TW202328567A - Vacuum pump, spacer component, and bolt fastening method - Google Patents

Abstract

To prevent bolt looseness, which would otherwise be caused by thermal stress created by a difference in linear expansion coefficient between multiple components. In a vacuum pump according to an embodiment of the present invention, when a component to be heated (fastened component) that is to be heated by internal heat is fastened by a bolt, a spacer that adjusts a linear expansion coefficient is placed to compensate for the thermal stress created by the difference in linear expansion coefficient between them. Placing the spacer allows the linear expansion coefficient of a combination of the component to be heated and the spacer to match the linear expansion coefficient of the bolt (the material of the bolt). This limits the creation of thermal stress in the portion fastened by the bolt.

Description

Fastening method of vacuum pump, spacer parts, and bolts

The invention relates to a method for fastening a vacuum pump, spacer parts and bolts. More specifically, it relates to a vacuum pump, spacer, and bolt fastening method that minimizes the influence of thermal stress generated when the bolt and the fastened material thermally expand due to heat generated during operation in the vacuum pump.

The vacuum pump has rotating blades and fixed blades fixed on the rotating shaft (shaft), so that the rotating shaft rotates at high speed, and through the interaction between the rotating blades and the fixed blades rotating at high speed, the vacuum exhaust of the air in the process chamber that requires high vacuum gas. The exhaust gas includes the process gas used in the semiconductor manufacturing process, and various substances are contained in the process gas. Because these products are accumulated between the internal parts in the vacuum pump, there will be incidents where parts that are not in contact with each other will come into contact. In a vacuum pump, the rotating shaft (rotating vane) rotates at high speed, and there is a risk of heavy damage due to contact accidents. Therefore, in order to prevent accumulation of products, it is required to increase the temperature inside the vacuum pump.

However, metals (aluminum, stainless steel) are used as components of vacuum pumps. Also, bolts for fastening parts are mainly made of iron or stainless steel. These metals have different linear expansion coefficients according to their types, and in the same temperature environment, the displacement of the material is also different. Because of the thermal stress generated by the difference in displacement, an additional load is generated to the load generated when the vacuum pump is assembled (in a normal temperature environment). Therefore, due to the additional load, a load exceeding the strength of the material is applied to the bolts of the vacuum pump. There is a risk of damage to the joined part.

Here, referring to FIG. 7 and FIG. 8 , the thermal stress generated by the difference in displacement of each metal due to thermal expansion will be described. Here, thermal stress means a force that suppresses deformation in a state where deformation is fixed. As shown in Figure 7(a), in the unrestrained state (the state of free deformation), no force acts at high temperature (during thermal expansion), and no thermal stress occurs. On the other hand, as shown in Fig. 7(b), in the restrained state (deformation is not a free state), a reaction force is generated to hinder deformation. That is, stress generated by hindering deformation by temperature change is thermal stress.

Next, referring to FIG. 8 , thermal stress generated in a state in which a plurality of metals are restrained will be described. As shown in Fig. 8(a), the two ends of the aluminum material A located on the outer peripheral side and the iron material (such as bolts) B located on the middle side are restrained. At this time, the lengths of the two are the same at room temperature, and no thermal stress occurs. Next, if the temperature changes from normal temperature to high temperature as shown in Figure 8(b), although the lengths of the two are finally the same due to the balance of force, the linear expansion coefficient of material A and material B is material A > material B, so The reaction force (compression) acting on material A to the force that intends to extend outward, and on the other hand, the reaction force (stretch) to the force that acts on material B to shrink. This is the thermal stress generation mechanism due to the difference in linear expansion coefficient between materials. In other words, in the state shown in FIG. 8( b ), if the coefficients of linear expansion are the same, the amount of displacement is the same, so no thermal stress is generated.

Here, "loosening of bolts" will be described as damage starting from bolts (fastening parts). As shown in Figure 9(b), use the fastening line diagram in the design to judge whether there is "bolt looseness". Here, the fastening line diagram is shown in Figure 9(a), which is a graph showing the balance relationship between the compressive force and the tensile force of the fastened/fastened parts. If the compression force and the tension force are displayed by coincidence, it is in a state of force balance (X in the figure) during assembly (normal temperature state), and an equal load is applied to the fastened/fastened parts. However, if the internal temperature is changed by, for example, operating a vacuum pump, thermal elongation accompanied by temperature rise occurs in the fastened/fastened parts, and thermal stress is applied to both parts as additional stress (additional load). At this time, due to the difference between the linear expansion coefficients of the two materials, the axial force generated by the fastened/fastened two parts increases, and "bolt tension" occurs due to the breakage of the fastening part and the plastic deformation of the fastened part. relaxation". [Prior Art Literature] [Patent Document]

[Patent Document 1] Japanese Patent Laid-Open No. 2017-89582

In Patent Document 1, in order to cope with the high temperature inside the vacuum pump, it is disclosed that an insulating part is arranged inside, thereby maintaining the exhaust performance of the vacuum pump, and responding to the high temperature inside the pump.

[Problem to be solved by the invention]

However, in the high-temperature vacuum pump shown in the prior art documents, there is a possibility of "loosening of bolts" due to thermal stress caused by the difference in the linear expansion coefficients of a plurality of parts as described above. If left in this state, it may cause damage to the vacuum pump.

Therefore, the present invention focuses on the bolts that are important for assembling mechanical products, and aims to provide a vacuum pump, spacer parts, and bolt fastening method that can prevent damage starting from the bolts in a high-temperature environment. [Technical means to solve the problem]

The present invention described in technical solution 1 provides a vacuum pump comprising: a housing; a heated part arranged in the housing and heated by the generated heat; and a bolt for fixing the heated part. at a specific position; and the vacuum pump is characterized by having: a thermal expansion difference reducing mechanism, which makes the above-mentioned heated part and the above-mentioned heated part less than the above-mentioned The thermal expansion difference in the fastening direction of the above-mentioned bolts of the linear expansion coefficient of the heating part is reduced. The present invention described in technical solution 2 provides the vacuum pump as described in technical solution 1, wherein the above-mentioned thermal expansion difference reducing mechanism is provided with a wire having a linear expansion coefficient smaller than that of the above-mentioned bolt at the position where the head of the above-mentioned bolt is in contact with the above-mentioned heated part. The expansion coefficient spacer part is used to fasten the bolt through the spacer part. The present invention described in technical solution 3 provides the vacuum pump as described in technical solution 2, wherein the above-mentioned thermal expansion difference reducing mechanism is limited by the difference between the thermal expansion of the above-mentioned spacer parts and the above-mentioned heated parts and the thermal expansion of the above-mentioned bolts. The method within the range determines the thickness of the above spacer parts in the fastening direction. The present invention described in Claim 4 provides the vacuum pump as described in Claim 1, wherein the thermal expansion difference reducing mechanism reduces the thickness of the heated part in the fastening direction. The present invention described in claim 5 provides a spacer part that is arranged in the casing of the vacuum pump and is arranged on the head of the bolt when the heated part heated by the generated heat is fixed to a specific position with a bolt. The portion that is in contact with the above-mentioned heated parts, and has a linear expansion coefficient that is smaller than that of the above-mentioned bolt. The present invention described in technical solution 6 provides a method for fastening bolts, which is used in a vacuum pump. The vacuum pump has: a casing; a heated part arranged in the casing and heated by the generated heat; And a bolt, which has a coefficient of linear expansion smaller than the above-mentioned heated part, and fixes the above-mentioned heated part at a specific position; it is characterized in that: at the part where the head of the above-mentioned bolt contacts the heated part, a linear expansion coefficient less than A spacer for the coefficient of linear expansion of the bolt is used to fasten the bolt and the heated part through the spacer. [Effect of Invention]

According to the present invention, it is possible to prevent loosening of bolts due to thermal stress caused by differences in linear expansion coefficients of a plurality of parts.

(i) Outline of Embodiment In the vacuum pump according to the embodiment of the present invention, when bolts are used to fasten heated parts (fastened parts) heated by generated heat (internal heat generated during operation, heating mechanism, etc.), in order to absorb The thermal stress generated by the difference between the two linear expansion coefficients, and the spacer used to adjust (eliminate) the difference between the two linear expansion coefficients is provided.

By setting the spacer, the linear expansion coefficient of the bolt (the material of the bolt) is consistent with (closer to) the thermal expansion of the total linear expansion coefficient of the heated part and the spacer, and it is possible to suppress the generation of thermal stress on the fastening part of the bolt or Reduce thermal stress.

(ii) Details of the implementation form Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to FIGS. 1 to 6 .

FIG. 1 shows a longitudinal sectional view of the turbomolecular pump (vacuum pump) 100 . In FIG. 1 , the turbomolecular pump 100 has an air inlet 101 formed at the upper end of a cylindrical outer tube 127 . And, inside the outer cylinder 127, a rotating body 103 is provided, and a plurality of rotating blades 102 (102a, 102b, 102c), which are turbine blades for suctioning and discharging gas, are radially formed on the circumference of the rotating body 127 in multiple stages. A rotor shaft 113 is installed at the center of the rotating body 103, and the rotor shaft 113 is suspended and supported in the air by, for example, a 5-axis controlled magnetic bearing and its position is controlled. Generally, the rotating body 103 is made of metal such as aluminum or aluminum alloy.

The upper radial electromagnet 104 is a pair of four electromagnets arranged on the X-axis and the Y-axis. Near the upper radial electromagnet 104 , four upper radial sensors 107 are provided corresponding to each of the upper radial electromagnets 104 . The upper radial sensor 107 detects the position of the rotor shaft 113 based on changes in the inductance of the conductive winding according to changes in the position of the rotor shaft 113 using, for example, an inductance sensor with a conductive winding or an eddy current sensor. The upper radial sensor 107 is configured to detect the radial displacement of the rotor shaft 113 , that is, the rotating body 103 fixed thereto, and send it to the control device 200 .

In the control device 200, for example, a compensation circuit having a PID (Proportion Integration Differentiation: Proportional Integral Differentiation) adjustment function generates excitation control of the upper radial electromagnet 104 based on the position signal detected by the upper radial sensor 107 According to the command signal, the amplifier circuit 150 shown in FIG. 2 (described later) excites and controls the upper radial electromagnet 104 based on the excitation control command signal, thereby adjusting the radial position of the upper side of the rotor shaft 113 .

Furthermore, the rotor shaft 113 is formed of a high magnetic permeability material (iron, stainless steel, etc.), and is attracted by the magnetic force of the upper radial electromagnet 104 . The adjustments are independently performed in the X-axis direction and the Y-axis direction. Also, the lower radial electromagnet 105 and the lower radial sensor 108 are arranged in the same manner as the upper radial electromagnet 104 and the upper radial sensor 107, and the radial position of the lower side of the rotor shaft 113 and the diameter of the upper side Adjust toward the position in the same way.

Furthermore, the axial electromagnets 106A and 106B are vertically arranged with the disc-shaped metal disk 111 provided on the lower part of the rotor shaft 113 interposed therebetween. The metal disk 111 is made of a high magnetic permeability material such as iron. In order to detect the axial displacement of the rotor shaft 113 , an axial sensor 109 is provided, and is configured to send the axial position signal to the control device 200 .

Moreover, in the control device 200, for example, a compensation circuit with a PID adjustment function generates the excitation control of each of the axial electromagnet 106A and the axial electromagnet 106B based on the axial position signal detected by the axial sensor 109. Command signal, and the amplifier circuit 150 (refer to FIG. 2 ) based on these excitation control command signals, respectively excite and control the axial electromagnet 106A and the axial electromagnet 106B, so that the axial electromagnet 106A attracts the metal disc 111 by magnetic force To the top, the axial electromagnet 106B attracts the metal disk 111 to the bottom to adjust the axial position of the rotor shaft 113 .

In this way, the control device 200 properly adjusts the magnetic force exerted by the axial electromagnets 106A and 106B on the metal disk 111, so that the rotor shaft 113 is magnetically suspended in the axial direction and kept in space in a non-contact manner. In addition, the amplifier circuit 150 for exciting and controlling the upper radial electromagnet 104, the lower radial electromagnet 105, and the axial electromagnets 106A and 106B will be described later.

On the other hand, the motor 121 includes a plurality of magnetic poles arranged in a circumferential shape to surround the rotor shaft 113 . Each magnetic pole is controlled by the control device 200 so that the rotor shaft 113 is rotationally driven by the electromagnetic force acting between it and the rotor shaft 113 . Also, a rotational speed sensor such as a hall element, a resolver, and an encoder (not shown) is incorporated in the motor 121, and the rotational speed of the rotor shaft 113 is detected from a detection signal of the rotational speed sensor.

Furthermore, for example, a phase sensor (not shown) is installed near the lower radial sensor 108 to detect the rotational phase of the rotor shaft 113 . In the control device 200, the detection signals of the phase sensor and the rotation speed sensor are used together to detect the position of the magnetic pole.

A plurality of fixed blades 123 (123a, 123b, 123c, . The rotating blades 102 ( 102 a , 102 b , 102 c ) are formed to incline at a specific angle from a plane perpendicular to the axis of the rotor shaft 113 in order to move the molecules of the exhaust gas downward by collision. The stationary blades 123 (123a, 123b, 123c, . . . ) are made of metal such as aluminum, iron, stainless steel, copper, or the like, or metals such as alloys containing these metals as components.

Also, the fixed blades 123 are also formed by inclining at a specific angle from a plane perpendicular to the axis of the rotor shaft 113 , and are arranged to be offset from the rotating blades 102 toward the inner side of the outer cylinder 127 . And, the outer peripheral end of the fixed blade 123 is supported in a state of being inserted between the fixed blades 125 (125a, 125b, 125c) in which a plurality of stages are stacked.

The fixed blade spacer 125 is an annular member made of metal such as aluminum, iron, stainless steel, copper, or an alloy containing these metals as components. On the outer periphery of the fixed blade spacer 125 , an outer cylinder 127 is fixed with a slight gap. A base portion 129 is disposed on the bottom of the outer cylinder 127 . An exhaust port 133 is formed in the base portion 129 to communicate with the outside. The exhaust gas that enters the suction port 101 from the chamber (vacuum chamber) side and is transferred to the base portion 129 is sent to the exhaust port 133 .

Furthermore, according to the use of the turbomolecular pump 100 , a threaded spacer 131 is provided between the lower part of the fixed vane spacer 125 and the base part 129 . The threaded spacer 131 is a cylindrical member made of metal such as aluminum, copper, stainless steel, iron, or an alloy containing these metals as a component, and a plurality of spiral threads are engraved on its inner peripheral surface. Thread groove 131a. The helical direction of the screw groove 131a is the direction in which the molecule of the exhaust gas is transferred to the exhaust port 133 when the molecule moves to the rotation direction of the rotating body 103 . The cylindrical portion 102d hangs down to the lowermost portion of the rotating blades 102 ( 102a , 102b , 102c ) following the rotating body 103 . The outer peripheral surface of the cylindrical portion 102d is cylindrical, protrudes toward the inner peripheral surface of the threaded spacer 131, and approaches the inner peripheral surface of the threaded spacer 131 with a predetermined gap. The exhaust gas transferred to the screw groove 131 a by the rotating blade 102 and the fixed blade 123 is guided to the screw groove 131 a and sent to the base portion 129 .

The base portion 129 is a disc-shaped member constituting the base portion of the turbomolecular pump 100 , and is generally made of metal such as iron, aluminum, and stainless steel. The base portion 129 physically holds the turbomolecular pump 100 and also functions as a heat conduction path, so it is desirable to use a rigid metal such as iron, aluminum, or copper with high thermal conductivity.

In this configuration, if the rotating vane 102 is rotationally driven by the motor 121 together with the rotor shaft 113 , the exhaust gas is sucked from the chamber through the suction port 101 by the action of the rotating vane 102 and the fixed vane 123 . The rotating speed of the rotating blade 102 is generally 20000 rpm-90000 rpm, and the peripheral speed of the front end of the rotating blade 102 reaches 200 m/s-400 m/s. The exhaust gas sucked from the suction port 101 passes between the rotating vane 102 and the fixed vane 123 , and is sent to the base part 129 . At this time, although the temperature of the rotating blade 102 rises due to the frictional heat generated when the exhaust gas contacts the rotating blade 102, or the heat generated by the motor 121, etc., the temperature of the rotating blade 102 rises, but the heat is transmitted by radiation or gas molecules of the exhaust gas. And transmitted to the fixed blade 123 side.

The stationary vane spacers 125 are joined to each other at outer peripheral portions, and transmit heat received by the stationary vanes 123 from the rotating vanes 102 or frictional heat generated when exhaust gas contacts the stationary vanes 123 to the outside.

In addition, as described above, the threaded spacer 131 is disposed on the outer periphery of the cylindrical portion 102d of the rotating body 103, and the threaded spacer 131 is provided with a threaded groove 131a on the inner peripheral surface. However, on the contrary, there is a case where a screw groove is engraved on the outer peripheral surface of the cylindrical portion 102d, and a spacer having a cylindrical inner peripheral surface is disposed around it.

Also, according to the purpose of the turbomolecular pump 100, there are also the following situations: so that the gas sucked from the suction port 101 does not intrude into the upper radial electromagnet 104, the upper radial sensor 107, the motor 121, and the lower diameter. Like the electrical part composed of the electromagnet 105, the lower radial sensor 108, the axial electromagnets 106A, 106B, the axial sensor 109, etc., the periphery of the electrical part is covered by the stator column 122, and the stator The inside of the column 122 is kept at a certain pressure by the purge gas.

In this case, piping (not shown) is arranged on the base portion 129, and the purge gas is introduced through the piping. The introduced purified gas is sent to the exhaust port 133 through the gap between the protective bearing 120 and the rotor shaft 113 , between the rotor and the stator of the motor 121 , and between the stator post 122 and the inner cylindrical part of the rotating blade 102 .

Here, the turbomolecular pump 100 needs to be controlled based on model-specific and individually adjusted inherent parameters (such as characteristics corresponding to the model). In order to store the control parameters, the turbomolecular pump 100 includes an electronic circuit unit 141 in its main body. The electronic circuit part 141 is composed of semiconductor memories such as EEP-ROM (Electrically Erasable Programmable-Read Only Memory) and electronic components such as semiconductor elements used for its access, and the Substrates and other components. The electronic circuit unit 141 is housed in the lower part of the rotation speed sensor (not shown) near the center of the base part 129 constituting the lower part of the turbomolecular pump 100 , and is closed by an airtight bottom cover 145 .

However, in the semiconductor manufacturing process, the process gas introduced into the chamber has the property of becoming solid when its pressure is higher than a certain value or its temperature is lower than a certain value. Inside the turbomolecular pump 100 , the pressure of the discharged gas is the lowest at the suction port 101 and the highest at the exhaust port 133 . During the transfer of the process gas from the suction port 101 to the exhaust port 133, when its pressure is higher than a certain value or its temperature is lower than a certain value, the process gas will become solid and accumulate inside the turbomolecular pump 100 .

For example, when SiCl4 is used as a process gas in an Al etching device (although 4 is a subscript, in order to prevent incorrect conversion of character codes, the characters in the upper and lower subscripts will be expressed in normal characters below) as the process gas, it can be known from the vapor pressure curve At low vacuum (760 [torr] ~ 10-2 [torr]) and low temperature (about 20 [°C]), solid products (such as AlCl3) are precipitated and deposited inside the turbomolecular pump 100 . Accordingly, when deposits of the process gas accumulate inside the turbomolecular pump 100 , the deposit narrows the pump flow path, which causes performance degradation of the turbomolecular pump 100 . In addition, the above-mentioned product is in a state of being easily solidified and adhered to a part of high pressure near the exhaust port 133 or near the threaded spacer 131 .

Therefore, in order to solve this problem, the heating of the heater or the cooling control of the water-cooled pipe 149 (hereinafter referred to as TMS. TMS; Temperature Management System: temperature management system) has conventionally been performed as follows: The water-cooled pipe 149 is wound around the outer periphery of the base portion 129, and for example, a temperature sensor (such as a thermistor) not shown is embedded in the base portion 129, and the base portion The temperature of 129 is maintained at a fixed higher temperature (set temperature).

Next, the amplifier circuit 150 for controlling the excitation of the upper radial electromagnet 104, the lower radial electromagnet 105, and the axial electromagnets 106A and 106B of the turbomolecular pump 100 thus configured will be described. FIG. 2 shows a circuit diagram of the amplifier circuit 150 .

In FIG. 2, one end of the electromagnet winding 151 constituting the upper radial electromagnet 104 etc. is connected to the positive pole 171a of the power supply 171 through the transistor 161, and the other end is connected to the positive pole 171a of the power supply 171 through the current detection circuit 181 and the transistor 162. Negative electrode 171b. Furthermore, the transistors 161 and 162 are so-called power MOSFETs (Metal Oxide Semiconductor Field Effect Transistors), which have a structure in which a diode is connected between the source and the drain.

At this time, the cathode terminal 161 a of the diode of the transistor 161 is connected to the anode 171 a, and the anode terminal 161 b is connected to one end of the electromagnet winding 151 . Moreover, the cathode terminal 162a of the diode of the transistor 162 is connected to the current detection circuit 181, and the anode terminal 162b is connected to the negative electrode 171b.

On the other hand, the cathode terminal 165a of the diode 165 for current regeneration is connected to one end of the electromagnet winding 151, and the anode terminal 165b thereof is connected to the negative electrode 171b. Also, similarly, the cathode terminal 166a of the diode 166 for current regeneration is connected to the positive electrode 171a, and the anode terminal 166b thereof is connected to the other end of the electromagnet winding 151 via the current detection circuit 181 . Furthermore, the current detection circuit 181 is constituted by, for example, a Hall sensor type current sensor or a resistance element.

The amplifier circuit 150 constituted as above corresponds to one electromagnet. Therefore, when the magnetic bearing is 5-axis control and there are ten electromagnets 104, 105, 106A, and 106B in total, the same amplifier circuit 150 is configured for each electromagnet, and the ten amplifier circuits 150 are connected in parallel to the power supply. 171.

Furthermore, the amplifier control circuit 191 is composed of, for example, a digital signal processing unit (hereinafter referred to as a DSP (Digital Signal Processing) unit) not shown in the control device 200, and the amplifier control circuit 191 switches the transistors 161, 162 on ( on)/disconnect (off).

The amplifier control circuit 191 compares the current value detected by the current detection circuit 181 (the signal reflecting the current value is referred to as a current detection signal 191c) with a specific current command value. Then, based on the comparison result, the magnitude of the pulse width generated in one cycle of PWM (Pulse Width Modulation) control, that is, the control cycle Ts (pulse width times Tp1 and Tp2 ) is determined. As a result, gate drive signals 191 a and 191 b having the pulse width are output from the amplifier control circuit 191 to the gate terminals of the transistors 161 and 162 .

In addition, high-speed and powerful position control of the rotating body 103 is required when the rotating speed of the rotating body 103 passes through a resonance point during accelerated operation or when disturbance occurs during constant speed operation. Therefore, a high voltage of, for example, about 50 V is used as the power supply 171 so that a rapid increase (or decrease) of the current flowing through the electromagnet winding 151 can be realized. In addition, in order to stabilize the power supply 171 , a normal capacitor (not shown) is connected between the positive electrode 171 a and the negative electrode 171 b of the power supply 171 .

In this configuration, if both of the transistors 161 and 162 are connected, the current flowing through the electromagnet winding 151 (hereinafter referred to as the electromagnet current iL) increases, and if the two are disconnected, the electromagnet current iL increases. iL decreases.

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

That is, when the detected current value (detection value) is greater than the current command value, as shown in FIG. is turned on, and the turn-on time is equivalent to the time amount of the pulse width time Tp1. Therefore, the electromagnet current iL in this period increases toward the current value iLmax (not shown) that can flow from the positive electrode 171a to the negative electrode 171b through the transistors 161 and 162 .

On the other hand, when the detected current value (detection value) is smaller than the current command value, in the control cycle Ts as shown in FIG. The off time corresponds to the amount of time of the pulse width time Tp2. Therefore, the electromagnet current iL in this period decreases toward the current value iLmin (not shown) that can be regenerated from the negative electrode 171b to the positive electrode 171a via the diodes 165 and 166 .

And, in any case, after the pulse width time Tp1, Tp2 elapses, either one of the transistors 161, 162 is turned on. Therefore, the flywheel current is maintained in the amplifier circuit 150 during this period.

Fig. 5 is a diagram for explaining a bolt fastening portion of the vacuum pump according to the first embodiment. Specifically, bolts 300 are used to fasten the position of the sub-pillar 122 . However, this is an example, and it can also be applied to bolts used in other parts in the vacuum pump 100 . In this first embodiment, the stator column 122 which is the fastened material is made of material A (aluminum), and the other bolt 300 is made of material B (for example, stainless steel). As shown in FIG. 5( a ), the fastened material is fastened by the head portion 300 a of the bolt 300 and the nut 302 (corresponding to the base portion 129 in the embodiment). In this state, when the vacuum pump 100 is operated, heat is generated inside, and since the coefficient of linear expansion is A>B, the fastened material expands more than the bolt 300 . Therefore, thermal stress is generated on the contact surface between the fastened material and the head portion 300 a of the bolt 300 and the contact surface between the fastened material and the nut 302 . At this time, the material to be fastened may be plastically deformed or the head portion 300a of the bolt 300 may be damaged due to the thermal stress.

Therefore, as shown in FIG. 5( b ), a spacer 400 including material C (such as titanium, tungsten, copper, brass, nickel, and Kovar) having a smaller linear expansion coefficient than material A and material B is arranged. With this spacer 400, the difference in the linear expansion coefficient (expansion amount) of material A and material B is corrected. Although the shape of the spacer 400 is a column, it can also be a prism. It is set to a size that completely touches the head portion 300a of the bolt 300 . A hole having a shape corresponding to the stator post 122 which is the material to be fastened is provided and arranged there. Although it can be bonded or welded, it can also be fastened and fixed by bolts 300 . In addition, since the bolt 300 has the same fastening structure in the case of fixing a headless embedded bolt (headless bolt) with a nut, the effect of the present invention can still be exhibited.

The thickness of the spacer 400 (the axial length of the bolt 300 ) is determined such that the sum of the expansion of the material A and the expansion of the material C is equal to the expansion of the material B. This means that the expansion amount of 300b of the bolt 300 is equal to the sum of the axial expansion amounts of the stator post 122 and the spacer 400 . That is, when the difference between the linear expansion coefficients of material A and material B is small, the thickness of the spacer 400 becomes thinner, and conversely, when the difference between the linear expansion coefficients of material A and material B is large, the spacer 400 becomes thinner. The thickness of 400 becomes thicker. In this way, by adjusting the thickness of the spacer 400, it is possible to prevent thermal stress from being generated on the bolt 300 and the fastened material due to thermal expansion.

Next, a second embodiment will be described with reference to FIG. 6 . In this embodiment, the thermal stress generated by the difference between the linear expansion coefficients of material A and material B is reduced by controlling the length of the two materials, and the result is to avoid the loosening of the bolts as much as possible. That is, since the thermal expansion (thermal elongation) of a part depends on the linear expansion coefficient of the material of the part and the length of the part, the length of the part is shortened to reduce thermal stress. Therefore, as shown in FIG. 6( b ), a hole (counterbore) 500 of the stator post 122 which is the material to be fastened is formed, and the difference in thermal elongation between the material to be fastened and the bolt 300 is shortened. In this way, the additional axial force on the fastening diagram becomes smaller (W1>W2), and the slack of the bolt can be reduced. In addition, from the viewpoint of thermal stress, although the depth of the hole (counterbore) 500 is desirably deeper, it is appropriately determined in consideration of the strength of the fastened material and the bolt 300 .

If the stress above the elastic region of the metal (the endurance of the material) is generated due to the increase of the axial force, the fastened material will be plastically deformed. Therefore, it is necessary to limit the difference in thermal expansion between material A and material B (the fastened material and the bolt) within a certain range (in the elastic region of the metal). Therefore, in the first embodiment, it is necessary to appropriately adjust the thickness of the spacer 400 , and in the second embodiment, it is necessary to appropriately adjust the depth of the hole (counterbore) 500 . In addition, the bolt 300 is used within the designated elastic region. However, if an additional axial force occurs, it will enter the plastic deformation region if it exceeds 0.2% without countermeasures. Thereby, measures are taken as shown in the first embodiment and the second embodiment by using it in the elastic region.

In the above-mentioned first and second embodiments, the stator post has been described as an example of the fastened material, but the present invention is not limited thereto, and can be applied to other fastening parts that thermally expand. For example, it can also be applied to the fastening part of the controller or the fastening part of the rotor shaft 113 . Moreover, 1st Embodiment and 2nd Embodiment can be used together. That is, the hole (counterbore) 500 may be provided in the fastened material, and the spacer 400 may be further provided.

In addition, the embodiment and each modification of this invention can also be made into the structure which combined each of them as needed.

In addition, the present invention can be modified variously without departing from the spirit of the present invention. And, of course, the present invention relates to such changers.

100: turbomolecular pump (vacuum pump) 101: Suction port 102: rotating blade 102a: rotating blade 102b: rotating blade 102c: rotating blade 102d: Cylindrical part 103: rotating body 104: Upper radial electromagnet 105: Lower side radial electromagnet 106A: Axial electromagnet 106B: Axial electromagnet 107: Upper radial sensor 108: Lower side radial sensor 109: Axial sensor 111: metal plate 113: rotor shaft 120: Protect the bearing 121: motor 122: Stator column 123: fixed blade 123a: fixed vane 123b: fixed blade 123c: fixed blade 125: Fixed blade spacer 125a: fixed blade 125b: fixed blade 125c: fixed blade 127: Outer cylinder 129: base part 131: spacer with thread 131a: thread groove 133: Exhaust port 141:Electronic Circuit Department 145: Bottom cover 149: water cooling tube 150: Amplifier circuit 151: Electromagnet winding 161:Transistor 161a: cathode terminal 161b: Anode terminal 162:Transistor 162a: cathode terminal 162b: Anode terminal 165: Diode 165a: cathode terminal 165b: Anode terminal 166: Diode 166a: cathode terminal 166b: Anode terminal 171: Power 171a: positive electrode 171b: negative pole 181: Current detection circuit 191: Amplifier control circuit 191a: Gate drive signal 191b: Gate drive signal 191c: current detection signal 200: Control device 300: Bolt 300a: head 302: Nut 400: spacer 500: hole A:Material B: material C: material iL: electromagnet current Tp1: Pulse width time Tp2: Pulse width time Ts: control loop W1: axial force W2: axial force ε: strain

FIG. 1 is a diagram showing a schematic configuration example of a turbomolecular pump according to an embodiment of the present invention. Fig. 2 is a diagram showing a circuit diagram of an amplifier circuit used in an embodiment of the present invention. Fig. 3 is a timing chart showing the control of the situation where the detection value is greater than the current command value in the embodiment of the present invention. Fig. 4 is a time chart showing the control of the situation where the detected value is smaller than the current command value in the embodiment of the present invention. 5( a ), ( b ) are diagrams for explaining the parts fastened by bolts of the vacuum pump according to the first embodiment of the present invention. Fig. 6(a), (b) are diagrams for explaining the fastening portion with bolts of the vacuum pump according to the second embodiment of the present invention. Fig. 7(a), (b) is a diagram for explaining thermal stress generated by temperature change. Fig. 8(a), (b) is a graph for explaining the relationship between the difference in linear expansion coefficient and thermal stress. Fig. 9 (a), (b) is a diagram for explaining the tightening diagram for judging the presence or absence of "bolt looseness".

122: Stator column

300: Bolt

300a: head

302: Nut

400: spacer

A:Material

B: material

C: material

Claims (6)

A vacuum pump comprising: case; a heated part arranged in the above-mentioned housing and heated by the generated heat; and Bolts used to fix the above-mentioned heated parts at specific positions; and The vacuum pump is characterized by: The thermal expansion difference reduction mechanism is to adjust the fastening direction of the heated part and the bolt having a coefficient of linear expansion smaller than that of the heated part when both are heated in a state where the heated part is fixed by the bolt. The difference in thermal expansion is reduced. The vacuum pump according to claim 1, wherein the thermal expansion difference reducing mechanism is provided with a spacer with a linear expansion coefficient smaller than that of the bolt at the position where the head of the bolt contacts the heated part, and the spacer is separated from the spacer Tighten the above bolts. The vacuum pump according to claim 2, wherein the thermal expansion difference reducing mechanism determines the difference between the thermal expansion of the spacer and the heated part and the thermal expansion of the bolt within a certain range. The thickness in the fastening direction. The vacuum pump according to claim 1, wherein the thermal expansion difference reducing mechanism reduces the thickness of the heated part in the fastening direction. A spacer part arranged in the casing of the vacuum pump, when the heated part heated by the generated heat is fixed at a specific position with a bolt, and arranged at the part where the head of the bolt contacts the heated part, And have a linear expansion coefficient smaller than that of the above-mentioned bolt. A method for fastening bolts, which is used in a vacuum pump. The vacuum pump includes: a casing; a heated part arranged in the casing and heated by the generated heat; and a bolt having a size smaller than the heated part. The coefficient of linear expansion fixes the above-mentioned heated parts at a specific position; it is characterized in that: A spacer with a coefficient of linear expansion smaller than that of the bolt is arranged at the portion where the head of the bolt is in contact with the heated part, and the bolt and the heated part are fastened through the spacer.