JP5541464B2 - Turbo molecular pump - Google Patents

Description

  The present invention relates to a structure of a rotor disk of a turbo molecular pump used for evacuation and a peripheral structure thereof.

  In a vacuum apparatus, a vacuum state is formed by sucking the inside of a vacuum container or the like with a suction mechanism such as a turbo molecular pump. In general, a turbo molecular pump includes a pump unit having a stator and a rotor, and the rotor is rotated by driving a power source of a motor to suck and exhaust the inside of the vacuum vessel. In many turbo molecular pumps, the rotating shaft of the rotor is supported without contact with the stator by magnetic levitation. In this support by magnetic levitation, the rotating shaft is supported in a non-contact manner by a magnetic bearing, and a position sensor and an electromagnet for the magnetic bearing are installed between the casing and the rotating shaft. In the radial direction of the rotation shaft, position sensors are arranged to face each other across the rotation shaft. The radial bearing electromagnet is controlled based on position information detected by the position sensor, and rotatably supports the rotor in a radial direction without contact.

  Further, a thrust target is installed at the lower end of the rotating shaft in the thrust direction of the rotating shaft, and a position sensor is arranged facing the thrust target. A rotor disk is fixed to the thrust target, and a thrust bearing electromagnet is installed with the rotor disk sandwiched in the thrust direction. The radial bearing electromagnet is controlled based on the position information in the thrust direction detected by the position sensor, and rotatably supports the rotor in the thrust direction without contact.

  In order to stably control the magnetic bearing, the feedback loop control circuit in which the feedback loop is configured can obtain a desired frequency response by providing a PID circuit, a phase compensation circuit, and a filter for stabilization. (For example, refer to Patent Document 1).

JP2007-270829

  The frequency response described above is designed to stabilize the response based on the natural frequency of the rotating body ("Rotating body" is defined as a combination of a rotor, a rotating shaft, and a rotor disk. The same applies hereinafter). Has been. However, this natural frequency varies from one aircraft to another due to a variation of 4M (Machine, Man, Method, Material) during mass production of the aircraft. Further, if the natural frequency of the fuselage fluctuates and the natural frequency exists in the unstable region of the filter inside the control circuit, the shaft vibration may be vibrated and oscillate. Therefore, in order to stabilize the shaft vibration, reducing the fluctuation of the natural frequency of the rotating body due to the variation of 4M is a problem in mass production.

  A first invention made to solve the above problems includes a magnetic bearing controlled by a feedback loop, a rotating shaft fixed to a rotating body and held via the magnetic bearing, and a rotor fixed to the rotating shaft. A turbo molecular pump comprising a disk, wherein a gap is formed in a central portion of a contact surface between the rotating shaft and the rotor disk. Conventionally, the bolt fastening surface between the rotor disk and the rotating shaft has a flat structure, but in this case, the fastening surface is unstable due to the influence of the processing accuracy of the fastening surface. Therefore, by forming a gap at the center of the contact surface between the rotating shaft and the rotor disk, the state of the fastening surface can be stabilized and the natural frequency can be stabilized. Although the natural frequency of the rotating body depends on the rigidity of the fastening portion, the natural frequency of the rotating body inevitably becomes stable if the state of the disk fastening surface is stabilized and the rigidity of the fastening portion is stabilized.

  According to a second invention for solving the above-mentioned problems, in the first invention, an outer periphery of the gap formed on a contact surface between the rotating shaft and the rotor disk is connected to the rotating shaft and the rotor disk. It is a turbo molecular pump characterized by overlapping with a through hole of a fastening member for fastening. When the fastening member of the rotary shaft 9 and the rotor disk is fastened so as to penetrate both the part where the gap between the rotary shaft and the rotor disk is formed and the part where the gap is not formed, the area of the gap part is reduced. Since the rotation shaft and the rotor disk can be fastened by the fastening member at the portion where the gap is not formed while making it as large as possible, the state of the fastening surface can be further stabilized.

  According to a third aspect of the present invention, there is provided a method of manufacturing a turbo molecular pump including a natural frequency adjusting step of adjusting a natural frequency of a rotating body by changing a mass of the rotating body. The number adjusting step is a method of manufacturing a turbo molecular pump, wherein the rotor disk used for the magnetic bearing for holding the rotating body is cut in a thrust direction or a radial direction. Since the rotor disk has a cylindrical shape, the thrust direction or radial direction of the rotor disk can be cut with a lathe, etc., making it possible to easily adjust the fine mass of the rotor disk, and the natural vibration of the rotor The number can be efficiently stabilized.

  A fourth invention made to solve the above problems is the balance adjustment in the third invention, wherein the balance of the rotating body is adjusted by changing the mass of the rotating body in the same step as the natural frequency adjusting step. A process for producing a turbomolecular pump, characterized in that a process is performed. In the manufacturing process of the turbo molecular pump, the balance adjustment process is performed in order to correct the unbalance generated in the rotating body. Therefore, if the natural frequency adjustment step of the rotating body is performed together with the balance adjustment step, the turbo molecular pump can be efficiently manufactured.

  A fifth invention made to solve the above problems is the magnetic bearing for the magnetic bearing according to the third or fourth invention, wherein the rotor disk is sandwiched when the rotor disk is cut in a thrust direction. The gap generated between the electromagnet and the rotor disk has a gap adjustment step of adjusting the gap by inserting a thickness adjusting member between the upper side and the lower side of the magnetic bearing. It is a manufacturing method of a turbo molecular pump. When the rotor balance adjustment process and the natural frequency adjustment process are performed by cutting the rotor disk in the thrust direction, the gap between the electromagnet for the magnetic bearing installed so as to sandwich the rotor disk and the rotor disk widens. Since the attractive force of the magnetic bearing is reduced, the gap may be adjusted by inserting a thickness adjusting member between the upper side and the lower side of the magnetic bearing. If it does so, while being able to stabilize the natural frequency of a rotary body, the attraction force of a timing bearing can also be stabilized easily.

  A sixth invention made to solve the above problem is a turbo molecular pump having a magnetic bearing controlled by a feedback loop. In the turbo molecular pump, the thickness of the central portion of the rotor disk used in the magnetic bearing is the thickness of the outer peripheral portion. The turbo molecular pump is characterized in that a thicker portion is provided on the rotor disk. The rotating body vibration modes are primary, secondary, and so on. However, in designing the control circuit parameters, it is desirable that the natural frequency intervals in each mode be as far apart as possible. In order to make this possible, the thickness of the central part of the rotor disk is made thicker than the thickness of the outer peripheral part, and the weight of the disk is reduced while maintaining the rigidity of the fastening part between the rotating shaft and the rotor disk. it can. As a result, it is possible to separate the natural frequency intervals of the respective rotating body vibration modes, and it is possible to obtain stable rotation of the rotating body over a wide frequency range.

  A seventh invention made to solve the above-mentioned problems is that, in the sixth invention, the outer shape and height of the thick portion are the same as those of the magnetic bearing when the rotor disk is installed on the magnetic bearing. It is a turbo molecular pump characterized by having a size or height that can be accommodated in a space formed inside. When the rotor disk is provided with a thick portion, the gap between the electromagnet for the magnetic bearing and the rotor disk may widen by the thickness, but according to the present invention, the gap is widened. It is possible to prevent the attraction force of the magnetic bearing from being lowered.

  According to the first invention, since the natural frequency of the rotating body is stabilized, feedback control can be performed in a stable region, and oscillation of shaft vibration can be prevented. Further, according to the second invention, since the natural frequency of the rotating body is more stable, more stable feedback control is possible.

  According to the third invention, the natural frequency can be adjusted efficiently by cutting the rotor disk, so that the adjustment time can be shortened and the cost can be reduced, and the natural frequency is adjusted precisely. Therefore, stable feedback control is possible. Further, according to the fourth invention, the turbo molecular pump in which the natural frequency of the rotating body is adjusted can be efficiently manufactured, so that the adjustment time can be shortened and the cost can be reduced. And according to 5th invention, the gap between the electromagnet for magnetic bearings and the rotor disk which spread by cutting a rotor disk in the thrust direction in 3rd or 4th invention can be adjusted easily. Therefore, even if the rotor disk is cut in order to stabilize the natural frequency, the attractive force of the magnetic bearing is not reduced.

  According to the sixth aspect of the invention, since feedback control can be performed in a stable region over a wide frequency range, oscillation of shaft vibration can be prevented. Further, according to the seventh aspect, it is possible to prevent the oscillation of the shaft vibration and the decrease in the attractive force of the magnetic bearing.

  As described above, according to the present invention, it is possible to reduce the occurrence of unstable vibration of the rotating body caused by 4M variation in the production process. As a result, it is possible to contribute to yield improvement at the production site.

It is a block diagram which shows schematic structure of a turbo-molecular pump. It is a schematic diagram of the pump unit of a turbo molecular pump. It is the schematic of the feedback loop used for control of a magnetic bearing. It is a figure which shows the fastening part structure of the rotor disk of this invention, and a rotary body. It is a figure which shows the modification of the fastening part structure of the rotor disk of this invention, and a rotary body. It is a structural diagram of a rotor disk cut in the radial direction of the present invention. It is a structural diagram of a rotor disk cut in the thrust direction of the present invention. It is a structural diagram of the thrust direction magnetic bearing part of this invention. It is a structural diagram of a rotor disk provided with a thick structure of the present invention. FIG. 6 is a structural diagram of a modified example of a rotor disk provided with a thick structure according to the present invention. 1 is a structural diagram of a magnetic bearing provided with a rotor disk provided with a thick structure according to the present invention. It is an enlarged view of the fastening part structure of the rotor disk of this invention, and a rotary body.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Pump main body 2 Power supply device 3 Rotor 4 Magnetic bearing 5 Motor 6 Motor control part 7 Bearing control part 8 Stator 9 Rotating shaft 10 Radial bearing electromagnet 11 Thrust bearing electromagnet 12 Radial position sensor 13 Thrust position sensor 14 Rotor disk 15 Clearance 16 Bolt 17 Rotor disc outer peripheral portion 18 Rotor disc thickness 19A, 19B Thrust magnetic bearing 20 Thickness adjusting member 21 Thick portion 22 Projection 23 Internal space of thrust magnetic bearing

BEST MODE FOR CARRYING OUT THE INVENTION

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. FIG. 1 is a diagram showing an embodiment of a rotary turbo molecular pump according to the present invention, and is a block diagram showing a schematic configuration of a magnetic bearing turbo molecular pump in which a DC brushless motor device is incorporated. The turbo molecular pump includes a pump body 1 and a power supply device 2. In the example shown in FIG. 1, the pump main body 1 and the power supply device 2 are configured to be connected by a cable. However, the pump main body 1 and the power supply device 2 may be configured integrally. The pump body 1 is provided with a rotor 3 on which rotary blades are formed. The rotor 3 is supported in a non-contact manner by a magnetic bearing 4 and is driven to rotate by a motor 5. A DC brushless motor is used for the motor 5. On the other hand, the power supply device 2 includes a motor control unit 6 that drives the motor 3 and a bearing control unit 7 that controls the excitation current supplied to the magnetic bearing 4.

  FIG. 2 is a view for explaining the outline of the pump unit of the turbo molecular pump of the present invention. The pump unit 1 includes a rotor 3 that is motor-driven in a casing. The rotor 3 includes rotor blades, and rotates at a high speed with respect to the stator 8 provided on the casing side, thereby sucking from the intake port and exhausting from the exhaust port and connected to the intake port (not shown). The gas molecules inside are exhausted.

  The rotor 3 is rotationally driven by a motor 5 via a rotary shaft 9 fixed coaxially with the rotor 3. The motor 5 includes a magnetic pole provided on the rotary shaft 9 and a coil (not shown) provided on the casing side. The rotating shaft 9 is supported in a non-contact manner by magnetic levitation by the radial bearing electromagnet 10 and the thrust bearing electromagnet 11, and the radial position sensor 12 and the thrust position sensor 13.

  The radial magnetic bearing (XY axial direction bearing) has a radial bearing electromagnet 10 disposed opposite to the rotary shaft 9 and a radial position sensor 12 that detects displacement in the radial direction of the rotary shaft 9. By controlling the current supplied to the radial bearing electromagnet 10 based on the position displacement detected by the sensor 12, the position of the rotary shaft 9 is controlled to be a predetermined position in the radial direction. In FIG. 2, two sets of radial bearings are provided above and below the motor 5.

  The thrust bearing (Z-axis direction bearing) includes a rotor disk 14 provided coaxially with the rotary shaft 9, a thrust bearing electromagnet 11 provided above and below the rotor disk 14, and displacement of the rotary shaft 9 in the thrust direction. The thrust position sensor 13 is detected, and the current supplied to the thrust bearing electromagnet 12 is controlled based on the position displacement detected by the thrust position sensor 13 so that the rotating shaft 9 is at a predetermined position in the thrust direction. Position control.

  FIG. 3 is a schematic diagram of a feedback loop used for controlling the magnetic bearing. In this control circuit, a desired frequency response can be obtained by providing a PID circuit, a phase compensation circuit, and a filter for stabilization. The electromagnetic current controlled by the bearing control unit 7 is input to the excitation amplifier 15 and output to the electromagnets 10 and 11. This is detected by the sensors 12 and 13, and feedback control is performed.

  The displacement signal detected by the radial position sensor 12 is converted into a desired signal through the bearing control unit 7, and the signal is input to the excitation amplifier 15. Based on the signal, the excitation amplifier 15 determines the current flowing through the radial bearing electromagnet 10, generates a magnetic flux, and generates a force in the rotor 3. The force controls the radial position. The same control is performed also in the thrust axis direction, and the displacement signal detected by the thrust position sensor 13 is converted into a desired signal through the bearing control unit 7, and the signal is input to the excitation 15 amplifier. The thrust bearing is controlled by the excitation amplifier 15, and the position of the rotor disk 14 is controlled in the thrust axis direction. A thrust bearing electromagnet 11 is embedded in the thrust shaft magnetic bearing 19 and is configured above and below the rotor disk 14 so that the thrust bearing electromagnet 11 sandwiches the rotor disk 14. In order to provide an appropriate gap between the thrust bearing electromagnet 11 and the rotor disk 14, a spacer ring (not shown) is sandwiched and adjusted between the upper and lower thrust magnetic bearings.

  FIG. 4 is an enlarged view of the contact surface between the rotating shaft 9 and the rotor disk 14 of the present invention. Even when the contact surface of the rotor disk 14 is processed with severe processing accuracy, the roughness of the contact surface is not uniform due to the influence of chips and the like due to processing. When the rotary shaft 9 and the rotor disk 14 are fastened, when the point contact is made in the vicinity of the center of the contact surface, the rigidity of the fastening portion is greatly reduced as compared with the case where the entire surface is touched. However, by providing the clearance 15 on the rotor disk contact surface, the rotating shaft 9 and the rotor disk 14 always make point contact or surface contact near the outside. In this case, the rigidity is reduced as compared with the case where contact is made with the entire surface, but the rigidity is increased as compared with the case where point contact is made near the center. The rotating shaft 9 and the rotor disk 14 are fastened by a fastening member 16. A bolt or the like is used for the fastening member 16. The number of the fastening members 16 may be any number as long as it is two or more, but the fastening of the rotating shaft 9 and the rotor disk 14 is more stable when the number of the fastening members 16 is larger. In addition, in order to prepare alignment of fastening the rotating shaft 9 and the rotor disk 14, the protrusion 22 may be provided on the upper surface of the rotor disk.

  FIG. 5 is a modification of the invention shown in FIG. In the invention shown in FIG. 4, the gap 15 is provided in the rotor disk 14. However, in order to make the rotary shaft 9 and the rotor disk 14 point-contact or surface-contact in the vicinity of the outside, the rotary shaft as shown in FIG. A gap 15 may be provided on the contact surface 9.

  As shown in FIGS. 4 and 5, the rotating shaft 9 and the rotor disk 14 are fastened by a fastening member 16. When this fastening is performed, it is desirable that the area of the contact surface between the rotary shaft 9 and the rotor disk 14 is large. However, when the area is increased, the area of the gap portion is reduced, and point contact occurs at a portion near the center. It becomes easy and is not preferable. Therefore, in order to prevent point contact at a portion close to the center, it is desirable to make the outer periphery of the gap 15 as large as possible. However, if the outer periphery of the gap 15 is too large, the fastening member 16 fastens the rotary shaft 9 and the rotor disk 14 via the gap 15, and the fastening of the rotary shaft 9 and the rotor disk 14 is not stable. In order to stabilize the fastening of the rotating shaft 9 and the rotor disk 14, it is desirable that the fastening member 16 penetrates a portion of the rotating shaft 9 and the rotor disk 14 where no gap 15 is formed. Therefore, the size of the outer periphery of the gap 15 is preferably set such that the outer periphery of the gap 15 overlaps the through hole of the fastening member 16 as shown in FIG. In addition, when the outer periphery of the clearance gap 15 here overlaps with the through-hole of the fastening member 16, the outer periphery of the clearance gap 15 shall also include the state which contact | connects the outer periphery of the through-hole of the fastening member 16. In this way, the size of the gap 15 is increased as much as possible, and the fastening member 16 passes through the portion of the rotating shaft 9 and the rotor disk 14 where the gap 15 is not formed, thereby rotating the rotating shaft 9 and the rotor disk 14. Can be concluded.

  FIG. 6 is an enlarged view of the rotor disk 14 with the outer peripheral portion 17 cut in order to adjust the natural frequency. Since the natural frequency of the rotating body depends on the mass of the rotating body (f = √ (K / M), f: natural frequency, K: rigidity, M: mass), the mass of the rotating body is adjusted. The natural frequency of the rotating body varies and the natural frequency can be adjusted. Therefore, the natural frequency of the rotating body can be obtained by cutting the rotor disk 14 and reducing its mass. In addition, as shown in FIG. 7, the same effect can be obtained even if the mass is changed by cutting the thickness 18 of the rotor disk 14.

  Moreover, in the manufacturing process of a turbo molecule, the balance adjustment process for adjusting the balance of a rotary body is performed. As a method of the balance adjustment process, for example, it is conceivable to attach a screw for balance adjustment to a specific portion of the rotor disk, or to partially apply an adhesive as a weight. If this balance adjustment step and the natural frequency adjustment step are performed in the same step, it is possible to save work time and work time compared to performing both steps separately, so that the work can be carried out efficiently. it can.

ここで、Ｌはインダクタンス、Ｒは抵抗、Ｎはコイルの巻数、Ｓは鉄心断面積、μ₀は真空の透磁率、ｚはギャップである。磁気軸受の時定数Ｔ（sec）が短くなり、外部の振動に対する外部減衰を大きくする効果も同時に得ることが可能となる。ただし、それを実施した場合、スラスト方向のギャップが変化することで磁気軸受の吸引力が低下し、回転体質量を浮上させるだけの十分な力を得られなくなるリスクも存在する。磁気軸受の吸引力を導出する基礎式は以下の式で表される。

ここで、Fは吸引力、μ₀は真空の透磁率、Ｎはコイルの巻数、iは電流、zはギャップである。以上の２式から、磁気軸受ステータのパラメータの中で、ギャップの影響は非常に大きいため、かかるギャップの大きさを調整することが重要なことがわかる。FIG. 8 is an enlarged view of the rotor disk 14 and the thrust magnetic bearing 19. When the thickness 18 of the rotor disk 14 is cut to adjust the natural frequency of the rotating body, the gap in the thrust direction is enlarged. Therefore, in order to adjust the gap amount, it is possible to adjust the gap amount by adopting a stacked structure in which a plurality of thickness adjusting members 20 sandwiched between the upper thrust magnetic bearing 19A and the lower thrust magnetic bearing 19B are stacked. Structure. The thickness adjusting member may have a shape that makes it easy to form a laminated structure, that is, a ring shape that matches the size of the outer peripheral portion of the magnetic bearing, or an arc shape that divides the ring into a plurality of parts. By cutting the rotor disk 14 in order to adjust the natural frequency of the rotating body, it is possible to increase the damping for attenuating the shaft vibration caused by the oscillation of the natural frequency of the rotating body. Damping is determined by the responsiveness of the magnetic bearing, but the responsiveness T (sec) of the magnetic bearing, which is an index of damping, is expressed by the following equation.

Here, L is the inductance, R is the resistance, N is the number of turns of the coil, S is the cross-sectional area of the iron core, μ ₀ is the permeability of vacuum, and z is the gap. The time constant T (sec) of the magnetic bearing is shortened, and the effect of increasing external damping against external vibration can be obtained at the same time. However, when it is carried out, there is a risk that the attractive force of the magnetic bearing decreases due to a change in the gap in the thrust direction, and a sufficient force for floating the mass of the rotating body cannot be obtained. The basic equation for deriving the attractive force of the magnetic bearing is expressed by the following equation.

Here, F is the attractive force, μ ₀ is the vacuum permeability, N is the number of turns of the coil, i is the current, and z is the gap. From the above two formulas, it can be seen that the influence of the gap is very large among the parameters of the magnetic bearing stator, and therefore it is important to adjust the size of the gap.

FIG. 9 is a structural diagram of a rotor disk provided with a thick portion according to the present invention. The rotor disk 14 is provided with a thick portion 21 in which the thickness of the central portion is thicker than the thickness of the outer peripheral portion of the rotor disk 14. In order to provide the thick portion 21, a method of further cutting the outer peripheral portion of the rotor disk that has been cut into a thick shape in advance and leaving the thickness of the inner peripheral portion is conceivable. As long as the rigidity of the fastening portion of the rotor disk can be increased, any method may be used. The natural frequency of the rotating body depends on the rigidity of the rotating shaft and the fastening portion of the rotor disk, but the magnitude of the influence of the fastening portion rigidity varies depending on the vibration mode of the rotating body. Therefore, when the thick portion 21 is provided on the rotor disk, the fastening portion rigidity at the thick portion is increased, and the natural frequency of the bending secondary vibration mode in which the rotor disk portion has a large runout can be set higher. It becomes possible. By providing the thick portion 21 in the rotor disk 14 in this way, the rigidity of the fastening portion is greatly increased, so that the natural frequency is greatly increased with respect to the bending natural frequency where the vibration of the rotor disk 14 is large. Therefore, it is possible to increase the natural vibration interval of each rotating body vibration mode. Further, the weight of the rotor disk 14 can be reduced while maintaining the rigidity of the fastening portion between the rotating shaft 9 and the rotor disk 14. Table 1 shows a comparison between the primary natural frequency and the secondary natural frequency in a normal rotor disk having no thick part and a rotor disk according to the present invention having a thick part. As shown in the table, when a rotor disk having a thick part is used, only the secondary natural frequency can be increased without changing the primary natural frequency so much.
Table 1 Comparison of natural frequencies by rotor disk shape

  As shown in FIG. 9, when the thick portion 21 is provided on the lower surface of the rotor disk, the alignment protrusion 22 when the rotary shaft 9 and the rotor disk 14 are fastened is provided on the upper surface of the rotor disk. Therefore, the thick portion 21 and the projection 22 need to be provided separately. However, if the thick portion 21 is provided on the upper surface of the rotor disk as shown in FIG. Can do.

  When the rotor disk 14 is provided with a thick portion, the distance between the upper and lower thrust bearing electromagnets 11 increases, and the gap between the rotor disk surface where the thick portion is not provided and the thrust bearing electromagnet 11 is increased. May increase, and the attractive force of the magnetic bearing may be reduced. Therefore, as shown in FIG. 11, the thick portion of the rotor disk is thick in the rotor disk so as to exist in the space 23 formed in the upper surface or the lower surface of the rotor disk 14 inside the thrust magnetic bearing 19. It is desirable to provide a portion and further install a rotor disk in the magnetic bearing. By doing so, since the gap does not become large due to the provision of the thick portion, it is possible to prevent a reduction in the attractive force of the magnetic bearing.

  In addition, all the invention demonstrated so far can be implemented simultaneously. That is, the rotor disk may be provided with a thick portion where the thickness of the central portion of the rotor disk is thicker than the thickness of the outer peripheral portion while forming a gap at the center portion of the contact surface between the rotating shaft and the rotor disk. In order to adjust the natural frequency of the rotor disk, the rotor disk may be cut.

Claims (7)

In a turbo molecular pump comprising a magnetic bearing controlled by a feedback loop, a rotating shaft fixed to a rotating body and held via the magnetic bearing, and a rotor disk fixed to the rotating shaft,
A turbo molecular pump, wherein a gap is formed in a central portion of a contact surface between the rotating shaft and the rotor disk.   The outer periphery of the said clearance gap formed in the contact surface of the said rotating shaft and the said rotor disc overlaps with the through-hole of the fastening member for fastening the said rotating shaft and the said rotor disc. Turbo molecular pump. The method for producing a turbo molecular pump according to claim 1 , comprising a natural frequency adjusting step of adjusting the natural frequency of the rotating body by changing the mass of the rotating body.
The natural frequency adjusting step is performed by cutting a rotor disk used in a magnetic bearing for holding the rotating body in a thrust direction or a radial direction.   The method for producing a turbo-molecular pump according to claim 3, wherein a balance adjusting step of adjusting the balance of the rotating body by changing the mass of the rotating body in the same step as the natural frequency adjusting step is performed.   When the rotor disk is cut in the thrust direction, a gap formed between the electromagnet for the magnetic bearing installed so as to sandwich the rotor disk and the rotor disk is defined between the upper side and the lower side of the magnetic bearing. The method for producing a turbo molecular pump according to claim 3, further comprising a gap adjusting step of adjusting the gap by inserting a thickness adjusting member therebetween. The turbo molecular pump according to claim 1 or 2 ,
A turbo-molecular pump characterized in that a thickness portion of a rotor disk used for the magnetic bearing is thicker than a thickness of an outer peripheral portion of the rotor disk.   The outer shape and the height of the thick part are a size or a height that fits in a space formed inside the magnetic bearing when the rotor disk is installed in the magnetic bearing. 6. The turbo molecular pump according to 6.

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