
About 100 said external force detection apparatuses, based on JISC6701, the test which gives a half-wave sine wave of 5000G from 6 directions was each performed 100 times. As a result, no abnormality was observed in any of the individuals. Moreover, the result of having measured the frequency change with time before and after the impact test of the crystal unit 20 for each individual is shown by a white bar graph in FIG. The average value of the frequency change was -0.02 ppm, and the standard deviation was 0.15 ppm. This measured value is based on the π circuit method (IEC 60444-1), and this result is within the measurement error in the π circuit method.

  On the other hand, as a comparative example, a similar test was performed on a conventional external force measuring device, that is, an external force detecting device that does not adjust the deflection of the crystal piece 2 according to the method of the present invention. In addition, FIG. 10 shows a gray bar graph showing the result of measuring the frequency change over time of the quartz resonator 20 before and after the impact test for each individual. The π circuit method was used for the measurement as in the above experimental example. The average value of the frequency change of the crystal resonator was −0.05 ppm, and the standard deviation was 0.32 ppm. This result exceeds the range of measurement error in the π circuit method.

  The above experiments were originally conducted for the purpose of measuring different effects. From these experimental results, the external force detection device of the present invention is superior in impact resistance effect compared to conventional external force measurement devices. It became clear. That is, at least according to the present invention, it is confirmed that the posture of the crystal piece 2 is changed.

  In the embodiments and examples described above, an AT-cut crystal piece is used as the material of the crystal piece 2. However, any crystal piece that can use thickness-shear vibration such as an SC cut or a BT cut is used. An orientation crystal piece may be used.

As described above, the present invention is not limited to detecting acceleration, but can also be applied to measurement of magnetic force, measurement of the degree of inclination of the object to be measured, measurement of fluid flow rate, measurement of wind speed, and the like.
A configuration example in the case of measuring the magnetic force will be described. A magnetic film is formed in a portion of the crystal piece 2 between the movable electrode 41 and the excitation electrode 33, and the crystal piece 2 is bent when the magnetic material is positioned in the magnetic field. To configure.

  Furthermore, the crystal piece 2 can be exposed to a fluid such as gas or liquid, and the flow velocity can be detected through frequency information corresponding to the amount of deflection of the crystal piece 2. In this case, the thickness of the crystal blank 2 is determined according to the measurement range of the flow velocity. Furthermore, the present invention can also be applied when measuring gravity.

  The present invention can detect vibration (frequency of vibration) according to the external force in addition to the case where the external force value itself is detected as in the above-described embodiment. Specifically, the present invention can be applied to a vibration detection device for earthquakes and the like.

DESCRIPTION OF SYMBOLS 1 Container 2 Crystal piece 16 Oscillation circuit 17 Power supply part 31, 33 Excitation electrode 41 Movable electrode 43 Attitude adjustment electrode 51 Fixed electrode 52 Attitude adjustment electrode 7 Base 100 Control part 101 Data processing part 102 Frequency information detection part

Claims (3)

In the external force detection device that detects external force,
A cantilever piezoelectric plate whose one end is supported by a support in the container;
One excitation electrode and the other excitation electrode provided respectively on one side and the other side of the piezoelectric plate;
A movable electrode for variable capacitance formation provided on the other end of the piezoelectric plate and electrically connected to the other excitation electrode;
An oscillation circuit electrically connected to the one excitation electrode;
A fixed electrode provided in the container so as to face the movable electrode, and for forming a variable capacitance with the movable electrode;
The other end of the piezoelectric plate and the container are provided so as to face each other, and one posture adjustment electrode and the other posture adjustment for adjusting the degree of bending of the piezoelectric plate according to the amount of electric charge of the capacitance therebetween Electrodes for
A DC power supply unit for applying a DC electrode between the posture adjusting electrodes;
A frequency information detection unit for detecting a signal that is frequency information corresponding to the oscillation frequency of the oscillation circuit;
The oscillation loop of the oscillation circuit includes the variable capacitor, one excitation electrode and the other excitation electrode,
The frequency information detected by the frequency information detector is for evaluating an external force acting on the piezoelectric plate.   The external force detection device according to claim 1, wherein the one posture adjusting electrode is provided on a surface of the piezoelectric plate opposite to the movable electrode.   The external force detection device according to claim 1, wherein the movable electrode and the fixed electrode also serve as an attitude adjustment electrode.

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