Vacuum pump with eddy current damper

Abstract

A vacuum pump, particularly a turbomolecular vacuum pump, includes a housing and a rotor shaft disposed within the housing and rotatably supported by at least one permanent magnetic bearing, the magnetic bearing being disposed at one end of the rotor shaft, the magnetic bearing including a stationary bearing element and a rotating bearing element disposed radially adjacent to one another, and an eddy current damper having a conductive disk coupled to the stationary bearing element.

Description

[Technical Field]

[0001] The present invention relates to vacuum pumps, and in particular to turbomolecular pumps. [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 one pumping element is coupled to the rotor shaft. In the case of a turbomolecular 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 transports a gaseous medium from the inlet to the outlet of the vacuum pump.

[0003] In particular, when the rotor shaft is rotatably supported by one or more magnetic bearings, it is necessary to damp radial vibrations of the rotor shaft in order to stabilize the rotation of the rotor shaft and to avoid contact between the pump elements and the housing. However, such dampers are an additional consideration and usually increase the size of the vacuum pump. Summary of the Invention [Problem to be solved by the invention]

[0004] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a compact vacuum pump with a damper for radial vibrations. [Means for solving the problem]

[0005] This problem is solved by a vacuum pump according to claim 1.

[0006] In a first aspect, a vacuum pump, preferably configured as a turbomolecular pump, is provided. The vacuum pump includes a housing and a rotor shaft disposed within the housing and rotatably supported by at least one bearing. At least one pump element is coupled to the rotor shaft and rotated together with the rotor shaft by an electric motor. The vacuum pump according to the present invention includes at least a Volvic stage, where the pump element is constructed of a cylinder coupled to the rotor shaft and a stator surrounding the cylinder and coupled to the housing. The stator includes a threaded groove for directing gas molecules to an outlet of the vacuum pump. To achieve a compact design of the vacuum pump, an eddy current damper (ECD) is disposed within the cylinder of the Volvic stage, enabling efficient damping of radial vibrations without increasing the space requirements of the vacuum pump. Typically, the cylinder of the Volvic stage has a diameter as large as possible to increase circumferential velocity. Therefore, an internal volume is formed within the cylinder of the Volvic stage. It is known to utilize this internal volume to place an electric motor. However, in the present invention, in order to minimize the space required and implement such an ECD without increasing the size of the vacuum pump, it has been found to be beneficial to use this internal volume for an eddy current damper as well.

[0007] Preferably, the eddy current damper comprises a disk coupled to the housing and at least one ring magnet coupled to the rotor shaft, the disk being axially adjacent to the ring magnet, such that the magnetic field of the ring magnet rotating with the rotor shaft induces eddy currents in the disk, which is made of a conductive material such as copper or aluminum.

[0008] Preferably, the housing includes an inner wall that extends into the cylinder of the Volvic stage, and the disc is attached to the inner wall to couple the disc to the housing.

[0009] Preferably, the rotor shaft is supported by two bearings, and the ECD is disposed between the two bearings. At least one bearing is constructed as a permanent magnetic bearing. Preferably, the bearing facing the inlet side or the high vacuum side of the vacuum pump is constructed as a permanent magnetic bearing. Alternatively, both bearings are constructed as permanent magnetic bearings.

[0010] Preferably, the ECD is located between the electric motor and the bearing on the exhaust side of the rotor shaft toward the outlet of the vacuum pump. At that point, the electric motor may be coupled to the inner wall and located within the cylinder of the Volvic stage.

[0011] Preferably, the disk is separated into at least two parts. The separation is along the circumferential direction of the disk. Separating the disk into at least two or more parts allows for assembly of the disk around the rotor shaft. Therefore, pre-assembly of at least one ring magnet to the rotor shaft can be performed outside the housing, providing the possibility of balancing the rotor shaft together with the at least one ring magnet. Then, after balancing, the disk is assembled around the rotor shaft, and the pre-assembled rotor shaft is inserted into the housing. As a final step, the disk is bonded to the housing, i.e., to the inner wall of the housing. Therefore, after assembling the rotor in the housing, it is not necessary to bond the at least one ring magnet to the rotor shaft inside the housing.

[0012] Preferably, the EDC includes a second ring magnet located on the opposite side of the disk from the first ring magnet, thereby creating a gap between the first and second ring magnets and placing the disk in the gap. This arrangement strengthens the magnetic field at the disk, thereby more efficiently inducing eddy currents in the disk.

[0013] Preferably, the disk includes one radial extension, preferably extending into the gap between the first and second ring magnets, and at least one axial extension, in that the axial extension acts as a conductor to enhance the flow of eddy currents through the disk and reduce the ohmic resistance of the disk.

[0014] The present invention will now be described in more detail with reference to the accompanying drawings. [Brief explanation of the drawings]

[0015] [Figure 1] 1 is a first embodiment of the present invention. [Figure 2] FIG. 4 is a detailed view of the second embodiment of the present invention. [Figure 3] FIG. 10 is a detailed view of another embodiment of the present invention. [Figure 4] FIG. 10 is a detailed view of another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0016] Reference is made to FIG. 1 , which illustrates a vacuum pump constructed as a molecular vacuum pump. For simplicity, only one half of the vacuum pump is shown, which is substantially symmetrical about a central axis (excess) 11. The vacuum pump includes a housing 10 within which a rotor shaft 12 is disposed. The rotor shaft 12 is rotatably supported by a first bearing 16 constructed as a permanent magnetic bearing and a second bearing 14 also constructed as a permanent magnetic bearing. The first magnetic bearing 16 includes a stationary bearing element 22 coupled to the housing via a trunnion 18 extending into a recess in the rotor shaft 12. The first magnetic bearing 16 further includes a rotary bearing element 24 coupled to the rotor shaft 12. The stationary bearing element 22 and the rotary bearing element 24 each include a plurality of mutually repelling ring magnets 27 to create radial support between the stationary bearing element 22 and the rotary bearing element 24. Similarly, the second magnetic bearing 14 comprises a stationary bearing element 26 having a plurality of ring magnets 27 and a plurality of ring magnets 27 that mutually repel the ring magnets 27 of the stationary bearing element 26. In that regard, the stationary bearing element is similarly coupled to the housing 10 via a trunnion 20, as shown in FIG.

[0017] 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 with each other to convey the gaseous medium. The vacuum pump further comprises a Holweck stage 37 including a cylinder 38 coupled to the rotor shaft and rotating therewith. The Holweck stage 37 further comprises a Holweck stator 40 having a threaded groove 41 for conveying the gaseous medium from the inlet 30 of the vacuum pump toward an outlet (not shown). At that point, the housing 10 comprises an inner wall 36 to which the stator of the electric motor 29 is coupled. The inner wall 36 extends into the internal volume of the cylinder 38 of the Holweck stage 37.

[0018] Furthermore, according to the present invention, the vacuum pump is provided with an eddy current damper 100 (ECD), which is located inside the cylinder 38 of the Holweck stage 37 in order to provide a compact design of the vacuum pump.

[0019] The ECD 100 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. Therefore, the disk 102 does not rotate. The ECD 100 further 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. Therefore, 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 location 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, and the created magnetic force is opposite to the vibrating motion, thereby creating a restoring force on the rotor shaft 12 and damping the radial vibration of the rotor.

[0020] At this point, the conductive disk 102 can be separated into two parts along its circumferential direction. Therefore, the first ring magnet 106A and the second ring magnet 106B can be pre-assembled to the rotor shaft 12. The conductive disk 102 is then assembled around the rotor shaft 12. The rotor shaft 12 is then 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 and 104B. Alternatively, the rotor shaft 12 can be inserted into the first housing element, then the conductive disk 102 is assembled around the rotor shaft 12, and then the cap element 101 with the inner wall 36 is inserted into the housing, i.e., into the rotor cylinder. In the final step, the conductive disk 102 is coupled to the inner wall 36.

[0021] The embodiment of Figure 1 therefore provides a compact vacuum pump design in which the space within the cylinder 38 of the Holweck stage 37 is efficiently used to position an ECD that damps radial vibrations of the rotor.

[0022] Referring to FIG. 2, there is shown a detailed view of the first magnetic bearing 16 on the inlet side of the vacuum pump, which may be constructed similarly to the vacuum pump of FIG.

[0023] In the following, identical or similar elements are designated with the same reference numerals.

[0024] 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 a spring 114. In this regard, the adjustment element 110 includes a radial protrusion 111, to which a conductive disk 112 is coupled. Thus, the radial protrusion 111 positions the conductive disk 112 axially adjacent to a ring magnet 116 of an 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. This configuration therefore allows the ECD to be integrated into the magnetic bearing, providing a compact design. Specifically, the ECD is positioned between the magnetic bearing and an end 119 of the rotor shaft 12. Therefore, efficient damping of radial vibrations can be achieved. Furthermore, due to its location, the ECD can be constructed compactly while still efficiently damping radial vibrations.

[0025] Alternatively, the ECD of Figure 2 can be mounted on a second magnetic bearing on the exhaust side of the vacuum pump.

[0026] 3, which shows a configuration similar to that of FIG. 2, a ferritic 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 rotation bearing element 24. The ferritic material element 120 therefore creates a magnetic circuit that strengthens the magnetic field at the location of the conductive disk 112. In particular, the tuning element 110 is also constructed from a ferritic material and further strengthens the magnetic field at the location of the conductive disk 116 by creating a completely or nearly closed magnetic circuit.

[0027] Although FIG. 3 shows the ECD mounted on a first magnetic bearing on the intake side of the vacuum pump, the ECD may alternatively or additionally be mounted on a second magnetic bearing on the exhaust side of the vacuum pump.

[0028] 4, which illustrates another embodiment of the present invention, an adjustment element 110 includes a radial protrusion 111 as a separate element supporting a conductive disk 112, which is axially adjacent to the outermost ring magnet 27 of the rotation bearing element 24. The outermost ring magnet 27 of the rotation bearing element 24 therefore simultaneously facilitates support of the rotor shaft 12 and is also used as a ring magnet for the ECD, which induces eddy currents when the rotor shaft vibrates. This allows for a compact design and avoids the need for an additional ring magnet just for the ECD.

[0029] Although FIG. 4 shows the ECD mounted on a first magnetic bearing on the intake side of the vacuum pump, the ECD may alternatively or additionally be mounted on a second magnetic bearing on the exhaust side of the vacuum pump.

[0030] Of course, the embodiments of Figures 1 and 2 to 4 can be freely combined. The vacuum pump can include an eddy current damper arranged in the cylinder 38 of the Holweck stage 37 and an additional eddy current damper integrated into one of the magnetic bearings 14, 16. Furthermore, the vacuum pump can include an ECD integrated into the first magnetic bearing 16 or the second magnetic bearing 14. Alternatively, the vacuum pump can include an ECD in the first magnetic bearing as well as in the second magnetic bearing. In that respect, the ECD can be constructed similarly to one of the embodiments of Figures 2 to 4 or differently from one of the embodiments of Figures 2 to 4. [Explanation of symbols]

[0031] 10. Housing 12 rotor shaft 14 Second bearing 16 First bearing 37 Holbeck Stage 40 Holbeck Stator 100 Eddy current damper

Claims

1. Housing and A rotor shaft is disposed within the housing and rotatably supported by at least one bearing, A Holbeck stage comprising a cylinder coupled to the rotor shaft and a stator surrounding the cylinder and coupled to the housing, The eddy current damper is disposed within the cylinder of the Holbeck stage, A vacuum pump equipped with, in detail, a turbomolecular vacuum pump.

2. The vacuum pump according to claim 1, wherein the eddy current damper comprises a disk coupled to the housing and at least one ring magnet coupled to the rotor shaft, the disk being arranged axially adjacent to the ring magnet.

3. The vacuum pump according to claim 2, comprising an inner wall extending into the cylinder, wherein the disk is attached to the inner wall.

4. The vacuum pump according to claim 1, wherein the rotor shaft is supported by two bearings, and the eddy current damper is positioned between the two bearings.

5. The vacuum pump according to claim 1, wherein at least one bearing, preferably all bearings, is constructed as a permanent magnet bearing.

6. The vacuum pump according to claim 2, wherein the disk is separated into at least two parts.

7. The vacuum pump according to claim 2, wherein the disk comprises a portion extending in one radial direction and a portion extending in at least one axial direction, the radial portion being positioned adjacent to the axial surface of at least one of the ring magnets or within a gap created by two of the ring magnets.

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