JPS61207892A - Turbomolecule pump - Google Patents

Abstract

PURPOSE:To enable precise regulation of balance of a rotor after assembly, by a method wherein split electromagnets are located to surfaces positioned facing each other of a thrust yoke located to the lower end of the outer periphery of a rotor to form a magnetic bearing, and this eliminates disassembly of a rotor constituting member during assembly. CONSTITUTION:An axial bearing 15 comprises a thrust yoke 15a, located to the lower end of a rotor 9, electromagnets 15b and 15c, situated to surfaces positioned facing each other in the axial direction of a yoke 15a, and an axial direction position sensor 16. The electromagnets 15b and 15c are so constituted as to be circumferentially split into at least two parts, and are located in a manner to extend further than a support member 5 supporting the rotor 9. This constitution causes the axial bearing 15 to be circumferentially split, and eliminates removal of the thrust yoke 15a from the rotor 9 during assembly. This prevents further losing of rotor balance during an assembling work, and enables provision of a low vibration rotor. Further, since the axial bearing 15 is located to the outer peripheral part of the rotor 9, regulation of a gap between the thrust yoke 15a and the bearing 15b, 15c is facilitated, resulting in improvement of assembling properties.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Application of the Invention] The present invention relates to a turbo-molecular pump, and particularly to a turbo-molecular pump in which a rotor is supported in a non-contact manner by a magnetic bearing.

[Background of the invention]

A turbomolecular pump has rotor blades and stator blades arranged alternately in several stages to several tens of layers, and by rotating the rotor blades at high speed, gas molecules are transferred to one side and a high vacuum is obtained. Conventional turbomolecular pumps have used mechanical contact type rolling bearings that require bearing oil for lubrication in the high-speed rotor bearings, but during operation, gas flows from the intake port to the exhaust port. Although the flow of molecules prevents leakage, evaporation, and diffusion of lubricating oil from contaminating the vacuum and provides a clean vacuum, rolling bearings have limited rotational capacity due to vibrations and other factors, and must be stopped once. Then, the oil vapor of the lubricating oil in the bearing would spread to the high vacuum side, potentially contaminating the pump blades and the vacuum chamber. In order to cope with this problem, a turbo-molecular pump having a bearing type has been considered, for example, as disclosed in Japanese Patent Publication No. 57-30998. This is a controlled magnetic bearing that actively controls five degrees of freedom other than rotation, and since the magnetic axial bearing is housed inside the rotor, it is effective in downsizing the device. However, with this structure, when assembling,
After performing rotor balancing work, the thrust yoke must be disassembled and reassembled, which takes 4 hours, which causes the rotor to become unbalanced, and vibrations increase in a high-speed rotating body that rotates at several hundred revolutions.

Furthermore, as a bearing device that controls the axial position of the rotor using two sets of magnetic radial bearings, and also controls the radial position of each magnetic bearing, Japanese Patent Laid-Open No. 59-93
There is a system such as that disclosed in Japanese Patent No. 992, but in this system, the magnetic bearing is constructed in one piece, and the above-mentioned function is achieved through a complicated magnetic path structure. However, this structure requires two sets of radial bearings, and there is a problem that the radial magnetic force and the axial magnetic force cannot be controlled separately.

[Purpose of the invention]

SUMMARY OF THE INVENTION An object of the present invention is to provide a turbomolecular pump that is constructed so as not to disturb the precise rotor balance performed before assembly.

[Summary of the invention]

The present invention includes stator vanes provided in multiple stages along the axial direction within a casing, and rotor blades provided on the outer periphery of the rotor located between the stator vanes and located at the center of the casing. This type of turbo molecular pump is actively supported by a radial bearing and a magnetically axial bearing, and the rotor is rotated at high speed by a drive motor placed between the radial bearing and the axial bearing. A thrust yoke is provided at the lower end of the outer periphery, an axial bearing is arranged on the axially corresponding surface of the thrust yoke extending from the support member of the rotor, and the axial bearing is configured with magnetic poles divided into at least two parts in the circumferential direction. The suction side of the molecular pump is connected to a vacuum device such as a nuclear fusion device, the rotor is rotated, and the vacuum is generated by the turbine compression action between the stator blades provided in multiple stages and the rotor blades facing between the stator blades. Evacuate the equipment to create a high vacuum. Furthermore, a technical means has been taken that allows assembly without removing the thrust yoke of the rotor.

[Embodiments of the invention]

Embodiments of the present invention will be described below with reference to FIGS. 1 to 7.

In FIG. 1, reference numeral 1 denotes a turbo-molecular pump, which has a suction port A at the top of a cylindrical casing 2, to which a vacuum chamber (not shown) to be evacuated is connected via a flange 3. A support member 5 of the rotating body 4 is connected to the lower part of the casing 2 by a flange 6, and the support member 5 is provided with a discharge port B.

Stator blades 7 are arranged in multiple stages along the axial direction of the casing 2.
are provided, and moving blades 8 are arranged between the stationary blades 7. The moving blades 8 are fixed to the outer periphery of a rotor 9 located at the center of the casing 2. A shaft 10 constituting an inner rotor is attached to the center of the rotor 9. Moving blade 8
The rotor 9 is supported by magnetic bearings in both the radial and axial directions, and rotates at a high speed of approximately 20,000 to 30,000 revolutions or more in order to obtain the effective characteristics of a turbomolecular pump. This rotor 9 is driven by a motor rotor ll attached to a shaft 10.
a, and a motor stator ll attached to a cylindrical member 12 extending from the support member 5 facing the motor rotor lla.
This is done by a drive motor 11 consisting of b. A magnetic radial bearing 13 that supports the rotor 9 in the radial direction includes an electromagnetic magnet 13a provided on the cylindrical member 12, and a shaft 10 corresponding to the electromagnetic magnet 13a.
The rotor 9 is moved to a predetermined position in the radial direction by controlling the current of the electromagnet 13a so that the amount of eccentricity of the rotor detected by the radial position sensor 14 is reduced. support. The axial bearing 15 includes a thrust yoke 15a provided at the lower end of the rotor 9,
Electromagnet 15b provided on the axially corresponding surface of this yoke 15a
, 15c, and an axial position sensor 16, the electromagnets 15b, 15c are configured to be divided into at least two parts in the circumferential direction, and are arranged to extend from the support member 5 that supports the rotor 9.

Since the present invention is constructed as described above, the axial bearing 15 is divided in the circumferential direction, and there is no need to remove the thrust yoke from the rotor 9 during assembly.

Therefore, the rotor balance will not be disturbed during assembly work, and a low-vibration rotor can be realized. Further, since the axial bearing 15 is provided on the outer circumferential portion of the rotor, the gap between the thrust yoke 15a and the bearings 15b and 15c can be easily adjusted, and the ease of assembly is improved.

For example, the bearing 15b of the axial bearing 15 is shown in FIG.

It is configured as shown in FIG. In this case, a configuration in which the bearing is divided into four parts in the circumferential direction will be exemplified. Figure 2 shows bearing 16
Fig. 3 is a plan view of Fig. 2 of Fig. b. -1 sectional view.

Each magnetic pole 15b is divided into four.

A coil 17 is wound around each of ~15b as shown in the figure, and a current is passed through each coil so that the polarity of each magnetic pole matches. It can achieve the same function as magnetic poles. Moreover, its cross section is an E-shaped electrode stone as shown in FIG.

Next, another embodiment of the present invention will be described with reference to FIGS. 4 to 7.

In FIG. 4, the same parts as in FIG. 1 are denoted by the same reference numerals, and explanations thereof will be omitted.

In this embodiment, the rotor 9 is supported by a shaft 10 extending from the center of the rotor 9 by a pair of magnetic radial bearings 13 and a pair of magnetic axial bearings 15 provided at the lower end of the rotor 9.
The bearing 15 also functions as a radial bearing. Its drive is done by a motor rotor attached to the shaft 10.
This is performed by a drive motor 11 consisting of a motor stator llb attached to a cylindrical member 12. Axial and radial position control is performed by position sensors 14 and 16.

With the above configuration, a set of magnetic radial bearings is not required, and the shaft 10 can be shortened.

The relationship between the critical speed of the rotor and the axial dimension of the shaft will be explained with reference to FIG.

The figure compares the state of passing the critical speed in the case of this embodiment and in the case of a conventional device of this type.In the conventional case with a long shaft length, three critical speeds were passed to reach the specified rotation speed. In the configuration of this embodiment, it is only necessary to pass through the primary and secondary critical speeds, so control is easy. 1
The second and second critical speeds are vibrations in a rigid body mode in which no bending moment of the shaft occurs, and the third critical speed is a bending moment that causes the shaft to vibrate in a cantilevered state, making it difficult to control. The solid line indicates the case of this embodiment, and the broken line indicates the conventional case. The fact that stable rotation can be obtained with the magnetic bearing system of this embodiment will be explained with reference to FIGS. 6 and 7. FIG. 6 is a diagram showing a magnetic configuration divided into three parts, and FIG. 7 is a diagram showing the resultant force of the magnetic forces acting on each magnetic pole in FIG. 6.

Since it is necessary to control three degrees of freedom in the radial direction and the axial direction in a bearing that can be used both in the radial direction and in the axial direction, it is necessary to have a magnetic pole configuration that is divided into at least three parts in the circumferential direction. In Figure 7, assuming that the resultant force of the magnetic force is F2°F, F3 is the radius of action r9, and the point of force is the center of the arc of each magnetic pole, then the force in the axial direction (two directions) Flly is the moment load around the axis M ,, When the moment load around the x-axis is M, the force balance is expressed by equation (1).

Output of axial position sensor 17 A z r position sensor 15
If the output in the X-axis and y-axis directions is Δx+Ay, the displacement δ1. δ2. δ is the formula (2), where A is 3
This is a coordinate transformation matrix with three rows and three columns. The magnetic force acting on each magnetic pole is a function of the displacement of the point of force (f1(δt),
Since f, (δ,), f, (δ,)).

is given by Therefore, the sensor output Az.

It is possible to control lx and /Jy so that they match set values.

Note that if the displacement sensor (position sensor) is installed at the center of the arc of the magnetic pole, δ1. δ2. Since δ3 can be directly measured, the coordinate transformation of equation (2) is not necessary, and the calculation speed can be increased.

As described above, stable rotation can also be achieved by the magnetic bearing of this embodiment.

〔Effect of the invention〕

As explained above, according to the present invention, a thrust yoke is provided at the lower end of the outer circumference of the rotor, and divided electrode stones are arranged on the corresponding surface of this thrust yoke to constitute a magnetic bearing. Since there is no need to disassemble the rotor during assembly, the precise rotor balance performed before assembly will not be disrupted.

[Brief explanation of the drawing]

FIG. 1 is a longitudinal sectional view of a turbomolecular pump showing an embodiment of the present invention, FIG. 2 is a plan view of the axial bearing in FIG. 1,
Fig. 3 is a sectional view taken along the line 1-1 in Fig. 2, Fig. 4 is a longitudinal sectional view of a turbomolecular pump showing another embodiment of the present invention, and Fig. 5 shows the relationship between shaft dimensions and critical speed. 6 is a plan view of the axial bearing shown in FIG. 4, and FIG. 7 is an explanatory view showing the resultant force of the magnetic force acting on each magnetic pole in FIG. 6. 1...Turbo molecular pump, 2...Casing, 5...
...Supporting member, 7... Stator blade, 8... Moving blade, 9...
Rotor, 10... Shaft, 11a... Motor rotor, llb... Motor stator, 12... Cylindrical member, 14... Radial position sensor, 15a... Thrust yoke, 15... Shaft ￥ 1 Zuryo 2 drawing ts bt 5b Y d Drawing 5 drawing Car old size Shitomi Otsu Kuchi Kasumi No. 7

Claims (1)

[Scope of Claims] 1. A rotor blade provided within a casing in multiple stages along its axial direction, and a moving blade provided on the outer periphery of the rotor located between the stator vanes and located at the center of the casing. , a turbo molecule in which the rotor is supported by a magnetic radial bearing and a magnetic axial bearing, and the rotor is rotated at high speed by a drive motor disposed between the radial bearing and the axial bearing. In the pump, a thrust yoke is provided at the lower end of the outer periphery of the rotor, an axial bearing is disposed on an axially corresponding surface of the thrust yoke extending from a supporting member of the rotor, and the axial bearing is arranged at least in the circumferential direction. A turbo molecular pump characterized by a two-part magnetic pole configuration. 2. In claim 1, a set of magnetic radial bearings is provided in the rotor, and a set of magnetic axial bearings is arranged on axially corresponding surfaces of the thrust yoke. . A turbo molecular pump, wherein the axial bearing has a magnetic pole structure divided into at least three parts in the circumferential direction so that it also serves as a radial bearing. 3. The turbo according to claim 1 or 2, wherein the divided axial bearing is configured such that a current is passed through each coil so that the polarities of the magnetic poles match. molecular pump. 4. In claim 1 or 2, the cross section of the electrode stone constituting the radial bearing and the axial bearing is E.
A turbo molecular pump characterized by a shaped iron core structure. 5. In claim 1 or 2, the drive motor includes a motor rotor attached to a shaft within the rotor, and a motor stator attached to a cylindrical member facing the motor rotor and extending from the support member. A turbo molecular pump characterized by comprising: