Turbo molecular pump and rotating body of turbo molecular pump

Abstract

[Problem] To provide a turbo molecular pump that can improve exhaust performance. [Solving Means] A turbo molecular pump includes: a rotor shaft (113); and 5 a rotor blade (102) that is fixed to the rotor shaft (113), is rotatable integrally, and includes a plurality of stages of blade rows. The turbo molecular pump sucks in and exhausts exhaust gas through rotation of the rotor blade (102). Among the plurality of stages of blade rows, blade rows (102a and 102b) at first and second stages from the top are made of 10 a magnesium alloy, which is a first material, while remaining blade rows (102c, 102d, ・・・) at third and subsequent stages are made of an aluminum alloy, which is a second material. Specific strength of the first material is higher than that of the second material.

Description

2023-031-GB 1TURBO MOLECULAR PUMP AND ROTATING BODY OF TURBO MOLECULAR PUMP[ Technical Field]

[0001] The present invention relates to a turbo molecular pump and a rotating body of a turbo molecular pump .[Background Art ]

[0002] As a related art in this technical field, for example , PLT 1 describes , in a turbo molecular pump in which moving blades and stationary blades are alternately arranged, a configuration in which an outer diameter of the moving blades on an inlet port side is made larger than that of the moving blades on an outlet port side . According to this configuration, a peripheral speed of the moving blades on the inlet port side increases , which enhances an exhaust speed without imposing severe stress conditions on the moving blades . [ Citation List ] [ Patent Literature ]

[0003] [ PTL 1 ] Japanese Patent Application Laid-open No . H05- 106587 [ Summary of Invention] [ Technical Problem]

[0004] In PLT 1 , focusing on a feature in which the stress occurring in the moving blades on the inlet port side is lower than that occurring in the moving blade on the outlet port side , a technology is devised for increasing the outer diameter of the moving blades on the inlet port side such that the stress occurring in the moving blades on the inlet port side becomes approximately equal to that occurring in the moving blades on the outlet port side . On the other hand, a technology for replacing a material for the moving blades on the inlet port side with a material having high speci fic strength and further increasing the outer diameter of the moving blades on the inlet port side is not disclosed . In recent years , further improvements in exhaust performance of turbo molecular pumps , which are widely used in vacuum pumps , particularly in semiconductor manufacturing devices , have been demanded . However, from a viewpoint of exhaust performance , it can be said that suf ficient performance has not yet been achieved, and there is still room for improvement .

[0005] Accordingly, an obj ect of the present invention is to provide a2023-031-GB 2 turbo molecular pump and a rotating body of a turbo molecular pump that employ a material having high specific strength as a material for moving blades on the inlet port side, thereby enabling further improvement in exhaust performance.[Solution to Problem]

[0006] In order to achieve the above object, a first aspect of the present invention provides a turbo molecular pump including: a rotor shaft; and a rotor blade that is fixed to the rotor shaft, is rotatable together with the rotor shaft, and includes a plurality of stages of blade rows, the turbo molecular pump sucking in and exhausting exhaust gas through rotation of the rotor blade, wherein an outer diameter of a specific blade row, which is constituted of at least one stage among the plurality of stages of blades rows, is formed to be larger than an outer diameter of blade rows other than the specific blade row and is made of a first material, the blade rows other than the specific blade row among the plurality of stages of blade rows are made of a second material, and specific strength of the first material is higher than specific strength of the second material.

[0007] In the above configuration, among the plurality of stages of blade rows, the specific blade row is a blade row located on a suction side for the exhaust gas.

[0008] In the above configuration, among the plurality of stages of blade rows, the specific blade row is a first stage on the suction side for the exhaust gas.

[0009] In the above configuration, the first material is a magnesium alloy, while the second material is an aluminum alloy.

[0010] In order to achieve the above object, a second aspect of the present invention provides a rotating body of a turbo molecular pump including a plurality of stages of blade rows, wherein an outer diameter of a specific blade row, which is constituted of at least one stage among the plurality of stages of blades rows, is formed to be larger than an outer diameter of blade rows other than the specific blade row and is made of a first material, the blade rows other than the specific blade row among the plurality of stages of blade rows are made of a second material, and specific strength of the first material is higher than specific strength of the second material.[Advantageous Effects of Invention]2023-031-GB 3

[0011] According to the present invention, the exhaust performance of a vacuum pump, particularly a turbo molecular pump, can be improved. Note that problems, configurations, and effects other than those described above are clarified in the description of the following embodiment.[Brief Description of Drawings]

[0012] [Fig. 1]Fig. 1 is a vertical cross-sectional view of a turbo molecular pump according to an embodiment of the present invention.[Fig. 2]Fig. 2 is a circuit diagram of the amplifier circuit of the turbo molecular pump shown in Fig. 1.[Fig. 3]Fig. 3 is a time chart showing the control of an amplifier controlling circuit performed when a current command value is greater than a detected value .[Fig. 4]Fig. 4 is a time chart showing the control of the amplifier controlling circuit performed when the current command value is smaller than the detected value.[Fig. 5]Fig. 5 is an explanatory diagram showing the relationship between the specific strength of a magnesium alloy and an aluminum alloy and temperature .[Fig. 6]Fig. 6 is a vertical cross-sectional view of a turbo molecular pump according to a modified example.[Description of Embodiments]

[0013] Hereinafter, an embodiment of a turbo molecular pump according to the present invention will be described with reference to the drawings .

[0014] Fig. 1 is a vertical cross-sectional view of a turbo molecular pump 100 according to the embodiment. As shown in Fig. 1, the turbo molecular pump 100 includes a cylindrical outer cylinder body 127 and an upper outer cylinder body 128 that constitute a casing, and the upper outer cylinder body 128 is integrally coupled to the upper portion of the outer cylinder body 127. The upper outer cylinder body 128 has an2023-031-GB 4 internal space with a diameter larger than that of the outer cylinder body 127 , and an inlet port 101 is formed at the upper end of the upper outer cylinder body 128 . Further, inside the outer cylinder body 127 and the upper outer cylinder body 128 , the turbo molecular pump 100 includes a rotating body 103 ( rotor ) with rotor blades 102 (blade rows 102a, 102b, 102c, 102d, • • • ) formed radially and in multiple stages at its peripheral portion, which serve as turbine blades to suck in and exhaust gas . A rotor shaft 113 is attached at the center of the rotating body 103 and is supported to float and be position-controlled in the air by, for example , a magnetic bearing that performs five-axis control . In this embodiment , the rotating body 103 is constituted by a combination of blade rows , which are made of an aluminum alloy, and blade rows , which are made of a magnesium alloy ( details will be described later ) .

[0015] Note that , in this embodiment , among the blade rows constituting the rotor blades 102 , the speci fic blade rows 102a and 102b at the first and second stages from the top are arranged inside the upper outer cylinder body 128 , while the blade rows 102c, 102d, - - - at the third and subsequent stages are arranged inside the outer cylinder body 127 . The configuration of the rotor blades 102 will be described in detail later .

[0016] Upper radial electromagnets 104 consist of four electromagnets arranged in pairs along X and Y axes . Four upper radial sensors 107 are provided to be in proximity to the upper radial electromagnets 104 and correspond to the respective upper radial electromagnets 104 . Inductance sensors , eddy-current sensors , or the like having a conductive coil are , for example , used as the upper radial sensors 107 . The upper radial sensors 107 detect the position of the rotor shaft 113 on the basis of a change in the inductance of the conductive coil that changes in accordance with the position of the rotor shaft 113 . The upper radial sensors 107 are configured to detect the radial displacement of the rotor shaft 113 , that is , the radial displacement of the rotating body 103 fixed to the rotor shaft 113 and transmit the detected displacement to a controlling device 50 .

[0017] In the controlling device 50 , for example , a compensating circuit having a FID adj usting function generates an excitation control command signal for the upper radial electromagnets 104 on the basis of a position signal detected by the upper radial sensors 107 , and an2023-031-GB 5 ampli fier circuit 150 ( that will be described later ) shown in Fig . 2 controls the excitation of the upper radial electromagnets 104 on the basis of the excitation control command signal . Thus , the upper radial position of the rotor shaft 113 is adj usted .

[0018] The rotor shaft 113 is made of a high permeability material ( such as iron and stainless steel ) or the like , and designed to be sucked by the magnetic forces of the upper radial electromagnets 104 . This adj ustment is separately performed in each of an X-axis direction and a Y-axis direction . Further, lower radial electromagnets 105 and lower radial sensors 108 are arranged like the upper radial electromagnets 104 and the upper radial sensors 107 , and adj ust the lower radial position of the rotor shaft 113 like the upper radial position .

[0019] In addition, axial electromagnets 106A and 106B are arranged, with a disc-shaped metal disc 111 at the lower portion of the rotor shaft 113 held therebetween in a vertical direction . The metal disc 111 is made of a high permeability material such as iron . An axial sensor 109 is provided to detect the axial displacement of the rotor shaft 113 , and the axial sensor 109 is provided to detect an axial position signal of the rotor shaft 113 , configuring such that the axial position signal is transmitted to the controlling device 50 .

[0020] Then, in the controlling device 50 , for example , the compensating circuit having the FID adj usting function generates an excitation control command signal for each of the axial electromagnet 106A and the axial electromagnet 106B on the basis of the axial position signal detected by the axial sensor 109 , and the ampli fier circuit 150 controls the excitation of each of the axial electromagnets 106A and 106B on the basis of these excitation control command signals . Thus , the axial electromagnet 106A sucks the metal disc 111 upward by a magnetic force , and the axial electromagnet 106B sucks the metal disc 111 downward by a magnetic force , so that the axial position of the rotor shaft 113 is adj usted .

[0021] As described above, the controlling device 50 appropriately adj usts a magnetic force applied to the metal disc 111 by the axial electromagnets 106A and 106B, and magnetically floats the rotor shaft 113 in an axial direction and retains the same in a non-contact manner in a space . Note that the ampli fier circuit 150 that controls the excitation of the upper radial electromagnets 104 , the lower radial electromagnets2023-031-GB 6105, and the axial electromagnets 106A and 106B will be described later.

[0022] Meanwhile, a motor 121 includes a plurality of magnetic poles circumferentially arranged to surround the rotor shaft 113. The respective magnetic poles are controlled by the controlling device 50 to rotate and drive the rotor shaft 113 via the electromagnetic force applied between the respective magnetic poles and the rotor shaft 113. Further, a rotating speed sensor not shown such as a hall element, a resolver, and an encoder is incorporated into the motor 121, and the rotating speed of the rotor shaft 113 is detected on the basis of the detection signal of the rotating speed sensor.

[0023] In addition, a phase sensor not shown is attached near, for example, the lower radial sensors 108 and detects the phase of the rotation of the rotor shaft 113. The controlling device 50 detects the positions of the magnetic poles using both the detection signals of the phase sensor and the rotating speed sensor.

[0024] A plurality of stages of stator blades 123 (123a, 123b, 123c,102d, •••) are disposed with a slight gap with respect to the rotor blades 102 (blade rows 102a, 102b, 102c, 102d, •••) . A turbo pump portion is constituted by the plurality of stages of blade rows 102a, 102b, ••• and the plurality of stages of stator blades 123. Each of the blade rows 102a, 102b, 102c, 102d, ••• is formed to be inclined by a prescribed angle from a plane perpendicular to the axial line of the rotor shaft 113 to transfer the molecules of exhaust gas downward by collision. The outer peripheral ends of the stator blades 123 (123a and 123b) at the first and second stages are supported by the inner surface of the upper outer cylinder body 128, while the outer peripheral ends of the stator blades 123 (123c, 102d, •••) at the third and subsequent stages are supported between the stator blade spacers 125, which are stacked in the outer cylinder body 127, in an inserted state. The stator blades 123 (123a, 123b, 123c, 102d, •••) are made of, for example, metal such as aluminum, iron, stainless steel, and copper or metal such as an alloy containing these metal as components.

[0025] Further, the stator blades 123 are similarly formed to be inclined by a prescribed angle from the plane perpendicular to the axial line of the rotor shaft 113. Further, the stator blades 123 (123a and 123b) at the first and second stages are alternately disposed with the internal rotor blades 102 (blade rows 102a and 102b) toward the inside of2023-031-GB 7 the upper outer cylinder body 128 . The stator blades 123 ( 123c, 102d, • • • ) at the third and subsequent stages are alternately disposed with the internal rotor blades 102 ( 102c, 102d, • • • ) toward the inside of the outer cylinder body 127 .

[0026] The stator blade spacers 125 are ring-shaped members and made of metal such as aluminum, iron, stainless steel , and copper, or metal such as an alloy containing these metal as components . The outer cylinder body 127 is fixed with a slight gap on the outer periphery of the stator blade spacers 125 . A base portion 129 is disposed at the bottom of the outer cylinder body 127 . An outlet port 133 is formed on the base portion 129 and communicates with an outside . Exhaust gas trans ferred toward the base portion 129 after entering the inlet port 101 from the side of a chamber (vacuum chamber ) is supplied to the outlet port 133 .

[0027] In addition, a thread spacer 131 that functions as a thread groove pump portion is disposed between the lower portion of the stator blade spacers 125 and the base portion 129 depending on the use of the turbo molecular pump 100 . The thread spacer 131 is a cylindrical member made of metal such as aluminum, copper, stainless steel , iron, and an alloy containing these metal as components , and has a plurality of spiral-shaped thread grooves 131a engraved on its inner peripheral surface . The spiral direction of the thread grooves 131a is a direction where the molecules of exhaust gas are trans ferred to the outlet port 133 when the molecules move in the rotating direction of the rotating body 103 . A cylindrical portion 102n suspends from the lowermost portion of the rotating body 103 following the rotor blades 102 (blade rows 102a, 102b, 102c, 102d, • • • ) . The outer peripheral surface of the cylindrical portion 102n has a cylindrical shape , overhangs toward the inner peripheral surface of the thread spacer 131 , and is positioned with a prescribed gap close to the inner peripheral surface of the thread spacer 131 . The exhaust gas trans ferred to the thread grooves 131a by the rotor blades 102 and the stator blades 123 is supplied to the base portion 129 while being guided by the thread grooves 131a .

[0028] The base portion 129 is a disc-shaped member that constitutes the base portion of the turbo molecular pump 100 and is generally made of metal such as iron, aluminum, and stainless steel . Since the base portion129 serves also as a heat conducting path while physically retaining the turbo molecular pump 100 , metal such as iron, aluminum, and copper having2023-031-GB 8 sti f fness and high heat conductivity is desirably used as such . Further, on the lateral side of the base portion 129 , a hermetic connector 10 is provided . The controlling device 50 is connected via this hermetic connector 10 .

[0029] In this configuration, exhaust gas is sucked from the chamber via the inlet port 101 by the operation of the rotor blades 102 and the stator blades 123 when the rotor blades 102 are rotationally driven by the motor 121 together with the rotor shaft 113 . The rotational speed of the rotor blades 102 is typically 20 , 000 rpm to 90 , 000 rpm, and the peripheral speed at the tip end of the rotor blades 102 reaches 200 m / s to 400 m / s . The exhaust gas sucked via the inlet port 101 is transferred to the base portion 129 after passing through between the rotor blades 102 and the stator blades 123 . At this time , the temperature of the rotor blades 102 increases due to friction heat generated when the exhaust gas contacts the rotor blades 102 , the conduction of heat generated by the motor 121 , or the like . However, the heat is trans ferred to the side of the stator blades 123 through radiation or conduction by the gas molecules or the like of the exhaust gas .

[0030] The stator blade spacers 125 are bonded to each other at an outer peripheral portion and trans fer heat received by the stator blades 123 from the rotor blades 102 , friction heat generated when exhaust gas contacts the stator blades 123 , or the like to the outside .

[0031] Note that the above description assumes that the thread stator 131 is disposed on the outer periphery of the cylindrical portion 102n of the rotating body 103 , and the thread grooves 131a are engraved on the inner peripheral surface of the thread stator 131 . Contrary to this , there may also be cases where thread grooves are engraved on the outer peripheral surface of the cylindrical portion 102n of the rotating body, and a spacer having a cylindrical inner peripheral surface is arranged around the thread grooves .

[0032] Further, depending on the use of the turbo molecular pump 100 , there may also be cases where the surrounding area of an electrical portion including the upper radial electromagnets 104 , the upper radial sensors 107 , the motor 121 , the lower radial electromagnets 105 , the lower radial sensors 108 , the axial electromagnets 106A and 106B, the axial sensor 109 , or the like is covered with a stator column 122 , and the pressure inside the stator column 122 is maintained at a prescribed2023-031-GB 9 level by purge gas in order to prevent gas sucked via the inlet port 101 from entering the electrical portion .

[0033] In this case , a pipe not shown is disposed on the base portion 129 , and purge gas is introduced via this pipe . The introduced purge gas is delivered to the outlet port 133 via the gap between a protecting bearing 120 and the rotor shaft 113 , the gap between the rotor and the stator of the motor 121 , and the gap between the stator column 122 and a cylindrical portion on the inner peripheral side of the rotor blades 102 . Note that as shown in Fig . 1 , the stator column 122 is provided to stand at the central position of the base portion 129 . Further, in this embodiment , the base portion 129 is provided with a water cooling pipe 149 , which serves as a cooling means . By supplying cooling water to the water cooling pipe 149 , the base portion 129 and the stator column 122 are maintained at an appropriate temperature .

[0034] Here , the turbo molecular pump 100 requires control based on the specification of a model and separately-adj usted unique parameters ( for example , various characteristics corresponding to the model ) . In order to store this control parameters , the above turbo molecular pump 100 includes an electronic circuit portion 141 inside its body . The electronic circuit portion 141 includes electronic components such as a semiconductor memory like an EEP-ROM and a semiconductor element for accessing the semiconductor memory, a substrate 143 for mounting these electronic components , or the like . The electronic circuit portion 141 is accommodated at , for example , a portion below a rotating speed sensor not shown near the center of the base portion 129 that constitutes the lower portion of the turbo molecular pump 100 , and is closed by an air-tight bottom lid 145 .

[0035] Meanwhile , in a semiconductor manufacturing process , some process gases introduced into a chamber have the property of becoming solid when their pressure becomes higher than a prescribed value or when their temperature becomes lower than a prescribed value . Inside the turbo molecular pump 100 , the pressure of exhaust gas is the lowest at the inlet port 101 and the highest at the outlet port 133 . When the pressure of process gas becomes higher than a prescribed value or when the temperature of the process gas becomes lower than a prescribed value during the trans fer of the process gas from the inlet port 101 to the outlet port 133 , the process gas becomes solid and adheres to and2023-031-GB 10 accumulates inside the turbo molecular pump 100 .

[0036] For example , when S1C14 is used as process gas in an Al etching device , it appears from a vapor pressure curve that a solid product ( for example , AICI3 ) precipitates and adheres to and accumulates inside the turbo molecular pump 100 under low vacuum conditions ( from 760 torr to 10~2torr ) and at low temperatures ( approximately 20 ° C ) . Therefore , when the precipitate of process gas accumulates inside the turbo molecular pump 100 , the deposited material narrows a pump flow path, causing a reduction in the performance of the turbo molecular pump 100 . Further, the above product is likely to solidi fy at and adhere to a high-pressure region near the outlet port 133 or the thread stator 131 .

[0037] Therefore , in order to solve this problem, a heater not shown or an annular water cooling pipe 149 is conventionally wound on the outer periphery of the base portion 129 or the like , and a temperature sensor ( for example , a thermistor ) not shown is embedded in, for example , the base portion 129 . Then, heating is performed by the heater or cooling control is performed by the water cooling pipe 149 (hereinafter referred to as TMS ( Temperature Management System) ) so that the temperature of the base portion 129 is maintained at a constant high level ( set temperature ) on the basis of a signal from the temperature sensor .

[0038] Next , in regard to the turbo molecular pump 100 thus configured, the ampli fier circuit 150 that controls the excitation of the upper radial electromagnets 104 , the lower radial electromagnets 105 , and the axial electromagnets 106A and 106B will be described . Fig . 2 shows a circuit diagram of this ampli fier circuit 150 .

[0039] In Fig . 2 , an electromagnet coil 151 that constitutes the upper radial electromagnets 104 or the like has one end connected to a positive electrode 171a of a power supply 171 via a transistor 161 , and the other end connected to a negative electrode 171b of the power supply 171 via a current detecting circuit 181 and a transistor 162 . The transistors 161 and 162 are so-called power MOSFETs and have a structure where a diode is connected between the source and the drain .

[0040] On this occasion, a cathode terminal 161a of the diode of the transistor 161 is connected to the positive electrode 171a, and an anode terminal 161b thereof is connected to one end of the electromagnet coil 151 . Further, a cathode terminal 162a of the diode of the transistor 162 is connected to the current detecting circuit 181 , and an anode terminal2023-031-GB 11162b thereof is connected to the negative electrode 171b .

[0041] On the other hand, a cathode terminal 165a of a diode 165 for current regeneration is connected to one end of the electromagnet coil 151 , and an anode terminal 165b thereof is connected to the negative electrode 171b . Further, a cathode terminal 166a of a diode 166 for current regeneration is similarly connected to the positive electrode 171a, and an anode terminal 166b thereof is connected to the other end of the electromagnet coil 151 via the current detecting circuit 181 . The current detecting circuit 181 includes , for example , a hall sensor type current sensor or an electric resistance element .

[0042] The ampli fier circuit 150 thus configured corresponds to one electromagnet . Therefore , in a case where the magnetic bearing performs five-axis control and the total number of the electromagnets 104 , 105 , 106A, and 106B is ten, the same ampli fier circuit 150 is configured for each of the electromagnets , and the ten ampli fier circuits 150 are connected in parallel to the power supply 171 .

[0043] In addition, an ampli fier controlling circuit 191 is constituted by, for example , a digital signal processor portion (hereinafter referred to as a DSP portion) not shown of the controlling device 50 . The ampli fier controlling circuit 191 switches the on / of f of the transistors 161 and 162 .

[0044] The ampli fier controlling circuit 191 compares a current value ( a signal reflecting the current value is referred to as a current detecting signal 191c ) detected by the current detecting circuit 181 with a prescribed current command value . Then, on the basis of a result of the comparison, the ampli fier controlling circuit 191 determines the si ze of a pulse width (pulse width time Tpl or Tp2 ) to be generated within a control cycle Ts that represents one cycle in PWM control . Consequently, the amplifier controlling circuit 191 outputs gate driving signals 191a and 191b having this pulse width to the gate terminals of the transistors 161 and 162 .

[0045] Note that when passing through a resonance point during the accelerating operation of the rotation of the rotating body 103 or when disturbance occurs during an operation at a constant speed, the position of the rotating body 103 is required to be controlled at a high speed and with a great force . Therefore , a voltage of , for example , approximately50 V is used as the power supply 171 so that a rapid increase ( or2023-031-GB 12 decrease ) in a current flowing through the electromagnet coil 151 is enabled . Further, a capacitor is generally connected between the positive electrode 171a and the negative electrode 171b of the power supply 171 to stabili ze the power supply 171 (not shown) .

[0046] In this configuration, a current (hereinafter referred to as an electromagnet current iL ) flowing through the electromagnet coil 151 increases when both the transistors 161 and 162 are turned on, and the electromagnet current iL decreases when both the transistors 161 and 162 are turned of f .

[0047] Further, a so-called flywheel current is maintained when one of the transistors 161 and 162 is turned on and the other thereof is turned of f . Then, the feeding of the flywheel current to the ampli fier circuit 150 as described above leads to a decrease in hysteresis loss in the ampli fier circuit 150 , enabling a reduction in the power consumption of the whole circuit . Further, the control of the transistors 161 and 162 as described above enables a reduction in high- frequency noise such as a higher harmonic wave caused in the turbo molecular pump 100 . In addition, the measurement of the flywheel current with the current detecting circuit 181 enables the detection of the electromagnet current iL flowing through the electromagnet coil 151 .

[0048] That is , when a detected current value is smaller than a current command value , the ampli fier circuit 150 turns on both the transistors 161 and 162 for a period corresponding to the pulse width time Tpl only once in the control cycle Ts ( for example , 100 ps ) as shown in Fig . 3 . Therefore , in the period, the electromagnet current iL increases toward a value iLmax (not shown) of the current capable of flowing through the transistors 161 and 162 from the positive electrode 171a to the negative electrode 171b .

[0049] On the other hand, when the detected current value is greater than the current command value , the ampli fier circuit 150 turns of f both the transistors 161 and 162 for a period corresponding to the pulse width time Tp2 only once in the control cycle Ts as shown in Fig . 4 . Therefore , in the period, the electromagnet current iL decreases toward a value iLmin (not shown) of the current capable of being regenerated through the diodes 165 and 166 from the negative electrode 171b to the positive electrode 171a .

[0050] Then, in both cases , the ampli fier circuit 150 turns on one of2023-031-GB 13 the transistors 161 and 162 after the elapse of the pulse width time Tpl or Tp2. Therefore, the flywheel current is maintained in the amplifier circuit 150 in this period.

[0051] <Conf iguration of Rotor Blades 102>Next, the configuration of the rotor blades 102 (blade rows 102a, 102b, 102c, 102d, •••) will be described in detail.

[0052] In this embodiment, among the rotor blades 102 (blade rows 102a, 102b, 102c, 102d, •••) , the blade rows 102a and 102b at the first and second stages from the top are made of a magnesium alloy, which is a first material, while the remaining blade rows 102c, 102d, ••• at the third and subsequent rows are made of an aluminum alloy, which is a second material. Here, the specific strength of the first material is designed to be higher than that of the second material. The specific strength [MPa / (g / cm3) ] is tensile strength per density (= tensile strength / density ) and serves as an index indicating strength relative to mass .

[0053] Fig. 5 is an explanatory diagram showing the relationship between the specific strength of a magnesium alloy and an aluminum alloy used in this embodiment and temperature. As is clear from Fig. 5, the specific strength of the magnesium alloy (first material) used in this embodiment is designed to be higher than that of the aluminum alloy (second material) over the entire range of the use environment temperature (for example, 0°C to 250°C) of the turbo molecular pump 100.

[0054] Since the specific strength of the magnesium alloy is higher than that of the aluminum alloy as described above, the outer diameter of the blade rows 102a and 102b at the first and second stages, which are made of the magnesium alloy, can be made larger than that of the blade rows 102c, 102d, ••• at the third and subsequent stages, which are made of the aluminum alloy as shown in Fig. 1. As a result, the peripheral speed at the tip end of the blade rows 102a and 102b, which are located on the upstream side of exhaust gas, becomes faster, making it possible to improve exhaust performance. In addition, since the magnesium alloy is a lighter material than the aluminum alloy, the center of gravity of the blade rows 102a and 102b at the first and second stages is less likely to shift even if their outer diameter is increased, making it possible to suppress misalignment of the rotor shaft 113.

[0055] Next, the effects of this embodiment thus configured will be2023-031-GB 14 described .

[0056] In the rotating body 103 of the turbo molecular pump 100 including the rotor blades 102 (blade rows 102a, 102b, 102c, 102d, • • • ) , the specific blade rows 102a and 102b are made of the first material , while the remaining blade rows 102c, 102d, • • • are made of the second material , and the speci fic strength of the first material is higher than that of the second material . Therefore , by increasing the outer diameter of the blade rows 102a and 102b made of the first material , the exhaust performance of the turbo molecular pump 100 can be improved .

[0057] Further, the blade rows 102a and 102b at the first and second stages are made of the magnesium alloy that is the first material , while the blade rows 102c, 102d, • • • at the third and subsequent stages are made of the aluminum alloy that is the second material . Therefore, only by increasing the outer diameter of the rotor blades (blade rows ) 102 on the side of the inlet port 101 , the exhaust performance can be improved . In addition, since the magnesium alloy is a lighter material than the aluminum alloy, the center of gravity of the blade rows 102a and 102b at the first and second stages is less likely to shi ft even i f their outer diameter is increased, making it possible to suppress misalignment of the rotor shaft 113 .

[0058] As described above, according to this embodiment , the rotating body 103 that enables an increase in the outer diameter of the rotor blades (blade rows ) 102 on the side of the inlet port 101 can be reali zed . Further, by incorporating the rotating body 103 into the turbo molecular pump 100 , the exhaust performance of the turbo molecular pump 100 can be improved .

[0059] When the inner diameter of the blade rows 102a and 102b at the first and second stages is not increased to match the outer diameter, and the blade portion is made longer than before , the natural frequency of the blade portion decreases , making resonance more probable . I f the resonance of the blade portion causes a problem, it is advisable to increase the thickness of the blade portion to improve its rigidity .

[0060] Note that the positions or stages of the blade rows made of the first material are not limited to the blade rows 102a and 102b at the first and second stages from the top . However, it is preferable that at least the blade row 102a located at the first stage on the suction side for exhaust gas be made of the first material (magnesium alloy) with high2023-031-GB 15 specific strength.

[0061] (Modified Example)Next, a modified example of the turbo molecular pump 100 will be described.

[0062] Fig. 6 is a vertical cross-sectional view of a turbo molecular pump 200 according to the modified example. Note that in Fig. 6, portions corresponding to Fig. 1 are denoted by the same symbols and their duplicated descriptions will be omitted.

[0063] As shown in Fig. 6, in the turbo molecular pump 200 according to the modified example, annular hollow portions 201 are formed at the central portions (bosses) of blade rows 102a and 102b at the first and second stages, which are made of a magnesium alloy. Other configurations are basically the same as those in the above embodiment.

[0064] According to the turbo molecular pump 200 in the modified example, the same functions and effects as those of the turbo molecular pump 100 in the above embodiment are achieved. Further, since the hollow portions 201 are formed in the blade rows 102a and 102b, which are made of a magnesium alloy, the rotor blades 102 (102a and 102b) can be made lighter .

[0065] Note that the present invention is not limited to the above embodiment, and various modifications are possible without departing from the essence of the present invention. All technical matters included in the technical concept described in the claims are within the scope of the present invention. The above embodiment illustrates a suitable example, but persons skilled in the art can implement various alternative examples, corrected examples, modified examples, combination examples, or improved examples on the basis of the contents disclosed in the specification, all of which fall within the technical scope described in the attached claims.

[0066] For example, the combination of the first material and the second material is not limited to the combination of the magnesium alloy and the aluminum alloy described in the above embodiment. As long as the specific strength of the first material is higher than that of the second material, any combination of materials other than the magnesium alloy and the aluminum alloy can be used. [Reference Signs List]

[0067] 2023-031-GB 16100 , 200 Turbo molecular pump101 Inlet port102 Rotor blade102a, 102b Blade row ( Speci fic blade row) made of first material 102c, 102d, • • • Blade row (Blade row other than speci fic blade row) made of second material103 Rotating body113 Rotor shaft123 Stator blade 127 Outer cylinder body128 Upper outer cylinder133 Outlet port

Claims

2023-031-GB 17Claims

1. A turbo molecular pump comprising: a rotor shaft; and a rotor blade that is fixed to the rotor shaft, is rotatable together with the rotor shaft, and includes a plurality of stages of blade rows, the turbo molecular pump sucking in and exhausting exhaust as through rotation of the rotor blade, wherein an outer diameter of a specific blade row, which is constituted of t least one stage among the plurality of stages of blades rows, is ormed to be larger than an outer diameter of blade rows other than the pecific blade row and is made of a first material, the blade rows other than the specific blade row among the plurality f stages of blade rows are made of a second material, and specific strength of the first material is higher than specific trength of the second material.

2. The turbo molecular pump according to claim 1, wherein among the plurality of stages of blade rows, the specific blade row s a blade row located on a suction side for the exhaust gas.

3. The turbo molecular pump according to claim 2, wherein among the plurality of stages of blade rows, the specific blade row s a first stage on the suction side for the exhaust gas.

4. The turbo molecular pump according to any one of claims 1 to 3, herein the first material is a magnesium alloy, while the second material s an aluminum alloy.

5. A rotating body of a turbo molecular pump including a plurality of tages of blade rows, wherein an outer diameter of a specific blade row, which is constituted of t least one stage among the plurality of stages of blades rows, is ormed to be larger than an outer diameter of blade rows other than the pecific blade row and is made of a first material, the blade rows other than the specific blade row among the plurality2023-031-GB 18 of stages of blade rows are made of a second material, and specific strength of the first material is higher than specific strength of the second material.

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