Magnetic bearing device and turbomolecular pump

Abstract

[Problem] To suppress an influence of noise from a motor on a sensor. [Means of Solution] A magnetic bearing device includes: a rotating body; a motor including poles whose number is an even number and is not a multiple of 4; a radial electromagnet; a radial displacement sensor; a first oscillator; a second oscillator; and a demodulation circuit, in which the radial displacement sensor includes a first sensor magnetic pole pair and a second sensor magnetic pole pair, each coil of the sensor magnetic pole pair is connected such that polarities of respective magnetic poles are different from each other, one end of the first sensor magnetic pole pair is connected to one end of the second sensor magnetic pole pair such that polarities of a pair of sensor magnetic poles radially facing each other, among the sensor magnetic poles of the first sensor magnetic pole pair and the second sensor magnetic pole pair, are opposite to each other, the other end of the first sensor magnetic pole pair is connected to the first oscillator, and the other end of the second sensor magnetic pole pair is connected to the second oscillator, and a midpoint voltage of the two sensor magnetic pole pairs is input to the demodulation circuit.

Description

[0001] 2024-020-GB 1

[0002] MAGNETIC BEARING DEVICE AND TURBOMOLECULAR PUMP

[0003] [Technical Field]

[0004]

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

[0005] [Background Art]

[0006]

[0002] As a background art of the technical field, there is Japanese Patent Application Laid-open No. 2000-240649 (PTL 1 ). This publication discloses a magnetic bearing device including a motor that drives a rotating shaft, two pairs of electromagnets arranged to face each other with the rotating shaft interposed therebetween, two pairs of displacement sensors arranged to face each other in the vicinity thereof, two pairs of electromagnets arranged to face each other, and two pairs of displacement sensors arranged to face each other in the vicinity thereof (see Fig. 5 ).

[0007] [Citation List]

[0008] [Patent Literature]

[0009]

[0003] [PTL 1 ] Japanese Patent Application Laid-open No. 2000-240649 [Summary of Invention]

[0010] [Technical Problem]

[0011]

[0004] In the configuration of PTL 1, the displacement sensor may be affected by noise from the motor.

[0012] Therefore, an obj ect of the present invention is to provide a configuration in which a displacement sensor suppresses an influence of noise from a motor.

[0013] [Solution to Problem]

[0014]

[0005] In order to solve the above problem, for example, the configuration described in the claims is adopted.

[0015] The present application includes a plurality of means for solving the above problem, and an example thereof includes

[0016] a magnetic bearing device including:

[0017] a rotating body;

[0018] a motor that rotationally drives the rotating body and includes poles whose number is an even number and is not a multiple of 4;

[0019] one or more radial electromagnets that generate a radial electromagnetic force in the rotating body; 2024-020-GB 2

[0020] a radial displacement sensor that measures radial displacement of the rotating body;

[0021] a first oscillator that outputs an alternating-current voltage as a modulated input signal to the radial displacement sensor;

[0022] a second oscillator that outputs an alternating-current voltage having a phase opposite to a phase of the first oscillator; and

[0023] a demodulation circuit that demodulates an output signal from the radial displacement sensor, in which

[0024] the radial displacement sensor includes:

[0025] a first sensor magnetic pole pair including two sensor magnetic poles arranged side by side in an axial direction along a rotating shaft of the rotating body; and

[0026] a second sensor magnetic pole pair including two sensor magnetic poles radially facing the first sensor magnetic pole pair and arranged side by side in the axial direction,

[0027] each coil of the first sensor magnetic pole pair and the second sensor magnetic pole pair is connected such that polarities of the respective magnetic poles are different from each other,

[0028] one end of the first sensor magnetic pole pair is connected to one end of the second sensor magnetic pole pair such that polarities of a pair of sensor magnetic poles radially facing each other, among the sensor magnetic poles of the first sensor magnetic pole pair and the sensor magnetic poles of the second sensor magnetic pole pair, are opposite to each other,

[0029] the other end of the first sensor magnetic pole pair is connected to the first oscillator,

[0030] the other end of the second sensor magnetic pole pair is connected to the second oscillator, and

[0031] a voltage at a connection point of the first sensor magnetic pole pair and the second sensor magnetic pole pair is input to the demodulation circuit.

[0032] [Advantageous Effects of Invention]

[0033]

[0006] According to the present invention, it is possible to suppress an influence of noise from the motor on the sensor.

[0034] Problems, configurations, and effects other than those described above will be clarified by the following description of embodiments.

[0035] [Brief Description of Drawings] 2024-020-GB 3

[0036]

[0007]

[0037] [Fig. 1 ]

[0038] Fig. 1 is a longitudinal sectional view of an example of a turbomolecular pump.

[0039] [Fig. 2 ]

[0040] Fig. 2 is a perspective view illustrating an example of an upper electromagnet unit according to a first embodiment.

[0041] [Fig. 3]

[0042] Fig. 3 is a longitudinal sectional view of an example of the upper electromagnet unit.

[0043] [Fig. 4 ]

[0044] Fig. 4A is a cross-sectional view taken along line D-D in Fig. 3, and Fig. 4B is a cross-sectional view taken along line E-E in Fig. 3.

[0045] [Fig. 5]

[0046] Fig. 5 is a diagram illustrating an example of a sensor circuit according to the first embodiment.

[0047] [Fig. 6]

[0048] Fig. 6 is a diagram illustrating an example of a theoretical sensor circuit model according to the first embodiment.

[0049] [Fig. 7 ]

[0050] Fig. 7 is a longitudinal sectional view of an example of a modification of the upper electromagnet unit according to the first embodiment.

[0051] [Fig. 8 ]

[0052] Fig. 8A is a cross-sectional view taken along line F-F in Fig. 7, and Fig. 8B is a cross-sectional view taken along line G-G in Fig. 7.

[0053] [Fig. 9]

[0054] Fig. 9 is a diagram illustrating an example of a configuration of a sensor circuit according to a second embodiment.

[0055] [Fig. 10]

[0056] Fig. 10 is a diagram illustrating an example of a theoretical sensor circuit model according to the second embodiment.

[0057] [Fig. 11 ]

[0058] Fig. 11 is a diagram illustrating an example of a sensor circuit according to Example 1.

[0059] [Fig. 12 ]

[0060] Fig. 12 is a diagram illustrating an example of a sensor circuit according to Example 2. 2024-020-GB 4

[0061] [Fig. 13]

[0062] Fig. 13 is a diagram illustrating an example of a sensor circuit according to Example 3.

[0063] [Fig. 14 ]

[0064] Fig. 14 is a diagram illustrating an example of a sensor circuit according to Example 4.

[0065] [Fig. 15]

[0066] Fig. 15 illustrates an example of an amplifier circuit for control of a rotor shaft of a turbomolecular pump.

[0067] [Fig. 16]

[0068] Fig. 16 is a time chart illustrating an example of control in a case where a current command value is larger than a detected value.

[0069] [Fig. 17 ]

[0070] Fig. 17 is a time chart illustrating an example of control in a case where the current command value is smaller than the detected value.

[0071] [Description of Embodiments]

[0072]

[0008] < First Embodiment>

[0073] Hereinafter, a turbomolecular pump 1 according to a first embodiment will be described with reference to the drawings. Some drawings illustrate axes, and each axis is drawn to be in a common direction in each drawing. However, the illustrated axes are merely directions for convenience of description and do not limit an installation mode of the turbomolecular pump 1 at all. In addition, a member may be denoted by a reference sign in one drawing, and the reference sign for the same member may be omitted in other drawings.

[0074]

[0009] ( 1 ) Basic Structure of Turbomolecular Pump

[0075] Fig. 1 illustrates a basic configuration of the turbomolecular pump 1 which is an example of a vacuum pump. The turbomolecular pump 1 generally includes a pump body 100 and a control device 200. In the turbomolecular pump 1, an upper side in Fig. 1 is an upstream (suction) side, and a vacuum chamber (not illustrated) of target equipment such as a semiconductor manufacturing device is connected to an inlet port 11. Further, in the turbomolecular pump 1, a lower side in Fig. 1 is a downstream (exhaust) side, and an auxiliary pump (not illustrated) is connected to an outlet port 51, for example. The turbomolecular pump 1 can be used not only in a vertical posture in a vertical direction as 2024-020-GB 5

[0076] illustrated in Fig. 1 but also in an inverted vertical posture, a horizontal posture, or an inclined posture.

[0077]

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

[0078]

[0011] The turbomolecular pump 1 includes the rotor 20 in which a plurality of rotor blades 22, which are turbine blades for sucking and exhausting gas, are radially formed in multiple stages in a peripheral portion inside of the housing 10. The rotor shaft 21 is attached to the center of the rotor 20, and the rotor shaft 21 is levitated, supported, and positionally controlled by, for example, a five-axis control magnetic bearing. The rotor 20 is generally made of metal such as aluminum or an aluminum alloy.

[0079]

[0012] The housing 10 is formed in a cylindrical shape. The inlet port 11 is formed at an upper end of the housing 10. The housing 10 is attached to a vacuum container such as a chamber of the semiconductor manufacturing device (not illustrated) via an upper flange 12. The inlet port 11 is connected to the vacuum container. The housing 10 is fixed to a base 50 in a state of being placed on the base 50.

[0080]

[0013] The rotor 20 includes the rotor shaft 21 and the rotor blades 22 fixed to an upper portion of the rotor shaft 21 and provided side by side concentrically with respect to an axial center of the rotor shaft 21. In the present example, five stages of rotor blades 22 are provided. Hereinafter, an axis direction of the rotor shaft 21 is referred to as an "axial direction", and a radial direction of the rotor shaft 21 is referred to as a "radial direction". Note that the radial direction and the radial direction are synonymous.

[0081]

[0014] The rotor shaft 21 is supported in a non-contact manner by a magnetic bearing device 60 and an axial magnetic bearing 70 described below. The rotor shaft 21 is formed of a high-permeability material ( Iron, stainless steel, or the like) or the like, is attracted by a magnetic force of a radial electromagnet 63 of the axial magnetic bearing 70, and is supported in a non-contact manner. The radial electromagnet 63 generates a radial electromagnetic force in the rotor shaft 21. 2024-020-GB 6

[0082]

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

[0083]

[0016] In the control device 200, for example, a compensation circuit having a PID adjustment function generates an excitation control command signal of the radial electromagnet 63 based on a position signal detected by the radial displacement sensor 64. Then, an amplifier circuit 150 performs excitation control of the radial electromagnet 63 based on the excitation control command signal, thereby adjusting a position of the rotor shaft 21 in the radial direction.

[0084]

[0017] The axial magnetic bearing 70 includes an axial electromagnet 71. The axial magnetic bearing 70 is connected to the control device 200. The control device 200 is supported in a state in which the rotor shaft 21 is levitated to a predetermined position by controlling an excitation current of the axial electromagnet 71 based on a detected value of an axial displacement sensor 72. The axial electromagnet 71 is arranged with a disc-shaped metal disc provided at a lower portion of the rotor shaft 21 interposed therebetween. The metal disc is made of a high-permeability material such as iron. The axial displacement sensor 72 is provided to detect axial displacement of the rotor shaft 21, and an axial position signal thereof is sent to the control device 200.

[0085]

[0018] Then, in the control device 200, for example, the compensation circuit having the PID adjustment function generates the excitation control command signals for the respective axial electromagnets 71 based on the axial position signal detected by the axial displacement sensor 72. Then, the amplifier circuit 150 performs excitation control of the respective axial electromagnets 71 based on the excitation control command signals. As a result, the axial electromagnet 71 attracts the metal disc upward by a magnetic force, and the axial electromagnet 71 attracts the metal disc downward, thereby adjusting a position of the rotor shaft 21 in the axial direction.

[0086]

[0019] In this manner, the control device 200 appropriately adjusts the magnetic force exerted by the axial electromagnet 71 on the rotor shaft 21, magnetically levitates the rotor shaft 21 in the axial direction, and holds the rotor shaft 21 in a non-contact manner in a space. The amplifier circuit 150 that performs the excitation control of 2024-020-GB 7

[0087] the radial electromagnet 63 and the axial electromagnet 71 is described below.

[0088]

[0020] The rotor blade 22 is formed of a blade inclined at a predetermined angle, and is formed integrally with an upper outer peripheral surface of the rotor 20. Further, the plurality of rotor blades 22 are radially installed around an axis of the rotor 20.

[0089]

[0021] An upper portion and the lower portion of the rotor shaft 21 are inserted into touch-down bearings 23. In a case where the rotor shaft 21 becomes uncontrollable, the rotor shaft 21 rotating at a high speed comes into contact with the touch-down bearing 23 to prevent damage to the turbomolecular pump 1.

[0090]

[0022] The rotor 20 is integrally attached to the rotor shaft 21 by inserting a bolt 25 into a rotor flange 26 and screwing the bolt 25 to a shaft flange 27 in a state in which the upper portion of the rotor shaft 21 is inserted into a boss hole 24.

[0091]

[0023] The motor 30 includes a rotator 31 attached to an outer periphery of the rotor shaft 21 and a stator 32 arranged so as to surround the rotator 31. The stator 32 is connected to the control device 200, and rotation of the rotor 20 is controlled by the control device 200.

[0092]

[0024] The motor 30 includes a plurality of magnetic poles circumferentially arranged so as to surround the rotor shaft 21. Each magnetic pole is controlled by the control device 200 to rotationally drive the rotor shaft 21 by an electromagnetic force acting between each magnetic pole and the rotor shaft 21. In the present embodiment, the number of poles of the motor 30 is two. Therefore, a magnetic flux of the motor 30 exhibits an opposite polarity under radial inversion ( 180-degree rotation in a circumferential direction). In the present embodiment, since attention is paid to the polarity of the magnetic flux of the motor 30 under the radial inversion (the 180-degree rotation in the circumferential direction), the same effect can be obtained as long as the number of poles is an even number and is not a multiple of 4, like 6 and 10. A rotational speed sensor (not illustrated) such as a Hall element, a resolver, or an encoder is incorporated in the motor 30, and a rotational speed of the rotor shaft 21 is detected by a detection signal of the rotational speed sensor. 2024-020-GB 8

[0093]

[0025] Further, for example, a phase sensor (not illustrated) is attached in the vicinity of the radial displacement sensor 64, and detects a phase of rotation of the rotor shaft 21. The control device 200 detects a position of the magnetic pole by using both a detection signal of the phase sensor and the detection signal of the rotational speed sensor.

[0094]

[0026] The stator column 40 is fixed to the base 50 via bolts 41 in a state of being placed on the base 50.

[0095]

[0027] A plurality of stator blades 80 are arranged with a slight gap from the rotor blades 22. Each of the rotor blades 22 is inclined at a predetermined angle from a plane perpendicular to the axis of the rotor shaft 21 in order to transfer molecules of exhaust gas downward by collision. The stator blade 80 is made of, for example, metal such as aluminum, iron, stainless steel, or copper, or metal such as an alloy containing the above metals as a component. The rotor blades 22 and the stator blades 80 are alternately arranged in multiple stages in the axial direction. In the present example, five stages of stator blades 80 are provided.

[0096]

[0028] The stator blade 80 is formed in an annular shape, includes a blade inclined in a direction opposite to the rotor blade 22 and a ring connected to both ends of the blade, and is positioned by being sandwiched in the axial direction by spacers 81 installed in a stacked manner on an inner peripheral surface of the housing 10. In addition, a plurality of blades of the stator blades 80 are also radially installed around the axis of the rotor 20. Lengths of the blades of the rotor blades 22 and the stator blades 80 are set so as to gradually decrease from an upper side to a lower side in the axial direction.

[0097]

[0029] The spacer 81 is a ring-shaped member, and is made of, for example, metal such as aluminum, iron, stainless steel, or copper, or metal such as an alloy containing the above metals as a component. An outer wall of the housing 10 is fixed to an outer periphery of the spacer 81 with a slight gap. The base 50 is arranged at a bottom portion of the housing 10. The outlet port 51 is formed in the base 50 and communicates with the outside. The exhaust gas having entered the inlet port 11 from a chamber (vacuum chamber) side and transferred to the base 50 is sent to the outlet port 51. 2024-020-GB 9

[0098]

[0030] Further, a threaded spacer 53 is arranged between a lower portion of the housing 10 and the base 50 according to an application of the turbomolecular pump 1. The threaded spacer 53 is a cylindrical member made of metal such as aluminum, copper, stainless steel, iron, or an alloy containing the above metals as a component, and a plurality of spiral thread grooves are engraved on an inner peripheral surface of the threaded spacer 53. A direction of a spiral of the thread groove is a direction in which the molecules of the exhaust gas are transferred toward the outlet port 51 when the molecules move in a rotation direction of the rotor 20. A cylindrical portion 20d extends downward from the lowermost portion of the rotor 20 that continues to the rotor blades 22. An outer peripheral surface of the cylindrical portion 20d has a cylindrical shape and protrudes toward the inner peripheral surface of the threaded spacer 53, and is close to the inner peripheral surface of the threaded spacer 53 with a predetermined gap therebetween. The exhaust gas transferred to the thread groove by the rotor blade 22 and the stator blade 80 is sent to the base 50 while being guided by the thread groove.

[0099]

[0031] The base 50 is a disc-shaped member forming a base portion of the turbomolecular pump 1, and is generally made of metal such as iron, aluminum, or stainless steel. Since the base 50 physically holds the turbomolecular pump 1 and also has a function of a heat conduction path, it is desirable to use rigid metal having high thermal conductivity, such as iron, aluminum, or copper. An 0-ring 52 is interposed between the base 50 and the housing 10.

[0100]

[0032] In such a configuration, when the rotor blades 22 are rotationally driven together with the rotor shaft 21 by the motor 30, the exhaust gas is sucked from the chamber through the inlet port 11 by an action of the rotor blades 22 and the stator blades 80. A rotational speed of the rotor blade 22 is usually 20, 000 to 90, 000 rpm, and a circumferential speed at a distal end of the rotor blade 22 reaches 200 to 400 m / s. The exhaust gas sucked from the inlet port 11 passes between the rotor blades 22 and the stator blades 80 and is transferred to the base 50. At this time, a temperature of the rotor blade 22 is increased due to frictional heat generated when the exhaust gas comes into contact with the rotor blade 22, conduction of heat generated by the motor 30, and the like, but such heat is transmitted to the stator blade 80 by radiation, conduction by gas molecules of the exhaust gas, or the like. 2024-020-GB 10

[0101]

[0033] Stator blade spacers 125 are bonded to each other at outer peripheral portions and transmit heat received by the stator blades 80 from the rotor blades 22, frictional heat generated when the exhaust gas comes into contact with the stator blades 80, and the like to the outside.

[0102]

[0034] In the above description, the threaded spacer 53 is arranged on an outer periphery of the cylindrical portion 20d of the rotor 20, and the threaded groove is engraved on the inner peripheral surface of the threaded spacer 53. However, conversely, a thread groove may be engraved on the outer peripheral surface of the cylindrical portion 20d, and a spacer having a cylindrical inner peripheral surface may be arranged around the thread groove.

[0103]

[0035] (2 ) Structure of Magnetic Bearing Device 60

[0104] Next, a specific configuration of the magnetic bearing device 60 will be described with reference to the drawings. Fig. 2 is a perspective view illustrating the upper electromagnet unit 61 according to the first embodiment.

[0105]

[0036] The upper electromagnet unit 61 includes four radial electromagnets 63 that support the rotor shaft 21 in the radial direction in a non-contact manner by the magnetic force, and four radial displacement sensors 64 that detect the radial displacement of the rotor shaft 21. As the radial displacement sensor 64, for example, an inductance sensor having a conductive winding, an eddy current sensor, or the like is used. The position of the rotor shaft 21 is detected on the basis of a change in inductance of the conductive winding depending on the position of the rotor shaft 21, and the detected position is sent to the control device 200.

[0106]

[0037] A coil 63a of the radial electromagnet 63 and a coil 64a of the radial displacement sensor 64 are wound around the same core 65, that is, coiled on the core 65. A plurality of radial electromagnets 63 are arranged side by side in the circumferential direction. The coil 64a of the radial displacement sensor 64 is arranged at a position between the plurality of radial electromagnets 63 in the circumferential direction.

[0107]

[0038] The respective radial electromagnets 63 are arranged while being spaced apart from each other by 90 degrees in the circumferential direction of the core 65. The radial electromagnet 63 includes a pair of magnetic poles 66, 66 formed by winding the coil 63a around a protrusion 2024-020-GB 11

[0108] 65a of the core 65. The pair of magnetic poles 66, 66 has different polarities by winding the coil 63a in opposite directions. The coils 63a adj acent to each other with the radial displacement sensor 64 interposed therebetween are wound around the cores 65 in the same direction, so that the magnetic poles 66, 66 adj acent to each other with the radial displacement sensor 64 interposed therebetween have the same polarity.

[0109] Alternatively, for example, a connection method of each coil 63a may be changed in a state in which all the coils 63a are wound in the same direction as long as the polarities of the respective magnetic poles 66 are the same as each other.

[0110]

[0039] The radial displacement sensor 64 is arranged between the radial electromagnets 63, 63 adj acent to each other in the circumferential direction of the core 65, and the respective radial displacement sensors 64 are arranged on an A axis and a B axis orthogonal to each other. The radial displacement sensor 64 includes a pair of magnetic poles formed by winding the coil 64a around a claw portion 65b of the core 65.

[0111]

[0040] The radial displacement sensor 64 arranged along the A axis detects displacement of the upper portion of the rotor shaft 21 in an A axis direction, and sends an original displacement signal corresponding to the displacement to the control device 200. The radial displacement sensor 64 arranged along the A axis detects displacement of the rotor shaft 21 in a B axis direction, and sends an original displacement signal corresponding to the displacement to the control device 200.

[0112]

[0041] Next, a polarity of the upper electromagnet unit 61 will be described. Fig. 3 is a longitudinal sectional view of the upper electromagnet unit 61. Fig. 4 illustrates cross-sectional views of the upper electromagnet unit 61 in the radial direction, in which Fig. 4A is a cross-sectional view taken along line D-D in Fig. 3, and Fig. 4B is a cross-sectional view taken along line E-E in Fig. 3.

[0113]

[0042] As illustrated in Fig. 3, in the upper electromagnet unit 61 according to the first embodiment, the radial displacement sensor 64 includes the radial displacement sensor 64 including 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. Alternatively, a connection method of each 2024-020-GB 12

[0114] coil 64a may be changed in a state in which the coils 64a may be wound in the same direction as long as the polarities of the upper magnetic pole 67a and the lower magnetic pole 67b are different from each other.

[0115]

[0043] The two radial displacement sensors 64 arranged along the A axis illustrated in Fig. 3 include a first sensor magnetic pole pair Pl and a second sensor magnetic pole pair P2. The two sensor magnetic pole pairs Pl and P2 form a uniaxial sensor unit along the A axis. Here, the magnetic pole pair refers to two magnetic poles that form a flow of a closed magnetic force line M. In the illustrated example, Au- and Al- form a flow of the closed magnetic force line M through the rotor shaft 21 and correspond to the first sensor magnetic pole pair Pl. In addition, a magnetic pole Au+and a magnetic pole Al+form a flow of the closed magnetic force line M through the rotor shaft 21 and correspond to the second sensor magnetic pole pair P2.

[0116]

[0044] That is, the first sensor magnetic pole pair Pl includes two sensor magnetic poles (the upper magnetic pole 67a and the lower magnetic pole 67b) arranged side by side in the axial direction along the rotor shaft 21 which is a rotating shaft. The second sensor magnetic pole pair P2 radially faces the first sensor magnetic pole pair Pl and includes two sensor magnetic poles (the upper magnetic pole 67a and the lower magnetic pole 67b) arranged side by side in the axial direction similarly to the first sensor magnetic pole pair Pl.

[0117]

[0045] As illustrated in Figs. 4A and 4B, similarly, also on the B axis orthogonal to the A axis, another first sensor magnetic pole pair Pl and another second sensor magnetic pole pair P2 radially facing the another first sensor magnetic pole pair Pl are arranged in the upper electromagnet unit 61. That is, in the present embodiment, the upper electromagnet unit 61 includes two sets of the first sensor magnetic pole pair Pl and the second sensor magnetic pole pair P2.

[0118]

[0046] (3) Configuration of Sensor Circuit

[0119] Fig. 5 is a diagram illustrating a sensor circuit according to the present embodiment. As illustrated in Fig. 5, a uniaxial sensor unit U1 arranged along the A axis and a uniaxial sensor unit U2 arranged along the B axis are connected in parallel to a first oscillator SI and a second oscillator S2.

[0120]

[0047] The first oscillator SI outputs an alternating-current voltage as a modulated input signal to the radial displacement sensor 64. The 2024-020-GB 13

[0121] second oscillator S2 outputs an alternating-current voltage having a phase opposite to a phase of the first oscillator SI. In the uniaxial sensor unit U1 arranged along the A axis, an end portion (magnetic pole A1-) of the first sensor magnetic pole pair Pl is connected to the second oscillator S2. An end portion (magnetic pole Au+) of the second sensor magnetic pole pair P2 is connected to the first oscillator SI. Similarly, in the uniaxial sensor unit U2 arranged along the B axis, an end portion (magnetic pole B1-) of the first sensor magnetic pole pair Pl is connected to the second oscillator S2. An end portion (magnetic pole Bu+) of the second sensor magnetic pole pair P2 is connected to the first oscillator SI.

[0122]

[0048] Both the first oscillator SI and the second oscillator S2 output a sine wave signal of 25 kHz. The second oscillator S2 outputs a signal having a phase opposite to a phase of the first oscillator SI. The signals output from the first oscillator SI and the second oscillator S2 may include an offset component. Each of the first oscillator SI and the second oscillator S2 that output a positive phase may be provided for each of the uniaxial sensor units U1 and U2.

[0123]

[0049] In the sensor circuit, one end of the first sensor magnetic pole pair Pl 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 Pl 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 Pl is connected to the magnetic pole Bl+forming one end of the second sensor magnetic pole pair P2.

[0124]

[0050] In the present embodiment, in the sensor circuit, coils of the sensor magnetic poles forming the sensor magnetic pole pairs Pl and P2 are connected in series. As a result, it can be expected to suppress noise of the sensor circuit.

[0125]

[0051] In the sensor circuit, in each of the uniaxial sensor units U1 and U2, a voltage at a connection point of the first sensor magnetic pole pair Pl and the second sensor magnetic pole pair P2 is input to a demodulation circuit RC. The demodulation circuit RC demodulates an output signal from the radial displacement sensor 64. The sensor circuit 2024-020-GB 14

[0126] may be a synchronous detection system in which a reference signal synchronized with an input signal of 25 kHz is multiplied by an input signal to the demodulation circuit RC, and a low-pass filter acts on the multiplied signal. Alternatively, the sensor circuit may be a sampling detection system that directly performs AD conversion of the input signal to the demodulation circuit RC, which is a carrier wave, in synchronization with the input signal of 25 kHz. The demodulation circuit RC demodulates a midpoint voltage of the first sensor magnetic pole pair Pl and the second sensor magnetic pole pair P2 as a displacement signal. The demodulation circuit RC may be an analog circuit or a digital circuit.

[0127]

[0052] In the present embodiment, among the sensor magnetic poles of each of the first sensor magnetic pole pair Pl and the second sensor magnetic pole pair P2, polarities of a pair of sensor magnetic poles radially facing each other are opposite to each other. As illustrated in Fig. 3, polarities of the magnetic pole Au~ and the magnetic pole Au+are opposite to each other. That is, in the magnetic pole Au~, the magnetic force line M is directed from an inner side to an outer side in the radial direction, but in the magnetic pole Au+, the magnetic force line M is directed from the outer side to the inner side in the radial direction.

[0128]

[0053] Similarly, in Fig. 3, in the magnetic pole Al~, the magnetic force line M is directed from the outer side to the inner side in the radial direction, but in the magnetic pole Al+radially facing the magnetic pole Al~, the magnetic force line M is directed from the inner side to the outer side in the radial direction. Therefore, polarities of the magnetic pole Al~ and the magnetic pole Al+are also opposite to each other.

[0129]

[0054] In addition, in two sensor magnetic pole pairs radially facing each other along the B axis, polarities of the magnetic poles Bu+and Bu~ corresponding to a pair of sensor magnetic poles radially facing each other are opposite to each other as illustrated in Fig. 4A. That is, in the magnetic pole Bu+, the magnetic force line M is directed from the outer side to the inner side in the radial direction, but in the magnetic pole Bu~, the magnetic force line M is directed from the inner side to the outer side in the radial direction. 2024-020-GB 15

[0130]

[0055] Similarly, in Fig. 4B, in the magnetic pole Bl+, the magnetic force line M is directed from the inner side to the outer side in the radial direction, but in the magnetic pole Bl~, the magnetic force line M is directed from the outer side to the inner side in the radial direction. Therefore, polarities of the magnetic pole Bl+and the magnetic pole Bl~ are also opposite to each other.

[0131]

[0056] Next, an electrical characteristic of the sensor circuit connected by such a circuit configuration will be described. Fig. 6 is a diagram illustrating a theoretical sensor circuit model. That is, the circuit model is a theoretical sensor circuit in which the configuration of the uniaxial sensor unit is simplified and which uses an ideal alternating-current power supply that has no internal resistance and does not cause a voltage drop in order to describe the electrical characteristic of the sensor circuit according to the present embodiment. In the sensor circuit, the magnetic poles radially facing each other in the two sensor magnetic pole pairs Pl and P2 have different polarities, and the midpoint voltage when voltages of opposite phases are applied from the respective power supplies is set as an output voltage of the uniaxial sensor unit U1.

[0132]

[0057] In the circuit model illustrated in Fig. 6, in the uniaxial sensor unit Ul, vectors of voltages of the first sensor magnetic pole pair Pl and the second sensor magnetic pole pair P2 are defined as the same direction. Here, since the first sensor magnetic pole pair Pl and the second sensor magnetic pole pair P2 radially face each other, if a gap on one side is widened, a gap on the other side exhibits the opposite behavior.

[0133]

[0058] Here, a leakage flux of the motor 30 enters the first sensor magnetic pole pair Pl and the second sensor magnetic pole pair P2.

[0134] Since the leakage flux of the motor 30 includes a time-varying component such as an electrical angle rotation frequency component or a switching frequency component, an electromotive force is generated for the coil 64a. The electromotive force causes noise to the radial displacement sensor 64 from the motor 30.

[0135]

[0059] Since the motor 30 is at a position different from that of the radial displacement sensor 64 in the axial direction, a distance between the motor 30 and the upper magnetic pole 67a in the axial direction and a 2024-020-GB 16

[0136] distance between the motor 30 and the lower magnetic pole 67b in the axial direction are different from each other.

[0137] Therefore, a magnetic flux density of the leakage flux of the motor 30 entering the upper magnetic pole 67a and a magnetic flux density of the leakage flux of the motor 30 entering the lower magnetic pole 67b have the same polarity but different magnitudes.

[0138]

[0060] The upper magnetic pole 67a and the lower magnetic pole 67b are connected in series so as to have different polarities. Therefore, the electromotive force generated in the upper magnetic pole 67a due to the leakage flux of the motor 30 and the electromotive force generated in the lower magnetic pole 67b due to the leakage flux of the motor 30 have different polarities and different magnitudes and do not thus completely cancel each other.

[0139] Therefore, in each of the sensor magnetic pole pairs Pl and P2, the electromotive force due to the leakage flux of the motor 30 is generated.

[0140]

[0061] The leakage flux of the motor 30 entering the two sensor magnetic poles radially facing each other has different polarities and substantially the same magnitude. On the other hand, the respective sensor magnetic poles radially facing each other have different polarities.

[0141] Therefore, the electromotive forces generated in the coils of the two sensor magnetic pole pairs Pl and P2 due to the leakage flux of the motor 30 have the same sign and substantially the same magnitude.

[0142]

[0062] On the premise of such a relationship, an impedance of each of the first sensor magnetic pole pair Pl and the second sensor magnetic pole pair P2 with respect to a motor noise frequency component is expressed by Expressions ( 1 ) and (2 ).

[0143] Zp= Rs + jω(L0 - L1x) ... (1)

[0144] Zn= Rs + jω(L0+ L1x) ... (2)

[0145] Zp: impedance of second sensor magnetic pole pair P2

[0146] Zn: impedance of first sensor magnetic pole pair P1

[0147] Rs: sensor coil resistance (Ω)

[0148] ω: frequency of noise voltage by motor (Hz)

[0149] L0: inductance of sensor coil (when rotor shaft is at center) (H)

[0150] L1: inclination of sensor coil inductance with respect to displacement amount of rotor shaft (H / mm)

[0151] x: displacement amount of rotor shaft (mm) 2024-020-GB 17

[0152]

[0063] That is, in Expressions ( 1 ) and (2 ), a change in inductance of the sensor coil is expressed as linear approximation with respect to the displacement amount of the rotor shaft 21. In the linear approximation, L1xis assumed to be sufficiently smaller than L0.

[0153]

[0064] Next, a voltage equation for motor noise based on Expressions ( 1 ) and (2 ) is obtained by Expression (3). However, since attention is paid to the motor noise frequency component, a voltage of an oscillator is set to 0.

[0154] Vnp+ Vnn+ 2(Rs+ jωL0) Is= 0 ... (3)

[0155] Vnp: electromotive force (V) of first sensor magnetic pole pair Pl due to leakage flux of motor

[0156] Vnn: electromotive force (V) of second sensor magnetic pole pair P2 due to leakage flux of motor

[0157] Is: current flowing through circuit (motor noise frequency component) (A)

[0065] Expression (4 ) and Expression (5) are obtained from Expression (3).

[0158] Is= -(Vnp+ Vnn) / 2(Rs+ jωL0) ... (4)

[0159] Vs= Vnn+ (Rs+ jω(L0+ L1x)) Is... (5)

[0160] Vs: output potential of radial displacement sensor (motor noise frequency component) (V)

[0161]

[0066] Then, Expression ( 6) is obtained by substituting Expression (4 ) into Expression (5).

[0162] Vs= -1 / 2(Vnp- Vnn) - (jωL1x)(Vnp+ Vnn) / 2(Rs+ jωL0) ... (6)

[0163] Here, since an absolute value of Lixis usually a sufficiently small value with respect to Lo, an absolute value of (jωL1x) / (Rs + jωL0) included in Expression ( 6) is a sufficiently smaller value than 1. Therefore, in Expression ( 6), a coefficient of the second term has a sufficiently smaller value than a coefficient of the first term. Vscan be reduced by connecting the sensor coils such that Vnpand Vnnhave the same sign so that the first term of Expression ( 6) is eliminated in the calculation expressions. As a result, it is theoretically derived that an influence of the motor noise on the radial displacement sensor 64 can be reduced.

[0164]

[0067] As described above, in the present example, the number of poles of the motor 30 is an even number and is not a multiple of 4, the leakage flux of the motor 30 exhibits an opposite polarity under radial inversion ( 180-degree rotation in the circumferential direction). In addition, the respective magnetic poles radially facing each other have opposite 2024-020-GB 18

[0165] polarities. Therefore, the electromotive forces Vnpand Vnngenerated in the two sensor magnetic pole pairs due to the leakage flux of the motor 30 have the same sign.

[0166] As described above, it is possible to reduce noise of the radial displacement sensor 64 caused by the motor 30.

[0167]

[0068] (4 ) Modification of First Embodiment

[0168] Next, a modification of the first embodiment will be described. Fig.

[0169] 7 is a longitudinal sectional view of a modification of the upper electromagnet unit 61 according to the first embodiment. Fig. 8 illustrates cross-sectional views of an upper electromagnet unit 61 according to the modification in the radial direction, in which Fig. 8A is a cross-sectional view taken along line F-F in Fig. 7, and Fig. 8B is a cross-sectional view taken along line G-G in Fig. 7.

[0170]

[0069] First, in a magnetic bearing device 60 according to the present modification, the number of poles of a motor 30 is different from that of the first embodiment. In the present modification, the number of poles of the motor 30 is four, which is an even number and a multiple of 4.

[0171] Therefore, a magnetic flux of the motor 30 exhibits the same polarity under radial inversion ( 180-degree rotation in a circumferential direction). In a case where the motor 30 includes four poles as in the present modification, a phase of noise entering magnetic poles of a radial displacement sensor 64 facing each other at 180 degrees changes. In the present modification, since attention is paid to the polarity of the magnetic flux of the motor 30 under the radial inversion ( 180-degree rotation in the circumferential direction), for example, the same effect can be obtained as long as the number of poles is a multiple of 4, like 8 and 12.

[0172]

[0070] In the present modification, a connection direction of a coil 64a is changed on the basis of the fact that the number of poles of the motor 30 is different from that of the first embodiment. Specifically, the connection direction of the coil 64a is changed by changing a winding direction of the coil 64a wound around a claw portion 65b of a core 65 from that in the configuration of the first embodiment. The connection direction of the coil 64a may be changed by changing a portion to be connected after the winding from that in the configuration of the first embodiment. In the present modification, as illustrated in Fig. 7, magnetic poles of two sensor magnetic poles (an upper magnetic pole 67a 2024-020-GB 19

[0173] and a lower magnetic pole 67b) arranged side by side in an axial direction are also different from each other.

[0174]

[0071] Furthermore, in the radial displacement sensor 64 according to the present modification, among the sensor magnetic poles of each of a first sensor magnetic pole pair Pl and a second sensor magnetic pole pair P2, polarities of a pair of sensor magnetic poles radially facing each other are the same as each other. As illustrated in Fig. 7, polarities of a magnetic pole Au- and a magnetic pole Au+radially facing each other are the same as each other. That is, in the magnetic pole Au-, a magnetic force line M is directed from an outer side to an inner side in a radial direction, and in the magnetic pole Au+, similarly, the magnetic force line M is directed from the outer side to the inner side in the radial direction. Therefore,

[0175]

[0072] Similarly, in Fig. 7, in a magnetic pole Al~, the magnetic force line M is directed from the inner side to the outer side in the radial direction, and also in a magnetic pole Al+, the magnetic force line M is directed from the inner side to the outer side in the radial direction. Therefore, polarities of the magnetic pole Al~ and the magnetic pole Al+radially facing each other are also the same as each other.

[0176]

[0073] In addition, in two sensor magnetic pole pairs radially facing each other along a B axis, polarities of a magnetic pole Bu+and a magnetic pole Bu~ radially facing each other are the same as each other as illustrated in Fig. 8A. That is, in the magnetic pole Bu+, the magnetic force line M is directed from the outer side to the inner side in the radial direction, and also in the magnetic pole Bu~, the magnetic force line M is directed from the outer side to the inner side in the radial direction.

[0177]

[0074] Similarly, in Fig. 8B, in a magnetic pole Bl+, the magnetic force line M is directed from the inner side to the outer side in the radial direction, and in a magnetic pole Bl~, the magnetic force line M is directed from the inner side to the outer side in the radial direction. Therefore, polarities of the magnetic pole Bl+and the magnetic pole Bl~ are also the same as each other.

[0178]

[0075] As described above, in the present modification, since the number of poles of the motor 30 is a multiple of 4, a leakage flux of the motor 30 exhibits the same polarity under radial inversion ( 180-degree 2024-020-GB 20

[0179] rotation in the circumferential direction). In addition, the respective magnetic poles radially facing each other have the same polarity.

[0180] Therefore, electromotive forces Vnpand Vnngenerated in two sensor magnetic pole pairs due to the leakage flux of the motor 30 have the same sign.

[0181] As described above, it is possible to reduce noise of the radial displacement sensor 64 caused by the motor 30.

[0182]

[0076] < Second Embodiment>

[0183] Next, a magnetic bearing device 60 according to a second embodiment will be described with reference to the drawings. In the present embodiment, the number of poles of a motor 30 is two. Therefore, a magnetic flux of the motor 30 exhibits an opposite polarity under radial inversion ( 180-degree rotation in a circumferential direction). In the present embodiment, since attention is paid to the polarity of the magnetic flux of the motor 30 under the radial inversion ( 180-degree rotation in the circumferential direction), the same effect can be obtained as long as the number of poles is an even number and is not a multiple of 4, like 6 and 10. A basic structure of a turbomolecular pump 1 and a configuration of the magnetic bearing device 60 are the same as those of the first embodiment, and a description thereof will be omitted.

[0184]

[0077] (5) Configuration of Sensor Circuit

[0185] Fig. 9 is a diagram illustrating a configuration of a sensor circuit according to the second embodiment. In a radial displacement sensor according to the present embodiment, similarly to the first embodiment, it is assumed that respective coils of a first sensor magnetic pole pair Pl and a second sensor magnetic pole pair P2 are connected such that polarities of respective magnetic poles are different from each other (see Fig. 3 ).

[0186]

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

[0187]

[0079] One end (Au+in the illustrated example) of the coil of the second sensor magnetic pole pair P2 is connected to the oscillator S via 2024-020-GB 21

[0188] a resistor R. One end of the coil of the second sensor magnetic pole pair P2 may be connected to the oscillator S via an inductor. The other end (Al+in the illustrated example) of the coil of the second sensor magnetic pole pair P2 is connected to the ground.

[0189]

[0080] A voltage at the end (Au-in the illustrated example) of the first sensor magnetic pole pair Pl that is adj acent to the oscillator S and a voltage at the end (Au+in the illustrated example) of the second sensor magnetic pole pair P2 that is adj acent to the oscillator S are input to a demodulation circuit RC via a differential circuit.

[0190]

[0081] In addition, in a sensor magnetic pole pair radially facing each other along a B axis, one end (Bu-in the illustrated example) of the coil of the first sensor magnetic pole pair Pl is connected to the oscillator S via a resistor R. One end of the coil of the first sensor magnetic pole pair Pl may be connected to the oscillator S via an inductor. The other end (Bl-in the illustrated example) of the coil of the first sensor magnetic pole pair Pl is connected to the ground.

[0191]

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

[0192]

[0083] A voltage at the end (Bu-in the illustrated example) of the first sensor magnetic pole pair Pl that is adj acent to the oscillator S and a voltage at the end (Bu+in the illustrated example) of the second sensor magnetic pole pair P2 that is adj acent to the oscillator S are input to a demodulation circuit RC via a differential circuit.

[0193]

[0084] In the magnetic bearing device 60 according to the second embodiment, similarly to the first embodiment, a pair of sensor magnetic poles radially facing each other among sensor magnetic poles of the first sensor magnetic pole pair Pl and the second sensor magnetic pole pair P2 is connected so as to have opposite polarities. Since such a configuration is the same as the configuration in Figs. 3 and 4 in the first embodiment, a detailed description thereof will be omitted. With such configurations, also in the present embodiment, an influence of motor noise can be reduced similarly to the first embodiment. This point 2024-020-GB 22

[0194] will be described as an electrical characteristic of a circuit model illustrated in Fig. 10.

[0195]

[0085] Fig. 10 is a diagram illustrating a theoretical sensor circuit model according to the second embodiment. The circuit model is a theoretical circuit model in which a configuration of a uniaxial sensor unit is simplified and which uses an ideal alternating-current power supply that has no internal resistance and does not cause a voltage drop in order to describe the electrical characteristic of the sensor circuit according to the present embodiment. In the circuit, the magnetic poles radially facing each other in the two sensor magnetic pole pairs Pl and P2 have different polarities, and in a state in which the same voltage is applied from respective power supplies, a difference between the respective voltages is an output voltage of a uniaxial sensor unit U1.

[0196]

[0086] In the circuit model illustrated in Fig. 10, in the uniaxial sensor unit Ul, vectors of electromotive forces Vnpand Vnnof the first sensor magnetic pole pair Pl and the second sensor magnetic pole pair P2 due to a leakage flux of the motor 30 are defined as the same direction. At this time, a voltage (motor noise frequency component) Vsinput to the demodulation circuit RC is expressed by Expression (7 ).

[0197] Vs= (Vnp- Vnn)... (7 )

[0198] Therefore, the influence of the motor noise can be reduced by connecting the sensor coil such that Vnpand Vnnhave the same sign in order to reduce Expression (7 ).

[0199]

[0087] As described above, in the present example, the number of poles of the motor 30 is an even number and is not a multiple of 4, the leakage flux of the motor 30 exhibits an opposite polarity under radial inversion ( 180-degree rotation in the circumferential direction). In addition, the respective magnetic poles radially facing each other have opposite polarities.

[0200] Therefore, the electromotive forces Vnpand Vnngenerated in the two sensor magnetic pole pairs due to the leakage flux of the motor 30 have the same sign.

[0201] As described above, it is possible to reduce noise of a radial displacement sensor 64 caused by the motor 30.

[0202]

[0088] ( 6) Modification of Second Embodiment

[0203] In the second embodiment, a modification similar to the first embodiment can be adopted, that is, the number of poles of the motor 30 2024-020-GB 23

[0204] can be changed to a multiple of 4 in a structure of the magnetic bearing device 60. Then, as illustrated in Figs. 7 and 8, connection is performed such that a pair of sensor magnetic poles radially facing each other among the sensor magnetic poles of each of a first sensor magnetic pole pair Pl and a second sensor magnetic pole pair P2 has the same polarity.

[0205]

[0089] Since a specific polarity of each coil in this case is the same as the configuration in Figs. 7 and 8, a detailed description will be omitted. As a result, similarly to the second embodiment, since a voltage (motor noise frequency component) Vs input to a demodulation circuit RC is expressed by Expression (7 ), an influence of motor noise can be reduced by connecting sensor coils such that Vnpand Vnnhave the same sign.

[0206]

[0090] As described above, in the present modification, since the number of poles of a motor 30 is a multiple of 4, a leakage flux of the motor 30 exhibits the same polarity under radial inversion ( 180-degree rotation in a circumferential direction). In addition, the respective magnetic poles radially facing each other have the same polarity.

[0207] Therefore, electromotive forces Vnpand Vnngenerated in two sensor magnetic pole pairs due to the leakage flux of the motor 30 have the same sign.

[0208] As described above, it is possible to reduce noise of a radial displacement sensor 64 caused by the motor 30.

[0209]

[0091] < Other Examples>

[0210] Next, other examples of the present invention will be described with reference to the drawings.

[0211]

[0092] (7 ) Other Examples of First Embodiment

[0212] Fig. 11 is a diagram illustrating a sensor circuit according to Example 1 as another example of the first embodiment. In Example 1 illustrated in Fig. 11, the sensor circuit includes one set of sensor magnetic pole pairs radially facing each other. In this case, for example, a uniaxial sensor unit U1 is arranged only on an A axis in an upper electromagnet unit 61.

[0213]

[0093] Fig. 12 is a diagram illustrating a sensor circuit according to Example 2 which is another example of the first embodiment. In Example 2 illustrated in Fig. 12, the sensor circuit includes four pairs of sensor magnetic poles radially facing each other. That is, in the illustrated example, five-axis control is performed for an axial magnetic bearing 70. 2024-020-GB 24

[0214] In Fig. 12, a suffix "h" at an end of a reference sign of a sensor magnetic pole indicates a configuration of an upper electromagnet unit 61, and a suffix "b" indicates a configuration of a lower electromagnet unit 62.

[0215]

[0094] In this case, a uniaxial sensor unit U1 and a uniaxial sensor unit U2 are arranged along an A axis and a B axis of the upper electromagnet unit 61. Further, a uniaxial sensor unit U3 and a uniaxial sensor unit U4 are arranged along an A axis and a B axis of the lower electromagnet unit 62. As such, the number of sensor magnetic pole pairs may be three or more.

[0216]

[0095] Fig. 13 is a diagram illustrating a sensor circuit according to Example 3 which is another example of the first embodiment. In Example 3 illustrated in Fig. 13, a power supply circuit based on practical implementation is constructed. That is, in an actual circuit, there is an influence of impedance of a sensor and the like, and thus, there is an influence of an internal resistance and a voltage drop. Therefore, in Example 3, an input resistor R1 is connected downstream of each of the first oscillator SI and the second oscillator S2, and a capacitor C is connected in parallel with a first sensor magnetic pole pair Pl and a second sensor magnetic pole pair P2. Since a resonance circuit is formed by an inductance of a sensor coil and the capacitor C, energy of an output voltage of the sensor can be efficiently transmitted.

[0217]

[0096] In addition, two voltage-dividing resistors R2 are connected in parallel with the first sensor magnetic pole pair Pl and the second sensor magnetic pole pair P2. A midpoint voltage of the two voltagedividing resistors R2 and a midpoint voltage of the first sensor magnetic pole pair Pl and the second sensor magnetic pole pair P2 are input to a demodulation circuit RC via a differential circuit. As a result, an influence of common mode noise occurring in the circuit can be reduced.

[0218]

[0097] ( 8 ) Other Examples of Second Embodiment

[0219] Fig. 14 is a diagram illustrating a sensor circuit according to Example 4 as another example of the second embodiment. In Example 4 illustrated in Fig. 14, the sensor circuit includes four pairs of sensor magnetic poles radially facing each other. That is, in the illustrated example, five-axis control is performed for an axial magnetic bearing 70.

[0220]

[0098] In this case, a uniaxial sensor unit U1 and a uniaxial sensor unit U2 are arranged along an A axis and a B axis of an upper 2024-020-GB 25

[0221] electromagnet unit 61. Further, a uniaxial sensor unit U3 and a uniaxial sensor unit U4 are arranged along an A axis and a B axis of a lower electromagnet unit 62.

[0222]

[0099] < Conf iguration of Control Circuit>

[0223] Next, the amplifier circuit 150 that performs the excitation control of the radial electromagnet 63 and the axial electromagnet 71 will be described with regard to the turbomolecular pump 1 configured as described above. A circuit diagram of the amplifier circuit 150 is illustrated in Fig. 15.

[0224]

[0100] In Fig. 15, one end of an electromagnet winding 151 forming the radial electromagnet 63 and the like is connected to a positive electrode 171a of a power supply 171 via a transistor 161. The other end of the electromagnet winding 151 is connected to a negative electrode 171b of the power supply 171 via a current detection circuit 181 and a transistor 162. The transistors 161 and 162 are so-called power metal-oxide-semiconductor field-effect transistors (MOSFETs), and have a structure in which a diode is connected between a source and a drain.

[0225]

[0101] At this time, in the transistor 161, a cathode terminal 161a of the diode is connected to the positive electrode 171a, and an anode terminal 161b is connected to one end of the electromagnet winding 151. In the transistor 162, a cathode terminal 162a of the diode is connected to the current detection circuit 181, and an anode terminal 162b is connected to the negative electrode 171b.

[0226]

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

[0227]

[0103] The amplifier circuit 150 configured as described above corresponds to one electromagnet. Therefore, for example, in a case where the magnetic bearing is the five-axis control magnetic bearing and the total number of electromagnets is 10, a similar amplifier circuit 150 is 2024-020-GB 26

[0228] configured for each of the electromagnets, and 10 amplifier circuits 150 are connected in parallel to the power supply 171.

[0229]

[0104] Furthermore, an amplifier control circuit 191 is implemented by, for example, a digital signal processor unit (hereinafter, referred to as a DSP unit, which is not illustrated) of the control device 200, and the amplifier control circuit 191 switches on / off of the transistors 161 and 162.

[0230]

[0105] The amplifier control circuit 191 compares a current value detected by the current detection circuit 181 (a signal reflecting the current value is referred to as a current detection signal 191c) with a predetermined current command value. A magnitude (pulse width times Tpl and Tp2 ) of a pulse width generated in a control cycle Ts that is one cycle of PWM control is determined on the basis of a result of the comparison. As a result, gate drive signals 191a and 191b having the pulse widths are output from the amplifier control circuit 191 to gate terminals of the transistors 161 and 162.

[0231]

[0106] It is necessary to control the position of the rotor shaft 21 at a high speed and with a strong force when the rotor shaft 21 passes through a resonance point during an acceleration operation for the rotational speed of the rotor shaft 21 or when a disturbance occurs during a constant-speed operation. Therefore, for example, a voltage of about 50 V is used as the power supply 171 so that a current flowing through the electromagnet winding 151 can be rapidly increased (or decreased). In addition, a capacitor (not illustrated) is usually connected between the positive electrode 171a and the negative electrode 171b of the power supply 171 in order to stabilize the power supply 171.

[0232]

[0107] In such a configuration, when both the transistors 161 and 162 are turned on, the current (hereinafter, referred to as an electromagnet current iL) flowing through the electromagnet winding 151 is increased, and when both the transistors 161 and 162 are turned off, the electromagnet current iL is decreased.

[0233]

[0108] In addition, when one of the transistors 161 and 162 is turned on and the other is turned off, a so-called flywheel current is held. Then, by causing the flywheel current to flow through the amplifier circuit 150 in this manner, a hysteresis loss in the amplifier circuit 150 can be reduced, and power consumption of the entire circuit can be suppressed low. By controlling the transistors 161 and 162 in this 2024-020-GB 27

[0234] manner, high-frequency noise such as harmonics occurring in the turbomolecular pump 1 can be reduced. Furthermore, by measuring the flywheel current with the current detection circuit 181, the electromagnet current iL flowing through the electromagnet winding 151 can be detected.

[0235]

[0109] That is, in a case where the detected current value is smaller than the current command value, as illustrated in Fig. 16, both the transistors 161 and 162 are turned on for a time corresponding to the pulse width time Tpl only once in the control cycle Ts ( for example, 100 ps). Therefore, the electromagnetic current iL during this period is increased toward a current value iLmax (not illustrated) that can flow from the positive electrode 171a to the negative electrode 171b via the transistors 161 and 162.

[0236]

[0110] On the other hand, in a case where the detected current value is larger than the current command value, as illustrated in Fig. 17, both the transistors 161 and 162 are turned off for a time corresponding to the pulse width time Tp2 only once in the control cycle Ts. Therefore, the electromagnet current iL during this period is decreased toward a current value iLmin (not illustrated) that can be regenerated from the negative electrode 171b to the positive electrode 171a via the diodes 165 and 166.

[0237]

[0111] In either case, either one of the transistors 161 and 162 is turned on after the pulse width times Tpl and Tp2 elapse. Therefore, during this period, the flywheel current is held in the amplifier circuit 150.

[0238]

[0112] < Others>

[0239] In each of the above-described embodiments, the plurality of radial electromagnets 63 are arranged side by side in the circumferential direction, and the sensor magnetic poles 67a and 67b are arranged at positions between the radial electromagnets 63 in the circumferential direction. However, the positions of the sensor magnetic poles 67a and 67b are not limited thereto. That is, the magnetic bearing device 60 may have a configuration in which the radial electromagnets 63 and the sensor magnetic poles 67a and 67b are arranged at positions separated from each other in the axial direction.

[0240]

[0113] In particular, when the sensor magnetic poles 67a and 67b are positioned between the motor 30 and the radial electromagnet 63 in the 2024-020-GB 28

[0241] axial direction, a distance between the sensor magnetic poles 67a and 67b and the motor 30 in the axial direction is short. Therefore, the leakage flux of the motor 30 entering the sensor magnetic poles 67a and 67b is increased, and the influence of noise is also increased. Therefore, by arranging the radial electromagnet 63 and the sensor magnetic poles 67a and 67b at the positions separated in the axial direction, it is possible to suitably reduce the noise from the motor 30 by adopting the configuration of the present invention.

[0242]

[0114] In each of the above-described embodiments, the radial electromagnet 63 and the sensor magnetic poles 67a and 67b are arranged side by side in the circumferential direction, and in particular, the sensor magnetic poles 67a and 67b are arranged side by side in the axial direction. For this reason, among the two sensor magnetic poles 67a and 67b, a sensor magnetic pole closer to the motor 30 in the axial direction is particularly susceptible to the noise from the motor 30. The present invention can particularly suitably reduce the influence of the noise from the motor 30 on the magnetic bearing device 60 having such a configuration.

[0243]

[0115] The present invention is not limited to the above-described embodiments, and includes various modifications. For example, the abovedescribed embodiments have been described in detail for easy understanding of the present invention, and the present invention is not necessarily limited to those having all the described configurations. In addition, a part of the configuration of one embodiment can be replaced with the configuration of another embodiment, and the configuration of another embodiment can be added to and combined with the configuration of one embodiment. In addition, it is possible to add, delete, and replace other configurations for a part of the configuration of each embodiment.

[0244] The above-described embodiments disclose at least the configurations described in the claims.

[0245] [Reference Signs List]

[0246]

[0116]

[0247] 1 Turbomolecular pump

[0248] 10 Housing

[0249] 20 Rotor

[0250] 22 Rotor blade

[0251] 21 Rotor shaft 2024-020-GB 29 30 Motor

[0252] 40 Stator column

[0253] 50 Base

[0254] 51 Outlet port

[0255] 63 Radial electromagnet

[0256] 63a Coil

[0257] 64 Radial displacement sensor

[0258] 64a Coil

[0259] 65 Core

[0260] 65a Protrusion

[0261] 65b Claw portion

[0262] 67a Upper magnetic pole

[0263] 67b Lower magnetic pole

[0264] 80 Stator blade

[0265] 60 Magnetic bearing device

[0266] 100 Pump body

[0267] 101 Inlet port

[0268] 200 Control device

[0269] Pl First sensor magnetic pole pair P2 First sensor magnetic pole pair Ul, U2, U3, U4 Uniaxial sensor unit S1 First oscillator

[0270] S2 Second oscillator

[0271] RC Demodulation circuit

[0272] R, Rl, R2 Resistor

Claims

2024-020-GB 30Claims

1. A magnetic bearing device comprising:a rotating body;a motor that rotationally drives the rotating body and includes poles whose number is an even number and is not a multiple of 4;one or more radial electromagnets that generate a radial electromagnetic force in the rotating body;a radial displacement sensor that measures radial displacement of the rotating body;a first oscillator that outputs an alternating-current voltage as a modulated input signal to the radial displacement sensor;a second oscillator that outputs an alternating-current voltage having a phase opposite to a phase of the first oscillator; anda demodulation circuit that demodulates an output signal from the radial displacement sensor, whereinthe radial displacement sensor includes:a first sensor magnetic pole pair including two sensor magnetic poles arranged side by side in an axial direction along a rotating shaft of the rotating body; anda second sensor magnetic pole pair including two sensor magnetic poles radially facing the first sensor magnetic pole pair and arranged side by side in the axial direction,each coil of the first sensor magnetic pole pair and the second sensor magnetic pole pair is connected such that polarities of the respective magnetic poles are different from each other,one end of the first sensor magnetic pole pair is connected to one end of the second sensor magnetic pole pair such that polarities of a pair of sensor magnetic poles radially facing each other, among the sensor magnetic poles of the first sensor magnetic pole pair and the sensor magnetic poles of the second sensor magnetic pole pair, are opposite to each other,the other end of the first sensor magnetic pole pair is connected to the first oscillator,the other end of the second sensor magnetic pole pair is connected to the second oscillator, and2024-020-GB 31a voltage at a connection point of the first sensor magnetic pole pair and the second sensor magnetic pole pair is input to the demodulation circuit.

2. A magnetic bearing device comprising:a rotating body;a motor that rotationally drives the rotating body and includes poles whose number is an even number and is a multiple of 4;one or more radial electromagnets that generate a radial electromagnetic force in the rotating body;a radial displacement sensor that measures radial displacement of the rotating body;a first oscillator that outputs an alternating-current voltage as a modulated input signal to the radial displacement sensor;a second oscillator that outputs an alternating-current voltage having a phase opposite to a phase of the first oscillator; anda demodulation circuit that demodulates an output signal from the radial displacement sensor, whereinthe radial displacement sensor includes:a first sensor magnetic pole pair including two sensor magnetic poles arranged side by side in an axial direction along a rotating shaft of the rotating body; anda second sensor magnetic pole pair including two sensor magnetic poles radially facing the first sensor magnetic pole pair and arranged side by side in the axial direction,each coil of the first sensor magnetic pole pair and the second sensor magnetic pole pair is connected such that polarities of the respective magnetic poles are different from each other,one end of the first sensor magnetic pole pair is connected to one end of the second sensor magnetic pole pair such that polarities of a pair of sensor magnetic poles radially facing each other, among the sensor magnetic poles of the first sensor magnetic pole pair and the sensor magnetic poles of the second sensor magnetic pole pair, are the same as each other,the other end of the first sensor magnetic pole pair is connected to the first oscillator,2024-020-GB 32the other end of the second sensor magnetic pole pair is connected to the second oscillator, anda voltage at a connection point of the first sensor magnetic pole pair and the second sensor magnetic pole pair is input to the demodulation circuit.

3. A magnetic bearing device comprising:a rotating body;a motor that rotationally drives the rotating body and includes poles whose number is an even number and is not a multiple of 4;one or more radial electromagnets that generate a radial electromagnetic force in the rotating body;a radial displacement sensor that measures radial displacement of the rotating body;an oscillator that outputs an alternating-current voltage as a modulated input signal to the radial displacement sensor; anda demodulation circuit that demodulates an output signal from the radial displacement sensor, whereinthe radial displacement sensor includes:a first sensor magnetic pole pair including two sensor magnetic poles arranged side by side in an axial direction along a rotating shaft of the rotating body; anda second sensor magnetic pole pair including two sensor magnetic poles radially facing the first sensor magnetic pole pair and arranged side by side in the axial direction,each coil of the first sensor magnetic pole pair and the second sensor magnetic pole pair is connected such that polarities of the respective magnetic poles are different from each other,one end of the coil of the first sensor magnetic pole pair is onnected to the oscillator via a resistor and / or an inductor,the other end of the coil of the first sensor magnetic pole pair is onnected to a ground,one end of the coil of the second sensor magnetic pole pair is onnected to the oscillator via a resistor and / or an inductor,the other end of the coil of the second sensor magnetic pole pair is onnected to a ground,2024-020-GB 33a pair of sensor magnetic poles radially facing each other among the sensor magnetic poles of the first sensor magnetic pole pair and the sensor magnetic poles of the second sensor magnetic pole pair is connected so as to have opposite polarities, anda voltage at an end portion of the first sensor magnetic pole pair that is adjacent to the oscillator and a voltage at an end portion of the second sensor magnetic pole pair that is adjacent to the oscillator are input to the demodulation circuit via a differential circuit.

4. A magnetic bearing device comprising:a rotating body;a motor that rotationally drives the rotating body and includes poles whose number is an even number and is a multiple of 4;one or more radial electromagnets that generate a radial electromagnetic force in the rotating body;a radial displacement sensor that measures radial displacement of the rotating body;an oscillator that outputs an alternating-current voltage as a modulated input signal to the radial displacement sensor; anda demodulation circuit that demodulates an output signal from the radial displacement sensor, whereinthe radial displacement sensor includes:a first sensor magnetic pole pair including two sensor magnetic poles arranged side by side in an axial direction along a rotating shaft of the rotating body; anda second sensor magnetic pole pair including two sensor magnetic poles radially facing the first sensor magnetic pole pair and arranged side by side in the axial direction,each coil of the first sensor magnetic pole pair and the second sensor magnetic pole pair is connected such that polarities of the respective magnetic poles are different from each other,one end of the coil of the first sensor magnetic pole pair is onnected to the oscillator via a resistor and / or an inductor,the other end of the coil of the first sensor magnetic pole pair is onnected to a ground,one end of the coil of the second sensor magnetic pole pair is onnected to the oscillator via a resistor and / or an inductor,2024-020-GB 34the other end of the coil of the second sensor magnetic pole pair is connected to a ground,a pair of sensor magnetic poles radially facing each other among the sensor magnetic poles of the first sensor magnetic pole pair and the sensor magnetic poles of the second sensor magnetic pole pair is connected so as to have the same polarities, anda voltage at an end portion of the first sensor magnetic pole pair that is adjacent to the oscillator and a voltage at an end portion of the second sensor magnetic pole pair that is adjacent to the oscillator are input to the demodulation circuit via a differential circuit.

5. The magnetic bearing device according to any one of claims 1 to 4, whereinthe one or more radial electromagnets are a plurality of radial electromagnets arranged side by side in a circumferential direction, and the sensor magnetic pole is arranged at a position between the plurality of radial electromagnets in the circumferential direction.

6. A turbomolecular pump comprising the magnetic bearing device according to any one of claims 1 to 4.

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