U.S. patent application number 10/275458 was filed with the patent office on 2003-09-11 for machine, preferably a vacuum pump, with magnetic bearings.
Invention is credited to Englander, Heinrich, Hodapp, Josef.
Application Number | 20030170132 10/275458 |
Document ID | / |
Family ID | 7640980 |
Filed Date | 2003-09-11 |
United States Patent
Application |
20030170132 |
Kind Code |
A1 |
Englander, Heinrich ; et
al. |
September 11, 2003 |
Machine, preferably a vacuum pump, with magnetic bearings
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).
Inventors: |
Englander, Heinrich;
(Linnich, DE) ; Hodapp, Josef; (Koln-Sulz,
DE) |
Correspondence
Address: |
Fay Sharpe Fagan Minnich & McKee
1100 Superior Avenue
Seventh floor
Cleveland
OH
44114-2518
US
|
Family ID: |
7640980 |
Appl. No.: |
10/275458 |
Filed: |
May 9, 2003 |
PCT Filed: |
April 21, 2001 |
PCT NO: |
PCT/EP01/04531 |
Current U.S.
Class: |
417/423.4 ;
417/423.12 |
Current CPC
Class: |
F16C 32/047 20130101;
F16C 32/0476 20130101; F16C 2360/45 20130101; F16C 32/0425
20130101; F16C 39/063 20130101; F04D 29/058 20130101; F04D 19/042
20130101 |
Class at
Publication: |
417/423.4 ;
417/423.12 |
International
Class: |
F04B 017/00 |
Foreign Application Data
Date |
Code |
Application Number |
May 6, 2000 |
DE |
100-22-062.2 |
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).
Description
[0001] 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.
[0002] 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.
[0003] 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.
[0004] 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.
[0005] This task is solved through the characterising features of
the patent claims.
[0006] 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.
[0007] Further advantages and details of the present invention
shall be explained with reference to.sup.1) drawing FIGS. 1 to 10.
.sup.1) Translator's note: The German text states "anhand von in
den Figuren" here whereas "anhand von Figuren" would be correct.
Therefore the latter has been assumed for the translation.
[0008] Depicted are in
[0009] 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,
[0010] drawing FIG. 3 a turbomolecular/molecular vacuum pump
equipped with a bearing in accordance with the present
invention,
[0011] drawing FIGS. 4 to 7 partial sectional views through
magnetic bearings in accordance with the present invention with
differently designed means for axial control and
[0012] drawing FIGS. 8 to 10 examples for embodiments of the
magnetic bearings with damping means.
[0013] In the machines 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.
[0014] The rotating 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.
[0016] The 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.
[0017] A 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.
[0018] The 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.
[0019] In the upper bearing 3 the cross section of the rotating
magnet can be maintained smaller compared to bearing 4. This saves
costs for the magnetic material.
[0020] In 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.
[0021] The rings of the magnetic-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.
[0022] 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 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.
[0023] Preferably the inner and outer rings of the 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.
[0024] In the machine 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.
[0025] The 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.
[0026] The 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.
[0027] The pump 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.
[0028] As the 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.
[0029] At the side of the rotor the already detailed pipe-shaped
reinforcement 14 is provided. It not only reinforces the ring set 8
but also the motor's armature 48.
[0030] In order to compensate for tolerances, bearing 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.
[0031] Drawing FIGS. 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.
[0032] In the embodiment in accordance with drawing 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.
[0033] Between each of the rings of the magnetic-ring sets 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.
[0034] Expedient designs for the 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.
[0035] If the material for the 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.
[0036] In the embodiment in accordance with drawing FIG. 9, for
example, the magnetic rings of ring set 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.
[0037] The annular spacing disks 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.
[0038] Moreover, the employment of spirally wound foil coils 23 has
been found to be expedient since their space requirement is
relatively small.
* * * * *