Vacuum pump and magnetic bearing device

Abstract

To provide a vacuum pump and a magnetic bearing device that can detect an abnormal state even when failures occur in an input circuit and an output circuit at the same time.SOLUTION: A magnetic bearing device 110 provided in a vacuum pump 100 includes: an opposing electromagnet 104 disposed with respect to a rotor 103; a current supply means 201 for supplying a current to the opposing electromagnet 104; a measurement means 202 for measuring a displacement of the rotor 103 with respect to the opposing electromagnet 104; and a control means 203 for controlling the current based on the displacement measured by the measurement means 202. A bias current Ib is included in the current supplied to the opposing electromagnet 104. The control means 203 determines an abnormal state when a sum Is of the current supplied to the opposing electromagnet 104 is smaller than a predefined current value If.SELECTED DRAWING: Figure 5

Description

Technical Field

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

Background Art

[0002] In a vacuum pump such as a turbo molecular pump, a magnetic bearing device that magnetically levitates a rotating body and holds it in a non-contact manner is used. The magnetic bearing device includes a sensor (measurement means) for measuring the displacement of the rotating body and an electromagnet for adjusting the position of the rotating body. Based on the displacement measured by the measurement means, the electromagnet is excited and controlled, whereby the rotating body can be magnetically levitated at a predetermined position.

[0003] When such a magnetic bearing device fails (for example, when a short circuit or disconnection occurs in an output circuit that supplies current to the electromagnet), it has a function of detecting the abnormal state caused by the failure and further notifying the abnormal state by sound or display (see, for example, Patent Document 1).

[0004] Generally, when it is detected that the state is abnormal, there are three cases: when the displacement of the rotating body measured by the measurement means is excessive (hereinafter referred to as "excessive displacement state"), when the current value supplied to the electromagnet exceeds a predetermined value (hereinafter referred to as "command current excessive state"), and when a short circuit or the like occurs in the above-mentioned output circuit and an excessive current flows and a protection means such as a fuse operates (hereinafter referred to as "overcurrent failure state").

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Incidentally, failures in such vacuum pumps are rare, and failures in multiple parts simultaneously are extremely rare. However, if, for example, a fixed blade breaks while the vacuum pump is in operation, there is a risk of a failure occurring where both the input circuit through which the position signal from the measuring device flows and the output circuit mentioned above are simultaneously disconnected. In this case, it has been found that even if the system has the function to detect the three conditions mentioned above, it may not be able to detect the abnormal condition. Therefore, even though the frequency of occurrence is low, such a malfunction could lead to a major problem.

[0007] In view of these points, the present invention aims to provide a vacuum pump and a magnetic bearing device that can detect an abnormal condition even when a failure occurs simultaneously in the input circuit through which a position signal from a measuring means flows and in the output circuit that supplies current to an electromagnet. [Means for solving the problem]

[0008] The present invention relates to a vacuum pump equipped with a magnetic bearing device for magnetically levitating and non-contact holding a rotating body, wherein the magnetic bearing device comprises opposing electromagnets positioned relative to the rotating body, a current supply means for supplying current to the opposing electromagnets, a measuring means for measuring the displacement of the rotating body relative to the opposing electromagnets, and a control means for controlling the current based on the displacement measured by the measuring means. A current measuring unit for measuring the current supplied to the opposing electromagnets, The system is characterized in that the current supplied to the opposing electromagnets includes a bias current, and the control means determines that there is an abnormality when the sum of the currents supplied to the opposing electromagnets is less than a predetermined current value.

[0009] In such a vacuum pump, it is preferable that the predetermined current value is 50% of the bias current value.

[0010] Furthermore, if the cumulative time during which the sum of the currents is less than the predetermined current value becomes longer than 50% of the predetermined time, starting from the point when the sum of the currents becomes less than the predetermined current value, the control means preferably determines that there is an abnormality.

[0011] Furthermore, it is preferable that the control means determine an abnormality if, starting from the point when the sum of the currents becomes smaller than the predetermined current value, the cumulative time during which the sum of the currents is smaller than the predetermined current value exceeds a specified time compared to the cumulative time during which the sum of the currents is equal to or greater than the predetermined current value.

[0012] Furthermore, the present invention relates to a magnetic bearing device for magnetically levitating and non-contact holding a rotating body, comprising: opposing electromagnets positioned relative to the rotating body; current supply means for supplying current to the opposing electromagnets; measuring means for measuring the displacement of the rotating body relative to the opposing electromagnets; and control means for controlling the current based on the displacement measured by the measuring means. A current measuring unit for measuring the current supplied to the opposing electromagnets, The device is also characterized in that the current supplied to the opposing electromagnets includes a bias current, and the control means determines that there is an abnormality when the sum of the currents supplied to the opposing electromagnets is less than a predetermined current value. [Effects of the Invention]

[0013] The inventors of this application focused on electromagnets used to magnetically levitate a rotating body in vacuum pumps and magnetic bearing devices, specifically on electromagnets positioned opposite a rotating body, and further focused on the bias current included in the current supplied to these opposing electromagnets. Although the value of the current supplied to each of the opposing electromagnets changes in accordance with the displacement of the rotating body, if each current includes a bias current, even considering various factors, the sum of the currents supplied to the opposing electromagnets will be greater than a predetermined current value, regardless of the displacement of the rotating body measured by the measuring means. In other words, by causing the control means to determine that an abnormal condition has occurred when the sum of the currents supplied to the opposing electromagnets is less than a predetermined current value, it is possible to detect an abnormal condition even if a failure occurs simultaneously in the input circuit through which the position signal from the measuring means flows and in the output circuit that supplies current to the electromagnets. [Brief explanation of the drawing]

[0014] [Figure 1]This is a schematic longitudinal cross-sectional view showing one embodiment of the vacuum pump according to the present invention. [Figure 2] Figure 1 is a circuit diagram of the amplifier circuit for the vacuum pump shown. [Figure 3] This is a time chart showing the control when the current command value is greater than the detected value. [Figure 4] This is a timing chart showing the control when the current command value is smaller than the detected value. [Figure 5] Figure 1 is a schematic diagram of the magnetic bearing device of the vacuum pump shown. [Figure 6] This diagram summarizes the abnormal conditions that occur when a malfunction occurs in the input circuit, through which the position signal from the measuring device flows, and the output circuit, which supplies current to the electromagnet. [Figure 7] This diagram shows the relationship between the sum of the currents supplied to opposing electromagnets and time. [Figure 8] This figure shows the results of the difference between a conventional general method for determining abnormal conditions and a determination method in one embodiment of the present invention. [Modes for carrying out the invention]

[0015] Hereinafter, a turbomolecular pump, which is one embodiment of the vacuum pump according to the present invention, will be described with reference to the drawings.

[0016] A longitudinal sectional view of this turbo molecular pump 100 is shown in Fig. 1. In Fig. 1, the X-axis direction is the left-right direction of the paper surface, the Z-axis direction is the up-down direction of the paper surface, and the Y-axis direction is the front-back direction of the paper surface. An intake port 101 is formed at the upper end of a cylindrical outer cylinder 127 that extends along a central axis CA parallel to the Z-axis direction in the turbo molecular pump 100. Inside the outer cylinder 127, a rotating body 103 is provided, on the circumferential part of which a plurality of rotating blades 102 (102a, 102b, 102c ···), which are turbine blades for sucking and exhausting gas (intake gas), are formed radially and in multiple stages. A rotor shaft 113 is attached to the center of this rotating body 103, and in this embodiment, the rotor shaft 113 is levitated and supported in the air and position-controlled by a five-axis control magnetic bearing device 110. The rotating body 103 is generally composed of a metal such as aluminum or an aluminum alloy. A detailed description of the magnetic bearing device 110 will be given later.

[0017] The magnetic bearing device 110 includes a total of four upper radial electromagnets 104, which are arranged on the outer side in the radial direction of the rotor shaft 113. Among them, two electromagnets face each other in the X-axis direction, and two electromagnets face each other in the Y-axis direction. In Fig. 1, regarding the two upper radial electromagnets 104 facing each other in the X-axis direction, the electromagnet located on the + side in the X-axis direction (the right side with respect to the central axis CA in Fig. 1) is shown as the upper radial electromagnet 104A, and the electromagnet located on the - side in the X-axis direction (the left side with respect to the central axis CA in Fig. 1) is shown as the upper radial electromagnet 104B.

[0018] Proximity to this upper radial electromagnet 104, a total of four upper radial sensors 107 for measuring the displacement of the rotor shaft 113 are provided. The upper radial sensors 107 are, for example, inductance sensors having conductive windings or eddy current sensors, etc. The upper radial sensors 107 of the present embodiment measure the displacement of the rotor shaft 113 in the X-axis direction and the Y-axis direction on the upper side. Two upper radial sensors 107 are provided corresponding to two upper radial electromagnets 104 facing each other in the X-axis direction, and two upper radial sensors 107 are provided corresponding to two upper radial electromagnets 104 facing each other in the Y-axis direction. In FIG. 1, regarding the upper radial sensor 107 located in the X-axis direction, the sensor located on the + side in the X-axis direction (the right side with respect to the central axis CA in FIG. 1) is shown as the upper radial sensor 107A, and the sensor located on the - side in the X-axis direction (the left side with respect to the central axis CA in FIG. 1) is shown as the upper radial sensor 107B. Also, the upper radial sensors 107 of the present embodiment are so-called differential type sensors that measure the X-axis direction and the Y-axis direction positions of the rotor shaft 113 from two directions of the + direction and the - direction respectively, and are configured to send a position signal corresponding to the radial position of the rotor shaft 113 to the controller 200. The controller 200 in FIG. 1 is shown as being provided outside the base portion 129, but it may also be provided inside the base portion 129. A detailed description of the controller 200 will be given later.

[0019] Also, on the radially outer side below the rotor shaft 113, a total of four lower radial electromagnets 105 are provided. Among them, two electromagnets face each other in the X-axis direction, and two electromagnets face each other in the Y-axis direction. In FIG. 1, regarding the two lower radial electromagnets 105 facing each other in the X-axis direction, the electromagnet located on the + side in the X-axis direction (the right side with respect to the central axis CA in FIG. 1) is shown as the lower radial electromagnet 105A, and the electromagnet located on the - side in the X-axis direction (the left side with respect to the central axis CA in FIG. 1) is shown as the lower radial electromagnet 105B.

[0020] And Upper radial sensor 107A total of four lower radial sensors 108 similar to the one above are provided in close proximity to the lower radial electromagnet 105. The lower radial sensors 108 measure the displacement in the X-axis and Y-axis directions on the lower side of the rotor shaft 113, and two of the lower radial sensors 108 are provided corresponding to two lower radial electromagnets 105 that face each other in the X-axis direction, and two Lower radial sensor 108 These are provided in correspondence with two lower radial electromagnets 105 that are opposite each other in the Y-axis direction. In Figure 1, with respect to the lower radial sensors 108 located in the X-axis direction, the sensor located on the + side in the X-axis direction (to the right of the central axis CA in Figure 1) is shown as the lower radial sensor 108A, and the sensor located on the - side in the X-axis direction (to the left of the central axis CA in Figure 1) is shown as the lower radial sensor 108B. Similar to the upper radial sensor 107, the lower radial sensor 108 is a so-called differential type sensor that measures the X-axis and Y-axis positions of the rotor shaft 113 from two directions, the + and - directions, respectively, and is configured to send a position signal corresponding to the radial position of the rotor shaft 113 to the controller 200.

[0021] In this controller 200, for example, a compensation circuit with a PID adjustment function generates an excitation control command signal for the upper radial electromagnet 104 based on the position signal measured by the upper radial sensor 107, and generates an excitation control command signal for the lower radial electromagnet 105 based on the position signal from the lower radial sensor 108. Then, the amplifier circuit 150 (described later) shown in Figure 2 excites the upper radial electromagnet 104 and the lower radial electromagnet 105 respectively based on these excitation control command signals, thereby adjusting the upper and lower radial positions of the rotor shaft 113.

[0022] The rotor shaft 113 is formed from a high-permeability material (such as iron or stainless steel) and is attracted by the magnetic force of the upper radial electromagnet 104 and the lower radial electromagnet 105. The attraction by the upper radial electromagnet 104 is performed independently in the X-axis and Y-axis directions, and similarly, the attraction by the lower radial electromagnet 105 is performed independently in the X-axis and Y-axis directions.

[0023] Furthermore, the axial electromagnets 106 are positioned above and below a disc-shaped metal disk 111 located at the bottom of the rotor shaft 113. In Figure 1, the upper electromagnet is shown as axial electromagnet 106A, and the lower electromagnet is shown as axial electromagnet 106B. The metal disk 111 is made of a high-permeability material such as iron.

[0024] Below the rotor shaft 113, an axial sensor 109 is provided to measure the axial displacement of the rotor shaft 113. The axial sensor 109 is configured to detect the axial position of the rotor shaft 113 by detecting the position of a sensor target embedded in the lower end of the rotor shaft 113, and to send a position signal corresponding to this axial position to the controller 200.

[0025] Then, in the controller 200, for example, a compensation circuit having a PID adjustment function generates excitation control command signals for the axial electromagnets 106A and 106B based on the axial position signal detected by the axial sensor 109, and the amplifier circuit 150 excites the axial electromagnets 106A and 106B based on these excitation control command signals, so that the axial electromagnet 106A attracts the metal disk 111 upward with magnetic force, and the axial electromagnet 106B attracts the metal disk 111 downward, thereby adjusting the axial position of the rotor shaft 113.

[0026] On the other hand, the motor 121 is equipped with multiple magnetic poles arranged circumferentially around the rotor shaft 113. Each magnetic pole is controlled by the controller 200 to rotate the rotor shaft 113 via the electromagnetic force acting between it and the rotor shaft 113. The motor 121 also incorporates a rotational speed sensor, such as a Hall element, resolver, or encoder (not shown), and the rotational speed of the rotor shaft 113 is detected by the detection signal from this rotational speed sensor.

[0027] Furthermore, for example, a phase sensor (not shown) is mounted near the lower radial sensor 108 to detect the phase of rotation of the rotor shaft 113. The controller 200 uses both the detection signals from this phase sensor and the rotational speed sensor to detect the position of the magnetic pole.

[0028] Multiple fixed blades 123 (123a, 123b, 123c...) are arranged with a small gap between them and the rotating blades 102 (102a, 102b, 102c...). Each of the rotating blades 102 (102a, 102b, 102c...) is formed at a predetermined angle from a plane perpendicular to the axis of the rotor shaft 113 in order to transport intake gas molecules downward by collision. The fixed blades 123 (123a, 123b, 123c...) are made of metals such as aluminum, iron, stainless steel, copper, or alloys containing these metals as components.

[0029] Similarly, the fixed wing 123 is formed at a predetermined angle from a plane perpendicular to the axis of the rotor shaft 113, and is arranged alternately with the stages of the rotor blade 102 toward the inside of the outer cylinder 127. The outer edge of the fixed wing 123 is supported by being fitted between a plurality of stacked fixed wing spacers 125 (125a, 125b, 125c, etc.).

[0030] The fixed-wing spacer 125 is a ring-shaped member and is made of a metal such as aluminum, iron, stainless steel, or copper, or an alloy containing these metals as components. An outer cylinder 127 is fixed to the outer circumference of the fixed-wing spacer 125 with a small gap in between. A base portion 129 is provided at the bottom of the outer cylinder 127. An exhaust port 133 is formed in the base portion 129 and communicates with the outside. Intake gas that enters the intake port 101 from the chamber (vacuum chamber) side and is transferred to the base portion 129 is sent to the exhaust port 133.

[0031] Furthermore, a threaded spacer 131 is provided between the lower part of the fixed-wing spacer 125 and the base portion 129. The threaded spacer 131 is a cylindrical member made of a metal such as aluminum, copper, stainless steel, iron, or an alloy containing these metals, and has multiple helical screw grooves 131a engraved on its inner circumferential surface. The direction of the helix of the screw grooves 131a is such that when the molecules of the intake gas move in the direction of rotation of the rotating body 103, these molecules are transported toward the exhaust port 133. A cylindrical portion 102d hangs down from the lowest part of the rotating body 103 following the rotor blades 102 (102a, 102b, 102c...). The outer circumferential surface of this cylindrical portion 102d is cylindrical and protrudes toward the inner circumferential surface of the threaded spacer 131, and is in close proximity to the inner circumferential surface of the threaded spacer 131 with a predetermined gap between them. The intake gas, which has been transferred to the screw groove 131a by the rotor blade 102 and the fixed blade 123, is guided along the screw groove 131a and sent to the base section 129.

[0032] The base portion 129 is a disc-shaped component that forms the base of the turbomolecular pump 100, and is generally made of a metal such as iron, aluminum, or stainless steel. The base portion 129 not only physically holds the turbomolecular pump 100 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.

[0033] In this configuration, when the rotor blade 102 is rotated by the motor 121 together with the rotor shaft 113, gas is drawn in from the chamber through the intake port 101 by the action of the rotor blade 102 and the fixed blade 123. The rotational speed of the rotor blade 102 is usually 20,000 rpm to 90,000 rpm, and the peripheral speed at the tip of the rotor blade 102 reaches 200 m / s to 400 m / s. The intake gas drawn in from the intake port 101 passes between the rotor blade 102 and the fixed blade 123 and is transferred to the base section 129. At this time, the temperature of the rotor blade 102 rises due to frictional heat generated when the intake gas comes into contact with the rotor blade 102 and heat conduction generated by the motor 121, but this heat is transferred to the fixed blade 123 side by radiation or conduction by gas molecules of the intake gas.

[0034] The fixed-wing spacers 125 are joined to each other at their outer circumference, and they transmit heat received by the fixed wing 123 from the rotor blade 102, as well as frictional heat generated when the intake gas comes into contact with the fixed wing 123, to the outside.

[0035] In the above description, the threaded spacer 131 is positioned on the outer circumference of the cylindrical portion 102d of the rotating body 103, and a threaded groove 131a is engraved on the inner surface of the threaded spacer 131. However, conversely, there are also cases where a threaded groove is engraved on the outer circumference of the cylindrical portion 102d, and a spacer having a cylindrical inner surface is positioned around it.

[0036] Depending on the application of the turbomolecular pump 100, the electrical components, which consist of an upper radial electromagnet 104, an upper radial sensor 107, a motor 121, a lower radial electromagnet 105, a lower radial sensor 108, an axial electromagnet 106, and an axial sensor 109, may be covered by a stator column 122 to prevent the intake gas drawn in from the intake port 101 from entering the electrical components, which consist of an upper radial electromagnet 104, an upper radial sensor 107, a motor 121, a lower radial electromagnet 105, a lower radial sensor 108, an axial electromagnet 106, and an axial sensor 109. In some cases, the inside of this stator column 122 may be maintained at a predetermined pressure with a purge gas.

[0037] In this case, piping (not shown) is provided in the base section 129, and purge gas is introduced through this piping. The introduced purge gas is sent to the exhaust port 133 through the gaps between the protective bearing 120 and the rotor shaft 113, between the rotor and stator of the motor 121, and between the stator column 122 and the inner cylindrical part of the rotor blade 102.

[0038] Here, the turbomolecular pump 100 requires model identification and control based on individually adjusted unique parameters (e.g., characteristics corresponding to the model). To store these control parameters, the turbomolecular pump 100 is equipped with an electronic circuit section 141 within its body. The electronic circuit section 141 consists of electronic components such as semiconductor memory such as EEP-ROM and semiconductor elements for accessing it, and a substrate 143 for mounting them. This electronic circuit section 141 is housed, for example, below a rotational speed sensor (not shown) near the center of the base section 129 that constitutes the lower part of the turbomolecular pump 100, and is closed by an airtight bottom cover 145.

[0039] Incidentally, in the semiconductor manufacturing process, some process gases introduced into the chamber have the property of becoming solid when their pressure exceeds a predetermined value or their temperature falls below a predetermined value. Inside the turbomolecular pump 100, the pressure of the intake gas is lowest at the intake port 101 and highest at the exhaust port 133. If the intake gas's pressure exceeds a predetermined value or its temperature falls below a predetermined value while it is being transferred from the intake port 101 to the exhaust port 133, the intake gas becomes solid and adheres to and accumulates inside the turbomolecular pump 100.

[0040] For example, when SiCl4 is used as the process gas in an Al etching apparatus, the vapor pressure curve shows that at low vacuum (760 to 10⁻² torr) and low temperature (approximately 20°C), solid products (e.g., AlCl3) precipitate and adhere to the inside of the turbomolecular pump 100. As a result, when precipitates of the process gas accumulate inside the turbomolecular pump 100, these deposits narrow the pump flow path, causing a decrease in the performance of the turbomolecular pump 100. Furthermore, the aforementioned products tended to solidify and adhere in areas with high pressure, such as near the exhaust port 133 and near the threaded spacer 131.

[0041] Therefore, in order to solve this problem, conventional methods involve wrapping a heater (not shown) or an annular water-cooling pipe 149 around the outer circumference of the base portion 129, and embedding a temperature sensor (e.g., a thermistor) (not shown) in the base portion 129. Based on the signal from this temperature sensor, heating by the heater and cooling by the water-cooling pipe 149 are controlled (hereinafter referred to as TMS; Temperature Management System) to maintain the temperature of the base portion 129 at a constant high temperature (set temperature).

[0042] Next, we will describe an amplifier circuit 150 that energizes and controls the upper radial electromagnet 104, the lower radial electromagnet 105, and the axial electromagnet 106 of the turbomolecular pump 100 configured in this way. The circuit diagram of this amplifier circuit 150 is shown in Figure 2.

[0043] In Figure 2, the electromagnet winding 151, which constitutes the upper radial electromagnet 104, has one end connected to the positive terminal 171a of the power supply 171 via transistor 161, and the other end 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.

[0044] 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.

[0045] 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.

[0046] The amplifier circuit 150 configured as described above corresponds to one electromagnet. The magnetic bearing device 110 in this embodiment is 5-axis controlled and has a total of 10 electromagnets 104, 105, and 106. A similar amplifier circuit 150 is configured for each electromagnet, and the 10 amplifier circuits 150 are connected in parallel to the power supply 171.

[0047] Furthermore, the amplifier control circuit 191 is composed of, for example, a digital signal processor (hereinafter referred to as the DSP section) of the controller 200 (not shown), and this amplifier control circuit 191 is configured to switch transistors 161 and 162 on and off.

[0048] 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.

[0049] Furthermore, when the rotating body 103 passes a resonance point during accelerated rotational speed operation, or when disturbances occur during constant-speed operation, it is necessary to control the position of the rotating body 103 with high speed and strong force. For this reason, a high voltage of, for example, 50V is used as 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).

[0050] 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.

[0051] 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 100 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.

[0052] 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 3. 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.

[0053] 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 4. 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.

[0054] 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.

[0055] Next, the magnetic bearing device 110 and controller 200 described above will be explained in detail with reference to Figure 5. In the following explanation, only the magnetic bearing device 110 and controller 200 related to the upper radial electromagnets 104A and 104B, which are opposite each other in the X-axis direction, will be described, but the configuration is the same for the other electromagnets. For this reason, the explanation of the other electromagnets will be omitted below, and the parts related to the other electromagnets will also be omitted from Figure 5.

[0056] As shown in Figure 5, the controller 200 includes a current supply means 201, a measuring means 202, and a control means 203. The current supply means 201 includes the amplifier circuit 150 described above and an output circuit 204 that connects the upper radial electromagnets 104A and 104B to the amplifier circuit 150. The measuring means 202 includes a levitation position measuring unit 205 and an input circuit 206 that connects the upper radial sensors 107A and 107B to the levitation position measuring unit 205. The control means 203 includes a levitation control unit 207 that sends an excitation control command signal to the current supply means 201, a current measuring unit 208 for measuring the current supplied to the upper radial electromagnets 104A and 104B, and a protection function processing unit 209. The output circuit 204 is provided with a protection means (such as a fuse) to cut off the current in the event of an excessive current flow due to a short circuit or the like. As shown in Figure 5, the magnetic bearing device 110 consists of upper radial electromagnets 104A and 104B, upper radial sensors 107A and 107B, a current supply means 201, a measuring means 202, and a control means 203.

[0057] In the magnetic bearing device 110 configured in this way, when the rotor shaft 113 is rotating by the motor 121, the levitation position measuring unit 205 of the measuring means 202 measures the displacement of the rotor shaft 113 using the upper radial sensors 107A and 107B. Specifically, when the distance between the upper radial sensor 107A and the rotor shaft 113 changes, the inductance of the coil of the upper radial sensor 107A changes according to that distance, so the output voltage of the upper radial sensor 107A changes. Similarly, when the distance between the upper radial sensor 107B and the rotor shaft 113 changes, the inductance of the coil of the upper radial sensor 107B changes according to that distance, so the output voltage of the upper radial sensor 107B changes. To avoid the influence of noise and the like, the difference between the output voltage of the upper radial sensor 107A and the output voltage of the upper radial sensor 107B is taken as the displacement of the rotor shaft 113, and a position signal corresponding to this displacement is fed back to the control means 203.

[0058] The levitation control unit 207 of the control means 203 calculates the deviation between the actual position of the rotor shaft 113 and the target position based on the position signal and target position command signal fed back from the measurement means 202, and sends a signal related to excitation control command to the current supply means 201 based on this deviation. The control means 203 also sends a signal related to bias current command to the current supply means 201. Based on this signal, the current supply means 201 supplies a current with a bias current Ib added from each amplifier circuit 150 to the upper radial electromagnets 104A and 104B. As a result, the magnetic attractive force from the upper radial electromagnet 104A and the magnetic attractive force from the upper radial electromagnet 104B acts on the rotor shaft 113, moving the rotor shaft 113 to the target position.

[0059] Here, the operation of the control means 203 and the current supply means 201 will be explained in detail. For example, if the rotor shaft 113 is displaced such that the distance from the upper radial electromagnet 104A is greater than the distance from the upper radial electromagnet 104B, the control means 203 will output a current Ip (Ip=Ib+Ic), which is the sum of the bias current Ib and the current corresponding to this displacement (control current Ic), from the amplifier circuit 150 connected to the upper radial electromagnet 104A to the current supply means 201, and a current Im (Im=Ib), which is the difference between the bias current Ib and the control current Ic. - A signal is sent to cause Ic) to be output from the amplifier circuit 150 connected to the upper radial electromagnet 104B.

[0060] Furthermore, the control means 203 of this embodiment includes a protection function processing unit 209 that has the function of determining that the magnetic bearing device 110 is in an abnormal state when the displacement of the rotor shaft 113 measured by the measuring means 202 is excessive (excessive displacement state), when the current value supplied to the upper radial electromagnets 104A and 104B exceeds a predetermined value (command current excessive state), and when an excessive current flows in the output circuit 204 and the protection means is activated (overcurrent fault state). The protection function processing unit 209 also has the function of activating an unillustrated notification means (which notifies of the abnormal state by sound or display, such as a buzzer or warning lamp) provided on the turbomolecular pump 100 when it determines that such an abnormal state is occurring, and the function of cutting off the current to the motor 121 to stop the rotating body 103.

[0061] Incidentally, the configuration that measures the displacement of the rotor shaft 113 and outputs a current based on that displacement from the amplifier circuit 150, thereby applying magnetic attraction force from the upper radial electromagnets 104A and 104B to the rotor shaft 113 to move the rotor shaft 113 to the target position, as well as the function of detecting the three abnormal conditions described above—excessive displacement, excessive command current, and overcurrent fault—is also provided in conventional magnetic bearing devices. However, if a failure occurs in which both the input circuit 206 through which the position signal from the measuring means 202 shown in Figure 5 flows, and the output circuit 204 connecting the upper radial electromagnets 104A and 104B to the amplifier circuit 150, are simultaneously disconnected, the function of detecting the three abnormal conditions described above may not be able to detect this failure as an abnormal condition. This point will be explained with reference to Figure 6.

[0062] In Figure 6, the "Circuit of Opposing Electromagnets" column on the left shows the state of the output circuit 204. "No Fault" means that no fault has occurred in the output circuit 204. "Short Circuit Fault" means that an excessive current has flowed through the output circuit 204 and the protective mechanism has been activated. "Partially Broken (Broken)" means that either the path connecting the upper radial electromagnet 104A and the amplifier circuit 150, or the path connecting the upper radial electromagnet 104B and the amplifier circuit 150, is broken. "Completely Broken (Broken)" means that both paths are broken.

[0063] In Figure 6, the upper row of "Opposite Sensor Circuits" indicates the state of the input circuit 206. "No Fault" means that there is no fault in the input circuit 206. "Partially Damaged" means that either the output voltage from the upper radial sensor 107A or the output voltage from the upper radial sensor 107B cannot be obtained (for example, the upper radial sensor 107A has failed, or the path to the upper radial sensor 107A in the input circuit 206 is broken). "Completely Damaged" means that neither the output voltage from the upper radial sensor 107A nor the output voltage from the upper radial sensor 107B can be obtained.

[0064] As mentioned above, the position signal fed back from the measuring means 202 to the control means 203 is based on the difference between the output voltage of the upper radial sensor 107A and the output voltage of the upper radial sensor 107B. Therefore, if the "circuit of the opposing sensor" is "partially destroyed," the output voltage from the upper radial sensor 107A or the output voltage from the upper radial sensor 107B becomes zero, and the position signal from the measuring means 202 becomes the signal as if the rotor shaft 113 had been displaced to near its maximum extent, even if it had not actually been displaced much relative to the upper radial sensor 107A or the upper radial sensor 107B. Also, if the "circuit of the opposing sensor" is "completely destroyed," both the output voltage of the upper radial sensor 107A and the output voltage of the upper radial sensor 107B become zero. In other words, the position signal from the measuring means 202 becomes the same as the signal as if the distance from the upper radial sensor 107A and the distance from the upper radial sensor 107B were equal relative to the rotor shaft 113.

[0065] In a magnetic bearing device 110 equipped with such functions, as shown in Figure 6, when the "circuit of opposing electromagnets" is "fault-free" and the "circuit of opposing sensors" is "fault-free", the control means 203 is in a state where it can correctly detect abnormalities. For example, if the displacement of the rotor shaft 113 measured by the measuring means 202 is excessive, it can be detected that it is in an excessive displacement state. If the current value supplied to the upper radial electromagnets 104A and 104B exceeds a predetermined value, it can be detected that it is in a command current overload state.

[0066] Furthermore, if there is "no obstruction" or "partial damage (disconnection)" in the "circuit of the opposing electromagnet," the control means 203 can detect that the command current is excessive when the current supplied to the upper radial electromagnets 104A and 104B exceeds a predetermined value. Also, if there is "no obstruction" or "partial damage (disconnection)" in the "circuit of the opposing electromagnet," and the "circuit of the opposing sensor" is "no obstruction" or "partial damage," it is possible to detect an abnormality as an excessive displacement state. In addition, if a "short circuit obstruction" occurs in the "circuit of the opposing electromagnet," the control means 203 can detect that an overcurrent obstruction state exists, regardless of the state of the "circuit of the opposing sensor."

[0067] Furthermore, if the "circuit of the opposing electromagnet" is "completely broken (disconnected)", and the "circuit of the opposing sensor" is "unaffected" or "partially broken", the control means 203 can detect an abnormality as an excessive displacement state. Also, if the current value supplied to the upper radial electromagnets 104A and 104B exceeds a predetermined value, it is possible to detect an excessive command current state even if the "circuit of the opposing electromagnet" is "completely broken (disconnected)" and the "circuit of the opposing sensor" is "completely broken". However, if the "circuit of the opposing sensor" is "completely broken", even if the rotor shaft 113 is significantly displaced relative to the upper radial sensor 107A or upper radial sensor 107B, the position signal from the measuring means 202 is the same as the signal when the distance from the upper radial sensor 107A to the rotor shaft 113 and the distance from the upper radial sensor 107B to the rotor shaft 113 are equal. Therefore, the upper radial electromagnets 104A and 104B are not energized in principle, and consequently, the current supplied to the upper radial electromagnets 104A and 104B does not exceed a predetermined value. Furthermore, if the "circuit of the opposing electromagnet" is in a state of "total failure (disconnection)", excessive current will not flow in the output circuit 204. For this reason, in conventional magnetic bearing devices, if the "circuit of the opposing electromagnet" is "total failure (disconnection)" and the "circuit of the opposing sensor" is also "total failure", it may not be possible to detect the three abnormal states described above (the state of failure notification failure shown in Figure 6), and for example, there was a risk that the rotating body 103 would continue to rotate for a long time without magnetic levitation.

[0068] In contrast, the control means 203 of this embodiment has a function that measures the sum of the currents supplied to the opposing upper radial electromagnets 104A and 104B using the current measurement unit 208, and determines that there is an abnormality if this sum of currents is smaller than a predetermined current value If. That is, the sum of the currents Is of the upper radial electromagnets 104A and 104B measured by the current measurement unit 208 is normally the current Ip (Ip=Ib+Ic) output from the amplifier circuit 150 connected to the upper radial electromagnet 104A and the current Im (Im=Ib) output from the amplifier circuit 150 connected to the upper radial electromagnet 104B -The sum of Ic) is approximately twice the bias current Ib (Is = Ip + Im = 2 × Ib). However, if a break in the output circuit 204 occurs and current is not supplied to both the opposing upper radial electromagnets 104A and 104B, the sum of currents Is measured by the current measurement unit 208 will be less than approximately twice the bias current Ib, even considering the effects of variations in the components constituting the turbomolecular pump 100, variations in assembly, and time delays in feedback control. Therefore, by setting a predetermined current value If to a value less than approximately twice the bias current Ib, and by determining an abnormality when the sum of currents Is of the opposing upper radial electromagnets 104A and 104B is less than the predetermined current value If, ​​the protection function processing unit 209 can stop the rotating body 103 even if the "circuit of the opposing electromagnets" is "completely destroyed (broken wire)" and the "circuit of the opposing sensor" is "completely destroyed".

[0069] If the predetermined current value If is set to a value close to approximately twice the bias current Ib, there is a risk that the turbomolecular pump 100 may be judged as being in an abnormal state even when it is functioning normally, depending on the operating conditions. For example, the turbomolecular pump 100 is not necessarily installed in the position shown in Figure 1 (with the rotor shaft 113 facing vertically). For example, if the rotor shaft 113 is installed in a position facing horizontally, a magnetic attractive force that takes into account the gravity acting on the rotating body 103 needs to be generated, and the sum of the currents Is of the upper radial electromagnets 104A and 104B may change depending on the installation position. Taking these points into consideration, the inventors of this application conducted repeated studies using various turbomolecular pumps 100 while considering various operating conditions, and found that when the predetermined current value If is set to 50% of the bias current Ib, it is possible to reliably determine whether or not it is in an abnormal state. For this reason, it is preferable to set the predetermined current value If to 50% of the bias current Ib.

[0070] Furthermore, the sum of the currents Is of the opposing upper radial electromagnets 104A and 104B may fluctuate, for example, as shown in Figure 7, due to the effects of fault conditions in the output circuit 204, observed current chattering, and ambient noise. Taking these fluctuations into account, we conducted extensive research on a method to more reliably determine whether or not an abnormal state is occurring. We found that it is effective to configure the control means 203 to determine an abnormal state when, starting from the point when the sum of currents Is becomes smaller than a predetermined current value If (50% of the bias current Ib in Figure 7), the cumulative time during which the sum of currents Is is smaller than the predetermined current value If (Td1 + Td2 + ... Tdm in Figure 7) becomes longer than 50% of the predetermined time Tra (i.e., when the condition (Td1 + Td2 + ... Tdm) > Tra × 50%).

[0071] Furthermore, to more reliably determine whether an abnormal state is present, the cumulative time during which the sum of currents Is falls below a predetermined current value If (in Figure 7, Td1 + Td2 + ... Tdm) is equal to or greater than the cumulative time during which the sum of currents Is falls above or below the predetermined current value If (in Figure 7, Tu1 + Tu2 + ... Tun) is equal to or greater than a specified time Trb (for example, the specified time Trb is 1 second) (i.e., the condition expression (Td1 + Td2 + ... Tdm)) - It was also effective to configure the control means 203 to determine an abnormality if (Tu1 + Tu2 + ...Tun) ≥ Trb is satisfied.

[0072] Here, we will explain the difference between the conventional general abnormal condition detection method and the above method with reference to Figure 8. The sum of currents Is shown in Figure 8 has time on the horizontal axis and the current value on the vertical axis, showing a situation where the current value gradually decreases over time and eventually stops flowing. Note that the fine changes in the sum of currents Is shown in Figure 8 are mainly due to the influence of noise, etc. The comparative example shows the results of the conventional general abnormal condition detection method. In the conventional general abnormal condition detection method, an abnormality is judged when the sum of currents Is remains below a predetermined current value If for a specified time Trb. If the specified time Trb is not reached, a reset is performed and time measurement starts again from the state where the sum of currents Is remains below the predetermined current value If. In the comparative example shown in Figure 8, the horizontal axis is time and the vertical axis is duration (the time during which the state in which the sum of currents Is remains below the predetermined current value If is maintained). When the sum of currents Is shown in Figure 8 is checked using the conventional method, several resets are performed if the specified time Trb is not reached, and an abnormality is detected at time T2. On the other hand, the embodiment shown in Figure 8 shows the results of a method in which an abnormality is determined when the cumulative time during which the sum of currents Is is less than a predetermined current value If exceeds a specified time Trb compared to the cumulative time during which the sum of currents Is is equal to or greater than the predetermined current value If. In the embodiment, the horizontal axis represents time, and the vertical axis represents duration (cumulative time during which the sum of currents Is is less than the predetermined current value If - cumulative time during which the sum of currents Is is equal to or greater than the predetermined current value If). When the sum of currents Is shown in Figure 8 is checked using the judgment method of this embodiment, a reset does not occur as in the conventional judgment method, and therefore, an abnormality can be detected at time T1, which is earlier than time T2.

[0073] Although one embodiment of the present invention has been described above, the present invention is not limited to such specific embodiments, and unless otherwise specifically limited in the above description, various modifications, changes, and combinations are possible within the scope of the spirit of the present invention as described in the claims. Furthermore, the effects described in the above embodiments are merely illustrative of the effects that may arise from the present invention, and do not mean that the effects of the present invention are limited to those described above.

[0074] For example, the functions described with reference to Figures 5 to 7 are not limited to the upper radial electromagnets 104A and 104B and the upper radial sensors 107A and 107B, but can also be applied to the other electromagnets 104, 105, and 106 and the other sensors 107, 108, and 109. [Explanation of Symbols]

[0075] 100: Turbomolecular pump (vacuum pump) 103: Solid of revolution 104: Upper radial electromagnet 105: Lower radial electromagnet 106: Axial electromagnet 107: Upper radial sensor 108: Lower radial sensor 109: Axial sensor 110: Magnetic bearing device 201: Current supply means 202:Measurement means 203: Control means

Claims

1. A vacuum pump equipped with a magnetic bearing device that magnetically levitates and holds a rotating body in a non-contact manner, The magnetic bearing device is Opposing electromagnets positioned relative to the rotating body, A current supply means for supplying current to the opposing electromagnets, A measuring means for measuring the displacement of the rotating body relative to the opposing electromagnet, A control means that controls the current based on the displacement measured by the measuring means, It includes a current measuring unit for measuring the current supplied to the opposing electromagnets, The current supplied to the opposing electromagnet includes a bias current. The control means is characterized in that it determines an abnormality when the sum of the currents supplied to the opposing electromagnets is less than a predetermined current value.

2. The vacuum pump according to claim 1, characterized in that the predetermined current value is 50% of the current value of the bias current.

3. Starting from the point when the sum of the currents becomes less than the predetermined current value, for a predetermined time period thereafter, The vacuum pump according to claim 1 or 2, characterized in that the control means determines an abnormality if the cumulative time during which the sum of the currents is less than the predetermined current value becomes longer than 50% of the predetermined time.

4. Starting from the point when the sum of the currents becomes less than the predetermined current value, The vacuum pump according to claim 1 or 2, characterized in that the control means determines an abnormality when the cumulative time during which the sum of the currents is less than the predetermined current value is equal to or greater than a specified time compared to the cumulative time during which the sum of the currents is equal to or greater than the predetermined current value.

5. A magnetic bearing device that magnetically levitates and holds a rotating body in a non-contact manner, Opposing electromagnets positioned relative to the rotating body, A current supply means for supplying current to the opposing electromagnets, A measuring means for measuring the displacement of the rotating body relative to the opposing electromagnet, A control means that controls the current based on the displacement measured by the measuring means, It includes a current measuring unit for measuring the current supplied to the opposing electromagnets, The current supplied to the opposing electromagnet includes a bias current. The magnetic bearing device is characterized in that the control means determines an abnormality when the sum of the currents supplied to the opposing electromagnets is less than a predetermined current value.

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