Vacuum pump

Abstract

To provide a vacuum pump in which deformation of outer peripheral components fastened to an outer cylinder can be prevented even if the number of bolts is increased.SOLUTION: A vacuum pump according to the present invention comprises a rotating body (103), an outer cylinder (127) housing the rotating body, outer peripheral components (126 and 128) arranged on the outer peripheral side of the rotating body and coaxially with the outer cylinder, a plurality of bolts (115 and 116) fastening the outer cylinder and the outer peripheral components, and axial tension reduction means (117) reducing bolt axial tension acting on the outer cylinder. The axial tension reduction means is comprised in at least one of the plurality of bolts.SELECTED DRAWING: Figure 7

Description

[Technical Field]

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

[0002] Generally, in vacuum pumps such as turbomolecular pumps, a casing (external cylinder) and peripheral components (e.g., cooling spacers, bases, etc.) are fastened together with bolts to form the exterior of the vacuum pump. A rotor having rotor blades is housed inside the casing and rotates at high speed (see Patent Document 1). If the rotor breaks while the vacuum pump is in operation, a large torsional torque (hereinafter referred to as "breaking torque") is generated in the rotational direction of the rotor. Because the breaking torque acts on the bolts fastening the casing and peripheral components, the bolts must absorb this breaking torque. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2014 / 045438 Summary of the Invention [Problem to be solved by the invention]

[0004] In recent years, the weight of rotating bodies has tended to increase due to the increase in size of pumps in response to increased workloads and the switch to highly heat-resistant materials in response to higher temperature requirements. As the weight of the rotating body increases, the breaking torque also increases, leading to an increase in the size and number of bolts. This results in a high axial force being applied to the casing and peripheral components, which may cause deformation of the peripheral components. In particular, when there is an axial gap between the casing and the peripheral components, as in Patent Document 1, a bending moment is applied to the peripheral components due to the axial force of the bolts, which may cause deformation of the peripheral components.

[0005] To absorb the increase in breaking torque without changing the bolt axial force, for example, the pitch circle diameter (PCD) of the bolt could be increased, but this would increase the size of the vacuum pump, which is not desirable. Also, using special high-strength bolts would avoid the need to increase the number of bolts, but this would be less versatile and would be more costly.

[0006] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a vacuum pump that can prevent deformation of the outer peripheral parts fastened to the outer cylinder even if the number of bolts increases. [Means for solving the problem]

[0007] In order to achieve the above object, one aspect of the present invention is a device comprising: a rotating body; an outer cylinder that houses the rotating body; an outer peripheral component that is arranged on the outer periphery of the rotating body and coaxially with the outer cylinder; a first bolt and a second bolt that fasten the outer cylinder and the outer peripheral component; and an axial force reducing means that reduces the bolt axial force acting on the outer cylinder, wherein the axial force reducing means is provided on the second bolt, and the head of the first bolt abuts against a first bolt fastening surface that is on the outer surface of the outer cylinder and faces the head of the first bolt, thereby causing the bolt axial force to act on the outer cylinder and the outer peripheral component, and the outer cylinder and the outer peripheral component are integrally fixed, and the axial force reducing means has a structure that forms a gap between the head of the second bolt and the second bolt fastening surface that is on the outer surface of the outer cylinder and faces the head of the second bolt. The gap prevents the bolt axial force of the second bolt from acting on the outer cylinder. This is a vacuum pump characterized by the above.

[0009] In the above configuration, the outer cylinder includes the No. 1 bolt and the second bolt a plurality of through holes through which the No. 1 bolt and the second bolt A cylindrical spacer serving as the axial force reducing means is inserted into at least one of the plurality of through holes, and the axial force reducing means is connected to the No. 2 Bolt head and No. 2 It is preferable that the gap is formed between the bolt fastening surface and the bolt fastening surface.

[0010] In the above configuration, the outer cylinder includes the No. 1 bolt and the second bolt a plurality of through holes through which the No. 1 bolt and the second bolt a plurality of screw holes that are screwed into the No. 2 The bolt is The aforementioned The length of the through hole and The aforementioned The nominal length is greater than the total value of the screw depth of the screw holes, and the screw functions as the axial force reducing means. No. 2 Bolt head and No. 2 It is preferable to form the gap between the bolt fastening surface and the bolt fastening surface.

[0011] In the above configuration, the outer cylinder includes the No. 1 bolt and the second bolt a plurality of through holes through which the No. 1 bolt and the second bolt a plurality of screw holes that screw into the shaft, and a stopper serving as the axial force reducing means is provided at the bottom of at least one of the plurality of screw holes; No. 2 When the tip of the bolt comes into contact with the stopper, No. 2 Bolt head and No. 2 It is preferable that the gap is formed between the bolt fastening surface and the bolt fastening surface.

[0012] In the above configuration, it is preferable that the axial force reducing means further includes an elastic member disposed in the gap.

[0013] In addition, in the above configuration, the first bolts and the second bolts are each plural; The aforementioned No. 2 The number of bolts is as above. No. 1 It may be less than the number of bolts.

[0014] In addition, in the above configuration, the first bolts and the second bolts are each plural; The aforementioned No. 2 The number of bolts is as above. No. 1 It may be more than the number of bolts.

[0015] In the above configuration, No. 1bolt and the second bolt are preferably the same bolt. [Effects of the Invention]

[0016] According to the vacuum pump of the present invention, even if the number of bolts increases, deformation of the outer peripheral part fastened to the outer cylinder can be prevented. Note that problems, configurations, and effects other than those described above will become clear from the description of the following embodiments. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a vertical cross-sectional view of a turbomolecular pump according to an embodiment of the present invention. [Figure 2] FIG. 2 is a circuit diagram of an amplifier circuit of the turbomolecular pump shown in FIG. [Figure 3] 10 is a time chart showing the control of the amplifier control circuit when a current command value is larger than a detection value. [Figure 4] 10 is a time chart showing the control of the amplifier control circuit when a current command value is smaller than a detection value. [Figure 5] FIG. 3 is a diagram schematically showing the positions of a first bolt and a second bolt as viewed from above the turbomolecular pump. [Figure 6] FIG. 10 is an enlarged view of a main portion of a fastening portion of a first bolt. [Figure 7] FIG. 10 is an enlarged view of a main portion of a fastening portion of a second bolt. [Figure 8] FIG. 10 is an enlarged view of a main part of a fastening portion of a second bolt according to Modification 1. [Figure 9] FIG. 10 is an enlarged view of a main part of a fastening portion of a second bolt according to Modification 2. [Figure 10] FIG. 11 is an enlarged view of a main part of a fastening portion of a second bolt according to Modification 3. [Figure 11] 10 is a diagram schematically showing a fastening portion of a second bolt according to Modification 4. FIG. DETAILED DESCRIPTION OF THE INVENTION

[0018] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, an embodiment of a vacuum pump according to the present invention will be described with reference to the drawings, taking a turbomolecular pump as an example.

[0019] 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 tube 127. Inside the outer tube 127 is provided a rotor 103, which has 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 a metal such as aluminum, an aluminum alloy, or stainless steel.

[0020] As shown in FIG. 1 , a water-cooled spacer 128 and an outer wall 126, which are peripheral components, are disposed on the outer periphery of the rotor 103. The water-cooled spacer 128 is a ring-shaped component that houses an annular cooling pipe 110 (see FIG. 6 ). Cooling water is supplied to the cooling pipe 110, thereby cooling the components around the water-cooled spacer 128. That is, heat generated by the rotation of the rotor 103 is cooled by the water-cooled spacer 128. The outer wall 126 is a cylindrical component that surrounds approximately the lower half of the turbomolecular pump 100. The water-cooled spacer 128 and the outer wall 126 are disposed below the outer cylinder 127, coaxially aligned with the outer cylinder 127. The outer cylinder 127, the water-cooled spacer 128, and the outer wall 126 are fastened together with a plurality of bolts 115 and 116 and, together with a base 129, constitute an exterior body (casing) of the turbomolecular pump 100 that houses the rotor 103.

[0021] 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.

[0022] 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.

[0023] 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.

[0024] 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.

[0025] 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.

[0026] 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.

[0027] 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.

[0028] 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.

[0029] 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.

[0030] 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.).

[0031] 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 (more specifically, at the bottom of the outer wall 126). An exhaust port 133 is formed above 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 transported toward the base portion 129 is sent to the exhaust port 133.

[0032] 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.

[0033] More specifically, the exhaust gas guided by the thread groove 131a is sent to annular space 135 formed above the base portion 129, and while circulating around the annular space 135, is discharged to the outside through the exhaust port 133. This annular space 135 is an annular space partitioned by the cylindrical portion 102d of the rotating body (rotor) 103, the threaded spacer (stator portion) 131, the heater spacer 153, and the base portion 129.

[0034] Here, the heater spacer 153 is a cylindrical member, and in this embodiment, is configured integrally with the threaded spacer 131. Of course, the heater spacer 153 and the threaded spacer 131 may be configured separately. The heater spacer 153 is configured from a metal such as aluminum or stainless steel. A heater 195 serving as a heating means is inserted into the heater spacer 153, and the heater 195 generates heat, thereby heating the threaded spacer 131 via the heater spacer 153. The heater 195 also heats the exhaust gas flowing through the annular space 135. This suppresses the formation of deposits due to a drop in the temperature of the exhaust gas.

[0035] 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.

[0036] 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.

[0037] 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.

[0038] 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 thread groove 131a is formed on the inner circumferential surface of the threaded spacer 131. However, there are also cases where the thread groove is formed on the outer circumferential surface of the cylindrical portion 102d, and a spacer having a cylindrical inner circumferential surface is disposed around the outer circumferential surface of the cylindrical portion 102d.

[0039] 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.

[0040] 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. As shown in FIG. 1, the stator column 122 is erected at the center of the base portion 129. In this embodiment, a water-cooled pipe 149 is provided in the base portion 129 as a cooling means. Cooling water is supplied to this water-cooled pipe 149, thereby maintaining the base portion 129 and the stator column 122 at an appropriate temperature.

[0041] 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.

[0042] 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.

[0043] 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.

[0044] 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).

[0045] 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.

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] It is necessary to control the position of rotor 103 at high speed and with strong force when, for example, the 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 high 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.

[0053] 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.

[0054] 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.

[0055] 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.

[0056] 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.

[0057] 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.

[0058] Next, the characteristic features of the turbomolecular pump 100 according to this embodiment will be described in detail. In this embodiment, the outer cylinder 127, the water-cooled spacer 128, and the outer wall 126 are fixed together with a plurality of bolts 115, 116, but the fixing methods are different between the first bolt 115 and the second bolt 116. Note that the first bolt 115 and the second bolt 116 are the same.

[0059] FIG. 5 is a diagram schematically illustrating the positions of the first bolts 115 and the second bolts 116 as viewed from above the turbomolecular pump 100. As shown in FIG. 5, the first bolts 115 and the second bolts 116 are arranged at equal intervals on a circle concentric with the center O of the outer casing 127. However, they do not have to be arranged at equal intervals, and the first bolts 115 and the second bolts 116 do not necessarily have to be arranged on a circle concentric with each other. In this embodiment, the number of first bolts 115 is 12 and the number of second bolts 116 is 4, which is fewer than the number of first bolts 115. Of course, the number of second bolts 116 may be more than the number of first bolts 115, or the number of second bolts 116 may be the same. The number of bolts may be determined appropriately taking into consideration the axial force required to fasten the outer casing 127, the water-cooled spacer 128, and the outer wall 126 together and the fracture torque that will be applied when the rotor 103 is broken. In FIG. 5, the first bolt 115 is tightened by a normal method, but the second bolt 116 is tightened via an axial force reducing means (spacer 117) which will be described later.

[0060] Fig. 6 is an enlarged view of a main portion of the fastening portion of the first bolt 115, and Fig. 7 is an enlarged view of a main portion of the fastening portion of the second bolt 116. As shown in Figs. 6 and 7, the outer cylinder 127 has a through hole 127a through which the first bolt 115 and the second bolt 116 pass. The water-cooled spacer 128 also has a similar through hole 128a. Meanwhile, the outer wall 126 has a threaded hole 126a that threadably engages with the threaded portion 115b of the first bolt 115 and the threaded portion 116b of the second bolt 116. The bolts 115 and 116 are inserted into the threaded hole 126a via the through holes 127a and 128a and tightened with a predetermined torque, thereby fixing the outer cylinder 127, the water-cooled spacer 128, and the outer wall 126 together. The through holes 127a and 128a through which the second bolt 116 passes have a larger diameter than the through holes 127a and 128a through which the first bolt 115 passes, since the spacer 117 described later is inserted therein.

[0061] 6, first bolt 115 is inserted into screw hole 126a via through holes 127a and 128a and tightened in the same manner as in the past. Therefore, head 115a of first bolt 115 abuts against bolt fastening surface 127b, and the axial force of first bolt 115 acts on outer cylinder 127 and water-cooled spacer 128.

[0062] In contrast, the second bolt 116 is configured to be tightened via a spacer 117, as shown in Fig. 7. The configuration of the spacer 117, which is an axial force reducing means, will be described in detail below.

[0063] The spacer 117 is a cylindrical, metal member that is inserted into the through-hole 127a of the outer cylinder 127 and the through-hole 128a of the water-cooled spacer 128, as shown in FIG. 7 . While the spacer 117 may be made of a material other than metal, metal is preferable because it is less susceptible to deformation due to changes in diameter over time after bolt fastening, which can cause loosening of the bolts. The spacer 117 has an outer diameter that allows it to be smoothly inserted and removed from the through-holes 127a and 128a, and an inner diameter that allows the threaded portion 116b of the second bolt 116 to be inserted and removed. The spacer 117 is formed with a dimension slightly longer than the combined length of the through-holes 127a and 128a. Therefore, as shown in FIG. 7 , when the spacer 117 is inserted into the through-holes 127a and 128a, it protrudes slightly from the surface of the outer cylinder 127 (the bolt fastening surface 127b).

[0064] When the second bolt 116 is inserted into the screw hole 126a via the spacer 117 and tightened with a predetermined torque, the length of the spacer 117 gets in the way and prevents the head 116a of the second bolt 116 from contacting the bolt fastening surface 127b. Therefore, a gap C is created between the head 116a of the second bolt 116 and the bolt fastening surface 127b on the surface of the outer casing 127 that faces the head 116a. As a result, the axial force of the second bolt 116 acts only on the outer wall 126, and does not act on the outer casing 127 or the water-cooled spacer 128. In other words, the spacer 117 reduces (prevents) the axial force of the second bolt 116 from acting on the outer casing 127 and the water-cooled spacer 128.

[0065] Next, the effects of this embodiment configured as above will be described.

[0066] For example, if the weight of the rotating body 103 increases due to a change in specifications, the destructive torque will naturally increase as well. The increase in destructive torque can be absorbed by using special bolts or by increasing the pitch circle diameter (PCD) of the bolts. However, if these measures are not to be adopted, the increase in destructive torque must be absorbed by increasing the number of bolts 115, 116.

[0067] In this case, if not only the first bolt 115 but also the second bolt 116 is tightened using the conventional method shown in Figure 6, unnecessary axial force will be applied to the outer cylinder 127 and the water-cooled spacer 128, which may cause deformation of the water-cooled spacer 128.

[0068] Explaining in more detail, when the second bolt 116 is tightened by the conventional method shown in Fig. 6, the axial force of the second bolt 116 acts on the outer tube 127 and the water-cooled spacer 128. As a result, the outer peripheral portion of the water-cooled spacer 128 is tightened and fixed by the second bolt 116. In other words, the outer peripheral side of the water-cooled spacer 128 becomes the fixed end.

[0069] The axial force of second bolt 116 also acts on outer cylinder 127, so outer cylinder 127 is subjected to the downward axial force in Figure 6. As a result, flange portion 127f (see Figure 1) at the upper end of outer cylinder 127 is also subjected to the downward axial force. Because flange portion 127f of outer cylinder 127 and the uppermost stator spacer 125a are in contact, and the stator spacers 125 of each stage (125a, 125b, 125c, etc.) are also in contact, when the axial force of second bolt 116 is applied to outer cylinder 127, the axial force is transmitted to stator spacer 125. In other words, flange portion 127f of outer cylinder 127 is subjected to the axial force of second bolt 116 and presses stator spacer 125 downward. As shown in Figure 6, the fixed vane spacer 125 and the water-cooled spacer 128 are in contact with each other in the axial direction, so that the axial force applied to the outer cylinder 127 acts on the inner peripheral portion of the water-cooled spacer 128 (the portion indicated by diagonal lines A in Figure 6) via the fixed vane spacer 125.

[0070] That is, the outer circumferential side of the water-cooled spacer 128 is the fixed end and the inner circumferential side is the free end, and the axial force of the second bolt 116 acts downward on the free end side. As a result, a bending moment acts on the water-cooled spacer 128 with the fixed end as the fulcrum, causing the inner circumferential portion to deform (bend) downward. Therefore, simply increasing the number of bolts to absorb the increase in breaking torque is not necessarily desirable, as it may cause deformation of the water-cooled spacer 128.

[0071] On the other hand, in this embodiment, as shown in Fig. 7, the second bolts 116 fasten the outer cylinder 127, the water-cooled spacer 128, and the outer wall 126 together via the spacers 117, so the axial force of the second bolts 116 does not act on the water-cooled spacer 128. In other words, no downward force is applied to the shaded area in Fig. 7. Therefore, according to this embodiment, even if the weight of the rotor 103 increases due to a change in the specifications of the turbomolecular pump 100, causing the breaking torque to increase, the increase in breaking torque can be absorbed by increasing the number of bolts while preventing deformation of the water-cooled spacer 128.

[0072] In other words, in this embodiment, the axial fastening between the outer tube 127, the water-cooled spacer 128, and the outer wall 126 is secured by the axial force of the first bolt 115, preventing deformation of the water-cooled spacer 128 while allowing the first bolt 115 and the second bolt 116 to absorb destructive torque.

[0073] As described above, according to this embodiment, even when a change in specifications is required due to an increase in the size or temperature of the turbomolecular pump 100, it is possible to reduce costs by using highly versatile bolts and changing the design by simply increasing the number of bolts 115, 116. In addition, there is also the advantage that there is no need to increase the pitch circle diameter (PCD) of the bolts, so there is no need to increase the size (particularly the outer diameter) of the turbomolecular pump 100.

[0074] (Variation 1) Next, a first modification of the axial force reducing means will be described. The axial force reducing means according to the first modification is characterized in that the nominal length L of the second bolt 116 is increased so that a gap C is formed between the head 116a of the second bolt 116 and the bolt fastening surface 127b of the outer cylinder 127. This will be described in detail with reference to Fig. 8. Fig. 8 is an enlarged view of a main part of the fastening portion of the second bolt 116 according to the first modification.

[0075] 8, in Modification 1, the nominal length L of the second bolt 116 is greater than the sum D of the length of the through hole 127a of the outer cylinder 127, the length of the through hole 128a of the water-cooled spacer 128, and the thread depth of the threaded hole 126a of the outer wall 126. Therefore, when the second bolt 116 is tightened, the tip of the threaded portion 116b of the second bolt 116 abuts against the bottom of the threaded hole 126a before the head 116a of the second bolt 116 contacts the bolt fastening surface 127b of the outer cylinder 127. As a result, a gap C is formed between the head 116a of the second bolt 116 and the bolt fastening surface 127b.

[0076] Also, Second bolt 116 The screw depth of the screw hole 126a is 115 It is also possible to configure a similar structure by making the screw depth shorter than that of the screw hole 126a.

[0077] Even in the configuration of this modified example 1, the gap C is formed so that the axial force of the second bolt 116 does not act on the outer tube 127 and the water-cooled spacer 128. That is, in modified example 1, the second bolt 116 itself functions as an axial force reducing means. Therefore, the same effects as those of the above embodiment are achieved. That is, deformation of the water-cooled spacer 128 can be prevented. Furthermore, since the spacer 117 is not required, this also contributes to a reduction in the number of parts.

[0078] (Variation 2) Next, a second modification of the axial force reducing means will be described. The second modification is characterized in that a stopper 118 is used as the axial force reducing means instead of the spacer 117. This will be described in detail with reference to FIG. 9 10 is an enlarged view of a main part of a fastening portion of a second bolt 116 according to a second modification.

[0079] figure 9As shown in Fig. 1, a metal stopper 118 is screwed and embedded in the bottom of screw hole 126a. Note that stopper 118 may be made of a material other than metal, but metal is preferable because it is less likely to deform over time after fastening the bolt, which could cause the bolt to loosen. When the tip of threaded portion 116b of second bolt 116 abuts stopper 118, gap C is formed between head 116a of second bolt 116 and bolt fastening surface 127b of outer cylinder 127 due to this stopper 118.

[0080] In this modification 2, since the gap C is formed by the stopper 118, the axial force of the second bolt 116 does not act on the outer cylinder 127 and the water-cooled spacer 128. Therefore, the same effect as in the above embodiment is achieved. That is, deformation of the water-cooled spacer 128 can be prevented.

[0081] (Variation 3) Next, a third variation of the axial force reducing means will be described. In addition to using stopper 118 as the axial force reducing means, the third variation is characterized by the placement of multiple disc springs 159 in gap C. This will be described in detail with reference to Fig. 10. Fig. 10 is an enlarged view of a main portion of the fastening portion of second bolt 116 according to the third variation.

[0082] 10, in Modification 3, a disc spring 159, which is an elastic member, is arranged in gap C. Specifically, a recess 127c is formed in outer cylinder 127, and three disc springs 159 are arranged in recess 127c in a stacked manner. Therefore, recess 127c serves as a space for accommodating disc springs 159.

[0083] According to this modification 3, the disc spring 159 can absorb thermal expansion, and is therefore effective in preventing loosening of the second bolt 116. Note that instead of the disc spring 159, a foaming agent, urethane rubber, or the like may be provided in the recess 127c as an elastic member. Of course, an elastic member such as the disc spring 159 can be applied to all of the embodiments and modifications disclosed in this specification.

[0084] (Variation 4) Next, a fourth modification of the axial force reducing means will be described. The fourth modification is characterized in that a shoulder bolt 160 is used as the second bolt. This will be explained in detail with reference to FIG. The cylindrical portion (step portion) 160a of the stepped bolt 160 abuts against the outer wall 126, and therefore has the same function as the spacer 117. That is, in Modification 4, instead of the configuration of the second bolt 116 and the spacer 117, the axial force reducing means is formed by the stepped bolt 160, which integrates the second bolt 116 and the spacer 117, and prevents axial force from acting on the outer cylinder 127. Modification 4 can also achieve the same effects as this embodiment. Furthermore, because the spacer 117 is not required, a reduction in the number of parts and a reduction in costs can be expected. Another advantage is that assembly is simple and workability is improved.

[0085] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the gist of the present invention. The present invention covers all technical matters included in the technical ideas described in the claims. The above-described embodiments are preferred examples, but a person skilled in the art can realize various alternatives, modifications, variations, combinations, or improvements from the contents disclosed in this specification, and these are included in the technical scope described in the appended claims.

[0086] The present invention is applicable to all kinds of vacuum pumps, such as a turbomolecular pump in which the water-cooled spacer 128 and the outer wall 126 are integrated to form an outer peripheral component, or a turbomolecular pump in which the outer casing 127 and the outer wall 126 are directly fastened together without the water-cooled spacer 128. That is, in a vacuum pump in which the outer casing and the outer peripheral component are fastened together with bolts, the present invention can be applied to locations where excessive axial force of the bolts should not be applied to the outer peripheral component. [Explanation of symbols]

[0087] 100 Turbomolecular pump (vacuum pump) 101 Air intake 102(102a, 102b, 102c) Rotor 102d Cylindrical part 103 Rotating Body 115 First Bolt 116 Second Bolt 116a Head 116b Threaded part 117 Spacer (means for reducing axial force) 118 Stopper (means for reducing axial force) 122 Stator column 123(123a,123 b , 123c) fixed wing 125(125a, 125b, 125c) Fixed wing spacer 126 Outer wall (periphery part) 126a screw hole 127 Outer cylinder 127a Through hole 127b Bolt fastening surface 127c recess 128 Water cooling spacer (periphery part) 128a Through hole 129 Base 131 Threaded spacer 133 Exhaust port 159 Disc spring 160 shoulder bolt (second bolt) C Gap

Claims

1. A rotating body; An outer cylinder that houses the rotating body; an outer peripheral part disposed on the outer peripheral side of the rotating body and coaxially with the outer cylinder; a first bolt and a second bolt that fasten the outer cylinder and the outer peripheral component; and an axial force reducing means for reducing the bolt axial force acting on the outer cylinder, The axial force reducing means is provided on the second bolt, When the head of the first bolt abuts against a first bolt fastening surface which is an outer surface of the outer tube and faces the head of the first bolt, the bolt axial force acts on the outer tube and the outer peripheral part, and the outer tube and the outer peripheral part are fixed together. the axial force reducing means has a structure for forming a gap between a head of the second bolt and a second bolt fastening surface which is an outer surface of the outer cylinder and faces the head of the second bolt, The gap prevents the bolt axial force of the second bolt from acting on the outer cylinder. A vacuum pump characterized by:

2. 2. The vacuum pump according to claim 1, The outer cylinder is provided with a plurality of through holes through which the first bolt and the second bolt pass, The outer peripheral part is provided with a plurality of screw holes into which the first bolt and the second bolt are screwed, a cylindrical spacer serving as the axial force reducing means is inserted into at least one of the plurality of through holes; The gap is formed between the head of the second bolt and the second bolt fastening surface via the spacer. A vacuum pump characterized by:

3. 2. The vacuum pump according to claim 1, The outer cylinder is provided with a plurality of through holes through which the first bolt and the second bolt pass, The outer peripheral part is provided with a plurality of screw holes into which the first bolt and the second bolt are screwed, The second bolt is formed with a nominal length greater than the total value of the length of the through hole and the thread depth of the screw hole, thereby functioning as the axial force reducing means and forming the gap between the head of the second bolt and the second bolt fastening surface. A vacuum pump characterized by:

4. 2. The vacuum pump according to claim 1, The outer cylinder is provided with a plurality of through holes through which the first bolt and the second bolt pass, The outer peripheral part is provided with a plurality of screw holes into which the first bolt and the second bolt are screwed, a stopper as the axial force reducing means is provided at a bottom of at least one of the plurality of screw holes; When the tip end of the second bolt abuts against the stopper, the gap is formed between the head of the second bolt and the second bolt fastening surface. A vacuum pump characterized by:

5. The vacuum pump according to any one of claims 1 to 4, 2. The vacuum pump according to claim 1 , wherein the axial force reducing means further comprises an elastic member disposed in the gap.

6. The vacuum pump according to any one of claims 1 to 5, The first bolt and the second bolt are each a plurality of bolts, A vacuum pump, wherein the number of the second bolts is smaller than the number of the first bolts.

7. The vacuum pump according to any one of claims 1 to 5, The first bolt and the second bolt are each a plurality of bolts, A vacuum pump, wherein the number of the second bolts is greater than the number of the first bolts.

8. The vacuum pump according to any one of claims 1 to 7, 2. A vacuum pump comprising: a first bolt and a second bolt, the first bolt and the second bolt being the same bolt.

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