JP2015166679A - External force detection apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately and easily detect an external force applied to a piezoelectric piece and to suppress influences of electrostatic charge charged in the piezoelectric piece.SOLUTION: A crystal piece 2 being a piezoelectric piece is cantilevered in the inside of a container 1. A tip end part of the underside of the crystal piece 2 is provided with a movable electrode 21, and a fixed electrode 22 is provided at a position facing the movable electrode 21. The movable electrode 21 and the fixed electrode 22 are connected to an oscillation circuit 41, and detects as a change in a frequency, a change in capacitance between the movable electrode 21 and the fixed electrode 22 due to warp caused by external force given to the crystal piece 2. Each of the container 1 and the crystal piece 2 is composed of a crystal having a volume resistivity lower than that of an ordinary crystal, and the movement of the electric charge is made easy. The container 1 is connected to the earth, and discharges an electrostatic charge accumulated in the crystal piece 2 by the influences of an electrostatic field and the like to the outside of a detector.

Description

  The present invention uses a quartz piece 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 quartz piece based on the oscillation frequency. Relates to the device.

  The external force acting on the system includes force acting on an object based on acceleration, pressure, flow velocity, magnetic force, electrostatic force, etc., and there is a demand for accurately measuring these external forces. For example, at the stage of developing a car, the impact force at the seat is measured when the car collides with an object, and in the event of an earthquake, the acceleration of the shake is as precise as possible to investigate vibration energy and amplitude. It is necessary to measure.

  In view of this, the present inventor is examining an external force detection device that measures an external force with high accuracy by using a change in capacitance based on the bending when an external force is applied to the crystal piece. Specifically, when the quartz crystal piece is cantilevered in the container, the amount of bending of the quartz crystal piece is determined by changing the capacitance between the tip side electrode and the container side electrode of the quartz crystal piece. This is a device that measures this frequency change. According to the apparatus, it is possible to measure a change in frequency with high accuracy.

  However, in the development process, for example, in an environment where static electricity is likely to occur, such as during winter drying, the crystal piece may be attracted and stuck to the electrostatic force generated in the container. In particular, in an external force detection device using a crystal piece, when both the container and the crystal piece are mirror-finished, they often do not separate even if the charge is removed later. Furthermore, even when the crystal piece is not attached to the container, a measurement error occurs due to the crystal piece being bent by the electrostatic force. The present inventor has also studied a type in which a crystal piece is supported by both ends as an external force detection device using the above-described principle. In this case, the crystal piece may be bent by an electrostatic force.

  In Patent Document 1, an external force that discharges unnecessary charges on a crystal piece via the static elimination path by connecting the static elimination path to the crystal piece and interlocking the switch of the main body of the external force detection device with the switch of the static elimination path. A detection device is disclosed. However, the principle is completely different from the present invention.

JP2013-124928A

  The present invention has been made under such a background, and an object of the present invention is to utilize the fact that a crystal piece supported in a container is deformed by an external force, and to detect the deformation as a change in a frequency signal and to detect the external force. An external force detection device for detecting the external force detection device that can eliminate the adverse effects of static electricity.

The external force detection device of the present invention is
An external force detection device that detects the external force by detecting the deformation as a change in the frequency signal, utilizing the fact that the crystal piece supported in the container is deformed by an external force,
At least one of the crystal piece and the container is made of an impurity-containing crystal having a volume resistivity of 10 ⁹ to 10 ¹³ Ωcm.

  The present invention utilizes the fact that a crystal piece supported in a container is deformed by an external force, and detects an external force by detecting the deformation as a change in a frequency signal, and at least one of the crystal piece and the container. As a crystal containing impurities, the conductivity is moderately high, so that adverse effects due to static electricity can be eliminated while suppressing a decrease in oscillation loss.

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 block diagram which shows the circuit structure of the said acceleration detection apparatus. It is an equivalent circuit diagram of the acceleration detection device. It is the schematic which showed a mode that the crystal piece of the said acceleration detection apparatus bent. It is a vertical side view which shows the principal part of the acceleration detection apparatus which concerns on 2nd Embodiment. It is a vertical side view which shows the principal part of the acceleration detection apparatus which concerns on 3rd Embodiment. It is the perspective view and transverse cross section of the tuning fork type gyro sensor which concern on 4th Embodiment. It is the table | surface which showed the experimental result performed about the external force detection apparatus which concerns on embodiment of this invention.

[First Embodiment]
A first embodiment in which an external force detection device of the present invention is applied to an acceleration detection device will be described with reference to FIGS. 1 and 2. In FIG. 1, reference numeral 1 denotes a rectangular parallelepiped sealed insulating material, for example, a container made of quartz, and an inert gas such as nitrogen gas is enclosed therein. The container 1 is provided on the wiring board 9 in a state where the terminal lands 13 are arranged at the four corners outside the bottom. The container 1 includes a main body portion 12 having a support portion 18 that supports the crystal piece 2, and a lid body 11 joined to the main body portion 12 at a peripheral edge portion.

  One end of the crystal piece 2 is cantilevered by the conductive adhesive 23 on the support portion 18 inside the container 1. A movable electrode 21 is formed on the lower surface side of the other end of the crystal piece 2, and an extraction electrode 24 extends around the other end portion of the crystal piece 2 from the movable electrode 21 and is extracted to the upper surface side of the crystal piece 2. It is extended to the adhesion site by the conductive adhesive 23. The conductive path 16 passes through the inside of the support portion 18 and one of the terminal lands 13 from the portion bonded by the conductive adhesive 23, and the oscillation portion including the crystal oscillator 3 and the oscillation circuit 41 through the wiring substrate 9. 5 is extended to the input end.

A fixed electrode 22 is provided at a portion facing the movable electrode 21 inside the container 1. From the fixed electrode 22, the conductive path 15 passes through another one of the main body 12 and the terminal land 13 and extends to the input end of the oscillating unit 5 through the wiring substrate 9. The subsequent stage of the oscillating unit 5 is connected to the frequency measuring unit 101, and the subsequent stage of the frequency measuring unit 101 is connected to the data processing unit 102.
One further end of the conductive path 17 for grounding the container 1 is connected to another one of the terminal lands 13 and the other end is connected to the ground.

  When an AT-cut crystal piece is used as the crystal piece 2, for example, the length dimension in the X-axis direction is 20 mm, the length dimension (width dimension) in the Z-axis direction is 2 mm, and the thickness is 0.021 mm. The frequency is, for example, 1 MHz or more, and an example is 78 MHz. These dimensions and the like are appropriately selected depending on the desired sensitivity.

Natural quartz and artificial quartz have a volume resistivity of 10 ¹⁹ Ωcm, but the quartz constituting the container 1 and the quartz piece 2 in this example has a reduced volume resistivity compared to the quartz used in a normal external force detection device. Having a composition. In the present embodiment, the container 1 and the crystal piece 2 have a preferable volume resistivity in the range of 10 ⁹ to 10 ¹³ Ωcm. If the volume resistivity is 10 ⁹ or less, the elastic properties of the crystal piece 2 may be impaired, and if the volume resistivity is 10 ¹³ or more, the container 1 and the crystal piece 2 may be pyroelectric. Because there is.

Further, considering the viewpoint of preferably reducing the oscillation loss of the high-frequency current and the viewpoint of moving the electrostatic charge to the ground in a short time (for example, within 0.1 seconds, preferably within 1 millisecond), the container 1 The volume resistivity of the crystal piece 2 is more preferably in the range of 10 ¹¹ to 10 ¹³ Ωcm.

  Thus, a crystal having a low volume resistivity can be obtained by adding a conductive material as an impurity. As a specific manufacturing method, for example, there is a method in which a metal such as iron is added to a molten crystal solution in an autoclave to grow an artificial crystal containing the metal. Moreover, you may dope metal ions etc. with respect to a crystal piece with an ion implantation apparatus. In these cases, a substance that generates free electrons or holes in the quartz is selected as the substance to be taken into the quartz. Further, a reduction treatment may be performed on the quartz wafer to remove oxygen atoms.

  FIG. 3 shows an equivalent circuit diagram of the acceleration detection device. 2 and 3, Cv is a variable capacitance formed between the movable electrode 21 and the fixed electrode 22, C0 is an effective parallel capacitance including the capacitance between electrodes, C1 is a series capacitance, and L1 is a crystal resonator 3. , R1 is a series resistance, and CL is a load capacity of the oscillation circuit 41.

Here, according to the international standard IEC 60122-1, the general formula of the crystal oscillation circuit is expressed by 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 FIG. 3, the load capacity of the crystal piece 2 is obtained by adding Cv to CL. Therefore, y represented by equation (2) is substituted as an alternative to CL in equation (1).
y = 1 / (1 / Cv + 1 / CL) (2)

Therefore, if the bending amount 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 following equation (3). The
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 piece 2, the distance between the movable electrode 21 and the fixed electrode 22 in the reference state is d 1, and the distance when the acceleration is applied to the crystal piece 2. Is d2, the following equation (4) is established.
Cv1 = S × ε / d1
Cv2 = S × ε / d2 (4)
Here, S is the area of the opposing region of the movable electrode 21 and the fixed electrode 22, and ε is the relative dielectric constant.
Since d1 is known, it can be seen that dFL and d2 are in a correspondence relationship.

Next, the operation of the above embodiment will be described.
In the acceleration detection device, when an earthquake occurs or a simulated vibration is applied, the crystal piece 2 bends as shown by a dotted line in FIG. As described above, when the capacitance between the movable electrode 21 and the fixed electrode 22 in the reference state where no external force is applied to the crystal piece 2 is Cv1, the external force is applied to the crystal piece 2 and the crystal piece 2 Since the distance between the electrodes 21 and 22 changes in a state where the electrode is bent, the capacitance changes from Cv1. For this reason, the oscillation frequency output from the oscillation circuit 41 changes.

  When the frequency detected by the frequency measuring unit 101, which is the frequency information detection unit, is FL1, and the frequency when vibration (acceleration) is applied is FL2, the frequency difference FL1-FL2 is the above-described (3). It is expressed by a formula. The present inventor calculates the frequency change rate when the state is changed from the state 1 to the state 2 from the frequency difference FL1-FL2, and examines the relationship between the frequency change rate {(FL1-FL2) / FL1} and the acceleration. To obtain a linear relationship. Therefore, it is possible to determine the acceleration by measuring the frequency difference. Here, the value of FL1 is a frequency value at a certain temperature, for example, 25 ° C. is defined as the reference temperature.

  Further, in the acceleration detecting device of the present embodiment, when a quartz crystal having a normal volume resistivity is used as the container 1 and the crystal piece 2, the container 1 or the An electrostatic charge is accumulated on the crystal piece 2. If measurement is performed in a state where static charge is accumulated, it causes a measurement result error. In particular, when the amount of electric charge accumulated in the container 1 or the crystal piece 2 is particularly large, the crystal piece 2 and the main body 12 come into contact with each other to cause a short circuit, or conversely, the crystal piece 2 is the lid 11 of the container 1. As a result, the measurement cannot be performed.

  Therefore, by using the crystal having a reduced volume resistivity as the material of the container 1 and the crystal piece 2 as described above, the electrostatic charge that affects the measurement to the container 1 and the crystal piece 2 is outside the external force detection device. Sufficient conductivity can be provided for release. Since the container 1 is grounded via the conductive path 17, even when an electrostatic field is generated around the external force detection device and the electrostatic charge is accumulated inside the external force detection device, the electrostatic charge is released to the outside. By doing so, it becomes possible to stably detect the magnitude of the external force based on the acceleration or the like.

Here, the acceleration detection device described above is manufactured by a manufacturer, shipped to the user, and arranged at a place where acceleration is measured. As described above, the volume resistance of the container 1 and the crystal piece 2 is larger than that of a normal crystal. Since the crystal containing impurities with a low rate is used, the accumulation of static charge can be suppressed even in the winter dry season. Therefore, for example, even if some impact is applied to the apparatus and the crystal piece 2 is shaken, there is no possibility that the crystal piece 2 sticks to the inner wall of the container 1. Further, there is no concern that the crystal piece 2 is bent by an electrostatic force during measurement of acceleration. Further, a high-frequency current flows from the oscillating unit 5 through the movable electrode 21 and the fixed electrode 22. However, although the container 1 and the crystal piece 2 are electrically conductive, the high-frequency current is moderately maintained. Loss is suppressed.
As described above, according to the above-described embodiment, when detecting the bending of the crystal piece as a change in the frequency signal and detecting the acceleration, it is possible to eliminate an adverse effect due to static electricity while suppressing a decrease in oscillation loss. is there.

In the above-described embodiment, the crystal having a reduced volume resistivity is used for both the container 1 and the crystal piece 2. However, in the present invention, at least one of the container 1 and the crystal piece 2 is a volume resistivity. What is necessary is just to comprise with the crystal | crystallization which lowered | hung.
Further, the fact that the container 1 is made of a crystal having a reduced volume resistivity is not limited to the case where the container 1 is entirely made of a crystal having a reduced volume resistivity, but an electrostatic force is applied to the crystal piece 2. If the part which exerts is made of quartz having a reduced volume resistivity, it corresponds to the present invention.

[Second Embodiment]
The acceleration detection apparatus according to the second embodiment will be described with a focus on differences from the first embodiment with reference to FIG. About the same site | part as 1st Embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.
In the present embodiment, an excitation electrode 31 is provided at the center on the upper surface side of the crystal piece 2, and the extraction electrode 33 extends from the excitation electrode 31 to a bonding portion with the support portion 18 by the conductive adhesive 23. . On the other hand, an excitation electrode 32 is provided at a position facing the excitation electrode 31 on the lower surface side of the crystal piece 2, and the excitation electrode 32 is electrically connected by the movable electrode 21 and the extraction electrode 34.

  The conductive path 16 is extended from the part bonded by the conductive adhesive 23 as in the first embodiment, and is connected to the oscillation circuit 41 on the substrate 9. On the other hand, the conductive path 15 extends from the fixed electrode 22 as in the first embodiment, and is connected to the oscillation circuit 41 on the substrate. Further, the container 1 is grounded via the conductive path 17. In the present embodiment, the crystal resonator 3 in the first embodiment is provided on a crystal piece 2.

[Third Embodiment]
The main part of the acceleration detection apparatus according to the third embodiment will be described with a focus on differences from the second embodiment with reference to FIG. About the same site | part as 1st Embodiment, the same code | symbol is attached | subjected and description is abbreviate | omitted.
The difference between the acceleration detecting device of the third embodiment and the first embodiment is that the crystal piece 2 is supported in both ends by the conductive adhesives 23a and 23b in the support portions 18a and 18b, respectively. It is a point. The movable electrode 21 is provided at the center of the upper surface of the crystal piece 2, and the fixed electrode 22 is provided at a portion facing the movable electrode 21 inside the container 1.

  Also in this embodiment, acceleration is applied to the apparatus, and the distance between the movable electrode 21 and the fixed electrode 22 changes. Therefore, the capacitance between the movable electrode 21 and the fixed electrode 22 changes, and the change in the pressure applied to the device can be detected by measuring the change in the oscillation frequency output from the oscillation circuit of the device.

Further, in each of the embodiments described above, the change in pressure is detected as a change in the oscillation frequency of the device. However, the present invention is not limited to this, and includes a case where the period of vibration with respect to the acceleration detection device is detected. It is. In this case, the crystal piece 2 vibrates due to the vibration with respect to the acceleration detection device, and the oscillation frequency output from the acceleration detection device periodically changes due to the vibration of the crystal piece 2. By detecting this period, the period of vibration applied to the acceleration detection device is detected.
Further, although the crystal resonator is used as the oscillation element, the present invention is not limited to this, and a resonance circuit including an inductor and a capacitor may be used.

[Fourth Embodiment]
FIG. 7 shows an example in which the low resistance crystal of the present invention is applied to the tuning fork type gyro sensor 6. In FIG. 7, the tuning fork type gyro sensor 6 has a main body made of the above-described low-resistance crystal, and includes a main body 62 and rectangular parallelepiped vibrating arms 61 a and 61 b extending from the main body 62. Each of the vibrating arms 61a and 61b has a piezoelectric element 63 that senses the vibration of the vibrating arms 61a and 61b, and includes electrodes 65a and 65b on a surface facing the piezoelectric element 63, and the electrodes 65a and 65b are grounded. Has been. Further, in each of the vibrating arms 61a and 61b, a set of excitation electrodes 64a and a set of 64b are provided on a plane orthogonal to the plane having the piezoelectric element 63 and the electrodes 65a and 65b.

  The piezoelectric element 63 is connected to a vibration detector (not shown), and the vibration detector is connected to a detection device. The excitation electrodes 64a and 64b are connected to an oscillation circuit (not shown) and are configured to have opposite attributes.

  The operation of the tuning fork type gyro sensor 6 will be briefly described. A reverse polarity voltage is alternately applied from the oscillation circuit to the excitation electrodes 64a and 64b, and the vibrating arms 61a and 61b bend and vibrate in the X-axis direction of FIG. 6 (the direction in which the excitation electrodes 64a and 64b face each other). When rotation is applied to the vibrating arms 61a and 61b in the Y-axis direction, Coriolis force acts in a direction orthogonal to the bending vibration, and the vibrating arms 61a and 61b are in directions opposite to each other in the Z-axis direction. Vibrate. The vibration is detected by the piezoelectric element 63, and a detection signal from the piezoelectric element 63 is transmitted to the detection device via the vibration detector. By processing this detection signal, the angular velocity of rotation with respect to the tuning fork type gyro sensor 6 can be obtained.

  Also in this embodiment, by using a crystal having a low resistance as the main body of the gyro sensor 6, the electrostatic charge accumulated in the main body of the gyro sensor 6 can be discharged to the outside of the gyro sensor 6 by an electrostatic field, and the angular velocity The measurement can be performed precisely.

  In the embodiment described above, the crystal having reduced resistance is used as the material of the container 1, the crystal piece 2, and the gyro sensor 6, but it is within the above-mentioned volume resistivity range by containing impurities. As long as the volume resistivity can be adjusted as described above, these materials are not limited to quartz. Examples include ceramics, glass, silicon and the like.

  An experiment was performed on four types of external force detection devices having the same structure as that of the first embodiment. First, an external force detection device comprising four types of containers having different volume resistivity and a crystal piece was prepared. Here, the four types of external force detection devices are connected to an oscillation circuit containing a crystal resonator having the same characteristics. Further, the characteristics of the crystal pieces are the same, the areas of the movable electrode and the fixed electrode are constant, and the initial value of the capacitance Cv is also the same.

For the four types of external force detection devices, the volume resistivity of the container is as follows.
A: 1 × 10 ¹⁰ Ωcm
B: 1 × 10 ¹¹ Ωcm
C: 1 × 10 ¹³ Ωcm
D: 1 × 10 ¹⁵ Ωcm
In addition, the nominal frequency Fn of the crystal resonator incorporated in the oscillation circuit is 30 MHz, and the resonance frequency Fs is 29.981743 MHz.
With respect to these external force detection devices, the oscillation frequency FL1 was first measured after neutralizing with a static eliminator, and then the oscillation frequency FL2 was measured again after generating a charge using a leather cloth. For the frequency measurement method, the π circuit method defined in IEC 60444-1 was used.

The experimental results are shown in FIG. In the π circuit method, an error of 1 ppm or less with respect to the nominal frequency cannot be guaranteed, so the difference FL1-FL2 of the measured values of the external force detection devices A, B, and C can be said to be within the error. On the other hand, regarding the external force detection device D, since FL2 is the same as the resonance frequency Fs of the crystal resonator, it is considered that a short circuit has occurred inside. Therefore, it was shown that by reducing the volume resistivity of the container to 1 × 10 ¹³ or less for the external force detection device, accumulation of electrostatic charges inside the external force detection device is suppressed, and measurement can be performed with high accuracy.

DESCRIPTION OF SYMBOLS 1 Container 2 Crystal piece 21 Movable electrode 22 Fixed electrode 3 Crystal oscillator 41 Oscillation circuit 5 Crystal oscillation circuit 9 Wiring board

Claims (7)

In the external force detection device that detects the external force by detecting the deformation as a change in the frequency signal using the fact that the crystal piece supported in the container is deformed by the external force,
At least one of the crystal piece and the container is constituted by an impurity-containing crystal having a volume resistivity of 10 ⁹ to 10 ¹³ Ωcm. The external force detection device according to claim 1, wherein the volume resistivity of the crystal with impurities is 10 ¹¹ to 10 ¹³ Ωcm.   The external force detection device according to claim 1, wherein the crystal containing impurities is used for the crystal piece.   The external force detection device according to any one of claims 1 to 3, wherein the impurity of the crystal containing impurities is a metal. A first electrode is provided on one side of the crystal piece;
A second electrode which is provided on the container side so as to face the first electrode, and a capacitance between the first electrode is changed by bending of the crystal piece, thereby forming a variable capacitance;
An oscillation circuit including an oscillation element connected to the variable capacitor, and
The external force detection device according to claim 1, wherein an external force is detected by a change in an oscillation frequency of an oscillation circuit based on the change in the variable capacitance. The crystal piece is supported by the container in a cantilevered one end side,
The external force detection device according to claim 5, wherein the first electrode is provided on the other end side of the crystal piece.   5. The external force detection device according to claim 1, wherein the crystal piece is a tuning-fork type crystal piece used for a gyro sensor as an external force detection device.

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