US20030170132A1

US20030170132A1 - Machine, preferably a vacuum pump, with magnetic bearings

Info

Publication number: US20030170132A1
Application number: US10/275,458
Authority: US
Inventors: Heinrich Englander; Josef Hodapp
Original assignee: Leybold Vakuum GmbH
Current assignee: Leybold GmbH
Priority date: 2000-05-06
Filing date: 2001-04-21
Publication date: 2003-09-11
Also published as: KR20040029945A; WO2001086158A1; EP1281007B1; JP2005504930A; TW521477B; DE10022062A1; EP1281007A1; DE50101200D1

Abstract

The invention relates to a machine (1), comprising a stator and a rotor (2) which is mounted with radially stable and axially unstable magnetic bearings (3, 4). Said magnetic bearings (3, 4) each consist of concentrically arranged magnetic ring sets (5, 6; 7, 8) in which the stationary magnetic ring set (5 or 7) is situated inside and the rotating magnetic ring set (6 or 8) is situated outside. The machine also comprises means (21, 23, 24, 27) for regulating the axial position of the rotor (2). The aim of the invention is to simplify a machine of this type. To this end, one (4) of the two magnetic bearings (3, 4) is itself equipped with the axial regulation means and at least one coil (23) controlled by a position sensor (21) and pole components (24) surround the outer magnetic ring set (8) of the axially regulated bearing (4).

Description

The present invention relates to a machine, comprising a stator and a rotor which is mounted with radially stable and axially unstable magnetic bearings whereby the magnetic bearings each consist of concentrically arranged magnetic ring sets in which the stationary magnetic ring set is situated inside and the rotating magnetic ring set is situated outside, as well as means for regulating the axial position of the rotor. The magnetic bearing shall be so designed that it is especially suited for suspending rotors in blowers or vacuum pumps, preferably drag vacuum pumps operating at high speed.

The employment of magnetic bearings in turbomolecular vacuum pumps is known (c.f. EP 414 127 A1) and is well-proven. The document mentioned discloses magnetic bearings consisting of engaging sets of magnetic stator and rotor magnetic rings. In the instance of magnetic bearings of this kind and the thus equipped machines, assembly is much involved. Moreover, changes in the length of the rotor due to temperature loads give rise to bearing problems.

From DE-A 38 18 556 a machine having the characteristics of the aforementioned kind is known. This is a turbomolecular vacuum pump with two passive radially stable and axially unstable magnetic bearings. The means of controlling the axial position of the rotor consist on the one hand of selecting the operating point for the magnetic bearings such that it is shifted with reference to the unstable point in the direction of the high-vacuum side, and on the other hand that a lifting system which is independent of the magnetic bearings be provided, said lifting system continually compensating the axial forces arising from the shift in the operating point. In the instance of a solution of this kind both control and also the related necessary means are involved.

It is the task of the present invention to create a machine having the characteristics detailed above which compared to state-of-the-art solutions is more simple.

This task is solved through the characterising features of the patent claims.

In the instance of a machine in accordance with the present invention, engaging magnetic ring sets are no longer present so that mounting complexity is reduced. A lifting system being independent of the magnetic bearings to control the axial position of the rotor is no longer required. In all, the bearing is composed of fewer different components so that production, warehousing and logistics are simplified.

Further advantages and details of the present invention shall be explained with reference to[0007] ¹⁾drawing FIGS. 1 to 10.
Depicted are in [0008]
drawing FIGS. 1 and 2 a schematic representation of machines with rotors which are each supported by a magnetic bearing designed in accordance with the present invention, [0009]
drawing FIG. 3 a turbomolecular/molecular vacuum pump equipped with a bearing in accordance with the present invention, [0010]
drawing FIGS. [0011] 4 to 7 partial sectional views through magnetic bearings in accordance with the present invention with differently designed means for axial control and
drawing FIGS. [0012] 8 to 10 examples for embodiments of the magnetic bearings with damping means.
In the machines [0013] 1 depicted schematically in drawing FIGS. 1 and 2, the rotating system 2 is suspended in two magnetic bearings 3, 4. Each magnetic bearing 3, 4 consists of two magnetic-ring sets 5, 6 (bearing 3) and 7, 8 (bearing 4) respectively. The inner ring set 5, 7 in each instance is mounted firmly, the outer ring sets 6, 8 which in each instance encompass the respective inner ring set concentrically and without making contact (slot 9) are components of the rotating system 2. The design is in all rotationally symmetric. A drive motor is not depicted.
The rotating [0014] system 2 is equipped at both face sides with central recesses 11, 12. The walls of these recesses form the receptacles 13, 14 for the rotating magnetic- ring sets 6, 8. Receptacle 14 is a pipe-shaped reinforcement made of non-magnetizable material, carbon fibre reinforced plastic, for example, which is fitted preferably by means of a press-fit seat at the rotating system 2. A section of the reinforcement 14 encompassing the recess 12 carries on its inside the magnetic-ring set 8.
[0015] Stationary carriers 15, 16 with receptacles 17, 18 for the stationary magnetic- ring sets 5, 7 project into the recesses 11, 12 in such a manner that the outer ring sets 6, 8 concentrically encompass the inner sets 5, 6. In the drawing figures each of the lower carriers 16 have a central bore 19 for a shaft end 20 of the rotating system 2, the face side of said shaft end being assigned to an axial sensor 21.
The [0016] axial sensor 21 is part of the means for axially controlling the magnetic bearing 4. One or several coils 23 each with an U-shaped yoke 24 open in the direction of the ring set 8, generate the magnetic fields indicated by the dashed lines and arrows 25. In drawing FIGS. 1 and 2 in each instance two coils 23 are provided encompassing the ring set 8. Their yoke components 24 are separated by a spacing disk 26 made of non-ferrite material.
A [0017] controller 27 serves the purpose of controlling the coils resp. the magnetic fields generated by the coils 23 depending on the signal output by the sensor 21. In the slot 28 located in each instance between the outer rotating rings sets 6, 8 and the coils 23, respectively the face side of the limbs of the yoke components 24, the magnetic forces serving the purpose of axial control become effective.
The [0018] ring sets 5 to 8 consist each of rings magnetized in the axial direction arranged with changing poles (as indicated by way of an example for bearing 3 in accordance with drawing FIG. 1) so that the ring sets 5, 6 resp. 7, 8 of the magnetic bearings 3, 4 repel each other. Preferably, so many outer and inner pairs of rings are provided that each of the magnetic-ring sets has at both its ends the same polarity. In the solution in accordance with drawing FIG. 1 the ring sets 5, 6 resp. 7, 8 each form two cylinders arranged concentrically with respect to each other. The dimensions of the magnetic- ring sets 5, 7 resp, 6, 8 are preferably identical in each instance. In the solution in accordance with drawing FIG. 2 the diameters of the circumferential surfaces of the rings of both ring sets 5, 6 resp. 7, 8 of the bearings 3, 4 facing each other change in distinct steps (in the same direction), so that also the slot 9 is step-shaped. Also the slot 28 in bearing 4 may (deviating from what is depicted in drawing FIG. 2) also be step-shaped.
In the upper bearing [0019] 3 the cross section of the rotating magnet can be maintained smaller compared to bearing 4. This saves costs for the magnetic material.
In [0020] bearing 4 it is required that the slot 28 between the pole surfaces of the yoke components and the magnets, which are held in place throughout the constant inside diameter of the carbon fibre reinforced plastic tube, be kept small so that the axial bearing can be effective on the magnets.
The rings of the magnetic-[0021] ring sets 5 to 8 are held firmly in place in their receptacles 13, 14, 17, 18. Annular spacing discs 31 made of non-ferric materials rest flush against the two face sides of each magnet ring so that the magnetic forces become effective preferably in the slots 9 and 28 respectively. If the material of the annular spacing discs 31 has in addition good electrical conducting properties (copper for example) damping of the rotor movements is already attained by this.
In addition to the spacing disks, the facing surfaces of the rings of the ring sets may be encapsulated so as to protect the magnetic materials against aggressive gases (for example, hydrogen in drag pumps). As an example, stepped [0022] sleeves 32, 33 for the in each instance stationary ring sets 5, 7 are depicted in drawing FIG. 2. At the side of the ring sets they are joined to the related receptacles in a gas-tight manner, welded, for example.
Preferably the inner and outer rings of the [0023] ring sets 5, 6 resp. 7, 8 are arranged in pairs. To the end of improving axial control it may be expedient to add to the outer rotating ring set 8 of the axially active magnetic bearing 4, further rings. Variants of this kind are depicted in drawing FIGS. 1 and 2. The ring set 8 has two more rings compared to ring set 7. The two outer rings, designated as 29, have been added to the set 8. These may be soft ferric rings; preferably, however, two further magnetic rings are added.
In the machine [0024] 1, a turbomolecular/molecular pump depicted in drawing FIG. 3, stator blades 37 are fitted in the casing 35 with the connecting flange 36. The magnetically suspended rotor 2 carries rotor blades 38 revolving between the stator blades 37, said rotor blades providing the pumping action for the gases. Pump 1 is a compound pump. The section equipped with blades is followed by a molecular pumping section 39.
The [0025] rotor 2 is suspended in both magnetic bearings 3 and 4. The magnetic bearing 3 is located at the high-vacuum side. The carrier 15 of the stationary magnetic-ring set 5 with its receptacle 17 is part of a bearing star 41.
The [0026] magnetic bearing 4 is located at the fore-vacuum side of the pump 1. Both bearings have approximately the same stiffness. The centre of gravity of the rotating system 2 is designated as 42.
The pump [0027] 1 is equipped with emergency bearings or touchdown bearings 44, 45. The touchdown bearing 44 at the high-vacuum side is located in a recess within the rotor 11. The touchdown 45 bearing at the fore-vacuum side is located under the magnetic bearing 4 between shaft end 20 and the stationary carrier 16.
As the [0028] drive motor 46, a high-frequency motor with stator 47 and armature 48 is provided. On the side of the stator there is furthermore provided a can 49 which seals off the stator chamber 50 against the fore-vacuum side in a vacuum-tight manner. The can 49 penetrates the slot 28 between the coils 23 with their yoke components 24 and the rotating magnetic-ring set 8. Said can is therefore expediently made of a non-magnetizable and electrically not well conducting material, carbon fibre reinforced plastic, for example.
At the side of the rotor the already detailed pipe-shaped [0029] reinforcement 14 is provided. It not only reinforces the ring set 8 but also the motor's armature 48.
In order to compensate for tolerances, bearing [0030] 4 is adjustable via adjustment screws 52 on which the carrier 16 for the stationary ring set 7 rests. Expediently the adjustment is performed such that the rotating system is located axially in the unstable operating point. Axial control can be effected with minimum energy requirements about this operating point.
Drawing FIGS. [0031] 4 to 7 depict different embodiments for the active magnetic bearing 4. In the solution in accordance with drawing FIGS. 4 (without magnetic field lines) and 5 (with magnetic field lines) each four magnetic rings form the rings sets 7 and 8. Only one coil 23 with its U-shaped yoke 24 is provided. The distance between the face sides of the U-limbs of yoke 24 corresponds approximately to the axial dimension of one magnetic ring of ring set 8. For the purpose of attaining an optimum interaction of the magnetic forces, the face sides of the U-limbs are located at the level of the centres of two neighbouring magnetic rings of ring set 8, in the embodiment depicted at the level of the centres of the two middle magnetic rings.
In the embodiment in accordance with drawing [0032] 6, there is also only provided one coil 23 with its yoke 24. The distance of the face sides of the limbs of the U-shaped yoke 24 facing the rings of the ring set 8 corresponds approximately to twice the axial dimension of a magnetic ring. Drawing FIG. 7 depicts a solution with five coils 23 and yokes 24. The ring set 8 has six magnetic rings. The face sides of the, in total six yoke limbs, are located approximately at the level of the centres of the magnetic rings.
Between each of the rings of the magnetic-ring sets [0033] 7, 8 there are located—as already detailed—annular spacing disks 31, which depending on the material have an influence on the formation of the magnetic field lines and/or the damping effect.
Expedient designs for the [0034] annular spacing disks 31, preferably for attaining a damping effect as well as supplementing the coatings of the magnetic rings are explained with reference to the embodiments of bearing 3 depicted in the drawing FIGS. 8 to 10.
If the material for the [0035] annular spacing disks 31 consists of a material with good electrical conducting properties expedient for attaining a damping effect, then it may be expedient for the purpose of improving the damping effect to reinforce the circumferences of the annular spacing disks 31 at the point where the magnetic field enters into the slot 9, for example increasing continuously outwards, and to adapt the shape of the magnetic rings to such circumferences. This embodiment is depicted in drawing FIG. 8. The reinforced circumference of the middle annular spacing disk 31 close to the slot is designated as 54. In that the magnetic fields pass through more conducting material, the counterforces generated by the eddy currents and providing the damping effect, increase.
In the embodiment in accordance with drawing FIG. 9, for example, the magnetic rings of ring set [0036] 5 are coated (coating 55) on all sides. At the side they have the function of spacing disks 31, so that when of sufficient thickness of the coating 55 and suitably selected materials, said spacing disks will influence the magnetic field lines and/or have a damping effect. In addition it is achieved that the magnetic rings are protected against aggressive gases. Such protection may also be attained in that a sleeve 32 is provided, be it step-shaped as already detailed with reference to drawing FIG. 2, or cylindrical as depicted in drawing FIG. 10 (ring set 5), for example.
The annular spacing disks [0037] 31 (resp. coating 55) of the magnetic rings need(s) to be sufficiently thick to fulfil their/its purpose, particularly since also the desired stiffness of the bearing depends on the thickness of the spacing disks. In medium size drag pumps a thickness in the range from 0.25 to 1 mm has been found to be practical.
Moreover, the employment of spirally wound foil coils [0038] 23 has been found to be expedient since their space requirement is relatively small.

Claims

1. Machine (1), comprising a stator and a rotor (2) which is mounted with radially stable and axially unstable magnetic bearings (3, 4), whereby the magnetic bearings (3, 4) each consist of concentrically arranged magnetic ring sets (5, 6; 7, 8) in which the stationary magnetic ring set (5 or 7) is situated inside and the rotating magnetic ring set (6 or 8) is situated outside as well as means (21, 23, 24, 27) for regulating the axial position of the rotor (2) wherein one (4) of the two magnetic bearings (3, 4) is itself equipped with the axial regulation means and at least one coil (23) is controlled by a position sensor (21) and pole components (24) surround the outer magnetic ring set (8) of the axially regulated bearing (4).

2. Machine in accordance with claim 1, wherein the magnetic ring sets (5 to 8) consist of rings magnetised in the axial direction which are arranged over each other with changing poles, and where the ring sets (5, 6 resp. 7, 8) of a bearing (3, 4) repel each other.

3. Machine in accordance with claim 2, wherein the cross section of the pole components (24) is designed to be U-shaped and where the face sides of the U-limbs of the pole components (24) face the outer magnetic ring set (8).

4. Machine in accordance with claim 3, wherein the face sides of the U-limbs of the pole components (24) have a distance which corresponds approximately to the single or multiple axial distance of a magnetic ring and where the coils/yoke components are so arranged that the face sides of the U-limbs are arranged at the level of the centers of the magnetic rings.

5. Machine in accordance with claim 4 or 5, wherein one or several coil(s) (23) with one, resp. one each U-shaped pole component (24) is/are provided.

6. Machine in accordance with one of the claims 2 or 5, wherein for n magnetic rings of the outer ring set (8) n−1 coils (23) are provided which are each encompassed by an arrangement of U-shaped pole components (24) and where the limbs of the U-shaped yoke components (24) are located approximately at the level of the centers of the magnetic rings.

7. Machine in accordance with one of the above claims, wherein the number of the magnetic rings of the two ring sets of a magnetic bearing differ.

8. Machine in accordance with claim 7, wherein the number of magnetic rings of the rotating magnetic-ring set (6, 8) is greater than the number of magnetic rings of the stationary pair of magnetic rings (5, 7).

9. Machine in accordance with one of the above claims, wherein the magnetic rings of the ring sets (5, 6, 7, 8) are affixed in receptacles, where as the receptacle for the magnetic rings of the outer ring set (8) of the axially active bearing (4) a pipe-shaped reinforcement is employed which is affixed to a first section at the rotating system (2) and with a second section that carries the magnetic rings of the ring set (8).

10. Machine in accordance with claim 9, wherein the reinforcement (14) also encompasses the armature (48) of a drive motor (46).

11. Machine in accordance with claim 2 and one the claims 3 to 10, wherein centrally arranged carriers (15, 16) are provided for the stationary magnetic-ring sets (5, 7) where one of the carriers (15, 16) is equipped with a central bore (19), where a shaft end (20) of the rotating system (2) penetrates the bore (19) and where an axial sensor (21) is related to the unoccupied face side of the shaft end (20).

12. Machine in accordance with claim 11, wherein one of the carriers (15, 16) is axially adjustable.

13. Machine in accordance with one of the above claims, wherein the diameters of the facing circumferential surfaces of the rings of a pair of ring sets (5, 6 resp. 7, 8) change in steps.

14. Machine in accordance with one of the above claims, wherein at least between a part of the magnetic rings of the magnetic ring sets (5, 6, 7, 8) there are located spacing ring disks (31) made of a non-ferrite material.

15. Machine in accordance with claim 1, wherein the material of the spacing disks (31) has a high electrical conductance.

16. Machine in accordance with claim 15, wherein the circumferences of the spacing disks (31) close to the slot are reinforced.

17. Machine in accordance with claim 14, 15 or 16, wherein the magnetic rings are encapsulated and where the layers of the encapsulation have the function of the spacing ring disks (31).

18. Machine in accordance with claim 14, 15 or 16, wherein a sleeve (32) is assigned to the circumferential surfaces of the magnetic rings close to the slot.

19. Machine in accordance with one of the above claims, wherein it is designed as a drag pump (1) and where the passive bearing (3) is located at the high-vacuum side, the axially active bearing (4) at the fore-vacuum side.

20. Machine in accordance with claim 19, wherein a drive motor (46) with a can (49) is provided and where the can (49) penetrates the slot (28) of the axially active bearing (4).