Foreign matter accumulation sensor and vacuum pump

Abstract

A foreign matter accumulation sensor includes: a stator disc 219 and an electrode 252 that are capable of constituting a gas flow path 227 inside a turbo molecular pump in a non-rotating state; a rotating disc 229 that is opposed to the stator disc 219 and the electrode 252 and is capable of constituting the gas flow path 227 in a rotating state; a first conducting wire 254 connected to the electrode 252; and a second conducting wire 256 connected to the stator disc 219, wherein estimation of an amount of foreign matter accumulation is made possible on a basis of a change in electrostatic capacitance between the stator disc 219, the rotating disc 229, and the electrode 252.

Description

2024-025-GB 1 FOREIGN MATTER ACCUMULATION SENSOR AND VACUUM PUMP [Technical Field]

[0001] The present invention relates, for example, to a foreign matter accumulation sensor capable of detecting an amount of foreign matter accumulation and to a vacuum pump. [Background Art]

[0002] Generally, turbomolecular pumps have been known as a type of vacuum pumps. The turbo molecular pumps are, for example, used for exhausting in manufacturing devices such as semiconductors and flat panels. In the turbo molecular pumps, rotor blades are rotated by energizing a motor inside a pump body to eject gaseous molecules (gas molecules) of gas (process gas) sucked into the pump body, thereby exhausting the gas. Further, some turbo molecular pumps include heaters or cooling pipes to appropriately manage temperatures inside the pumps.

[0003] In vacuum pumps for exhausting in manufacturing devices such as semiconductors and flat panels, reactive products (foreign matter) generated in manufacturing processes of semiconductors or flat panels may accumulate inside, for instance, the vacuum pumps. If a large amount of the foreign matter accumulates, the accumulation may lead to problems such as disruption of gas flow inside a vacuum pump due to the foreign matter or collisions between the foreign matter and a rotating portion. Therefore, in order to enable determination of a timing for maintenance inside the vacuum pump in advance, technologies have been devised to detect the amount of foreign matter accumulation on the basis of changes in electrostatic capacitance.

[0004] In the invention disclosed in PTL 1 (paragraphs

[0035] to

[0039] , Fig. 2, etc.) listed below, changes in electrostatic capacitance caused by deposits accumulating between parallel plate type electrodes are measured. Further, in the invention disclosed in PTL 2 (paragraphs

[0073] and

[0074] , Fig. 7, etc.), changes in electrostatic capacitance caused by deposits on a front surface of a comb-tooth type electrode are measured. [Citation List] [Patent Literature]

[0005] [PTL 1] Japanese Patent Application Laid-open No. 2018-1596322024-025-GB 2 [PTL 2] Japanese Patent Application Laid-open No. 2021-195893 [Summary of Invention] [Technical Problem]

[0006] In the invention disclosed in PTL 1, installation within a narrow gas flow path inside a pump is assumed, leading to problems below. (1) Since there is insufficient installation space, only a small sensor can be installed, resulting in unsatisfactory detection sensitivity. (2) The sensor blocks the gas flow path, adversely affecting exhaust performance.

[0007] Conversely, in the invention disclosed in PTL 2, the sensor is thin and can be installed on the front surface of a gas flow path, preventing the gas flow path from being blocked unlike the invention disclosed in PTL 1. However, there is a problem where while detection is possible when a thickness of deposit is small (thin), as the thickness increases, sensitivity decreases, and detection becomes difficult.

[0008] An object of the present invention is to provide a foreign matter accumulation sensor capable of effectively detecting the amount of foreign matter accumulation in a small space, as well as a vacuum pump. [Solution to Problem]

[0009] In order to achieve the above object, a foreign matter accumulation sensor according to the present invention includes: a first conductive portion and an electrode that are capable of constituting a gas flow path inside a vacuum pump in a non-rotating state; a second conductive portion that is opposed to the first conductive portion and the electrode and is capable of constituting the gas flow path in a rotating state; a first conducting wire connected to the electrode; and a second conducting wire connected to the first conductive portion, wherein estimation of an amount of foreign matter accumulation is made possible on a basis of a change in electrostatic capacitance between the first conductive portion, the second conductive portion, and the electrode. Further, a vacuum pump according to the present invention includes the above foreign matter accumulation sensor. [Advantageous Effects of Invention]2024-025-GB 3

[0010] According to the above invention, a foreign matter accumulation sensor capable of effectively detecting the amount of foreign matter accumulation in a small space, as well as a vacuum pump, can be provided. [Brief Description of Drawings]

[0011] [Fig. 1] Fig. 1 is an explanatory view schematically showing the configurations of a foreign matter accumulation sensor according to a first embodiment of the present invention and a turbo molecular pump. [Fig. 2] Fig. 2 is a circuit diagram of an amplifier circuit. [Fig. 3] Fig. 3 is a time chart showing control performed when a current command value is greater than a detected value. [Fig. 4] Fig. 4 is a time chart showing control performed when the current command value is smaller than the detected value. [Fig. 5] Fig. 5 is a plan view schematically showing the stator disc of a Sigburn type exhaust mechanism portion. [Fig. 6] Fig. 6 is an explanatory view showing the foreign matter accumulation sensor according to the first embodiment in an enlarged manner. [Fig. 7] Fig. 7(a) is an explanatory view showing the theoretical model of the foreign matter accumulation sensor according to the first embodiment, and Fig. 7(b) is a circuit diagram showing an equivalent circuit related to the theoretical model shown in Fig. 7(a). [Fig. 8] Fig. 8 is an explanatory view showing, in order, the state of foreign matter accumulating on the foreign matter accumulation sensor shown in Fig. 7(a). [Fig. 9] Fig. 9 is a graph showing the relationship between deposit thickness and electrostatic capacitance for two types of deposits. [Fig. 10] Fig. 10 is an explanatory view showing the transition of a principle2024-025-GB 4 model related to the foreign matter accumulation sensor of the first embodiment. [Fig. 11] Fig. 11 is an explanatory view schematically showing the configurations of a foreign matter accumulation sensor according to a second embodiment of the present invention and a turbo molecular pump. [Fig. 12] Fig. 12 is an explanatory view showing the foreign matter accumulation sensor according to the second embodiment in an enlarged manner. [Description of Embodiments]

[0012] <Basic Configuration of Turbo Molecular Pump 100 According to Embodiments> Hereinafter, a foreign matter accumulation sensor 250 according to embodiments and a turbo molecular pump 100 including the foreign matter accumulation sensor 250 will be described. Here, the basic configuration of the turbo molecular pump 100 will first be described, and then foreign matter accumulation sensor 250 will be described.

[0013] Fig. 1 shows the turbo molecular pump 100 serving as a vacuum pump according to a first embodiment of the present invention. The turbo molecular pump 100 is designed to be connected to, for example, a vacuum chamber (not shown) of target equipment such as a semiconductor manufacturing device.

[0014] Fig. 1 shows a vertical cross-sectional view of the turbo molecular pump 100. In Fig. 1, the turbo molecular pump 100 has an inlet port 101 at the upper end of a cylindrical outer cylinder 127. Further, inside the outer cylinder 127, the turbo molecular pump 100 includes a rotating body 103 with a plurality of rotor blades 102 (102a, 102b, 102c, etc.) formed radially and in multiple stages at its peripheral portion, the rotor blades 102 serving as turbine blades for sucking and exhausting gas. A rotor shaft 113 is attached at the center of the rotating body 103 and the rotor shaft 113 is supported to float and be position-controlled in the air by, for example, a magnetic bearing that performs five-axis control.

[0015] 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. Inductance2024-025-GB 5 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 200.

[0016] In the controlling device 200, for example, a compensating circuit having a PID adjusting 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 an amplifier 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 adjusted.

[0017] 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 adjustment 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 adjust the lower radial position of the rotor shaft 113 like the upper radial position.

[0018] In addition, axial electromagnets 106A and 106B are arranged, with a disc-shaped metal disc (referred also to as an “armature 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 200.

[0019] Then, in the controlling device 200, for example, the compensating circuit having the PID adjusting function generates an excitation control command signal for each of the axial electromagnet2024-025-GB 6 106A and the axial electromagnet 106B on the basis of the axial position signal detected by the axial sensor 109, and the amplifier 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 adjusted.

[0020] As described above, the controlling device 200 appropriately adjusts 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 amplifier 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 later.

[0021] 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 200 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.

[0022] 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 200 detects the positions of the magnetic poles using both the detection signals of the phase sensor and the rotating speed sensor.

[0023] A plurality of stator blades 123 (123a, 123b, 123c, etc.) are disposed with a slight gap with respect to the rotor blades 102 (102a, 102b, 102c, etc.). Each of the rotor blades 102 (102a, 102b, 102c, etc.) 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.

[0024] Further, the stator blades 123 are also similarly formed to be inclined by a prescribed angle from the plane perpendicular to the axial2024-025-GB 7 line of the rotor shaft 113 and disposed alternately with the stages of the rotor blades 102 toward the inside of the outer cylinder 127. Further, the outer peripheral ends of the stator blades 123 are supported in a state of being fitted and inserted between a plurality of stacked stator blade spacers 125 (125a, 125b, 125c, etc.).

[0025] 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 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 127. An outlet port 133 is formed on the base portion 129 and communicates with an outside. Exhaust gas transferred to 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.

[0026] In addition, depending on the application of the turbo molecular pump 100, a stator disc 219 is disposed between the lower portion of the stator blade spacers 125 and the base portion 129. The stator disc 219 is a disc-shaped member and has a plurality of Sigburn spiral groove portions 229 (Fig. 5) formed on its upper surface (the surface facing a rotating disc 220, which will be described later). The stator disc 219 and the rotating disc 220 (which will be described later) constitute a Sigburn type exhaust mechanism portion 201. The details of the Sigburn type exhaust mechanism portion 201 will be described later.

[0027] 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 portion 129 serves also as a heat conducting path while physically retaining the turbo molecular pump 100, metal such as iron, aluminum, and copper having stiffness and high heat conductivity is desirably used as such.

[0028] In the 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 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 blades2024-025-GB 8 102, the conduction of heat generated by the motor 121, or the like. However, the heat is transferred to the side of the stator blades 123 through radiation or conduction by the gas molecules or the like of the exhaust gas.

[0029] The stator blade spacers 125 are bonded to each other at an outer peripheral portion and transfer 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.

[0030] 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 prescribed level by purge gas in order to prevent gas sucked via the inlet port 101 from entering the electrical portion.

[0031] In this case, a purge gas port (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 a gap 134 between a cylindrical portion on the inner peripheral side of the rotor blades 102 (the lower cylindrical portion 103b of the rotating body) and the stator column 122 or the base portion 129.

[0032] Here, the turbo molecular pump 100 requires control based on the specification of a model and separately-adjusted 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-tight2024-025-GB 9 bottom lid 145.

[0033] 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 transfer of the process gas from the inlet port 101 to the outlet port 133, the process gas becomes solid and adheres to and accumulates inside the turbo molecular pump 100.

[0034] For example, when SiCl4 is used as process gas in an Al etching device, it appears from a vapor pressure curve that a solid product (for example, AlCl3) 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 solidify at and adhere to a high-pressure region near the outlet port 133 or the stator disc 219.

[0035] 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. In this embodiment, the thread stator 131 is heated by a heater (not shown) embedded in the stator disc 219, and the base portion 129 is cooled by the water cooling pipe 149 embedded in the bottom lid 145.

[0036] Next, in regard to the turbo molecular pump 100 thus configured, the amplifier circuit 150 that controls the excitation of the upper radial electromagnets 104, the lower radial electromagnets 105, and2024-025-GB 10 the axial electromagnets 106A and 106B will be described. Fig. 2 shows a circuit diagram of this amplifier circuit.

[0037] 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.

[0038] 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 terminal 162b thereof is connected to the negative electrode 171b.

[0039] 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.

[0040] The amplifier 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 amplifier circuit 150 is configured for each of the electromagnets, and the ten amplifier circuits 150 are connected in parallel to the power supply 171.

[0041] In addition, an amplifier 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 200. The amplifier controlling circuit 191 switches the on / off of the transistors 161 and 162.

[0042] The amplifier controlling circuit 191 compares a current value (a signal reflecting the current value is referred to as a current2024-025-GB 11 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 amplifier controlling circuit 191 determines the size of a pulse width (pulse width time Tp1 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.

[0043] 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 high voltage of, for example, approximately 50 V is used as the power supply 171 so that a rapid increase (or 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 stabilize the power supply 171 (not shown).

[0044] 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 off.

[0045] 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 off. Then, the feeding of the flywheel current to the amplifier circuit 150 as described above leads to a decrease in hysteresis loss in the amplifier 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.

[0046] That is, when a detected current value is smaller than a current command value, the amplifier circuit 150 turns on both the transistors 161 and 162 for a period corresponding to the pulse width2024-025-GB 12 time Tp1 only once in the control cycle Ts (for example, 100 μs) 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.

[0047] On the other hand, when the detected current value is greater than the current command value, the amplifier circuit 150 turns off 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.

[0048] Then, in both cases, the amplifier circuit 150 turns on one of the transistors 161 and 162 after the elapse of the pulse width time Tp1 or Tp2. Therefore, the flywheel current is maintained in the amplifier circuit 150 in this period.

[0049] In the turbo molecular pump 100 having such a basic configuration, an upper side in Fig. 1 (the side of the inlet port 101) serves as a sucking portion connected to the side of target equipment, and a lower side (the side of the base portion 129 where an exhausting port 15 that constitutes the outlet port 133 is provided to protrude to the right in the figure) serves as an exhausting portion connected to an auxiliary pump (back pump) or the like not shown. Further, the turbo molecular pump 100 can be used not only in a vertical attitude in a vertical direction as shown in Fig. 1 but also in an inverted attitude, a horizontal attitude, or an inclined attitude.

[0050] Further, in the turbo molecular pump 100, the above outer cylinder 127 and the base portion 129 are combined together to constitute one case. Note that the outer cylinder 127 and the base portion 129 may collectively be referred to as a “casing,” a “body casing,” or the like below. Further, the outer cylinder 127 or only the base portion 129 alone may also be referred to as a “casing.” The turbo molecular pump 100 is electrically (and structurally) connected to a box-shaped electric case (not shown), and the above controlling device 200 is incorporated into the electric case.

[0051] The internal configuration of the body casing (here, a2024-025-GB 13 combination of the outer cylinder 127 and the base portion 129) of the turbo molecular pump 100 can be divided into a rotation mechanism portion 136 where the rotor shaft 113 or the like is rotated by the motor 121, and an exhaust mechanism portion 137 that is rotationally driven by the rotation mechanism portion 136. Further, it can be considered that the exhaust mechanism portion 137 is divided into a turbo molecular pump mechanism portion 138 that is constituted by the rotor blades 102, the stator blades 123, and the like, and a thread groove pump mechanism portion (Sigburn type exhaust mechanism portion 204) that is constituted by the stator disc 219, the rotating disc 220, and the like.

[0052] Further, the above purge gas (protective gas) is used to protect a bearing portion, the rotor blades 102, or the like, preventing corrosion caused by exhaust gas (process gas) and cooling the rotor blades 102. The supply of the purge gas can be performed by a general method.

[0053] For example, the above purge gas port (not shown) that extends linearly in a radial direction is provided at a prescribed position on the base portion 129 (such as a position 90 degrees or 120 degrees away from the outlet port 133). Then, the purge gas is supplied to the purge gas port (not shown) via a purge gas cylinder (such as an N2 gas cylinder), a flow rate regulating device (valve device), or the like from the outside of the base portion 129.

[0054] The above protecting bearing 120 is referred also to as a “touchdown (T / D) bearing,” a “backup bearing,” or the like. For example, these protecting bearings 120 ensure that, even if troubles in an electric system or troubles such as atmospheric entry occur, the position or attitude of the rotor shaft 113 does significantly change, preventing damage to the rotor blades 102 or their surrounding portions.

[0055] In Fig. 1 showing the structure of the turbo molecular pump 100 or the rotating body 103, hatch markings indicating the cross sections of components are omitted to avoid complicating the drawing.

[0056] <Foreign Matter Accumulation Sensor 250> The turbo molecular pump 100 shown in Fig. 1 is equipped with the foreign matter accumulation sensor 250. In the example shown in Fig. 1, the foreign matter accumulation sensor 250 is provided in the Sigburn type exhaust mechanism portion 201. Hereinafter, the basic configuration of the Sigburn type exhaust mechanism portion 201 will first be2024-025-GB 14 described, and then the foreign matter accumulation sensor 250 will be described.

[0057] <<Sigburn Type Exhaust Mechanism Portion 201>> The Sigburn type exhaust mechanism portion 201 is a Sigburn type exhaust mechanism and is formed to be spatially continuous with the next stage (immediately downstream side) of the turbo molecular pump mechanism portion 138. In the Sigburn type exhaust mechanism portion 201 shown in the example of Fig. 1, gas is transferred in a radial direction with the axial line of the rotor shaft 113 as the reference.

[0058] The Sigburn type exhaust mechanism portion 201 has the stator disc 219 and the rotating disc 220. The rotating disc 220 is integrally formed with the rotating body 103 and is flat in shape. In addition, the rotating disc 220 overhangs in the radial direction of the rotating body 103. In this embodiment, the material for the rotating disc 220 is the same as that for the rotating body 103 and includes, for example, metal such as aluminum, iron, stainless steel, and copper, or metal such as an alloy containing these metal as components.

[0059] The rotating disc 220 rotates in the same direction as the rotor shaft 113 and the rotating body 103 as the rotating body 103 rotates. Further, the rotating disc 220 rotates integrally with the rotor blades 102 (102a, 102b, 102c, etc.).

[0060] The stator disc 219 is assembled integrally with the body casing (a combination of the outer cylinder 127 and the base portion 129). The stator disc 219 is fixed in a state of being held between an annular spacer 225 and an annularly protruding part of the base portion 129. The stator disc 219 has a through-hole 226 (Fig. 5) at its central part, and the stator column 122 described above passes through the through-hole 226. As shown in Fig. 1, the stator disc 219 and the rotating disc 220 are opposed to each other in parallel. As shown in Fig. 6 in an enlarged manner, a gas flow path 227 is formed between the stator disc 219 and the rotating disc 220.

[0061] As the material for the stator disc 219, metal such as aluminum, iron, stainless steel, and copper, or metal such as an alloy containing these metal as components can be employed similar to the rotating disc 220.

[0062] As shown in Figs. 1, 5, and 6, a multiplicity of protruding portions 228 with a rectangular cross-section are formed between the2024-025-GB 15 stator disc 219 and the rotating disc 220. In this embodiment, the protruding portions 228 are integrally formed with the stator disc 219. As schematically shown in Fig. 5, the Sigburn spiral groove portions 229, which serve as spiral groove flow paths, are formed between the adjacent protruding portions 228.

[0063] The Sigburn spiral groove portions 229 are formed in multiple locations in a curved radial shape on the stator disc 219. In addition, the Sigburn spiral groove portions 229 are formed such that the flow paths gradually narrow from the outside (outer peripheral side) to the inside (inner peripheral side) of the stator disc 219 in the radial direction. Further, the gas introduced into the gas flow path 227 is transferred from the outer peripheral side to the inner peripheral side while being compressed, as the rotor shaft 113, the rotor blades 102, and the like rotate.

[0064] The gas transferred to the inner peripheral side passes through the through-hole 226 from each Sigburn spiral groove portion 229. Then, the gas is ejected from the through-hole 226 into an exhaust flow path 260 formed inside the base portion 129 (Fig. 1). The exhaust flow path 260 is spatially continuous with the outside of the turbo molecular pump 100 via the outlet port 133.

[0065] Note that in this embodiment, the protruding portions 228 are formed on the stator disc 219 as described above. However, even without being limited to this, the protruding portions 228 may be formed on the rotating disc 220, and the opposed surface of the stator disc 219, which is opposed to the rotating disc 220, may be formed flat. Further, in this embodiment, there is one set of the stator disc 219 and the rotating disc 220. However, a plurality of sets of the stator discs 219 and the rotating discs 220 may constitute the Sigburn type exhaust mechanism portion 201.

[0066] <<Configuration and Function of Foreign Matter Accumulation Sensor 250>> Next, the configuration and function of the foreign matter accumulation sensor 250 will be described. In the example of the foreign matter accumulation sensor 250 shown in Fig. 1, the stator disc 219 and the rotating disc 220, which face the gas flow path 227, form a part of the components of the foreign matter accumulation sensor 250.

[0067] Fig. 6 shows the foreign matter accumulation sensor 250 in an2024-025-GB 16 enlarged manner, which is enclosed by a rectangular frame indicated by a two-dot chain line in Fig. 1. The foreign matter accumulation sensor 250 has the stator disc 219 (first conductive component), an electrode 252, a first conducting wire 254, the rotating disc 220 (second conductive component), and a second conducting wire 256.

[0068] The stator disc 219 and the rotating disc 220 are made of, for example, metal such as aluminum, or an alloy containing these metal as components. Further, the stator disc 219 and the rotating disc 220 are components (conductive components) having electricity conducting properties.

[0069] The electrode 252 is, for example, formed in the shape of a rectangular flat plate. Various shapes such as a parallelogram, a trapezoid, a triangle, and a circle can, for example, be employed for the shape of the electrode 252. In the example shown in Fig. 5, the electrode 252 is formed in the shape of a circle. The electrode 252 has a thickness t0of, for example, approximately 1 mm. As the material for the electrode, metal such as aluminum, iron, stainless steel, and copper, or an alloy containing these metal as components can, for example, be employed. Further, materials other than these materials may be used as the material for the electrode as long as they have sufficient conductivity.

[0070] The electrode 252 is arranged in a part of a bottom portion 232 of the Sigburn spiral groove portions 229 on the stator disc 219. A concave portion 234 is formed in a part of the bottom portion 232 of the Sigburn spiral groove portions 229, and the electrode 252 is accommodated in the concave portion 234.

[0071] The electrode 252 is installed such that its front surface 262 is on the same plane (flush with) as the bottom portion 232 of the Sigburn spiral groove portions 229. In addition, a gap (air gap) t1with a prescribed interval is interposed between the electrode 252 and the rotating disc 220. Further, the front surface 262 of the electrode 252 and the rotating disc 220 are opposed to each other in parallel and constitute the gas flow path 227.

[0072] As described above, the gap t2is interposed between the stator disc 219 and the rotating disc 220. The gap t2refers to the gap between the bottom portion 232 of the Sigburn spiral groove portions 229 in the stator disc 219 and the rotating disc 220. In the example shown in Fig.2024-025-GB 17 6, the size of the gap t2is the same as that of a gap t1. Further, the size of the gap t2remains constant since the stator disc 219 and the rotating disc 220 face each other in parallel.

[0073] The concave portion 234 at the bottom portion 232 of the Sigburn spiral groove portions 229 is formed in a stepped shape that narrows toward the back side. In the concave portion 234, the first insulating collar 266, which is made of a material (insulating material) having electric insulating properties, is accommodated. The first insulating collar 266 is formed in a cylindrical shape (for example, a circular cylinder shape).

[0074] One end (the upper end in Fig. 6) of the first insulating collar 266 in the axial direction contacts a rear surface 264 of the electrode 252 in such a state as to slightly protrude from the bottom portion 232 of the Sigburn spiral groove portions 229. The multi-end (the lower end in Fig. 6) of the first insulating collar 266 in the axial direction contacts the stator disc 219. The electrode 252 is opposed to the bottom portion 232 of the Sigburn spiral groove portions 229 in parallel in a floating state.

[0075] A gap (air gap) t3with a prescribed interval is interposed between the electrode 252 and the bottom portion 235 of the concave portion 234 (the stator disc 219). In addition, the rear surface 264 of the electrode 252 and the bottom portion 235 of the concave portion 234 constitute the gas flow path 227. Further, the electrode 252 is provided with a plurality of gas passing holes 267, which penetrate in the thickness direction and connect the gas flow path 227 to the gap t3spatially. Note that the symbols “t1” to “t3” corresponding to the gaps t1to t3, respectively, are used not only to denote their meanings but also, where necessary, to express their sizes.

[0076] A shaft portion 268b of a fixing bolt 268 penetrates through the electrode 252 and the first insulating collar 266. The shaft portion 268b of the fixing bolt 268 penetrates through the stator disc 219 in the thickness direction and protrudes from the rear surface 270 (the surface on the side of the outlet port 133) of the stator disc 219.

[0077] On the side of the rear surface 270 of the stator disc 219, a second insulating collar 272, a pressure terminal 274, and a nut 276 are arranged. The shaft portion 268b of the fixing bolt 268 passes through the second insulating collar 272 and the pressure terminal 274.2024-025-GB 18

[0078] The second insulating collar 272 is made of a material (insulating material) having electric insulating properties. One end (the upper end in Fig. 6) of the second insulating collar 272 in the axial direction contacts the rear surface 270 of the stator disc 219. The other end (the lower end in Fig. 6) of the second insulating collar 272 in the axial direction contacts the pressure terminal 274.

[0079] The tip end of the shaft portion 268b of the fixing bolt 268 is threaded into the nut 276. Further, the electrode 252, the first insulating collar 266, the second insulating collar 272, and the pressure terminal 274 are fixed to the stator disc 219, while being held between a head portion 268a of the fixing bolt 268 and the nut 276.

[0080] The first conducting wire 254 is connected to the pressure terminal 274 to enable energization. The first conducting wire 254 is connected to a prescribed conducting pin 278 of a male connector member 280 shown in Fig. 1 to enable energization. The male connector member 280 is attached onto the base portion 129. A female connector member 284 of an electrical cable 282 is connected to the male connector member 280.

[0081] The electrode 252, the fixing bolt 268, and the pressure terminal 274 are connected to the male connector member 280 via the first conducting wire 254 to enable energization. In addition, the electrode 252, the fixing bolt 268, and the pressure terminal 274 are electrically insulated from the stator disc 219 by the first insulating collar 266 and the second insulating collar 272.

[0082] As shown in Fig. 1, a pressure terminal 281 is fixed to the base portion 129, and the second conducting wire 256 is connected to the pressure terminal 281 to enable energization. The second conducting wire 256 is connected to a prescribed conducting pin 279 in the male connector member 280 described above to enable energization.

[0083] A voltage is applied to the electrode 252 via the first conducting wire 254. Further, since the gap t1is formed between the electrode 252 and the rotating disc 220 as described above, the electrode 252 and the rotating disc 220 constitute a capacitor C1as schematically shown in Fig. 7.

[0084] Further, a voltage is applied to the stator disc 219 via the second conducting wire 256. Since the gap t2is formed between the stator disc 219 and the rotating disc 220 as described above, the stator disc 219 and the rotating disc 220 constitute a capacitor C2as shown in Fig.2024-025-GB 19 7.

[0085] In addition, since the gap t3is formed between the electrode 252 and the stator disc 219 as described above, the electrode 252 and the stator disc 219 constitute a capacitor C3as shown in Fig. 7.

[0086] Here, in Fig. 7, a model is shown where the second conducting wire 256 is connected to the stator disc 219. On the other hand, in Figs. 1 and 6, the second conducting wire 256 is connected to the base portion 129, and the base portion 129 contacts the stator disc 219 to enable energization. That is, with respect to the connection of the second conducting wire 256, it can be said that the example of the model shown in Fig. 7 and the example of the embodiment shown in Figs. 1 and 6 are electrically equivalent. Accordingly, unless there are exceptional circumstances, various descriptions will be provided below without distinguishing between the example of the embodiment shown in Figs. 1 and 6 and the example of the model shown in Fig. 7 with respect to the connection of the second conducting wire 256.

[0087] Further, the second conducting wire 256 may be directly connected to a conductive component (such as the stator disc 219) to which the electrode 252 is attached. However, when this conductive component is electrically conducted to a casing (such as the outer cylinder 127 and the base portion 129), or is attached to the casing to enable energization, the second conducting wire 256 may be attached to the outside (atmosphere side) of the casing.

[0088] <<Theoretical Models of Capacitors C1to C3>> Fig. 7(b) shows the theoretical models of the capacitors C1to C3in Fig. 7(a). When a voltage is applied to the capacitors C1to C3, the capacitors C1to C3become charged according to their potential difference and electrostatic capacitances since the gaps t1to t3are formed in the capacitors C1to C3, respectively. The charge is represented by the following equation (1). Q (= CV) (1) C: electrostatic capacitance V: potential difference

[0089] The potential difference V is known. Therefore, by detecting (measuring) the charge Q and performing the calculation (C = Q / V), it is possible to determine the electrostatic capacitance C. In addition, by determining the difference between electrostatic capacitances calculated2024-025-GB 20 at different timings, it is possible to determine the change (ΔC) in the electrostatic capacitance C over the time or the slope of a line representing the change in the electrostatic capacitance C.

[0090] As shown in Fig. 7(b), the capacitor C1(the capacitor between the electrode 252 and the rotating disc 220) and the capacitor C2(the capacitor between the stator disc 219 and the rotating disc 220) are connected in series. The capacitor C3(the capacitor between the electrode 252 and the stator disc 219) is parallel to the capacitors C1and C2.

[0091] A combined electrostatic capacitance Callof the capacitors C1to C3can be represented by the following equation (2). Call= {1 / ((1 / C1) + (1 / C2))} + C3= {C1 / (1 + C1 / C2)} + C3(2) Here, when C2>> C1, Call≈ C1+ C3(3) is established.

[0092] In general, the electrostatic capacitance of a capacitor can be represented by the following equation (4) using the opposed area of a conductor and the distance between conductors. Cn = ε × εr× A / d (4) In this equation (4), the meaning of each symbol is as follows. Cn: electrostatic capacitance ε: dielectric constant in vacuum εr: relative dielectric constant (relative permittivity) of a substance between conductors A: opposed area of a conductor d: distance between conductors

[0093] In this embodiment, the substance between the conductors corresponds to an accumulated foreign material. Further, the distance d between the conductors corresponds to (the sizes) of the gaps t1to t3in the capacitors C1to C3.

[0094] In the capacitor C1, the opposed area A of the conductor corresponds to the area (hereinafter referred to as the “area A1”) of the front surface 262 of the electrode 252. Further, in the capacitor C2, the opposed area A corresponds to the opposed area (hereinafter referred to as the “area A2”) between the stator disc 219 and the rotating disc 220.

[0095] Here, the area of the stator disc 219 is regarded as the total area of the bottom portions 232 of the Sigburn spiral groove portions2024-025-GB 21 229, or the like. However, the combined electrostatic capacitance Call≈ C1+ C3is established when C2>> C1as in equation (3) described above, and the area of the stator disc 219 has little impact on the combined electrostatic capacitance Call. Accordingly, a strict definition of the area of the stator disc 219 may be omitted.

[0096] Further, in the capacitor C3, the opposed area A (hereinafter referred to as the “area A3”) of the conductor corresponds to the area of the portion of the rear surface 264 of the electrode 252 that protrudes outward from the first insulating collar 266 and is opposed to the bottom portion 235 of the concave portion 234.

[0097] The size relationships between the opposed areas A1to A3of the conductors corresponding to the capacitors C1to C3are as follows: A2>> A1, A2>> A3, and A1> A3.

[0098] <<Estimation of Amount of Foreign Matter Accumulation>> Fig. 8 shows the state of foreign matter accumulating on the foreign matter accumulation sensor of this embodiment in order from the top. As shown in the upper view, the gas (indicated by arrow D) flowing through the gas flow path 227 passes through the gap t1between the electrode 252 and the rotating disc 220, the gap t2between the stator disc 219 and the rotating disc 220, and the gap t3between the electrode 252 and the stator disc 219.

[0099] As shown in the middle view, deposit E, which is foreign matter, gradually accumulates on the front surface of the stator disc 219, the front surface 262 of the electrode 252, and the rear surface 264 of the electrode 252. As the thickness (the amount of accumulation) of the deposit E increases, the gap t3(the lower portion of the electrode) between the electrode 252 and the stator disc 219, which is the narrowest gap among the gaps t1to t3, becomes filled with the deposit E. The middle view schematically shows a state where the gap t3between the electrode 252 and the stator disc 219 has become filled with the deposit E, while the other gaps t1and t2remain unfilled. As the accumulation progresses, the electrode 252 becomes entirely filled with the deposit E as shown in the lower view.

[0100] Here, the deposit E also accumulates on tip end surfaces 228a of the protruding portions 228 of the stator disc 219 shown in Fig. 6. Further, the size of the gap (symbol omitted) between the tip end surfaces 228a of the protruding portions 228 and the rotating disc 220 is2024-025-GB 22 set to be larger than the gap t3.

[0101] The size of the gap (symbol omitted) between the tip end surfaces 228a of the protruding portions 228 and the rotating disc 220 is, by simple calculation, equivalent to the value obtained by subtracting the protruding amount of the protruding portions 228 from the gap t2between the stator disc 219 and the rotating disc 220.

[0102] Fig. 9 is an example of a graph showing the relationship between deposit thickness and electrostatic capacitance. The horizontal axis represents the thickness of the deposit E (deposit thickness), while the vertical axis represents the combined electrostatic capacitance Call. As the deposit thickness increases, the combined electrostatic capacitance Callincreases since d (distance between conductors) in equation (4) described above decreases.

[0103] When the deposit thickness further increases and the gap t3between the electrode 252 and the stator disc 219 becomes filled as shown in the middle and lower views of Fig. 8, C3in equation (3) described above becomes saturated and reaches a constant value. Assuming that the value at that time is C3S, the combined electrostatic capacitance Callis represented by the following equation (5). Call≈ C1+ C3S(5)

[0104] Therefore, as shown in Fig. 9, the trend of an increase in the combined electrostatic capacitance Callchanges, the slope of a curve changes, and an inflection point F emerges. That is, as in this embodiment, by setting one gap (here, the gap t3) among the gaps t1to t3to be smaller than the other gaps (here, the gaps t1and t2) so that the gap becomes filled with the deposit E earlier than the other gaps, it is possible to selectively saturate the electrostatic capacitance of the gap t3. As a result, the inflection point F is enabled to emerge in the curve of the combined electrostatic capacitance Call.

[0105] In addition, since the size of the gap t3between the electrode 252 and the stator disc 219 is known, it is possible to estimate that the amount of accumulation of the deposit E at the time when the inflection point F emerges is equivalent to the size of the gap t3.

[0106] Here, in Fig. 9, the inflection point F represents the inflection point corresponding to a certain type of deposit (here, deposit E1), while another inflection point G represents the inflection point corresponding to another type of deposit (here, deposit E2). The2024-025-GB 23 inflection points F and G emerge at the same deposit thickness when the foreign matter accumulation sensor 250 with the same configuration and dimensions is used. However, the rate of change (the slope or gradient of a line) at points other than the inflection point varies depending on the type (component) of the deposit, and the combined electrostatic capacitance Callat the inflection point also varies.

[0107] Assuming that the amount of accumulation of the deposit E is equivalent to the size of the gap t3at the inflection point, the dielectric constant εrof the deposit can be estimated using the combined electrostatic capacitance Callat the inflection point.

[0108] It is possible to estimate that the deposit accumulates inside the capacitor C1with a thickness of t3at the inflection point. Therefore, the electrostatic capacitance of the capacitor C1is regarded as a combination of a capacitor C1afilled with the deposit at the gap t3and a capacitor C1bunfilled with the deposit at the gap t1– t3that are connected in series. The electrostatic capacitance can be represented by the following equations (6) to (8). C1a= ε × εr× A1 / t3(6) C1b= ε × 1 × A1 / (t1– t3) (7) C1= {1 / ((1 / C1a) + (1 / C1b))} (8)

[0109] On the other hand, at the inflection point, the capacitor C3can be represented by the following equation (9). C3S= ε × εr× A3 / t3(9) Using equations (5) to (9) described above, the dielectric constant εrof the deposit can be estimated. Therefore, even if the dielectric constant of the deposit is unknown in advance, the amount of accumulation of the deposit E can be estimated.

[0110] For example, by connecting the foreign matter accumulation sensor 250 to the controlling device 200 (Fig. 1), it is possible to perform various calculations related to the estimation of the amount of foreign matter accumulation as described above in the controlling device 200. The various calculations include calculations based on an expression that includes a conversion factor. The controlling device 200 monitors changes on the basis of the combined electrostatic capacitance Callbefore and after the emergence of the inflection points F and G, and determines that the gap t3has become filled with foreign matter (deposits) when detecting the emergence of the inflection points F and G.2024-025-GB 24

[0110] The controlling device 200 estimates the dielectric constant of the foreign matter on the basis of the trend (such as the slope of the line) of the change in the electrostatic capacitance, using the electrostatic capacitance obtained when the gap t3has become filled with the foreign matter (deposits) (such as the combined electrostatic capacitance obtained when the inflection points F and G have emerged).

[0110] Note that even without being limited to the controlling device 200, it is also possible to perform the various calculations related to the estimation of the amount of foreign matter accumulation using computer equipment (not shown) other than the controlling device 200. The computer equipment may also output the results of the various calculations related to the estimation of the amount of the foreign matter accumulation to the controlling device 200.

[0111] Further, the computer equipment described above can also include inspection terminal equipment and the like carried by maintenance operators. The maintenance operators can include operators for the turbo molecular pump 100, operators for a vacuum exhaust system including the turbo molecular pump 100, and the like. Further, the computer equipment can be considered as a part of the turbo molecular pump 100 or the controlling device 200, regardless of whether the computer equipment performs communication through wired connection or wireless connection.

[0112] <Distinctive Merits of Foreign Matter Accumulation Sensor 250 According to First Embodiment, As Well As Turbo Molecular Pump 100> According to the foreign matter accumulation sensor 250 of the first embodiment described above, as well as the turbo molecular pump 100 (vacuum pump) including the foreign matter accumulation sensor 250, it is possible to form the foreign matter accumulation sensor 250 between the rotating disc 220, which serves as a rotating component, and the stator disc 219, which serves as a non-rotating component (stator component). Therefore, it becomes possible to effectively detect the amount of foreign matter accumulation in a small space. Furthermore, by performing calculations using the detection results of the foreign matter accumulation sensor 250, it becomes possible to estimate the amount of foreign matter accumulation.

[0113] In addition, the foreign matter accumulation sensor 250 can be formed using the rotating component (here, the rotating disc 220), making it possible to increase flexibility in the installation place of the2024-025-GB 25 foreign matter accumulation sensor 250.

[0114] Further, the amount of foreign matter accumulation inside the turbo molecular pump 100 can be estimated, enabling an understanding of the operating state of the pump and making it easier to plan maintenance for the turbo molecular pump 100. For example, the occurrence of an accident where the rotor blades 102 (102a, 102b, 102c, etc.) contact deposits (foreign matter), causing the turbo molecular pump 100 to suddenly stop, can be prevented.

[0115] Further, the gap t3is provided between the electrode 252 and the component (for example, the stator disc 219) on which the electrode 252 is installed, and this gap t3is smaller than the other gaps t1and t2, making it possible for the gap t3to be filled with deposits (foreign matter) first. In addition, the gas passing holes 267 are provided on the electrode 252, making it easier to introduce the gas into the gap t3from the gas flow path 227.

[0116] Further, using the relationship between the deposit thickness and the combined electrostatic capacitance shown in Fig. 9, it is possible to derive the dielectric constants of deposits on the basis of the inflection points (for example, the inflection points F and G) related to the curves of combined electrostatic capacitances. Further, the types of the deposits (for example, the types of gases) can be estimated on the basis of the dielectric constants. In general, the dielectric constants of deposits vary depending on their types or physical properties. However, if the types or physical properties are unknown in advance, they can be estimated using the relationship between the deposit thickness and the combined electrostatic capacitance at the inflection points (for example, the inflection points F and G).

[0117] Further, it is possible to correct a conversion factor (for example, correct 1.0 to 0.5) on the basis of the trend (for example, the slope) of the combined electrostatic capacitance after the inflection points (for example, the inflection points F and G).

[0118] Further, by sufficiently increasing the distance between the first conducting wire 254 and the second conducting wire 256, the parasitic capacitance occurring between the conducting wires can be reduced. Furthermore, it becomes easier to detect an increase in the combined electrostatic capacitance Callas foreign matter (deposits E) accumulates.2024-025-GB 26

[0119] <Principle Model Related to Foreign Matter Accumulation Sensor 250 of First Embodiment> Here, the principle of the foreign matter accumulation sensor 250 of this embodiment will be described with reference to Fig. 10. The four views from the uppermost stage to the lowermost stage in Fig. 10 show the transition of the principle model related to the foreign matter accumulation sensor 250. In Fig. 10, portions corresponding to the configuration of the foreign matter accumulation sensor 250 are labeled with the same symbols for functional purposes even if they have different names.

[0120] In the uppermost view of Fig. 10, a first electrode 252 and a second electrode 253 are simply opposed to each other with a gap. A first conducting wire 254 is connected to the first electrode 252 to enable energization, and a second conducting wire 256 is connected to the second electrode 253 to enable energization. The model shown in the uppermost view of Fig. 10 does not yet include a component that is in a rotating state, and therefore does not have the same configuration as that of the foreign matter accumulation sensor 250 according to the first embodiment.

[0121] In the second-uppermost view of Fig. 10, the first electrode 252 and the second electrode 253 are installed on a first conductive component 219 via insulating bodies 266 and 272, which have electric insulating properties. The first electrode 252 and the second electrode 253 are opposed to a second conductive component 220 via a gap t1(= t2) of the same size. Since the conducting wires 254 and 256 are not connected to the second conductive component 220 to enable energization, the second conductive component 220 is a component (rotating component) capable of rotating (horizontal rotation in the figure).

[0122] The gap t1(= t2) between the first electrode 252 and the second conductive component 220 serves as a gas flow path 227. The first conducting wire 254 is connected to the first electrode 252 to enable energization, and the second conducting wire 256 is connected to the second electrode 253 to enable energization.

[0123] As indicated using the same symbols as those of the foreign matter accumulation sensor 250, the first conductive component 219 corresponds to the stator disc 219, and the second conductive component 220 corresponds to the rotating disc 220. The first electrode 252 corresponds to the electrode 252, and the second electrode 2532024-025-GB 27 corresponds to the portion of the stator disc 219 that is opposed to the rotating disc 220. The first electrode 252 and the second electrode 253 are installed via the insulating bodies 266 and 272, which have electric insulating properties. The first electrode 252 and the second electrode 253 are opposed to the second conductive component 220 via the gap t1(= t2) of the same size.

[0124] On the basis of the principle model described above, it is possible to extract the following invention. A foreign matter accumulation sensor (such as the foreign matter accumulation sensor 250) including: a first conductive portion (such as the first conductive component 219) and an electrode (such as the first electrode 252) that are capable of constituting a gas flow path (such as the gas flow path 227) inside a vacuum pump in a non-rotating state; a second conductive portion (such as the second conductive component 220) that is opposed to the first conductive portion and the electrode and is capable of constituting the gas flow path in a rotating state; a first conducting wire (such as the first conducting wire 254) connected to the electrode; and a second conducting wire (such as the second conducting wire 256) connected to the first conductive portion, wherein estimation of the amount of foreign matter accumulation is made possible on the basis of a change in electrostatic capacitance between the first conductive portion, the second conductive portion, and the electrode.

[0124] Note that, in a strict sense, it is desirable to remove the outer peripheral portion of the insulating body 266 and form the above- described gap t3between the first electrode 252 and the first conductive component 219.

[0125] In the third-uppermost view of Fig. 10, the second electrode 253 shown in the second-uppermost view is integrated with the first conductive component 219. Further, the second conducting wire 256 is connected to the first conductive component 219.

[0126] In the fourth-uppermost view (the lowermost view) of Fig. 10, the gap t3is formed between the first electrode 252 and a bottom portion 235 of a concave portion 234 formed on the first conductive component 219. Further, a plurality of gas passing holes 267 are formed on the2024-025-GB 28 first electrode 252.

[0127] The second-uppermost to fourth-uppermost views of Fig. 10 correspond to the invention of the higher-level concept of the foreign matter accumulation sensor 250 according to the first embodiment, as well as the embodiments of the invention. Further, the second-uppermost to fourth-uppermost views of Fig. 9 approach the foreign matter accumulation sensor 250 according to the first embodiment in ascending order. However, the example in the fourth-uppermost view shows the principle model that is the closest to the foreign matter accumulation sensor 250 according to the first embodiment.

[0128] <Second Embodiment> Next, a foreign matter accumulation sensor 450 according to a second embodiment of the present invention, as well as a turbo molecular pump 300, will be described with reference to Fig. 11. Note that the same portions as those of the first embodiment will be denoted by the same symbols, and their descriptions will be omitted as needed.

[0129] <<Holweck Type Exhaust Mechanism Portion 401>> Fig. 11 shows the foreign matter accumulation sensor 450 according to the second embodiment of the present invention, as well as the turbo molecular pump 300. In the example shown in Fig. 9, the foreign matter accumulation sensor 450 is provided in a Holweck type exhaust mechanism portion 401. Hereinafter, the basic configuration of the Holweck type exhaust mechanism portion 401 will first be described, and then the foreign matter accumulation sensor 450 will be described.

[0130] <<Holweck Type Exhaust Mechanism Portion 401>> The Holweck type exhaust mechanism portion 401 is a Holweck type exhaust mechanism and is formed to be spatially continuous with the next stage (immediately downstream side) of a turbo molecular pump mechanism portion 138. In the Holweck type exhaust mechanism portion 401 shown in the example of Fig. 11, gas is transferred in an axial direction with the axial line of a rotor shaft 113 as the reference.

[0131] The Holweck type exhaust mechanism portion 401 shown in the example of Fig. 11 has a thread spacer 131 and a lower cylindrical portion 103b of a rotating body. With regard to the thread spacer 131, the thread spacer 131 is disposed between the lower portion of stator blade spacers 125 and a base portion 129. The thread spacer 131 is a cylindrical member made of metal such as aluminum, copper, stainless2024-025-GB 29 steel, iron, or an alloy containing these metal as components and has a plurality of spiral 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 transferred to an outlet port 133 when the molecules move in the rotating direction of the rotating body 103.

[0132] The lower cylindrical portion 103b of the rotating body suspends from the lower portion of a main rotating body 103a where rotor blades 102 (102a, 102b, 102c, etc.) of the rotating body 103 are formed. The outer peripheral surface of the lower cylindrical portion 103b of the rotating body 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. In this embodiment, the material for the lower cylindrical portion 103b of the rotating body is the same as that for the rotating body 103 and includes, for example, metal such as aluminum, iron, stainless steel, and copper, or metal such as an alloy containing these metal as components. The exhaust gas transferred to the thread grooves 131a by the rotor blades 102 and stator blades 123 is supplied to the base portion 129 while being guided by the thread grooves 131a.

[0133] Note that the above description assumes that the thread spacer 131 is disposed on the outer periphery of the lower cylindrical portion 103b of the rotating body 103, and the thread grooves 131a are engraved on the inner peripheral surface of the thread spacer 131. Contrary to this, there may also be cases where thread grooves are engraved on the outer peripheral surface of the lower cylindrical portion 103b of the rotating body, and a spacer having a cylindrical inner peripheral surface is arranged around the thread grooves.

[0134] <<Configuration and Function of Foreign Matter Accumulation Sensor 450>> Next, the configuration and function of the foreign matter accumulation sensor 450 will be described. In the foreign matter accumulation sensor 450 shown in the example of Fig. 11, the thread spacer 131 and the lower cylindrical portion 103b of the rotating body form parts of the components of the foreign matter accumulation sensor 450.

[0135] Fig. 12 shows the foreign matter accumulation sensor 450 in an2024-025-GB 30 enlarged manner, which is enclosed by a rectangular frame indicated by a two-dot chain line in Fig. 11. The foreign matter accumulation sensor 450 has the thread spacer 131 (first conductive component), an electrode 252, a first conducting wire 254, the lower cylindrical portion 103b of the rotating body (second conductive component), and a second conducting wire 256.

[0136] The foreign matter accumulation sensor 450 according to the second embodiment differs significantly from the foreign matter accumulation sensor 250 (Figs. 1 and 6) according to the first embodiment in that the stator disc 219 and the rotating disc 220 of the first embodiment are replaced with the thread spacer 131 and the lower cylindrical portion 103b of the rotating body, respectively, and that the axial direction of the electrode 252, a first insulating collar 266, a fixing bolt 268, a second insulating collar 272, a pressure terminal 274, and a nut 276 is oriented toward the radial direction of the rotating body 103 and the like.

[0136] Further, in the foreign matter accumulation sensor 450 according to the second embodiment, an electrode retaining body 452 is partially mounted on the thread spacer 131. Furthermore, the electrode 252, the first insulating collar 266, the fixing bolt 268, the second insulating collar 272, and the pressure terminal 274 are attached to the electrode retaining body 452. The fixing bolt 268 penetrates through the electrode retaining body 452 in the thickness direction. The electrode retaining body 452 can be made of metal such as aluminum, copper, stainless steel, iron, or an alloy containing these metal as components.

[0137] In the foreign matter accumulation sensor 450 according to the second embodiment, the electrode 252 and the lower cylindrical portion 103b of the rotating body constitute a capacitor C1, the thread spacer 131 and the lower cylindrical portion 103b of the rotating body constitute a capacitor C2, and the electrode 252 and the thread spacer 131 constitute a capacitor C3.

[0137] In the example shown in Fig. 12, a gap t2is not uniform since the bottom portion of the thread grooves 131a of the thread spacer 131 is inclined relative to the rotating shaft. Therefore, for the gap t2, it is possible to adopt the average value from one end (the lower end in Figs. 11 and 12) to the multi-end (the upper end in Fig. 11) of the thread spacer 131 as the value of the gap t2. However, the combined2024-025-GB 31 electrostatic capacitance Call≈ C1+ C3is established when C2>> C1as in equation (3) described above, and the area of the thread spacer 131 has little impact on the combined electrostatic capacitance Call. Accordingly, a strict definition of the area of the thread spacer 131 may be omitted.

[0138] The combined electrostatic capacitance of the capacitors C1to C3can be calculated in the same manner as the first embodiment. Further, it is possible to estimate the amount of foreign matter (deposits) accumulation by applying the same calculations as those of the invention according to the first embodiment.

[0139] Note that by rotating the principle model of the first embodiment shown in Fig. 10 by 90 degrees to the right, it is possible to use the principle model as the principle model of the foreign matter accumulation sensor 450 according to the second embodiment.

[0140] <Invention Extractable from Embodiments> It is possible to extract the following invention from the respective embodiments described above. (1) A foreign matter accumulation sensor including: a first conductive portion (such as the stator disc (first conductive component) 219 and the thread spacer 131) and an electrode (such as the electrode (first electrode) 252) that are capable of constituting a gas flow path (such as the gas flow path 227) inside a vacuum pump (such as turbo molecular pumps 100 and 300) in a non-rotating state; a second conductive portion (such as the rotating disc (second conductive component) 229 and the lower cylindrical portion 103b of the rotating body) that is opposed to the first conductive portion and the electrode and is capable of constituting the gas flow path in a rotating state; a first conducting wire (such as the first conducting wire 254) connected to the electrode; and a second conducting wire (such as the second conducting wire 256) connected to the first conductive portion, wherein estimation of an amount of foreign matter (such as the deposits E, E1, and E2) accumulation is made possible on a basis of a change in electrostatic capacitance between the first conductive portion, the second conductive portion, and the electrode. (2) The foreign matter accumulation sensor according to (1), wherein2024-025-GB 32 an opposed area between the electrode and the second conductive portion is smaller than an opposed area between the first conductive portion and the second conductive portion, and the electrode is retained by the first conductive portion via an insulating material (such as the first insulating collar (insulating body) 266). (3) The foreign matter accumulation sensor according to (1), wherein at least one of the first conductive portion and the second conductive portion is a disc-shaped component (such as the stator disc (first conductive component) 219 and the rotating disc (second conductive component) 220) constituting a Sigburn type thread groove pump (such as the Sigburn type exhaust mechanism portion 201). (4) The foreign matter accumulation sensor according to (1), wherein at least one of the first conductive portion and the second conductive portion is a cylindrical component (such as the thread spacer 131 and the lower cylindrical portion 103b of the rotating body) constituting a Holweck type thread groove pump (such as the Holweck type exhaust mechanism portion 401). (5) The foreign matter accumulation sensor according to (2), wherein at least parts of opposed surfaces of the electrode and the first conductive portion are partially opposed to each other, with the insulating material being not interposed therebetween, and are in communication with the gas flow path. (6) The foreign matter accumulation sensor according to (5), wherein the electrode has a communication port (such as the gas passing hole 267) that connects a space (such as the space of the gap t3) between the electrode and the first conductive portion to a space (such as the space of the gap t2) between the electrode and the second conductive portion. (7) The foreign matter accumulation sensor according to (5), including: a computation unit (such as the controlling device 200 and other computer equipment) that performs calculation to estimate the amount of the foreign matter accumulation, wherein the computation unit uses an expression to calculate the change in the electrostatic capacitance, and2024-025-GB 33 with the expression including a conversion factor, determines whether a space between the electrode and the first conductive portion becomes filled with foreign matter (such as whether the inflection points F and G emerge) on a basis of the change in the electrostatic capacitance, and moreover estimates a dielectric constant of the foreign matter from the electrostatic capacitance when the space between the electrode and the first conductive portion becomes filled with the foreign matter on a basis of a trend of the change in the electrostatic capacitance. (8) The foreign matter accumulation sensor according to (7), wherein the conversion factor is corrected on a basis of the change in the electrostatic capacitance after determining that the space between the electrode and the first conductive portion becomes filled with the foreign matter. (9) A vacuum pump (such as the turbo molecular pumps 100 and 300) including: the foreign matter accumulation sensor according to any one of (1) to (7).

[0141] <Other> Note that present invention is not limited to the respective embodiments described above but various modifications or combinations of the embodiments are possible without departing from its gist.

[0142] For example, the conductive portions of the electrode 252, the stator disc 219, and the rotating disc 220 according to the first embodiment, or the conductive portions of the electrode 252, the thread spacer 131, and the lower cylindrical portion 103b of the rotating body according to the second embodiment may be formed as thin films (may be thinned).

[0142] Further, as shown in the second-uppermost view of Fig. 10, the second electrode 253 may be installed, and the foreign matter accumulation sensors 250 and 450 may be configured using the second electrode 253 as the first conductive portion. [Reference Signs List]

[0143] 100, 300 Turbo molecular pump 102 Rotor blade 103 Rotating body2024-025-GB 34 103a Main rotating body 103b Lower cylindrical portion of rotating body 113 Rotor shaft 121 Motor 122 Stator column 123 Stator blade 125 Stator blade spacer 127 Outer cylinder 129 Base portion 131 Thread spacer 131a Thread groove 133 Outlet port 136 Rotation mechanism portion 137 Exhaust mechanism portion 138 Turbo molecular pump mechanism portion 200 Controlling device 201 Sigburn type exhaust mechanism portion 219 Stator disc (First conductive component) 220 Rotating disc (Second conductive component) 227 Gas flow path 228 Protruding portion 229 Sigburn spiral groove portion 232 Bottom portion (Bottom portion of Sigburn spiral groove portion) 234 Concave portion 235 Bottom portion (Bottom portion of concave portion) 250, 450 Foreign matter accumulation sensor 252 Electrode (First electrode) 253 Second electrode 254 First conducting wire 256 Second conducting wire 266 First insulating collar 267 Gas passing hole 272 Second insulating collar 274 Pressure terminal 276 Nut 401 Holweck type exhaust mechanism portion 452 Electrode retaining body2024-025-GB 35 C1to C3Capacitor t1to t3Gap

Claims

2024-025-GB 36 Claims

1. A foreign matter accumulation sensor comprising: a first conductive portion and an electrode that are capable of constituting a gas flow path inside a vacuum pump in a non-rotating state; a second conductive portion that is opposed to the first conductive ortion and the electrode and is capable of constituting the gas flow ath in a rotating state; a first conducting wire connected to the electrode; and a second conducting wire connected to the first conductive portion, herein estimation of an amount of foreign matter accumulation is made ossible on a basis of a change in electrostatic capacitance between the irst conductive portion, the second conductive portion, and the lectrode. Claim 2] The foreign matter accumulation sensor according to claim 1, wherein an opposed area between the electrode and the second conductive ortion is smaller than an opposed area between the first conductive ortion and the second conductive portion, and the electrode is retained by the first conductive portion via an nsulating material. Claim 3] The foreign matter accumulation sensor according to claim 1, wherein at least one of the first conductive portion and the second onductive portion is a disc-shaped component constituting a Sigburn type hread groove pump. Claim 4] The foreign matter accumulation sensor according to claim 1, wherein at least one of the first conductive portion and the second onductive portion is a cylindrical component constituting a Holweck type hread groove pump. Claim 5] The foreign matter accumulation sensor according to claim 2, wherein at least parts of opposed surfaces of the electrode and the first2024-025-GB 37 conductive portion are partially opposed to each other, with the insulating material not being interposed therebetween, and are in communication with the gas flow path.

6. The foreign matter accumulation sensor according to claim 5, wherein the electrode has a communication port that connects a space between the electrode and the first conductive portion to a space between the electrode and the second conductive portion. Claim 7] The foreign matter accumulation sensor according to claim 5, omprising: a computation unit that performs calculation to estimate the amount f the foreign matter accumulation, wherein the computation unit uses an expression to calculate the change in the electrostatic apacitance, and with the expression including a conversion factor, determines whether a space between the electrode and the first onductive portion becomes filled with foreign matter on a basis of the hange in the electrostatic capacitance, and moreover estimates a dielectric constant of the foreign matter from the lectrostatic capacitance when the space between the electrode and the irst conductive portion becomes filled with the foreign matter on a asis of a trend of the change in the electrostatic capacitance. Claim 8] The foreign matter accumulation sensor according to claim 7, wherein the conversion factor is corrected on a basis of the change in the lectrostatic capacitance after determining that the space between the lectrode and the first conductive portion becomes filled with the oreign matter. Claim 9] A vacuum pump comprising: the foreign matter accumulation sensor according to any one of laims 1 to 8.

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