US20240318666A1

US20240318666A1 - Vacuum pump and spacer

Info

Publication number: US20240318666A1
Application number: US18/261,032
Authority: US
Inventors: Haruki SUZUKI
Original assignee: Edwards Japan Ltd
Current assignee: Edwards Japan Ltd
Priority date: 2021-01-27
Filing date: 2022-01-11
Publication date: 2024-09-26
Also published as: JP7652576B2; JP2022114559A; WO2022163341A1

Abstract

There are proposed a vacuum pump capable of suppressing a temperature increase of a stator blade by heat from a heating source without increasing the number of components, and a spacer used in such a vacuum pump. The present invention is a vacuum pump including a plurality of rotor blades which rotate together with rotating shafts, a plurality of stator blades which are disposed in multiple tiers between the rotor blades, and a plurality of spacers which are provided in multiple tiers inside casings and hold respectively the stator blades at predetermined positions, and, in the vacuum pump, at least one spacer of the plurality of spacers holding the stator blade has a concave surface in a contact surface which comes into contact with the stator blade.

Description

CROSS-REFERENCE OF RELATED APPLICATION

This application is a Section 371 National Stage Application of International Application No. PCT/JP2022/000593, filed Jan. 11, 2022, which is incorporated by reference in its entirety and published as WO 2022/163341A1 on Aug. 4, 2022 and which claims priority of Japanese Application No. 2021-010866, filed Jan. 27, 2021.

FIELD

The present invention relates to a vacuum pump and a spacer used in the vacuum pump.

BACKGROUND

A vacuum pump such as a turbo-molecular pump is used in exhaust processing in a vacuum chamber provided in a semiconductor manufacturing apparatus. Manufacturing processes of a semiconductor include a process in which various process gases are caused to act on a semiconductor substrate, and the vacuum pump is used not only when a chamber of a semiconductor apparatus is evacuated but also when the process gas is exhausted from the chamber.
When the process gas flows in a flow path in the vacuum pump, in a part in which a relationship between pressure and temperature represented by a vapor pressure curve changes from a vapor phase to a solid phase, the process gas is solidified and is deposited on an inner wall surface of the flow path. For example, in the vacuum pump which has a turbo-molecular pump mechanism portion constituted of a stator blade and rotor blade on an inlet side and has a thread groove pump mechanism portion constituted of a cylindrical portion of a rotating body and a thread groove of a threaded spacer on an outlet side, a pressure of the process gas is increased in the thread groove pump mechanism portion. Consequently, there are cases where a solidified product is deposited particularly on a wall surface of the flow path on the outlet side, hence performance of the pump is reduced.
To cope with such a problem, conventionally, the deposition of the product is suppressed by heating an outlet-side peripheral portion of the vacuum pump by using a heating source such as a heater and increasing a temperature of the process gas in the flow path on the outlet side.
Incidentally, heat from the above-described heating source is conducted to a stator blade positioned adjacent to the outlet-side peripheral portion or a stator blade spacer (hereinafter referred to as spacer in some cases) which holds the stator blade at a predetermined position, and hence extra energy for heating the process gas becomes necessary.
In addition, when a temperature of a rotor blade is increased by frictional heat with air with which the rotor blade comes into contact, there is a possibility that durability may be impaired by a creep phenomenon, and hence it is important to release heat to the stator blade to suppress a temperature increase by radiation or the like. However, when a temperature of the stator blade or the stator blade spacer is increased by the heat from the heating source, it is not possible to efficiently dissipate heat from the rotor blade to the stator blade, and there is a possibility that the temperature of the rotor blade is excessively increased.
Conventionally, for the purpose of solving such a problem, a vacuum pump in PTL 1 is proposed. In the vacuum pump, a plurality of insulating members are intermittently disposed circumferentially in a connection portion between an upper casing which covers an outer periphery of a turbo-molecular pump mechanism portion and an intermediate casing which is provided with a heater and is disposed so as to be connected to the upper casing, heat of the heater is thereby prevented from being transmitted to a stator blade via the upper casing, and a temperature of the stator blade is thereby suppressed.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background.

SUMMARY

The present invention is a vacuum pump including: a casing; a rotating shaft which is rotatably supported inside the casing; a plurality of rotor blades which are provided in multiple tiers on an outer periphery of the rotating shaft and rotate together with the rotating shaft; a plurality of stator blades which are disposed in multiple tiers between the rotor blades; and a plurality of spacers which are provided in multiple tiers inside the casing and hold respectively the stator blades at predetermined positions, wherein at least one of the plurality of spacers holding the stator blade has a concave surface in a contact surface which comes into contact with the stator blade.
In the vacuum pump described above, the concave surface is preferably provided in the contact surface positioned on an outlet side.
In addition, the plurality of spacers include a spacer which is positioned closest to the outlet side preferably has the concave surface.
Further, the spacer having the concave surface is preferably formed from a wrought material by cutting.
Herein, the wrought material is preferably an aluminum alloy.
In addition, the present invention is a spacer used in a vacuum pump including: a casing; a rotating shaft which is rotatably supported inside the casing; a plurality of rotor blades which are provided in multiple tiers on an outer periphery of the rotating shaft and rotate together with the rotating shaft; and a plurality of stator blades which are disposed in multiple tiers between the rotor blades, the spacer being provided in multiple tiers inside the casing, and holding respectively the stator blades at predetermined positions, wherein at least one of a plurality of the spacers holding the stator blade has a concave surface in a contact surface which comes into contact with the stator blade.

Advantageous Effects of Invention

In the vacuum pump of the present invention, the spacer which holds the stator blade at the predetermined position has the concave surface in the contact surface which comes into contact with the stator blade and, with this, a contact area with the stator blade is reduced and thermal resistance on the contact surface is increased, and hence it is possible to suppress transmission of heat between the spacer and the stator blade and suppress a temperature increase of the stator blade. In addition, by providing the concave surface, a thermal path of the spacer is narrowed and movement of the heat is prevented, and hence it is possible to suppress the temperature decrease of a portion such as a thread groove pump mechanism portion of which temperature is preferably maintained.
The Summary is provided to introduce a selection of concepts in a simplified form that are further described in the Detail Description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a longitudinal sectional view schematically showing an embodiment of a vacuum pump according to the present invention.

FIG. 2 is a circuit diagram of an amplifier circuit of the vacuum pump shown in FIG. 1 .

FIG. 3 is a time chart showing control in the case where a current command value is larger than a detection value.

FIG. 4 is a time chart showing control in the case where the current command value is smaller than the detection value.

FIG. 5 shows a partially enlarged view of an A portion shown in FIG. 1 and a partially enlarged view of a spacer.

FIG. 6 is a view showing a modification of the spacer.

FIG. 7 is a view related to a manufacturing method of the spacer shown in FIG. 6 .

FIG. 8 is a view related to a manufacturing method of the spacer shown in FIG. 5 .

DETAILED DESCRIPTION

Hereinbelow, a turbo-molecular pump 100 which is an embodiment of a vacuum pump according to the present invention will be described with reference to the drawings. First, an overall configuration of the turbo-molecular pump 100 will be described with reference to FIGS. 1 to 4 . Note that a “casing” according to the present invention described above is constituted by a main body casing portion 114 including an outer tube 127 and a base portion 129 in the turbo-molecular pump 100 of the present embodiment. In addition, a “rotating shaft” according to the present invention is constituted by a rotating body 103 and a rotor shaft 113 described below in the present embodiment.
FIG. 1 shows a longitudinal sectional view of the turbo-molecular pump 100. In FIG. 1 , in the turbo-molecular pump 100, an inlet port 101 is provided at an upper end of the cylindrical outer tube 127. In addition, inside the outer tube 127, the rotating body 103 in which a plurality of rotor blades 102 (102 a, 102 b, 102 c . . . ) which are turbine blades for sucking and exhausting gas are formed radially in multiple tiers in a peripheral portion is provided. The rotor shaft 113 is attached to the center of the rotating body 103, and the rotor shaft 113 is supported so as to be levitated in the air by, e.g., a five-axis control magnetic bearing and a position of the rotor shaft 113 is controlled also by the five-axis control magnetic bearing. In general, the rotating body 103 is constituted by a metal such as aluminum or an aluminum alloy.
Upper radial electromagnets 104 are disposed such that four electromagnets are paired in an X-axis and a Y-axis. Four upper radial sensors 107 are provided so as to be close to the upper radial electromagnets 104 and correspond to the individual upper radial electromagnets 104. As the upper radial sensor 107, an inductance sensor having, e.g., a conductive winding or an eddy current sensor is used, and the upper radial sensor 107 detects a position of the rotor shaft 113 based on change of inductance of the conductive winding which changes according to the position of the rotor shaft 113. The upper radial sensor 107 is configured to detect a radial displacement of the rotor shaft 113, i.e., the rotating body 103 fixed to the rotor shaft 113, and send the radial displacement thereof to a control device 200.
In the control device 200, for example, a compensation circuit having a PID adjustment function generates an excitation control command signal of the upper radial electromagnet 104 based on a position signal detected by the upper radial sensor 107, and an amplifier circuit 150 (described later) shown in FIG. 2 performs excitation control on the upper radial electromagnet 104 based on the excitation control command signal, whereby an upper radial position of the rotor shaft 113 is adjusted.
This rotor shaft 113 is formed of a high-permeability material (iron, stainless steel, or the like), and is attracted by magnetic force of the upper radial electromagnet 104. Such adjustment is performed in an X-axis direction and in a Y-axis direction independently. In addition, a lower radial electromagnet 105 and a lower radial sensor 108 are disposed similarly to the upper radial electromagnet 104 and the upper radial sensor 107, and adjust a lower radial position of the rotor shaft 113 similarly to the upper radial position.
Further, axial electromagnets 106A and 106B are disposed so as to vertically sandwich a disc-shaped metal disc 111 provided below the rotor shaft 113. The metal disc 111 is constituted by a high-permeability material such as iron. A configuration is adopted in which an axial sensor 109 is provided for detecting an axial displacement of the rotor shaft 113, and an axial position signal is sent to the control device 200.
In the control device 200, for example, the compensation circuit having the PID adjustment function generates an excitation control command signal of each of the axial electromagnet 106A and the axial electromagnet 106B based on the axial position signal detected by the axial sensor 109, and the amplifier circuit 150 performs excitation control on each of the axial electromagnet 106A and the axial electromagnet 106B based on the excitation control command signals, whereby the axial electromagnet 106A attracts the metal disc 111 upward with magnetic force, the axial electromagnet 106B attracts the metal disc 111 downward, and an axial position of the rotor shaft 113 is thereby adjusted.
Thus, the control device 200 properly adjusts the magnetic force exerted on the metal disc 111 by this axial electromagnets 106A and 106B to magnetically levitate the rotor shaft 113 in an axial direction and hold the rotor shaft 113 in space in a non-contact manner. Note that the amplifier circuit 150 which performs the excitation control on the upper radial electromagnets 104, the lower radial electromagnet 105, and the axial electromagnets 106A and 106B will be described later.
A motor 121 includes a plurality of magnetic poles which are disposed circumferentially so as to surround the rotor shaft 113. Each magnetic pole is controlled by the control device 200 so as to rotationally drive the rotor shaft 113 via an electromagnetic force acting between the magnetic pole and the rotor shaft 113. In addition, a rotational speed sensor such as, e.g., a Hall element, a resolver, or an encoder which is not shown is incorporated into the motor 121, and a rotational speed of the rotor shaft 113 is detected by a detection signal of the rotational speed sensor.
Further, a phase sensor which is not shown is mounted in the vicinity of, e.g., the lower radial sensor 108, and is configured to detect a phase of rotation of the rotor shaft 113. The control device 200 is configured to detect a position of the magnetic pole by using detection signals of both of the phase sensor and the rotational speed sensor.
A plurality of stator blades 123 (123 a, 123 b, 123 c . . . ) are provided so as to be slightly spaced from the rotor blades 102 (102 a, 102 b, 102 c . . . ). Each of the rotor blades 102 (102 a, 102 b, 102 c . . . ) transfers a molecule of exhaust gas downward by collision, and hence each of the rotor blades 102 is formed so as to be inclined from a plane perpendicular to an axis of the rotor shaft 113 by a predetermined angle. The stator blades 123 (123 a, 123 b, 123 c . . . ) are constituted by a metal such as, e.g., aluminum, iron, stainless steel, or copper, or metals such as alloys containing these metals as ingredients.
In addition, similarly, each of the stator blades 123 is also formed so as to be inclined from the plane perpendicular to the axis of the rotor shaft 113 by a predetermined angle, and the stator blades 123 are disposed so as to extend toward an inner side of the outer tube 127 and alternate with tiers of the rotor blades 102. Further, outer peripheral ends of the stator blades 123 are supported in a state in which the outer peripheral ends thereof are inserted between a plurality of stator blade spacers 125 (125 a, 125 b, 125 c . . . ) which are stacked on each other.
Each of the stator blade spacers 125 is a ring-shaped member, and is constituted by a metal such as, e.g., aluminum, iron, stainless steel, or copper, or metals such as alloys containing these metals as ingredients. The outer tube 127 is fixed to an outer periphery of the stator blade spacer 125 so as to be slightly spaced from the outer periphery thereof. A base portion 129 is disposed at a bottom portion of the outer tube 127. An outlet port 133 is formed in the base portion 129, and is caused to communicate with the outside. Exhaust gas which has entered the inlet port 101 from a side of a chamber (vacuum chamber) and has been transferred to the base portion 129 is sent to the outlet port 133.
Further, depending on usage of the turbo-molecular pump 100, a threaded spacer 131 is disposed between a portion below the stator blade spacer 125 and the base portion 129. The threaded spacer 131 is a cylindrical member constituted by metals such as aluminum, copper, stainless steel, iron, or alloys containing these metals as ingredients, and a spiral thread groove 131 a having a plurality of threads is formed in an inner peripheral surface of the threaded spacer 131. A direction of the spiral of the thread groove 131 a is a direction in which, when the molecule of the exhaust gas moves in a rotation direction of the rotating body 103, this molecule is transferred toward the outlet port 133. At the lowest portion of the rotating body 103 subsequent to the rotor blades 102 (102 a, 102 b, 102 c . . . ), a cylindrical portion 102 d is disposed so as to extend downward. An outer peripheral surface of the second cylindrical portion 102 d is cylindrical, is protruded toward the inner peripheral surface of the threaded spacer 131, and is disposed close to the inner peripheral surface of the threaded spacer 131 with a predetermined gap formed between the outer peripheral surface thereof and the inner peripheral surface thereof. The exhaust gas having been transferred to the thread groove 131 a by the rotor blades 102 and the stator blades 123 is sent to the base portion 129 while being guided by the thread groove 131 a.
The base portion 129 is a disc-shaped member constituting a base bottom portion of the turbo-molecular pump 100 and, in general, the base portion 129 is constituted by a metal such as iron, aluminum, or stainless steel. The base portion 129 physically holds the turbo-molecular pump 100 and also has a function of a heat conductive path, and hence it is preferable to use a metal having rigidity of iron, aluminum, or copper and having high heat conductivity.
In such a configuration, when the rotor blade 102 is rotationally driven together with the rotor shaft 113 by the motor 121, the exhaust gas is sucked from the chamber through the inlet port 101 by actions of the rotor blade 102 and the stator blade 123. The rotational speed of the rotor blade 102 is usually 20000 rpm to 90000 rpm, and a circumferential velocity at a tip of the rotor blade 102 reaches 200 m/s to 400 m/s. The exhaust gas sucked from the inlet port 101 passes between the rotor blade 102 and the stator blade 123 and is transferred to the base portion 129. At this point, a temperature of the rotor blade 102 rises due to frictional heat generated when the exhaust gas comes into contact with the rotor blade 102 and conduction of heat generated in the motor 121, and this heat is transmitted to a side of the stator blade 123 by radiation or conduction by a gas molecule of the exhaust gas.
The stator blade spacers 125 are bonded to each other at their outer peripheral portions, and transmit heat received from the rotor blade 102 by the stator blade 123 and frictional heat generated when the exhaust gas comes into contact with the stator blade 123 to the main body casing portion 114. In the present embodiment, in order to efficiently release the heat transmitted to the main body casing portion 114, an annular water cooled tube 115 is wound around an outer peripheral surface in an upper portion of the outer tube 127.
Note that, in the foregoing, the description has been made on the assumption that the threaded spacer 131 is disposed on the outer periphery of the cylindrical portion 102 d of the rotating body 103, and the thread groove 131 a is formed in the inner peripheral surface of the threaded spacer 131. However, reversely to this, there are cases where the thread groove is formed in an outer peripheral surface of the cylindrical portion 102 d, and a spacer having a cylindrical inner peripheral surface is disposed around the outer peripheral surface thereof.
In addition, depending on usage of the turbo-molecular pump 100, in order to prevent gas sucked from the inlet port 101 from entering an electrical component portion constituted by the upper radial electromagnet 104, the upper radial sensor 107, the motor 121, the lower radial electromagnet 105, the lower radial sensor 108, the axial electromagnets 106A and 106B, and the axial sensor 109, there are cases where a surrounding portion of the electrical component portion is covered with a stator column 122, and a pressure in the stator column 122 is maintained at a predetermined pressure by purge gas.
In these cases, piping which is not shown is disposed in the base portion 129, and the purge gas is introduced through the piping. The introduced purge gas is sent to the outlet port 133 through gaps between a protection 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 cylindrical portion of the rotor blade 102.
Herein, the turbo-molecular pump 100 requires control based on identification of a model and inherent parameters which are adjusted individually (e.g., various characteristics corresponding to the model). For storing the control parameters, the above-described turbo-molecular pump 100 includes an electronic circuit portion 141 in a main body of the turbo-molecular pump 100. The electronic circuit portion 141 is constituted by electronic components such as a semiconductor memory such as an EEP-ROM and a semiconductor element for accessing the semiconductor memory, and a substrate 143 for implementing the electronic components. The electronic circuit portion 141 is housed in a lower portion of a rotational speed sensor which is not shown in the vicinity of, e.g., the center of the base portion 129 constituting a lower portion of the turbo-molecular pump 100, and the lower portion is closed by a hermetic bottom lid 145.
Incidentally, in a manufacturing process of a semiconductor, some process gases introduced into a chamber have properties which make the process gases solid when pressure of the process gases becomes higher than a predetermined value or temperature of the process gases becomes lower than a predetermined value. Inside the turbo-molecular pump 100, pressure of the exhaust gas is minimized at the inlet port 101 and is maximized at the outlet port 133. When the pressure of the process gas becomes higher than a predetermined value or the temperature thereof becomes lower than a predetermined value during transfer of the process gas from the inlet port 101 to the outlet port 133, the process gas becomes solid, and is adhered to and deposited on the inside of the turbo-molecular pump 100.
For example, in the case where SiCl₄is used as process gas in an Al etching device, it can be seen from a vapor pressure curve that a solid product (e.g., AlCl₃) is precipitated at a low degree of vacuum (760 [torr] to 10⁻²[torr]) and at a low temperature (about 20 [° C.]) and the solid product is adhered to and deposited on the inside of the turbo-molecular pump 100. With this, when the precipitate of the process gas is deposited on the inside of the turbo-molecular pump 100, the deposit narrows a pump flow path and becomes a cause of a reduction in performance of the turbo-molecular pump 100. In addition, the above-described product is in a situation in which the product is easily coagulated and adhered in a portion in which pressure is high in the vicinity of the outlet port 133 or in the vicinity of the threaded spacer 131.
Accordingly, in order to solve this problem, conventionally, a heater 116 is disposed on an outer periphery of the main body casing portion 114 or the base portion 129, the annular water cooled tube 115 or 149 is wound around the outer periphery thereof, a temperature sensor (e.g., a thermistor) which is not shown is embedded in, e.g., the base portion 129, and control of heating by the heater or cooling by the water cooled tube 149 is performed such that a temperature of the base portion 129 is maintained at a constant high temperature (set temperature) based on a signal of the temperature sensor (hereinafter referred to as TMS. TMS; Temperature Management System).
Next, with regard to the thus-configured turbo-molecular pump 100, a description will be given of the amplifier circuit 150 which performs excitation control on the upper radial electromagnets 104, the lower radial electromagnet 105, and the axial electromagnets 106A and 106B. FIG. 2 shows a circuit diagram of the amplifier circuit 150.
In FIG. 2 , one end of an electromagnet winding 151 constituting the upper radial electromagnet 104 or the like is connected to a positive electrode 171 a of a power source 171 via a transistor 161, and the other end thereof is connected to a negative electrode 171 b of the power source 171 via a current detection circuit 181 and a transistor 162. In addition, each of the transistors 161 and 162 is a so-called power MOSFET, and has a structure in which a diode is connected between a source and a drain.
At this point, in the transistor 161, a cathode terminal 161 a of its diode is connected to the positive electrode 171 a, and an anode terminal 161 b is connected to the one end of the electromagnet winding 151. In addition, in the transistor 162, a cathode terminal 162 a of its diode is connected to the current detection circuit 181, and an anode terminal 162 b is connected to the negative electrode 171 b.
On the other hand, in a diode for current regeneration 165, its cathode terminal 165 a is connected to the one end of the electromagnet winding 151, and its anode terminal 165 b is connected to the negative electrode 171 b. In addition, similarly to this, in a diode for current regeneration 166, its cathode terminal 166 a is connected to the positive electrode 171 a, and its anode terminal 166 b is connected to the other end of the electromagnet winding 151 via the current detection circuit 181. The current detection circuit 181 is constituted by, e.g., a Hall sensor-type current sensor and an electrical resistance element.
The thus-configured amplifier circuit 150 corresponds to one electromagnet. Accordingly, in the case where a magnetic bearing is a five-axis control magnetic bearing and the total number of electromagnets 104, 105, 106A, and 106B is ten, the same amplifier circuit 150 is configured for each of the electromagnets, and ten amplifier circuits 150 are connected in parallel to the power source 171.
Further, an amplifier control circuit 191 is constituted by, e.g., a digital signal processor portion (hereinafter referred to as a DSP portion) of the control device 200 which is not shown, and the amplifier control circuit 191 is configured to switch between on/off of the transistors 161 and 162.
The amplifier control circuit 191 is configured to compare a current value (a signal in which this current value is reflected is referred to as a current detection signal 191 c) detected by the current detection circuit 181 with a predetermined current command value. Subsequently, the amplifier control circuit 191 is configured to determine magnitudes of a pulse width (pulse width time periods Tp1 and Tp2) generated in a control cycle Ts which is one cycle by PWM control based on a comparison result. As a result, gate drive signals 191 a and 191 b each having this pulse width are output to gate terminals of the transistors 161 and 162 from the amplifier control circuit 191.
Note that, at the time of passage of a resonance point during acceleration operation of the rotational speed of the rotating body 103 or at the time of occurrence of disturbance during constant speed operation, it is necessary to perform position control of the rotating body 103 at high speed with a strong force. To cope with this, a high voltage of about, e.g., 50 V is used as the power source 171 such that a sharp increase (or decrease) of a current flowing to the electromagnet winding 151 is allowed. In addition, a capacitor (depiction is omitted) is usually connected between the positive electrode 171 a and the negative electrode 171 b of the power source 171 for stabilization of the power source 171.
In such a configuration, a current flowing to the electromagnet winding 151 (hereinafter referred to as an electromagnet current iL) is increased when both of the transistors 161 and 162 are turned on, and the electromagnet current iL is decreased when both of the transistors 161 and 162 are turned off.
In addition, when one of the transistors 161 and 162 is turned on and the other one thereof is turned off, a so-called flywheel current is maintained. By flowing the flywheel current to the amplifier circuit 150 in this manner, it is possible to reduce hysteresis loss in the amplifier circuit 150 and suppress power consumption in the entire circuit to a low level. In addition, by controlling the transistors 161 and 162 in this manner, it is possible to reduce high frequency noise such as harmonics generated in the turbo-molecular pump 100. Further, by measuring the flywheel current in the current detection circuit 181, it becomes possible to detect the electromagnet current iL flowing in the electromagnet winding 151.
That is, in the case where a detected current value is smaller than a current command value, as shown in FIG. 3 , both of the transistors 161 and 162 are turned on only once in the control cycle Ts (e.g., 100 μs) for a time period corresponding to the pulse width time period Tp1. Consequently, the electromagnet current iL during this time period is increased toward a current value iLmax (not shown) which can be flowed from the positive electrode 171 a to the negative electrode 171 b via the transistors 161 and 162.
On the other hand, in the case where the detected current value is larger than the current command value, as shown in FIG. 4 , both of the transistors 161 and 162 are turned off only once in the control cycle Ts for a time period corresponding to the pulse width time period Tp2. Consequently, the electromagnet current iL during this time period is decreased toward a current value iLmin (not shown) which can be regenerated from the negative electrode 171 b to the positive electrode 171 a via the diodes 165 and 166.
In either case, after a lapse of the pulse width time period Tp1 or Tp2, one of the transistors 161 and 162 is turned on. Accordingly, during this time period, the flywheel current is maintained in the amplifier circuit 150.
Next, the above-described stator blade spacers 125 (125 a, 125 b, 125 c . . . ) will be described in detail with reference to FIGS. 1 and 5 . The turbo-molecular pump 100 of the present embodiment includes, as the stator blade spacers 125, first stator blade spacers 125 a, 125 b, and 125 c and second stator blade spacers 125 d and 125 e.
As shown in FIGS. 1 and 5 , each of the first stator blade spacers 125 a, 125 b, and 125 c is a ring-shaped member with a central axis CA serving as the center. The first stator blade spacers 125 a, 125 b, and 125 c include flat upper surfaces 125 a 1, 125 b 1, and 125 c 1 which extend in a horizontal direction. In outer edge portions of the upper surfaces 125 a 1, 125 b 1, and 125 c 1, first positioning portions 125 a 2, 125 b 2, and 125 c 2 which are formed to be depressed downward are provided. In addition, the first stator blade spacers 125 a, 125 b, and 125 c include flat lower surfaces 125 a 3, 125 b 3, and 125 c 3 which extend in parallel to the upper surfaces 125 a 1, 125 b 1, and 125 c 1. In outer edge portions of the lower surfaces 125 a 3, 125 b 3, and 125 c 3, second positioning portions 125 a 5, 125 b 5, and 125 c 5 which are formed to be protruded downward are provided.
As shown in FIGS. 1 and 5 , each of the second stator blade spacers 125 d and 125 e is a ring-shaped member with the central axis CA serving as the center, and the second stator blade spacers 125 d and 125 e include flat upper surfaces 125 d 1 and 125 e 1 which extend in the horizontal direction, and first positioning portions 125 d 2 and 125 e 2 which are provided in outer edge portions of the upper surfaces 125 d 1 and 125 e 1 and are formed to be depressed downward. In addition, the second stator blade spacers 125 d and 125 e have lower surfaces 125 d 3 and 125 e 3 which extend in parallel to the upper surfaces 125 d 1 and 125 e 1, and concave surfaces 125 d 4 and 125 e 4 obtained by depressing the lower surfaces 125 d 3 and 125 e 3 upward are provided in the lower surfaces 125 d 3 and 125 e 3. Second positioning portions 125 d 5 and 125 e 5 which are formed to be protruded downward are provided in outer edge portions of the lower surfaces 125 d 3 and 125 e 3.
As shown in FIGS. 1 and 5 , the first stator blade spacers 125 a, 125 b, and 125 c in such a form and the second stator blade spacers 125 d and 125 e in such a form are disposed in multiple tiers inside the outer tube 127 between an overhang portion 114 a provided in an upper portion of the main body casing portion 114 and the threaded spacer 131 from an upper portion toward a lower portion (from a side of the inlet port 101 toward a side of the outlet port 133) in the order of the first stator blade spacers 125 a, 125 b, and 125 c and the second stator blade spacers 125 d and 125 e. At this point, outer peripheral ends of the stator blades 123 (123 a, 123 b, 123 c . . . ) are inserted between the individual stator blade spacers 125 which are stacked on each other. Herein, the lower surfaces 125 a 3, 125 b 3, 125 c 3, 125 d 3, and 125 e 3 of the first stator blade spacer 125 a and the like are in contact with outer-peripheral-end upper surfaces of the stator blades 123 (123 a, 123 b, 123 c . . . ), while the upper surfaces 125 b 1, 125 c 1, 125 d 1, and 125 e 1 of the first stator blade spacer 125 b and the like, or an upper surface of the threaded spacer 131 are in contact with outer-peripheral-end lower surfaces of the stator blades 123, and the stator blades 123 are held therebetween. That is, the stator blades 123 are held at predetermined positions in a vertical direction by the first stator blade spacer 125 a and the like. In addition, outer peripheral surfaces of the stator blades 123 are in contact with inner peripheral surfaces of the second positioning portions 125 a 5, 125 b 5, 125 c 5, 125 d 5, and 125 e 5 of the first stator blade spacer 125 a and the like. Herein, the inner peripheral surfaces of the second positioning portions 125 a 5, 125 b 5, 125 c 5, 125 d 5, and 125 e 5 are also in contact with inner peripheral surfaces of the first positioning portions 125 a 2, 125 b 2, 125 c 2, 125 d 2, and 125 e 2. That is, the stator blades 123 (123 a, 123 b, 123 c . . . ) are held at predetermined positions in a radial direction by the first stator blade spacer 125 a and the like.
Incidentally, in the present embodiment, in order to suppress deposition of a precipitate on the threaded spacer 131, the heater 116 is provided in the threaded spacer 131, and the threaded spacer 131 is thereby heated. In addition, this heat is conducted also to the stator blade 123 e in the lowest tier which comes into contact with the threaded spacer 131. Note that, as a structure for heating the threaded spacer 131, as described above, the heater 116 may also be provided in the base portion 129.
On the other hand, the concave surface 125 e 4 is provided in the lower surface 125 e 3 of the second stator blade spacer 125 e which comes into contact with the stator blade 123 e in the lowest tier. That is, a contact area between the stator blade 123 and the second stator blade spacer 125 e is reduced and thermal resistance on a contact surface is increased, and hence it is possible to suppress transmission of heat from the stator blade 123 e in the lowest tier to the second stator blade spacer 125 e, and suppress temperature increases of the stator blades 123 (123 a, 123 b, 123 c . . . ) in tiers above the lowest tier. In addition, a thermal path of the second stator blade spacer 125 e is narrowed by providing the concave surface 125 e 4, and hence movement of heat from the threaded spacer 131 is prevented and it is possible to suppress a temperature decrease of the threaded spacer 131.
In the present embodiment, the second stator blade spacer 125 d positioned in a tier immediately above a tier of the second stator blade spacer 125 e also includes the concave surface 125 d 4 in its lower surface 125 d 3. Consequently, it is possible to suppress the temperature increase of the stator blade 123 and the temperature decrease of the threaded spacer 131 more effectively.
Note that, in the present embodiment, two second stator blade spacers 125 d and 125 e are used, but the number of second stator blade spacers may also be one, or three or more. In addition, positions at which the second stator blade spacers 125 d . . . are disposed are not limited to examples shown in the drawing, and the second stator blade spacers 125 d . . . may also be disposed in, e.g., the second tier, the third tier . . . from below. Note that, when the second stator blade spacer is disposed in the lowest tier like the second stator blade spacer 125 e of the present embodiment, the number of the stator blades 123 of which the temperature increases can be suppressed is increased and it is possible to effectively suppress the temperature increases of the rotor blades 102 (102 a, 102 b, 102 c . . . ), and hence it is more preferable to dispose the second stator blade spacer in the lowest tier.
While the concave surfaces 125 d 4 and 125 e 4 are provided in the lower surfaces 125 d 3 and 125 e 3 in the second stator blade spacers 125 d and 125 e described above, the concave surfaces 125 d 4 and 125 e 4 may also be provided in the upper surfaces 125 d 1 and 125 e 1, as in the second stator blade spacers 125 d and 125 e shown in FIG. 6 .
Note that it is possible to form the second stator blade spacers 125 d and 125 e by casting or cutting from a wrought material and, in the case where the second stator blade spacers 125 d and 125 e are formed by cutting from the wrought material, it is preferable that the concave surfaces 125 d 4 and 125 e 4 are provided in the lower surfaces 125 d 3 and 125 e 3 of the second stator blade spacers 125 d and 125 e. This point will be described with reference to FIGS. 7 and 8 .
FIG. 7 shows the case where the concave surfaces 125 d 4 and 125 e 4 are provided in the upper surfaces 125 d 1 and 125 e 1 when the second stator blade spacers 125 d and 125 e are formed by cutting from the wrought material. Herein, it is assumed that a pipe material P which is formed into a cylindrical shape is used as the wrought material. A material of the wrought material is not particularly limited, and it is preferable to use an aluminum alloy in view of ease of machining when the wrought material is formed into the cylindrical shape, and ease of execution of subsequent cutting. When the second stator blade spacers 125 d and 125 e are formed from such a pipe material P, as shown in the drawing, one end portion of the pipe material P is held by a chuck C or the like, and an h1 portion and an h2 portion which are hatched in the other end portion thereof are cut by a cutting tool T. Subsequently, the other end portion of the pipe material P is separated along a line L by the cutting tool T, and an h3 portion is further cut by the cutting tool T from the separated portion. That is, when the h3 portion is cut, it is necessary to hold the separated portion by the chuck C or the like again.
On the other hand, when the concave surfaces 125 d 4 and 125 e 4 are provided in the lower surfaces 125 d 3 and 125 e 3 of the second stator blade spacers 125 d and 125 e, as shown in FIG. 8 , after one end portion of the pipe material P is held by the chuck C or the like, an h4 portion and an h5 portion which are hatched in the other end portion are cut by the cutting tool T. Thereafter, the second stator blade spacers 125 d and 125 e are formed by separating the other end portion of the pipe material P along the line L. That is, in the case where the concave surfaces 125 d 4 and 125 e 4 are provided in the lower surfaces 125 d 3 and 125 e 3, re-holding by the chuck C or the like becomes unnecessary and manufacturing processes can be simplified, and hence it is possible to achieve a reduction in machining time and a reduction in cost.
While one embodiment of the present invention has bee described thus far, the present invention is not limited to such a specific embodiment, and various modifications and changes can be made without departing from the gist of the present invention described in the scope of claims unless otherwise particularly limited in the above description. In addition, the effects in the above-described embodiment are merely examples of the effects obtained by the present invention, which does not mean that the effects by the present invention are limited to the above-described effects.
Although elements have been shown or described as separate embodiments above, portions of each embodiment may be combined with all or part of other embodiments described above.
Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are described as example forms of implementing the claims.

Claims

1. A vacuum pump comprising:

a casing;

a rotating shaft which is rotatably supported inside the casing;

a plurality of rotor blades which are provided in multiple tiers on an outer periphery of the rotating shaft and rotate together with the rotating shaft;

a plurality of stator blades which are disposed in multiple tiers between the rotor blades; and

a plurality of spacers which are provided in multiple tiers inside the casing and hold respectively the stator blades at predetermined positions, wherein

at least one of the plurality of spacers holding the stator blade has a concave surface in a contact surface which comes into contact with the stator blade.

2. The vacuum pump according to claim 1, wherein

the concave surface is provided in the contact surface positioned on an outlet side.

3. The vacuum pump according to claim 1, wherein

the plurality of spacers include a spacer which is positioned closest to the outlet side has the concave surface.

4. The vacuum pump according to claim 1, wherein

the spacer having the concave surface is formed from a wrought material by cutting.

5. The vacuum pump according to claim 4, wherein

the wrought material is an aluminum alloy.

6. A spacer used in a vacuum pump including:

a casing;

a rotating shaft which is rotatably supported inside the casing;

a plurality of rotor blades which are provided in multiple tiers on an outer periphery of the rotating shaft and rotate together with the rotating shaft; and

a plurality of stator blades which are disposed in multiple tiers between the rotor blades,

the spacer being provided in multiple tiers inside the casing, and holding respectively the stator blades at predetermined positions, wherein

at least one of a plurality of the spacers holding the stator blade has a concave surface in a contact surface which comes into contact with the stator blade.