Vacuum pump

Abstract

A vacuum pump which can suppress precipitation of by-products in a pump is provided. A vacuum pump 300 is provided, which includes a casing 310, a. rotor shaft 113 disposed, in the casing' 310, and a rotor blade 102 rotatable together with the rotor shaft 113, with gas being' exhausted by rotation of the rotor blade 102 the vacuum pump 300 further including heating means 340 for heating a gas flow" passage in the vacuum pump 300, wherein the heating means 340 has a coil 342, a heated, portion 343, which is a magnetic body heated, by electromagnetic induction by causing an. AC current to flow through the coil 342, and a high-permeability magnetic body 341 covering an opposite side to a front surface 344 side, on which the heated portion 343 is disposed, of the coil 342.

Description

VACUUM PUMP

[0001] The present invention relates to a vacuum pump.

[0002] A semiconductor manufacturing device, a liquid-crystal manufacturing device, an electron microscope, a surface analyzing device, a fine machining device and the like require that an environment inside the device is brought into a high vacuum state. In order to bring the insides of these devices into the high vacuum state, a vacuum pump is used. As an example of a vacuum pump to be used, a combination pump, in which a turbomolecular pump and a thread groove pump or the like are combined, is cited, for example.

[0003] In the vacuum pump, in which the turbomolecular pump and the thread groove pump are combined, the thread groove pump is disposed on a downstream side of the turbo pump having a rotor blade and a stator blade aligned alternately in an axial direction. Exhaust gas taken in through an inlet port is compressed by the turbomolecular pump and the thread groove pump and is exhausted to outside the vacuum pump through an outlet port.

[0004] The exhaust gas exhibits a behavior like a viscous flow when a pressure becomes relatively high on a flow passage particularly on the downstream. Therefore, by-products may precipitate easily at a spot where the flow of the exhaust gas settles in a flow passage of the vacuum pump. When a by-product precipitates in the flow passage, a phenomenon occurs in which a spot which is not contacted normally is contacted, and this causes damage of the vacuum pump or variation in temperature distribution accompanying a change in conduction performances of an internal structure, and there is a concern that safety / productivity is damaged.

[0005] Therefore, in the vacuum pump, in order to suppress the precipitation of by-products in the gas flow passage, heating means for heating a component forming the gas flow passage is disposed in some cases. In PTL 1, for example, a structure in which a heating portion which heats, by electromagnetic induction heating, a stator component on a stator blade side is disclosed.

[0006] The heating portion has a yoke fixed to the stator component, a coil disposed on the yoke, and a heating plate connected to the stator component. The heating plate and the yoke are formed of a magnetic material such as a ferrous material, a stainless material and the like.When a high-frequency AC current is made to flow through a coil, the coil, the heating plate, and the yoke are electromagnetically coupled, and an eddy current is generated inside the heating plate and the yoke. Since the heating plate and the yoke have specific electric resistance, Joule heat is generated. Moreover, iron-loss heat generation occurs in the heating plate and the yoke, and copper-loss heat generation in the coil, and by means of such heat, too, the stator component is heated.

[0007] [PTL 1] WO 2014 / 119191

[0008] Since a metal member exists in the periphery of the coil in the vacuum pump described in PTL 1, parts other than the heated portion are also heated, and the heating plate cannot be heated efficiently. Thus, there is a possibility that by-products precipitate in the pump.

[0009] The present invention has been made in order to solve the aforementioned problem and has an object to provide a vacuum pump which can suppress precipitation of by-products in the pump.

[0010] The aforementioned object is achieved by the invention described in the following (1).

[0011] (1) A vacuum pump according to the present invention is a vacuum pump including a casing, a rotor shaft disposed in the casing, and a rotor blade rotatable together with the rotor shaft, with gas being exhausted by rotation of the rotor blade, the vacuum pump further including heating means for heating a gas flow passage in the vacuum pump, wherein the heating means has a coil, a heated portion, which is a magnetic body heated by electromagnetic induction by causing an AC current to flow through the coil and a, preferably high-permeability, magnetic body covering an opposite side to a front side, on which the heated portion is disposed, of the coil.

[0012] Since the vacuum pump described in the aforementioned (1) can form a magnetic path so that a magnetic flux can pass through the high- permeability magnetic body on the opposite side to the front side, on which the heated portion is disposed, of the coil, the heated portion to be heated by the electromagnetic induction can be efficiently heated. Thus, the vacuum pump can efficiently heat the gas flow passage and suppress precipitation of by-products in the pump.

[0013] (2) In the vacuum pump described in the aforementioned (1), the heated portion may be a part connected to a stator component forming thegas flow passage or a part of the stator component. As a result, the vacuum pump can effectively heat the stator blade.

[0014] (3) In the vacuum pump described in the aforementioned (1), the heated portion may be connected to the rotor blade or may be a part of the rotor blade. As a result, the vacuum pump can effectively heat the rotor blade for which heating from an outside is difficult.

[0015] (4) The vacuum pump described in any one of the aforementioned (1) to (3) may have a magnetic bearing which magnetically levitates and supports the rotor shaft. As a result, the gas flow passage of the vacuum pump having the magnetic bearing can be efficiently heated. When the heated portion is connected to the rotor blade, the rotor blade for which electric conduction is difficult can be effectively heated.

[0016] (5) In the vacuum pump described in any one of the aforementioned (1) to (4), a frequency of an electric current applied to the coil may be same as or a multiple of a control frequency of the magnetic bearing. As a result, occurrence of a noise generated by a difference between the frequency of the electric current applied to the coil and the control frequency of the magnetic bearing can be suppressed.

[0017] (6) In the vacuum pump described in any one of the aforementioned (1) to (5), a part of the high-permeability magnetic body may be disposed on a lateral side perpendicular to a direction from the coil toward the heated portion on a section perpendicular to an electric conduction direction of the coil. As a result, the vacuum pump can efficiently heat the heated portion by forming a magnetic path so that a magnetic flux passes through the high-permeability magnetic body on a side opposite to the front side on which the heated portion of the coil is disposed and the lateral side.

[0018] (7) In the vacuum pump described in any one of the aforementioned (1) to (6), the coil may be disposed in the gas flow passage. As a result, since the coil forms the magnetic path in a high- vacuum flow passage, the heated portion can be heated efficiently.

[0019] (8) In the vacuum pump described in any one of the aforementioned (1) to (7), the high-permeability magnetic body may be soft-magnetic ferrite containing manganese and zinc. As a result, a high- permeability magnetic body has high specific resistance and thus, an eddy current is hardly generated, and a loss at a high frequency is small.Therefore, heat generation in the high-permeability magnetic body is suppressed, and the heated portion can be efficiently heated.

[0020] [Fig. 1] Fig. 1 is a vertical sectional view of a vacuum pump. [Fig. 2] Fig. 2 is a circuit diagram of an amplifier circuit. [Fig. 3] Fig. 3 is a time chart showing control when a current instruction value is larger than a detection value. [Fig. Fig. 4 is a time chart showing control when a current instruction value is smaller than a detection value. [Fig. 5] Fig. 5 is a vertical sectional view of a vacuum pump according to First Embodiment. [Fig. 6] Fig. 6 is a perspective view showing heating means. [Fig. 7] Fig. 7 is an enlarged sectional view of a vicinity of the heating means of the vacuum pump according to First Embodiment. [Fig. 8] Fig. 8 is a vertical sectional view of a vacuum pump according to Second Embodiment. [Fig. 9] Fig. 9 is an enlarged sectional view of a vicinity of heating means of the vacuum pump according to Second Embodiment. [Fig. 10] Fig. 10 is a partially enlarged sectional view showing a variation of the vacuum pump according to First Embodiment.

[0021] Hereinafter, Embodiments of the present invention will be explained with reference to drawings. Note that, dimensions in the drawings might be exaggerated for convenience of explanation and different from actual dimensions in some cases. Moreover, in the Description and drawings, constituent elements having substantially the same functional configurations are given the same signs, whereby duplicated explanation will be omitted.

[0022] A vacuum pump 100 is a turbomolecular pump 100 which exhausts gas by flicking gas molecules by rotor blades of a rotating body rotating at a high speed. The turbomolecular pump 100 is used for sucking and exhausting the gas through the chamber such as a semiconductor manufacturing device or the like, for example. First, a basic configuration of the turbomolecular pump 100 will be explained.

[0023] A vertical sectional view of this turbomolecular pump 100 is shown in Fig. 1. In Fig. 1, the turbomolecular pump 100 has an inlet port 101 formed on an upper end of a cylindrical outer cylinder 127. And inside the outer cylinder 127, a rotor 103 on which a plurality of rotor blades 102 (102a, 102b, 102c ...), which are turbine blades for sucking / exhausting a gas, are formed radially and in multiple stages on a peripheral part is provided. At a center of this rotor 103, a rotor shaft 113 is mounted, and this rotor shaft 113 is levitated / supported in the air and position-controlled by a magnetic bearing of 5-axis control, for example. The rotating body 103 is constituted in general by metal such as aluminum or an aluminum alloy.

[0024] As upper-side radial-direction electromagnets 104, four electromagnets are disposed by making a pair in an X-axis and a Y-axis. Close to the upper-side radial-direction electromagnets 104 and corresponding each of the upper-side radial-direction electromagnets 104, four upper-side radial-direction sensors 107 are provided. As the upper- side radial-direction sensor 107, an inductance sensor having a conductive wiring, an eddy-current sensor or the like is used, and a position of the rotor shaft 113 is detected on the basis of a change in the inductance of the conductive wiring changing accordingly to the position of the rotor shaft 113. This upper-side radial-direction sensor 107 is configured to detect displacement in the radial direction of the rotor shaft 113, that is, the displacement in the radial direction of the rotor 103 fixed thereto and to send it to the control device 200.

[0025] In this control device 200, a compensation circuit having a PID adjustment function, for example, generates an excitation-control instruction signal of the upper-side radial-direction electromagnet 104 on the basis of a position signal detected by the upper-side radial- direction sensor 107, and an amplifier circuit 150 (which will be described later) shown in Fig. 2 excites / controls the upper-side radial- direction electromagnet 104 on the basis of this excitation-controlinstruction signal so that the radial-direction position on the upper side of the rotor shaft 113 is adjusted.

[0026] And this rotor shaft 113 is formed of a high-permeability material (such as iron, stainless or the like) or the like and is attracted by a magnetic force of the upper-side radial-direction electromagnet 104. Such adjustment is performed independently in the X- axis direction and in the Y-axis direction, respectively. Moreover, a lower-side radial-direction electromagnet 105 and a lower-side radial- direction sensor 108 are disposed similarly to the upper-side radial- direction electromagnet 104 and the upper-side radial-direction sensor 107 and adjust the radial-direction position on the lower side or the rotor shaft 113 similarly to the radial-direction position on the upper side.

[0027] Furthermore, the axial-direction electromagnets 106A, 106B are disposed by vertically sandwiching a disc-shaped metal disc 111 provided on a lower part of the rotor shaft 113. The metal disc 111 is constituted by a high-permeability material such as iron. An axial-direction sensor 109 is provided for detecting displacement in the axial direction of the rotor shaft 113 and is configured to send the axial-direction position signal thereof to the control device 200.

[0028] Then, in the control device 200, a compensation circuit having the PID adjustment function, for example, generates an excitation-control instruction signal for each of the axial-direction electromagnet 106A and the axial-direction electromagnet 106B on the basis of the axial- direction position signal detected by the axial-direction sensor 109, and the amplifier circuit 150 excites / controls the axial-direction electromagnet 106A and the axial-direction electromagnet 106B, respectively, on the basis of these excitation-control instruction signals, whereby the axial-direction electromagnet 106A attracts the metal disc 111 upward by the magnetic force, and the axial-direction electromagnet 106B attracts the metal disc 111 downward, and the axial- direction position of the rotor shaft 113 is adjusted.

[0029] As described above, the control device 200 is configured to adjust the magnetic force of the axial-direction electromagnets 106A, 106B exerted on the metal disc 111 adequately so that the rotor shaft 113 is magnetically levitated in the axial direction and is held in a space in a non-contact manner. Note that the amplifier circuit 150 whichexcites / controls the upper-side radial-direction electromagnet 104, the lower-side radial-direction electromagnet 105, and the axial-direction electromagnets 106A, 106B will be described later.

[0030] On the other hand, a motor 121 includes a plurality of magnetic poles disposed circumferentially so as to surround the rotor shaft 113. Each of the magnetic poles is controlled by the control device 200 so as to rotate / drive the rotor shaft 113 via an electromagnetic force acting between them and the rotor shaft 113. Moreover, in the motor 121, a rotation-speed sensor such as a Hall element, a resolver or an encoder, no shown, is incorporated, and the rotation speed of the rotor shaft 113 is detected by a detection signal of this rotation-speed sensor.

[0031] Furthermore, in the vicinity of the lower-side radial-direction sensor 108, for example, a phase sensor, not shown, is mounted and is configured to detect a phase of rotation of the rotor shaft 113. In the control device 200, detection signals of the phase sensor and the rotation-speed sensor 115 are used together so as to detect a position of the magnetic pole.

[0032] A plurality of stator blades 123 (123a, 123b, 123c, ...) are disposed with a slight gap from the rotor blades 102 (102a, 102b, 102c, ...). Since each of the rotor blades 102 (102a, 102b, 102c, ...) transfers molecules of the exhaust gas to a lower direction by collision, it is formed by being inclined only by a predetermined angle from a plane perpendicular to an axis of the rotor shaft 113. The stator blades 123 (123a, 123b, 123c, ...) are constituted by metal such as aluminum, iron, stainless, copper and the like or an alloy containing these metals as components, for example.

[0033] Moreover, the stator blades 123 are also formed by being inclined only by a predetermined angle from a plane perpendicular to the axis of the rotor shaft 113 and are disposed alternately with the steps of the rotor blades 102 toward the inside of the outer cylinder 127. And outer peripheral ends of the stator blades 123 are supported in a state fitted and inserted between a plurality of stator-blade spacers 125 (125a, 125b, 125c, ...) stacked.

[0034] The stator-blade spacers 125 are ring-shaped members and are constituted by metal such as aluminum, iron, stainless and the like or an alloy containing these metals as components, for example. On an outer periphery of the stator-blade spacer 125, the outer cylinder 127 is fixedwith a slight gap between them. On a bottom part of the outer cylinder 127, a base portion 129 is disposed. On the base portion 129, the outlet port 133 is formed and communicates with the outside. The exhaust gas having entered the inlet port 101 from a chamber (vacuum chamber) side and transferred to the base portion 129 is sent to the outlet port 133.

[0035] Furthermore, depending on an application of the turbomolecular pump 100, a thread groove spacer 131 (fixing member) is disposed between a lower part of the stator-blade spacer 125 and the base portion 129. The thread groove spacer 131 is a cylindrical member constituted by metal such as aluminum, copper, stainless, iron or an alloy containing these metals as components, and a plurality of spiral thread grooves 131a are engraved in an inner peripheral surface thereof. A direction of the spiral of the thread groove 131a is a direction in which, when the molecules of the exhaust gas move in a rotating direction of the rotor 103, the molecules are transferred toward the outlet port 133. At a lowest part continuing to the rotor blades 102 (102a, 102b, 102c, ...) of the rotor 103, a cylinder portion 102d is suspended. An outer peripheral surface of this cylinder portion 102d is cylindrical and extended toward the inner peripheral surface of the thread groove spacer 131 and is closer to the inner peripheral surface of this threaded spacer 131 with a predetermined gap amount. The exhaust gas having been transferred to the thread groove 131a by the rotor blades 102 and the stator blades 123 is sent to the base portion 129 by being guided by the thread groove 131a.

[0036] The base portion 129 is a disc-shaped member constituting a bottom part of the turbomolecular pump 100 and is constituted in general by metal such iron, aluminum, stainless and the like. The base portion 129 physically holds the pump main body 100 and also functions as a conduction path of a heat and thus, metal having rigidity and high heat conductivity such as iron, aluminum, copper and the like is preferably used.

[0037] In the configuration as above, when the rotor blades 102 are rotated / driven together with the rotor shaft 113 by the motor 121, by means of an action of the rotor blade 102 and the stator blade 123, the exhaust gas is sucked from the chamber through the inlet port 101. A rotation speed of the rotor blade 102 is 20000 rpm to 90000 rpm, and a peripheral speed at a distal end of the rotor blade 102 reaches 200 m / s to 400 m / s. The exhaust gas sucked from the inlet port 101 passes betweenthe rotor blade 102 and the stator blade 123 and is transferred to the base portion 129. At this time, a temperature of the rotor blade 102 rises by a friction heat generated when the exhaust gas is brought into contact with the rotor blade 102 or conduction of the heat generated in the motor 121, and this heat is conducted to the stator blade 123 side by radiation or conduction by gas molecules of the exhaust gas and the like.

[0038] The stator-blade spacers 125 are joined to each other on the outer peripheral part and conduct a heat received by the stator blade 123 from the rotor blade 102 and the frictional heat generated when the exhaust gas is brought into contact with the stator blade 123 or the like to the outside.

[0039] Note that it was explained in the above that the thread groove spacer 131 is disposed on the outer periphery of the cylinder portion 102d of the rotor 103, and the thread groove 131a is engraved in the inner peripheral surface of the threaded spacer 131. However, to the contrary, the thread groove is engraved in the outer peripheral surface of the cylinder portion 102d, and the spacer having a cylindrical inner peripheral surface around it is disposed in some cases.

[0040] Moreover, depending on the application of the turbomolecular pump 100, the periphery of an electric equipment part is covered with a stator column 122, and an inside of this stator column 122 is held at a predetermined pressure with a purge gas in some cases so that a gas sucked through the inlet port 101 does not intrude into the electric equipment part constituted by the upper-side radial-direction electromagnet 104, the upper-side radial-direction sensor 107, the motor 121, the lower-side radial-direction electromagnet 105, the lower-side radial-direction sensor 108, the axial-direction electromagnets 106A, 106B, the axial-direction sensor 109 and the like.

[0041] In this case, a piping, not shown, is disposed in the base portion 129, and the purge gas is introduced through this piping. The introduced purge gas is sent out to the outlet port 133 through gaps between a protective bearing 120 and the rotor shaft 113, between a rotor and a stator of the motor 121, and between the stator column 122 and an inner-peripheral side cylinder portion of the rotor blade 102.

[0042] Here, the turbomolecular pump 100 requires specification of a model and control based on specific parameters (various characteristics corresponding to models, for example) adjusted individually. In order tostore this control parameter, the aforementioned turbomolecular pump 100 includes an electronic circuit portion 141 in a main body thereof. The electronic circuit portion 141 is constituted by semiconductor memories such as EEP-ROM, electronic components such as semiconductor elements for accesses thereof, and boards 143 for mounting them and the like. This electronic circuit portion 141 is accommodated in a lower part of a rotation-speed sensor, not shown, provided in the vicinity of a center, for example, of the base portion 129 constituting a lower part of the turbomolecular pump 100 and is closed by an air-tight bottom lid 145.

[0043] By the way, in a manufacturing process of a semiconductor, some of process gases introduced into the chamber have such natures that pressures are higher than a predetermined value, or when the temperatures thereof become lower than the predetermined value, they become solid. Inside the turbomolecular pump 100, the pressure of the exhaust gas is the lowest at the inlet port 101 and the highest at the outlet port 133. In the middle of transfer of the process gas from the inlet port 101 to the outlet port 133, if the pressure thereof becomes higher than the predetermined value or the temperature thereof becomes lower than the predetermined value, the process gas becomes solid, adheres to the inside of the turbomolecular pump 100, and deposits thereon.

[0044] If SiCl4 is used as a process gas in an Al etching device, for example, at a low vacuum (760 torr to 10-2 torr) and a low temperature (approximately 20ºC), it is known from a steam pressure curve that a solid product (AlCl3, for example) precipitates and adheres and deposits on the inside of the turbomolecular pump 100. As a result, when the precipitates of the process gas deposit on the inside of the turbomolecular pump 100, the deposits narrow a flow passage of the pump and cause performances of the turbomolecular pump 100 to lower. And the aforementioned product is easily coagulated and adheres at a part with a high pressure in the vicinity of the outlet port 133 or the thread groove spacer 131.

[0045] Thus, in order to solve this problem, conventionally, a heater, not shown, or an annular water cooling pipe 149 is wound around an outer periphery of the base portion 129 or the like, a temperature sensor (thermistor, for example), not shown, is embedded in the base portion 129, for example, and control of heating by a heater or cooling by the water cooling pipe 149 in order to keep the temperature of the baseportion 129 at a certain high temperature (set temperature) on the basis of a signal of this temperature sensor is executed (hereinafter, referred to as TMS. TMS: Temperature Management System).

[0046] Subsequently, regarding the turbomolecular pump 100 constituted as above, the amplifier circuit 150 which excites / controls the upper-side radial-direction electromagnet 104, the lower-side radial-direction electromagnet 105, and the axial-direction electromagnets 106A, 106B will be explained. A circuit diagram of this amplifier circuit 150 is shown in Fig. 2.

[0047] In Fig. 2, an electromagnet wiring 151 constituting the upper- side radial-direction electromagnet 104 or the like has one end thereof connected to a positive pole 171a of the power source 171 through a transistor 161, while the other end thereof is connected to a negative pole 171b of the power source 171 through a current detection circuit 181 and a transistor 162. And the transistors 161, 162 are so-called power MOSFET, which has a structure in which a diode is connected between source-drain thereof.

[0048] At this time, the transistor 161 is configured such that a cathode terminal 161a of the diode is connected to the positive pole 171a and an anode terminal 161b is connected to one end of the electromagnet wiring 151. Moreover, the transistor 162 is configured such that a cathode terminal 162a of the diode is connected to the current detection circuit 181 and an anode terminal 162b is connected to the negative pole 171b.

[0049] On the other hand, a diode 165 for current regeneration is configured such that a cathode terminal 165a thereof is connected to one end of the electromagnet wiring 151 and an anode terminal 165b thereof is connected to the negative pole 171b. Moreover, similarly to the above, a diode 166 for current regeneration is configured such that a cathode terminal 166a thereof is connected to the positive pole 171a and an anode terminal 166b thereof is connected to the other end of the electromagnet wiring 151 through the current detection circuit 181. And the current detection circuit 181 is constituted by a Hall-sensor type current sensor or an electric resistance element, for example.

[0050] The amplifier circuit 150 constituted as above is configured to correspond to one electromagnet. Thus, when the magnetic bearing is 5- axis control, and the number of the electromagnets 104, 105, 106A, 106Bis 10 in total, the similar amplifier circuit 150 is constituted for each of the electromagnets, and ten units of the amplifier circuits 150 are connected in parallel with the power source 171.

[0051] Moreover, an amplifier control circuit 191 is constituted by a digital signal processor portion (Hereinafter, referred to as a DSP portion.), not shown, of the control device 200, for example, and this amplifier control circuit 191 is configured to switch on / off the transistors 161, 162.

[0052] 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) and a predetermined current instruction value. And on the basis of this comparison result, it is configured such that a magnitude of a pulse width (pulse-width times Tp1, Tp2) generated in a control cycle Ts, which is one cycle by PWM control, is determined. As a result, gate drive signals 191a, 191b having this pulse width are configured to be output from the amplifier control circuit 191 to gate terminals of the transistors 161, 162.

[0053] Note that, when passing a resonant point during an acceleration operation of a rotation speed of the rotor 103 or if disturbance occurs during a constant-speed operation and the like, position control of the rotor 103 at a high speed and with strong power is required. Thus, as the power source 171, it is configured that a voltage of approximately 50V, for example, is used so that a current flowing through the electromagnet wiring 151 can be rapidly increased (or decreased). Moreover, between the positive pole 171a and the negative pole 171b of the power source 171, a capacitor is usually connected in order to stabilize the power source 171 (not shown).

[0054] In the configuration as above, when the transistors 161, 162 are both turned on, the current flowing through the electromagnet wiring 151 (hereinafter, referred to as an electromagnet current iL) increases, while when both of the transistors are turned off, the electromagnet current iL decreases.

[0055] Moreover, when either one of the transistors 161, 162 is turned on, while the other is turned off, a so-called flywheel current is held. And by causing the flywheel current to flow through the amplifier circuit 150 as above, a hysteresis loss in the amplifier circuit 150 isdecreased, and power consumption as the entire circuit can be kept low. Moreover, by controlling the transistors 161, 162 as above, a high- frequency noise such as a harmonic generated in the turbomolecular pump 100 can be reduced. Furthermore, by measuring this flywheel current by the current detection circuit 181, the electromagnet current iL flowing through the electromagnet wiring 151 can be detected.

[0056] That is, when the detected current value is smaller than the current instruction value, both the transistors 161, 162 are turned on only for a period of time corresponding to the pulse-width time Tp1 only once during the control cycle Ts 3. Thus, the electromagnet current iL during this period increases toward a current value iLmax (not shown) that can be made to flow from the positive pole 171a to the negative pole 171b through the transistors 161, 162.

[0057] On the other hand, when the detected current value is larger than the current instruction value, both the transistors 161, 162 are turned off only for a period of time corresponding to the pulse-width time Tp2 only once during the control cycle Ts as shown in Fig. 4. Thus, the electromagnet current iL during this period decreases toward a current value iLmin (not shown) that can be regenerated from the negative pole 171b to positive pole 171a through the diodes 165, 166.

[0058] And in the both cases, after elapse of the pulse-width times Tp1, Tp2, either one of the transistors 161, 162 is turned on. Thus, during this period, the flywheel current is held in the amplifier circuit 150.

[0059] <First Embodiment> Subsequently, a vacuum pump 300 according to First Embodiment will be explained.

[0060] The vacuum pump 300 includes, as shown in Figs. 5 to 7, a casing 310 forming an outer shell of the vacuum pump 300, a rotor shaft 113 disposed rotatably inside the casing 310, a magnetic bearing 320 which supports the rotor shaft 113, a motor 121 which rotates the rotor shaft 113, rotor blades 102 in plural steps, fixed to the rotor shaft 113 and rotatable with the rotor shaft 113, stator blades 123 in plural steps, fixed with respect to the casing 310 and disposed among the rotor blades 102, and heating means 340 which heats a gas flow passage in the vacuum pump 300.

[0061] The casing 310 is formed by a plurality of stator components. Specifically, the casing 310 includes an upper case 311, a lower case 312, a stator-blade spacer 125, and a base portion 129. Moreover, the casing 310 includes a heater spacer 330 and the thread-groove spacer 131 inside the lower case 312. The casing 310 is made in a substantially cylindrical shape with the base portion 129 as a bottom part, and various interior components are installed in an internal space thereof. Each of these components is disposed coaxially and is integrally connected by a fastening member such as a bolt. In this Embodiment, the stator component heated by the heating means 340 is the thread-groove spacer 131, but the thread-groove spacer 131 is not limiting but may be other stator components. Moreover, the stator blade 123 can also become the stator component to be heated by the heating means 340.

[0062] On an upstream side (sucking side) of the upper case 311, the inlet port 101 is disposed, and on the heater spacer 330 on an upstream side of the base portion 129, the outlet port 133 is disposed.

[0063] The lower case 312 is formed cylindrically and is provided away from the heater spacer 330 so as to cover an outer peripheral surface of the heater spacer 330.

[0064] The heater spacer 330 is disposed so as to heat the thread- groove spacer 131. The heater spacer 330 is formed substantially cylindrically and is disposed inside the lower case 312. The heater spacer 330 is disposed between the stator-blade spacer 125 and the base portion 129 in the axial direction.

[0065] The heater spacer 330 has a substantially cylindrical shape and has a ring-shaped first recess portion 331 for disposing the heating means 340 on a face directed to the upstream side (sucking side) in contact with the thread-groove spacer 131.

[0066] The heating means 340 has a high-permeability magnetic body 341 disposed in the first recess portion 331, a coil 342 disposed adjacent to the high-permeability magnetic body 341, and a heated portion 343 connected to the thread-groove spacer 131, which is one of the stator components.

[0067] The high-permeability magnetic body 341 is a ring-shaped member disposed in the first recess portion 331 and has a recessed accommodating portion 345 extending in a circumferential direction on a front surface 344, which is a surface on a side on which the heated portion 343 isdisposed. The accommodating portion 345 can accommodate the coil 342. The accommodating portion 345 includes a first wall surface 346 located on an inner peripheral side of the coil 342 to be accommodated, a second wall surface 347 located on an outer peripheral side of the coil 342, and an accommodating surface 348 directed to the heated portion 343 between the first wall surface 346 and the second wall surface 347. The accommodating portion 345 has a hole and a groove for introducing a metal wire of the coil 342 from an outside formed from an outer surface. The high-permeability magnetic body 341 covers a side opposite to the front surface 344 side on which the heated portion 343 of the coil 342 is disposed. A thickness of the high-permeability magnetic body 341 is not particularly limited and approximately 1 mm to 2 mm, for example, but it may be less than 1 mm or 2 mm or more.

[0068] The high-permeability magnetic body 341 is a soft magnetic body having high permeability and is magnetic ceramics which conducts electricity more hardly than metal magnetic material. The high- permeability magnetic body 341 is ferrite, which is a magnetic oxide with a ferric oxide as a main component, for example, and it is preferably Mn- Zn ferrite, which is a soft-magnetic ferrite containing manganese and zinc or Ni-Zn ferrite, which is a soft magnetic ferrite containing nickel and zinc. The high-permeability magnetic body 341 is more preferably Mn- Zn ferrite.

[0069] The coil 342 is formed by winding a wire formed of a good conductor (copper, for example) several times and of at least one layer (plural layers in this Embodiment). The coil 342 is accommodated in the accommodating portion 345 from outside the casing 310 through a passage (not shown) and is disposed in contact with the accommodating surface 348. The coil 342 may be constituted by disposing a plurality of the coils in parallel. The number of winding times of the wire of the coil 342 is not particularly limited but it is 15 to 20 windings, for example.

[0070] The heated portion 343 is connected to the thread groove spacer 131 forming the gas flow passage and is disposed so as to cover the accommodating portion 345 of the high-permeability magnetic body 341. That is, the heated portion 343 is opposed to the front surface 344 of the accommodating portion 345 and is disposed so as to cover the front surface 344 side of the coil 342. The heated portion 343 is accommodated in a ring-shaped second recess portion 350 formed on a surface on thedownstream side (sucking side) in contact with the heater spacer 330 of the thread groove spacer 131. Noe that a position where the heated portion 343 is in contact with the thread groove spacer 131 is not particularly limited. Note that, when the thread groove spacer 131 (stator component) is formed by a metal material having magnetism such as a stainless material, the heated portion 343 may be a part of the thread groove spacer 131.

[0071] The heated portion 343 is formed of a ring-shaped flat plate having a substantially constant thickness corresponding to the shape of the accommodating portion 345 of the high-permeability magnetic body 341. The heated portion 343 is away from the front surface 344 of the accommodating portion 345 only by a slight distance. The heated portion 343 is formed of a metal material having magnetism such as a ferrous material (pure iron, S15C, S25C, for example), a stainless material having magnetism (ferrite stainless material, SUS430, SUS420J2, for example) and the like.

[0072] Subsequently, an action of the vacuum pump 300 according to First Embodiment will be explained.

[0073] When a high-frequency AC current flows through the coil 342, the coil 342, the high-permeability magnetic body 341, and the heated portion 343 are electromagnetically coupled, and an eddy current is generated inside the heated portion 343. The frequency of the AC current to be applied is 20 kHz to 60 kHz, for example, but the frequency may be different from that. A voltage is 100V to 300V, for example, but this is not limiting. Since the heated portion 343 has specific electric resistance, Joule heat is generated by the eddy current. Moreover, the heated portion 343 generates also iron-loss heat generation. Therefore, the temperature of the heated portion 343 becomes high, and the thread groove spacer 131 in contact can be heated. Note that the high- permeability magnetic body 341 hardly conduct electricity and thus, Joule heat by the eddy current is not generated. Moreover, since the coil 342 is disposed in the accommodating portion 345 of the high-permeability magnetic body 341, the side opposite to the direction, in which the front surface 344 is directed (downstream side in this Embodiment), and the lateral side (the inner side and the outer side in the radial direction in this Embodiment) are covered by the high-permeability magnetic body 341. Therefore, as shown in Fig. 7, magnetic flux leakage of the coil 342is suppressed. Thus, generation of Joule heat or heat generation by a loss in the metal material (the heater spacer 330 in this Embodiment) located on the outer side of the high-permeability magnetic body 341 can be suppressed. Therefore, the heating means 340 can efficiently heat the heated portion 343.

[0074] The frequency of the current applied to the coil 342 is preferably the same as or a multiple of the control frequency of the magnetic bearing 320. If the frequency of the current applied to the coil 342 has a difference from the control frequency or a multiple thereof of the magnetic bearing 320, there is a possibility that a noise at the frequency of the difference is generated. On the other hand, if the frequency of the current applied to the coil 342 is the same or a multiple of the control frequency of the magnetic bearing 320, occurrence of the noise generated by the aforementioned difference can be suppressed.

[0075] Note that the high-permeability magnetic body 341 only needs to cover the side opposite to the front surface 344 side on which the heated portion 343 of the coil 342 is disposed, and it does not have to be disposed on the lateral side (the inner side and the outer side in the radial direction in this Embodiment) perpendicular to the direction from the coil 342 toward the heated portion 343 on the section perpendicular to the electric conduction direction of the coil 342. That is, the high- permeability magnetic body 341 does not have to have the first wall surface 346 and / or the second wall surface 347 as long as it has the accommodating surface 348. However, in that case, the magnetic flux becomes susceptible to an influence from the metal component around it (the heater spacer 330, for example) and thus, it is preferable that a distance between the coil 342 and the heater spacer 330 is sufficiently taken on a surface where the permeability magnetic body 341 is not disposed.

[0076] As described above, the vacuum pump 300 according to First Embodiment is the vacuum pump 300 which includes the casing 310, the rotor shaft 113 disposed in the casing 310, and the rotor blade 102 rotatable with the rotor shaft 113 and exhausts the gas by rotation of the rotor blade 102, has the heating means 340 which heats the gas flow passage in the vacuum pump 300, and the heating means 340 has the coil 342, the heated portion 343, which is a magnetic body heated byelectromagnetic induction by causing the AC current to flow through the coil 342, and the high-permeability magnetic body 341 which covers the side opposite to the front surface 344 side on which the heated portion 343 of the coil 342 is disposed. As a result, in the vacuum pump 300, the magnetic path can be formed so that the magnetic flux can pass through the high-permeability magnetic body 341 on the side opposite to the front surface 344 side on which the heated portion 343 of the coil 342 is disposed and thus, the heated portion 343 heated by the electromagnetic induction can be efficiently heated. Therefore, the vacuum pump 300 can suppress precipitation of by-products in the pump by efficiently heating the gas flow passage.

[0077] Moreover, the heated portion 343 is connected to the stator component (thread groove spacer 131) forming the gas flow passage or is a part of the stator component. As a result, the vacuum pump 300 can effectively heat the stator blade 123.

[0078] Moreover, the vacuum pump 300 has the magnetic bearing 320 which magnetically levitates and supports the rotor shaft 113. As a result, the gas flow passage of the vacuum pump 300 having the magnetic bearing 320 can be efficiently heated. When the heated portion 343 is connected to the rotor blade 102, the rotor blade 102 for which electric conduction is difficult can be effectively heated.

[0079] Moreover, the frequency of the current applied to the coil 342 is the same as or a multiple of the control frequency of the magnetic bearing 320. As a result, occurrence of a noise generated by the difference between the frequency of the current applied to the coil 342 and the control frequency of the magnetic bearing 320 can be suppressed.

[0080] Moreover, a part of the high-permeability magnetic body 341 is disposed on the lateral side perpendicular to the direction from the coil 342 toward the heated portion 343 on the section perpendicular to the electric conduction direction of the coil 342. As a result, the vacuum pump 300 can efficiently heat the heated portion 343 by forming the magnetic path so that the magnetic flux passes through the high- permeability magnetic body 341 on the side opposite to the front surface 344 side on which the heated portion 343 of the coil 342 is disposed and the lateral side.

[0081] Note that, in First Embodiment, the installation position of the coil 342 was set to a vacuum side, but it may be on an atmosphericair side. The atmospheric air side is preferable when considering necessity of a measure against discharge of the coil 342 in the case of disposition on the vacuum side.

[0082] Moreover, the high-permeability magnetic body 341 is soft- magnetic ferrite containing manganese and zinc. As a result, the high- permeability magnetic body 341 has high specific resistance and thus, hardly generates an eddy current, and a loss at a high frequency is small. Therefore, heat generation in the high-permeability magnetic body 341 is suppressed, and the heated portion 343 can be efficiently heated.

[0083] <Second Embodiment> Subsequently, a vacuum pump 400 according to Second Embodiment will be explained. Second Embodiment is different from First Embodiment in a point that a heated portion 443 of heating means 440 is connected to the rotor blade 102.

[0084] The heating means 440 has, as shown in Fig. 8 and Fig. 9, a cylindrical high-permeability magnetic body 441 covering an outer peripheral surface of the stator column 122 (stator component) surrounding an electric equipment portion, a coil 442 disposed so as to wind around an outer peripheral surface of the high-permeability magnetic body 441, and a cylindrical heated portion 443 connected to the rotor blade 102.

[0085] The high-permeability magnetic body 441 is a cylindrical member, and the coil 442 is wound around a front surface 444, which is a surface on a side on which the heated portion 443 is disposed, that is, an outer peripheral surface. An end part on the upstream side of the high-permeability magnetic body 441 is preferably located closer to the upstream side than an end part on the upstream side of the coil 442 from a viewpoint of suppression of magnetic flux leakage of the coil 442. Moreover, an end part on the downstream side of the high-permeability magnetic body 441 is preferably located closer to the downstream side then an end part on the downstream side of the coil 442. The high- permeability magnetic body 441 does not have a recess-shaped accommodating portion in Second Embodiment but may have a recess-shaped accommodating portion 445 similarly to First Embodiment. That is, a part of the high-permeability magnetic body 441 may be disposed on a lateral side (upstream side and / or downstream side in Second Embodiment) perpendicular to a direction from the coil 442 toward the portion 443 ona section perpendicular to an electric conduction direction of the coil 442. The coil 442 is disposed in the gas flow passage. That is, the coil 442 is disposed under high vacuum of the gas flow passage.

[0086] The heated portion 443 is a cylindrical member fixed to the inner peripheral surface of the rotor blade 102, for example. The heated portion 443 may be a member fixed to the inner peripheral surface of the rotor blade 102 by plating or the like. The heated portion 443 is formed by a metal material having magnetism such as a stainless material or the like. Note that, when the rotor blade 102 is formed of a metal material having magnetism such as a stainless material or the like, the heated portion 443 may be a part of the rotor blade 102.

[0087] Subsequently, an action of the vacuum pump 400 according to Second Embodiment will be explained.

[0088] In the vacuum pump 400 according to Second Embodiment, when the rotor blade 102 is rotated, the heated portion 443 connected to the rotor blade 102 or the heated portion 443, which is a part of the rotor blade 102, is rotated. In this state, when a high-frequency AC current flows through the stationary coil 442, the coil 442, the high-permeability magnetic body 441, and the heated portion 443 are electromagnetically coupled, and an eddy current is generated inside the heated portion 443. The heated portion 443 generates Joule heat by the eddy current and generates iron-loss heat generation. Thus, the temperature of the heated portion 443 becomes high, and the rotor blade 102 connected to the heated portion 443 or the rotor blade 102 having the heated portion 443 can be heated. Therefore, the heating means 440 can efficiently heat the rotor blade 102 by the coil 442 disposed on the fixed side. Note that the high- permeability magnetic body 441 hardly conduct electricity and thus, Joule heat by the eddy current is not generated. Moreover, since the coil 442 is disposed on the outer peripheral surface of the high-permeability magnetic body 441, as shown in Fig. 9, the magnetic flux leakage of the coil 442 is suppressed. Therefore, heat generation of the metal material (the stator column 122 in this Embodiment) located on the inner side in the radial direction of the high-permeability magnetic body 441 due to Joule heat or a loss can be suppressed. Therefore, the heating means 440 can efficiently heat the heated portion 443.

[0089] Moreover, the heated portion 443 is connected to the rotor blade 102 or is a part of the rotor blade 102. As a result, the vacuumpump 400 can effectively heat the rotor blade 102 which is difficult to be heated from the outside.

[0090] Moreover, the coil 442 is disposed in the high-vacuum gas flow passage. As a result, the coil 442 forms a magnetic path close to the heated portion 443 and thus, efficient heating can be realized.

[0091] Note that, in Second Embodiment, too, the installation position of the coil 442 was set to the vacuum side, but it may be on the atmospheric air side. The atmospheric air side is preferable when considering necessity of a measure against discharge of the coil 442 in the case of disposition on the vacuum side, but this is not limiting.

[0092] Note that the present invention is not limited only to the aforementioned Embodiments, but various changes or combinations are possible by a person ordinarily skilled in the art within a technical idea of the present invention. For example, the aforementioned First Embodiment and Second Embodiment may be combined.

[0093] Moreover, as in the variation of First Embodiment shown in Fig. 10, a coil 542 may be located on an inner side in the radial direction of a high-permeability magnetic body 541, and a heated portion 543 may be located on the inner side in the radial direction of the high- permeability magnetic body 541 and the coil 542.

[0094] Moreover, the vacuum pump 300 may be a structure only of a turbomolecular pump not having a thread-groove pump portion. Moreover, the thread groove pump of each of the aforementioned embodiments is a Holweck-type thread groove pump by a spiral groove in the axial direction, but it may be a Zigbahn-type thread groove pump by a spiral- shaped groove in a radial direction or may be configured by having the both.

[0095] 102 Rotor blade 113 Rotor shaft 123 Stator blade 131 Thread-groove spacer (stator component) 300, 400 Vacuum pump 310 Casing 320 Magnetic bearing 330 Heater spacer 340, 440, 540 Heating means, 441, 541 High-permeability magnetic body , 442, 542 Coil , 443, 543 Heated portion, 444, 544 Front surface

Claims

CLAIMS [Claim A vacuum pump comprising: a casing; a rotor shaft disposed in the casing; and a rotor blade rotatable together with the rotor shaft, with gas being exhausted by rotation of the rotor blade, the vacuum pump further comprising heating means for heating a gas low passage in the vacuum pump, wherein the heating means has: a coil; a heated portion, which is a magnetic body heated by electromagnetic nduction by causing an AC current to flow through the coil; and a magnetic body covering an opposite side to a front side, on which he heated portion is disposed, of the coil. Claim 2] The vacuum pump according to claim 1, wherein the heated portion is onnected to a stator component which forms the gas flow passage or is a art of the stator component. Claim 3] The vacuum pump according to claim 1, wherein the heated portion is onnected to the rotor blade or is a part of the rotor blade. Claim 4] The vacuum pump according to claim 1, further comprising a magnetic earing which magnetically levitates and supports the rotor shaft. Claim 5] The vacuum pump according to claim 4, wherein a frequency of an lectric current applied to the coil is same as or a multiple of a ontrol frequency of the magnetic bearing. Claim 6] The vacuum pump according to claim 1, wherein a part of the magnetic ody is disposed on a lateral side perpendicular to a direction from the oil toward the heated portion on a section perpendicular to an electric onduction direction of the coil. Claim 7] The vacuum pump according to claim 1, wherein the coil is disposed n the gas flow passage.

8. The vacuum pump according to claim 1, wherein the magnetic body isferrite containing manganese and zinc.

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