Magnetic bearing device and turbomolecular pump

Abstract

This suppresses the influence of motor noise on the sensor. [Solution] A magnetic bearing device comprising a rotating body, a motor with an even number of poles that is not a multiple of 4, a radial electromagnet, a radial displacement sensor, a first oscillator, a second oscillator, and a demodulation circuit, wherein the radial displacement sensor has a first sensor pole pair and a second sensor pole pair, and each coil of the sensor pole pair is wired so that the polarity of each pole is different, one end of the first sensor pole pair is connected to one end of the second sensor pole pair such that pairs of sensor poles that are radially opposite to each other are opposite poles, the other end of the first sensor pole pair is connected to the first oscillator, the other end of the second sensor pole pair is connected to the second oscillator, and the midpoint voltage of the two sensor pole pairs is input to the demodulation circuit.

Description

[Technical Field]

[0001] The present invention relates to a magnetic bearing device and a turbomolecular pump. [Background technology]

[0002] As background technology for this field, there is Japanese Patent Publication No. 2000-240649 (Patent Document 1). This publication discloses a magnetic bearing device comprising a motor for driving a rotating shaft, two pairs of electromagnets arranged opposite each other on either side of the rotating shaft, two pairs of displacement sensors arranged opposite each other in the vicinity of the electromagnets, and two pairs of opposing electromagnets and two pairs of opposing displacement sensors arranged opposite each other in the vicinity of the electromagnets (see Figure 5). [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2000-240649 [Overview of the Initiative] [Problems that the invention aims to solve]

[0004] In the configuration described in Patent Document 1, the displacement sensor was sometimes affected by noise from the motor. Therefore, the present invention aims to provide a configuration in which a displacement sensor suppresses the influence of noise from the motor. [Means for solving the problem]

[0005] To solve the above problems, for example, the configuration described in the claims may be adopted. This application includes several means for solving the above-mentioned problems, but one example is: A magnetic bearing device, Rotating body and The aforementioned rotating body is driven by a motor with an even number of poles that is not a multiple of 4, The rotating body is provided with one or more radial electromagnets that generate a radial electromagnetic force, A radial displacement sensor for measuring the radial displacement of the rotating body, A first oscillator that outputs an AC voltage as a modulated input signal to the radial displacement sensor, A second oscillator that outputs an AC voltage in the opposite phase to the first oscillator, The system includes a demodulation circuit that demodulates the output signal from the radial displacement sensor, The radial displacement sensor is, A first sensor pole pair consisting of two sensor poles arranged side by side in the axial direction along the rotation axis of the rotating body, It comprises a first pair of sensor poles and a second pair of sensor poles consisting of two sensor poles that are radially opposite to each other and arranged side by side in the axial direction, The coils of the first sensor pole pair and the second sensor pole pair are wired such that the polarity of each pole is different. One end of the first sensor pole pair is connected to one end of the second sensor pole pair such that, among the sensor poles of the first sensor pole pair and the second sensor pole pair, pairs of sensor poles that are radially opposite to each other are opposite poles. The other end of the first sensor pole pair is connected to the first oscillator. The other end of the second sensor pole pair is connected to the second oscillator. The voltage at the connection point between the first sensor pole pair and the second sensor pole pair is input to the demodulation circuit. [Effects of the Invention]

[0006] According to the present invention, the influence of noise from the motor on the sensor can be suppressed. Other issues, configurations, and effects not mentioned above will be clarified by the following description of the embodiments. [Brief explanation of the drawing]

[0007] [Figure 1] Figure 1 is a longitudinal cross-sectional view of an example of a turbomolecular pump. [Figure 2]Figure 2 is a perspective view showing an example of an upper electromagnet unit according to the first embodiment. [Figure 3] Figure 3 is a longitudinal cross-sectional view of an example of an upper electromagnet unit. [Figure 4] Figure 4A is a cross-sectional view along line DD in Figure 3, and Figure 4B is a cross-sectional view along line EE in Figure 3. [Figure 5] Figure 5 shows an example of a sensor circuit according to the first embodiment. [Figure 6] Figure 6 shows an example of a theoretically calculated sensor circuit model according to the first embodiment. [Figure 7] Figure 7 is a longitudinal cross-sectional view of an example of a modified upper electromagnet unit according to the first embodiment. [Figure 8] Figure 8A is a cross-sectional view along the FF line in Figure 7, and Figure 8B is a cross-sectional view along the GG line in Figure 7. [Figure 9] Figure 9 shows an example of the configuration of a sensor circuit according to the second embodiment. [Figure 10] Figure 10 shows an example of a theoretically calculated sensor circuit model according to the second embodiment. [Figure 11] Figure 11 shows an example of a sensor circuit according to Example 1. [Figure 12] Figure 12 shows an example of a sensor circuit according to Example 2. [Figure 13] Figure 13 shows an example of a sensor circuit according to Example 3. [Figure 14] Figure 14 shows an example of a sensor circuit according to Example 4. [Figure 15] Figure 15 shows an example of an amplifier circuit for controlling the rotor shaft of a turbomolecular pump. [Figure 16] Figure 16 shows an example of a timing chart illustrating control when the current command value is greater than the detected value. [Figure 17] Figure 17 shows an example of a timing chart illustrating control when the current command value is smaller than the detected value. [Modes for carrying out the invention]

[0008] <First Embodiment> The turbomolecular pump 1 according to the first embodiment will be described below with reference to the drawings. Some drawings show axes, and each axis is drawn in a direction common to all drawings. However, these directions are merely for the convenience of explanation and do not limit the installation configuration of the turbomolecular pump 1 in any way. In addition, the same component may be labeled with a reference numeral in one drawing and omitted in another drawing.

[0009] (1) Basic structure of a turbomolecular pump Figure 1 shows the basic configuration of a turbomolecular pump 1, which is an example of a vacuum pump. The turbomolecular pump 1 generally comprises a pump body 100 and a control device 200. In this turbomolecular pump 1, the upper part of Figure 1 is the upstream (intake) side, and the intake port 11 is connected to a vacuum chamber (not shown) of, for example, a target device such as semiconductor manufacturing equipment. The lower part of the turbomolecular pump 1 is the downstream (exhaust) side, and the exhaust port 51 is connected to an auxiliary pump (not shown), for example. In addition to the vertical orientation shown in Figure 1, the turbomolecular pump 1 can also be used in an inverted vertical orientation, a horizontal orientation, or an inclined orientation.

[0010] The turbomolecular pump 1 comprises a housing 10, a rotor 20 having a rotor shaft 21 (rotating body) rotatably supported within the housing 10, a motor 30 that rotates the rotor shaft 21, and a stator column 40 that houses a part of the rotor shaft 21 and the motor 30.

[0011] The turbomolecular pump 1 is equipped with a rotor 20 inside a housing 10, which has multiple rotating blades 22, which are turbine blades for drawing in and exhausting gas, arranged radially and in multiple stages around its circumference. A rotor shaft 21 is attached to the center of the rotor 20, and this rotor shaft 21 is suspended in the air and its position is controlled by, for example, a 5-axis controlled magnetic bearing. The rotor 20 is generally made of a metal such as aluminum or an aluminum alloy.

[0012] The housing 10 is formed in a cylindrical shape. An air intake port 11 is formed at the upper end of the housing 10. The housing 10 is attached to a vacuum container such as a chamber of a semiconductor manufacturing apparatus (not shown) via an upper flange 12. The air intake port 11 is connected to the vacuum container. The housing 10 is fixed to the base 50 in a state where it is placed on the base 50.

[0013] The rotor 20 comprises a rotor shaft 21 and rotor blades 22 fixed to the upper part of the rotor shaft 21 and arranged concentrically with respect to the axis of the rotor shaft 21. In this embodiment, five stages of rotor blades 22 are provided. Hereinafter, the axial direction of the rotor shaft 21 will be referred to as the "axial direction," and the radial direction of the rotor shaft 21 will be referred to as the "radial direction." Note that the radial direction and radial direction are synonymous.

[0014] The rotor shaft 21 is non-contact supported by a magnetic bearing device 60 (described later) and an axial magnetic bearing 70. The rotor shaft 21 is made of a high-permeability material (iron, stainless steel, etc.) and is attracted and non-contact supported by the magnetic force of the radial electromagnet 63 of the axial magnetic bearing 70. The radial electromagnet 63 generates a radial electromagnetic force on the rotor shaft 21.

[0015] The magnetic bearing device 60 includes an upper electromagnet unit 61 and a lower electromagnet unit 62, each having a radial displacement sensor 64 inside. The radial displacement sensor 64 measures the radial displacement of the rotor shaft 21.

[0016] The control device 200, for example, has a compensation circuit with PID adjustment functionality that generates an excitation control command signal for the radial electromagnet 63 based on the position signal detected by the radial displacement sensor 64. The amplifier circuit 150 then controls the excitation of the radial electromagnet 63 based on this excitation control command signal, thereby adjusting the radial position of the rotor shaft 21.

[0017] The axial magnetic bearing 70 is equipped with an axial electromagnet 71. The axial magnetic bearing 70 is connected to a control device 200. The control device 200 controls the excitation current of the axial electromagnet 71 based on the detection value of the axial displacement sensor 72, thereby supporting the rotor shaft 21 in a levitated state. The axial electromagnet 71 is positioned above and below a disc-shaped metal disk located at the bottom of the rotor shaft 21. The metal disk is made of a high-permeability material such as iron. An axial displacement sensor 72 is provided to detect the axial displacement of the rotor shaft 21, and its axial position signal is sent to the control device 200.

[0018] Then, in the control device 200, a compensation circuit having, for example, a PID adjustment function generates excitation control command signals for each of the axial electromagnets 71 based on the axial position signal detected by the axial displacement sensor 72. The amplifier circuit 150 then excites each of the axial electromagnets 71 based on these excitation control command signals. As a result, the axial electromagnets 71 attract the metal disk upward and downward with magnetic force, adjusting the axial position of the rotor shaft 21.

[0019] In this way, the control device 200 appropriately adjusts the magnetic force exerted by the axial electromagnet 71 on the rotor shaft 21, causing the rotor shaft 21 to magnetically levitate in the axial direction and be held in contact with space. The amplifier circuit 150 that excites and controls these radial electromagnets 63 and axial electromagnets 71 will be described later.

[0020] The rotor blades 22 consist of blades inclined at a predetermined angle and are integrally formed on the upper outer surface of the rotor 20. Multiple rotor blades 22 are also arranged radially around the axis of the rotor 20.

[0021] The upper and lower parts of the rotor shaft 21 are inserted into the touchdown bearing 23. If the rotor shaft 21 becomes uncontrollable, the high-speed rotating rotor shaft 21 will come into contact with the touchdown bearing 23 to prevent damage to the turbomolecular pump 1.

[0022] The rotor 20 is integrally attached to the rotor shaft 21 by inserting the upper part of the rotor shaft 21 through the boss hole 24, and then inserting a bolt 25 through the rotor flange 26 and screwing it into the shaft flange 27.

[0023] The motor 30 comprises a rotor 31 attached to the outer circumference of the rotor shaft 21, and a stator 32 arranged to surround the rotor 31. The stator 32 is connected to a control device 200, which controls the rotation of the rotor 20.

[0024] The motor 30 is equipped with multiple magnetic poles arranged circumferentially around the rotor shaft 21. Each magnetic pole is controlled by the control device 200 to rotate the rotor shaft 21 via an electromagnetic force acting between it and the rotor shaft 21. In this embodiment, the motor 30 has two poles. Therefore, the polarity of the magnetic flux of the motor 30 is reversed with respect to radial reversal (180-degree rotation in the circumferential direction). In this embodiment, since the focus is on the polarity of the magnetic flux of the motor 30 with respect to radial reversal (180-degree rotation in the circumferential direction), the same effect can be obtained with any number of poles that is an even number and not a multiple of 4, such as 6 or 10. In addition, the motor 30 incorporates a rotational speed sensor, such as a Hall element, resolver, or encoder (not shown), and the rotational speed of the rotor shaft 21 is detected by the detection signal of this rotational speed sensor.

[0025] Furthermore, for example, a phase sensor (not shown) is mounted near the radial displacement sensor 64 to detect the phase of rotation of the rotor shaft 21. The control device 200 uses both the detection signals from this phase sensor and the rotational speed sensor to detect the position of the magnetic pole.

[0026] The stator column 40 is mounted on the base 50 and fixed to the base 50 via bolts 41.

[0027] Multiple fixed blades 80 are arranged with a small gap between them and the rotor blades 22. Each rotor blade 22 is formed at a predetermined angle from a plane perpendicular to the axis of the rotor shaft 21 in order to transport exhaust gas molecules downward by collision. The fixed blades 80 are made of metals such as aluminum, iron, stainless steel, copper, or alloys containing these metals as components. The rotor blades 22 and fixed blades 80 are arranged alternately in multiple stages along the axial direction. In this embodiment, five stages of fixed blades 80 are provided.

[0028] The fixed wing 80 is formed in an annular shape and comprises blades inclined in the opposite direction to the rotor blade 22 and rings connected to both ends of the blades. It is positioned by being sandwiched in the axial direction by spacers 81 which are stacked on the inner surface of the housing 10. Multiple blades of the fixed wing 80 are also arranged radially around the axis of the rotor 20. The lengths of the blades of the rotor blade 22 and the fixed wing 80 are set to gradually decrease from the top to the bottom in the axial direction.

[0029] The spacer 81 is a ring-shaped component and is made of a metal such as aluminum, iron, stainless steel, or copper, or an alloy containing these metals as components. The outer wall of the housing 10 is fixed to the outer circumference of the spacer 81 with a small gap in between. A base 50 is provided at the bottom of the housing 10. An exhaust port 51 is formed in the base 50 and communicates with the outside. Exhaust gas that enters the intake port 11 from the chamber (vacuum chamber) side and is transferred to the base 50 is sent to the exhaust port 51.

[0030] Furthermore, depending on the application of the turbomolecular pump 1, a threaded spacer 53 is provided between the lower part of the housing 10 and the base 50. The threaded spacer 53 is a cylindrical member made of a metal such as aluminum, copper, stainless steel, iron, or an alloy containing these metals, and has multiple spiral threads engraved on its inner surface. The direction of the spiral of the threads is such that when exhaust gas molecules move in the direction of rotation of the rotor 20, these molecules are transported toward the exhaust port 51. A cylindrical portion 20d hangs down from the lowest part of the rotor 20 following the rotor blades 22. The outer surface of this cylindrical portion 20d is cylindrical and protrudes toward the inner surface of the threaded spacer 53, and is in close proximity to the inner surface of the threaded spacer 53 with a predetermined gap between them. The exhaust gas transported to the threads by the rotor blades 22 and the fixed blades 80 is guided by the threads and sent toward the base 50.

[0031] The base 50 is a disc-shaped component that forms the base of the turbomolecular pump 1, and is generally made of a metal such as iron, aluminum, or stainless steel. The base 50 not only physically holds the turbomolecular pump 1 but also functions as a heat conduction path, so it is desirable to use a metal that is rigid and has high thermal conductivity, such as iron, aluminum, or copper. An O-ring 52 is interposed between the base 50 and the housing 10.

[0032] In this configuration, when the rotor blades 22 are rotated by the motor 30 together with the rotor shaft 21, exhaust gas is drawn in from the chamber through the intake port 11 by the action of the rotor blades 22 and the fixed blades 80. The rotational speed of the rotor blades 22 is usually 20,000 rpm to 90,000 rpm, and the peripheral speed at the tip of the rotor blades 22 reaches 200 m / s to 400 m / s. The exhaust gas drawn in from the intake port 11 passes between the rotor blades 22 and the fixed blades 80 and is transferred to the base 50. At this time, the temperature of the rotor blades 22 rises due to frictional heat generated when the exhaust gas comes into contact with the rotor blades 22 and heat conduction generated by the motor 30, but this heat is transferred to the fixed blades 80 side by radiation or conduction by gas molecules of the exhaust gas.

[0033] The fixed-wing spacers 125 are joined to each other at their outer circumference, and they transmit heat received by the fixed wing 80 from the rotor blade 22, as well as frictional heat generated when exhaust gases come into contact with the fixed wing 80, to the outside.

[0034] In the above description, the threaded spacer 53 is positioned on the outer circumference of the cylindrical portion 20d of the rotor 20, and the threaded spacer 53 has threads engraved on its inner surface. However, conversely, there are also cases where the threads are engraved on the outer surface of the cylindrical portion 20d, and a spacer having a cylindrical inner surface is positioned around it.

[0035] (2) Structure of the magnetic bearing device 60 Next, the specific configuration of the magnetic bearing device 60 will be described based on the drawings. Figure 2 is a perspective view showing the upper electromagnet unit 61 according to the first embodiment.

[0036] The upper electromagnet unit 61 includes four radial electromagnets 63 that provide non-contact magnetic support to the rotor shaft 21 in the radial direction, and four radial displacement sensors 64 that detect radial displacement of the rotor shaft 21. The radial displacement sensors 64 can be, for example, inductance sensors or eddy current sensors with conduction windings. The system is configured to detect the position of the rotor shaft 21 based on the change in the inductance of these conduction windings, which changes according to the position of the rotor shaft 21, and to send this information to the control device 200.

[0037] The coil 63a of the radial electromagnet 63 and the coil 64a of the radial displacement sensor 64 are wound around the same core 65, that is, they are wound around the core 65. Multiple radial electromagnets 63 are arranged in a circumferential direction. The coil 64a of the radial displacement sensor 64 is positioned between the multiple radial electromagnets 63 in the circumferential direction.

[0038] Each radial electromagnet 63 is positioned at a 90-degree interval along the circumferential direction of the core 65. Each radial electromagnet 63 has a pair of magnetic poles 66, 66 formed by winding a coil 63a around a protrusion 65a of the core 65. The pair of magnetic poles 66, 66 have different polarities by winding the coils 63a in opposite directions. Furthermore, adjacent coils 63a connected via the radial displacement sensor 64 are wound in the same direction around the core 65 so that adjacent magnetic poles 66, 66 connected via the radial displacement sensor 64 have the same polarity. Alternatively, if the polarity of each magnetic pole 66 is the same, for example, all coils 63a may be wound in the same direction, and then the connection method of each coil 63a may be changed.

[0039] The radial displacement sensors 64 are positioned between adjacent radial electromagnets 63, 63 in the circumferential direction of the core 65, and each radial displacement sensor 64 is positioned on the mutually orthogonal A-axis and B-axis. The radial displacement sensors 64 have a pair of magnetic poles formed by winding a coil 64a around the claw portion 65b of the core 65.

[0040] The radial displacement sensor 64, positioned along the A-axis, detects the displacement of the upper part of the rotor shaft 21 in the A-axis direction and sends a raw displacement signal corresponding to this displacement to the control device 200. The radial displacement sensor 64, also positioned along the A-axis, detects the displacement of the rotor shaft 21 in the B-axis direction and sends a raw displacement signal corresponding to this displacement to the control device 200.

[0041] Next, the polarity of the upper electromagnet unit 61 will be explained. Figure 3 is a longitudinal cross-sectional view of the upper electromagnet unit 61. Figure 4 is a radial cross-sectional view of the upper electromagnet unit 61, where Figure 4A is a cross-sectional view along line DD in Figure 3, and Figure 4B is a cross-sectional view along line EE in Figure 3.

[0042] As shown in Figure 3, in the upper electromagnet unit 61 according to the first embodiment, the radial displacement sensor 64 includes a radial displacement sensor 64 having an upper magnetic pole 67a and a lower magnetic pole 67b arranged side by side in the axial direction. Specifically, the upper magnetic pole 67a and the lower magnetic pole 67b have different polarities because the coils 64a are wound in opposite directions to each other. Alternatively, if the polarities of the upper magnetic pole 67a and the lower magnetic pole 67b are different, the coils 64a may be wound in the same direction and the wiring method of each coil 64a may be changed.

[0043] The two radial displacement sensors 64 arranged along the A-axis in Figure 3 have a first sensor pole pair P1 and a second sensor pole pair P2. The two sensor pole pairs P1 and P2 constitute a uniaxial sensor unit along the A-axis. Here, a pole pair refers to two magnetic poles that create a closed flow of magnetic field lines M. In the illustrated example, Au - and Al - However, it creates a closed flow of magnetic field lines M via the rotor shaft 21, which corresponds to the first sensor magnetic pole pair P1. Also, magnetic pole Au + and magnetic pole Al + However, it creates a closed flow of magnetic field lines M via the rotor shaft 21, which corresponds to the second sensor magnetic pole pair P2.

[0044] In other words, the first sensor pole pair P1 consists of two sensor poles (upper pole 67a and lower pole 67b) arranged side by side in the axial direction along the rotor shaft 21, which is the axis of rotation. The second sensor pole pair P2 is radially opposite to the first sensor pole pair P1 and, similar to the first sensor pole pair P1, consists of two sensor poles (upper pole 67a and lower pole 67b) arranged side by side in the axial direction.

[0045] Furthermore, as shown in Figures 4A and 4B, similarly, on the B axis perpendicular to the A axis, the upper electromagnet unit 61 is equipped with another first sensor pole pair P1 and another second sensor pole pair P2 radially opposite to it. In other words, in this embodiment, the upper electromagnet unit 61 is equipped with two sets of the first sensor pole pair P1 and the second sensor pole pair P2.

[0046] (3) Sensor circuit configuration Figure 5 shows a sensor circuit according to this embodiment. As shown in Figure 5, a single-axis sensor unit U1 arranged along the A-axis and a single-axis sensor unit U2 arranged along the B-axis are connected in parallel to the first oscillator S1 and the second oscillator S2.

[0047] The first oscillator S1 outputs an AC voltage as a modulated input signal to the radial displacement sensor 64. The second oscillator S2 outputs an AC voltage that is in opposite phase to the first oscillator S1. In the uniaxial sensor unit U1 arranged along the A axis, the end of the first sensor magnetic pole pair P1 (magnetic pole Al - The end of the second sensor pole pair P2 (magnetic pole Au + ) is connected to the first oscillator S1. Similarly, in a uniaxial sensor unit U2 arranged along the B axis, the end of the first sensor pole pair P1 (magnetic pole Bl - The end of the second sensor pole pair P2 (magnetic pole Bu) is connected to the second oscillator S2. + ) is connected to the first oscillator S1.

[0048] Both the first oscillator S1 and the second oscillator S2 output a 25kHz sine wave signal. The second oscillator S2 outputs a signal that is out of phase with the first oscillator S1. The signals output from the first oscillator S1 and the second oscillator S2 may include an offset component. In addition, each of the uniaxial sensor units U1 and U2 may be provided with a first oscillator S1 and a second oscillator S2 that output a positive phase signal.

[0049] In the sensor circuit, one end of the first sensor magnetic pole pair P1 is connected to one end of the second sensor magnetic pole pair P2. In the illustrated example, in the uniaxial sensor unit U1 arranged along the A axis, the magnetic pole Au forming one end of the first sensor magnetic pole pair P1 - is connected to the magnetic pole Al forming one end of the second sensor magnetic pole pair P2 + In the uniaxial sensor unit U2 arranged along the B axis, the magnetic pole Bu forming one end of the first sensor magnetic pole pair P1 - is connected to the magnetic pole Bl forming one end of the second sensor magnetic pole pair P2 + is connected to.

[0050] In this embodiment, in the sensor circuit, the coils of each sensor magnetic pole constituting the sensor magnetic pole pairs P1 and P2 are all connected in series. Thereby, it can be expected to suppress the noise of the sensor circuit.

[0051] In the sensor circuit, in each of the uniaxial sensor units U1 and U2, the voltage at the connection point of the first sensor magnetic pole pair P1 and the second sensor magnetic pole pair P2 is input to the demodulation circuit RC. The demodulation circuit RC demodulates the output signal from the radial displacement sensor 64. The sensor circuit may be a synchronous detection method in which a reference signal synchronized with the 25 kHz input signal is multiplied by the input signal to the demodulation circuit RC, and a low-pass filter is applied to the multiplied signal. Further, the sensor circuit may be a sampling detection method in which the input signal to the demodulation circuit RC, which is a carrier wave, is directly AD-converted in synchronization with the 25 kHz input signal. By the demodulation circuit RC, the midpoint voltage of the first sensor magnetic pole pair P1 and the second sensor magnetic pole pair P2 is demodulated as a displacement signal. Note that the demodulation circuit RC may be an analog circuit or a digital circuit.

[0052] In this embodiment, among the sensor magnetic poles of the first sensor magnetic pole pair P1 and the second sensor magnetic pole pair P2, a pair of sensor magnetic poles facing each other in the radial direction are opposite poles to each other. As shown in FIG. 3, the magnetic pole Au - and the magnetic pole Au + are opposite poles to each other. That is, the magnetic pole Au -So, the magnetic field lines M are directed from the inside out in the radial direction, but the magnetic pole Au + Therefore, the magnetic field lines M are pointing from the outside to the inside in the radial direction.

[0053] Similarly, in Figure 3, the magnetic pole Al - So, the magnetic field lines M are directed from the outside to the inside in the radial direction, but the magnetic poles Al - And the magnetic pole Al facing the radial direction + Therefore, the magnetic field lines M are pointing from the inside to the outside in the radial direction. Thus, the magnetic pole Al - and magnetic pole Al + They are also at opposite poles.

[0054] Furthermore, upon examining two pairs of sensor magnetic poles facing each other radially along the B-axis, as shown in Figure 4A, the magnetic poles Bu correspond to a pair of sensor magnetic poles that face each other radially. + and magnetic pole Bu - However, they are opposite poles. That is, magnetic pole Bu + So, the magnetic field lines M are directed from the outside to the inside in the radial direction, but the magnetic pole Bu - Therefore, the magnetic field lines M are pointing from the inside to the outside in the radial direction.

[0055] Similarly, in Figure 4B, magnetic pole Bl + So, the magnetic field lines M are directed from the inside outwards in the radial direction, but the magnetic pole Bl - Therefore, the magnetic field lines M are pointing from the outside to the inside in the radial direction. Thus, the magnetic pole Bl + and magnetic pole Bl - They are also at opposite poles.

[0056] Next, the electrical characteristics of the sensor circuit connected by this circuit configuration will be explained. Figure 6 is a diagram showing a theoretically calculated sensor circuit model. That is, this circuit model simplifies the configuration of the uniaxial sensor unit and is a theoretical sensor circuit using an ideal AC power supply with no internal resistance and no voltage drop, in order to explain the electrical characteristics of the sensor circuit according to this embodiment. In this sensor circuit, the radially opposing magnetic poles of the two sensor magnetic pole pairs P1 and P2 have opposite polarities, and the midpoint voltage when voltages with opposite phases are applied from each power supply is taken as the output voltage of the uniaxial sensor unit U1.

[0057] In the circuit model shown in Figure 6, the voltage vectors of the first sensor pole pair P1 and the second sensor pole pair P2 in the uniaxial sensor unit U1 are defined as being in the same direction. Here, since the first sensor pole pair P1 and the second sensor pole pair P2 are facing each other in the radial direction, they exhibit opposite behavior: if the gap of one widens, the gap of the other narrows.

[0058] Here, the leakage flux from the motor 30 enters the first sensor pole pair P1 and the second sensor pole pair P2. The leakage flux from the motor 30 contains time-varying components such as electrical angular rotation frequency components and switching frequency components, which generate an electromotive force in the coil 64a. This electromotive force is the cause of noise transmitted to the radial displacement sensor 64 by the motor 30.

[0059] Since the motor 30 is located at a different position in the axial direction from the radial displacement sensor 64, the axial distance between the motor 30 and the upper magnetic pole 67a and the axial distance between the motor 30 and the lower magnetic pole 67b are different from each other. Therefore, the magnetic flux density of the leakage flux of the motor 30 entering the upper magnetic pole 67a and the magnetic flux density of the leakage flux of the motor 30 entering the lower magnetic pole 67b will have the same polarity but different magnitudes.

[0060] Furthermore, the upper magnetic pole 67a and the lower magnetic pole 67b are connected in series such that they have opposite polarities. As a result, the electromotive force generated by the leakage flux of the motor 30 at the upper magnetic pole 67a and the electromotive force generated by the leakage flux of the motor 30 at the lower magnetic pole 67b have different polarities and magnitudes, and therefore do not completely cancel each other out. Therefore, electromotive forces are generated in the sensor pole pairs P1 and P2, respectively, due to the leakage magnetic flux of the motor 30.

[0061] Furthermore, the leakage magnetic flux of the motor 30 entering the two radially opposing sensor magnetic poles has different polarities but is approximately equal in magnitude. On the other hand, each radially opposing sensor magnetic pole is configured to have different polarities from one another. Therefore, the electromotive forces generated in the coils of the two sensor pole pairs P1 and P2 by the leakage magnetic flux of the motor 30 have the same sign and are approximately equal in magnitude.

[0062] Based on this relationship, the impedances of the first sensor pole pair P1 and the second sensor pole pair P2 with respect to the motor noise frequency components are expressed by equations (1) and (2). Z p =Rs+jω(L0-L1x)···(1) Z n =Rs+jω(L0+L1x)···(2) Z p : Impedance of the second sensor magnetic pole pair P2 Z n : Impedance of the first sensor pole pair P1 R s Sensor coil resistance (Ω) ω: Frequency (Hz) of noise voltage generated by the motor. L0: Sensor coil inductance (when the rotor shaft is at the center) (H) L1: The inclination of the sensor coil inductance with respect to the displacement of the rotor shaft (H / mm) x: Rotor shaft displacement (mm)

[0063] In other words, equations (1) and (2) express the change in the inductance of the sensor coil as a linear approximation with respect to the displacement of the rotor shaft 21. And in the linear approximation, it is assumed that L1x is sufficiently small compared to Lo.

[0064] Next, the voltage equation due to motor noise, based on equations (1) and (2), is obtained by equation (3). However, since we are focusing on the frequency components of the motor noise, the oscillator voltage is set to 0. V np +V nn +2(R s +jωL0)I s =0···(3) V np : Electromotive force (V) due to the motor leakage flux of the first sensor pole pair P1 V nn : Electromotive force (V) due to the motor's leakage flux in the second sensor pole pair P2 I s : Current flowing through the circuit (frequency components of motor noise) (A)

[0065] From equation (3), we obtain equations (4) and (5). I s =-(V np +V nn ) / 2(R s +jωL0)···(4) V s =V nn +(R s +jω(L0+L1x))I s ...(5) V s Output potential of radial displacement sensor (frequency component of motor noise) (V)

[0066] Then, by substituting equation (4) into equation (5), we obtain equation (6). V s =-1 / 2(V np -V nn )-(jωL1x)(V np +V nn ) / 2(R s +jωL0)···(6) Here, the absolute value of L1x is usually sufficiently small for L0, so (jωL1x) / (R s The absolute value of (+jωL0) is a value well less than 1. Therefore, in equation (6), the coefficient of the second term is a value well less than the coefficient of the first term. From these calculations, V is used so that the first term of equation (6) does not remain. np and V nn By connecting the sensor coils so that they have the same sign, V s This can be made smaller. As a result, it can be theoretically derived that the influence of motor noise on the radial displacement sensor 64 can be reduced.

[0067] Thus, in this embodiment, since the number of poles of the motor 30 is even and not a multiple of 4, the polarity of the leakage flux of the motor 30 is opposite to the radial reversal (180-degree rotation in the circumferential direction). Also, each magnetic pole facing each other in the radial direction has opposite polarity. Therefore, the electromotive force V generated in the two sensor pole pairs by the leakage flux of the motor 30 is np , V nn These have the same sign. As a result, it is possible to reduce the noise of the radial displacement sensor 64 caused by the motor 30.

[0068] (4) Modified form of the first embodiment Next, a modified example of the first embodiment will be described. Figure 7 is a longitudinal cross-sectional view of a modified example of the upper electromagnet unit 61 according to the first embodiment. Figure 8 is a radial cross-sectional view of the upper electromagnet unit 61 according to the modified example, where Figure 8A is a cross-sectional view along the FF line in Figure 7, and Figure 8B is a cross-sectional view along the GG line in Figure 7.

[0069] First, in the magnetic bearing device 60 according to this modified example, the number of poles of the motor 30 differs from that of the first embodiment. In this modified example, the motor 30 has 4 poles, which is an even number and a multiple of 4. Therefore, the polarity of the magnetic flux of the motor 30 is the same with respect to radial reversal (180-degree rotation in the circumferential direction). When the motor 30 has 4 poles as in this modified example, the phase of the noise entering the magnetic poles of the radial displacement sensor 64, which are 180 degrees opposite each other, changes. In this modified example, we focus on the polarity of the magnetic flux of the motor 30 with respect to radial reversal (180-degree rotation in the circumferential direction), so a similar effect can be obtained with any number of poles that is a multiple of 4, such as 8 or 12.

[0070] In this modified example, taking into account that the number of poles of the motor 30 is different from that of the first embodiment, the orientation of the coil 64a connections is changed. Specifically, the orientation of the coil 64a connections is changed by changing the winding direction of the coil 64a wound around the claw portion 65b of the core 65 from the configuration of the first embodiment. Alternatively, the orientation of the coil 64a connections may be changed by changing the location where the connections are made after winding from the configuration of the first embodiment. Furthermore, in this modified example as well, as shown in Figure 7, the magnetic poles of the two sensor magnetic poles (upper magnetic pole 67a, lower magnetic pole 67b) arranged side by side in the axial direction are different from each other.

[0071] Furthermore, in the radial displacement sensor 64 according to this modified example, among the sensor poles of the first sensor pole pair P1 and the second sensor pole pair P2, pairs of sensor poles that face each other radially are of the same polarity. As shown in Figure 7, the magnetic poles Au that face each other radially - and magnetic pole Au + However, they have the same polarity. That is, magnetic pole Au - In this case, the magnetic field lines M are directed from the outside to the inside in the radial direction, and the magnetic pole Au + However, similarly, the magnetic field lines M point from the outside to the inside in the radial direction.

[0072] Similarly, in Figure 7, the magnetic pole Al - So, the magnetic field lines M are directed from the inside outwards in the radial direction, and the magnetic poles Al +However, the magnetic field lines M are directed from the inside outwards in the radial direction. Therefore, the magnetic poles Al are facing each other radially. - and magnetic pole Al + They are also polar to each other.

[0073] Furthermore, upon examining the two pairs of sensor magnetic poles facing each other radially along the B-axis, as shown in Figure 8A, the magnetic poles Bu are radially opposed to each other. + and magnetic pole Bu - However, they have the same polarity. That is, magnetic pole Bu + So, the magnetic field lines M are directed from the outside to the inside in the radial direction, and the magnetic pole Bu - However, the magnetic field lines M are pointing from the outside in the radial direction towards the inside.

[0074] Similarly, in Figure 8B, magnetic pole Bl + So, the magnetic field lines M are directed from the inside outwards in the radial direction, and the magnetic pole Bl - However, the magnetic field lines M are pointing from the inside outwards in the radial direction. Therefore, the magnetic pole Bl + and magnetic pole Bl - They are also polar to each other.

[0075] Thus, in this modified example, since the number of poles of the motor 30 is a multiple of 4, the polarity of the leakage flux of the motor 30 is the same polarity with respect to radial reversal (180-degree rotation in the circumferential direction). Also, each magnetic pole facing each other in the radial direction has the same polarity. Therefore, the electromotive force V generated in the two sensor pole pairs by the leakage flux of the motor 30 is np , V nn These have the same sign. As a result, it is possible to reduce the noise of the radial displacement sensor 64 caused by the motor 30.

[0076] <Second Embodiment> Next, the magnetic bearing device 60 according to the second embodiment will be described with reference to the drawings. In this embodiment, the motor 30 has 2 poles. Therefore, the polarity of the magnetic flux of the motor 30 is reversed with respect to radial reversal (180-degree rotation in the circumferential direction). In this embodiment, since the focus is on the polarity of the magnetic flux of the motor 30 with respect to radial reversal (180-degree rotation in the circumferential direction), the same effect can be obtained with any number of poles that is even and not a multiple of 4, such as 6 or 10. The basic structure of the turbomolecular pump 1 and the configuration of the magnetic bearing device 60 are the same as in the first embodiment, so their description will be omitted.

[0077] (5) Sensor circuit configuration Figure 9 shows the configuration of the sensor circuit according to the second embodiment. In the radial displacement sensor according to this embodiment, as in the first embodiment, the coils of the first sensor pole pair P1 and the second sensor pole pair P2 are wired so that the polarity of each pole is different (see Figure 3).

[0078] As shown in Figure 9, in this embodiment, one end of the coil of the first sensor pole pair P1 (Au in the illustrated example) - The coil of the first sensor pole pair P1 is connected to the oscillator S via a resistor R. One end of the coil of the first sensor pole pair P1 may be connected to the oscillator S via an inductor. The other end of the coil of the first sensor pole pair P1 (Al in the illustrated example) - ) is connected to the ground.

[0079] Also, one end of the coil of the second sensor pole pair P2 (Au in the illustrated example) + The coil of the second sensor pole pair P2 is connected to the oscillator S via a resistor R. One end of the coil of the second sensor pole pair P2 may be connected to the oscillator S via an inductor. The other end of the coil of the second sensor pole pair P2 (Al in the illustrated example) + ) is connected to the ground.

[0080] Then, the oscillator side end of the first sensor pole pair P1 (Au in the illustrated example) -) voltage and the voltage at the oscillator S side end of the second sensor magnetic pole pair P2 (in the illustrated example, Au + ) voltage is input to the demodulation circuit RC via a differential circuit.

[0081] Also, when checking in the sensor magnetic pole pairs facing each other in the radial direction along the B axis, one end of the coil of the first sensor magnetic pole pair P1 (in the illustrated example, Bu - ) is connected to the oscillator S via a resistor R. Note that one end of the coil of the first sensor magnetic pole pair P1 may be connected to the oscillator S via an inductor. And the other end of the coil of the first sensor magnetic pole pair P1 (in the illustrated example, Bl - ) is connected to the ground.

[0082] Also, one end of the coil of the second sensor magnetic pole pair P2 (in the illustrated example, Bu + ) is connected to the oscillator S via a resistor R. Note that one end of the coil of the second sensor magnetic pole pair P2 may be connected to the oscillator S via an inductor. And the other end of the coil of the second sensor magnetic pole pair P2 (in the illustrated example, Bl + ) is connected to the ground.

[0083] And the voltage at the oscillator S side end of the first sensor magnetic pole pair P1 (in the illustrated example, Bu - ) and the voltage at the oscillator S side end of the second sensor magnetic pole pair P2 (in the illustrated example, Bu + ) voltage is input to the demodulation circuit RC via a differential circuit.

[0084] And also in the magnetic bearing device 60 according to the second embodiment, as in the first embodiment, among the sensor magnets of the first sensor magnetic pole pair P1 and the second sensor magnetic pole pair P2, a pair of sensor magnets facing each other in the radial direction are connected so as to have opposite polarities to each other. Since this configuration is the same as the configurations of FIGS. 3 and 4 in the first embodiment, detailed description thereof is omitted. With these configurations, also in the present embodiment, as in the first embodiment, the influence of motor noise can be reduced. This point will be described as the electrical characteristics of the circuit model shown in FIG. 10.

[0085] Figure 10 is a diagram showing a theoretical calculation sensor circuit model according to the second embodiment. This circuit model is a theoretical circuit model that simplifies the configuration of the uniaxial sensor unit and uses an ideal AC power source without internal resistance and no voltage drop in order to explain the electrical characteristics of the sensor circuit according to this embodiment. In this circuit, the poles facing each other in the radial direction of the two sensor magnetic pole pairs P1 and P2 have different polarities from each other, and in a state where the same voltage is applied from each power source, the difference between the respective voltages is used as the output voltage as the uniaxial sensor unit U1.

[0086] In the circuit model shown in Figure 10, in the uniaxial sensor unit U1, the electromotive force V np、 V nn generated by the leakage magnetic flux of the motor 30 of the first sensor magnetic pole pair P1 and the second sensor magnetic pole pair P2 is defined to be in the same direction. At this time, the voltage (frequency component of motor noise) V s input to the demodulation circuit RC is represented by Equation (7). V s = (V np - V nn ) ··· (7) Therefore, in order to reduce Equation (7), by connecting the sensor coils so that V np and V nn have the same sign, the influence of motor noise can be reduced.

[0087] Thus, in this embodiment, since the number of poles of the motor 30 is an even number and not a multiple of 4, the polarity of the leakage magnetic flux of the motor 30 becomes the opposite polarity with respect to the radial inversion (rotation of 180 degrees in the circumferential direction). Also, each pair of poles facing each other in the radial direction has opposite polarities to each other. Therefore, the electromotive forces V [[ID=3৪]] np and V nn generated in the two sensor magnetic pole pairs by the leakage magnetic flux of the motor 30 have the same sign. As described above, it becomes possible to reduce the noise of the radial displacement sensor 64 caused by the motor 30.

[0088] (6) Modified form of the second embodiment In the second embodiment, the same modifications as in the first embodiment can be adopted; that is, the structure of the magnetic bearing device 60 can be modified so that the number of poles of the motor 30 is a multiple of 4. Then, as shown in Figures 7 and 8, the sensor poles of the first sensor pole pair P1 and the second sensor pole pair P2 are connected such that pairs of sensor poles that are radially opposite to each other are of the same polarity.

[0089] The specific polarity of each coil in this case is the same as in the configurations of Figures 7 and 8, so a detailed explanation is omitted. As a result, similar to the second embodiment, the voltage (frequency component of motor noise) V input to the demodulation circuit RC is... s Since it is expressed by equation (7), V np and V nn By connecting the sensor coils so that they have the same sign, the influence of motor noise can be reduced.

[0090] Thus, in this modified example, since the number of poles of the motor 30 is a multiple of 4, the polarity of the leakage flux of the motor 30 is the same polarity with respect to radial reversal (180-degree rotation in the circumferential direction). Furthermore, each magnetic pole facing each other in the radial direction has the same polarity. Therefore, the electromotive force V generated in the two sensor pole pairs by the leakage magnetic flux of the motor 30 np , V nn These have the same sign. As a result, it is possible to reduce the noise of the radial displacement sensor 64 caused by the motor 30.

[0091] <Other examples> Next, other embodiments of the present invention will be described with reference to the drawings.

[0092] (7) Other embodiments of the first embodiment Figure 11 shows a sensor circuit according to Embodiment 1, which is another embodiment of the first embodiment. In Embodiment 1 shown in Figure 11, the sensor circuit has one pair of sensor magnetic poles that face each other in the radial direction. In this case, for example, a single-axis sensor unit U1 is arranged only on the A axis of the upper electromagnet unit 61.

[0093] Figure 12 shows a sensor circuit according to Embodiment 2, which is another embodiment of the First Embodiment. In Embodiment 2 shown in Figure 12, the sensor circuit has four pairs of sensor magnetic poles facing each other in the radial direction. That is, in the illustrated example, control is performed in five axes in combination with the axial magnetic bearing 70. In this figure, the subscript "h" at the end of the sensor magnetic pole notation indicates that it is part of the upper electromagnet unit 61, and the subscript "b" indicates that it is part of the lower electromagnet unit 62.

[0094] In this case, single-axis sensor units U1 and U2 are positioned along the A and B axes of the upper electromagnet unit 61. Also, single-axis sensor units U3 and U4 are positioned along the A and B axes of the lower electromagnet unit 62. Thus, the number of sensor pole pairs may be three or more.

[0095] Figure 13 shows a sensor circuit according to Embodiment 3, which is another embodiment of the first embodiment. In Embodiment 3 shown in Figure 13, a power supply circuit is constructed that takes into account a realistic implementation. That is, in an actual circuit, the internal resistance and voltage drop are affected due to the influence of the sensor impedance, etc. For this reason, in Embodiment 3, an input resistor R1 is connected downstream of the first oscillator S1 and the second oscillator S2, and a capacitor C is connected in parallel with the first sensor pole pair P1 and the second sensor pole pair P2. A resonant circuit is formed by the inductance of the sensor coil and the capacitor C, so that the energy of the sensor output voltage can be efficiently transmitted.

[0096] Furthermore, two voltage divider resistors R2 are connected in parallel with the first sensor pole pair P1 and the second sensor pole pair P2. The midpoint voltages of the two voltage divider resistors R2 and the midpoint voltages of the first sensor pole pair P1 and the second sensor pole pair P2 are input to the demodulation circuit RC via a differential circuit. This reduces the influence of common-mode noise generated in the circuit.

[0097] (8) Other embodiments of the second embodiment Figure 14 shows a sensor circuit according to Embodiment 4, which is another embodiment of the second embodiment. In Embodiment 4 shown in Figure 14, the sensor circuit has four pairs of sensor magnetic poles facing each other in the radial direction. That is, in the illustrated example, control is performed in five axes in combination with the axial magnetic bearing 70.

[0098] In this case, single-axis sensor units U1 and U2 are positioned along the A and B axes of the upper electromagnet unit 61. Additionally, single-axis sensor units U3 and U4 are positioned along the A and B axes of the lower electromagnet unit 62.

[0099] <Control circuit configuration> Next, we will describe the amplifier circuit 150 that energizes and controls the radial electromagnet 63 and the axial electromagnet 71 of the turbomolecular pump 1 configured in this way. The circuit diagram of this amplifier circuit 150 is shown in Figure 15.

[0100] In Figure 15, the electromagnet winding 151, which constitutes the radial electromagnet 63, has one end connected to the positive terminal 171a of the power supply 171 via transistor 161. The other end of the electromagnet winding 151 is connected to the negative terminal 171b of the power supply 171 via current detection circuit 181 and transistor 162. Transistors 161 and 162 are so-called power MOSFETs, and have a structure in which a diode is connected between their source and drain.

[0101] In this configuration, transistor 161 has its diode cathode terminal 161a connected to the positive terminal 171a, and its anode terminal 161b connected to one end of the electromagnet winding 151. Transistor 162 has its diode cathode terminal 162a connected to the current detection circuit 181, and its anode terminal 162b connected to the negative terminal 171b.

[0102] On the other hand, the diode 165 for current regeneration has its cathode terminal 165a connected to one end of the electromagnet winding 151, and its anode terminal 165b connected to the negative terminal 171b. Similarly, the diode 166 for current regeneration has its cathode terminal 166a connected to the positive terminal 171a, and its anode terminal 166b connected to the other end of the electromagnet winding 151 via the current detection circuit 181. The current detection circuit 181 is composed of, for example, a Hall sensor type current sensor or an electrical resistance element.

[0103] The amplifier circuit 150 configured as described above corresponds to one electromagnet. Therefore, for example, if the magnetic bearing is 5-axis controlled and there are a total of 10 electromagnets, a similar amplifier circuit 150 is configured for each electromagnet, and 10 amplifier circuits 150 are connected in parallel to the power supply 171.

[0104] Furthermore, the amplifier control circuit 191 is configured, for example, by a digital signal processor (hereinafter referred to as the DSP section) of the control device 200 (not shown), and this amplifier control circuit 191 is configured to switch transistors 161 and 162 on and off.

[0105] The amplifier control circuit 191 compares the current value detected by the current detection circuit 181 (the signal reflecting this current value is called the current detection signal 191c) with a predetermined current command value. Based on this comparison, it determines the magnitude of the pulse width (pulse width time Tp1, Tp2) to be generated within the control cycle Ts, which is one period of PWM control. As a result, gate drive signals 191a and 191b with this pulse width are output from the amplifier control circuit 191 to the gate terminals of transistors 161 and 162.

[0106] Furthermore, when the rotor shaft 21 passes a resonance point during acceleration operation or when disturbances occur during constant-speed operation, it is necessary to control the position of the rotor shaft 21 with high speed and strong force. For this reason, a voltage of approximately 50V is used for the power supply 171 so that the current flowing through the electromagnet winding 151 can be rapidly increased (or decreased). In addition, a capacitor is usually connected between the positive electrode 171a and the negative electrode 171b of the power supply 171 to stabilize the power supply 171 (not shown).

[0107] In this configuration, when both transistors 161 and 162 are turned on, the current flowing through the electromagnet winding 151 (hereinafter referred to as the electromagnet current iL) increases, and when both are turned off, the electromagnet current iL decreases.

[0108] Furthermore, by turning one of transistors 161 and 162 on and the other off, a so-called flywheel current is maintained. By allowing this flywheel current to flow through the amplifier circuit 150, hysteresis loss in the amplifier circuit 150 can be reduced, and the overall power consumption of the circuit can be kept low. In addition, by controlling transistors 161 and 162 in this way, high-frequency noise such as harmonics generated in the turbomolecular pump 1 can be reduced. Moreover, by measuring this flywheel current with the current detection circuit 181, the electromagnet current iL flowing through the electromagnet winding 151 can be detected.

[0109] In other words, if the detected current value is smaller than the current command value, both transistors 161 and 162 are turned on only once during the control cycle Ts (e.g., 100 μs) for a duration corresponding to the pulse width time Tp1, as shown in Figure 16. Therefore, the electromagnet current iL during this period increases from the positive electrode 171a to the negative electrode 171b, towards the current value iLmax (not shown) that can flow through transistors 161 and 162.

[0110] On the other hand, if the detected current value is greater than the current command value, both transistors 161 and 162 are turned off only once during the control cycle Ts for a duration corresponding to the pulse width time Tp2, as shown in Figure 17. Therefore, during this period, the electromagnet current iL decreases from the negative electrode 171b towards the positive electrode 171a, towards a regenerative current value iLmin (not shown) via diodes 165 and 166.

[0111] In either case, after the pulse width time Tp1 and Tp2 have elapsed, one of transistors 161 or 162 is turned on. Therefore, during this period, the flywheel current is maintained in the amplifier circuit 150.

[0112] <Other> In the embodiments described above, a plurality of radial electromagnets 63 are arranged in a circumferential direction, and the sensor magnetic poles 67a and 67b are positioned between them in the circumferential direction. However, the positions of the sensor magnetic poles 67a and 67b are not limited to this. That is, the magnetic bearing device 60 may be configured such that the radial electromagnets 63 and the sensor magnetic poles 67a and 67b are positioned at axially separated positions.

[0113] In particular, when the sensor poles 67a and 67b are located between the motor 30 and the radial electromagnet 63 in the axial direction, the axial distance between the sensor poles 67a and 67b and the motor 30 is short. As a result, the leakage flux from the motor 30 entering the sensor poles 67a and 67b becomes large, and the influence of noise also increases. Therefore, by adopting the configuration of the present invention, noise from the motor 30 can be suitably reduced.

[0114] In the embodiments described above, the radial electromagnet 63 and the sensor poles 67a and 67b are arranged side by side in the circumferential direction, and in particular, the sensor poles 67a and 67b are arranged side by side in the axial direction. As a result, of the two sensor poles 67a and 67b, the sensor pole closer to the motor 30 in the axial direction is particularly susceptible to noise from the motor 30. The present invention is particularly suitable for reducing the influence of noise from the motor 30 on a magnetic bearing device 60 with such a configuration.

[0115] It should be noted that the present invention is not limited to the embodiments described above, and various modifications are included. For example, the embodiments described above are described in detail for the purpose of explaining the present invention in an easy-to-understand manner, and are not necessarily limited to those having all the configurations described. Furthermore, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add and combine the configuration of one embodiment with the configuration of another embodiment. In addition, it is possible to add, delete, or replace parts of the configuration of each embodiment with other configurations. Furthermore, the embodiments described above disclose at least the configuration described in the claims. [Explanation of Symbols]

[0116] 1...Turbo molecular pump, 10...Housing, 20...Rotor, 22...Rotor blades, 21...Rotor shaft, 30...Motor, 40...Stator column, 50...Base, 51...Exhaust port, 63...Radial electromagnet, 63a...Coil, 64...Radial displacement sensor, 64a...Coil, 65...Core, 65a...Protrusion, 65b...Claw, 67a...Upper magnetic pole, 67b...Lower magnetic pole, 80...Fixed blade, 60...Magnetic bearing device, 100...Pump body, 101...Intake port, 200...Control device, P1...First sensor pole pair, P2...First sensor pole pair, U1, U2, U3, U4...Uniaxial sensor unit, S1...First oscillator, S2...Second oscillator, RC...Demodulation circuit, R, R1, R2...Resistors,

Claims

1. A magnetic bearing device, Rotating body and The aforementioned rotating body is driven by a motor with an even number of poles that is not a multiple of 4, The rotating body comprises one or more radial electromagnets that generate a radial electromagnetic force, A radial displacement sensor for measuring the radial displacement of the rotating body, A first oscillator that outputs an AC voltage as a modulated input signal to the radial displacement sensor, A second oscillator that outputs an AC voltage in the opposite phase to the first oscillator, The system includes a demodulation circuit that demodulates the output signal from the radial displacement sensor, The radial displacement sensor is, A first sensor pole pair consisting of two sensor poles arranged side by side in the axial direction along the rotation axis of the rotating body, It comprises a second pair of sensor poles, which are radially opposite to the first pair of sensor poles and arranged side by side in the axial direction, The coils of the first sensor pole pair and the second sensor pole pair are wired so that the polarity of each pole is different. One end of the first sensor pole pair is connected to one end of the second sensor pole pair such that, among the sensor poles of the first sensor pole pair and the second sensor pole pair, a pair of sensor poles that are radially opposite to each other are opposite poles. The other end of the first sensor pole pair is connected to the first oscillator. The other end of the second sensor pole pair is connected to the second oscillator. The voltage at the connection point between the first sensor pole pair and the second sensor pole pair is input to the demodulation circuit. Magnetic bearing device.

2. A magnetic bearing device, Rotating body and A motor that rotates the aforementioned rotating body and has an even number of poles that is a multiple of 4, The rotating body comprises one or more radial electromagnets that generate a radial electromagnetic force, A radial displacement sensor for measuring the radial displacement of the rotating body, A first oscillator that outputs an AC voltage as a modulated input signal to the radial displacement sensor, A second oscillator that outputs an AC voltage in the opposite phase to the first oscillator, The system includes a demodulation circuit that demodulates the output signal from the radial displacement sensor, The radial displacement sensor is, A first sensor pole pair consisting of two sensor poles arranged side by side in the axial direction along the rotation axis of the rotating body, It comprises a second pair of sensor poles, which are radially opposite to the first pair of sensor poles and arranged side by side in the axial direction, The coils of the first sensor pole pair and the second sensor pole pair are wired so that the polarity of each pole is different. One end of the first sensor pole pair is connected to one end of the second sensor pole pair such that, among the sensor poles of the first sensor pole pair and the second sensor pole pair, a pair of sensor poles that are radially opposite to each other become the same pole. The other end of the first sensor pole pair is connected to the first oscillator. The other end of the second sensor pole pair is connected to the second oscillator. The voltage at the connection point between the first sensor pole pair and the second sensor pole pair is input to the demodulation circuit. Magnetic bearing device.

3. A magnetic bearing device, Rotating body and The aforementioned rotating body is driven by a motor with an even number of poles that is not a multiple of 4, The rotating body comprises one or more radial electromagnets that generate a radial electromagnetic force, A radial displacement sensor for measuring the radial displacement of the rotating body, An oscillator that outputs an AC voltage as a modulated input signal to the radial displacement sensor, The system includes a demodulation circuit that demodulates the output signal from the radial displacement sensor, The radial displacement sensor is, A first sensor pole pair consisting of two sensor poles arranged side by side in the axial direction along the rotation axis of the rotating body, It comprises a second pair of sensor poles, which are radially opposite to the first pair of sensor poles and arranged side by side in the axial direction, The coils of the first sensor pole pair and the second sensor pole pair are wired so that the polarity of each pole is different. One end of the coil of the first sensor pole pair is connected to the oscillator via a resistor and / or inductor. The other end of the coil of the first sensor pole pair is connected to ground. One end of the coil of the second sensor pole pair is connected to the oscillator via a resistor and / or inductor. The other end of the coil of the second sensor pole pair is connected to ground. Of the sensor poles in the first sensor pole pair and the second sensor pole pair, pairs of sensor poles that are radially opposite to each other are connected such that they are opposite poles. The voltage at the oscillator-side end of the first sensor pole pair and the voltage at the oscillator-side end of the second sensor pole pair are input to the demodulation circuit via a differential circuit. Magnetic bearing device.

4. A magnetic bearing device, Rotating body and A motor that rotates the aforementioned rotating body and has an even number of poles that is a multiple of 4, The rotating body comprises one or more radial electromagnets that generate a radial electromagnetic force, A radial displacement sensor for measuring the radial displacement of the rotating body, An oscillator that outputs an AC voltage as a modulated input signal to the radial displacement sensor, The system includes a demodulation circuit that demodulates the output signal from the radial displacement sensor, The radial displacement sensor is, A first sensor pole pair consisting of two sensor poles arranged side by side in the axial direction along the rotation axis of the rotating body, It comprises a second pair of sensor poles, which are radially opposite to the first pair of sensor poles and arranged side by side in the axial direction, The coils of the first sensor pole pair and the second sensor pole pair are wired so that the polarity of each pole is different. One end of the coil of the first sensor pole pair is connected to the oscillator via a resistor and / or inductor. The other end of the coil of the first sensor pole pair is connected to ground. One end of the coil of the second sensor pole pair is connected to the oscillator via a resistor and / or inductor. The other end of the coil of the second sensor pole pair is connected to ground. Of the sensor poles in the first sensor pole pair and the second sensor pole pair, pairs of sensor poles that face each other radially are connected so that they are of the same polarity. The voltage at the oscillator-side end of the first sensor pole pair and the voltage at the oscillator-side end of the second sensor pole pair are input to the demodulation circuit via a differential circuit. Magnetic bearing device.

5. The one or more radial electromagnets mentioned above are a plurality of radial electromagnets arranged in a circumferential direction, The magnetic bearing device according to any one of claims 1 to 4, wherein the sensor magnetic pole is positioned between the circumferential positions of the plurality of radial electromagnets.

6. A turbomolecular pump equipped with a magnetic bearing device according to any one of claims 1 to 4.

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