Vacuum pump, and magnetic bearing device

Abstract

[Project] We propose a vacuum pump and magnetic bearing device capable of detecting abnormal conditions even when failures occur simultaneously in the input and output circuits. [Solution] A magnetic bearing device (110) equipped with a vacuum pump (100) comprises an opposing electromagnet (104) positioned against a rotating body (103), a current supply means (201) for supplying current to the opposing electromagnet (104), a measuring means (202) for measuring the displacement of the rotating body (103) against the opposing electromagnet (104), and a control means (203) for controlling the current based on the displacement measured by the measuring means (202). The current supplied to the opposing electromagnet (104) includes a bias current (Ib), and the control means (203) is characterized by determining that there is an abnormality when the sum (Is) of the currents supplied to the opposing electromagnet (104) is less than a predetermined current value (If).

Description

Technology Field

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

[0002] In vacuum pumps such as turbo molecular pumps, a magnetic bearing device is used to magnetically levitate a rotating body and maintain it in a non-contact manner. The magnetic bearing device is equipped with a sensor (measuring means) for measuring the displacement of the rotating body and an electromagnet for adjusting the position of the rotating body, and the electromagnet is energized and controlled based on the displacement measured by the measuring means, thereby allowing the rotating body to be magnetically levitated at a predetermined position.

[0003] Such a magnetic bearing device is equipped with a function to detect an abnormal state caused by a failure when a failure occurs (for example, when a short circuit or open circuit occurs in the output circuit supplying current to the electromagnet) and to notify the abnormal state by sound or indication (for example, see Patent Document 1).

[0004] Generally, there are three cases in which an abnormal state is detected: when the displacement of the rotating body measured by the measuring means is excessive (hereinafter referred to as the "excessive displacement state"), when the current value supplied to the electromagnet exceeds a predetermined value (hereinafter referred to as the "excessive command current state"), and when a short circuit or the like occurs in the output circuit described above, causing an excessive current to flow and a protective means such as a fuse to operate (hereinafter referred to as the "overcurrent fault state"). Prior art literature

[0005] Japanese Patent Publication No. 2002-295398 The problem to be solved

[0006] However, in such vacuum pumps, failures occur infrequently, and failures in multiple locations simultaneously are extremely rare. However, for example, if a problem occurs where a fixed vane breaks during the operation of the vacuum pump, there is a risk of failure occurring, such as a simultaneous disconnection in both the input circuit through which a position signal from a measuring means flows and the output circuit. In this case, it has been found that even if the device has the function to detect the three states mentioned above, it cannot detect the abnormal state. Therefore, even though the frequency of occurrence is low, there is a risk that such problems may lead to major trouble.

[0007] Taking these points into consideration, the present invention aims to provide a vacuum pump and a magnetic bearing device capable of detecting an abnormal state even when a failure occurs simultaneously in an input circuit through which a position signal from a measuring means flows and an output circuit that supplies current to an electromagnet. means of solving the problem

[0008] The present invention relates to a vacuum pump equipped with a magnetic bearing device that maintains a rotating body by magnetically levitating it without contact, wherein the magnetic bearing device comprises an opposing electromagnet disposed with respect to the rotating body, a current supply means for supplying current to the opposing electromagnet, a measuring means for measuring the displacement of the rotating body relative to the opposing electromagnet, and a control means for controlling the current based on the displacement measured by the measuring means, wherein the current supplied to the opposing electromagnet includes a bias current, and the control means determines that there is an abnormality when the sum of the currents supplied to the opposing electromagnet is less than a predetermined current value.

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

[0010] And, starting from the point where the sum of the currents becomes smaller than the predetermined current value, if the cumulative time of the state in which the sum of the currents becomes smaller than the predetermined current value in a subsequent predetermined time is longer than 50% of the predetermined time, it is preferable to determine that the control means is abnormal.

[0011] In addition, starting from the point when the sum of the currents becomes smaller than the predetermined current value, if the accumulated time of the state in which the sum of the currents becomes smaller than the predetermined current value is longer than the prescribed time with respect to the accumulated time of the state in which the sum of the currents becomes greater than or equal to the predetermined current value, it is preferable for the control means to determine that there is an abnormality.

[0012] The present invention is also characterized in that it is a magnetic bearing device for magnetically levitating a rotating body and maintaining it in a non-contact manner, comprising: an opposing electromagnet disposed with respect to the rotating body; a current supply means for supplying current to the opposing electromagnet; a measuring means for measuring the displacement of the rotating body relative to the opposing electromagnet; and a control means for controlling the current based on the displacement measured by the measuring means, wherein the current supplied to the opposing electromagnet includes a bias current, and the control means determines that there is an abnormality when the sum of the currents supplied to the opposing electromagnet is less than a predetermined current value. Effects of the invention

[0013] The inventors of the present invention, regarding electromagnets used to magnetically levitate a rotating body in a vacuum pump or magnetic bearing device, focused on an electromagnet positioned opposite to the rotating body and also focused on a bias current included in the current supplied to the opposing electromagnet. Although the value of the current applied to each opposing electromagnet changes in correspondence with the displacement of the rotating body, when a bias current is included in each current, the sum of the currents supplied to the opposing electromagnets becomes greater than a predetermined current value regardless of the displacement of the rotating body measured by a measuring means, even when various factors are taken into account. That is, by determining through a control means that an abnormal state has occurred when the sum of the currents supplied to the opposing electromagnets is less than a predetermined current value, an abnormal state can be detected even when a failure occurs simultaneously in the input circuit through which a position signal from the measuring means flows and the output circuit supplying current to the electromagnet. Brief explanation of the drawing

[0014] FIG. 1 is a cross-sectional view schematically showing one embodiment of a vacuum pump according to the present invention. Figure 2 is a circuit diagram of the amplifier circuit of the vacuum pump shown in Figure 1. Figure 3 is a time chart showing control when the current command value is greater than the detection value. Figure 4 is a time chart showing control when the current command value is smaller than the detection value. FIG. 5 is a schematic diagram of the magnetic bearing device of the vacuum pump shown in FIG. 1. Figure 6 is a diagram summarizing the abnormal state in the case where a fault occurs in the input circuit through which a position signal from a measuring means flows and the output circuit that supplies current to the electromagnet. Figure 7 is a diagram showing the relationship between the sum of the currents supplied to opposing electromagnets and time. FIG. 8 is a diagram showing the result of the difference between a conventional general abnormal state judgment method and a judgment method in one embodiment according to the present invention. Specific details for implementing the invention

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

[0016] A cross-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. In the turbo molecular pump (100), an intake port (101) is formed at the top of a cylindrical outer tube (127) that extends along a central axis (CA) parallel to the Z-axis direction. And, inside the outer tube (127), a rotating body (103) is provided with a plurality of rotating blades (102) (102a, 102b, 102c…) which are turbine blades for sucking in and exhausting gas (intake gas), formed radially and in multiple stages on the circumference. A rotor shaft (113) is mounted at the center of this rotating body (103), and in this embodiment, this rotor shaft (113) is supported in the air and position-controlled by a 5-axis control magnetic bearing device (110). The rotating body (103) is generally made of a metal such as aluminum or an aluminum alloy. In addition, a detailed description of the magnetic bearing device (110) will be provided later.

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

[0018] A total of four upper radial sensors (107) are provided in close proximity to the upper radial electromagnet (104) to measure the displacement of the rotor shaft (113). For example, the upper radial sensors (107) may be inductance sensors having a conductive winding or eddy current sensors. The upper radial sensors (107) of this embodiment measure displacement in the X-axis direction and Y-axis direction from the upper side of the rotor shaft (113). Two upper radial sensors (107) are installed corresponding to two upper radial electromagnets (104) facing each other in the X-axis direction, and two upper radial sensors (107) are installed 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 X-axis direction + side (to the right of the center axis (CA) in FIG. 1) is shown as the upper radial sensor (107A), and the sensor located on the X-axis direction - side (to the left of the center axis (CA) in FIG. 1) is shown as the upper radial sensor (107B). Furthermore, the upper radial sensor (107) of this embodiment is a so-called differential type sensor that measures the X-axis direction and Y-axis direction positions of the rotor shaft (113) from two directions, the + direction and the - direction, respectively, and is configured to send a position signal according to the radial position of the rotor shaft (113) to the controller (200). Although the controller (200) in FIG. 1 is shown as being installed outside the base part (129), it may also be installed inside the base part (129). Additionally, a detailed description of the controller (200) will be given later.

[0019] Additionally, a total of four lower radial electromagnets (105) are installed on the outer side of the lower rotor shaft (113), two of which are facing in the X-axis direction and two are facing in the Y-axis direction. In FIG. 1, regarding the two lower radial electromagnets (105) facing in the X-axis direction, the electromagnet located on the X-axis direction + side (to the right of the center axis (CA) in FIG. 1) is shown as the lower radial electromagnet (105A), and the electromagnet located on the X-axis direction - side (to the left of the center axis (CA) in FIG. 1) is shown as the lower radial electromagnet (105B).

[0020] In addition, a total of four lower radial sensors (108), identical to the upper radial electromagnet (104), are installed in close proximity to the lower radial electromagnet (105). The lower radial sensors (108) measure displacement in the X-axis direction and Y-axis direction at the lower side of the rotor shaft (113). Two lower radial sensors (108) are installed in correspondence with two lower radial electromagnets (105) facing each other in the X-axis direction, and two upper radial sensors (107) are installed in correspondence with two lower radial electromagnets (105) facing each other in the Y-axis direction. In FIG. 1, regarding the lower radial sensor (108) located in the X-axis direction, the sensor located on the X-axis direction + side (to the right of the center axis (CA) in FIG. 1) is shown as the lower radial sensor (108A), and the sensor located on the X-axis direction - side (to the left of the center axis (CA) in FIG. 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 direction and Y-axis direction positions of the rotor shaft (113) from two directions, the + direction and the - direction, respectively, and is configured to send a position signal according to the radial position of the rotor shaft (113) to the controller (200).

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

[0022] And, this rotor shaft (113) is formed by a high permeability material (iron, stainless steel, etc.) and is designed to be attracted by the magnetic force of the upper radial electromagnet (104) and also attracted by the magnetic force of the lower radial electromagnet (105). The attraction by the upper radial electromagnet (104) is performed independently in the X-axis direction and the Y-axis direction, respectively, and likewise, the attraction by the lower radial electromagnet (105) is performed independently in the X-axis direction and the Y-axis direction, respectively.

[0023] Additionally, an axial electromagnet (106) is positioned above and below a disc-shaped metal disk (111) provided at the lower part of the rotor shaft (113). In FIG. 1, the upper electromagnet is shown as an axial electromagnet (106A), and the lower electromagnet is shown as an axial electromagnet (106B). The metal disk (111) is made of a high permeability material such as iron.

[0024] An axial sensor (109) for measuring the axial displacement of the rotor shaft (113) is installed below 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 part of the rotor shaft (113), and to send a position signal corresponding to this axial position to the controller (200).

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

[0026] Meanwhile, the motor (121) is provided with a plurality of magnetic poles arranged in a circumferential shape to surround the rotor shaft (113). Each magnetic pole is controlled by a controller (200) to drive the rotation of the rotor shaft (113) by interposing an electromagnetic force acting between it and the rotor shaft (113). In addition, the motor (121) has a rotational speed sensor built in, such as a Hall element, a resolver, or an encoder, which is not shown, and the rotational speed of the rotor shaft (113) is detected by the detection signal of this rotational speed sensor.

[0027] Additionally, 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) is configured to detect the position of the stimulus by using both the detection signals of this phase sensor and the rotation speed sensor.

[0028] A plurality of fixed blades (123) (123a, 123b, 123c…) are arranged with a small gap between 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 molecules of the intake gas downward by collision. The fixed blades (123) (123a, 123b, 123c…) are composed of metals such as aluminum, iron, stainless steel, copper, etc., or alloys containing these metals as components.

[0029] Also, the fixed wing (123) is formed at a predetermined angle from a plane perpendicular to the axis of the rotor shaft (113) and is also arranged alternately with the ends of the rotating wing (102) toward the inside of the outer tube (127). And, the outer end of the fixed wing (123) is supported while being inserted between a plurality of stacked fixed wing spacers (125) (125a, 125b, 125c…).

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

[0031] Additionally, a screw-type spacer (131) is disposed between the lower part of the fixed wing spacer (125) and the base part (129). The screw-type spacer (131) is a cylindrical member made of a metal such as aluminum, copper, stainless steel, iron, or an alloy composed of these metals, and has multiple spiral-shaped screw grooves (131a) formed on its inner surface. The direction of the spiral of the screw grooves (131a) is the direction in which the molecules of the intake gas are transported toward the exhaust port (133) when the molecules move in the rotational direction of the rotating body (103). A cylindrical part (102d) is suspended at the lowest part leading to the rotating wings (102) (102a, 102b, 102c…) of the rotating body (103). The outer surface of this cylindrical part (102d) is cylindrical in shape and protrudes toward the inner surface of the screw-equipped spacer (131), and is in close proximity to the inner surface of the screw-equipped spacer (131) with a predetermined gap. The intake gas, which has been transported to the screw groove (131a) by the rotating blade (102) and the fixed blade (123), is guided into the screw groove (131a) and sent to the base part (129).

[0032] The base portion (129) is a disc-shaped member that constitutes the base of the turbo molecular pump (100) and is generally made of a metal such as iron, aluminum, or stainless steel. Since the base portion (129) physically supports the turbo molecular pump (100) and also serves as a heat conductor, it is preferable to use a metal that has high rigidity and high thermal conductivity, such as iron, aluminum, or copper.

[0033] In this configuration, when the rotating 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 rotating blade (102) and the fixed blade (123). The rotational speed of the rotating blade (102) is typically 20,000 rpm to 90,000 rpm, and the circumferential speed at the tip of the rotating blade (102) reaches 200 m / s to 400 m / s. The intake gas drawn in from the intake port (101) passes between the rotating blade (102) and the fixed blade (123) and is transferred to the base part (129). At this time, the temperature of the rotating blade (102) rises due to frictional heat generated when the intake gas comes into contact with the rotating blade (102) or heat generated from the motor (121) being conducted, 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 the outer periphery and transfer to the outside heat received by the fixed wing (123) from the rotating wing (102) or frictional heat generated when intake gas comes into contact with the fixed wing (123).

[0035] Additionally, as described above, a screw-equipped spacer (131) is positioned on the outer circumference of the cylindrical portion (102d) of the rotating body (103), and a screw groove (131a) is formed by being engraved on the inner circumference of the screw-equipped spacer (131). However, conversely, there are cases where a screw groove is formed by being engraved on the outer circumference of the cylindrical portion (102d), and a spacer having a cylindrical inner circumference is positioned around it.

[0036] Depending on the application of the turbo molecular pump (100), the intake gas sucked in from the intake port (101) may not enter the electrical section composed 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), an axial sensor (109), etc., so that the electrical section is covered with a stator column (122) and the inside of the stator column (122) is maintained at a predetermined pressure with purge gas.

[0037] In this case, a pipe not shown is arranged in the base portion (129), and purge gas is introduced through this pipe. The introduced purge gas is discharged to the exhaust port (133) through the gap between the protective bearing (120) and the rotor shaft (113), between the rotor and the stator of the motor (121), and between the stator column (122) and the inner circumferential cylindrical portion of the rotating blade (102).

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

[0039] However, in the semiconductor manufacturing process, among the process gases introduced into the chamber, there are some that have the property of becoming solid when their pressure rises above a predetermined value or when their temperature falls below a predetermined value. Inside the turbo molecular pump (100), the pressure of the intake gas is lowest at the intake port (101) and highest at the exhaust port (133). While the intake gas is being transported from the intake port (101) to the exhaust port (133), if the pressure rises above a predetermined value or the temperature falls below a predetermined value, the intake gas becomes solid and adheres to and accumulates inside the turbo molecular pump (100).

[0040] For example, when SiCl4 is used as a process gas in an Al etching device, low vacuum (760 [torr] ~ 10 -2 [torr]) Also, from the vapor pressure curve, it can be seen that when the temperature is low (about 20°C), a solid product (e.g., AlCl3) precipitates and adheres to the inside of the turbo molecular pump (100). Consequently, when the precipitate of the process gas is deposited inside the turbo molecular pump (100), this deposit narrows the pump flow path, causing a decrease in the performance of the turbo molecular pump (100). Furthermore, the aforementioned product was in a situation where it was easy to solidify and adhere in high-pressure areas near the exhaust port (133) or near the screw-equipped spacer (131).

[0041] Therefore, in order to solve this problem, conventionally, a heater or an annular water cooling pipe (149) not shown is wound on the outer circumference of the base part (129), and a temperature sensor (e.g., a thermistor) not shown is embedded in the base part (129), and based on the signal of this temperature sensor, heating of the heater or cooling by the water cooling pipe (149) is controlled (hereinafter referred to as TMS; Temperature Management System) to maintain the temperature of the base part (129) at a constant high temperature (set temperature).

[0042] Next, regarding the turbo molecular pump (100) configured in this manner, an amplifier circuit (150) that controls the excitation of the upper radial electromagnet (104), the lower radial electromagnet (105), and the axial electromagnet (106) will be described. A circuit diagram of this amplifier circuit (150) is shown in FIG. 2.

[0043] In FIG. 2, the electromagnet winding (151) constituting the upper radial electromagnet (104), etc., has one end connected to the positive electrode (171a) of the power source (171) via a transistor (161), and the other end connected to the negative electrode (171b) of the power source (171) via a current detection circuit (181) and a transistor (162). The transistors (161, 162) are so-called power MOSFETs and have a structure in which a diode is connected between the source and drain.

[0044] At this time, the transistor (161) is configured such that the cathode terminal (161a) of the diode is connected to the positive electrode (171a), and the anode terminal (161b) is connected to one end of the electromagnet winding (151). Additionally, the transistor (162) is configured such that the cathode terminal (162a) of the diode is connected to the current detection circuit (181), and the anode terminal (162b) is connected to the negative electrode (171b).

[0045] Meanwhile, the current regeneration diode (165) is configured such that its cathode terminal (165a) is connected to one end of the electromagnet winding (151), and its anode terminal (165b) is connected to the negative electrode (171b). Likewise, the current regeneration diode (166) is configured such that its cathode terminal (166a) is connected to the positive electrode (171a), and its anode terminal (166b) is connected to the other end of the electromagnet winding (151) via a 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 a single electromagnet. The magnetic bearing device (110) of this embodiment is a 5-axis control, and a total of 10 electromagnets (104, 105, 106) are installed, and the same amplifier circuit (150) is configured for each electromagnet, and the 10 amplifier circuits (150) are connected in parallel to the power supply (171).

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

[0048] The amplifier control circuit (191) is configured to compare a current value detected by the current detection circuit (181) (a signal reflecting this current value is called a current detection signal (191c)) with a predetermined current command value. Based on the result of this comparison, the magnitude of the pulse width (pulse width time (Tp1, Tp2)) generated within one control cycle (Ts) of PWM control is determined. As a result, a gate driving signal (191a, 191b) having this pulse width is output from the amplifier control circuit (191) to the gate terminal of the transistor (161, 162).

[0049] In addition, it is necessary to control the position of the rotating body (103) with high speed and strong force, such as when passing through a resonance point during accelerated operation of the rotating body (103) or when a disturbance occurs during constant speed operation. For this reason, a high voltage of, for example, about 50V is used as the power source (171) so that a rapid increase (or decrease) in the current flowing through the electromagnet winding (151) is possible. Also, a capacitor is connected between the positive electrode (171a) and the negative electrode (171b) of the power source (171) to stabilize the power source (171) (not shown).

[0050] In this configuration, when both transistors (161, 162) are turned on, the current flowing through the electromagnet winding (151) (hereinafter referred to as electromagnet current (iL)) increases, and when both are turned off, the electromagnet current (iL) decreases.

[0051] In addition, if one of the transistors (161, 162) is turned on and the other is turned off, the so-called flywheel current is maintained. And, by allowing the flywheel current to flow through the amplifier circuit (150) in this way, the hysteresis loss in the amplifier circuit (150) is reduced, and the power consumption of the entire circuit can be kept low. Also, by controlling the transistors (161, 162) in this way, high-frequency noise such as harmonics generated in the turbo molecular pump (100) can be reduced. In addition, 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] That is, when the detected current value is smaller than the current command value, both transistors (161, 162) are turned on for a time equivalent to the pulse width time (Tp1) only once during the control cycle (Ts) (e.g., 100 μs) as shown in FIG. 3. Accordingly, the electromagnet current (iL) during this period increases toward a current value (iLmax) (not shown) that can be made to flow from the positive electrode (171a) to the negative electrode (171b) through the transistors (161, 162).

[0053] Meanwhile, if the detected current value is greater than the current command value, both transistors (161, 162) are turned off for a time equivalent to the pulse width time (Tp2) only once during the control cycle (Ts), as shown in FIG. 4. Accordingly, the electromagnet current (iL) during this period decreases from the negative electrode (171b) to the positive electrode (171a) toward a current value (iLmin) (not shown) that can be restored through the diodes (165, 166).

[0054] And, in any case, after the pulse width time (Tp1, Tp2) has elapsed, one of the transistors (161, 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 FIG. 5. In addition, in the following description, only the magnetic bearing device (110) and controller (200) related to the upper radial electromagnets (104A, 104B) facing in the X-axis direction among the electromagnets (104, 105, 106) described above will be explained, but the configuration is the same for the other electromagnets. For this reason, the description of the other electromagnets will be omitted below, and the part regarding the other electromagnets in FIG. 5 will also be omitted.

[0056] As shown in FIG. 5, the controller (200) is equipped with a current supply means (201), a measuring means (202), and a control means (203). The current supply means (201) is configured to include the amplifier circuit (150) described above and an output circuit (204) that connects the upper radial electromagnet (104A or 104B) and the amplifier circuit (150); the measurement means (202) is configured to include a levitation position measuring unit (205) and an input circuit (206) that connects the upper radial sensor (107A or 107B) and the levitation position measuring unit (205); and the control means (203) is configured to include 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 electromagnet (104A or 104B), and a protection function processing unit (209). In addition, the output circuit (204) is equipped with a protection means (such as a fuse) to cut off the current in the event that an excessive current flows due to, for example, a short circuit. And the magnetic bearing device (110) is composed of an upper radial electromagnet (104A, 104B), an upper radial sensor (107A, 107B), a current supply means (201), a measuring means (202), and a control means (203), as shown in FIG. 5.

[0057] In the magnetic bearing device (110) configured in this manner, when the rotor shaft (113) is rotated by the motor (121), the floating position measuring unit (205) of the measuring means (202) measures the displacement of the rotor shaft (113) by the upper radial sensors (107A, 107B). Specifically, when the distance between the upper radial sensor (107A) and the rotor shaft (113) changes, the output voltage of the upper radial sensor (107A) changes because the inductance of the coil provided by the upper radial sensor (107A) changes according to the distance. Similarly, when the distance between the upper radial sensor (107B) and the rotor shaft (113) changes, the output voltage of the upper radial sensor (107B) changes because the inductance of the coil provided by the upper radial sensor (107B) changes according to the distance. And, in order to avoid the influence of noise, the difference between the output voltage of the upper radial sensor (107A) and the output voltage of the upper radial sensor (107B) is used 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 and the target position of the rotor shaft (113) based on the position signal fed back from the measurement means (202) and the signal regarding the target position command, and sends a signal regarding the excitation control command to the current supply means (201) based on this deviation. The control means (203) also sends a signal regarding the bias current command to the current supply means (201). Then, the current supply means (201) supplies the current, with the bias current (Ib) added, from each amplifier circuit (150) to the upper radial electromagnet (104A) and the upper radial electromagnet (104B) based on this signal. By this, the magnetic attraction force from the upper radial electromagnet (104A) and the magnetic attraction force from the upper radial electromagnet (104B) act on the rotor shaft (113), thereby moving the rotor shaft (113) to a target position.

[0059] Here, the operation of the control means (203) and the current supply means (201) is described in detail. For example, when 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) sends a signal to the current supply means (201) to output a current (Ip) (Ip=Ib+Ic), which is the sum of the above-described bias current (Ib) and the current (control current (Ic)) due to this displacement, from the amplifier circuit (150) connected to the upper radial electromagnet (104A), and to output a current (Im) (Im=Ib-Ic), which is the difference between the bias current (Ib) and the control current (Ic), from the amplifier circuit (150) connected to the upper radial electromagnet (104B).

[0060] In addition, the control means (203) of the present embodiment is provided with a protection function processing unit (209) having a function to determine 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 electromagnet (104A, 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 failure state). In addition, the protection function processing unit (209) has a function to activate an unillustrated notification means (which indicates an abnormal state by sound or display, such as a buzzer or warning lamp, etc.) installed in the turbo molecular pump (100) when it is determined that such an abnormal state is present, or a function to cut off the current to the motor (121) and stop the rotating body (103).

[0061] However, the configuration of measuring the displacement of the rotor shaft (113), outputting a current based on that displacement from the amplifier circuit (150), and thereby applying a magnetic attraction force from the upper radial electromagnets (104A, 104B) to the rotor shaft (113) to move the rotor shaft (113) to a target position, and the function of detecting the three abnormal states described above—an excessive displacement state, an excessive command current state, and an overcurrent fault state—is also provided in conventional magnetic bearing devices. However, if a fault occurs in which two circuits—an input circuit (206) through which a position signal from the measuring means (202) shown in FIG. 5 flows, and an output circuit (204) connecting the upper radial electromagnets (104A, 104B) and the amplifier circuit (150)—are simultaneously disconnected, there were cases where this fault could not be detected as an abnormal state by the function of detecting the three abnormal states described above. This point will be explained with reference to FIG. 6.

[0062] In FIG. 6, the “circuit of opposing electromagnets” in the left column indicates 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 in the output circuit (204) and the protection means has been activated, “half-short circuit (short circuit)” means that either the path connecting the upper radial electromagnet (104A) and the amplifier circuit (150) in the output circuit (204) or the path connecting the upper radial electromagnet (104B) and the amplifier circuit (150) is disconnected, and “full circuit (short circuit)” means that both paths are disconnected.

[0063] And in FIG. 6, the “circuit of opposing sensors” in the upper row indicates the state of the input circuit (206), “no fault” means a state in which no fault occurs in the input circuit (206), “half fault” means a state in which either the output voltage from the upper radial sensor (107A) or the output voltage from the upper radial sensor (107B) is not obtained (for example, the upper radial sensor (107A) is broken or the path to the upper radial sensor (107A) in the input circuit (206) is disconnected), and “full fault” means a state in which neither the output voltage from the upper radial sensor (107A) nor the output voltage from the upper radial sensor (107B) is obtained.

[0064] Additionally, as described 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, when the "circuit of the opposing sensor" is "half-dead," the output voltage from the upper radial sensor (107A) or the output voltage from the upper radial sensor (107B) becomes zero, so the position signal from the measuring means (202) becomes a signal when the rotor shaft (113) is displaced to a state close to the maximum, even if the rotor shaft (113) is actually almost displaced relative to the upper radial sensor (107A) or the upper radial sensor (107B). Also, when the "circuit of the opposing sensor" is "full-dead," the output voltage of the upper radial sensor (107A) and the output voltage of the upper radial sensor (107B) both become zero. That is, the position signal from the measuring means (202) becomes the same as the signal when the distance from the upper radial sensor (107A) and the distance from the upper radial sensor (107B) are equal with respect to the rotor shaft (113).

[0065] In a magnetic bearing device (110) having such functions, as shown in FIG. 6, when the “circuit of opposing electromagnets” is “no fault” and the “circuit of opposing sensors” is “no fault,” 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) becomes excessive, it is possible to detect that it is in an excessive displacement state, and if the current value supplied to the upper radial electromagnets (104A, 104B) exceeds a predetermined value, it is possible to detect that it is in an excessive command current state.

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

[0067] And when the “circuit of the opposing electromagnet” is “full (open)”, if the “circuit of the opposing sensor” is “no fault” or “half-full”, the control means (203) can detect an abnormality as an excessive displacement state. Also, when the current value supplied to the upper radial electromagnet (104A, 104B) exceeds a predetermined value, it is possible to detect that the command current is in an excessive state even when the “circuit of the opposing electromagnet” is “full (open)” and the “circuit of the opposing sensor” is “full”. However, when the “circuit of the opposing sensor” is in a “block” state, even if the rotor shaft (113) is significantly displaced relative to the upper radial sensor (107A) or the 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) and the distance from the upper radial sensor (107B) relative to the rotor shaft (113) are equal. Therefore, the upper radial electromagnet (104A, 104B) is basically not energized, and thus, the case where the current value supplied to the upper radial electromagnet (104A, 104B) exceeds a predetermined value basically does not occur. Furthermore, if the “circuit of the opposing electromagnet” is in a “block (short circuit)” state, there is no case where an excessive current flows in the output circuit (204). For this reason, in conventional magnetic bearing devices, if the "circuit of the opposing electromagnet" is "unclear (short circuit)" and the "circuit of the opposing sensor" is also "unclear," it may be impossible to detect the three abnormal states described above (the state of failure notification failure shown in FIG. 6), and there was a risk that the rotating body (103) would continue to rotate for a long time in a state where it was not magnetically levitating.

[0068] In this regard, the control means (203) of the present embodiment has the function of measuring the sum of the currents supplied to the opposing upper radial electromagnet (104A) and the upper radial electromagnet (104B) using a current measuring unit (208), and determining that there is an abnormality if the sum of the currents is less than a predetermined current value (If). That is, the sum of the currents (Is) of the upper radial electromagnet (104A) and the upper radial electromagnet (104B) measured by the current measuring unit (208) is typically the sum of 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-Ic) output from the amplifier circuit (150) connected to the upper radial electromagnet (104B), and represents a value approximately twice that of the bias current (Ib) (Is=Ip+Im=2×Ib). However, if a disconnection or the like occurs in the output circuit (204) and current is not supplied to both the opposing upper radial electromagnet (104A) and the upper radial electromagnet (104B), even if the effects of deviations in the components constituting the turbo molecular pump (100), deviations in assembly, and time delays in feedback control are taken into account, the sum of the currents (Is) measured by the current measuring unit (208) is smaller than approximately twice the value of the bias current (Ib). Accordingly, a value smaller than approximately twice the bias current (Ib) is set as a predetermined current value (If), and when the sum of the currents (Is) of the opposing upper radial electromagnets (104A, 104B) is smaller than the predetermined current value (If), the protection function processing unit (209) determines that it is abnormal, so that the rotating body (103) can be stopped even when the “circuit of the opposing electromagnet” is “electrical ingot (short circuit)” and the “circuit of the opposing sensor” is also “electrical ingot.”

[0069] In addition, if a predetermined current value (If) is set to a value close to about twice the bias current (Ib), there is a risk that the turbo molecular pump (100) may be judged to be in an abnormal state even though it is normal depending on the usage state. For example, the turbo molecular pump (100) is not limited to being installed in the posture shown in FIG. 1 (a posture in which the rotor shaft (113) faces the vertical direction), and for example, if it is installed in a posture in which the rotor shaft (113) faces the horizontal direction, a magnetic attractive force with added gravity acting on the rotating body (103) needs to be manifested, and there is a possibility that the sum of the currents (Is) of the upper radial electromagnets (104A, 104B) may change depending on the installation posture. Taking these points into consideration, the inventor of the present invention repeatedly examined various turbo molecular pumps (100) while assuming various usage conditions, and found that when a predetermined current value (If) is set to 50% of the current value of the bias current (Ib), it is possible to reliably determine whether there is an abnormal state. For this reason, it is preferable to set the predetermined current value (If) to 50% of the current value of the bias current (Ib).

[0070] Also, the sum of the currents (Is) of the opposing upper radial electromagnets (104A, 104B) may fluctuate, for example as shown in FIG. 7, due to the influence of a fault condition in the output circuit (204), chatter of the observed current, noise from the surroundings, etc. Taking into account the influence of such fluctuations, and as a result of repeated examinations on a method to more reliably determine whether there is an abnormal state, it was found effective to configure the control means (203) to determine that there is an abnormal state when, starting from when the sum of currents (Is) becomes smaller than a predetermined current value (If) (50% of the current value of the bias current (Ib) in FIG. 7), the cumulative time of the state in which the sum of currents (Is) becomes smaller than the predetermined current value (If) (Td1+Td2+…Tdm in FIG. 7) becomes longer than 50% of the predetermined time (Tra) (i.e., when the condition (Td1+Td2+…Tdm) > Tra × 50%) is satisfied).

[0071] In addition, to more reliably determine whether there is an abnormal state, it was also effective to configure the control means (203) to determine that there is an abnormal state when the cumulative time of the state in which the sum of currents (Is) becomes smaller than the predetermined current value (If) (in FIG. 7, Td1+Td2+…Tdm) is greater than the predetermined current value (If) with respect to the cumulative time of the state in which the sum of currents (Is) becomes greater than the predetermined current value (If) (in FIG. 7, Tu1+Tu2+…Tun) is greater than the specified time (Trb) (for example, the specified time (Trb) is 1 second) (i.e., when the condition equation (Td1+Td2+…Tdm)-(Tu1+Tu2+…Tun)≥Trb is satisfied).

[0072] Here, the difference between the conventional general abnormal state judgment method and the judgment method above is explained with reference to FIG. 8. The sum of currents (Is) shown in FIG. 8 is represented with the horizontal axis representing time and the vertical axis representing the current value, indicating a situation where the current value gradually decreases over time and eventually stops flowing. In addition, the minute changes in the sum of currents (Is) shown in FIG. 8 are mainly due to the influence of noise, etc. The comparative example shows the result of the conventional general abnormal state judgment method. In the conventional general abnormal state judgment method, an abnormality is determined when the sum of currents (Is) becomes smaller than a predetermined current value (If) and this state continues for a specified time (Trb). If the specified time (Trb) is not reached, a reset is performed, and time measurement is started again from the state where the sum of currents (Is) becomes smaller than the predetermined current value (If). The comparative example shown in FIG. 8 is represented with the horizontal axis as time and the vertical axis as the duration (time during which the state in which the sum of currents (Is) is smaller than a predetermined current value (If) continues). When the sum of currents (Is) shown in FIG. 8 is checked using a conventional judgment method, if the specified time (Trb) is not reached, a reset is performed several times, and an abnormality is detected at the time T2 stage. On the other hand, the embodiment shown in FIG. 8 shows the result of a method in which the cumulative time of the state in which the sum of currents (Is) is smaller than a predetermined current value (If) is greater than or equal to the specified time (Trb) when the cumulative time of the state in which the sum of currents (Is) is greater than or equal to the predetermined current value (If) is determined to be an abnormality. The embodiment is represented with the horizontal axis as time and the vertical axis as the duration (cumulative time of the state in which the sum of currents (Is) is smaller than a predetermined current value (If) minus the cumulative time of the state in which the sum of currents (Is) is greater than or equal to the predetermined current value (If)).When the sum of currents (Is) shown in Fig. 8 is verified using the judgment method of the present embodiment, a reset is not performed as in the conventional judgment method, and therefore, an abnormality can be detected at the time T1, which is earlier than time T2.

[0073] The foregoing has described an embodiment of the present invention, but the invention is not limited to a specific embodiment according to the invention. Unless specifically limited in the foregoing description, various modifications, changes, and combinations are possible within the scope of the intent of the invention as described in the patent claims. Furthermore, the effects in the foregoing embodiment are merely illustrative of the effects resulting from the present invention and do not imply that the effects of the present invention are limited to the effects described above.

[0074] For example, the function described with reference to FIGS. 5 to 7 is not limited to the upper radial electromagnet (104A, 104B) and the upper radial sensor (107A, 107B), but can also be applied to other electromagnets (104, 105, 106) and other sensors (107, 108, 109). Explanation of the symbols

[0075] 100: Turbo molecular pump (vacuum pump) 103: Rotating body 104: Upper radial electromagnet 105: Lower radial electromagnet 106: Axial electromagnet 107: Upper radial direction sensor 108: Lower radial sensor 109: Axial sensor 110: Magnetic bearing device 201: Means of supplying current 202: Measuring means 203: Control means

Claims

Claim 1 A vacuum pump equipped with a magnetic bearing device that maintains a rotating body by magnetically levitating it without contact, wherein the magnetic bearing device comprises an opposing electromagnet disposed relative to the rotating body, a current supply means for supplying current to the opposing electromagnet, a measuring means for measuring the displacement of the rotating body relative to the opposing electromagnet, and a control means for controlling the current based on the displacement measured by the measuring means, wherein the current supplied to the opposing electromagnet includes a bias current, and the control means determines that it is abnormal when the sum of the currents supplied to the opposing electromagnet is less than a predetermined current value. Claim 2 A vacuum pump according to claim 1, characterized in that the predetermined current value is 50% of the current value of the bias current. Claim 3 A vacuum pump according to claim 1 or claim 2, characterized in that, starting from the point when the sum of the currents becomes smaller than the predetermined current value, if the cumulative time of the state in which the sum of the currents becomes smaller than the predetermined current value becomes longer than 50% of the predetermined time, the control means determines that it is abnormal. Claim 4 A vacuum pump according to claim 1 or claim 2, characterized in that, starting from the point when the sum of the currents becomes smaller than the predetermined current value, if the cumulative time of the state in which the sum of the currents becomes smaller than the predetermined current value is greater than or equal to the prescribed time for the cumulative time of the state in which the sum of the currents becomes greater than or equal to the predetermined current value, the control means determines that there is an abnormality. Claim 5 A magnetic bearing device for maintaining a rotating body by magnetically levitating it without contact, comprising: an opposing electromagnet disposed relative to the rotating body; a current supply means for supplying current to the opposing electromagnet; a measuring means for measuring the displacement of the rotating body relative to the opposing electromagnet; and a control means for controlling the current based on the displacement measured by the measuring means, wherein the current supplied to the opposing electromagnet includes a bias current, and the control means determines that there is an abnormality when the sum of the currents supplied to the opposing electromagnet is less than a predetermined current value.

Images