JP2005331362A - Vacuum gauge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To realize a vacuum gage robust against disturbance and capable of detecting precisely a degree of vacuum. <P>SOLUTION: A vibration body 1, a beam 2 and a housing 3 cut out of one sheet are fixed onto a base panel 6 via a spacer 5. The vibration body 1 has an asymmetric outer shape with respect to a Y-axis passing through the gravity center 4, and generates inertia rotation vibration around the beam 2 of an elastic body, in accompaniment to translational vibration of the vibration body 1, when exciting force is applied in the gravity center position of the vibration body 1 by an excitation electrode 7 on the base panel 6. A speed increase in an amplitude (rotation angle) of the inertia rotation vibration is detected since the inertia rotation vibration is increased by force received from an atmosphere, and a detected value is compared with a reference data to find atmospheric pressure. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a vacuum gauge that measures atmospheric pressure in a decompression chamber, a vacuum chamber, and the like, and more particularly, to a vacuum gauge that is suitable for measuring the degree of vacuum in a high and medium vacuum region with high accuracy.

  As disclosed in Patent Document 1, a conventional vacuum gauge includes a structure in which a vibrating body and a support are integrally formed by etching and a control circuit.

  For example, as shown in FIG. 12, a structure having a torsion bar 101 and a vibrating body 102 formed by hollowing out a single plate 103, an excitation electrode 105 and a circuit 108, a detection electrode 106 and a circuit 109 And the substrate 104 that supports the control circuit 110, and the vibrating body 102 elastically supported by the torsion bar 101 is vibrated, and the frequency at which the vibration amplitude at that time is maximized, that is, the resonance frequency is measured. Devices for measuring degrees have been developed.

In this way, when the vibrating body is vibrated in a vacuum, the resonance frequency changes depending on the degree of vacuum, or the viscosity of the atmosphere changes depending on the degree of vacuum in the molecular flow region of medium vacuum or higher. It is known that the force received from the air changes according to the degree of vacuum.
Japanese Patent No. 2518814

  The above conventional apparatus has the following unsolved problems.

  (1) The sensitivity on the high vacuum side is poor.

  As the degree of vacuum in the atmosphere increases, the number of molecules involved decreases, so the force that the vibrating body receives becomes extremely small. As a result, the change in the resonance frequency of the vibrating body is also reduced. In the conventional method, since the change of the resonance frequency is measured, the sensitivity is poor.

  And since the sensitivity on the high vacuum side is low, a vacuum gauge with a wide pressure measurement range cannot be realized.

  (2) Sensitive to errors in excitation force.

  The electrical noise of the control circuit that supplies voltage to the excitation electrode changes the vibration amplitude of the vibrating body. The conventional method for searching for the maximum value of the vibration amplitude is directly affected by the amplitude fluctuation of the vibrating body due to this electrical noise. Therefore, the measurement result of the degree of vacuum is also directly affected by the error of the excitation force.

  (3) Weak against disturbance vibration.

  When disturbance vibration is applied, the vibrating body vibrates. This vibration affects the measurement result of the degree of vacuum as well as the error of the excitation force due to electrical noise. Particularly in the vacuum chamber, there are many opportunities to arrange mechanical devices such as vacuum pumps that are likely to be vibration sources in the vicinity, and disturbance vibrations in places where vacuum gauges are used cannot be ignored.

  The present invention has been made in view of the above-mentioned unsolved problems of the prior art, and is a vacuum gauge that has high sensitivity even in a high vacuum, and can stably measure even if there is an error in excitation force or disturbance vibration. Is intended to provide.

  In order to achieve the above object, a vacuum gauge according to the present invention includes a vibrating body having an asymmetric shape with respect to a first axis passing through the center of gravity, and an elastic body that horizontally supports the vibrating body along the first axis. A housing having a vibration means for generating a translational vibration in the vibrating body along a second axis perpendicular to the first axis by a driving force acting on the center of gravity, and the vibration generated in association with the translational vibration. Detecting means for detecting inertial rotational vibration around the first axis of the body, and determining an ambient pressure around the vibrating body based on an output of the detecting means.

  Inertial rotational vibration generated along with the translational vibration of the vibrating body by the vibrating means is increased by the force received from the atmosphere around the vibrating body. Although the force received from the vacuum or the reduced-pressure atmosphere is small, since the force is repeatedly received by the translational vibration of the vibrating body, the inertial rotation vibration is reliably amplified and can be detected even in a high vacuum. Further, since the disturbance only temporarily acts on the center of gravity of the vibrating body via the housing and the elastic body, it does not affect the inertial rotational vibration of the vibrating body.

  The detecting means measures the time from when the vibrating body starts inertial rotation vibration until it reaches a predetermined amplitude (rotation angle), or the maximum amplitude when vibration is applied until the predetermined time elapses. It is configured to detect the speed at which the amplitude increases.

  In this way, by averaging the errors included in the excitation force of the detection means and reducing the influence thereof, a highly sensitive vacuum gauge with less noise can be realized.

  Further, by configuring the resonance frequency of the translational vibration of the vibrating body by the vibration means to be equal to the resonance frequency of the inertial rotation vibration, the inertial rotation vibration can be expanded and a vacuum gauge with higher sensitivity can be realized.

  By making the housing, elastic body, and vibration body into an integrated flat plate structure, it becomes possible to cut out the main components from a single flat plate, and it can be manufactured easily and at low cost by semiconductor lithography technology together with detection means and excitation electrodes. .

  As shown in FIG. 1, the vibrating body 1 is supported by the housing 3 via two beams 2 that are elastic bodies. The two beams 2 are arranged at symmetrical positions with respect to the center of gravity 4 of the vibrating body 1, and the vibrating body 1 horizontally supported by the beam 2 has rotational vibration around the Y axis that is the first axis passing through the center of gravity 4. It is free. The housing 3 is supported on the base substrate 6 via the spacer 5, and the base substrate 6 has a vibration electrode 7 that is a vibration means for vibrating the vibrating body 1, and the vibration force (driving force) thereof. Is configured to coincide with the Z axis that is the second axis that penetrates the center of gravity 4 of the vibrator 1. The shape of the vibrating body 1 is asymmetric with respect to the Y axis, which is the center of rotational vibration. The vibration electrode 1 reciprocates the center of gravity 4 of the vibrating body 1 in the Z direction, and the vibration of the vibrating body 1 in the Z direction is translated. A change in the amplitude of the inertial rotational vibration of the vibrating body 1 due to the detection is detected by the detection electrodes 8 and 9 as detection means, and the detected value is compared with a reference value prepared in advance to obtain the degree of vacuum.

  FIG. 2 is a schematic diagram showing the measurement principle of the vacuum gauge of FIG. The vibrating body 1a is supported by an elastic body 2a such as a torsion bar, and the elastic body 2a is disposed on the Y axis passing through the center of gravity 4a of the vibrating body 1a. Assuming that the vibrating body 1a is a rigid body, generally, the equation of motion of vibration can be considered independently by dividing it into six vibration modes around the center of gravity 4a. That is, the vibration in the translation direction along the X, Y, and Z axes in FIG. 2 and the rotational vibration around the three inertia main axes. The inertial main axis is determined by the weight and shape of the vibrating body 1a, but in the rectangular shape as shown in FIG. 2, it almost coincides with the X, Y, and Z axes. Hereinafter, in order to explain the direction and the like, the orthogonal X, Y, and Z coordinates where the origin is at the center of gravity and is stationary are used.

  In the present embodiment, two vibration modes are used among the six vibration modes. As shown in FIG. 3A, the first vibration mode is a reciprocating vibration in the vertical axis direction including the center of gravity 4a, that is, a translational vibration in the Z direction.

  The second vibration mode is a vibration around the horizontal axis shown in FIG. 3B generated by the translational vibration, that is, an inertial rotation vibration around the Y axis. The shape of the vibrating body 1a is asymmetric with respect to the Y axis, which is the rotational axis of rotational vibration. For example, by increasing the thickness of a part of the vibrating body 1a, the shape is asymmetrical on the left and right of the center of gravity. An excitation force in the Z-axis direction is applied to the vibrating body 1a so that the line of action just passes through the center of gravity 4a. The exciting force may be applied directly to the vibrating body 1a using electromagnetic force or electrostatic attraction and repulsion, or the entire housing supporting the elastic body 2a may be vibrated up and down. . The excitation frequency f at this time is substantially the same as the natural vibration frequency of the second vibration mode. These two vibrations can be considered independently in the first vibration mode and the second vibration mode as described above.

  Considering only the translational vibration caused by the reciprocating displacement z which is the first vibration mode, the vibration is vibrated by the force of the vibration frequency f acting on the center of gravity 4a. As is well known, the natural frequency at this time is Varies with atmospheric pressure. However, the vacuum gauge using this translational vibration cannot solve the unsolved problems of the prior art. Since the vector of the exciting force passes through the center of gravity 4a, the rotational vibration that is the second vibration mode is not excited by this force alone.

  Rotational vibration, which is the second vibration mode, is not a force that excites the first vibration mode in which the action line passes through the center of gravity 4a, but the vibration body 1a having an asymmetric shape with translational vibration in the first vibration mode. It is inertial rotation vibration that is vibrated by the force received from the atmosphere.

  First, consider the case where the atmosphere is ultra-high vacuum and there are almost no air molecules. In this case, since there is no force received from the atmosphere, the second vibration mode by the rotation angle θ is not excited. The vibration waveform at this time is shown in FIG. When vibration is applied in the first vibration mode, the amplitude A of the translational vibration gradually increases, but the amplitude becomes constant where the vibration energy and the damping of the structural material are balanced, and does not increase beyond that. On the other hand, the rotational vibration which is the second vibration mode does not vibrate because there is no excitation force received from the atmosphere.

  On the other hand, in the case of high, medium vacuum, that is, incomplete vacuum, the vibrating body 1a moves in the atmosphere, so that the vibrating body 1a receives force due to the action of the viscosity of the atmosphere. Since this force changes depending on the area in contact with the atmosphere, the vibrating body 1a having an asymmetric outer shape receives an asymmetric force across the center of gravity 4a. As a result, the rotational vibration in the second vibration mode is excited by the force from the atmosphere. That is, the second vibration mode is a vibration mode that is not affected by the translational vibration of the center of gravity 4a and the like, and is excited only when there is interaction with the atmosphere.

  This is shown in FIG. Even if the force received from the atmosphere is slight, the amplitude B of the second vibration mode gradually increases by repeatedly applying vibration. Eventually, the energy received from the atmosphere and the attenuation of the structural material are balanced and do not increase beyond that.

  At this time, the speed at which the amplitude B gradually increases varies depending on the viscosity of the atmosphere. When the atmosphere has a high viscosity, the force received from the atmosphere also increases, so the amplitude B increases quickly, and when the viscosity is low, it increases slowly. Since it is known that the viscosity of the atmosphere changes with pressure, the degree of vacuum can be obtained by measuring the speed at which the amplitude B increases.

  Note that the force for exciting the second vibration mode is maximized because the speed of the first vibration mode is maximized. Therefore, as shown in FIG. 4B, the first vibration mode is the first vibration mode. The phase is shifted between the reciprocating vibration and the rotational vibration that is the second vibration mode.

  In the case of high vacuum, since the number of molecules in the atmosphere is small, the force received by the vibrating body 1a is small. However, even if it is a slight force, the force is repeatedly applied. As shown in FIG. 4B, it gradually increases. Moreover, the force for exciting the second vibration mode is only the force received from the atmosphere and is not affected by the excitation force applied from the outside. Therefore, there is sensitivity even to a weak excitation force, and there is no possibility that the measurement sensitivity is lowered in a high vacuum region unlike the conventional example.

  Also, if there is an error in the excitation force in the first vibration mode, the translational vibration in the first vibration mode changes, but this change directly affects the second vibration mode, which is rotational vibration around the center of gravity 4a. There is nothing. This is because, in the stationary coordinate system, the motion may be considered independently in the translational motion and the rotational vibration around the inertial main axis.

  However, the force from the atmosphere that vibrates the second vibration mode changes due to the change in the first vibration mode. However, the influence from the atmosphere is small because it is originally small. Then, small changes are integrated and averaged during the measurement time taken to measure the speed at which the amplitude B of the second vibration mode increases. Therefore, it is possible to measure the degree of vacuum which is not easily affected by the error of the excitation force.

  When disturbance vibration is applied to the vibrating body 1a, the excitation force due to the disturbance is transmitted to the elastic body 2a and acts on the vibrating body 1a. The elastic body 2a is disposed on the Y axis passing through the center of gravity 4a of the vibrating body 1a. Therefore, the second vibration mode is not directly affected as in the case where there is an error in the excitation force acting on the center of gravity 4a of the vibrating body 1a after all. Therefore, it is possible to measure the degree of vacuum which is not easily affected by disturbance vibration.

  Further, the sensitivity can be further improved by designing the shape or the like so that the first vibration mode and the second vibration mode have the same resonance frequency. This is because if the amplitude is increased by making the excitation frequency f the same as the resonance frequency of the first vibration mode, the force received from the atmosphere also increases.

  As shown in FIG. 1, the vibrating body 1 is supported at both ends by two beams 2 and supported by a housing 3. This structure is fabricated using, for example, lithography and etching techniques. The origin is the center of gravity 4 of the vibrating body 1, the vertical direction in the figure is the Z direction, and the horizontal direction supported by the beam 2 is the Y direction. Each beam 2 is disposed on the Y axis passing through the center of gravity 4 of the vibrating body 1, and the vibrating body 1 has an asymmetric outer shape with respect to the Y axis. That is, on both sides of the Y axis, the thickness of one side of the vibrating body 1 is thick and the area is small, and the thickness of the opposite side is thin and the area is wide.

  Of the two vibration modes possessed by this structure, the first vibration mode is a reciprocal vibration mode based on a displacement z in the Z direction in which the center of gravity 4 moves up and down, as shown in FIG. Since the beam 2 supporting the vibrating body 1 is arranged at a symmetrical position with respect to the center of gravity 4, it vibrates up and down as shown.

  The second vibration mode is a rotational vibration mode with a rotation angle θ about the Y axis passing through the center of gravity 4. In general, the motion of an object can be considered by dividing it into a translational motion of the center of gravity and a rotational motion around the center of gravity. Therefore, even if the first vibration mode vibrates, the second vibration mode can be considered independently. . It is a force received from the atmosphere that vibrates the second vibration mode. In particular, a vibrating body vibrating in the vertical direction receives a force corresponding to the viscosity of the atmosphere. As a result, the amplitude of vibration gradually increases.

  As shown in FIG. 1, the vibrating body 1, the beam 2, and the housing 3 are made of a conductive material and are electrically connected. As such a material, for example, silicon doped with impurities to increase conductivity can be used. The housing 3 is joined to the base substrate 6 via an insulating spacer 5. As the insulator material, for example, glass that can be easily bonded to silicon by anodic bonding can be used.

  An excitation electrode 7 for exciting the vibrating body 1 is disposed on the base substrate 6. The excitation electrode 7 has a symmetrical shape with respect to the position of the center of gravity of the vibrating body 1 and is arranged so that the resultant force vector in the Z direction of the generated force passes through the center of gravity 4. That is, it is arranged directly below the center of gravity 4. At this time, since the spacer 5 is sandwiched between the base substrate 6 and the housing 3, the excitation electrode 7 and the vibrating body 1 do not contact each other.

  The base substrate 6 is provided with a first detection electrode 8 and a second detection electrode 9 for detecting the position and orientation of the vibrating body 1. Since the spacer 5 is sandwiched between the base substrate 6 and the housing 3, the detection electrodes 8 and 9 do not contact the vibrating body 1.

  An excitation circuit 10 is provided on the base substrate 6 and connected to the housing 3 and the excitation electrode 7. This is a voltage source that applies a voltage between the housing 3 and the excitation electrode 7. By controlling the voltage, an electrostatic force is generated between the vibrating body 1 and the excitation electrode 7. The vibrating body 1 is vibrated by this force. A first detection circuit 11 is provided on the base substrate 6 and connected to the housing 3 and the first detection electrode 8. This is an electric circuit that detects the electrostatic capacitance between the housing 3 and the first detection electrode 8, and its output represents the distance between the vibrating body 1 and the first detection electrode 8.

  A second detection circuit 12 is provided on the base substrate 6 and connected to the housing 3 and the second detection electrode 9. This is an electric circuit that detects the electrostatic capacitance between the housing 3 and the second detection electrode 9, and its output represents the distance between the vibrating body 1 and the second detection electrode 9.

A control circuit 13 is provided on the base substrate 6 to connect the vibration circuit 10, the first detection circuit 11, and the second detection circuit 12. In the control circuit 13, the signals from the detection circuits 11 and 12 are processed as follows. The distance projected on the base foundation 6 of the centroid 4 of the vibration member 1 and the first detecting electrode 8 and L _a, the projection on the base foundation 6 of the centroid 4 of the vibration member 1 and the second detecting electrode 9 the distances and L _b. Assuming that the output of the first detection circuit 11 is S _a and the output of the second detection circuit 12 is S _b , the amplitude signal S ₁ of the first vibration mode of the vibrating body ₁ , that is, the vertical vibration is higher or lower than the center of gravity position. Since it is a motion, the following formula is used.

S ₁ = (L _b S _a + L _a S _b ) / (L _a + L _b )

In addition, the amplitude signal S ₂ of the second vibration mode of the vibrating body 1, that is, the rotational vibration around the Y axis is calculated by the following equation.

S ₂ = S _b / L _b −S _a / L _a

In the above configuration, the measurement operation of the degree of vacuum will be described using the flowchart of FIG. This measurement sequence is generated by the control circuit 13. In step 100, it is determined whether the amplitude signals S ₁ and S ₂ are sufficiently small. That is, it is confirmed that the vibrating body 1 is not vibrating. In step 101, if it vibrates, wait for time, and if it still vibrates, stop the error. In step 102, a timer is provided in the controller, and the timer is reset to zero.

  In step 103, a timer is started, and an AC voltage having an excitation frequency f is applied between the excitation electrode 7 and the vibrating body 1 using the excitation circuit 10. At this time, since the excitation electrode 7 is arranged so that the electrostatic force vector generated in the excitation electrode 7 passes through the center of gravity 4 of the vibration body 1, the first vibration mode of the vibration body 1 is vibrated. However, the second vibration mode is not excited, and only the first vibration mode of the vibrating body 1 starts to vibrate at the excitation frequency f.

The amplitudes of the first and second vibration modes at this time are represented by the amplitude signals S ₁ and S ₂ described above. This excitation force does not excite the second vibration mode because the line of action passes through the center of gravity 4. That is, the amplitude signal S ₁ is output by this excitation force, but the amplitude signal S ₂ is not output only by this excitation force.

In step 104, rotational vibration is generated in the second vibration mode, and the amplitude gradually increases due to the force received from the atmosphere. Wait until the amplitude signal S2 of the _second vibration mode reaches a predetermined amplitude or the timer reaches a predetermined time. Here, the predetermined amplitude is determined within a range in which the first detection circuit 11 or the second detection circuit 12 does not overflow. The predetermined amplitude is determined within a range where the vibrating body 1 and the electrodes 7, 8, 9 do not contact each other. For example, the value is 10 μm. The predetermined time is the time from when the vacuum gauge starts measurement until the measurement result is output, and is a value such as 10 seconds.

Step 105 divided by the amplitude signal S ₂ at the value of timer, i.e., to calculate how fast the amplitude signal S ₂ becomes large, previously prepared from the corresponding table between the speed and degree of vacuum vibration amplitude is large, The degree of vacuum is obtained by comparison with a reference value. This table can be easily obtained by attaching a high-precision vacuum gauge and the present vacuum gauge to a vacuum vessel and comparing the two.

  According to the vacuum gauge of the present embodiment, when the degree of vacuum increases, the force received from the atmosphere also decreases, but the second vibration mode receives a repeated force, so that the amplitude gradually increases. That is, as described in step 104 of the flowchart, the amplitude increases with time. Therefore, a highly sensitive vacuum gauge can be realized by accumulating the effect even with a slight force received from the atmosphere in the high vacuum region.

  In addition, if there is an error in the excitation force, the amplitude and frequency of translational vibration in which the vibrating body moves up and down change, but this does not directly cause a measurement error. This is because the motion can be considered independently in the motion in the translational direction and the rotational vibration around the principal axis of inertia in the stationary coordinate system. However, the force from the atmosphere that vibrates the second vibration mode changes due to the change in the first vibration mode. However, the influence from the atmosphere is small because it is originally small. Moreover, as described in step 104 of the flowchart, it may be considered that the error is averaged until the amplitude of the second vibration mode increases. Accordingly, it is possible to measure the degree of vacuum which is not easily affected by an error in the force applied.

  When the environment where this vacuum gauge is installed vibrates, the housing vibrates. The vibration is transmitted to the vibrating body through the beam. However, since the beam is arranged symmetrically with respect to the center of gravity, the second vibration mode is vibrated even if the first vibration mode is vibrated. There is no. And since the change of the amplitude of a 2nd vibration mode is measured, the vacuum gauge which is hard to receive to the influence of the disturbance vibration of an installation environment is realizable.

  In this embodiment, the shape of the vibrating body is rectangular. However, if the shape is asymmetric with respect to the rotation axis passing through the center of gravity, the force received from the atmosphere is also asymmetrical, so the same effect can be obtained even when the corners of the vibrating body are rounded.

  In the present embodiment, if the first vibration mode and the second vibration mode are designed to have the same resonance frequency, the vibrating body vibrates with a very large amplitude in the first vibration mode due to resonance. Become. Therefore, the force received from the atmosphere can be increased, and the sensitivity of the vacuum gauge can be improved.

  The design at this time can be realized by changing the shape of the beam. For example, by changing the thickness, width, and length of the beam, the bending stiffness of the beam governing the resonance frequency of the first vibration mode and the torsional stiffness of the beam governing the resonance frequency of the second vibration mode are adjusted. can do. As a result, the first and second vibration modes can be designed to have the same resonance frequency.

  FIG. 7 shows a second embodiment. In the first embodiment, the beam 2 that supports the vibrating body 1 supports the vibrating body 1 at both ends. However, one of the beams 2 is cut and the vibrating body 1 is supported by the single beam 2. Since the first vibration mode is a cantilever beam, the first vibration mode is a reciprocating vibration whose fulcrum is near the root of the beam 2, and the second vibration mode is a rotational vibration around the Y axis. Since other configurations and operations are the same as those in the embodiment, description thereof is omitted.

  According to the present embodiment, compared with the first embodiment, since the structure is a cantilever, the resonance frequency of the first vibration mode can be easily lowered. Lowering the resonance frequency makes it easier to increase the amplitude of the translational vibration, so the force received from the atmosphere can be increased.

  As in the case of the first embodiment, the sensitivity of the vacuum gauge can be improved by matching the resonance frequency of the first vibration mode with the resonance frequency of the second vibration mode. At this time, since the configuration of the cantilever is added to the configuration of the cantilever, the degree of freedom in design can be improved, and an advantage that the design becomes simpler is added.

  FIG. 8 shows a third embodiment. In the first and second embodiments, the asymmetric vibrating body is configured by changing the thickness of the vibrating body. However, in the present embodiment, the asymmetric vibrating body 21 is configured with the same thickness. The vibrating body 21, the beam 22, and the housing 23 have a single thin plate structure with a uniform thickness. The two beams 22 are disposed on the Y axis, and the vibrating body 21 has a center of gravity 24 on the Y axis. Since the thickness of the vibrating body 21 is constant, the outer shape is designed so that the areas are equal on the left and right sides of the Y axis. That is, the left side is a range close to the rotation axis, which is the Y axis, and the right side is extended to a range far from the rotation axis, thereby forming an asymmetric shape on the left and right.

  This embodiment has an advantage that it can be easily manufactured by photolithography because the thickness is constant as compared with the first and second embodiments.

  Further, since the thickness is constant, the only dimension error is a horizontal dimension shift. Therefore, compared to the first and second embodiments that are affected by the error due to both the thickness and the dimensional deviation, the present embodiment can form the vibrating body with higher accuracy. As a result, the displacement of the center of gravity, which is one of the error factors, is reduced, and a highly accurate vacuum gauge can be created.

  FIG. 9 shows a fourth embodiment. In the first embodiment, one excitation electrode is arranged corresponding to the position of the center of gravity of the vibrating body and directly below the position of the center of gravity, but in this embodiment, two excitation electrodes 37a and 37b are used. And the position to arrange | position is made into equal distance from right under from the gravity center position of the vibrating body 31, and each excitation electrode 37a, 37b is connected to the 1st, 2nd excitation circuit 40a, 40b. The vibration circuits 40 a and 40 b are connected to the voltage distribution circuit 44, and the voltage distribution circuit 44 is connected to the control circuit 13. The voltage distribution circuit 44 distributes the voltage signal from the control circuit 13 at a constant ratio and outputs the voltage signal to the first and second vibration circuits 40a and 40b. As a result, the voltage generated in the excitation electrodes 37a and 37b has a constant ratio.

  As in the first embodiment, the vibrating body 31 is vibrated according to the flowchart of FIG. At this time, by adjusting the ratio of the voltages applied to the two excitation electrodes 37a and 37b, the resultant force vector of the excitation force can be adjusted so as to pass through the position of the center of gravity. That is, in the first embodiment, there is a concern that the excitation force and the position of the center of gravity may be shifted due to the position error and the dimension error in forming the excitation electrode. In this embodiment, this deviation is adjusted by the ratio of the voltage to be distributed. be able to.

  Therefore, dimensional errors of the excitation electrode and the vibrating body can be allowed, and the vacuum gauge can be easily manufactured. In addition, this adjustment makes it possible to precisely adjust the excitation force and the center of gravity, so that a more accurate vacuum gauge can be configured.

  The voltage distribution ratio of the voltage distribution circuit can be easily determined by installing this vacuum gauge in an ultra-high vacuum chamber and adjusting the voltage distribution ratio so that the support value is zero, that is, the second vibration mode signal is not output. it can.

  FIG. 10 shows a fifth embodiment. In the first embodiment, the vibrating body is vibrated using the electrostatic force generated between the vibrating electrode and the vibrating body. However, in this embodiment, the vibration is performed by the piezoelectric element 57 that supports the base substrate 56. The vibrating body 51 is supported at both ends by two beams 52 and supported by a housing 53. This structure is fabricated using, for example, lithography and etching techniques. The origin is the center of gravity 53 of the vibrating body 51, the vertical direction in the figure is the Z direction, and the direction supported by the beam 52 is the Y direction. A beam 52 is disposed on the Y axis passing through the center of gravity 54 of the vibrating body 51, and the vibrating body 51 is asymmetric with respect to the Y axis. That is, the thickness on one side is thick and the area is small, and the thickness on the opposite side is thin and the area is wide.

  The first vibration mode of this structure is a reciprocating vibration mode in which the center of gravity 54 moves up and down. Since the two beams 52 that support the vibrating body 51 are arranged symmetrically with respect to the center of gravity 54, they vibrate up and down as shown.

  The second vibration mode is rotational vibration about the Y axis that passes through the center of gravity 54. In general, the motion of an object can be considered by dividing it into a translational motion of the center of gravity and a rotational motion around the center of gravity. Therefore, even if the first vibration mode vibrates, the second vibration mode can be considered independently. . It is a force received from the atmosphere that vibrates the second vibration mode. In particular, the vibrating body 51 vibrating in the vertical direction receives a force according to the viscosity of the atmosphere. As a result, the vibration amplitude gradually increases.

  The vibrating body 51, the beam 52, and the housing 53 are made of a conductive material and are electrically connected. As such a material, for example, silicon doped with impurities to increase conductivity can be used. The housing 53 is joined to the base substrate 56 via an insulating spacer 55. As the insulator material, for example, glass that can be easily bonded to silicon by anodic bonding can be used.

  A piezo element 57 is fixed to the base substrate 56, and the piezo element 57 is supported on a base plate 66. The vibration circuit 60 is provided on the base substrate 56, the voltage signal from the vibration circuit 60 is provided with an amplifier 67 and connected to the amplifier 67, and the output of the amplifier 67 is connected to the piezo element 57.

  A first detection circuit 61 is provided on the base substrate 56 and connected to the housing 53 and the first detection electrode 58. This is an electric circuit that detects the electrostatic capacitance between the housing 53 and the first detection electrode 58, and the output represents the distance between the vibrating body 51 and the first detection electrode 58. A second detection circuit 62 is provided on the base substrate 56 and is connected to the housing 53 and the second detection electrode 59. This is an electric circuit that detects the electrostatic capacitance between the housing 53 and the second detection electrode 59, and the output represents the distance between the vibrating body 51 and the second detection electrode 59.

A control circuit 63 is provided on the base substrate 56, and the vibration circuit 60, the first detection circuit 61, and the second detection circuit 62 are connected. In the control circuit 63, signals from the detection circuits 61 and 62 are processed as follows. The distance projected onto the base platform 56 between the center of gravity 54 of the vibrator 51 and the first detection electrode 58 and L _a, projected in the base foundation 56 between the center of gravity 54 of the vibrator 51 and the second detection electrode 59 Let L _b be the distance. Assuming that the output of the first detection circuit 61 is S _a and the output of the second detection circuit 62 is S _b , the amplitude signal S ₁ of the first vibration mode of the vibrating body 51, that is, the vertical vibration is higher or lower than the center of gravity position. Since it is a motion, the following formula is used.

S ₁ = (L _b S _a + L _a S _b ) / (L _a + L _b )

In addition, the amplitude signal S ₂ of the second vibration mode of the vibrating body 51, that is, the rotational vibration around the Y axis is calculated by the following equation.

S ₂ = S _b / L _b −S _a / L _a

In the above configuration, the measurement operation of the degree of vacuum is performed according to the same flow as the flowchart of FIG. This measurement sequence is generated by the control circuit 63. In step 200, it is determined whether the amplitude signals S ₁ and S ₂ are sufficiently small. That is, it is confirmed that the vibrating body 51 is not vibrating. In step 201, if it vibrates, wait for a time, and if it still vibrates, stop the error. In step 202, a timer is provided in the controller, and the timer is reset to zero.

  In step 203, a timer is started, and an AC voltage having an excitation frequency f is output to the amplifier 67 using the excitation circuit 60. The amplifier 67 applies a voltage obtained by amplifying this voltage to the piezo element 57. Since the piezo element 57 expands and contracts according to the applied voltage, the entire base substrate 56 is vibrated. When the entire base substrate 56 vibrates, the vibration is transmitted to the spacer 55, the housing 53, and the beam 52 to vibrate the vibrating body 51. At this time, since the beam 52 is arranged at a symmetrical position with respect to the center of gravity 54, the first vibration mode is vibrated, but the second vibration mode is not vibrated. As a result, the first vibration mode of the vibrating body 51 starts to vibrate at the excitation frequency f.

The amplitudes of the first and second vibration modes at this time are the amplitude signals S ₁ and S ₂ described above. This excitation force does not excite the amplitude of the second vibration mode because the line of action passes through the center of gravity 54. That is, the amplitude signal S ₁ is output by this excitation force, but the amplitude signal S ₂ is not output only by this excitation force.

In step 204, the amplitude of the second vibration mode gradually increases depending on the force received from the atmosphere. Wait until the amplitude signal S ₂ reaches a predetermined amplitude or the timer reaches a predetermined time. Here, the predetermined amplitude is determined within a range in which the first detection circuit 61 or the second detection circuit 62 does not overflow. The predetermined amplitude is determined in a range where the vibrating body 51 and the electrodes 57, 58, 59 are not in contact with each other. For example, the value is 10 μm. The predetermined time is the time from when the vacuum gauge starts measurement until the measurement result is output, and is a value such as 10 seconds.

Divided by the amplitude signal S ₂ with a value of the timer in step 205, i.e., to calculate how fast the amplitude signal S ₂ becomes large. The degree of vacuum is obtained from a correspondence table prepared in advance between the speed at which the vibration amplitude increases and the degree of vacuum. This table can be easily obtained by attaching a high-precision vacuum gauge and the present vacuum gauge to a vacuum vessel and comparing the two.

  If the vacuum gauge is configured as described above, vibration can be performed with a large force because vibration is performed by a piezoelectric element. Therefore, vibration with a higher frequency and a larger amplitude is possible. As the vibration of the vibrating body increases, the force that the vibrating body receives from the atmosphere also increases. Since the force received by the vibrating body from the atmosphere increases, the force for exciting the second vibration mode also increases and the amplitude increases. In this way, a more sensitive vacuum gauge can be realized.

  FIG. 11 shows a sixth embodiment. In the fifth embodiment, one piezo element that supports the base substrate is used. However, in this embodiment, a plurality of piezo elements 77a and 77b are used. The positions to be arranged are equidistant from right below the center of gravity of the vibrating body 51 to both sides, and the piezo elements 77 a and 77 b are connected to the voltage distribution circuit 84. The voltage distribution circuit 84 distributes the voltage signal transmitted from the control circuit 63 via the amplifier 67 at a constant ratio, and drives the piezo elements 77a and 77b.

  When the vibrating body 51 is vibrated, the applied position of the resultant force vector of the exciting force can be adjusted by adjusting the ratio of the voltages applied to the two piezoelectric elements 77a and 77b. That is, even if there is a concern that the excitation force and the position of the center of gravity of the vibrating body 51 are shifted, the adjustment can be made by the ratio of the voltage to be distributed.

  Therefore, a dimensional error of the vibrating body or the like can be allowed, and a vacuum gauge can be easily manufactured. In addition, this adjustment makes it possible to precisely adjust the excitation force and the center of gravity, so that a more accurate vacuum gauge can be configured.

  The voltage distribution ratio of the voltage distribution circuit can be easily determined by installing this vacuum gauge in an ultra-high vacuum chamber and adjusting the voltage distribution ratio so that the support value is zero, that is, the second vibration mode signal is not output. it can.

It is a disassembled perspective view which decomposes | disassembles and shows the vacuum gauge by Example 1. FIG. 2 is a schematic diagram illustrating a basic structure of Example 1. FIG. It is a figure explaining the 1st and 2nd vibration mode of the apparatus of FIG. The vibration waveforms of the first and second vibration modes are shown. It is a figure explaining the 1st and 2nd vibration mode in Example 1. FIG. 3 is a flowchart illustrating a measurement operation according to the first embodiment. It is a disassembled perspective view which decomposes | disassembles and shows the vacuum gauge by Example 2. FIG. FIG. 10 is a partial plan view showing a main part of Example 3. It is a disassembled perspective view which decomposes | disassembles and shows the vacuum gauge by Example 4. FIG. It is a disassembled perspective view which decomposes | disassembles and shows the vacuum gauge by Example 5. FIG. It is a disassembled perspective view which decomposes | disassembles and shows the vacuum gauge by Example 6. FIG. It is a figure which shows one prior art example.

Explanation of symbols

1, 1a, 21, 31, 51 Vibrating body 2, 22, 52 Beam 2a Elastic body 3, 23, 53 Housing 4, 4a, 24, 54 Center of gravity 5, 55 Spacer 6, 56 Base base 7, 37a, 37b Excitation Electrode 8, 58 First detection electrode 9, 59 Second detection electrode 10, 40a, 40b, 60 Excitation circuit 11, 61 First detection circuit 12, 62 Second detection circuit 13, 63 Control circuit 44, 84 Voltage distribution circuit 57, 77a, 77b Piezo element 66 Base plate 67 Amplifier

Claims (7)

  A vibrating body having an asymmetric shape with respect to a first axis passing through the center of gravity, a housing having an elastic body that horizontally supports the vibrating body along the first axis, and a driving force acting on the center of gravity, the first Excitation means for generating translational vibrations in the vibrating body along a second axis orthogonal to one axis, and detection for detecting inertial rotational vibrations around the first axis of the vibrating body generated along with the translational vibrations And a vacuum gauge for obtaining an atmospheric pressure around the vibrating body based on an output of the detecting means.   2. The vacuum gauge according to claim 1, wherein the detecting means is configured to detect a speed at which an amplitude of an inertial rotational vibration of the vibrating body increases.   3. The vacuum gauge according to claim 1, wherein the resonance frequency of the translational vibration of the vibrating body along the second axis is equal to the resonance frequency of the inertial rotation vibration around the first axis.   A housing, an elastic body, and a vibrating body have a flat plate structure, and the elastic body includes at least one beam disposed on a first axis passing through the center of gravity of the vibrating body. The vacuum gauge according to any one of claims 1 to 3.   2. A base substrate for supporting the housing via a spacer is provided, and the excitation means has an excitation electrode disposed on the base substrate so as to face the vibrating body. The vacuum gauge of any one of thru | or 4.   The vacuum gauge according to any one of claims 1 to 4, wherein the vibration means includes a piezoelectric element that integrally reciprocates the housing, the elastic body, and the vibration body.   The vacuum gauge according to any one of claims 1 to 6, wherein the excitation means includes a plurality of excitation electrodes or a plurality of piezoelectric elements that are individually controllable.

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