Vacuum pump equipped with an eddy current damper

Abstract

A vacuum pump, in particular a turbomolecular vacuum pump, comprises a housing and a rotor shaft which is arranged in the housing and is rotatably supported by at least one permanent magnet bearing. In that regard, the magnetic bearing is arranged at one end of the rotor shaft, and the magnetic bearing comprises a stationary bearing element and a rotating bearing element which are arranged radially adjacent to each other. An eddy current damper having a conductive disk coupled to the stationary bearing element is provided.

Description

Technical Field

[0001] The present invention relates to a vacuum pump, and more particularly to a turbo molecular pump.

Background Art

[0002] A general vacuum pump includes a housing having an inlet and an outlet. A rotor is disposed within the housing and is rotatably supported by at least one bearing. The rotor includes a rotor shaft, and at least one pump element is coupled to the rotor shaft. In the case of a turbo molecular vacuum pump, a plurality of vanes are coupled to the rotor shaft and interact with a plurality of vanes of a stator coupled to the housing. Rotation of the rotor by an electric motor causes a gaseous medium to be conveyed from the inlet to the outlet of the vacuum pump.

[0003] Specifically, when the rotor shaft is rotatably supported by one or more magnetic bearings, it is necessary to attenuate the radial vibration of the rotor shaft in order to stabilize the rotation of the rotor shaft and avoid contact between the pump element and the housing. However, such dampers are additional elements to be considered and usually increase the size of the vacuum pump.

Summary of the Invention

Problems to be Solved by the Invention

[0004] Accordingly, an object of the present invention is to provide a compact vacuum pump provided with a damper for radial vibration.

Means for Solving the Problems

[0005] This problem is solved by the vacuum pump according to claim 1 and the vacuum pump according to claim 8.

[0006] In a first aspect, there is provided a vacuum pump, preferably constructed as a turbomolecular pump. The vacuum pump comprises a housing and a rotor shaft disposed within the housing and rotatably supported by at least one bearing. In that regard, at least one pump element is coupled to the rotor shaft, and rotation of the rotor shaft by an electric motor causes a gaseous medium to be conveyed from an inlet of the vacuum pump towards an outlet of the vacuum pump. In that regard, a magnetic bearing is disposed at one end of the rotor shaft, the magnetic bearing comprising a static bearing element coupled to the housing of the vacuum pump and not rotating. Further, the magnetic bearing comprises a rotating bearing element coupled radially to the rotor shaft and rotating relative to the static bearing element. The rotating bearing element is disposed adjacent to the static bearing element in order to support the rotor shaft by mutual magnetic repulsion between the static bearing element and the rotating bearing element.

[0007] According to the present invention, there is provided an eddy current damper (ECD) having a conductive disk coupled to the static bearing element. Thus, according to the present invention, an eddy current damper for damping radial vibrations of the rotor shaft is integrated into the magnetic bearing, thereby reducing the space required. Further, since the magnetic bearing is disposed at one end of the rotor shaft, radial vibrations of the rotor shaft due to tilt or nutation of the rotor shaft are greatest at the end of the rotor shaft. Therefore, it is most efficient to damp this movement at the end of the rotor shaft. Thus, the ECD can be constructed in a small size while maintaining the damping efficiency.

[0008] Preferably, the static bearing element is coupled to a trunnion extending into a recess of the rotor shaft.

[0009] Preferably, the static bearing element and the rotating bearing element comprising a plurality of ring magnets repel each other. Thus, a repulsive magnetic force is created between them by the ring magnets of the static bearing element and the rotating bearing element.

[0010] Preferably, the magnetic bearing comprises an adjustment element coupled to the stationary bearing element for adjusting the axial position of the stationary bearing element relative to the rotating bearing element, and the conductive disk is attached to the adjustment element. Thus, by inserting the adjustment element into the magnetic bearing during assembly, the ECD including the conductive disk is assembled simultaneously.

[0011] Preferably, the adjustment element is made of a ferrite-based material. Thus, the magnetic field of the static bearing element penetrates the ferrite-based adjustment element to create a magnetic circuit and strengthen the magnetic field at the position of the conductive disk.

[0012] Preferably, the stationary bearing element comprises a radially protruding portion, and the conductive disk is coupled to the radially protruding portion. Thus, by the radially protruding portion, the conductive disk can be arranged axially adjacent to each ring magnet of the ECD coupled to the rotating bearing element to induce eddy currents in the conductive disk. In that regard, more preferably, the radially protruding portion can be constructed by an additional element arranged between the outermost ring magnet in the axial direction of the stationary bearing element and the adjustment element, or can be constructed as an integral part with the adjustment element to facilitate assembly.

[0013] Preferably, the conductive disk is arranged axially adjacent to the rotating bearing element such that eddy currents are induced in the conductive disk by the magnetic field of the rotating bearing element.

[0014] Preferably, the outermost ring magnet of the rotating bearing element is simultaneously the magnet ring of the ECD, and the magnetic field of the outermost ring element of the rotating bearing element is adapted to induce eddy currents in the conductive disk. There is no need to add a ring magnet for the ECD, and the magnetic field of the rotating bearing element can also be used for the ECD. Alternatively, the ECD comprises an additional ring magnet coupled to the rotating bearing element and separated from the ring magnet of the rotating bearing element by a non-magnetic material. Thereby, the magnetic circuit is created by the additional ring magnet across the gap between the rotating bearing element and the adjustment element, preferably made of a ferrite-based material.

[0015] Preferably, the ECD is disposed at the axial end of the rotor shaft, i.e., between the magnetic bearing and the end of the rotor shaft, in order to efficiently attenuate the radial vibration of the rotor shaft by arranging the ECD at the outermost position of the rotor shaft.

[0016] Preferably, the eddy current damper is disposed on the exhaust side of the rotor shaft. Alternatively, the ECD is disposed on the intake side or the high-vacuum side of the rotor shaft. More preferably, the ECDs are disposed at both ends of the rotor shaft. In that regard, the ECDs at both ends can have the same or different structures and can be constructed as described above in detail.

[0017] Accordingly, a compactly designed eddy current damper incorporated into the magnetic bearing of a vacuum pump is provided. In that regard, at the same time, the ECD is disposed at the position where the rotor shaft receives the largest vibration due to tilting of the rotor shaft around the center of gravity of the rotor shaft.

[0018] Hereinafter, the present invention will be described in more detail with reference to the accompanying drawings.

Brief Description of the Drawings

[0019]

Figure 1

Figure 2

Figure 3

Figure 4

Modes for Carrying Out the Invention

[0020] Refer to FIG. 1 showing a vacuum pump constructed as a molecular vacuum pump. In that regard, for the sake of simplicity, only half of the vacuum pump that is substantially symmetric around the central axis (excess) 11 is shown. The vacuum pump comprises a housing 10, and a rotor shaft 12 is disposed within the housing. The rotor shaft 12 is rotatably supported by a first bearing 16 constructed as a permanent magnet bearing and a second bearing 14 also constructed as a permanent magnet bearing. The first magnetic bearing 16 comprises a stationary bearing element 22 coupled to the housing via a trunnion 18 extending into a recess of the rotor shaft 12. Further, the first magnetic bearing 16 comprises a rotating bearing element 24 coupled to the rotor shaft 12. Each of the stationary bearing element 22 and the rotating bearing element 24 comprises a plurality of ring magnets 27 that repel each other to create a radial support between the stationary bearing element 22 and the rotating bearing element 24. Similarly, the second magnetic bearing 14 comprises a stationary bearing element 26 comprising a plurality of ring magnets 27 and a plurality of ring magnets 27 that repel the ring magnets 27 of the stationary bearing element 26. In that regard, as shown in FIG. 1, the stationary bearing element is also coupled to the housing 10 via a trunnion 20.

[0021] The rotor shaft 12 is rotated by an electric motor 29. A plurality of pump elements 32 constructed as vanes are coupled to the rotor shaft 12 and interact with stator elements 34 arranged alternately with respect to the pump elements 32 and interact with each other to convey a gaseous medium. Further, the vacuum pump comprises a Holweck stage 37 including a cylinder 38 coupled to the rotor shaft and rotating together with the rotor shaft. Further, the Holweck stage 37 comprises a Holweck stator 40 having a helical groove 41 for conveying a gaseous medium from the inlet 30 of the vacuum pump towards an outlet (not shown). In that regard, the housing 10 comprises an inner wall 36, and the stator of the electric motor 29 is coupled to this inner wall. The inner wall 36 extends into the internal volume of the cylinder 38 of the Holweck stage 37.

[0022] Furthermore, according to the present invention, the vacuum pump is provided with an eddy current damper 100 (ECD). The ECD is disposed inside the cylinder 38 of the Holbeck stage 37 to provide a compact design of the vacuum pump.

[0023] The ECD includes a disk 102 made of a conductive material such as copper or aluminum. The disk 102 is coupled to the inner wall 36 of the housing 10 via coupling elements 104A and 104B. Thus, the disk 102 does not rotate. Further, the ECD 100 includes a first ring magnet 106A and a second ring magnet 106B disposed axially adjacent to the disk 102. A gap is created between the first ring magnet 106A and the second ring magnet 106B, and the conductive disk 102 of the ECD 100 extends into the gap. The first ring magnet 106A and the second ring magnet 106B are attached to the rotor shaft 12 and rotate together with the rotor shaft 12. Thus, due to the rotation and radial vibration of the rotor shaft 12, eddy currents are induced in the conductive disk 102 by the magnetic field at the position of the conductive disk 102, and the induced eddy currents create a magnetic field that interacts with the magnetic fields of the first ring magnet 106A and the second ring magnet 106B. The generated magnetic force is opposite to the vibrating movement, thereby creating a restoring force against the rotor shaft 12 and damping the radial vibration of the rotor.

[0024] In that regard, the conductive disk 102 can be separated into two parts along its circumferential direction. Thus, the first ring magnet 106A and the second ring magnet 106B can be pre-assembled to the rotor shaft 12. Thereafter, the conductive disk 102 is assembled around the rotor shaft 12. Thereafter, the rotor shaft 12 is inserted into the housing 10 and attached to the inner wall 36 of the cap element 101 of the housing 10 by the coupling elements 104A, 104B. Alternatively, the rotor shaft 12 is inserted into the first housing element, then the conductive disk 102 is assembled around the rotor shaft 12, and then the cap element 101 having the inner wall 36 is inserted into the housing, i.e., the cylinder of the rotor. In the last step, the conductive disk 102 is coupled to the inner wall 36.

[0025] Thus, according to the embodiment of FIG. 1, a compact vacuum pump design is provided in which the space within the cylinder 38 of the holbeck stage 37 is efficiently used to dispose an ECD that attenuates the radial vibration of the rotor.

[0026] Referring to FIG. 2, a detailed view of a first magnetic bearing 16 on the inlet side of a vacuum pump that can be constructed similarly to the vacuum pump of FIG. 1 is shown.

[0027] Hereinafter, the same or similar elements are denoted by the same reference numerals.

[0028] In FIG. 2, the stationary bearing element 22 includes an adjustment element 110 for adjusting the axial position of the stationary bearing element 22 by adjusting the position of the stationary bearing element 22 against the restoring force of the spring 114. In that regard, the adjustment element 110 includes a radially projecting portion 111, and the conductive disk 112 is coupled to the radially projecting portion 111. Accordingly, by the radially projecting portion 111, the conductive disk 112 is disposed axially adjacent to the ring magnet 116 of the ECD coupled to the rotor shaft 12. The ring magnet 116 of the ECD is separated from the ring magnet 27 of the rotary bearing element 24 by a non-magnetic ring element 118. Thus, with this configuration, the ECD is integrated into the magnetic bearing, providing a compact design. Specifically, the ECD is disposed between the magnetic bearing and the end 119 of the rotor shaft 12. Thus, efficient attenuation of radial vibration can be achieved. Further, due to its position, the ECD can be constructed in a small size while efficiently attenuating radial vibration.

[0029] Alternatively, the ECD of FIG. 2 can also be implemented in a second magnetic bearing on the exhaust side of the vacuum pump.

[0030] Referring to FIG. 3, which shows a configuration similar to that of FIG. 2, a ferrite-based material element 120 is disposed between the ring magnet 116 of the ECD and a non-magnetic material element 118 that separates the ring magnet 116 of the ECD from the ring magnet 27 of the rotary bearing element 24. Thus, the ferrite-based material element 120 creates a magnetic circuit that strengthens the magnetic field at the position of the conductive disk 112. Specifically, the adjustment element 110 is also constructed from a ferrite-based material and further strengthens the magnetic field at the position of the conductive disk 116 by creating a completely or almost closed magnetic circuit.

[0031] FIG. 3 shows that the ECD is implemented in a first magnetic bearing on the intake side of the vacuum pump. However, the ECD can alternatively or additionally be implemented in a second magnetic bearing on the exhaust side of the vacuum pump.

[0032] Referring to FIG. 4, which shows another embodiment of the present invention, the adjustment element 110 includes a radially projecting portion 111 as a separate element that supports the conductive disk 112. In that regard, the conductive disk 112 is axially adjacent to the outermost ring magnet 27 of the rotary bearing element 24. Thus, the outermost ring magnet 27 of the rotary bearing element 24 simultaneously facilitates the support of the rotor shaft 12 and is used as a ring magnet for the ECD that induces eddy currents during vibration of the rotor shaft. Thereby, a compact design is achieved and it is possible to avoid adding a ring magnet solely for the ECD.

[0033] FIG. 4 shows that the ECD is implemented in a first magnetic bearing on the intake side of the vacuum pump. However, the ECD can alternatively or additionally be implemented in a second magnetic bearing on the exhaust side of the vacuum pump

[0034] Of course, the embodiments of FIGS. 1 and 2 to 4 can be freely combined. The vacuum pump can include an eddy current damper disposed within the cylinder 38 of the Holbeck stage 37 and an additional eddy current damper integrated with one of the magnetic bearings 14, 16. Further, the vacuum pump can include an ECD integrated with the first magnetic bearing 16 or the second magnetic bearing 14. Alternatively, the vacuum pump includes an ECD in both the first magnetic bearing and the second magnetic bearing. In that regard, the ECD can be constructed similarly to one of the embodiments 2 to 4 or can be constructed differently from one of the embodiments of FIGS. 2 to 4.

Claims

1. A housing, a rotor shaft disposed within the housing and rotatably supported by at least one permanent magnet bearing, comprising: the magnetic bearing is disposed at one end of the rotor shaft, the magnetic bearing includes a stationary bearing element and a rotating bearing element arranged adjacent to each other in the radial direction, and an eddy current damper having a conductive disk coupled to the stationary bearing element, and is specifically a turbo molecular vacuum pump, a vacuum pump.

2. The vacuum pump according to claim 1, wherein each of the stationary bearing element and the rotating bearing element includes a plurality of ring magnets that mutually repel each other.

3. The magnetic bearing according to claim 1 or 2, further comprising an adjustment element coupled to the stationary bearing element for adjusting an axial position of the stationary bearing element with respect to the rotating bearing element, and the conductive disk is attached to the adjustment element.

4. The vacuum pump according to claim 3, wherein the adjustment element is made of a ferrite-based material.

5. The vacuum pump according to any one of claims 1 to 4, wherein the stationary bearing element includes a radially protruding portion, and the conductive disk is coupled to the radially protruding portion.

6. The vacuum pump according to claim 5, wherein the conductive disk is disposed axially adjacent to the rotating bearing element, and eddy currents can be induced in the conductive disk by a magnetic field of the rotating bearing element.

7. The vacuum pump according to any one of claims 1 to 6, wherein the eddy current damper includes a ring magnet coupled to the rotating bearing element and separated from the ring magnet of the rotating bearing element by a non-magnetic material.

8. The vacuum pump according to any one of claims 1 to 7, wherein the eddy current damper is disposed at an axial end of the rotor shaft.

9. The vacuum pump according to any one of claims 1 to 8, wherein the eddy current damper is disposed on an exhaust side of the rotor shaft.

10. The vacuum pump according to any one of claims 1 to 9, wherein eddy current dampers are disposed at both ends of the rotor shaft.

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