The present invention relates to a vacuum pump and in particular to a turbo- molecular pump.

Common vacuum pumps comprise a housing having an inlet and an outlet. A rotor is disposed in the housing and rotatably supported by at least one bearing. The rotor comprises a rotor shaft, wherein at least one pump element is connected to the rotor shaft. In the case of a turbomolecular vacuum pump a plurality of vanes is connected to the rotor shaft and interacting with a plurality of vanes of a stator being connected to a housing. Upon rotation of the rotor by an electromotor a gaseous medium is conveyed from the inlet towards the outlet of the vacuum pump.

In particular, if the rotor shaft is rotatably supported by one or more magnetic bearings the radial vibrations of the rotor shaft need to be damped in order to stabilize rotation of the rotor shaft and avoid contact between the pump elements and the housing. However, such a damper is an additional element which need to be considered and usually increases the size of the vacuum pump.

Thus, it is an object of the present invention to provide a vacuum pump with a damper for radial vibrations which is compact.

The problem is solved by a vacuum pump according to claim 1.

In a first aspect a vacuum pump, preferably built as turbomolecular pump, is provided. The vacuum pump comprises a housing and a rotor shaft disposed in the housing and rotatably supported by at least one bearing. At least one pump element is connected to the rotor shaft and rotated with the rotor shaft by an electromotor. Therein, the vacuum pump according to the present invention comprises at least a Holweck stage wherein the pump element is built by a cylinder connected to the rotor shaft and a stator surrounding the cylinder connected to the housing. Therein, the stator comprises a threaded groove for guiding of the gas molecules towards the outlet of the vacuum pump. In order to achieve a compact design of the vacuum pump an eddy current damper (ECD) is arranged inside the cylinder of the Holweck stage to provide efficient damping of radial vibration without increasing the space requirements of the vacuum pump. Usually the cylinder of the Holweck stage is as large as possible in diameter in order to increase the circumferential speed. Thus, an interior volume is created within the cylinder of the Holweck stage. It is known to use this interior volume to place the electromotor. However, it was found to be beneficial by the present invention to also use this interior volume for the eddy current damper in order to minimize the space requirements and implement such ECD without increasing the size of the vacuum pump.

Preferably, the eddy current damper comprises a disk connected to the housing and at least one ring magnet connected to the rotor shaft wherein the disk is arranged axially next to the ring magnet. Thus, by the magnetic field of the ring magnet rotated together with the rotor shaft eddy currents are induced into the disk which is made from a conductive material such as copper, aluminum or the like.

Preferably, the housing comprises an interior wall extending into the cylinder of the Holweck stage wherein the disk is attached to the interior wall for connecting the disk to the housing.

Preferably, the rotor shaft is supported by two bearings wherein the ECD is disposed between the two bearings. Therein, at least one bearing is built as permanent magnetic bearing. Preferably, the bearing towards the inlet side or high vacuum side of the vacuum pump is built as permanent magnetic bearing. Alternatively, both bearings are built as permanent magnetic bearings. Preferably, the ECD is disposed between the electromotor and the bearing of the exhaust side of the rotor shaft towards the outlet of the vacuum pump. Therein, the electromotor can also be connected to the interior wall and also placed within the cylinder of the Holweck stage.

Preferably, the disk is separated into at least two parts. Separation is along a circumferential direction of the disk. By separating the disk into at least two or more parts assembly of the disk around the rotor shaft is feasible. Thus, preassembly of the at least one ring magnet to the rotor shaft can be carried out outside the housing providing the possibility to balance the rotor shaft together with the at least one ring magnet. Subsequently, after balancing, the disk is assembled around the rotor shaft and the preassembled rotor shaft is inserted into the housing. As last step, the disk is connected to the housing, i.e. the interior wall of the housing. Thus, it is not necessary to join the at least one ring magnet to the rotor shaft within the housing after assembly of the rotor into the housing.

Preferably, the EDC comprises a second ring magnet arranged opposite to the first ring magnet relative to the disk. Thus, by the first ring magnet and the second ring magnet a gap is created, wherein the disk is arranged in the gap. Thus, by this arrangement the magnet fields at the position of the disk is enhanced thereby more efficiently induce eddy currents into the disk.

Preferably, the disk comprises one radial extending part preferably extending into the gap between the first ring magnet and the second ring magnet and further comprising at least one axial extending part. Therein, the axial extending part serves as conductor in order to decrease ohmic resistance of the disk enhancing flow of the eddy currents through the disk.

In the following the present invention is described with reference to the accompanied figures. The figures show:

Figure 1 a first embodiment according to the present invention,

Figure 2 a detailed view of the second embodiment of the present invention,

Figure 3 a detailed view of another embodiment of the present invention and

Figure 4 a detailed view of another embodiment of the present invention.

Referring to figure 1 showing a vacuum pump built as molecular vacuum pump. Therein, for simplicity only one half of the vacuum pump is shown being substantially symmetrical around the center excess 11. The vacuum pump comprises a housing 10 wherein in the housing a rotor shaft 12 is disposed. The rotor shaft 12 is rotatably supported by a first bearing 16 built as permanent magnetic bearing and a second bearing 14 also built as permanent magnetic bearing. The first magnetic bearing 16 comprises a static bearing element 22 connected to the housing via a trunnion 18 extending into recess of the rotor shaft 12. Further, the first magnetic bearing 16 comprises a rotated bearing element 24 connected to the rotor shaft 12. The static bearing element 22 and the rotated bearing element 24 comprise each a number of ring magnets 27 being in mutual repulses to each other in order to create radial support between the static bearing element 22 and the rotated bearing element 24. Similar, the second magnetic bearing 14 also comprises a static bearing element 26 comprises a plurality of ring magnets 27 and a rotated bearing element 28 being connected to the rotor shaft 12 also comprising a plurality of ring magnets 27 being in mutual repulsing to the ring magnets 27 of the static bearing element 26. Therein, as shown in figure 1, the static bearing element is also connected to the housing 10 via a trunnion 20.

The rotor shaft 12 is rotated by an electromotor 29. A plurality of pump elements 32 built as vanes are connected to the rotor shaft 12 and interacting with stator elements 34 alternating arranged to the pump elements 32 and interacting with each other in order to convey a gaseous medium. Further, the vacuum pump comprises a Holweck stage 37 including a cylinder 38 being connected to the rotor shaft and rotated together with the rotor shaft. Further, the Holweck stage 37 comprises a Holweck stator 40 having a threaded groove 41 in order to convey the gaseous medium from the inlet 30 towards an outlet of the vacuum pump (not shown). Therein, the housing 10 comprises an interior wall 36 wherein the stator of the electromotor 29 is connected to the interior wall. The interior wall 36 is extending into the inner volume of the cylinder 38 of the Holweck stage 37.

Further, according to the present invention the vacuum pump comprises an eddy current damper 100 (ECD). The ECD is arranged inside the cylinder 38 of the Holweck stage 37 in order to provide a compact design of the vacuum pump.

The ECD comprises a disk 102 made of a conductive material such as copper or aluminum. The disk 102 is connected via connecting elements 104A and 104B to the interior wall 36 of the housing 10. Thus, the disk 102 is non-rotating. Further, the ECD 100 comprises a first ring magnet 106A and a second ring magnet 106B being arranged axially next to the disk 102. By the first ring magnet 106A and the second ring magnet 106B a gap is created, wherein the conductive disk 102 of the ECD 100 extends into the gap. First ring magnet 106A and second ring magnet 106B are attached to the rotor shaft 12 and rotated together with the rotor shaft 12. Thus, due to rotation and upon radial vibrations of the rotor shaft 12, by the magnetic field at the position of the conductive disk 102 eddy currents are induced into the conductive disk 102 wherein the induced eddy currents create a magnetic field interacting with the magnetic field of the first ring magnet 106A and second ring magnet 106B wherein the created magnetic force is opposite to the movement of vibration thereby creating a restoring force to the rotor shaft 12 and damping the radial vibration of the rotor.

Therein, the conductive disk 102 can be separated into two parts along its circumferential direction. Thus, the first ring magnet 106A and second ring magnet 106B can be preassembled to the rotor shaft 12. Afterwards the conductive disk 102 is assembled around the rotor shaft 12. Subsequently, the rotor shaft 12 is inserted into the housing 10 and attached by the connecting elements 104A, 104B to the interior wall 36 of the cap element 101 of the housing 10. Alternatively, the rotor shaft 12 is inserted into a first housing element, subsequently, the conductive disk 102 is assembled around the rotor shaft 12 and afterwards the cap element 101 with the interior wall 36 is inserted into the housing, i.e. into the cylinder of the rotor. In a last step, the conductive disk 102 is connected to the interior wall 36.

Thus, by the embodiment of figure 1 a compact design for vacuum pump is provided wherein the space within the cylinder 38 of the Holweck stage 37 is efficiently used in order to place an ECD to damper radial vibrations of the rotor.

Referring to figure 2 showing a detailed view of the first magnet bearing 16 at the inlet side of the of a vacuum pump which can be built similar than the vacuum pump of figure 1.

In the following same or similar elements are indicated by the same reference sings.

In figure 2 the static bearing element 22 comprises an adjustment element 110 in order to adjust the axial position of the static bearing element 22 by adjusting the position of the static bearing element 22 against the restoring force of the spring 114. Therein, the adjustment element 110 comprises a radial protrusion 111 wherein a conductive disk 112 is connected to the radial protrusion 111. Thus, by the radial protrusion 111 the conductive disk 112 is arranged axially next to a ring magnet 116 of the ECD connected to the rotor shaft 12. The ring magnet 116 of the ECD is separated by a non-magnetic ring element 118 from the ring magnets 27 of the rotated bearing element 24. Thus, by this configuration, the ECD is integrated into the magnetic bearing providing a compact design. In particular, the ECD is positioned between the magnetic bearing and the end 119 of the rotor shaft 12. Thus, efficient damping of radial vibrations can be achieved. Further, due to its position, the ECD can be built small while still efficiently damping the radial vibrations.

Alternatively, the ECD of figure 2 can also be implemented in the second magnetic bearing at the exhaust side of the vacuum pump.

Referring to figure 3 showing a similar configuration to figure 2 wherein a ferritic material element 120 is placed between the ring magnet 116 of the ECD and the non-magnetic material element 118 separating the ring magnet 116 of the ECD from the ring magnets 27 of the rotated bearing element 24. Thus, by the ferritic material element 120 a magnetic circuit is created enhancing the magnetic field at the position of the conductive disk 112. In particular, the adjustment element 110 is also built from a ferritic material further enhancing the magnetic field at the position of the conductive disk 116 by creating a full or almost closed magnetic circuit.

Although shown in figure 3 that the ECD is implemented in the first magnetic bearing at the inlet side of the vacuum pump, the ECD can also be implemented, alternatively or additionally, in the second magnetic bearing at the exhaust side of the vacuum pump. Referring to figure 4 showing another embodiment of the present invention wherein the adjustment 110 includes a radial protrusion 111 as separate element carrying the conductive disk 112. Therein, the conductive disk 112 is axially next to the outermost ring magnet 27 of the rotated bearing element 24. Thus, the outermost ring magnet 27 of the rotated bearing element 24 simultaneously facilitates supporting the rotor shaft 12 and at the same time is used as ring magnet for the ECD inducing eddy currents upon vibration of the rotor shaft. Thereby, a compact design is achieved and an additional ring magnet only for the ECD can be avoided.

Although shown in figure 4 that the ECD is implemented in the first magnetic bearing at the inlet side of the vacuum pump, the ECD can also be implemented, alternatively or additionally, in the second magnetic bearing at the exhaust side of the vacuum pump.

Of course, the embodiments of figure 1 and figure 2 to 4 can be freely combined. The vacuum pump may comprise an eddy current damper placed within the cylinder 38 of the Holweck stage 37 in connection with an additional eddy current damper integrated in one of the magnetic bearings 14, 16. Furthermore the vacuum pump may comprise an ECD integrated in the first magnetic bearing 16 or in the second magnetic bearing 14. Alternatively, the vacuum pump comprises an ECD in the first magnetic bearing as well as in the second magnetic bearing. Therein, the ECDs can be built identically along with one of the embodiments 2 to 4 or can be built different according to one of the embodiments of figures 2 to 4.