Eddy current damper and vacuum pump

Abstract

An eddy current damper for a vacuum pump comprising a conductive ring that can be coupled to a housing and a magnetic element that can be coupled to a rotor shaft so as to rotate relative to the conductive ring. In that regard, the conductive ring is made of a conductive material and has an axially extending portion and a radially extending portion. Further, the magnetic element comprises at least one ring magnet, and the radially extending portion of the conductive ring is arranged axially adjacent to the at least one ring magnet.

Description

[Technical Field]

[0001] The present invention relates to an eddy current damper for a vacuum pump, in particular a turbomolecular vacuum pump, and further to a vacuum pump including such an eddy current damper. [Background technology]

[0002] A typical vacuum pump includes a housing having an inlet and an outlet. A rotor is disposed within the housing and rotatably supported by at least one bearing. The rotor includes a rotor shaft and at least a pumping element. When rotated by an electric motor, the pumping element transports a gaseous medium from the inlet to the outlet.

[0003] It is known to use frictionless magnetic bearings to support the rotor, however, particularly when using magnetic bearings, it is important to avoid radial vibrations of the rotor caused, for example, by rotor imbalance or magnetic bearing inaccuracies.

[0004] It is known to use eddy current dampers to reduce radial vibrations of a rotor. The eddy current damper includes a magnetic element coupled to the rotor that rotates with the rotor and at least one non-rotating conductive element coupled to the housing. Radial vibrations induce eddy currents in the conductive element, which create a magnetic force that acts in the opposite direction to the vibratory motion, providing a restoring force on the rotor, thereby damping the rotor's radial vibrations. However, typical eddy current dampers are bulky, and the additional elements of the eddy current damper can exceed space requirements, increasing the overall size of the vacuum pump. Summary of the Invention [Problem to be solved by the invention]

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an efficient eddy current damper that is compact in size.

Means for Solving the Problem

[0006] This problem is solved by the eddy current damper according to claim 1 and the vacuum pump according to claim 20.

[0007] The eddy current damper (EDC) for a vacuum pump according to the present invention includes a conductive ring that can be fixedly coupled to the housing of the vacuum pump. In that regard, the conductive ring is made of a conductive material such as copper or aluminum. The conductive ring further preferably comprises an axially extending portion and a radially extending portion constructed as an integral part. Accordingly, the cross-section of the conductive ring can be L-shaped or T-shaped. Thus, the axially extending portion and the radially extending portion can be joined to each other at their respective ends to form an L-shaped cross-section. Alternatively, to form a T-shaped cross-section, the radially extending portion can be joined to the axially extending portion by joining the end of the radially extending portion to a position between the two ends of the axially extending portion.

[0008] According to the present invention, the ECD further comprises a magnetic element having at least one ring magnet preferably constructed as a permanent magnet. The magnetic element can be coupled to the rotor shaft of the vacuum pump so as to rotate with respect to the conductive ring. In that regard, the radially extending portion of the conductive ring is arranged axially adjacent to at least one ring magnet. Accordingly, the magnetic field of at least one ring magnet induces eddy currents in the radially extending portion of the conductive ring. At the same time, the axially extending portion of the conductive ring functions as a conductor to enable an efficient flow of eddy currents in the conductive ring in order to efficiently create a magnetic field by the eddy currents. Accordingly, the ohmic resistance of the conductive ring is reduced by the axially extending portion of the conductive ring to reduce the attenuation of the eddy currents in the conductive ring. Accordingly, the specific shape of the conductive ring can provide a compact and efficient design that can reliably and efficiently attenuate the radial vibrations of the rotor of the vacuum pump.

[0009] Preferably, the magnetic element includes a second ring magnet disposed on the opposite side of the first ring magnet with respect to the conductive ring. Accordingly, the magnetic field applied to the radially extending portion of the conductive ring is enhanced by the second ring magnet. Specifically, when the second ring magnet is included in the magnetic element, the cross section of the conductive ring is preferably T-shaped.

[0010] Preferably, the first ring magnet and the second ring magnet have magnetic poles in the same direction in order to enhance the magnetic field at the position of the radially extending portion of the conductive ring.

[0011] Preferably, the second ring magnet can be coupled to the housing and thus is stationary and does not rotate. Alternatively, the second ring magnet can be coupled to the rotor shaft like the first ring magnet and rotates with respect to the conductive ring.

[0012] Preferably, a radially extending gap is formed by the first ring magnet and the second ring magnet, and the radially extending portion of the conductive ring extends at least partially into the gap. Accordingly, the first ring magnet and the second ring magnet are disposed directly adjacent to the radially extending portion of the conductive ring along the axial direction. By creating a gap between the first ring magnet and the second ring magnet, the magnetic field at the position of the radially extending portion of the conductive ring is enhanced, thereby efficiently inducing eddy currents in the conductive ring.

[0013] Preferably, a yoke made of a magnetic material that creates a magnetic circuit and further enhances the magnetic field at the position of the radially extending portion of the conductive ring is provided to magnetically couple the first ring magnet and the second ring magnet.

[0014] Preferably, the yoke includes two radially extending portions each magnetically coupled to the first ring magnet and the second ring magnet, and an axially extending portion that couples the two radially extending portions of the yoke. Accordingly, the yoke is substantially U-shaped.

[0015] Preferably, the yoke is coupled to the rotor shaft and rotates together with the first ring magnet and the second ring magnet. As a result, the yoke, specifically the two radially extending portions of the yoke, are directly attached to the first ring magnet and the second ring magnet.

[0016] Alternatively, the yoke is stationary and coupled to the housing. As a result, the yoke, specifically the two radially extending portions of the yoke, are not directly attached to the first ring magnet and the second ring magnet, and the magnetic field permeates across the gap between the stationary yoke and the rotating ring magnet to create a magnetic circuit.

[0017] Preferably, the radial width of the axial extension of the yoke is smaller than the axial width of the first ring magnet. Alternatively or additionally, the radial width of the axial extension of the yoke is smaller than the axial width of the second ring magnet. In that regard, it has been surprisingly found to be beneficial to the attenuation efficiency when the radial width of the axial extension of the yoke is smaller than the axial width of the first ring magnet, and / or when the radial width of the axial extension of the yoke is smaller than the axial width of the second ring magnet.

[0018] Preferably, the axial width of at least one, preferably two, of the radially extending portions of the yoke is smaller than the axial width of the first ring magnet. Alternatively or additionally, the axial width of at least one, preferably both, of the two radially extending portions of the yoke is smaller than the axial width of the second ring magnet. In that regard, it has been surprisingly found to be beneficial to the attenuation efficiency when the axial width of at least one, preferably two, of the two radially extending portions of the yoke is smaller than the axial width of the first ring magnet, and / or when the axial width of at least one, preferably both, of the two radially extending portions of the yoke is smaller than the axial width of the second ring magnet.

[0019] Preferably, the radial distance between the outermost surface in the radial direction of the axial extension of the yoke and the first ring magnet is between 1 and 5 times the axial width of the first ring magnet. Alternatively or additionally, the distance between the outermost surface in the radial direction of the axial extension of the yoke and the second ring magnet is between 1 and 5 times the axial width of the second ring magnet. In that regard, it has been surprisingly found that when the radial distance between the outermost surface in the radial direction of the axial extension of the yoke and the first ring magnet and / or the second ring magnet is between 1 and 5 times the axial width of the first ring magnet and / or the second ring magnet, it is beneficial to the attenuation efficiency.

[0020] Preferably, the first ring magnet extends axially beyond the axially extending element of the conductive ring. Alternatively or additionally, the second ring magnet extends axially beyond the axially extending element of the conductive ring. Thus, it has been surprisingly found that when the axially extending element of the conductive ring partially surrounds the first ring magnet and / or the second ring magnet in the radial direction, it is beneficial to the attenuation efficiency.

[0021] Preferably, the conductive ring includes a second axially extending portion disposed on the opposite side of the first axially extending portion at the end opposite to the radially extending portion. Thus, the cross-section of the conductive ring is substantially H-shaped or U-shaped, and the first ring magnet is disposed in the valley of the U-shaped or H-shaped cross-section. Specifically, when the second ring magnet is included, the conductive ring has an H-shaped cross-section, and the second ring magnet is disposed in the second valley of the H-shaped cross-section of the conductive ring. The second axially extending element of the conductive ring increases the cross-section of the conductive ring, thereby further enhancing the conductance of the conductive ring, reducing the ohmic resistance of the conductive ring, and enabling an efficient flow of eddy currents within the conductive ring.

[0022] Preferably, the conductive ring is separated into two parts along the circumferential direction of the conductive ring. Therefore, the conductive rings can be easily assembled into each other in an interconnected manner around the rotor shaft and preferably around the first ring magnet and the second ring magnet. Since the magnetic field lines of the magnetic field are arranged in the axial direction and the intersection of each part of the conductive ring is also in the axial direction, separating the conductive ring into two or more parts has little or no effect on the magnetic field. Preferably, a conductive reinforcing material such as a conductive paste can be arranged at the intersection.

[0023] Preferably, the conductive ring and the magnetic element are rotationally symmetric.

[0024] Preferably, the distance between the outermost radial surface of the conductive ring and each outermost radial surface of the first ring magnet is smaller than the radial width of the first ring magnet, and / or smaller than the radial width of the second ring magnet. Alternatively or additionally, the distance between the innermost radial surface of the conductive ring and each innermost radial surface of the second ring magnet is smaller than the radial width of the first ring magnet or the radial width of the second ring magnet. In that regard, it has been surprisingly found that when the distance between the outermost / innermost radial surface of the conductive ring and each outermost / innermost radial surface of the first ring magnet is smaller than the radial width of the first ring magnet, and / or smaller than the radial width of the second ring magnet, it is beneficial to the attenuation efficiency.

[0025] Preferably, the axial width of the radial extension of the conductive ring is smaller than the axial width of the first ring magnet, and / or smaller than the axial width of the second ring magnet. In that regard, it has been surprisingly found that when the axial width of the radial extension of the conductive ring is smaller than the axial width of the first ring magnet, and / or smaller than the axial width of the second ring magnet, it is beneficial to the attenuation efficiency.

[0026] Preferably, the radial width of the first ring magnet is between 2 mm and 20 mm, more preferably between 3 mm and 10 mm. Alternatively or additionally, the radial width of the second ring magnet is between 2 mm and 20 mm, more preferably between 3 mm and 10 mm. In that regard, it has been surprisingly found that when the radial width of the first ring magnet is between 2 mm and 20 mm, more preferably between 3 mm and 10 mm, it is beneficial for the attenuation efficiency while maintaining the space requirements.

[0027] Preferably, the axial distance between the radial extension of the conductive ring and the first ring magnet is between 0.05 mm and 2 mm, more preferably between 0.1 mm and 1 mm. Alternatively or additionally, the axial distance between the radial extension of the conductive ring and the second ring magnet is between 0.05 mm and 2 mm, more preferably between 0.1 mm and 1 mm. In that regard, it has been surprisingly found that when the axial distance between the radial extension of the conductive ring and the first ring magnet and / or the second ring magnet is between 0.05 mm and 2 mm, more preferably between 0.1 mm and 1 mm, it is beneficial for the attenuation efficiency while maintaining the space requirements.

[0028] Preferably, the radial distance between the inner surface of the first axial extension of the conductive ring and the first ring magnet and / or the second ring magnet is between 0.05 mm and 2 mm, more preferably between 0.1 mm and 1 mm. In that regard, it has been surprisingly found that when the radial distances between the inner surface of the first axial extension of the conductive ring and the first ring magnet / the second ring magnet are each between 0.05 mm and 2 mm, more preferably between 0.1 mm and 1 mm, it is beneficial for the attenuation efficiency while maintaining the space requirements.

[0029] Preferably, the radial distance between the outer surface of the second axially extending portion of the conductive ring and the first ring magnet and / or the second ring magnet is between 0.05 mm and 2 mm, more preferably between 0.1 mm and 1 mm. In that regard, it has been surprisingly found that when the radial distance between the outer surface of the second axially extending portion of the conductive ring and the first ring magnet / second ring magnet is between 0.05 mm and 2 mm, more preferably between 0.1 mm and 1 mm, respectively, it is beneficial for the attenuation efficiency while maintaining the space requirements.

[0030] Preferably, the eddy current damper comprises at least one second conductive ring that can be coupled to the housing and at least one corresponding second magnetic element that can be coupled to the rotor shaft so as to rotate with respect to this conductive ring. Accordingly, the eddy current damper has a stacked configuration having two or more conductive rings and a corresponding number of magnetic elements along the axial direction of the rotor shaft. In that regard, at least one second conductive ring and at least one second magnetic ring are constructed in accordance with the features described above with respect to the conductive ring and each magnetic element. In that regard, the conductive rings with the corresponding magnetic elements may be constructed identically or differently.

[0031] Preferably, the ring magnet of one conductive ring is simultaneously the ring magnet of the second conductive ring. Accordingly, one ring magnet functions simultaneously as a magnetic element that induces eddy currents in two conductive rings arranged directly adjacent to each other in a stacked or alternating pattern.

[0032] In a further aspect of the present invention, a vacuum pump is provided that includes a housing, a rotor disposed within the housing, and the eddy current damper described above. In that regard, the first ring magnet is coupled to the rotor and rotates with the rotor, and the conductive ring is coupled to the housing.

[0033] Preferably, the vacuum pump is constructed in accordance with the features described above in relation to the eddy current damper.

[0034] The present invention will be described in more detail below with reference to the accompanying drawings.

Brief Description of the Drawings

[0035]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0036] Referring to FIG. 1, a vacuum pump constructed as a turbomolecular pump is shown. The vacuum pump includes a housing 10 having an inlet 12 and an outlet 14. A rotor 16 is disposed within the housing and is supported by a first radial bearing 18 constructed as a permanent magnet bearing and a second radial bearing 20 also constructed as a permanent magnet bearing. The first radial bearing 18 and the second radial bearing each include a plurality of magnet rings 22, 23. In that regard, the stationary magnet ring 23 of the first radial bearing 18 is attached to a trunnion 24 that extends into a recess 26 of the rotor shaft 16. The rotating magnet ring 22 is disposed on the inner surface of the recess adjacent to the stationary magnet ring 23 in the radial direction. In the second radial bearing 20, the rotating magnet ring 22 is attached inside a bell-shaped element 28 adjacent to the stationary magnet ring 23 coupled to the housing in the radial direction. In that regard, the stationary magnet rings 23 of the first radial bearing 18 and the second radial bearing 20 respectively repel each of the rotating magnet rings 22 of the first radial bearing 18 and the second radial bearing, thereby rotatably supporting the rotor 16 within the housing 10.

[0037] Furthermore, the first radial bearing 18 and the second radial bearing 20 comprise an emergency operation bearing 30 constructed as a ball bearing. The rotor shaft 16 is driven by an electric motor 32. Mounted on the rotor shaft 16 are a plurality of pump elements 34 constructed as vanes that interact with stator elements 36, which are coupled to the housing 10 of the vacuum pump and are arranged alternately with the pump elements 34. Additionally, the vacuum pump of FIG. 1 comprises a Horweck stage 38 that includes a rotary cylinder 40 that interacts with a threaded stator 42 coupled to the housing. Rotation of the rotor shaft 16 conveys the gaseous medium from the inlet 12 of the vacuum pump toward the outlet 14.

[0038] Furthermore, the vacuum pump shown in FIG. 1 comprises an eddy current damper (ECD) 100. The ECD 100 comprises a first ring magnet 104 and a second ring magnet 106 that are coupled by a magnetic yoke 102 to create a magnetic circuit. A gap 105 is created by the first ring magnet 104 and the second ring magnet 106. The ECD 100 further comprises a conductive ring 108 that includes an axially extending portion 110A and a radially extending portion 112. In that regard, the radially extending portion 112 extends into the gap 105 between the first ring magnet 104 and the second ring magnet 106. In that regard, the first ring magnet is coupled to the rotor shaft 16 and rotates with the rotor shaft 16. Furthermore, the conductive ring 108 is coupled to the housing and is stationary. Radial vibration of the rotor shaft 16 induces eddy currents in the conductive element, and these eddy currents create a magnetic force that acts in a direction opposite to the vibratory motion, providing a restoring force to the rotor and thereby damping the radial vibration of the rotor.

[0039] Next, referring to FIG. 2, a rotationally symmetric ECD configuration about the axis 101 is shown in detail. The same or similar elements are denoted by the same reference numerals. Furthermore, in the following description and the description of FIG. 1 as well, references to the axial direction 99 and the radial direction 98 of the vacuum pump are made as shown in FIG. 2.

[0040] Simulations and experiments have shown that it is advantageous to use certain dimensions to provide efficient attenuation with minimal space requirements. In that regard, to enhance the magnetic field at the location of the radial extension 112 of the conductive ring 108 and create larger eddy currents, the first ring magnet 104 and the second ring magnet 106 should be as close as possible, and the size h of the gap 105 should be as small as possible. l and the axial width h of the radially extending portion 112 of the conductive ring 108 k2 However, the axial width h of the radially extending portion 112 of the conductive ring 108 must be reduced. k2 Reducing the cross section of the conductor formed by the conductive ring 108 reduces the cross section, thereby increasing the ohmic resistance, which leads to attenuation of eddy currents induced in the conductive ring 108. Therefore, the axial extension 110A is coupled to the radial extension 112 of the conductive ring 108 to increase the cross section and reduce the ohmic resistance, which efficiently generates eddy currents in the conductive ring 108 and creates magnetic forces on the first ring magnet 104 and the second ring magnet 106 that are in a direction opposite to the vibrating motion, which acts as a restoring force for the rotor shaft 16. As shown in FIG. 2, a second axial extension 110B can be coupled to the opposite end of the radial extension 112 of the conductive ring 108 to further enhance the flow of eddy currents within the conductive ring 108. Thus, the conductive ring 108 in FIG. 2 has an H-shaped cross section.

[0041] Therefore, it may be shown that the most efficient and compact ECD can be constructed by satisfying one or more of the following conditions (see Figure 2): -For Conductive Ring 108: 0 <d kma <d m and 0 <d kmi <d m -Furthermore, with respect to the conductive ring 108: 0 <h k2 <h m - the axial extension 110A / 110B is arranged to radially surround the ring magnet with a larger and / or smaller diameter, i.e. <h k1 <hl +h m The conductive ring 108 is formed so as to satisfy the following conditions - For the first ring magnet 104: 3 mm < d m < 10 mm - For the second ring magnet 106: 3 mm < d m < 10 mm - For the gap between the first ring magnet 104 and the radially extending portion 112 of the conductive ring 108: 0.1 mm < h l < 1 mm - For the gap between the second ring magnet 106 and the radially extending portion 112 of the conductive ring 108: 0.1 mm < h l < 1 mm - For the gap between the first ring magnet and / or the second ring magnet and the first axially extending portion 110A of the conductive ring 108: 0.1 mm < d ka1 - d ma < 1 mm - For the gap between the first ring magnet and / or the second ring magnet and the second axially extending portion 110B of the conductive ring 19: 0.1 mm < d mi - d ki2 < 1 mm - For the yoke: 0 < h r < h m - For the yoke: 0 < d r < h m - For the yoke: h m < d mi - d ra < 5h m 〔ID=52〕 That is.

[0042] Referring to FIG. 3 showing an alternative embodiment of the eddy current damper, the cross section of the conductive ring 108 is T-shaped. Further, it is shown that the yoke 102 is separated into a first yoke portion 102A and a second yoke portion 102B in the axial direction to facilitate assembly.

[0043] Referring to FIG. 4 showing the conductive ring 108 in plan view, the axial extension 110 of the conductive ring extends outwardly from the plane of the paper, and the radial extension 112 of the conductive ring extends within the plane of the paper. In that regard, the conductive ring 108 is constructed by two portions 108A and 108B that separate the conductive ring along the circumferential direction. Accordingly, the conductive ring 108 can be easily assembled around the rotor shaft 16 in a manner that interconnects with the first and second ring magnets 104, 106.

[0044] Referring to FIG. 5 showing the first ring magnet 104 including a part of the yoke 102A, the first ring magnet 104 is surrounded by a reinforcing element 118 in order to withstand the rotational force during the operation of the vacuum pump.

[0045] Accordingly, with the configured ECD found, a compact and efficient ECD can be realized, which can be implemented in various types of vacuum pumps. Although the ECD according to the present invention is shown in a turbomolecular pump, other types of vacuum pumps and pump stages can also benefit from the ECD according to the present invention.

Description of Reference Numerals

[0046] 16 Rotor shaft 100 Eddy current damper (ECD) 101 Axis 102 Magnetic yoke 104 First ring magnet 105 Gap 106 Second ring magnet 108 Conductive ring 110A First axial extension 110B Second axial extension 112 Radial extension

Claims

1. A conductive ring that can be coupled to a housing, A magnetic element that can be coupled to a rotor shaft so as to rotate with respect to the conductive ring, A eddy current damper for a vacuum pump, comprising: The conductive ring is made of a conductive material and has an axially extending portion and a radially extending portion, The magnetic element includes at least one ring magnet, and the radially extending portion of the conductive ring is disposed axially adjacent to the at least one ring magnet. Eddy current damper.

2. The eddy current damper according to claim 1, wherein the magnetic element includes a second ring magnet disposed on the side opposite to the first ring magnet with respect to the conductive ring.

3. The eddy current damper according to claim 2, wherein the first ring magnet and the second ring magnet have magnetic poles in the same direction.

4. The eddy current damper according to claim 2 or 3, wherein the second ring magnet can be coupled to the housing or can be coupled to the rotor shaft.

5. The eddy current damper according to any one of claims 2 to 4, wherein a radially extending gap is formed by the first ring magnet and the second ring magnet, and the radially extending portion of the conductive ring extends at least partially into the gap.

6. The eddy current damper according to any one of claims 2 to 5, further comprising a yoke made of a magnetic material that magnetically couples the first ring magnet and the second ring magnet.

7. The eddy current damper according to claim 6, wherein the yoke includes two radially extending portions each magnetically coupled to the first ring magnet and the second ring magnet, and an axially extending portion that couples the two radially extending portions.

8. The eddy current damper according to claim 7, wherein the radial width of the axially extending portion of the yoke is smaller than the axial width of the first ring magnet and / or the second ring magnet.

9. The eddy current damper according to claim 7 or 8, wherein the axial width of at least one of the two radially extending portions of the yoke is smaller than the axial width of the first ring magnet and / or the second ring magnet.

10. The distance between the outermost surface in the radial direction of the axially extending portion of the yoke and the first ring magnet and / or the second ring magnet is between 1 time and 5 times the axial width of the first ring magnet and / or the second ring magnet. The eddy current damper according to any one of claims 7 to 9.

11. The first ring magnet and / or the second ring magnet axially extends beyond the axially extending element of the conductive ring. The eddy current damper according to any one of claims 1 to 10.

12. The conductive ring includes a second axially extending portion disposed on the opposite side of the first axially extending portion at an end portion opposite to the radially extending portion. The eddy current damper according to any one of claims 1 to 11.

13. The conductive ring is separated into at least two parts along the circumferential direction of the conductive ring. The eddy current damper according to any one of claims 1 to 12.

14. The conductive ring and the magnetic element are rotationally symmetric. The eddy current damper according to any one of claims 1 to 13.

15. The distance between the outermost or innermost radial surface of the conductive ring and the outermost or innermost radial surface of each of the first ring magnet and / or the second ring magnet is smaller than the radial width of the first ring magnet and / or the second ring magnet. The eddy current damper according to any one of claims 1 to 14.

16. The axial width of the radially extending portion of the conductive ring is smaller than the axial width of the first ring magnet and / or the second ring magnet. The eddy current damper according to any one of claims 1 to 15.

17. The radial width of the first ring magnet and / or the second ring magnet is between 2 mm and 20 mm, preferably between 3 mm and 10 mm. The eddy current damper according to any one of claims 1 to 16.

18. The axial distance between the radially extending portion of the conductive ring and the first ring magnet and / or the second ring magnet is between 0.05 mm and 2 mm, preferably between 0.1 mm and 1 mm. The eddy current damper according to any one of claims 1 to 17.

19. The radial distance between the inner surface of the axially extending portion of the conductive ring and the first ring magnet and / or the second ring magnet is between 0.05 mm and 2 mm, preferably between 0.1 mm and 1 mm, for the eddy current damper according to any one of claims 1 to 18.

20. A vacuum pump comprising a housing, a rotor disposed within the housing, and an eddy current damper according to any one of claims 1 to 19, wherein the first ring magnet is coupled to the rotor and the conductive ring is coupled to the housing.

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