Servo type vibration detector and vibration control device

Abstract

To solve the issue of a conventional servo-type vibration detector made of a coil, a permanent magnet, and a displacement detector, the issue being that processing an extremely thin line of a coil is complicated and a high yield cannot be obtained at the time of mass production due to a high cost resulting from the complicity of a structure.SOLUTION: A pole piece part is put on a front side and a rear side across a permanent magnet magnetized in an axial direction and a coil is arranged on a fixation side facing each pole piece part, whereby driving means of a moving magnet type acceleration sensor is formed. That structure eliminates the necessity of complicated wiring processing of coils and allows a significant increase of mass productivity.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a vibration sensor or vibration isolation control device that detects signals over a wide frequency band of the acceleration, absolute velocity relative to inertial space, or absolute displacement of a control object that is supported on a foundation and vibrates due to external disturbances. [Background technology]

[0002] 1. Trends in the world The use of vibration control to block and suppress minute vibrations is becoming more widespread in various fields, including semiconductor manufacturing processes, liquid crystal manufacturing processes, and precision machining. The fine processing and inspection equipment used in these processes, such as scanning electron microscopes and semiconductor exposure equipment (steppers), require strict vibration tolerance conditions to ensure equipment performance. In the future, as products become increasingly highly integrated and miniaturized, processing processes will become faster and equipment will become larger, and vibration tolerance conditions will tend to become increasingly strict.

[0003] 2. Disturbances that the vibration isolation system should remove In recent years, active vibration control technology has become widespread, in which control devices are controlled by creating control signals based on displacement, velocity, and acceleration information from vibration sensors placed at multiple locations on the structure to be vibration-controlled (for example, a precision vibration isolation table).

[0004] FIG. 9 shows a model diagram of a conventional active vibration isolation table. This active vibration isolation table is well known, as described in Patent Documents 1 and 2. A plurality of pairs of pneumatic actuators (502a, 502b) are arranged on a floor 500 to support a surface plate 501. A precision device (not shown) is mounted on the surface plate 501. Reference numeral 503 denotes an acceleration sensor for detecting the vertical and horizontal acceleration of the surface plate 501, and reference numeral 504 denotes an acceleration sensor for detecting the acceleration of the floor 500 (the vibration state of the foundation). Reference numerals 505a and 505b denote displacement sensors for detecting the vertical and horizontal relative displacement of the surface plate 501 with respect to the floor 500, respectively. Output signals from these sensors are input to a controller 506. A servo valve 508 controlled by the controller 506 is connected to the pneumatic actuator 502a via piping 507. This servo valve 508 adjusts the flow rate of compressed air supplied to and exhausted from the pneumatic actuator 502a, thereby controlling the internal pressure of the actuator 502a and driving the pneumatic actuator.

[0005] Disturbances to be removed by a vibration isolation system are roughly divided into ground motion disturbances caused by vibrations of the installation floor and direct-acting disturbances input from above the vibration isolation table.

[0006] Sources of vibration that cause ground disturbances include walking vibrations caused by people moving about, which are 1 to 3 Hz, motors such as those for air conditioners, which are 6 to 35 Hz, and the resonance points of floors and walls being around 10 to 100 Hz. High-rise, seismically isolated buildings have a natural frequency of around 0.2 to 0.3 Hz. Wind sway also causes buildings to generate micro-vibrations of 0.1 to 1.0 Hz. Therefore, vibration isolation tables are required to not only suppress high-frequency vibrations, but also to remove low-frequency vibrations.

[0007] If the vibration isolation table is equipped with, for example, a positioning stage 509 as a source of high-frequency vibration caused by linear disturbance, the structure including the vibration isolation table will be struck by the stage's acceleration / deceleration operation and will oscillate due to the drive reaction force. The performance of the stage cannot be maintained unless the vibration caused by this strike and the oscillating due to the drive reaction force are suppressed. In short, a vibration isolation device is required to have the function of both "isolating" from ground disturbances and "damping" from linear disturbances.

[0008] 3. Role of vibration sensors in active vibration isolation systems Active vibration control employs a control method based on state feedback. This is a method of controlling a control device based on acceleration, velocity, and displacement information from vibration sensors placed at multiple locations on the structure to be vibration controlled. In order to obtain vibration isolation performance over a wide frequency range, for example, acceleration signals are used to control state quantities above 10 Hz, velocity signals are used to control state quantities between 1 and 10 Hz, and displacement signals are used to control state quantities below 1 Hz. For example, (i) If acceleration feedback is performed using the signal from the acceleration sensor (503 in Figure 9) placed on the surface plate 501, it becomes equivalent to an increase in mass M, and has the effect of lowering the natural frequency and reducing the resonance peak. (ii) If the signal from the acceleration sensor (503 in FIG. 9) is converted into an absolute velocity or absolute displacement signal and feedback or feedforward is applied, the vibration isolation performance can be significantly improved over a wide frequency range. (iii) By using the signal from the acceleration sensor (504 in Fig. 9) placed directly below the surface plate 501 and converting the signal into an absolute velocity or absolute displacement signal, and similarly applying feedforward, it is possible to improve vibration isolation performance over a wide frequency range. To perform the above controls (ii) and (iii), velocity and position information relative to inertial space is required. Since an acceleration sensor can measure acceleration relative to inertial space, attaching an acceleration sensor to the controlled object makes it possible to detect the acceleration applied to the controlled object. Therefore, conventional active vibration isolation systems employ a method in which the output of the acceleration sensor is integrated once to obtain a velocity signal, and then integrated twice to obtain a displacement signal.

[0009] 4. Basic configuration and detection principle of acceleration sensors Figure 10 is a model diagram showing the basic configuration and detection principle of a capacitance-type acceleration sensor. 301 is the main body that houses each component of the sensor, 302 is the mass, 303 is a spring that mechanically supports mass 302 with respect to vibration measurement surface A, and 304 is a damper. Mass 302 also serves as the movable electrode of the capacitance-type sensor. 305 is the fixed electrode located on the opposite side of the movable electrode (mass 302), and 306 is the gap between the two electrodes.

[0010] Reference numeral 307 denotes an electromagnetic actuator that drives the mass body 302 in a direction perpendicular to the vibration measurement surface A. Since the capacitance C is determined by the size of the gap in the gap portion 306, by measuring this capacitance C, it is possible to detect the relative displacement UX, which is the difference between the absolute displacement U of the ground motion and the absolute displacement X of the mass body. A servo circuit 310 (shown by a two-dot chain line) converts the relative displacement signal UX into a signal with a gain K P The amplifier 311 amplifies the signal by a factor of 1.

[0011] The detection principle of the acceleration sensor will be explained below using mathematical expressions. The mass of the mass body 302 is m, the spring constant of the mechanical spring 303 supporting the mass body is k, the damping coefficient of the damper 304 is c, and the driving force of the actuator 307 is F=A f If we set i0, the following equation of motion holds:

[0012]

number

[0013] The proportional gain constant K is set so that the relative displacement ux becomes zero. P The amplifier The current i0 is controlled.

[0014]

number

[0015]

number

[0016] Proportional gain constant K P is sufficiently large, and the first term is smaller than the third term on the right side of equation (3). If the second term can be ignored,

[0017]

number

[0018] If the current i0 flowing through the actuator is detected from equations (2) and (4), the acceleration of the mass body 302 can be calculated as It can be calculated approximately.

[0019] 5. Specific structure of conventional servo-type acceleration sensors The specific structures of servo-type accelerometers can be broadly divided into two types: (1) a type in which the mass part moves linearly, and (2) a type in which the mass part moves oscillatingly. Below, examples of these two types of conventional sensors will be explained.

[0020] [5-1] Conventional example of a linear motion acceleration sensor Figure 11 is a front cross-sectional view showing a specific example of the structure of a conventional linear motion acceleration sensor. The basic principle of the linear motion acceleration sensor is disclosed in Patent Document 1. It is constructed using the basic configuration and detection principle shown in Figure 10. Reference numeral 11 denotes a permanent magnet, 12 denotes a pole piece portion, 13 denotes a pole piece protrusion, 14 denotes a permanent magnet side yoke material, 15 denotes a coil side yoke material, 16a denotes a force coil, 16b denotes a calibration coil, 17 denotes a coil bobbin, 18 and 19 denote coil bobbin support members made of nonmagnetic and nonconductive material, 20 denotes a front side disc-shaped spring, 21 denotes a rear side disc-shaped spring, 22 denotes a front side connecting member between the front side disc-shaped spring 20 and the coil side yoke material 15, and 23 denotes a rear side connecting member between the rear side disc-shaped spring 21 and the coil side yoke material 15. Reference numeral 24 denotes a movable side electrode, 25 denotes a fixed side electrode, 26 denotes a front side panel, 27 denotes a center plate, and 28 denotes a fastening member between the fixed side electrode 25 and the front side panel 26.

[0021] A radial magnetic gap 29 is formed between the outer periphery of the pole piece 12 and the inner periphery of the coil-side yoke material 15. Reference numeral 29a denotes the permanent magnet-side gap, and 29b denotes the yoke material-side gap. A closed-loop magnetic circuit is formed by the permanent magnet 11 → pole piece 12 → magnetic gap 29 → coil-side yoke material 15 → permanent magnet-side yoke material 14. When current flows through the force coil 16a located in the space of the magnetic gap 29, a Lorentz force is generated that moves the movable electrode 24 axially. Reference numeral 30 denotes the gap formed by the movable electrode 24 and the fixed electrode 25. Since the capacitance C is determined by the size of the gap 30, measuring the capacitance C allows the detection of relative displacement UX, which is the difference between the absolute ground displacement U and the absolute mass displacement X. The servo circuit is composed of a displacement detector 31, an amplifier 32, and a driver 33. The amplifier 32 and driver 33 convert the relative displacement signal UX into a gain K. P The proportional gain constant K is set so that the relative displacement ux becomes zero. P The current i0 of the actuator is controlled by this amplifier. By detecting the current i0 flowing through the force coil 16a, the acceleration acting on the movable part can be determined, as described above.

[0022] [5-2] Conventional example of a swing-motion acceleration sensor (1) Overall Configuration of Sensor Fig. 13 is a front cross-sectional view showing an example of an oscillating motion sensor disclosed in Patent Document 2, in which 590a is a pendulum located within a disk-shaped frame 590. Pendulum 590a is formed in a tongue shape with a portion of its periphery cut out, and is supported by frame 590 via hinge 590b. Frame 590, pendulum 590a, and hinge 590b are integrally formed from, for example, quartz glass. Hinge 590b is thin and elastically deformable, allowing pendulum 590a to be displaced in the vertical direction of the figure in response to input acceleration.

[0023] Numerals 591 and 592 denote a pair of magnetic yokes. These magnetic yokes are made of Invar alloy, a low-thermal expansion material. Invar alloy is a difficult-to-process material made by adding 36% nickel and 0.7% manganese to iron. Numeral 593 denotes the pole piece bottom, 594 denotes a permanent magnet, and 595 denotes the pole piece top. Permanent magnet 594 is magnetized in the thickness direction, forming annular magnetic gaps 596 between the inner circumferential surfaces of the open ends of magnetic yokes 591 and 592 and the outer circumferential surface of pole piece top 598. Coil bobbins 598, around which torque coils 597 are wound, are attached to both plate surfaces of pendulum 590a so as to be positioned within these annular magnetic gaps 596.

[0024] On both plate surfaces of pendulum 590a, arc-shaped capacitance electrodes 590c are formed along the outer periphery of the tongue-shaped tip. Electrode surfaces 591e and 592e face capacitance electrode 590c with a predetermined gap therebetween.

[0025] In a servo-type accelerometer with this configuration, the displacement of pendulum 590a due to acceleration input is detected as a change in capacitance between capacitance electrode 590c and electrode surfaces 591e and 592e. Electrode surfaces 591e and 592e are at a common potential, and the detection signals from capacitance electrodes 590c on both surfaces of pendulum 590a are differentially amplified by a servo amplifier (not shown). Torque currents based on the capacitance difference are passed through a pair of torque coils 597. The interaction between this torque current and the magnetic field generated by permanent magnet 594 returns the displaced pendulum 590a to its original position and balances it at the neutral point. Since the torque current at this time is proportional to the acceleration applied to pendulum 590a, the input acceleration can be calculated from this current. Coil terminals 597a and 597b of torque coil 597 are electrically connected by adhesive to a metal conductor (not shown) on pendulum 590a.

[0026] (2) Pendulum structure FIG. 14 shows a plan view of pendulum 590a. FIG. 14(a) shows one side, and FIG. 14(b) shows the other side. Frame 590, pendulum 590a, and hinges 590b1 and 590b2 are formed, for example, by etching a single disk of quartz glass. Pendulum conductor A is formed on one side of frame 590 in an arc shape with a width approximately half the width of frame 590. One end of the arc-shaped metal conductor extends along one hinge 590b1 in its extension direction, passes beyond the center of pendulum 590a, and then is folded back toward the center in a hook-like shape. Arc-shaped pendulum conductor A constitutes one input / output end of the torque current.

[0027] Pendulum conductor B is formed on one surface from the end of pendulum conductor A located in the center of pendulum 590a, across the center of pendulum 590a, at a position spaced apart at a distance approximately equal to the distance between bobbin conductors (described later), toward the outer edge of pendulum 10a, with the same width as pendulum conductor A. Furthermore, pendulum conductor B is formed continuously along the side surface of the outer edge of pendulum 590a between a pair of hinges 590b1, 590b2 to the other surface. The shape of pendulum conductor B on the other surface is the same as the shape on one surface described above. Pendulum conductor B connects two torque coils 597, one on the left and one on the right, in series.

[0028] A pendulum conductor C is formed on the other surface in approximately the same shape as the pendulum conductor A described above. The end of the pendulum conductor C is formed in an arc shape on one surface of the frame 590 with a width approximately equal to that of the frame 590. The end of the pendulum conductor C on one surface and the pendulum conductor C on the other surface are formed continuously along the inner diameter side of the frame 590. The arc-shaped pendulum conductor C constitutes the other input / output end of the torque current. A capacitance detection electrode D is formed in an arc shape along the outer edge of the pendulum 590a on one surface of the pendulum 590a, and further extends over the hinge 590b2 to form an arc-shaped end on the frame 590 along the outer periphery of the frame 590 with a width approximately half the width of the frame 590.

[0029] Furthermore, a capacitance detection electrode E is formed on the other surface of the pendulum 590a in the same manner as the capacitance detection electrode D. Furthermore, the capacitance detection electrode E continues along the inner diameter side surface of the frame body 590 onto one surface of the frame body 590, and an end portion is formed on one surface of the frame body 590 in an arc shape with approximately the same width as the frame body 10. The ends of the capacitance detection electrodes D and E on one surface of the frame body 590 are connected to a servo amplifier (not shown).

[0030] Each of the pendulum conductors described above is formed as a thin film of gold (Au) sputtered or vacuum-deposited on the surface of frame 590, pendulum 590a, and hinges 590b1, 590b2, which are made of quartz glass. The basic structural differences between the linear motion acceleration sensor and the oscillating motion acceleration sensor described above can be classified by the method of elastically supporting the moving part. In the linear motion type, the axis is the direction of movement of the moving part, and springs are arranged circumferentially around this axis. In the oscillating motion type, the moving part is supported by a cantilever with one end fixed and the other free. [Prior art documents] [Patent documents]

[0031] [Patent Document 1] Japanese Patent Application Laid-Open No. 2006-283966 [Patent Document 2] Japanese Patent Application Laid-Open No. 2007-155038 [Patent Document 3] Japanese Patent Application Laid-Open No. 2004-205284 [Patent Document 4] Japanese Patent Application Laid-Open No. 2010-96509 Summary of the Invention [Problem to be solved by the invention]

[0032] The linear motion acceleration sensor disclosed in Patent Document 1 had major issues in terms of production technology due to its basic operating principle and structure. Fig. 12(a) is a front view showing the shape of the front-side disk-shaped spring, and Fig. 12(b) is a front cross-sectional view of the entire sensor (Fig. 11) with the front panel 26, fixed electrode 25, etc. removed. Fig. 12(c) is an enlarged view of part A in Fig. 12(b), showing the state in which the movable electrode 24 is deformed in the axial direction.

[0033] Four conductive paths are required to connect the terminals of the force coil 16a and the calibration coil 16b to an externally installed control circuit. Including the conductive path connecting the movable electrode 24 and the displacement detector 31 (FIG. 11), a total of five independent conductive paths are required. Because the two coils and the movable electrode move axially, it is not possible to connect the five terminals to the external fixed part with lead wires. Therefore, as shown in FIGS. 12(a) and 12(c), the five conductive paths are formed using the front disc-shaped spring 20 and the rear disc-shaped spring 21. In other words, the two disc-shaped springs 20 and 21 serve both to elastically support the movable part (coil bobbin 17, movable electrode 24, etc.) and to provide the five independent conductive paths.

[0034] In FIG. 12(a), 34a, 34b, and 34c denote the outer peripheral fixing portions of the front-side disk-shaped spring 20. These three outer peripheral fixing portions are cut at three circumferential locations as indicated by the chain-line circle AA to ensure electrical insulation. 35a, 35b, and 35c denote the inner peripheral spring portions of the front-side disk-shaped spring. These three inner peripheral spring portions are cut at three circumferential locations as indicated by the chain-line circle BB to ensure electrical insulation. 36a, 36b, and 36c denote soldering portions for electrically connecting the coil terminals to the inner peripheral spring portions. FIG. 12(c) shows the terminal of the test coil 16b connected to the inner peripheral spring portion 35c at the soldering portion 36c. Incidentally, the coil wire diameter used in servo-type acceleration sensors is, for example, an extremely thin wire with a diameter of approximately 30 μm.

[0035] Conventional servo-type acceleration sensors pose a production technology challenge due to their basic operating principles and structure, requiring the processes of "cutting, insulating, and soldering" between the disk spring and the coil. This complicated process reduces yield and reliability during mass production. Considering long-term reliability, small-diameter disk springs used in linear motion acceleration sensors must be made of metal. This is because, from the perspective of sensor performance, the mechanical resonance frequency, determined by the inertial mass of the moving part and the spring stiffness, must be sufficiently low, and the spring stiffness value must be set small. Small-diameter disk springs deform significantly with small external forces. This makes it difficult to adopt a structure combining a non-metallic material (such as quartz glass) with a conductive thin film (conductive path), as used in oscillatory motion acceleration sensors.

[0036] The conventional oscillating motion acceleration sensor disclosed in Patent Document 4 uses thin-film techniques, such as sputtering and vacuum deposition, which require expensive processing equipment. This is because it requires (i) conductive paths connecting a pair of oscillating torque coils to an external control circuit, and (ii) conductive paths connecting capacitance electrodes formed on the surface of oscillating pendulum 590a to an external control circuit. The multiple independent conductive paths are formed as thin films on the surfaces of thin, elastically deformable hinges 590b1 and 590b2. Figure 15 shows an enlarged view of pendulum 590a as it oscillates.

[0037] Another possible alternative is to solder multiple thin wires to the moving and fixed components, or to connect them with conductive adhesive. In this case, the spring load caused by the deformation of the wires is applied in parallel to the spring stiffness of the hinge, affecting the mechanical resonance frequency. Furthermore, the repeated stress on the wires can lead to fatigue failure and other degradation in reliability.

[0038] Therefore, in both linear motion and oscillating motion servo acceleration sensors, the conductive paths that connect the movable and fixed parts and carry multiple signals must be formed using elastic materials that connect the two. As a result, a complex structure and production method are required, which increases costs and is a major factor in reducing yield and reliability during mass production.

[0039] As an example of configuring an active vibration isolation table, let's consider four-point support active control. In this case, actuators are placed at the four corners, with two points in the horizontal X direction and two points diagonally in the Y direction. Each actuator also incorporates an actuator that supports the load in the Z direction. This means that a total of eight actuators are placed, and eight acceleration sensors are required to control each actuator. If a sensor to detect floor acceleration is included, a total of nine expensive acceleration sensors are required. Therefore, in the case of a multi-axis control active vibration isolation table, the large number of acceleration sensors required poses a serious problem in that it accounts for a high proportion of the overall cost. [Means for solving the problem]

[0040] As mentioned above, the difficulty of wiring, which is the main cause of yield reduction, is an unavoidable issue with the moving coil type (MC type) due to the movement of the coil in the moving part. This invention returns to the origin of this issue and focuses on the fact that the actuator part of a servo-type acceleration sensor forms a closed-loop magnetic circuit with three elements: a permanent magnet, a coil, and a yoke material. If the coil, one of these three elements, can be fixed, the fatal issue of the moving coil type (MC type), namely the difficulty of wiring, which is the main cause of yield reduction, can be solved in one fell swoop.

[0041] This embodiment focuses on the moving magnet (MM) type, which eliminates the need for ultra-fine wire processing because the permanent magnet moves and the coil is fixed. Conventional servo-type acceleration sensors use a moving coil (MC) type, in which the coil moves linearly or oscillates in the axial direction. In contrast, in this embodiment, the coil is fixed and the permanent magnet moves axially. However, there has never been a precedent for an MM-type servo-type acceleration sensor. This is likely due to a tacit assumption (blind spot) that the increased inertial mass of the moving part of the MM type makes it difficult to achieve high-frequency transmission characteristics and high-speed response. The present invention addresses this "blind spot" through the following innovations. Specifically, this embodiment uses (i) a magnetic circuit configuration that reduces the weight of the moving part, (ii) a magnetic pole shape that reduces the effects of leakage flux, and (iii) a coil specification that utilizes the increased coil storage volume to simultaneously increase power generation and suppress heat generation. These innovations eliminate the weaknesses of the MM type and achieve sensor performance that surpasses that of the MC type.

[0042] Thus, a servo type vibration detector according to a first aspect of the present invention comprises a fixed member, a movable member provided so as to be movable in a predetermined direction relative to the fixed member, an elastic support member supporting the movable member so as to be disposed relative to the fixed member via a gap, a displacement detection unit which detects displacement of the movable member in the predetermined direction, drive means which is driven by a servo amplifier so as to generate a force which returns the movable member to the original position when a relative displacement of the movable member from an original position is detected by the displacement detection unit, a movable side electrode provided on the movable member, and a fixed side electrode provided on the fixed member opposite to the movable side electrode, wherein the displacement detection unit is configured to detect an electrostatic capacitance formed in the gap between the movable side electrode and the fixed side electrode, and the movable member is configured to The movable member comprises a magnetized permanent magnet, a front pole piece and a ball piece including a rear pole piece portion, which are arranged so that magnetic flux flows on either side of the permanent magnet in the axial direction, and further comprises a front coil fixed to the fixed member within a gap between the outer periphery of the front pole piece portion and the inner periphery of the fixed member, and a rear coil fixed to the fixed member within a gap between the outer periphery of the rear pole piece portion and the inner periphery of the fixed member, wherein the driving means is configured to form a closed loop magnetic circuit with the permanent magnet, the front pole piece portion, the fixed member, the rear pole piece portion, and the permanent magnet, thereby generating an electromagnetic force that moves the movable member in the axial direction.

[0043] In other words, the present invention configures a driving means (actuator) for an MM type acceleration sensor by sandwiching an axially magnetized permanent magnet, attaching pole piece sections to the front and rear sides, and arranging coils on the fixed side facing each of the pole piece sections.

[0044] In terms of performance, for example, when evaluating the generated force of the actuator, the coil storage volume can be increased because two coil bobbins equivalent to those of an MC type can be installed on the outer periphery of the pole piece, which can be set to a larger outer diameter. This allows for the use of a thick wire coil and a large number of coil turns without increasing the electrical resistance that generates heat. Because the generated force is proportional to the number of coil turns, this eliminates the weakness of the MM type, which requires generated force to compensate for the increase in inertial mass.

[0045] From the viewpoint of productivity, a movable part structure using axially magnetized permanent magnets is easier to assemble during mass production than a structure using radially magnetized magnets. Furthermore, because the outer diameter of the pole piece can be increased, the disk (the aforementioned elastic support member) that supports the movable part at both ends can be stably installed. Therefore, the perpendicularity of the disk surface and the movable electrode surface relative to the axis of the sensor body can be achieved with high precision.

[0046] The servo-type vibration detector of the second invention of the present application is characterized in that, when the axis of the movable member is set as the Z axis and the X axis is set at the axial center of the permanent magnet so as to be perpendicular to the Z axis, the front pole piece portion and the rear pole piece portion, the front coil and the rear coil, and the front side and the rear side of the fixed member are configured approximately axially symmetrically with respect to the Z axis and are configured approximately mirror-symmetrically with respect to the X axis.

[0047] In other words, the present invention places a permanent magnet in the center and configures the actuator section with "axial symmetry and mirror symmetry." The outer diameters and axial lengths of the front pole piece section and the rear pole piece section are also configured symmetrically. The front and rear coils and fixed members are similarly configured symmetrically. In terms of quality, for example, when evaluating the effect of thermal expansion on the thermal deformation of components, the axial symmetry and mirror symmetry of the coil, which is the heat source, is extremely effective in countering thermal expansion. Conventional oscillation-type sensors have a pendulum structure with one end fixed, and because they have a non-mirror symmetry structure, the effect of deformation of each member due to thermal expansion on the sensor characteristics cannot be avoided.

[0048] The servo-type vibration detector of the third invention of the present application is characterized in that the winding directions of the front side coil and the rear side coil are set so that the electromagnetic forces acting on the front side coil and the rear side coil act on the movable member in the same direction.

[0049] In other words, in the present invention, independent coils are placed on the fixed side opposite the pole piece parts on the front and rear sides of the permanent magnet. M is formed in the following order: permanent magnet → front pole piece → front magnetic gap → coil side yoke material → rear magnetic gap → permanent magnet. The front coil is located in the front magnetic gap, and the rear coil is located in the rear magnetic gap. Therefore, the magnetic flux passing through each coil flows in opposite directions. If the winding direction of each coil (clockwise and counterclockwise) is set so that the electromagnetic forces acting on each coil cause the forces acting on the moving part to be in the same direction, the generated force will be the sum of the two electromagnetic forces.

[0050] A servo type vibration detector according to a fourth aspect of the present invention is characterized in that the front pole piece portion and the rear pole piece portion are made of hollow members.

[0051] That is, in the present invention, the pole piece portion that forms the magnetic path through which magnetic flux flows is configured with a hollow shape having a cross-sectional area that does not cause magnetic saturation. The magnetic flux Φ that flows through the closed loop magnetic circuit is constant, and if the cross-sectional area of ​​the magnetic path is S, then the magnetic flux density is B (= Φ / S). By setting the inner diameter of the hollow portion so that the cross-sectional area is S, at which magnetic saturation does not occur, it is possible to reduce the weight of the moving part while maintaining the same generated force.

[0052] The servo-type vibration detector of the fifth invention of the present application is characterized in that the movable side electrode is fixed to one or both ends of the front side pole piece portion or the rear side pole piece portion via a non-conductive material, and the fixed side electrode is arranged on the opposite surface of the movable side electrode.

[0053] In other words, in the present invention, the movable electrode is fixed to the end of the pole piece via a non-conductive material. By achieving complete electrical insulation from the pole piece, through which eddy currents flow, it is possible to process minute capacitance signals between the electrodes.

[0054] The servo-type vibration detector of the sixth invention of the present application is characterized in that the elastic support member also serves as a conductive path for transmitting the capacitance signal of the movable side electrode, and is fixed to the fixed member at its outer periphery via a non-conductive material.

[0055] In other words, in the present invention, the elastic support member (disk) that supports the movable member also serves as a conductive path for transmitting minute capacitance signals. Because eddy currents flow in the fixed member, the outer periphery of the elastic support member is fixed to the fixed member via a non-conductive material.

[0056] The servo-type vibration detector of the seventh invention of the present application is characterized in that the movable side electrode comprises a front movable side electrode fixed to the end of the front pole piece portion via a non-conductive material, and a rear movable side electrode fixed to the end of the rear pole piece portion via a non-conductive material, and the fixed side electrode comprises a front fixed side electrode provided on the fixed member side opposite the front movable side electrode, and a rear fixed side electrode provided on the fixed member side opposite the rear movable side electrode, and a differential sensor is constituted by detecting two capacitance differences formed between the front movable side electrode and the front fixed side electrode, and between the rear movable side electrode and the rear fixed side electrode.

[0057] With this configuration, the elastic support member can be electrically connected to the movable electrode, and both the elastic support member and the movable electrode can be electrically insulated from the pole piece portion.

[0058] The servo-type vibration detector of the eighth invention of the present application is characterized in that a plurality of grooves for accommodating the lead wires of the front coil and the rear coil are formed on the inner surface of the fixed member, and the circumferential positions of the plurality of grooves are axially symmetrical. [Effects of the Invention]

[0059] The present invention uses a thick wire coil, allowing a large number of coil turns to be set without increasing the electrical resistance that generates heat, and provides a servo-type vibration detector that is easier to assemble during mass production than a structure using a radially magnetized magnet. [Brief explanation of the drawings]

[0060] [Figure 1] FIG. 1 is a front cross-sectional view of a servo-type acceleration sensor according to a first embodiment of the present invention. [Figure 2] FIG. 10 is an external view showing the rear disc and support member configured in a spiral shape. [Figure 3] FIG. 2 is an exploded view showing the component configuration of the sensor according to the embodiment. [Figure 4] Model diagram of the actuator part of the MM type sensor. [Figure 5] Numerical analysis results of MM type sensor. [Figure 6] A model diagram of the actuator part of a conventional MC type sensor. [Figure 7] Numerical analysis results for conventional MC type sensors. [Figure 8] 8A and 8B show a differential servo type acceleration sensor according to a second embodiment of the present invention, in which FIG. 8A is a front cross-sectional view, and FIG. 8B is a view taken along the line AA in FIG. 8A. [Figure 9] A model diagram of a conventional active vibration isolation table. [Figure 10] A model diagram showing the basic configuration and detection principle of a conventional capacitive acceleration sensor. [Figure 11] FIG. 10 is a front cross-sectional view showing a specific structural example of a conventional linear motion acceleration sensor. [Figure 12]In a conventional linear motion acceleration sensor, Figure 12(a) is a front view showing the shape of the front-side disk-shaped spring, Figure 12(b) is a front cross-sectional view with the front-side panel 26, fixed-side electrode 25, etc. removed from Figure 11, and Figure 12(c) is an enlarged view of part A in Figure 12(b). [Figure 13] FIG. 10 is a front cross-sectional view showing an example of a conventional swing motion type acceleration sensor. [Figure 14] 14A and 14B are plan views of the pendulum of the swing-motion acceleration sensor, where FIG. 14A shows one side of the pendulum and FIG. 14B shows the other side. [Figure 15] FIG. 2 is an enlarged view showing a state in which a pendulum of the swinging motion type acceleration sensor swings; DETAILED DESCRIPTION OF THE INVENTION

[0061] [First embodiment] Axially magnetized permanent magnet FIG. 1 is a front cross-sectional view of a servo-type acceleration sensor according to a first embodiment of the present invention. FIG. 2 is an external view showing the spiral-shaped rear disk and support member, and FIG. 3 is an exploded view showing the component configuration of the sensor according to this embodiment. The chain line AA in FIG. 1 indicates a moving magnet type (MM type) actuator that drives the movable part in the axial direction. The chain line BB indicates a displacement detection part that detects electrostatic capacitance. The inventors have already filed a patent application for an MM-type servo-type acceleration sensor. This embodiment proposes a new MM-type sensor structure that was not disclosed in the previously filed application. The specific structure will be explained below, dividing it into the actuator part and the displacement detection part.

[0062] [1] Sensor structure of this embodiment [1-1] Actuator section Reference numeral 801 denotes an axially magnetized permanent magnet, 802a denotes a front pole piece, 802b denotes a rear pole piece, 803 denotes a coil-side yoke material (fixed member), 804 denotes a coil bobbin, 805 denotes a fastening bolt connecting the coil bobbin and the coil-side yoke material, 806a denotes a front coil, and 806b denotes a rear coil. The winding direction of each coil is set so that the Lorentz forces acting on the front coil and the rear coil are in the same direction. Reference numerals 807a and 807b denote gaps formed in the centers of the front and rear pole piece portions 802a and 802b.

[0063] The front pole piece and rear pole piece are configured with a stepped hollow shape to reduce the weight of the moving parts. The magnetic flux Φ flowing through the closed loop magnetic circuit is constant, and if the cross-sectional area of ​​the magnetic path is S, then the magnetic flux density is B (= Φ / S). The magnetic flux Φ and magnetic flux density decrease with increasing distance from the permanent magnet, so the thickness of the sleeve near the open end of the pole piece is made thin within the range of the cross-sectional area where magnetic saturation does not occur.

[0064] 808a is a front-side magnetic gap, and 808b is a rear-side magnetic gap, each of which indicates a radial gap between the two pole piece parts and the coil-side yoke material. A closed loop magnetic circuit B is formed by "permanent magnet 801 → front-side pole piece part 802a → front-side magnetic gap 808a → coil-side yoke material (fixed member) 803 → rear-side magnetic gap 808b → permanent magnet 801". MThe pole piece portion 802a is formed with a front inner peripheral support member 809a and a rear inner peripheral support member 809b. The front and rear inner peripheral support members are made of a non-conductive material. The front inner peripheral support member and the rear inner peripheral support member are pre-adhesively fixed to the pole piece portions 802a and 802b. 810a is a front disk, 810b is a rear disk, and 811 is a movable electrode. 812 is a screw fastening portion formed between the inner peripheral side of the front inner peripheral support member 809a and the movable electrode 811. The inner peripheral side of the front disk 810a is clamped between the front inner peripheral support member 809a and the movable electrode 811 by screw fastening. 813 is a rear fastener, and 814 is a screw fastening portion formed between the inner peripheral side of the rear inner peripheral support member 809b and the rear fastener. The inner periphery of the rear disc 810b is clamped between the rear inner periphery support member and the rear fastener by screw fastening, similar to the front disc.

[0065] As shown in section AA of Figure 3, the outer periphery of front-side disc 810a is secured to coil-side yoke material 803 by bolts 817 with insulating sheets 815a and 815b sandwiched between them and washer 816. The outer periphery of rear-side disc 810b is secured to coil-side yoke material 803 by bolts 819 with washers 818a and 818b sandwiched between them. When considering conversion to a differential type, which will be described later, the outer periphery of rear-side disc 810b can be secured using the insulating sheet (not shown) in the same way as the front side, in order to ensure compatibility of the sensor body.

[0066] The movable part of this embodiment is primarily composed of a permanent magnet 801, pole pieces 802a and 802b, a movable electrode 811, and a rear fastener 813. The fixed part is composed of a coil bobbin 804 housing each coil and a coil-side yoke material 803. In this acceleration sensor, the movable part's driving mechanism uses an improved structure of a previously proposed moving magnet type. As is well known, when a current flows through a conductor placed in a magnetic field, a Lorentz force, an electromagnetic force, is generated. In all actuators, regardless of the driving principle, the force relationship between the fixed side and the movable side is relative. In other words, if either the fixed side or the movable side is fixed, the other side moves. In this embodiment, when a current flows through force coils 806a and 806b housed in the coil bobbin 804, a Lorentz force reaction is generated, moving the movable part axially.

[0067] 2 shows an external view of the rear disc and support member configured in a spiral shape used in this embodiment. The front disc is similar.

[0068] [1-2] Displacement detection unit In the displacement detection section (dash line BB) in Figure 1, 820 is a fixed electrode, 821 is an insulating ring, 822 is a fixed ring, and 823 is a central through-hole formed in the center of the fixed electrode. The fixed electrode 820 is clamped against the fixed ring with the insulating ring interposed therebetween. 824 is a positioning bolt for the fixed electrode, and 825 is a tapered portion (described below) formed at the boundary between the coil side yoke member 803 and the fixed ring. After setting the inter-electrode gap between the fixed electrode 820 and the movable electrode 811, the positioning bolt 824 fixes the fixed ring 822 to the coil side yoke member 803.

[0069] [2] Assembling the sensor body [2-1] Unit configuration 3 is a diagram showing the component configuration of the sensor of this embodiment. The acceleration sensor of this embodiment is based on the following units, which are made up of multiple components, and is configured by fastening individual components to these units with bolts. (i) Fixed electrode side unit 851: Consists of a fixed electrode 820, an insulating ring 821, and a fixed ring 822 (ii) Movable member unit 852: Comprised of a front pole piece portion 802a, a front inner peripheral support member 809a, a permanent magnet 801, a rear pole piece portion 802b, and a rear inner peripheral support member 809b (iii) Coil unit 853: Comprised of a coil bobbin 804, a front force coil 806a, and a rear force coil 806b. The fixed electrode side unit 851 and the movable member unit 852 are constructed by previously fixing a plurality of parts together with an adhesive.

[0070] [2-2] Bolt fastening of unit and individual parts Once each unit is assembled, the bolts are fastened between each unit and the individual components. Coil unit 853 is inserted into the center of coil side yoke material (fixing member) 803 and fixed at multiple points in the circumferential direction with fastening bolts 805.

[0071] The left end of the movable member unit 852 is fixed with screws to the front-side inner peripheral support member 809a, with the front-side disk 810a sandwiched between them. The outer periphery of the front-side disk 810a is fastened with screws to the coil-side yoke material 803, with the insulating sheets 815a, 815b sandwiched between them on the front and back to ensure electrical insulation between the coil-side yoke material 803 and the disk. Fastening the movable member unit 852 with screws ensures that the perpendicularity of the electrode surface of the movable-side electrode 811 and the front-side disk 810a relative to the axis of the movable member unit is highly accurate, compared to conventional MC-type adhesive construction methods that are prone to uneven thickness.

[0072] Similarly, the right end of the movable electrode side unit 852 is screwed together with the rear side fastener 813 while holding the rear side disk 810b. Because there is no need to ensure electrical insulation between the coil side yoke material 803 and the disk, the outer periphery of the rear side disk 810b is fixed to the coil side yoke material 803 with the metal washers 818a and 818b sandwiched between them. However, to ensure compatibility with the differential type (second embodiment) described below, the insulating sheets 815a and 815b may be used instead of the metal washers 818.

[0073] [2-3] Fix the fixed electrode with screws After the actuator assembly is completed in step [2-2] above, the inter-electrode gap of the displacement detection unit is set. The absolute value of the inter-electrode gap and the inclination angle of the gap are measured by optically measuring the slit (gap) between the electrodes from the outer surfaces of the two electrodes using a high-magnification camera or other optical means. While holding the fixed electrode side unit 851, a jig capable of fine-tuning the axial position and angle of the fixed electrode 820 is used to screw the fixing ring 822 into place with the positioning bolts 824 so that the specified inter-electrode gap is achieved.

[0074] As an alternative to the above method, the present inventors have proposed in a separate application the following inter-electrode gap adjustment method that utilizes the structural features of the MM type. That is, by utilizing the MM type's open-end shaft structure, the movable member unit 852 is fixed from both ends using jigs. In this state, a gap adjustment sheet is inserted into the inter-electrode gap. Then, while keeping the fixed electrode 820 pressed against the movable electrode 811, the fixed electrode is fixed with positioning bolts 824 (the above construction method is not shown). In either method, the sensor structure of the present invention enables inter-electrode gap adjustment without the use of adhesive and assembly of the sensor body by bolt fastening.

[0075] [3] Quality evaluation of the sensor body Once the above process is complete, the product is ready for basic performance evaluation or reliability evaluation, etc. If a defect is found in the product during the above evaluation stage, the basic cycle of "disassembling the sensor body → investigating the cause → taking measures → reassembling → reevaluation" can be repeated.

[0076] As shown in the disassembly diagram of the sensor of this embodiment in Figure 3, the fixed electrode side unit 851 is not the only part that can be disassembled from the sensor of this embodiment. The sensor body can be disassembled into the above-mentioned units that are made up of multiple parts, as well as into individual components. Quality defects in the finished product can be detected by inspecting the following items for each unit and individual component after disassembly.

[0077] For example, detailed inspections can be carried out to check for dust particles floating in the narrow gap between the electrodes, the precision of part processing, the basic specifications of each part (the rigidity of the front and rear disks, the magnetization characteristics of the permanent magnet), the precision of assembly (gaps in the magnetic circuit, etc.), and the electrical insulation characteristics (the insulating support members 815, 816 of the front disk, etc.). As a result, the cause of the defect can be quickly identified, and each part can be reprocessed and reused. With conventional servo-type acceleration sensors, it is not easy to determine the cause of a defect, not just the electrode gap adjustment process. In many cases, the product itself must be discarded.

[0078] In the acceleration sensor of the present invention, if it is confirmed after quality evaluation that the mass production specifications are completely satisfied, adhesive may be used to prevent the fastening bolts at each screw fastening point in order to ensure even longer-term reliability. For example, at the joint between fixing ring 822 and coil side yoke material 803, which are fastened with bolts to provide a predetermined inter-electrode gap, tapered portion 825 (chain circle in FIG. 1) may be provided separately to apply adhesive to both members. In this case, fastening bolt 824 may be removed at the final stage.

[0079] [4] Numerical magnetic field analysis [4-1] Analysis results Below, we will show the results of determining the magnetic flux density distribution in the actuator section of the MM-type sensor of this embodiment, in comparison with the conventional MC-type sensor. Fig. 4 is a model diagram of the actuator section of the MM-type sensor, Fig. 5 is the numerical analysis result of the MM-type sensor, Fig. 6 is a model diagram of the actuator section of the conventional MC-type sensor, and Fig. 7 is the numerical analysis result of the conventional MC-type sensor. The numerical analysis results of the MM-type sensor show that the magnetic flux density distribution is axially symmetrical and mirror-symmetrical, and that the magnitude of the magnetic flux density decreases the further away from the permanent magnet. The generated force (Lorentz force) can be determined from the number of turns and current value of the coil placed in the magnetic field.

[0080] [Table 1]

[0081] The analysis conditions were: MM type: coil wire diameter Φ0.05 mm, coil winding number 2400 turns (equivalent to two coils), neodymium permanent magnet; MM type: coil wire diameter Φ0.03 mm, coil winding number 1000 turns, samarium cobalt permanent magnet.

[0082] [4-2] Generated force and electrical resistance The mass of the moving part of the MM type is 2.29 times that of the MC type, but the generated force is even greater at 2.77 times. This means that the weakness of the MM type, which is that the moving part mass is larger compared to the MC type, is eliminated. Also, the number of coil turns in the MM type is 2.4 times that of the MC type, but by utilizing the structural feature that allows for a large coil storage volume, the increase in coil electrical resistance is suppressed. In other words, by making the coil wire diameter larger and the coil cross-sectional area 2.78 times larger than that of the MC type, the MM type suppresses the increase in coil electrical resistance R, which leads to heat generation.

[0083] [5] Features of this embodiment [5-1] Overview of the basic structure In this embodiment, pole pieces are arranged on the front and rear sides so as to sandwich an axially magnetized permanent magnet, and coils are installed on the fixed side opposite each of the pole pieces, thereby configuring a driving means (actuator) for an MM type acceleration sensor. In other words, this is an "axially symmetrical and mirror-symmetrical" actuator structure with a permanent magnet installed in the center.

[0084] [5-2] Features of this embodiment 1. Performance effects For example, when evaluating the generated force of an actuator, the coil storage volume can be increased because two MC coil bobbins can be installed on the outer periphery of the pole piece, which can be set to a larger outer diameter. This allows for a large number of coil turns to be set without increasing the electrical resistance that generates heat by using a thick wire coil. Because the generated force is proportional to the number of coil turns, this eliminates the weakness of the MM type, which requires generated force to compensate for the increase in inertial mass.

[0085] Since the outer diameter of the pole piece can be made the same as the outer diameter of the permanent magnet, it can be made larger than in actuator structures that are magnetized in the radial direction.In order to reduce the weight of the moving part, the pole piece is made hollow, and even if its thickness is made sufficiently thin, a sufficient magnetic path area can be set, making it less likely to cause magnetic saturation.

[0086] Furthermore, because the magnetic flux flowing in the axial direction of the moving part becomes smaller the further away from the permanent magnet, as shown in Figure 1, by making the thickness of the hollow pole piece thinner toward the ends, the weight of the moving part can be further reduced without causing magnetic saturation. The permanent magnet may have a through-hole structure (not shown). In addition, since the outer diameter of both ends of the pole piece can be increased, the moving part can be supported with high rigidity at the center. There is no need to cut the disk as in conventional MC types, and the effective support length in the radial direction of the disk can be made longer. Therefore, the moving part can be supported dynamically and stably.

[0087] 2. Productivity improvement effect From the viewpoint of productivity, a moving part using an axially magnetized permanent magnet is easier to assemble during mass production than a radially magnetized magnet. Furthermore, because the outer diameter of the pole piece can be increased, the disk (the aforementioned elastic support member) that supports the moving part at both ends can be installed stably. Therefore, the perpendicularity of the disk surface and the moving electrode surface relative to the axis of the sensor body can be achieved with high precision.

[0088] Furthermore, the sensor of this embodiment can be assembled using an adhesive-free method based on bolt fastening, both for units made up of multiple parts and for individual components. If a defect is found in a product during the performance evaluation stage, the basic cycle of "disassembling the sensor body → investigating the cause → taking measures → reassembling → reevaluation" can be quickly implemented. This allows for a significant improvement in production yield compared to the conventional MC method.

[0089] 3. Quality benefits In terms of quality, for example, when evaluating the impact of thermal expansion on the thermal deformation of components, the axially symmetrical and mirror-symmetrical structure of the coil, which is the heat source, is extremely effective in countering thermal expansion. A comparison of the numerical analysis results for the MM type of this embodiment shown in Figure 5 and the conventional MC type shown in Figure 7 reveals that the MM type actuator of this embodiment has a completely mirror-symmetrical magnetic flux density distribution. Furthermore, in the case of the MM type of this embodiment, the coils arranged symmetrically on the left and right also serve as heat sources, so the heat distribution also becomes mirror-symmetrical. The conventional oscillating type sensor (Figure 13) has a pendulum structure with one end fixed, and because it is a non-mirror-symmetrical structure, it is unavoidable that deformation of each component due to thermal expansion will have an effect on the sensor characteristics. The conventional MC type (Figure 11) has an axially symmetrical structure, but not a mirror-symmetrical structure.

[0090] [Second embodiment] The present invention is applied to a differential type 8A and 8B show a differential servo type acceleration sensor according to a second embodiment of the present invention, in which FIG. 8A is a front cross-sectional view, and FIG. 8B is a view taken along the line AA in FIG. 8A.

[0091] [1] Conversion to a differential sensor In this embodiment, taking note of the structural characteristics of the linear MM type, in which both left and right output shafts are open ends, a differential capacitance sensor is constructed by providing electrodes for detecting capacitance in two locations, left and right. By making the acceleration sensor differential, a high-resolution sensor can be realized in which the sensor output is less susceptible to the influence of disturbance signals such as noise and drift. The reason that high resolution can be achieved with a differential type is that disturbance signals such as noise and drift are canceled out by taking the difference between two main signals with a phase difference of 180 degrees.

[0092] In Figure 8(b), the portion indicated by imaginary line B is the portion that will be added to the sensor of the first embodiment. Converting the sensor of the first embodiment to a differential type (version up) is easy. First, remove the rear-side fastener 813 (Figure 1) from the sensor of the first embodiment and attach the movable-side electrode 811R instead. Next, after a gap adjustment process between the electrodes, the fixed electrode R-side unit 851R can be fixed with a positioning bolt 824R. The fixed electrode R-side unit is composed of a fixed-side electrode 820a, an insulating ring 821R, and a fixed ring 822R.

[0093] [2] Axisymmetric and mirror symmetric structures By using a differential sensor, the entire sensor, including the actuator and displacement detection units, can be made axially symmetrical and mirror-symmetrical. In this embodiment, the grooves formed in the fixing member and the fastening bolts are equally spaced in the circumferential direction, achieving a perfect axially symmetrical structure. Each component of the sensor body is made of materials with different thermal expansion coefficients. For example, if the acceleration sensor is installed in an ambient temperature higher than room temperature, the sensor body will thermally deform three-dimensionally due to the differences in the thermal expansion coefficients of the components. In this sensor, even if the inter-electrode gap changes due to thermal deformation, the distribution of the change in the inter-electrode gap between the left and right electrodes is the same due to the axially symmetrical and mirror-symmetrical structure. Therefore, the sensor output is not affected by thermal deformation of the components. As mentioned above, the housing of a conventional oscillating acceleration sensor (Figure 13) is made of Invar alloy, a low-thermal expansion material. However, Invar alloy is difficult to process, posing significant challenges in terms of productivity and cost. The sensor of the present invention takes advantage of the characteristics of the MM type and avoids the effects of thermal expansion through ingenuity in the sensor structure, so there are no major restrictions on the type of magnetic material, allowing for significant cost reductions.

[0094] FIG. 8(b) is a view taken along the line AA in FIG. 8(a), in which 805a, 805b, and 805c denote fastening bolts that secure the coil bobbin 804 to the coil-side yoke member (fixing member) 803. 826a, 826b, and 826c denote grooves formed in the axial direction on the inner peripheral surface of the coil-side yoke member 803. 827a, 827b, and 827c denote radial through-holes formed in the coil-side yoke member and having openings in the grooves. In FIG. 8(b), 828 denotes lead wires for the front-side force coil 806a and the rear-side force coil 806b. Lead wires 828 are arranged axially along groove 826a and are led to the outside via radial through-hole 827a.

[0095] In this embodiment, the three grooves and through-holes formed on the inner surface of the coil-side yoke member (fixed member) 803 are divided into three equal parts at 120-degree intervals in the circumferential direction. The same applies to the fastening bolts that secure the coil bobbin. The reason for dividing them into three equal parts in the circumferential direction is to maintain an axisymmetric structure. Only one groove 826a and one through-hole 827a may be used as the lead wires of the force coil (including the calibration coil). Signal wires from the movable electrode for detecting inter-electrode capacitance may use other grooves (not shown). The presence or absence of coil lead wires and electrode signal wires does not affect deformation of the components due to thermal expansion. There are no restrictions on the number of grooves and through-holes; even if unused, they may be arranged axially symmetrically. The effect of forming the grooves and through-holes axially symmetrically according to the present invention is not limited to differential sensors. Furthermore, a mirror-symmetric structure is not required; an axisymmetric structure sensor can reduce the impact of deformation of the components due to thermal expansion. [Explanation of symbols]

[0096] 801 Permanent Magnets 802a Front piece 802b Rear piece 803 Fixing member 806a Front coil 806b Rear coil 810a, 810b Elastic support members 811 Movable side electrode 820 Fixed side electrode

Claims

1. A fixing member; a movable member provided so as to be movable in a predetermined direction relative to the fixed member; an elastic support member that supports the movable member so that the movable member is disposed relative to the fixed member via a gap; a displacement detection unit that detects a displacement of the movable member in a predetermined direction; When the displacement detection unit detects a relative displacement of the movable member from an origin position, a driving means driven by a servo amplifier to generate a force that returns the movable member to its original position; a movable-side electrode provided on the movable member; a fixed-side electrode provided on the fixed member side to face the movable-side electrode, the displacement detection unit is configured to detect electrostatic capacitance formed in a gap between the movable electrode and the fixed electrode, The movable member is a permanent magnet magnetized in the axial direction; a ball piece including a front pole piece portion and a rear pole piece portion, each of which is arranged so that magnetic flux flows across the permanent magnet in the axial direction; a front coil fixed to the fixed member within a gap between the outer periphery of the front pole piece portion and the inner periphery of the fixed member; a rear-side coil fixed to the fixed member within a gap between the outer circumferential side of the rear-side pole piece portion and the inner circumferential side of the fixed member, A servo-type vibration detector characterized in that the driving means is configured to generate an electromagnetic force that moves the movable member in the axial direction by forming a closed loop magnetic circuit with the permanent magnet, the front pole piece portion, the fixed member, the rear pole piece portion, and the permanent magnet.

2. When the axis of the movable member is set as a Z axis and the X axis perpendicular to the Z axis is set at the axial center of the permanent magnet, 2. The servo-type vibration detector according to claim 1, characterized in that the front pole piece portion and the rear pole piece portion, the front coil and the rear coil, and the front side and the rear side of the fixing member are configured approximately axially symmetrically with respect to the Z axis and are configured approximately mirror-symmetrically with respect to the X axis.

3. A servo-type vibration detector as described in claim 1, characterized in that the winding directions of the front side coil and the rear side coil are set so that the electromagnetic forces acting on the front side coil and the rear side coil act on the movable member in the same direction.

4. 2. The servo type vibration detector according to claim 1, wherein the front pole piece portion and the rear pole piece portion are formed of hollow members.

5. the movable electrode is fixed to one or both ends of the front pole piece portion or the rear pole piece portion via a non-conductive material, 2. A servo type vibration detector according to claim 1, wherein the fixed electrode is disposed on a surface opposite to the movable electrode.

6. A servo-type vibration detector as described in claim 1, characterized in that the elastic support member also serves as a conductive path for transmitting the capacitance signal of the movable side electrode, and is fixed to the fixed member at its outer periphery via a non-conductive material.

7. The movable electrode is a front-side movable electrode fixed to an end of the front-side pole piece portion via a non-conductive material; a rear movable electrode fixed to an end of the rear pole piece portion via a non-conductive material, The fixed electrode is a front fixed electrode provided on the fixed member side and facing the front movable electrode; a rear fixed electrode provided on the fixed member side opposite the rear movable electrode, 2. The servo-type vibration detector according to claim 1, characterized in that a differential sensor is constructed by detecting two capacitance differences formed between the front movable electrode and the front fixed electrode, and between the rear movable electrode and the rear fixed electrode.

8. A servo-type vibration detector as described in claim 1, characterized in that a plurality of grooves for accommodating the lead wires of the front coil and the rear coil are formed on the inner surface of the fixed member, and the circumferential positions of the plurality of grooves are axially symmetrical.

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