Vacuum pump and fixing disk

Abstract

To provide a vacuum pump having a Sigh-burn exhaust mechanism in which an exhaust amount is stable even when a large amount of exhaust gas flows and an exhaust performance (P-Q performance) is improved, and a fixing disk used in vacuum pump and a Sigh-burn exhaust mechanism.SOLUTION: In a vacuum pump having a Sigh-burn exhaust mechanism according to the present embodiment, an inner diameter folding position is provided in front of a minimum diameter of a rotation disk 9, or specifically, an inner folding is done at a middle of the passage. The fixing disk 50 includes, at the corresponding position, a circular rib part 250 for maintaining a sealing property of the exhaust gas and a communication port 260 as a passage of the exhaust gas to a lower step. The rib part 250 and the communication port 260 can prevent the use at a location in the exhaust passage where the exhaust speed is lowered, preventing a reduction in a flow speed of the exhaust gas. This can prevent a reduction in exhaust speed of the gas at the vicinity of a rotation center of the rotation disk 9 which has been a problem of the Sigh-burn exhaust mechanism.SELECTED DRAWING: Figure 12

Description

[Technical Field]

[0001] The present invention relates to a vacuum pump and a fixed disk used in the vacuum pump, and more particularly to a vacuum pump equipped with a Sigburn pumping mechanism, which can suppress exhaust gas clogging and improve pumping performance at large displacements, and a fixed disk used in the Sigburn pumping mechanism. [Background technology]

[0002] A vacuum pump has a casing that forms an exterior body with an intake port and an exhaust port, and the casing houses a structure that enables the vacuum pump to perform its exhaust function. This structure that enables the vacuum pump to perform its exhaust function is broadly divided into a rotating part (rotor part) fixed to a rotating shaft that rotates at high speed, and a fixed part (stator part) fixed to the casing. In addition, a motor is provided to rotate the rotating shaft at high speed. When the rotating shaft rotates at high speed due to the action of this motor, the rotor blades (rotating disc) fixed to the rotating shaft rotate together with the rotating shaft, and gas is sucked in through the intake port and expelled from the exhaust port due to interaction with the stator blades (fixed disc).

[0003] Known types of vacuum pumps include one with a vertical screw (Hollweck type) exhaust mechanism (Y in the figure) at the bottom (exhaust port side) of the exhaust mechanism consisting of multiple fixed vanes and multiple rotary vanes, as shown in Figure 22, and another with a horizontal screw (hereinafter referred to as Sigburn, X in the figure) at the bottom (exhaust port side) of the exhaust mechanism consisting of multiple fixed vanes and multiple rotary vanes, as shown in Figure 23. Among these, the Sigburn type vacuum pump comprises a rotating disk (rotating disk) and a fixed disk installed with a gap (clearance) in the axial direction from the rotating disk, with spiral grooves (radial screw grooves) engraved on the surface facing the gap of at least one of the rotating disk or the fixed disk. The gas molecules that have diffused into the spiral groove channel are given momentum by the rotating disk in the tangential direction of the rotating disk (i.e., the tangential direction to the rotation direction of the rotating disk), and the spiral grooves give a dominant directionality from the intake port to the exhaust port, thereby performing exhaust. This Sigburn type vacuum pump has excellent back pressure performance because it can make the exhaust gas flow path longer by using multiple stages. Also, because it has a horizontal screw, it has the advantage that the height of the vacuum pump itself can be reduced compared to a vertical screw. Vacuum pumps with a vertical screw exhaust mechanism have the advantages of simple structure and excellent stability. In addition, the vertical screw also ensures that the peripheral speed of the exhaust gas is constant.

[0004] FIG. 20 is a diagram for explaining a conventional Sigburn vacuum pump 1000, showing a schematic configuration example of the conventional Sigburn vacuum pump 1000. Arrows indicate the flow of gas molecules. . FIG. 21 is a diagram for explaining a fixed disk 5000 disposed in a conventional Sigburn vacuum pump 1000, and is a cross-sectional view of the fixed disk 5000 as viewed from the intake port 101 side. The arrows inside the fixed disk 5000 indicate the flow of gas molecules, and the arrows outside the fixed disk 5000 indicate the direction of rotation of a rotating disk (not shown). [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2005-30209 A

[0006] Patent Document 1 discloses a Siegbahn type vacuum pump in which an auxiliary intake port is provided to improve the exhaust efficiency without increasing the axial size. Summary of the Invention [Problem to be solved by the invention]

[0007] In Sigburn-type vacuum pumps, the flow rate of exhaust gas inevitably slows near the center of rotation of the rotating disk (close to the rotating axis), creating a condition where the exhaust gas becomes clogged. This results in localized pressure buildup. This problem becomes even more apparent when the vacuum pump is enlarged (the rotating disk and fixed disk are enlarged) to allow a large amount of exhaust gas to flow. In addition, in Sigbahn vacuum pumps, exhaust gas is sent from the upper stage to the lower stage at point X, but the exhaust gas tends to gather (stagnate) at this point, making the flow less smooth. This has led to issues such as backflow being more likely to occur and the flow rate being less constant. Therefore, an object of the present invention is to provide a vacuum pump equipped with a Sigburn pumping mechanism, which has a stable pumping volume and improved pumping performance (PQ characteristics) even when a large amount of gas is passed through it, and a fixed disk for use in the Sigburn pumping mechanism. [Means for solving the problem]

[0008] The invention described in claim 1 provides a vacuum pump comprising a casing, a rotating shaft supported for free rotation within the casing, a magnetic bearing device that magnetically levitates the rotating shaft and holds it without contact, a plurality of rotating disks that rotate together with the rotating shaft, and at least one fixed disk arranged opposite the plurality of rotating disks and having a spiral groove consisting of peaks and valleys on the surface facing the plurality of rotating disks, the vacuum pump being equipped with a Sigburn exhaust mechanism that exhausts the gas by interaction between the plurality of rotating disks and the fixed disk, wherein the position of the turning portion of the fixed disk for sending the exhaust gas to a lower axial stage is located at a position that is 90% or less of the radial length from the outer end of the opposing rotating disk. A second aspect of the present invention provides the vacuum pump according to the first aspect, wherein the turning portion is provided at a position where the peripheral speed of the exhaust gas is 50% or more of that at the inlet of the rotary disk. The invention of claim 3 provides a vacuum pump as described in claim 1, characterized in that the folded portion is provided at a position where the peripheral speed of the opposing rotating disk is 50% or more of the peripheral speed of the inlet portion of the spiral groove. The invention of claim 4 provides the vacuum pump of claim 1, further comprising: a communication port, arranged in the valley portion of the fixed disk, in the folded portion for sending exhaust gas to a lower stage in the axial direction; and an annular rib portion, concentric with the rotating shaft, having a height corresponding to the peak portion and continuous with the peak portion to provide sealing against exhaust gas, the communication port being arranged adjacent to the rib portion. The invention of claim 5 provides the vacuum pump of claim 4, characterized in that the radial width of the rib portion is 5% or more of the radial length of the opposing rotary disk. The invention of claim 6 provides the vacuum pump of claim 4, characterized in that the size of the communication port is 90% or more of the area obtained by multiplying the outer circumferential length of the rib portion between the peaks by the height of the rib portion. The invention of claim 7 provides a vacuum pump according to any one of claims 4 to 6, characterized in that the communication port is provided in a range where the upstream and downstream flow paths of the spiral groove overlap when viewed from the axial direction. The invention described in claim 8 provides a fixed disk used in a vacuum pump equipped with a Sigburn exhaust mechanism that exhausts by interaction with a rotating disk, characterized in that a spiral groove consisting of peaks and valleys is provided on the surface facing the rotating disk, and the position of a folded portion in the valley for sending exhaust gas to a lower axial position is located at a position 90% or less of the radial length from the outer end of the opposing rotating disk. In the invention of claim 9, the folded portion may include a communication port disposed in the valley portion for sending exhaust gas to a lower stage in the axial direction, and an annular rib portion concentric with the rotation axis, having a height corresponding to the peak portion and continuing from the peak portion in order to provide sealing performance against exhaust gas. The stationary disk according to claim 8, further comprising: a communication port disposed adjacent to the rib portion. In a tenth aspect of the present invention, there is provided the stationary disk according to the ninth aspect, wherein the height of the rib portion is equal to or greater than the height of the peak portion. [Effects of the Invention]

[0009] According to the present invention, in a vacuum pump equipped with a Sigburn pumping mechanism, the pumping volume is stable even when a large amount of gas is passed through, and the pumping performance (PQ characteristics) can be improved. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a diagram showing a schematic configuration of a turbomolecular pump according to an embodiment of the present invention. [Figure 2] FIG. 2 is a circuit diagram of an amplifier circuit used in an embodiment of the present invention. [Figure 3] 5 is a time chart showing control when a detected value is smaller than a current command value in the embodiment of the present invention. [Figure 4] 5 is a time chart showing control when a detected value is greater than a current command value in the embodiment of the present invention. [Figure 5] 1 is a diagram showing a schematic configuration example of a Sigbahn type vacuum pump according to an embodiment of the present invention. [Figure 6] 1 is a cross-sectional view of a vacuum pump including a Sigburn pumping mechanism according to a first embodiment of the present invention. [Figure 7] FIG. 2 is a perspective view of a fixed disk used in the first embodiment. [Figure 8] FIG. 2 is a plan view of a fixed disk used in the first embodiment. [Figure 9] FIG. 2 is a plan view of a fixed disk used in the first embodiment. [Figure 10] FIG. 4 is a cross-sectional view of a vacuum pump including a Sigburn pumping mechanism according to a second embodiment of the present invention. [Figure 11] FIG. 10 is a diagram for explaining the positional relationship of each component in the second embodiment. [Figure 12] FIG. 10 is a cross-sectional view of a vacuum pump including a Sigburn pumping mechanism according to a third embodiment of the present invention. [Figure 13] FIG. 10 is a cross-sectional view of a vacuum pump including a Sigburn pumping mechanism according to a fourth embodiment of the present invention. [Figure 14] 1 is a diagram showing the relationship between the exhaust gas flow rate and the suction pressure of a vacuum pump including a conventional Sigburn exhaust mechanism, a vacuum pump according to this embodiment, and a vacuum pump including a longitudinal screw (Hollweck type) exhaust mechanism. [Figure 15] 10 is a diagram showing the relationship between the screw flow path and the flow velocity of the exhaust gas in a vacuum pump including a conventional Sigburn exhaust mechanism and the vacuum pump according to this embodiment. FIG. [Figure 16] FIG. 10 is a perspective view of a fixed disk used in the second to fourth embodiments. [Figure 17] FIG. 10 is a plan view of a fixed disk used in the second to fourth embodiments. [Figure 18] FIG. 10 is a plan view of a fixed disk used in the second to fourth embodiments. [Figure 19]FIG. 10 is a diagram for explaining the "flow path area of ​​the minimum diameter portion" used in the second to fourth embodiments. [Figure 20] FIG. 1 is a cross-sectional view showing a schematic configuration example of a conventional Sigbahn type vacuum pump. [Figure 21] FIG. 10 is a diagram for explaining a fixed disk disposed in a conventional Sigbahn type vacuum pump. [Figure 22] FIG. 1 is a cross-sectional view illustrating a vacuum pump of a type equipped with a conventional vertical screw exhaust mechanism (Holbeck exhaust mechanism). [Figure 23] FIG. 1 is a cross-sectional view illustrating a vacuum pump of a type equipped with a conventional horizontal screw exhaust mechanism (Sigburn exhaust mechanism). DETAILED DESCRIPTION OF THE INVENTION

[0011] (i) Overview of the embodiment In the vacuum pump including the Sigburn exhaust mechanism according to this embodiment, the inner diameter side turning position is provided just before the minimum diameter of the rotary disk 9. That is, the inner diameter side turning position is performed midway through the flow path (i.e., not to the root). In this way, by providing a turn-back portion midway along the inner diameter side turn-back flow path, it is possible to use only the portion of the exhaust flow path where the exhaust speed is high, thereby increasing the exhaust speed of the vacuum pump. Also, at this location, a circular rib portion 250 for maintaining the sealing performance of the fixed disk 50 against exhaust gas and a communication port 260 for the passage of exhaust gas to the lower stage may be arranged. The arrangement of the rib portion 250 and the communication port 260 avoids the use of a portion of the exhaust flow path where the exhaust speed decreases, and as a result, the flow speed of the exhaust gas is less likely to decrease. In other words, it is possible to prevent (reduce) the decrease in the exhaust speed of gas near the center of rotation of the rotating disk 9, which is an issue with the Sigburn exhaust mechanism that has a flow path that turns back in the radial direction.

[0012] (ii) Details of the embodiment Preferred embodiments of the present invention will now be described in detail with reference to FIGS. In this embodiment, the vacuum pump to which the present invention is applied is a vacuum pump equipped with a Sigburn exhaust mechanism in the thread groove exhaust section (hereinafter referred to as a Sigburn type vacuum pump). First, the configuration of a turbomolecular pump, which is a common vacuum pump, will be described, and then the Sigbahn type vacuum pump will be described. In this embodiment, the direction perpendicular to the diameter direction of the rotary disk is defined as the axial direction, and the horizontal direction is defined as the radial direction. In the following description, the intake port side of one (single) fixed disk is referred to as the upstream region of the Sigbahn vacuum pump, and the exhaust port side is referred to as the downstream region of the Sigbahn vacuum pump.

[0013] A longitudinal cross-sectional view of this turbomolecular pump 100 is shown in FIG. 1. In FIG. 1, the turbomolecular pump 100 has an intake port 101 formed at the upper end of a cylindrical outer cylinder 127. Inside the outer cylinder 127 is provided a rotor 103 having a plurality of rotors 102 (102a, 102b, 102c, etc.), which are turbine blades for sucking in and exhausting gas, formed radially and in multiple stages around its periphery. A rotor shaft 113 is attached to the center of this rotor 103, and this rotor shaft 113 is levitated and supported in the air and its position is controlled by, for example, a five-axis controlled magnetic bearing. The rotor 103 is generally made of metal such as aluminum or an aluminum alloy.

[0014] The upper radial electromagnets 104 are arranged in pairs on the X-axis and the Y-axis. Four upper radial sensors 107 are provided adjacent to the upper radial electromagnets 104 and corresponding to each upper radial electromagnet 104. The upper radial sensors 107 are, for example, inductance sensors or eddy current sensors having conductive windings, and detect the position of the rotor shaft 113 based on changes in the inductance of the conductive windings, which change according to the position of the rotor shaft 113. The upper radial sensors 107 are configured to detect the radial displacement of the rotor shaft 113, i.e., the rotating body 103 fixed thereto, and send the detected displacement to the control device 200.

[0015] In this control device 200, for example, a compensation circuit having a PID adjustment function generates an excitation control command signal for 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 Figure 2 controls the excitation of the upper radial electromagnet 104 based on this excitation control command signal, thereby adjusting the upper radial position of the rotor shaft 113.

[0016] The rotor shaft 113 is made of a high magnetic permeability material (iron, stainless steel, etc.) and is attracted by the magnetic force of the upper radial electromagnets 104. Such adjustment is performed independently in the X-axis direction and the Y-axis direction. The lower radial electromagnets 105 and the lower radial sensors 108 are arranged in the same manner as the upper radial electromagnets 104 and the upper radial sensors 107, and adjust the radial position of the lower side of the rotor shaft 113 in the same manner as the radial position of the upper side.

[0017] Furthermore, axial electromagnets 106A and 106B are arranged above and below a circular metal disk 111 provided at the bottom of rotor shaft 113. Metal disk 111 is made of a highly magnetic permeable material such as iron. An axial sensor 109 is provided to detect the axial displacement of rotor shaft 113, and an axial position signal is sent to control device 200.

[0018] In the control device 200, a compensation circuit having, for example, a PID adjustment function generates excitation control command signals for 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 controls the excitation of the axial electromagnet 106A and the axial electromagnet 106B based on these excitation control command signals, so that the axial electromagnet 106A attracts the metal disc 111 upward by magnetic force, and the axial electromagnet 106B attracts the metal disc 111 downward, thereby adjusting the axial position of the rotor shaft 113.

[0019] In this way, the control device 200 appropriately adjusts the magnetic forces that the axial electromagnets 106A and 106B exert on the metal disk 111, magnetically levitating the rotor shaft 113 in the axial direction and holding it in space without contact. The amplifier circuit 150 that controls the excitation of the upper radial electromagnet 104, the lower radial electromagnet 105, and the axial electromagnets 106A and 106B will be described later.

[0020] Meanwhile, motor 121 has a plurality of magnetic poles arranged circumferentially so as to surround rotor shaft 113. Each magnetic pole is controlled by control device 200 so as to rotate rotor shaft 113 via electromagnetic force acting between the magnetic pole and rotor shaft 113. Motor 121 also incorporates a rotational speed sensor (not shown), such as a Hall element, resolver, or encoder, and the rotational speed of rotor shaft 113 is detected by the detection signal of this rotational speed sensor.

[0021] Furthermore, a phase sensor (not shown) is attached, for example, near the lower radial sensor 108, to detect the phase of rotation of the rotor shaft 113. The control device 200 uses the detection signals of both this phase sensor and the rotational speed sensor to detect the position of the magnetic pole.

[0022] A plurality of fixed blades 123 (123a, 123b, 123c...) are arranged at small gaps from the rotating blades 102 (102a, 102b, 102c...). Each of the rotating blades 102 (102a, 102b, 102c...) is formed at an angle of a predetermined degree from a plane perpendicular to the axis of the rotor shaft 113 in order to transport exhaust gas molecules downward through collision. The fixed blades 123 (123a, 123b, 123c...) are made of metal such as aluminum, iron, stainless steel, copper, or an alloy containing any of these metals as an ingredient.

[0023] Similarly, the fixed blades 123 are formed at a predetermined angle from a plane perpendicular to the axis of the rotor shaft 113, and are arranged in a staggered manner with the rows of rotor blades 102 toward the inside of the outer cylinder 127. The outer peripheral ends of the fixed blades 123 are supported by being inserted between a plurality of stacked rows of fixed blade spacers 125 (125a, 125b, 125c, etc.).

[0024] The fixed vane spacer 125 is a ring-shaped member made of a metal such as aluminum, iron, stainless steel, or copper, or an alloy containing any of these metals. An outer cylinder 127 is fixed to the outer periphery of the fixed vane spacer 125 with a small gap between them. A base portion 129 is disposed at the bottom of the outer cylinder 127. An exhaust port 133 is formed in the base portion 129 and communicates with the outside. Exhaust gas that enters the intake port 101 from the chamber (vacuum chamber) side and is transferred to the base portion 129 is sent to the exhaust port 133.

[0025] Furthermore, depending on the application of the turbomolecular pump 100, a threaded spacer 131 is disposed between the lower portion of the stator spacer 125 and the base portion 129. The threaded spacer 131 is a cylindrical member made of a metal such as aluminum, copper, stainless steel, iron, or an alloy containing any of these metals, and has multiple spiral thread grooves 131a engraved on its inner circumferential surface. The spiral direction of the threaded grooves 131a corresponds to the direction in which exhaust gas molecules are transported toward the exhaust port 133 when they move in the rotational direction of the rotor 103. A cylindrical portion 102d hangs down from the lowest portion of the rotor 103, adjacent to the rotor blades 102 (102a, 102b, 102c, etc.). The outer circumferential surface of this cylindrical portion 102d is cylindrical and protrudes toward the inner circumferential surface of the threaded spacer 131, and is adjacent to the inner circumferential surface of the threaded spacer 131 with a predetermined gap therebetween. The exhaust gas transferred to the thread groove 131a by the rotor 102 and the fixed blade 123 is sent to the base portion 129 while being guided by the thread groove 131a.

[0026] The base portion 129 is a disk-shaped member that forms the base of the turbomolecular pump 100, and is generally made of metal such as iron, aluminum, stainless steel, etc. The base portion 129 not only physically holds the turbomolecular pump 100, but also functions as a heat conduction path, so it is desirable to use a metal that is rigid and has high thermal conductivity, such as iron, aluminum, or copper.

[0027] In this configuration, when the rotor 102 is rotated together with the rotor shaft 113 by the motor 121, the action of the rotor 102 and the stator 123 draws exhaust gas from the chamber through the intake port 101. The rotational speed of the rotor 102 is typically 20,000 rpm to 90,000 rpm, and the peripheral speed at the tip of the rotor 102 reaches 200 m / s to 400 m / s. The exhaust gas drawn in through the intake port 101 passes between the rotor 102 and the stator 123 and is transported to the base 129. At this time, the temperature of the rotor 102 rises due to frictional heat generated when the exhaust gas comes into contact with the rotor 102 and conduction of heat generated by the motor 121, but this heat is transferred to the stator 123 side by radiation or conduction through gas molecules of the exhaust gas.

[0028] The stator spacers 125 are joined together at their outer peripheries and transmit to the outside heat received by the stator 123 from the rotor 102 and frictional heat generated when exhaust gas comes into contact with the stator 123.

[0029] In the above description, the threaded spacer 131 is disposed on the outer periphery of the cylindrical portion 102d of the rotor 103, and the threaded spacer 131 has the thread groove 131a formed on its inner circumferential surface. However, conversely, there are also cases where a thread groove is formed on the outer peripheral surface of the cylindrical portion 102d, and a spacer having a cylindrical inner peripheral surface is disposed around the thread groove.

[0030] Depending on the application of the turbomolecular pump 100, the electrical equipment section may be surrounded by a stator column 122 to prevent the gas sucked in from the intake port 101 from entering the electrical equipment section, which is composed of 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, the axial sensor 109, etc., and the interior of this stator column 122 may be kept at a predetermined pressure by purge gas.

[0031] In this case, piping (not shown) is provided in the base portion 129, and purge gas is introduced through this piping. The introduced purge gas is sent to the exhaust port 133 through gaps between the protective bearing 120 and the rotor shaft 113, between the rotor and stator of the motor 121, and between the stator column 122 and the inner cylindrical portion of the rotor blades 102.

[0032] Here, the turbomolecular pump 100 requires control based on specific parameters (e.g., various characteristics corresponding to the model) that have been individually adjusted and identified for the model. To store these control parameters, the turbomolecular pump 100 is provided with an electronic circuit section 141 within its body. The electronic circuit section 141 is composed of a semiconductor memory such as an EEPROM, electronic components such as semiconductor elements for accessing the memory, and a substrate 143 for mounting these components. The electronic circuit section 141 is housed below a rotational speed sensor (not shown) near the center of a base section 129 that constitutes the lower part of the turbomolecular pump 100, and is closed by an airtight bottom lid 145.

[0033] In the semiconductor manufacturing process, some process gases introduced into a chamber have the property of solidifying when their pressure exceeds a predetermined value or their temperature falls below a predetermined value. Inside the turbomolecular pump 100, the pressure of the exhaust gas is lowest at the inlet port 101 and highest at the outlet port 133. If the pressure of the process gas exceeds a predetermined value or the temperature falls below a predetermined value while the process gas is being transferred from the inlet port 101 to the outlet port 133, the process gas solidifies and adheres to and accumulates inside the turbomolecular pump 100.

[0034] For example, when SiCl4 is used as the process gas in an Al etching apparatus, the vapor pressure curve shows that at low vacuum (760 [torr] to 10-2 [torr]) and low temperature (approximately 20 [°C]), solid products (e.g., AlCl3) precipitate and adhere to and accumulate inside the turbomolecular pump 100. As a result, when process gas precipitates accumulate inside the turbomolecular pump 100, these deposits narrow the pump flow path, causing a decrease in the performance of the turbomolecular pump 100. Furthermore, the above-mentioned products are prone to solidification and adhesion in high-pressure areas near the exhaust port 133 and the threaded spacer 131.

[0035] Therefore, in order to solve this problem, conventionally, a heater (not shown) or a circular water-cooled pipe 149 is wrapped around the outer periphery of the base portion 129, etc., and a temperature sensor (e.g., a thermistor) (not shown) is embedded in the base portion 129, and the heating of the heater and the cooling by the water-cooled pipe 149 are controlled based on the signal from this temperature sensor to maintain the temperature of the base portion 129 at a constant high temperature (set temperature) (hereinafter referred to as TMS; Temperature Management System).

[0036] Next, a description will be given of the amplifier circuit 150 that controls excitation of the upper radial electromagnets 104, the lower radial electromagnets 105, and the axial electromagnets 106A and 106B in the turbomolecular pump 100. A circuit diagram of this amplifier circuit 150 is shown in FIG.

[0037] 2, one end of the electromagnet winding 151 constituting the upper radial electromagnet 104 etc. is connected to a positive electrode 171a of a power supply 171 via a transistor 161, and the other end is connected to a negative electrode 171b of the power supply 171 via a current detection circuit 181 and a transistor 162. The transistors 161 and 162 are so-called power MOSFETs, and have a structure in which a diode is connected between the source and drain.

[0038] At this time, the transistor 161 has a diode cathode terminal 161a connected to the positive electrode 171a and an anode terminal 161b connected to one end of the electromagnet winding 151. The transistor 162 has a diode cathode terminal 162a connected to the current detection circuit 181 and an anode terminal 162b connected to the negative electrode 171b.

[0039] Meanwhile, current regeneration diode 165 has its cathode terminal 165a connected to one end of electromagnet winding 151 and its anode terminal 165b connected to negative electrode 171b. Similarly, current regeneration diode 166 has its cathode terminal 166a connected to positive electrode 171a and its anode terminal 166b connected to the other end of electromagnet winding 151 via current detection circuit 181. Current detection circuit 181 is configured, for example, with a Hall sensor type current sensor or an electrical resistance element.

[0040] The amplifier circuit 150 configured as above corresponds to one electromagnet. Therefore, if the magnetic bearing is controlled in five axes and there are a total of ten electromagnets 104, 105, 106A, and 106B, a similar amplifier circuit 150 is configured for each electromagnet, and the ten amplifier circuits 150 are connected in parallel to the power supply 171.

[0041] Furthermore, the amplifier control circuit 191 is configured, for example, by a digital signal processor section (hereinafter referred to as a DSP section) not shown in the figure of the control device 200, and this amplifier control circuit 191 is configured to switch the transistors 161 and 162 on / off.

[0042] The amplifier control circuit 191 compares the current value detected by the current detection circuit 181 (a signal reflecting this current value is called a current detection signal 191c) with a predetermined current command value. Based on the comparison result, the amplifier control circuit 191 determines the size of the pulse width (pulse width times Tp1 and Tp2) to be generated within a control cycle Ts, which is one period under PWM control. As a result, gate drive signals 191a and 191b having these pulse widths are output from the amplifier control circuit 191 to the gate terminals of the transistors 161 and 162.

[0043] It is necessary to control the position of rotor 103 at high speed and with strong force when, for example, rotor 103 passes through a resonance point during acceleration of its rotational speed or when a disturbance occurs during constant-speed operation. For this reason, a voltage of, for example, about 50 V is used as power supply 171 so that the current flowing through electromagnet winding 151 can be rapidly increased (or decreased). In addition, a capacitor (not shown) is usually connected between positive electrode 171a and negative electrode 171b of power supply 171 to stabilize power supply 171.

[0044] In this configuration, when both transistors 161 and 162 are turned on, the current flowing through the electromagnet winding 151 (hereinafter referred to as electromagnet current iL) increases, and when both are turned off, the electromagnet current iL decreases.

[0045] Furthermore, when one of the transistors 161 and 162 is turned on and the other is turned off, a so-called flywheel current is maintained. By passing a flywheel current through the amplifier circuit 150 in this manner, hysteresis loss in the amplifier circuit 150 can be reduced, and the power consumption of the entire circuit can be kept low. Furthermore, by controlling the transistors 161 and 162 in this manner, high-frequency noise such as harmonics generated in the turbomolecular pump 100 can be reduced. Furthermore, by measuring this flywheel current with the current detection circuit 181, the electromagnet current iL flowing through the electromagnet winding 151 can be detected.

[0046] That is, when the detected current value is smaller than the current command value, both transistors 161 and 162 are turned on for a time period corresponding to pulse width time Tp1 only once in a control cycle Ts (for example, 100 μs), as shown in Fig. 3. Therefore, during this period, the electromagnet current iL increases toward a current value iLmax (not shown) that can flow from the positive electrode 171a to the negative electrode 171b via the transistors 161 and 162.

[0047] On the other hand, if the detected current value is greater than the current command value, both transistors 161 and 162 are turned off for a time period corresponding to pulse width time Tp2 only once during the control cycle Ts, as shown in Fig. 4. Therefore, 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 the positive pole 171a via diodes 165 and 166.

[0048] In either case, after the pulse width times Tp1 and Tp2 have elapsed, one of the transistors 161 and 162 is turned on. Therefore, a flywheel current is maintained in the amplifier circuit 150 during this period.

[0049] Next, we will explain the configuration of a Sigburn type vacuum pump that exhausts gas in the upstream region from the outer diameter side to the inner diameter side, and exhausts gas in the downstream region from the inner diameter side to the outer diameter side.

[0050] (ii-1) Configuration FIG. 5 is a diagram showing a schematic configuration example of a Sigbahn vacuum pump 1 according to an embodiment of the present invention. 5 shows a cross section of the Sigbahn vacuum pump 1 in the axial direction. The casing 2 that forms the exterior of the Sigburn vacuum pump 1 has a substantially cylindrical shape, and together with a base 3 provided at the bottom (exhaust port 133 side) of the casing 2, constitutes the housing of the Sigburn vacuum pump 1. A gas transfer mechanism, which is a structure that enables the Sigburn vacuum pump 1 to perform its exhaust function, is housed inside this housing. This gas transfer mechanism is broadly composed of a rotating part that is held rotatably and a fixed part that is fixed to the housing.

[0051] An intake port 101 for introducing gas into the Sigbahn vacuum pump 1 is formed at the end of the casing 2. A flange portion 5 extending outward is formed on the end face of the casing 2 on the intake port 101 side. The base 3 is also formed with an exhaust port 133 for exhausting gas from the Sigbahn vacuum pump 1 .

[0052] The rotating part (rotor part) is composed of a shaft 7 which is a rotating axis, a rotor 8 disposed on this shaft 7, a plurality of rotating disks 9 provided on the rotor 8, and a rotating cylinder 10. The shaft 7 and rotor 8 make up the rotor part. Each of the rotary disks 9 is made of a disk-shaped member extending radially perpendicular to the axis of the shaft 7 . The rotary cylinder 10 is made of a cylindrical member having a cylindrical shape concentric with the rotation axis of the rotor 8 .

[0053] A motor unit 20 for rotating the shaft 7 at high speed is provided in the middle of the shaft 7 in the axial direction. Furthermore, radial magnetic bearing devices 30, 31 are provided on the intake port 101 side and the exhaust port 133 side of the motor section 20 of the shaft 7 to support (axially support) the shaft 7 in a non-contact manner in the radial direction (diameter direction), and an axial magnetic bearing device 40 is provided at the lower end of the shaft 7 to support the shaft 7 in an axial direction (axial direction) in a non-contact manner.

[0054] A fixed portion (stator portion) is formed on the inner periphery of the housing. This fixed portion is composed of a plurality of fixed disks 50 provided on the intake port 101 side, and the fixed disks 50 are engraved with spiral grooves composed of fixed disk valleys 51 and fixed disk peaks 52. In this embodiment, a spiral groove is engraved on the fixed disk 50, but this is not limited to this, and it is sufficient that a spiral groove flow path is engraved on the gap-facing surface of at least one of the rotating disk 9 or the fixed disk 50 described above. Each fixed disk 50 is made up of a disk-shaped member extending radially perpendicular to the axis of the shaft 7 . The fixed disks 50 of each stage are fixed and spaced from one another by cylindrical spacers 60 (stator parts). The axial height of the spacers 60 is formed so as to decrease along the axial direction of the Sigburn vacuum pump 1, so that the volume of the flow path gradually decreases toward the exhaust port 133 of the Sigburn vacuum pump 1, compressing the gas passing through the gas transfer mechanism. The arrows in Figure 5 indicate the flow of gas. In the Sigburn type vacuum pump 1, the rotating disks 9 and the fixed disks 50 are arranged alternately to form multiple stages in the axial direction, but any number of rotor components and stator components can be provided as needed to satisfy the exhaust performance required of the vacuum pump. The Sigburn vacuum pump 1 configured in this manner is adapted to perform evacuation processing within a vacuum chamber (not shown) disposed in the Sigburn vacuum pump 1 .

[0055] FIG. 6 is a cross-sectional view of a vacuum pump 1 including a Sigburn pumping mechanism (indicated by X in the drawing) according to the first embodiment of the present invention. On the other hand, in a conventional structure in which the inner diameter side turning position in a vacuum pump 1 including a Sigburn exhaust mechanism is the smallest diameter of the rotating disk 9 (near the center of rotation of the rotating disk 9), as shown in Figure 23, the rotation speed of the rotating disk 9 is slow at the inner diameter side turning position, and as a result, the flow rate of the exhaust gas is also slow. This means that the peripheral speed of the rotating disk 9 is determined by the radius x angular velocity, so the peripheral speed is slower inside the flow passage where the radius is small, and therefore the force dragging the exhaust gas is weaker. This causes the exhaust gas to become clogged at the turning point, resulting in a localized increase in pressure and a decrease in exhaust performance. Therefore, in this first embodiment, the inner diameter side turn-back position is located just before the minimum diameter of the rotating disk 9 (outside in the radial direction), thereby avoiding exhaust action at a location where the rotation speed of the rotating disk 9 becomes slow. In other words, the turn-back portion of the fixed disk 50 for sending exhaust gas to the axially lower stage is located midway along the radial length from the outer end of the opposing rotating disk, specifically at a position 90% or less of the radial length from the outer end of the rotating disk 9.

[0056] The reason why the radial length from the outer end of the rotating disk 9 is set to 90% or less is that if the exhaust action in the range of 10% of the radial length from the inner end of the rotating disk 9, which is the part where the rotation speed of the rotating disk 9 is slow, can be eliminated, the performance of the vacuum pump 1 (Sigburn exhaust mechanism) can be improved to a certain extent (for example, about 2% to several percent). The length may be 80%, 70%, 60%, or 50%. It can be set appropriately to a length of 90% or less. That is, the optimum turning position is determined by comparing the merit of removing the slow rotation speed portion of the rotary disk 9 from the exhaust action with the demerit of shortening the length of the exhaust flow path of the Sigburn exhaust mechanism. Ultimately, the optimum solution for the turning position is determined by comprehensively taking into consideration the size of the vacuum pump, the rotation speed of the rotary disk 9, the number of stages of the Sigburn exhaust mechanism (length of the exhaust flow path), and the like. The folded portion may be provided at a position where the circumferential speed of the opposing rotary disk 9 is 50% or more of the circumferential speed at the entrance of the spiral groove. Furthermore, the folded portion may be provided at a position where the peripheral speed of the opposing rotary disk 9 is 50% or more of the peripheral speed at the entrance of the spiral groove.

[0057] The turning-back portion may be determined based on the outer diameter of the cylindrical portion 102d (rotating cylinder 10) of the Holweck-type vacuum pump 101 shown in FIG. 1 or 22, which has a similar exhaust structure that relies on the drag effect of the rotating portion. For example, when a high-strength aluminum alloy is used, the peripheral speed at the outermost diameter of the cylindrical portion 102d (rotating cylinder 10) is set to 250 m / sec or more. From this peripheral speed, the diameter at a rotational speed (20,000 to 30,000 rpm) is calculated, resulting in a radius of 0.12 m (120 mm) at 20,000 rpm and a radius of 0.08 m (80 mm) at 30,000 rpm. Therefore, these diameters may be used as a guide for the position of the turning-back portion.

[0058] Fig. 7 is a perspective view of the fixed disk 50 used in this embodiment, and Figs. 8 and 9 are plan views. As shown in these figures, the fixed disk 50 is provided with a fixed disk valley portion 51 and a fixed disk crest portion 52 that form a spiral groove. The portion indicated by (Y) in the figures, which includes a communication port structure formed by a notch or the like, corresponds to the folded portion. The notched communication port here is formed for the purpose of increasing the flow path area so that when the exhaust gas is turned back from the inner diameter side to the outer diameter side (or from the outer diameter side to the inner diameter side) in the Sigburn exhaust mechanism, the amount of exhaust gas remaining at the turning point is reduced and the exhaust can be discharged efficiently. The turning position is defined as the outermost position in the radial direction of the portion that constitutes the gas flow path of the SIGBAHN exhaust mechanism, including the communication port.

[0059] FIG. 10 is a cross-sectional view of a vacuum pump 1 including a Sigburn exhaust mechanism according to the second embodiment, and shows an enlarged view at the bottom for explaining a rib portion 250 and a communication port 260. On the other hand, in a conventional structure in which the inner diameter side turning position in a vacuum pump 1 including a Sigburn exhaust mechanism is the smallest diameter of the rotating disk 9 (near the center of rotation of the rotating disk 9), as shown in Figure 23, the rotation speed of the rotating disk 9 is slow at the inner diameter side turning position, and as a result, the flow rate of the exhaust gas is also slow. Therefore, in this second embodiment, the inner diameter side turn-back position is located just before the minimum diameter of the rotating disc 9 (outside in the radial direction), and a circular rib portion 250 for maintaining exhaust gas sealing and a communication port 260 for allowing exhaust gas to pass through to the lower level are arranged on the fixed disc 50 at that location. By arranging the rib portion 250 and the communication port 260, it is possible to avoid using the area where the exhaust speed decreases, and as a result, the flow rate of the exhaust gas is less likely to decrease. In other words, it is possible to prevent (reduce) the decrease in the exhaust speed of the gas near the center of rotation of the rotating disk 9, which is an issue with the Sigburn exhaust mechanism that has a flow path that turns back in the radial direction.

[0060] FIG. 11 is a diagram for explaining the positional relationship between the components in the second embodiment. L is the length of the rotating disc 9, l is the length of the fold, h is the height of the rib portion 250 from the fixed disc 50, and r is the distance (outer diameter) from the center of rotation of the outer end of the rib portion 250. As defined above, the turning position is the outermost position in the radial direction of the portion that constitutes the gas flow path of the SIGBAHN exhaust mechanism, and in this embodiment, it is the outermost position in the radial direction of the communication port 260.

[0061] Furthermore, the rib portion 250 and the communication port 260 act to ensure a seal with gaps inside the vacuum pump 1, preventing the exhaust gas from merging with other flow paths and leaking. This further improves the exhaust performance. Furthermore, since the exhaust speed can be ensured, when the exhaust gas moves from the upper section to the lower section of the Sigburn exhaust port, it can be prevented from stagnating or flowing backward at that point.

[0062] FIG. 12 is a cross-sectional view of a vacuum pump 1 including a Sigburn exhaust mechanism according to the third embodiment, and shows an enlarged view at the bottom for explaining a rib portion 250 and a communication port 260. In this third embodiment, there are two pairs of rotating discs 9 and fixed discs 50, and both fixed discs 50 are provided with annular rib portions 250 and communication ports 260 that serve as a passage for exhaust gas to the lower level. In the third embodiment, as in the second embodiment, it is possible to overcome the problem of a decrease in the gas pumping speed near the rotation center of the rotary disk 9. In other words, even with a multi-stage Sigburn pumping mechanism, various effects can be achieved. In each of the embodiments, the rib portions 250 and the communication ports 260 are arranged in all of the multiple stages, but the rib portions 250 and the communication ports 260 may be arranged in only one of the multiple stages. For example, in the case of a three-stage SIGBURN exhaust mechanism, the rib portions 250 and the communication ports 260 may be arranged in only one stage or two stages.

[0063] FIG. 13 is a cross-sectional view of a vacuum pump 1 including a Sigburn exhaust mechanism according to the fourth embodiment, and shows an enlarged view at the bottom for explaining a rib portion 250 and a communication port 260. In the fourth embodiment, the radial width (annular width) of the rib portion 250 is set larger than those of the second and third embodiments, which further improves the sealing performance of the rib portion 250 and makes it possible to better prevent exhaust gas from merging with other flow paths and from leaking.

[0064] FIG. 14 is a diagram showing the relationship between the exhaust gas flow rate and the suction pressure of a vacuum pump including a conventional Sigburn exhaust mechanism, a vacuum pump according to this embodiment, and a vacuum pump including a vertical screw exhaust mechanism. As is clear from this diagram, the intake pressure is prevented (suppressed) from easily increasing when the flow rate of exhaust gas increases, which was a problem with the conventional technology.

[0065] FIG. 15 is a diagram showing the relationship between the screw flow path and the flow velocity of the exhaust gas in a vacuum pump including a conventional Sigburn exhaust mechanism and the vacuum pump according to this embodiment. For example, in the screw flow path (gas flow path) of a Sigburn type vacuum pump, the first stage shows the flow rate of exhaust gas from the outer diameter side to the inner diameter side, the second stage shows the flow rate of exhaust gas from the inner diameter side to the outer diameter side, and the third stage shows the flow rate of exhaust gas from the outer diameter side to the inner diameter side and then to the exhaust port. As is clear from this figure, in this embodiment, a decrease in the flow velocity of the exhaust gas near the turning position of the second stage is prevented.

[0066] Fig. 16 is a perspective view of the fixed disk 50 used in the second to fourth embodiments, and Figs. 17 and 18 are plan views. As shown in these figures, the fixed disk 50 is provided with fixed disk valleys 51 and fixed disk crests 52 that form spiral grooves. An annular rib 250 is also provided concentrically with the fixed disk 50. The height of this rib 250 is set to be equal to the height of the fixed disk crest 52. To further improve the sealing performance of the rib 250, it may be set to be higher than the height of the fixed disk crest 52.

[0067] The radial width of the rib portion 250 (the width of the annulus) can be set appropriately in consideration of sealing performance, for example, to 5% or more of the radial length of the opposing rotary disk 9. As shown in Figure 17, the communication openings 260 are provided at positions adjacent to the rib portions 250 of all of the fixed disk valley portions 51. The communication openings 260 can have any shape as long as they do not impede ventilation, such as a triangle, a square, or a semicircle. As shown in FIG. 18A, this communication port 260 is provided in a range where the upstream side and downstream side of the spiral groove overlap when viewed in the axial direction.

[0068] The size (opening area) of this communication port 260 can be set appropriately based on the flow path cross section (flow path area) of the screw flow path. As an example, it is desirable that the size be equivalent to the "minimum diameter flow path area" (area calculated by multiplying the outer periphery length of the rib portion 250 by the height of the rib portion 250) shown in Figure 19. It is required that it be at least 90% or more.

[0069] Next, the position of the folded portion can be appropriately set in relation to the flow velocity of the exhaust gas and the peripheral speed of the rotating disk. As an example, the folded portion (formed by the outer diameter of the rib portion 250 and the communication port 260) is provided at a position that avoids the minimum diameter portion of the rotary disk 9 where the flow velocity becomes slow. Specifically, the contact hole 11 may be provided at a position that is 70% or less of the radial length from the outer end of the opposing rotary disk 9. Alternatively, the exhaust gas may be provided at a position where the peripheral speed of the exhaust gas is 50% or more of that at the inlet of the rotary disc 9. Furthermore, the spiral groove may be provided at a position where the peripheral speed of the opposing rotary disk 9 is 50% or more of the peripheral speed at the entrance of the spiral groove.

[0070] In the second to fourth embodiments, examples in which the rib portion 250 is provided have been described, but the present invention can also be realized by replacing the rib portion 250 with other alternative means. For example, by forming the cylindrical portion of the fixed portion of the rotating disk 9 to be thicker on the outer diameter side, it is possible to obtain the same effect as when the rib portion 250 is provided.

[0071] According to each of the present embodiments, in a vacuum pump equipped with a Sigburn pumping mechanism, the pumping volume is stable even when a large amount of gas is passed through, and the pumping performance (PQ characteristics) can be improved. Furthermore, if the rotor were to break while the vacuum pump was in operation, the ribs and communication ports would cushion the broken rotor, reducing the breaking torque (the torque that rotates the entire vacuum pump). In addition, by shortening the exhaust gas flow path, the opposing area of ​​the fixed disc and the rotating disc is reduced, making it more difficult for heat to flow from the fixed disc to the rotating side, thereby reducing the risk of heat buildup.

[0072] According to the second to fourth embodiments, by providing the rib portion 250 on the fixed disk 50, it is possible to apply the conventional rotary disk 9 without changing the position, shape, size, etc. Therefore, it is possible to introduce it with few changes to parts and design, and without incurring large costs. Furthermore, by providing the rib portion 250 on the fixed disk 50, warping of the product can be suppressed when the fixed disk 50 is manufactured by die casting. This allows the gap between the fixed disk 50 and the rotating disk 9 to be set more precisely. As a result, the performance of the vacuum pump 1 can be further improved.

[0073] Exhaust performance can be improved by increasing the diameter of the rotor (rotating disc), but this increases the weight and moment of inertia, which can increase the breaking torque. Also, elongation due to creep increases the risk of contact. In the present embodiments, such concerns can be avoided.

[0074] The embodiments and modifications of the present invention may be combined as necessary.

[0075] Furthermore, the present invention can be modified in various ways without departing from the spirit of the present invention, and it goes without saying that the present invention also covers such modifications. [Explanation of symbols]

[0076] 1 Sigburn type vacuum pump 2 Casing 3. Bass 5 Flange 7 shaft 8 rotors 9 Rotating disc 10 Rotating Cylinder 20 Motor section 30 Radial magnetic bearing device 31 Radial magnetic bearing device 40 Axial magnetic bearing device 50 Fixed disc 51 Fixed disk valley 52 Fixed disk mountain 60 spacer 100 Turbomolecular pump (vacuum pump) 101 Air intake 102 Rotor 102d Cylindrical part 103 Rotating Body 113 Rotor shaft 122 Stator column 123 Fixed wing 125 Fixed wing spacer 127 Outer cylinder 129 Base 131 Threaded spacer 131a screw groove 133 Exhaust port 200 control device 250 Rib section 260 Communication port (communication hole) 1000 Sigburn type vacuum pump (conventional) 5000 Fixed disc (conventional)

Claims

1. A casing; a rotating shaft rotatably supported inside the casing; a magnetic bearing device that magnetically levitates and contactlessly holds the rotating shaft; a plurality of rotary disks that rotate together with the rotary shaft; at least one or more fixed disks arranged to face the plurality of rotary disks and having spiral grooves consisting of peaks and valleys on a surface facing the plurality of rotary disks; Equipped with A vacuum pump equipped with a Sigburn exhaust mechanism that exhausts air by interaction between the plurality of rotating disks and the fixed disk, a fixed disk having a turn-back portion for sending exhaust gas to a lower axial stage, the turn-back portion being located at a position that is 90% or less of the radial length from the outer end of the opposing rotary disk.

2. 2. The vacuum pump according to claim 1, wherein the turning portion is provided at a position where the peripheral speed of the exhaust gas is 50% or more of that at the inlet of the rotary disk.

3. 2. The vacuum pump according to claim 1, wherein the turning portion is provided at a position where the peripheral speed of the opposing rotating disk is 50% or more of the peripheral speed of the inlet of the spiral groove.

4. a communication port disposed in the valley portion of the fixed disk in the folded portion, for sending exhaust gas to a lower stage in the axial direction; and an annular rib portion concentric with the rotary shaft, having a height corresponding to the peak portion and continuous with the peak portion in order to provide a sealing property against exhaust gas. Further provided with 2. The vacuum pump according to claim 1, wherein the communication port is disposed adjacent to the rib portion.

5. 5. The vacuum pump according to claim 4, wherein the radial width of said rib portion is 5% or more of the radial length of the opposing rotary disk.

6. 5. The vacuum pump according to claim 4, wherein the size of the communication port is 90% or more of an area obtained by multiplying the outer periphery of the rib portion between the peaks by the height of the rib portion.

7. 7. The vacuum pump according to claim 4, wherein the communication port is provided in a range where the upstream and downstream flow paths of the spiral groove overlap when viewed in the axial direction.

8. A fixed disk used in a vacuum pump equipped with a Sigburn pumping mechanism that performs exhaust by interaction with a rotating disk, a spiral groove consisting of peaks and valleys is provided on the surface facing the rotary disk, A fixed disk characterized in that the position of the turn-back portion in the valley portion for sending exhaust gas to a lower axial stage is located at a position that is 90% or less of the radial length from the outer end of the opposing rotating disk.

9. a communication port disposed in the valley portion of the turn-back portion, for sending exhaust gas to a lower stage in the axial direction; an annular rib portion that is concentric with the rotation axis and has a height corresponding to the ridge portion and is continuous with the ridge portion to provide sealing properties against exhaust gas; Further provided with The stationary disk according to claim 8, wherein the communication port is disposed adjacent to the rib portion.

10. 10. The stationary disk according to claim 9, wherein the height of the rib portion is equal to or greater than the height of the peak portion.

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