JP2013007734A - External force detection device and external force detection sensor - Google Patents

Abstract

To provide an external force detection device capable of detecting an external force applied to a piezoelectric plate with a simple structure with high accuracy.
A crystal plate is supported in a cantilever in a container. Excitation electrodes 31 and 41 are formed on the upper and lower surfaces, for example, at the center of the quartz plate 2. The movable electrode 5 connected to the excitation electrode 41 on the lower surface side through the extraction electrode 42 is formed at the tip portion on the lower surface side of the crystal plate 2, and the fixed electrode 6 is formed on the bottom of the container 1 so as to face the movable electrode 5. Is provided. The excitation electrode 31 on the upper surface side and the fixed electrode 6 are connected to the oscillation circuit 14. When an external force is applied to the quartz plate 2 and the quartz plate 2 is bent, the capacitance between the movable electrode 5 and the fixed electrode 6 changes, and this capacitance change is regarded as a change in the oscillation frequency of the quartz plate. Further, in order to suppress damage to the tip portion of the crystal plate 2, when the crystal plate 2 is excessively bent, the crystal plate 2 comes into contact with the body portion of the crystal plate 2 before colliding with the inner wall of the container 1. Protrusions 7 are provided as described above.
[Selection] Figure 1

Description

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

  As external forces acting on the system, there are forces acting on an object based on acceleration, pressure, flow velocity, magnetic force, electrostatic force, etc., but it is often necessary to accurately measure these external forces. For example, when an automobile collides with an object at the stage of developing the automobile, the impact force at the seat 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 during an earthquake. Furthermore, examples of measuring the external force include a case where the flow velocity of the liquid or gas is accurately checked and the detected value is reflected in the control system, or the performance of the magnet is measured.

  In performing such measurement, the measuring apparatus is required to have a structure as simple as possible and to measure with high accuracy. For this reason, the present inventor is considering measurement using a crystal resonator, but in that case, it is necessary to consider the breakage of the crystal plate of the crystal resonator.

Patent Document 1 describes that a piezoelectric film is supported in a cantilever manner, the piezoelectric film is deformed by a change in the surrounding magnetic force, and the current flowing through the piezoelectric film changes.
Further, Patent Document 2 includes a capacitively coupled pressure sensor and a crystal resonator disposed in a space partitioned with respect to the region where the pressure sensor is disposed. Are connected in parallel, and the pressure is detected by changing the anti-resonance point of the crystal resonator by changing the capacitance of the pressure sensor.
In addition, in a device in which the piezoelectric vibrator is cantilevered, Patent Document 3 describes a technique for avoiding a collision of the tip portion with the inner wall by providing a step on the inner wall of the device facing the piezoelectric vibrator in the bending direction. Patent Document 4 describes a technique for regulating vibration at the tip by providing a pillow member so as to face the bending direction of the piezoelectric vibrator.
These patent documents 1 to 4 are completely different in principle from the present invention.

JP 2006-138852 A (paragraph 0021, paragraph 0028) JP 2008-39626 A (FIGS. 1 and 3) Japanese Patent Laid-Open No. 2003-133883 Japanese Patent Laid-Open No. 11-112269

  The present invention has been made under such a background, and provides an external force detection device and an external force detection sensor capable of detecting an external force applied to a piezoelectric plate with a simple structure with high accuracy.

The external force detection device of the present invention is
An external force detection device for detecting an external force acting on a piezoelectric plate,
The cantilevered piezoelectric plate whose one end is supported by a base in the container;
In order to vibrate this piezoelectric plate, one excitation electrode and the other excitation electrode respectively provided on one surface side and the other surface side of the piezoelectric plate;
An oscillation circuit electrically connected to one excitation electrode;
A movable electrode for forming a variable capacitor provided on the other end of the piezoelectric plate and electrically connected to the other excitation electrode;
It is provided so as to face the movable electrode apart from the piezoelectric plate and is connected to the oscillation circuit, and the capacitance between the movable electrode changes due to the bending of the piezoelectric plate, thereby forming a variable capacitance. A fixed electrode to
A frequency information detection unit for detecting a signal that is frequency information corresponding to the oscillation frequency of the oscillation circuit;
When the piezoelectric plate is excessively bent, the body of the piezoelectric plate comes into contact with the inner wall portion of the container facing the movable electrode of the piezoelectric plate, so that the tip of the piezoelectric plate comes into contact with the inner wall portion. In order not to collide, provided with a protrusion that protrudes the inner wall to the piezoelectric plate side,
An oscillation loop that returns from the oscillation circuit to the oscillation circuit through one excitation electrode, the other excitation electrode, the movable electrode, and the fixed electrode is formed,
The frequency information detected by the frequency information detector is for evaluating an external force acting on the piezoelectric plate.
The shape of the cut surface in the length direction of the surface facing the piezoelectric plate in the protrusion may be a mountain shape.

Moreover, as a preferable aspect of the present invention, as a set including the piezoelectric plate, the excitation electrode, the movable electrode, and the fixed electrode, a first set and a second set are provided,
An oscillation circuit is provided corresponding to each of the first group and the second group,
The frequency information detection unit may have a function of obtaining a signal corresponding to a difference between an oscillation frequency corresponding to the first set and an oscillation frequency corresponding to the second set. In this configuration, the oscillation circuit can be made common to the first group and the second group. In this case, the first group of oscillation loops and the second group of oscillation loops are alternately formed. As described above, a changeover switch unit may be provided between the oscillation circuit and the loop.

The external force detection sensor of the present invention is
An external force detection sensor for detecting an external force acting on a piezoelectric plate based on an oscillation frequency of the piezoelectric plate,
The cantilevered piezoelectric plate whose one end is supported by a base in the container;
In order to vibrate this piezoelectric plate, one excitation electrode provided on one side of the piezoelectric plate and electrically connected to the oscillation circuit;
The other excitation electrode provided on the other surface side of the piezoelectric plate;
A movable electrode for forming a variable capacitor provided on the other end of the piezoelectric plate and electrically connected to the other excitation electrode;
It is provided so as to face the movable electrode apart from the piezoelectric plate and is connected to the oscillation circuit, and the capacitance between the movable electrode changes due to the bending of the piezoelectric plate, thereby forming a variable capacitance. A fixed electrode to
When the piezoelectric plate is excessively bent, the body of the piezoelectric plate comes into contact with the inner wall portion of the container facing the movable electrode of the piezoelectric plate, so that the tip of the piezoelectric plate comes into contact with the inner wall portion. In order not to collide, a projection is provided that projects the inner wall to the piezoelectric plate side.
The shape of the cut surface in the length direction of the surface facing the piezoelectric plate in the protrusion may be a mountain shape.

  In order to prevent the portion where the excitation electrode is provided from being bent when an external force is applied to the piezoelectric piece, the present invention is a portion on the lower surface side of the piezoelectric piece, the excitation electrode in the piezoelectric piece. A support portion that supports a portion between the movable electrode and the movable electrode may be provided on the base.

  In the present invention, when an external force is applied to the piezoelectric plate to bend or the degree of the bending is changed, the distance between the movable electrode on the piezoelectric plate side and the fixed electrode facing the movable electrode is changed. The capacitance changes, and this capacitance change and the degree of bending of the piezoelectric plate are regarded as changes in the oscillation frequency of the piezoelectric plate. Furthermore, since the risk of damaging the piezoelectric plate can be reduced by providing a protrusion for regulating the amplitude of the other end of the piezoelectric plate, more stable measurement can be performed. Even a slight deformation of the piezoelectric plate can be detected as a change in the oscillation frequency, so that the external force applied to the piezoelectric plate can be measured with high accuracy, and the apparatus configuration is simple.

It is a vertical side view which shows the principal part of 1st Embodiment which applied the external force detection apparatus which concerns on this invention as an acceleration detection apparatus. It is a top view which shows the upper surface and lower surface of the crystal oscillator used for 1st Embodiment. It is a block diagram which shows the circuit structure of an acceleration detection apparatus. It is a circuit diagram which shows the equivalent circuit of the said acceleration detection apparatus. It is a characteristic view which shows the relationship between the acceleration acquired using the said acceleration detection apparatus, and a frequency difference. It is a vertical side view which shows the modification of 1st Embodiment. It is a vertical side view which shows embodiment which applied the external force detection apparatus which concerns on this invention as an acceleration detection apparatus. It is a cross-sectional plan view along the AA line in FIG. FIG. 8 is a cross-sectional plan view along the line BB in FIG. 7. It is a top view which shows the back surface side of the quartz plate used for the said embodiment. In the said embodiment, it is a vertical side view which shows a mode that a crystal plate bends with external force, and the dimension of each part. It is an external view which shows the external appearance of a part of the acceleration detection apparatus which concerns on the said embodiment. It is a block circuit diagram which shows the circuit of the acceleration detection apparatus which concerns on the said embodiment. It is a vertical side view which shows the other modification of this invention. It is a vertical side view which shows the other modification of this invention. It is explanatory drawing which shows a mode that a crystal plate vibrates. It is a frequency characteristic figure which shows a mode that an oscillation frequency changes with the vibration of a quartz plate. It is a vertical side view which shows the principal part which concerns on 3rd Embodiment. It is a cross-sectional plan view along the CC line in FIG. It is a top view which shows the other example of 3rd Embodiment.

[First Embodiment]
An embodiment in which the present invention is applied to an acceleration detection device will be described. FIG. 1 is a view showing an acceleration sensor corresponding to an external force detection sensor which is a sensor portion of the acceleration detection device. In FIG. 1, reference numeral 1 denotes a rectangular parallelepiped sealed container made of, for example, quartz, and has an inert gas inside. For example, nitrogen gas is sealed. This container is comprised from the lower part which makes a base, and the upper part joined to this lower part by a peripheral part. The container 1 is not necessarily limited to a sealed container. A pedestal 11 made of crystal is provided in the container 1, and one end side of a crystal plate 2, which is a piezoelectric plate, is fixed to the upper surface of the pedestal 11 by a conductive adhesive 10. That is, the crystal plate 2 is cantilevered by the pedestal 11. The quartz plate 2 is formed by, for example, X-cut quartz in a strip shape, and has a thickness of, for example, an order of several tens of μm, for example, 0.03 mm. Therefore, when the acceleration is applied in the direction intersecting the crystal plate 2, the tip end portion is bent.

  The quartz plate 2 is provided with one excitation electrode 31 at the center of the upper surface as shown in FIG. 2 (a), and at the portion of the lower surface facing the excitation electrode 31 as shown in FIG. 2 (b). The other excitation electrode 41 is provided. A strip-shaped extraction electrode 32 is connected to the excitation electrode 31 on the upper surface side, and this extraction electrode 32 is folded back to the lower surface on one end side of the crystal plate 2 and is in contact with the conductive adhesive 10. A conductive path 12 made of a metal layer is provided on the upper surface of the pedestal 11, and this conductive path 12 is connected to one end of the oscillation circuit 14 on the insulating substrate 13 through the insulating substrate 13 supporting the container 1. ing.

  A strip-shaped extraction electrode 42 is connected to the excitation electrode 41 on the lower surface side, and the extraction electrode 22 is extracted to the other end side (tip side) of the crystal plate 2 and connected to the movable electrode 5 for forming the variable capacitance. ing. On the other hand, a fixed electrode 6 for forming a variable capacitance is provided on the container 1 side. On the bottom of the container 1, a protrusion 7 made of convex quartz is provided. The projection 7 is a quadrangle when seen in a plan view, and when the length direction of the crystal plate 2 is the front-rear direction, the upper surface of the cross-section viewed from the left-right direction is a curved curve. That is, the protrusion 7 is bent in an arc shape with the upper surface protruding toward the crystal plate 2 along the length direction of the crystal plate 2, and when the crystal plate 2 is excessively swollen toward the protrusion 7, Also, the base end side is configured to collide with the protruding portion 7.

  The fixed electrode 6 is provided at the protruding portion 7 so as to substantially face the movable electrode 5. When the crystal plate 2 touches excessively and the tip collides with the bottom of the container 1, the crystal plate 2 has a property of being easily broken by a crystal lump due to a phenomenon called “cleavage”. For this reason, the shape of the protrusion is determined so that the base end side (one end side) of the crystal plate 2 with respect to the movable electrode 5 collides with the protrusion 7 when the crystal plate 2 touches excessively. In FIG. 1 and the like, the image is slightly different from that of an actual device. However, when the container 1 is actually shaken greatly, a portion closer to the center than the tip of the crystal plate 2 collides with the protrusion 7.

  The fixed electrode 6 is connected to the other end of the oscillation circuit 14 through a conductive path 15 wired through the surface of the protrusion 7 and the insulating substrate 13. FIG. 3 shows a connection state of the acceleration sensor wiring, and FIG. 4 shows an equivalent circuit. L1 is a series inductance corresponding to the mass of the crystal resonator, C1 is a series capacitance, R1 is a series resistance, C0 is an effective parallel capacitance including interelectrode capacitance, and CL is a load capacitance of the oscillation circuit 14. The upper surface side excitation electrode 31 and the lower surface side excitation electrode 41 are connected to the oscillation circuit 14, and are formed between the movable electrode 5 and the fixed electrode 6 between the lower surface side excitation electrode 41 and the oscillation circuit 14. The variable capacitor Cv is interposed.

A weight may be provided at the tip of the crystal plate 2 so that the amount of bending increases when acceleration is applied. In this case, the thickness of the variable electrode 5 may be increased to serve as a weight, the weight may be provided separately from the variable electrode 5 on the lower surface side of the crystal plate 2, or the upper surface of the crystal plate 2 A weight may be provided on the side.
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 this embodiment, as shown in FIGS. 3 and 4, the load capacity of the crystal plate 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)
Accordingly, assuming that the amount of bending of the quartz plate 2 changes from the state 1 to the state 2 and thereby the variable capacitor Cv changes from Cv1 to Cv2, the frequency change ΔF is expressed by 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 acceleration is not applied to the crystal plate 2, the distance between the movable electrode 5 and the fixed electrode 6 in the reference state is d1, and the distance when the acceleration is applied to the crystal plate 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 5 and the fixed electrode 6, and (epsilon) is a dielectric constant.
Since d1 is known, it can be seen that dFL and d2 are in a correspondence relationship.

The acceleration sensor which is the sensor portion of such an embodiment is in a state where the crystal plate 2 is slightly bent even when an external force corresponding to the acceleration is not applied. Whether the crystal plate 2 is bent or maintained in a horizontal position depends on the thickness of the crystal plate 2 and the like.
As the acceleration sensor having such a configuration, for example, an acceleration sensor for detecting roll and an acceleration sensor for detecting pitch are used. The former is installed so that the quartz plate 2 is vertical, and the latter is arranged so that the quartz plate 2 is horizontal. It is installed to become.

  When an earthquake occurs or a simulated vibration is applied, the quartz plate 2 bends as shown by a chain line in FIG. 1 or as shown by a solid line in FIG. When the frequency detected by the frequency detection unit 100, which is a frequency information detection unit, is FL1, and the frequency when vibration (acceleration) is applied is FL2, the frequency difference FL1-FL2 is expressed by the following equation (3). expressed. The present inventor investigated the relationship between (FL1-FL2) / FL1 and acceleration, and obtained the relationship shown in FIG. Therefore, it is supported that the acceleration can be obtained by measuring the frequency difference.

  In FIG. 3, reference numeral 101 denotes a data processing unit made up of, for example, a personal computer. This data processing unit 101 is based on frequency information obtained from the frequency detection unit 100, for example, when no acceleration is applied to the crystal plate 2. It has a function of obtaining the difference between the frequency f0 and the frequency f1 when the acceleration is applied, and obtaining the acceleration by referring to a data table in which the frequency difference is associated with the acceleration. The frequency information is not limited to the frequency difference but may be a frequency change rate [(f1−f0) / f0] that is information corresponding to the frequency difference.

  According to the first embodiment, when an external force is applied to the crystal plate 2 to bend or when the degree of the bend changes, the crystal plate 2 is moved between the movable electrode 5 and the fixed electrode 6 facing the movable electrode 5. The distance changes and the capacitance between the electrodes 5 and 6 changes. For this reason, this capacitance change and deformation of the crystal plate 2 appear as changes in the oscillation frequency of the crystal plate 2. As a result, even a slight deformation of the crystal plate 2 can be detected as a change in the oscillation frequency, so that the external force applied to the crystal plate 2 can be measured with high accuracy, and the apparatus configuration is simple. Furthermore, the tip portion of the crystal plate 2 has a property that it is easily chipped by a crystal lump due to the phenomenon of “breaking”, but in this embodiment, the tip portion of the crystal plate 2 even when the crystal plate 2 is bent excessively. Since the projection 7 is provided so as to collide with the body part (the part on the base end side with respect to the tip part) earlier than the tip part, the tip part of the crystal plate 2 is less likely to collide with the inner wall of the apparatus container 1. The risk of breakage of the tip of the cage can be reduced. At this time, since the body portion of the crystal plate 2 collides with the curved surface portion of the protrusion 7, the crystal plate 2 is hardly damaged even in the body portion.

Further, in the modification shown in FIG. 6, a square having the same width as that of the crystal plate 2 is formed at a position closer to the base end side than the movable electrode 5 of the crystal plate 2. And the protrusion part 7 of the upper surface curved surface shape is provided so that it may respond to the bending shape when force is applied to the quartz plate 2. Thereby, the risk that the tip of the quartz plate 2 collides with the container 1 side is suppressed. The fixed electrode 6 is provided on a pedestal 61 separated from the protrusion 7. In FIG. 6, excitation electrodes and the like are omitted.
[Second Embodiment]
FIG. 7 shows another example of the acceleration sensor. This embodiment is different from the first embodiment described above in that two sets of the crystal plate 2, the excitation electrodes 31, 34, the variable electrode 5, the fixed electrode 6, and the oscillation circuit 14 are provided. Reference numeral 301 denotes a lower part constituting the base constituting the lower side of the container 1, and 302 an upper part constituting a lid forming the upper side of the container 1. Regarding the crystal plate 2 and the oscillation circuit 14, one set of parts is given a symbol “A”, and the other set of parts is given a symbol “B”. In FIG. 7, the quartz plate 2 on one side is shown, and the side view is the same as FIG. When the inside of the pressure sensor of FIG. 7 is viewed in plan, the first crystal plate 2A and the second crystal plate 2B are arranged in parallel in the horizontal direction as shown in FIG.

  Since these crystal plates 2A and 2B have the same structure, one crystal plate 2A will be described. On one side (upper surface side) of the crystal plate 2A, a lead electrode 32 having a narrow width from one end side toward the other end side. One excitation electrode 31 is formed in a square shape at the distal end portion of the extraction electrode 32. On the other surface side (lower surface side) of the crystal plate 2A, as shown in FIGS. 8 and 10, the other excitation electrode 41 is formed opposite to the one excitation electrode 31, and the crystal plate 2A in the excitation electrode 41 is formed. A lead electrode 42 having a narrow width extends toward the front end side. Further, a strip-shaped variable capacitance forming movable electrode 5 is formed on the leading end side of the lead electrode 42. These electrodes 31 and the like are formed of a conductive film such as a metal film.

  The bottom of the container 1 is provided with a convex portion 7 made of a convex-shaped crystal as in FIG. 1, but the lateral width of the convex portion 7 is a size corresponding to the arrangement of the two crystal plates 2A and 2B. Is set to That is, the protrusion 7 is set to a size including the projection areas of the two quartz plates 2A and 2B. As shown in FIGS. 8 and 9, strip-shaped fixed electrodes 6 are provided on the protrusion 7 for each of the movable electrode 5 of the crystal plate 2 </ b> A and the movable electrode 5 of the crystal plate 2 </ b> B. In FIG. 7 and the like, priority is given to the ease of understanding of the structure, so the bending shape of the crystal plate 2A (2B) is not accurately described. If 2A (2B) shakes excessively, the center side of the quartz plate 2A (2B) will collide with the protrusion 7 rather than the tip.

  With respect to the quartz plate 2A (2B) and its peripheral parts, an example of the dimensions of each part will be described with reference to FIG. The length dimension S and the width dimension of the quartz plate 2A (2B) are 20 mm and 1.6 mm, respectively. The thickness of the crystal plate 2A (2B) is, for example, 30 μm. If the support surface on one end side of the quartz plate 2A (2B) is set parallel to the horizontal plane, it will be bent due to its own weight when it is left without acceleration and its deflection d1 is about 151 μm, for example. The depth d0 of the recessed space in the lower part of 1 is, for example, 156 μm. The height of the protrusion 7 is, for example, about 105 μm. These dimensions are only an example.

  FIG. 12 shows a circuit of the acceleration detection device of this embodiment. FIG. 13 shows the appearance of a part of the acceleration detection device. The difference from the first embodiment is that the first oscillation circuit 14A and the second oscillation circuit 14B are connected to the first crystal plate 2A and the second crystal plate 2B, respectively. An oscillation loop including the oscillation circuit 14A (14B), the excitation electrodes 31, 41, the movable electrode 5, and the fixed electrode 6 is formed for each of the one crystal plate 2A and the second crystal plate 2B. The outputs from the oscillation circuits 14A and 14B are sent to the frequency information detection unit 102, where the difference in oscillation frequency from each oscillation circuit 14A and 14B or the difference in frequency change rate is detected.

The frequency change rate has the following meaning. In the oscillation circuit 14A, if the frequency in the reference state in which the crystal plate 2A is bent by its own weight is referred to as a reference frequency, when the frequency is changed by further bending the crystal plate 2A due to acceleration, the frequency change / reference frequency is expressed. For example, expressed in units of ppb. Similarly, the change rate of the frequency is calculated for the crystal plate 2B, and the difference between the change rates is output to the data processing unit 101 as information corresponding to the frequency. In the data processing unit 101, for example, data in which the difference between the change rate and the magnitude of the acceleration are associated is stored in the memory, and the acceleration can be detected based on the data and the difference between the change rates.
An example of the relationship between the amount of bending of the quartz plate 2A (2B) (the difference in height level between the tip portion when the quartz plate is in a straight line and the bending state) and the amount of change in frequency is given. For example, when the tip of the crystal plate 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. Therefore, even extremely small external forces such as acceleration can be detected accurately.

According to the second embodiment described above, in addition to the effects of the first embodiment, the crystal plate 2A and the crystal plate 2B are arranged in the same temperature environment, so that each of the crystal plate 2A and the crystal plate 2 is provided. Even if the frequency changes due to temperature, this change is canceled, and as a result, only the change in frequency based on the bending of the quartz plates 2A and 2B can be detected, so that the detection accuracy is high.
Further, when the quartz plates 2A and 2B vibrate excessively, the center of the quartz plates 2A and 2B collides with the protruding portion 7 and the other end does not collide with the inner wall of the apparatus container. Protrusions 7 having the same surface shape as the bending shapes of the quartz plates 2A and 2B are provided. Thereby, since the damage risk of quartz plate 2A, 2B can be reduced, a more stable measurement can be performed.
[Modifications and Application Examples of the Present Invention]
14 and 15 show further modifications of the present invention.
In the acceleration sensor shown in FIG. 14, excitation electrodes 31 and 41 of the crystal plate 2 are formed on the tip side of the crystal plate 2, and the excitation electrode 41 on the lower surface side also serves as the movable electrode 5.

  The acceleration sensor shown in FIG. 15 employs a structure in which the upper surface and the lower surface of the crystal plate 2A (2B) used in the second embodiment are reversed as a crystal resonator including the crystal plate 2. In this case, the quartz plate 2 is interposed between the movable electrode 5 and the fixed electrode 6, but the same operation and effect can be obtained in this structure.

  The acceleration sensor shown in FIG. 15 is a container in which the movable electrode 5 on the lower surface side turns around the upper surface side and faces the movable electrode 6 in the crystal plate 2A (2B) used in the second embodiment. The fixed electrode 6 is provided on the inner wall upper surface side of the internal space 1. In this case, the same action and effect can be obtained.

[Third Embodiment]
This embodiment is a support part provided in the lower part of the container 1 corresponding to a base between a part having a role as a crystal resonator and a part in which bending is generated by an external force in the crystal piece 2. It is an example supported by a supporting member. That is, the support part by the support part in the crystal piece 2 is between the part where the excitation electrodes 31 and 41 are provided and the part where the movable electrode 5 is provided. In order to increase the degree of bending of the crystal piece 2 when an external force is applied to the crystal piece 2, that is, to obtain high sensitivity, the distance from the support portion to the tip of the crystal piece 2 is increased. It is preferable to ensure.

  Such an example is shown in FIGS. In this example, a square support portion 8 is provided at the bottom of the container, and the upper surface of the support portion 8 is, for example, 0.1 mm to several mm away from the excitation electrode 41 on the lower surface of the crystal piece 2. Supports the part that is close to. The lateral width of the support portion 8 is preferably the same as or larger than the width dimension of the crystal piece 2, but when the function that can sufficiently prevent the bending of the portion where the excitation electrodes 31 and 41 are disposed can be exhibited. May be smaller than the width dimension of the crystal piece 2. The height dimension of the support portion 8 is set to a dimension that contacts the lower surface of the crystal piece 2 in a state where the crystal piece 2 extends horizontally from the upper surface of the pedestal 11, for example.

  In FIG. 18, since the structure inside the container is exaggerated, the image is slightly different from the structure of an example of an actual external force sensor. As an example of the dimensions of the support portion 8, the height is, for example, 0.5 mm to 1 mm, the thickness is 0.3 mm, and the lateral width is 1.6 mm, which is the same as the width of the crystal piece 2. This dimension is an example, and is determined according to the structure of the container 1 and the installation position of the crystal piece 2.

  The support 8 and the lower surface of the crystal piece 2 (the surface on the side facing the fixed electrode 6) are fixed to each other by a fixing material such as a conductive adhesive or low dielectric glass. The support 8 and the lower surface of the crystal piece 2 may be not fixed to each other.

  As a method of providing the support portion 8, for example, a method of forming by etching when the lower portion 301 of the container 1 is manufactured, the support portion 8 is manufactured separately from the lower portion 301, and an adhesive is used. You may make it adhere | attach.

  The structure using the support portion 8 may be applied to the second embodiment, which is an example in which two sets of crystal resonators are provided and the difference between the oscillation frequencies of these crystal resonators is obtained. In this case, the portion between the excitation electrodes 31 and 41 and the variable electrode 5 is supported by the support portion 8 as shown in FIGS. 18 and 20 for each pair of crystal pieces 2A and 2B (see, for example, FIG. 9). It becomes the structure to do. The support part 8 may be provided independently for each of the crystal pieces 2A and 2B, or the crystal pieces 2A and 2B are provided by a common support part 8 extending from the left edge of the crystal piece 2A to the right edge of the crystal piece 2B. May be supported. FIG. 20 shows a configuration using the support portion 8 for an example using two sets of crystal resonators.

  Here, in the structure shown in FIG. 18, a sample in which the excitation electrode 41 is directly connected to the oscillation circuit is prepared, and the oscillation frequency f0 when placed on a horizontal surface is low, and the tip side of the crystal piece 2 is low by 10 degrees from the horizontal plane. The oscillation frequency f10 when placed on the inclined surface was measured a plurality of times. The value of (f0−f10) / f0, which is the frequency change rate, was 0.1 ppb to 5 ppb.

On the other hand, when the same test was performed on the sample in which the support portion 8 was not provided in the sample, the value of (f0−f10) / f0 as the frequency change rate was 8 ppb to 45 ppb. From this result, when the crystal piece 2 is bent by an external force, the change in frequency due to the bending of the vibration part (the part where the excitation electrodes 31 and 41 are provided) of the crystal piece 2 in the change in the oscillation frequency. It can be seen that the structure in which the support portion 8 is provided is smaller with respect to the proportion of the minute. This result can be said to be a result based on the fact that the vibration portion hardly bends due to the presence of the support portion 8 even if the tip end side of the support portion 8 in the crystal piece 2 is bent.
Since the change in the frequency of the vibration site lacks reproducibility, the frequency change corresponding to the bending of the crystal piece 2 can be obtained more accurately by adopting the structure in which the support portion 8 is provided as described above.

In the above, the present invention is not limited to measuring 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 for measuring magnetic force will be described. A magnetic film is formed in a portion of the quartz plate 2 between the movable electrode 5 and the excitation electrode 41, and the quartz plate 2 is configured to bend when the magnetic body is positioned in a magnetic field.
Furthermore, the quartz plate 2 is exposed to a fluid such as gas or liquid, and the flow velocity can be detected via the frequency information according to the amount of deflection of the quartz plate. In this case, the thickness of the quartz plate 2 is determined by 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. This will be described here. Since the structure of the vibration detection device in this embodiment is the same as that of the external force detection device in the second embodiment, the description thereof is omitted. When an earthquake occurs and vibration is applied to the vibration detection device, the crystal plate 2 is shaken, for example, the first state shown in FIG. 16A and the second state shown in FIG. 16B are repeated. . When the values of the variable capacitors Cv in the first state and the second state are Cv3 and Cv4, respectively, the respective oscillation frequencies FL3 and FL4 are obtained from the above equations (1) and (2), and the oscillation frequencies are FL3 and It changes with time between FL4 as shown in FIG. Therefore, by analyzing the frequency data detected by the frequency information detection unit 102 by the data processing unit 101, the period T (corresponding to the frequency) of the frequency change wave shown in FIG. 17 can be obtained.

  When the vibration detection device vibrates due to the seismic wave, acceleration is applied to the quartz plate 2 in one direction and in the opposite direction, so that, for example, the frequency data shown in FIG. Even personality can be detected.

  In the above, the present invention can be applied not only to the vibration of an earthquake but also to the case of detecting a period of vibration generated in a simulated manner. Further, for example, the present invention may be applied to a case where the period of vibration generated in the washing machine main body due to a rotating water flow including laundry when the washing machine is operated is detected.

DESCRIPTION OF SYMBOLS 1 Container 11 Base 12 Conductive path 2 Crystal plate 31, 41 Excitation electrode 14 Oscillation circuit 5 Movable electrode 6 Fixed electrode 7 Protrusion part 100 Frequency detection part 101 Data processing part 102 Frequency information detection part

Claims (7)

An external force detection device for detecting an external force acting on a piezoelectric plate,
The cantilevered piezoelectric plate whose one end is supported by a base in the container;
In order to vibrate this piezoelectric plate, one excitation electrode and the other excitation electrode respectively provided on one surface side and the other surface side of the piezoelectric plate;
An oscillation circuit electrically connected to one excitation electrode;
A movable electrode for forming a variable capacitor provided on the other end of the piezoelectric plate and electrically connected to the other excitation electrode;
It is provided so as to face the movable electrode apart from the piezoelectric plate and is connected to the oscillation circuit, and the capacitance between the movable electrode changes due to the bending of the piezoelectric plate, thereby forming a variable capacitance. A fixed electrode to
A frequency information detection unit for detecting a signal that is frequency information corresponding to the oscillation frequency of the oscillation circuit;
When the piezoelectric plate is excessively bent, the body of the piezoelectric plate comes into contact with the inner wall portion of the container facing the movable electrode of the piezoelectric plate, so that the tip of the piezoelectric plate comes into contact with the inner wall portion. In order not to collide, provided with a protrusion that protrudes the inner wall to the piezoelectric plate side,
An oscillation loop that returns from the oscillation circuit to the oscillation circuit through one excitation electrode, the other excitation electrode, the movable electrode, and the fixed electrode is formed,
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 a shape of a cut surface in a length direction of a surface of the protruding portion facing the piezoelectric plate is a mountain shape. As a set comprising the piezoelectric plate, excitation electrode, movable electrode and fixed electrode, a first set and a second set are provided,
An oscillation circuit is provided corresponding to each of the first group and the second group,
The frequency information detection unit obtains a signal according to a difference between an oscillation frequency corresponding to the first set and an oscillation frequency corresponding to the second set. External force detection device.   A support portion for supporting a portion between the excitation electrode and the movable electrode on the lower surface side of the piezoelectric piece in order to prevent the portion where the excitation electrode is provided from being bent when an external force is applied to the piezoelectric piece. The external force detection device according to claim 1, wherein the external force detection device is provided on the base.   The external force detection device according to claim 4, wherein the tip of the support portion and the piezoelectric piece are fixed to each other. An external force detection sensor for detecting an external force acting on a piezoelectric plate based on an oscillation frequency of the piezoelectric plate,
The cantilevered piezoelectric plate whose one end is supported by a base in the container;
In order to vibrate this piezoelectric plate, one excitation electrode provided on one side of the piezoelectric plate and electrically connected to the oscillation circuit;
The other excitation electrode provided on the other surface side of the piezoelectric plate;
A movable electrode for forming a variable capacitor provided on the other end of the piezoelectric plate and electrically connected to the other excitation electrode;
It is provided so as to face the movable electrode apart from the piezoelectric plate and is connected to the oscillation circuit, and the capacitance between the movable electrode changes due to the bending of the piezoelectric plate, thereby forming a variable capacitance. A fixed electrode to
When the piezoelectric plate is excessively bent, the body of the piezoelectric plate comes into contact with the inner wall portion of the container facing the movable electrode of the piezoelectric plate, so that the tip of the piezoelectric plate comes into contact with the inner wall portion. An external force detection sensor, comprising: a protrusion that protrudes the inner wall toward the piezoelectric plate so as not to collide.   The external force detection sensor according to claim 6, wherein a shape of a cut surface in a length direction of a surface of the protrusion facing the piezoelectric plate is a mountain shape.

Images