Vacuum pump

Abstract

Vacuum pump, in particular a turbo-molecular vacuum pump, comprising: a housing defining a pump chamber; a rotor assembly arranged in the pump chamber comprising a rotor shaft having a first end and an opposite second end; and an active thrust-bearing assembly arranged at the second end of the rotor shaft, the active thrust-bearing assembly comprises a cartridge inserted into the housing, wherein an active magnetic bearing and an eddy current damper are arranged in the cartridge.

Description

[0001] Vacuum Pump

[0002] The present invention relates to a vacuum pump and in particular a turbo-molecular vacuum pump. Further, the present invention relates to a method for providing a pre-assembled active thrust-bearing assembly and a method for assembly of a vacuum pump and in particular a turbo-molecular pump using such a preassembled active thrust-bearing assembly.

[0003] Common vacuum pumps comprise a housing having an inlet and an outlet. In the housing a rotatably supported rotor assembly is disposed that is rotated by an electromotor. The rotor assembly is rotatably supported by bearings, wherein in common vacuum pumps these bearings can either be roller bearing or magnet bearings. Further, the rotor assembly comprises at least one rotor element. In the case of a turbo-molecular pump, the rotor assembly comprises a plurality of rotor elements built as vanes arranged in one or more stages interacting with respective stator elements connected to the housing. In the case of a turbo-molecular pump also the stator elements are built as vanes arranged in an alternating manner with the one or more stages of the rotor assembly. By the rotation of the rotor assembly, a gaseous medium is conveyed from the inlet of the vacuum pump to the outlet of the vacuum pump.

[0004] In order to provide a compact vacuum pump that is fully magnetic levitated the respective components such as the magnetic radial bearings, the magnetic axial bearing and, if included, a vibration damper such as an eddy current damper need to be arranged inside the housing of the vacuum pump. However, these components require interlocking components which impose difficulties when assembling the vacuum pump. These difficulties are increased if it is desired to provide a compact vacuum pump combining one or more of the required components in an integral manner.

[0005] Hence, it is an object of the present invention to provide a vacuum pump which can be easily assembled in a simplified assembly method.

[0006] The problem is solved by a vacuum pump according to claim 1, a method for providing a preassembled active thrust-bearing assembly according to claim 11 and a method for assembly of a vacuum pump according to claim 13.In an aspect of the present invention a vacuum pump is provided which is in particular built as a turbo-molecular vacuum pump. The vacuum pump comprises a housing defining a pump chamber. In particular, the housing comprises an inlet to be connected to a vacuum chamber or vessel to be evacuated by the vacuum pump, and an outlet. A rotor assembly arranged in the pump chamber comprises a rotor shaft having a first end and an opposite second end. Therein, the first end is directed towards the inlet or arranged at the inlet in the area of low pressure or high vacuum. The second end may be arranged towards the outlet but is in general opposite to the first end of the rotor shaft. Further, the rotor assembly may comprise one or more rotor elements which in case of a turbo-molecular pump are provided by vanes arranged in one or more rotor stages. The one or more rotor elements interact with stator elements connected to the housing of the vacuum pump. In case of a turbo-molecular vacuum pump the stator elements are provided by a plurality of vanes arranged in stator stages alternating with the rotor stages. The rotor assembly is rotated by an electromotor. When rotated, a gaseous medium is conveyed from the inlet of the vacuum pump towards the outlet of the vacuum pump. Therein, the rotor assembly is rotatably supported by at least two bearings. In particular, the vacuum pump comprises a first bearing at the first end of the rotor shaft, wherein the first bearing is built as permanent magnetic bearing in order to radially support the rotor assembly. Further, the vacuum pump may comprise a second bearing which may also be built as permanent magnetic bearing providing another radial support of the rotor assembly. The second bearing is arranged along the rotor shaft towards the second end of the rotor shaft.

[0007] According to the present invention, the vacuum pump comprises an active thrust-bearing assembly arranged at the second end of the rotor shaft. The active thrust-bearing assembly comprises a cartridge inserted into the housing, wherein an active magnetic bearing and an eddy current damper are arranged in the cartridge. In particular, the active magnetic bearing is built as axial magnetic bearing. Hence, in a preferred embodiment, the rotor assembly of the vacuum pump is fully magnetically levitated by the first bearing, the second bearing, both built as permanent magnetic bearing, and the active axial magnetic bearing arranged in the active thrust-bearing assembly. By the eddy current damper arranged in the cartridge of the active thrust-bearing assembly, vibrations of the rotor assembly are suppressed via the generation of eddy currents in the eddy current damper. Therein, the active magnetic bearing and the eddy current damper are arranged in the cartridge in an integral manner and thus are able to be preassembled. The active magnetic bearing and the eddy currentdamper are combined in the cartridge providing a compact assembly, reducing the overall size of the vacuum pump. Therein, the active thrust-bearing assembly does not have any interlocking elements with other parts of the vacuum pump and can be simply inserted into the housing for ease of manufacturing of the vacuum pump. Therein, all elements of the active magnetic bearing and the eddy current damper are completely enclosed by the cartridge and are structurally held within the cartridge. Thus, also for service of the vacuum pump disassembly of the vacuum pump is simplified since the cartridge of the active thrustbearing assembly can be removed in one piece. No special tools are necessary.

[0008] Preferably, the cartridge is secured in the housing by a cap element. Thus, in particular the housing comprises a recess to receive the active thrust-bearing assembly. After inserting the active thrust-bearing assembly into the recess, the cartridge is secured in the housing by a cap element.

[0009] Preferably, the cap element is secured to the housing by a single set of screws or bolts. Hence, the individual parts of the active th rust- bearing assembly, such as the active magnetic bearing and the eddy current damper, need not to be individually secured to the housing by individual set of screws. Instead, the whole cartridge of the active thrust-bearing assembly is mounted at once to the housing by a single set of screws or bolts, reducing the number or screw connection for assembly and disassembly of the vacuum pump.

[0010] Preferably, the cartridge is made from a ferromagnetic material. In particular, the cartridge is part of the magnetic circuit necessary in order to operate the active magnetic bearing. Hence, when using a ferromagnetic material for the cartridge, magnetic flux through the cartridge is possible.

[0011] Preferably, the active thrust-bearing assembly comprises a static yoke extending in an axial direction. Therein, preferably the static yoke is made from a ferromagnetic material and is part of the magnetic circuit for the active magnetic bearing. In particular, the static yoke extends from a direction corresponding to the second end of the rotor shaft towards the first end of the rotor shaft when mounted in the housing of the vacuum pump.

[0012] Preferably, a static coil is arranged radially between the cartridge and the static yoke to generate a magnetic field. By the magnetic field control of an axial position of the rotorassembly is facilitated. Therein, the magnetic flux is guided through the cartridge as well as the static yoke.

[0013] Preferably, an axial gap is formed between the cartridge and an axial end of the static yoke. In particular, a rotated yoke is connected to the rotor shaft and extending in a radial direction, wherein the rotated yoke is at least partially arranged axially between the cartridge and an axial end of the static yoke to be affected by the magnetic field generated by the static coil. In other words, the rotated yoke extends into the axial gap formed between the cartridge and an axial end of the static yoke. Thus, by the magnetic field generated by the static coil an axial magnetic force is exerted onto the rotated yoke in order to control the axial position of the rotor assembly. Thus, the cartridge provides a double function, i.e. it is part of the magnetic circuit, guiding the magnetic flux towards the rotated yoke, and at the same time provides structural support of the active thrust-bearing assembly.

[0014] Preferably, the static yoke is clamped between the cap element and the cartridge. Therein, the clamping force from the cap element may be applied directly or indirectly via other parts. However, when fixing the cap element to the housing of the vacuum pump a clamping force is applied to the static yoke. Therefore, the static yoke may comprise a radially outward facing shoulder receiving an axial end of the cartridge. Via the shoulder a pressing surface between the cartridge and the static yoke is provided in order to clamp the static yoke and fix its radial position as well as its axial position.

[0015] Preferably, the eddy current damper comprises a first rotated ring magnet connected to the rotor shaft and rotated together with the rotor shaft. Further, the eddy current damper comprises a static damper element. In particular, the static damper element is built as sleeve or cylinder. The static damper element is made from a conductive material such as copper. The static damper element is connected to the static yoke. In particular, the static damper element is connected to the static yoke opposite to the static coil or radially inside the static yoke.

[0016] Preferably, the eddy current damper comprises a second rotated ring magnet, wherein a radial extension of the static damper element extends into a gap between the first rotated ring magnet and the second rotated ring magnet.Preferably, the rotated yoke and the first rotated ring magnet and preferably the second rotated ring magnet are connected together to the rotor shaft by a clamping force. Hence, only one means for clamping of these elements is required and the rotated yoke as well as the rotated ring magnets are clamped together in a stacked manner. Preferably, the clamping force is applied by a shaft bolt inserted into the second end of the rotor shaft. By tightening the shaft bolt, the clamping force is applied to the rotated ring magnets as well as the rotated yoke at a shoulder of the rotor shaft. Thereby, the axial position of the rotated yoke and the rotated ring magnets is defined and these elements are securely held in place.

[0017] Preferably, the cartridge has a substantially cylindrical shape.

[0018] Preferably, the cartridge has a first opening at a first end surface in order to receive the rotor shaft. Further, the cartridge may have a second opening at the second end surface opposite the first surface in order to access the shaft bolt for fixing one or more rotated ring magnets and the rotated yoke to the rotor shaft.

[0019] Preferably, the active thrust-bearing assembly comprises an opening in particular formed by the static yoke and the cartridge, wherein the opening is covered by a cover element. Therein, in particular the cover element is clamped between the cap element and the static yoke or between the cap element and a positioning ring described in more detail below.

[0020] Preferably, the cover element is disk shaped which means that the lateral extensions exceed the thickness of the cover element. In particular, the cover element is made by a non-metallic material such as a fiber reinforced plastic.

[0021] Preferably, the cap element comprises an opening in the area of the second end of the rotor shaft, i.e. the shaft bolt fixing the one or more rotated ring magnets and the rotated yoke to the second end of the rotor shaft. Therein, in particular an axial sensor is arranged in this opening or in the proximity of this opening in order to detect the axial positioning of the rotor assembly via detection of the axial position of the second end of the rotor shaft and / or the shaft bolt connected to the second end of the rotor shaft. Therein, the detected axial position of the rotor assembly is used in order to control the static coil of the active thrust-bearing assembly and in particular the active axial magnetic bearing of the active thrust-bearing assembly in order to maintain the axial position of the rotor assembly. Therein, the axialsensor can be arranged outside of the vacuum, i.e. outside of the active thrust-bearing assembly and is thus easily accessible.

[0022] Preferably, the active thrust-bearing assembly comprises a positioning ring, wherein a pressing force of the cap element is transferred to the yoke and preferably the cartridge by the positioning ring. Therein, in particular the positioning ring and the static yoke comprises a common pressing surface, i.e. are in direct contact with each other in order to transfer a clamping force or pressing force applied by the cap element to the static yoke via the positioning ring. As described before, the static yoke and the cartridge comprise a common pressing surface such that a pressing force or clamping force applied by the cap element is transferred via the positioning ring and the static yoke to the cartridge. Hence, by tightening the cap element of the active thrust-bearing assembly at the same time, the positioning ring, the static yoke and the cartridge are mounted and fixed in their position. Hence, it is not necessary to individually secure the elements of the active thrust-bearing assembly to each other. Instead, the parts of the active thrust-bearing assembly are mounted together by clamping with the cap element. Hence, the steps for assembly of the vacuum pump are reduced and the number of screw connections is reduced in order to simplify the manufacturing process.

[0023] Preferably, the positioning ring is a separate element. Thus, the positioning ring can be inserted after tightening the shaft bolt. Thus, easy access to the shaft bolt is provided and consequently no special tools need to be used to tighten the shaft bolt.

[0024] Preferably, the positioning ring is placed axially next to the rotated ring magnets of the eddy current damper. In particular, the positioning ring is made of a ferromagnetic material. Thus, the positioning ring is part of the magnetic circuit of the eddy current damper. Thus, damping effect of the eddy current damper is improved.

[0025] Preferably, a seal element, in particular formed as an O-ring, is arranged between the static yoke and the cover element and / or the cap element and the cover element. Hence, by the seal element a vacuum tight connection between the cover element and the static yoke is provided or between the cap element and the cover element.Preferably, a seal element, in particular formed as an O-ring, is arranged between the static yoke and the cartridge. In particular, a vacuum tight connection is provided by a seal element arranged between the cartridge and the static coil as well as the static coil and the static yoke. Hence, by the static coil a sealing function is provided in connection with the respective seal elements.

[0026] Preferably, the active thrust-bearing assembly does not comprise any screw connections. Thus, the components of the active thrust-bearing assembly are only clamped and mounted together by the one set of screws mounting the cap element to the housing of the vacuum pump.

[0027] In another aspect, a method for providing a preassembled active thrust-bearing assembly is provided. The method includes:

[0028] providing a static yoke;

[0029] connecting a static damper element to the static yoke;

[0030] inserting from a first side a first rotated ring magnet into the static damper element; connecting a rotated yoke from the first side to the rotated ring magnet; surrounding the static yoke by a coil; and

[0031] inserting the static yoke, the static damper element, the first rotated ring magnet, the rotated yoke, and the coil into a cartridge.

[0032] In particular, the preassembled active thrust-bearing assembly is further built along the features described with respect to the vacuum pump above.

[0033] Preferably, the method further comprises inserting a second rotated ring magnet from a second side opposite to the first side into the static damper element. Thus, the interlocking static damper element would prevent inserting the first rotated ring magnet and the second rotated ring magnet from the same side. Consequently, before providing the rotated yoke and / or the cartridge, the first rotated ring magnet and the second rotated ring magnet are inserted from different sides into the static damper element.

[0034] In another aspect of the present invention a method for assembly of a vacuum pump is provided. The method includes:providing a housing defining a pump chamber;

[0035] providing a rotor assembly and inserting the rotor assembly into the pump chamber; the rotor assembly comprising a rotor shaft having a first end and an opposite second end; and

[0036] inserting a preassembled active thrust-bearing assembly into the housing.

[0037] In particular, the preassembled active thrust-bearing assembly is provided according to the method described before.

[0038] In particular, the vacuum pump is further built along the features as described before with respect to the vacuum pump.

[0039] Preferably, the second end of the rotor shaft is inserted into the preassembled active thrustbearing assembly upon inserting the preassembled active thrust-bearing assembly into the housing. The method preferably further comprises fixing at least a first rotated ring magnet and a rotated yoke of the preassembled active thrust-bearing assembly to the rotor shaft. In particular, fixing the first rotated ring magnet and the rotated yoke is facilitated by a shaft bolt connected to the second end of the rotor shaft. If the active thrust-bearing assembly comprises more than one rotated ring magnets, also the other rotated ring magnets together with the rotated yoke are fixed to the rotor shaft by the common fixing means, i.e. the shaft bolt.

[0040] Preferably, the method includes fixing the preassembled active th rust- bearing assembly to the housing. In particular, fixing the active thrust-bearing assembly to the housing is facilitated by a cap element, wherein a clamping force is applied by the cap element to the preassembled active thrust-bearing assembly in order to fix the positions of the components of the active thrust-bearing assembly together.

[0041] Preferably, the method further includes inserting a positioning ring into the preassembled active thrust-bearing assembly to transfer a clamping force from the cap element onto the preassembled active thrust-bearing assembly. Hence, by the positioning ring the clamping force or pressing force applied by the cap element are directly transferred to the static yoke and the cartridge defining their position. Therein, the positioning ring may have a direct contact or pressing surface to the static yoke and the static yoke comprises a direct contactor pressing surface with the cartridge. Hence, the pressing force of the cap element is transferred indirectly via the positioning ring and the static yoke to the cartridge.

[0042] Preferably, a cover element is inserted between the cap element and the preassembled active thrust-bearing assembly providing a vacuum tight seal of the preassembled active thrust-bearing assembly, wherein the cover element is clamped between the cap element and the static yoke and / or the cap element and the positioning ring.

[0043] In the following the present invention is described, by way of example only, with reference to the accompanying Figures:

[0044] The figures show:

[0045] Figure 1 a vacuum pump according to the present invention,

[0046] Figure 2 a detailed view of the active thrust-bearing assembly according to the present invention,

[0047] Figures 3A-3E individual steps of the method of assembly of the active thrust-bearing assembly, and

[0048] Figure 4 a schematic flow diagram of the method of assembly of the vacuum pump.

[0049] Figure 1 shows a vacuum pump 10 according to the present invention. The vacuum pump 10 comprises a housing 12 having an inlet 14 and an outlet 17. By means of the inlet 14 the vacuum pump 10 is connected to a chamber or vessel to be evacuated. In the housing 12 a rotor shaft 16 is arranged which is rotated by an electromotor 32. In a turbomolecular pumping stage 33 a plurality of rotor vanes 34 are connected to the rotor shaft 16, interacting with stator vanes 36 connected to the housing and arranged in an alternating manner with the rotor vanes. Downstream of the turbomolecular pumping stage 33 a molecular drag stage 38 is arranged, built as a Holweck stage. The molecular drag stage 38 comprises a cylinder 40 interacting with a stator 43 having a threaded channel. By rotation of the rotor shaft 16, a gaseous medium is conveyed from the inlet 14 towards the outlet 17. Thereby, the rotor shaft 16 is rotatably supported by a first magnetic bearing 18 at the inlet side ofthe rotor shaft 16. The first magnetic bearing 18 is built as a permanent magnetic bearing comprising a plurality of rotated ring magnets 22 connected to the rotor shaft 16 and rotated together with the rotor shaft 16. Opposite to the rotated ring magnets 22, the first magnetic bearing 18 comprises a plurality of static ring magnets 23 connected to a trunnion 24 radially opposite to the rotated ring magnets 22 thereby rotatably supporting the rotor shaft 16 in a contact-free manner due to mutual repulsion of the ring magnets 22, 23. Further, an emergency bearing 30 is implemented in the first magnetic bearing 18 which is not in contact with a pin 31 of the rotor shaft 16 and only comes into contact with the pin 31 of the rotor shaft 16 upon failure of the first magnetic bearing 18.

[0050] Furthermore, the vacuum pump 10 comprises a second magnetic bearing 26 which is arranged towards the inlet side of the rotor shaft 16 in a similar way as the first magnetic bearing 18, i.e. it comprises a plurality of rotated ring magnets 22' connected to rotor shaft 16 and rotated therewith. The rotated ring magnets 22’ of the second magnetic bearing 26 are located opposite to static ring magnets 23', wherein by the repulsive magnetic force between the rotated ring magnets 22' and the static ring magnets 23' the rotor shaft 16 is rotatably supported. As for the first magnetic bearing 18 also the second magnetic bearing 26 comprises an emergency bearing 30' which only comes into contact with the rotor shaft 16 upon failure of the second magnetic bearing 26.

[0051] Thus, by the first magnetic bearing 18 and the second magnetic bearing 26 radial support of the rotor shaft is provided. Further, the vacuum pump 10 comprises an active axial bearing 42 together with an eddy current damper 103. The eddy current damper 103 comprises a static damper element 108 which is connected to the housing 12. In particular, the static damper element 108 is made of a conductive material such as copper. Further, the eddy current damper 103 comprises, in the example of the Figures, two magnet assemblies each comprising a rotated ring magnet 104, 106 being connected to and rotated with the rotor shaft 16. In particular, the rotated ring magnets are connected to the shaft via respective magnet hubs 110, 112. In the example of Fig. 2, the two shown magnet assemblies are built identically but may also differ in other embodiments.

[0052] Figure 2 shows a detailed view of the active thrust-bearing assembly 100. The active thrustbearing assembly 100 comprises an active magnetic bearing 102 and in particular an axial active magnetic bearing together with an eddy current damper 103 arranged in a cartridge118 in an integrated manner. Therein, the cartridge 118 provides an outer housing of the active thrust-bearing assembly 100 which can be inserted into the housing 12 of the vacuum pump 10. Therein, the cartridge 118 comprises a substantially cylindrical shape and has no interlocking elements or components with the other parts of the vacuum pump. However, within the active thrust-bearing assembly 100 housed within the cartridge 118 a plurality of interlocking components is arranged that can be preassembled. The active thrust-bearing assembly 100 comprises a static yoke 120 arranged within the cartridge 118. Therein, the cartridge 118 and the static yoke 120 are in direct contact at a shoulder 148 providing a pressing surface. Between the cartridge 118 and the static yoke 120 a static coil 116 is provided. The static coil 116 provides a magnetic field for the active magnetic bearing 102. Therein, the magnetic flux is guided through the cartridge 118 and the static yoke 120 as indicated by a magnetic field lines 117. Between an axial end of the static yoke 120 and a radial extension 150 of the cartridge 118 a gap is formed, wherein a rotated yoke 114 which is connected to the rotor shaft 16 extends radially in the gap axially between the static yoke 120 and the radial extension. By the magnetic field generated by the static coil 116 a magnetic force can be applied to the rotated yoke 114 thereby controlling the axial position of the rotor shaft 16 and the rotor assembly in a dynamic manner.

[0053] Radially inside the static yoke 120 the eddy current damper 103 is arranged. The eddy current damper 103 comprises a static damper element 108 which is connected to the static yoke 120 and arranged radially inside the static yoke 120 or on an opposite side to the static coil 116. Therein, the static damper element 108 has a substantially sleeve shape extending in the axial direction and further comprises a radial extension extending into a gap between a first rotated ring magnet 104 and a second rotated ring magnet 106. Therein, the first rotated ring magnet 104 and the second rotated ring magnet 106 are connected to the rotor shaft 16. Therein, the rotated yoke 114, the first rotated ring magnet 104 and the second rotated ring magnet 106 are clamped between a shaft bolt 130 and a shoulder 131 of the shaft. Hence, by the single shaft bolt 130 the rotated ring magnets 104, 106 of the eddy current damper 103 as well as the rotated yoke 114 of the active magnetic bearing 102 are clamped together.

[0054] The active thrust-bearing assembly 100 is mounted into the housing 12 by a cap element 124. Therein, components of the active thrust-bearing assembly 100 are only inserted into the cartridge 118 and not fixed by screws or any other means. Just by fixing the activethrust-bearing assembly 100 to the housing 12 by the cap element 124 the positions of the individual components of the active thrust-bearing assembly 100 are fixed and tensioned. Therein, the cap element 124 is fixed to the housing by only one set of screws, indicated by dashed lines 126. Hence, mounting the active thrust-bearing assembly to the housing 12 only requires a single set of screws or bolts simplifying the assembly procedure and reducing the necessary steps of assembly.

[0055] Therein, between the cap element 124 and the active thrust-bearing assembly 100, and in particular the static yoke 120, a cover element 122 is provided, providing a vacuum tight seal of the active thrust-bearing assembly 100. Therein, the cover element 122 is clamped between the cap element 124 and the static yoke 120. Therein, the cover element 122 is made from a non-metallic material such as fiber reinforced plastic. A vacuum tight connection is provided by a seal element 132 between the static yoke 120 and the cover element 122. Compression force of the cap element 124 is transferred via the cover element 122 to either the static yoke 120 or a positioning ring 146. Compression force applied by the cap element 124 is transferred to the positioning ring 146. The positioning ring 146 surrounds the shaft bolt 130 and allows access to the shaft bolt 130. The compression force applied to the positioning ring 146 is transferred via a shoulder 144 or pressing surface to the static yoke 120 and from there, as described before, by a shoulder 148 to the cartridge 118 providing a compression and tensioning in the direction 128, thereby securely fixing the active thrust-bearing assembly 100 in the housing 12. Thus, by only fixing the cap element 124 to the housing 12, at the same time the complete active thrust-bearing assembly 100 is mounted and their components are fixed in their precise positions.

[0056] Figures 3A-3E show the individual steps of assembly of the active thrust-bearing assembly 100. In Figure 3A, first, a static yoke 120 is provided. Therein, a static damper element 108 is inserted into the static yoke 120 and in particular in direct contact with a radial inner surface of the static yoke 120.

[0057] According to Figure 3B a first rotated ring magnet 104 including the first magnet hub 110 is inserted from a first side or a first direction according to arrow 140. Similar, a second rotated ring magnet 106 with the second magnet hub 112 is inserted from a second side along a second direction indicated by arrow 142. Hence, the first rotated ring magnet 104 and the second rotated ring magnet 106 are located on opposite sides of the radial extension of thestatic damper element 108. In addition, a rotated yoke 114 is inserted from the same side as the first rotated ring magnet 104.

[0058] Referring to Figure 3C a static coil 116 is connected to the static yoke 120 and in particular at a radial outer surface of the static yoke 120 opposite to the static damper element 108. The static yoke 120 together with the static coil 116, the first and second rotated ring magnets 104, 106, and the rotated yoke 114 are inserted into a cartridge 118. Alternatively, the static coil 116 is inserted into the cartridge 118 first and subsequently the static yoke 120 together with the static damper element 108, the first and second rotated ring magnets 104, 106 and the rotated yoke 114 are inserted into the cartridge 118. Therein, a vacuum tight connection between the static coil 116 and the cartridge 118 is provided by a seal element 134 in particular in form of an O-ring, wherein a vacuum tight connection between the static yoke 120 and the static coil 116 is provided by a seal element 136 provided in particular by an O-ring. Up to this step, the components in the active thrust-bearing assembly 100 are not fixed to each other and only inserted. In particular, no screw or bolt connections are used for fixing the components of the active thrust-bearing assembly 100.

[0059] Referring to Figure 3D, when inserting the active thrust-bearing assembly 100 into the housing 12, at the same time the second end of the rotor shaft 16 is inserted into the active thrust-bearing assembly 100 and in particular into the rotated yoke 114, the first rotated ring magnet 104 and the second rotated ring magnet 106 along direction 145. Subsequently, the rotated components of the active thrust-bearing assembly 100 are connected and fixed to the rotor shaft 16 by shaft bolt 130 which is inserted from the opposite side along direction 147. Therein, the active thrust-bearing assembly 100 comprises an opening through which access to the second end of the rotor shaft 16 is possible. Thus, by the shaft bolt 130 as explained in connection with the Figure 2, the first rotated ring magnet 104, the second rotated ring magnet 106 and the rotated yoke 114 are clamped between the shaft bolt 130 and the shoulder 131 of the rotor shaft 16.

[0060] Referring to Figure 3E, after inserting the cartridge 118 of the active thrust-bearing assembly 100 into the housing 12, the active thrust-bearing assembly 100 is fixed to the housing 12 by a cap element 124. Therein, the cap element 124 is inserted in direction 149 as indicated in Figure 3E and fixed by a single set of screws connecting the cap element 124 to the housing 12 as indicated by arrows 152. By tightening the screws 152 tensioning of thecomponents of the active thrust-bearing assembly 100 is facilitated. Prior to inserting and fixing the cap element, the positioning ring 146 and the cover element 122 are inserted. Therein, pressure of the cap element 124 is transferred via the cover element 122 to the positioning ring 146 and from there as described before to the static yoke 120. Compression force is transferred from the static yoke 120 to the cartridge 118 fixing the active thrustbearing assembly into the housing 12.

[0061] In the following it is referred to Figure 4 in a schematic flow diagram for the method of assembly of a vacuum pump. The method includes:

[0062] in step S01 , a housing is provided defining a pump chamber;

[0063] in step S02, a rotor assembly is provided and the rotor assembly is inserted into the pump chamber; the rotor assembly comprising a rotor shaft having a first end and an opposite second end; and

[0064] in step S03, a preassembled active thrust-bearing assembly is inserted into the housing.

[0065] Hence, by the present invention a vacuum pump is provided which can be easily assembled and in particular by use of an active thrust-bearing assembly interlocking components of an active magnetic bearing as well as an eddy current damper can be preassembled separate from the rotor assembly or other components of the vacuum pump in a compact manner. Therein, also disassembly is simplified by using a single set of screws fixing the active thrust-bearing assembly to the housing of the vacuum pump via a cap element.Reference List:

[0066] 10 vacuum pump

[0067] 12 housing

[0068] 14 inlet

[0069] 16 rotor shaft

[0070] 17 outlet

[0071] 18 first magnetic bearing

[0072] 22, 22' rotated ring magnets

[0073] 23, 23' static ring magnets

[0074] 24 trunnion

[0075] 26 second magnetic bearing 30, 30' emergency bearing

[0076] 31 pin

[0077] 32 electromotor

[0078] 33 turbomolecular pumping stage 34 rotor vanes

[0079] 36 stator vanes

[0080] 38 molecular drag stage

[0081] 40 rotated cylinder

[0082] 42 active axial bearing

[0083] 43 stator

[0084] 100 active thrust-bearing assembly 102 active magnetic bearing

[0085] 103 eddy current damper

[0086] 104 first rotated ring magnet

[0087] 106 second rotated ring magnet 108 static damper element

[0088] 110 first magnet hub

[0089] 112 second magnet hub

[0090] 114 rotated yoke

[0091] 116 static coil

[0092] 117 magnetic field lines118 cartridge

[0093] 120 static yoke 122 cover element 124 cap element 126 dashed line 128, 145, 147, 149 direction

[0094] 130 shaft bolt 131, 144, 148 shoulder

[0095] 132 seal element 134, 136 seal element 146 positioning ring 150 radial extension 152 arrows

Claims

CLAIMS1. Vacuum pump, in particular a turbo-molecular vacuum pump, comprising:a housing defining a pump chamber;a rotor assembly arranged in the pump chamber comprising a rotor shaft having a first end and an opposite second end; andan active thrust-bearing assembly arranged at the second end of the rotor shaft, the active thrust-bearing assembly comprising a cartridge inserted into the housing, wherein an active magnetic bearing and an eddy current damper are arranged in the cartridge.

2. Vacuum pump according to claim 1, wherein the cartridge is secured in the housing by a cap element.

3. Vacuum pump according to claim 1 or 2, wherein the cap element is secured to the housing by a single set of screws or bolts.

4. Vacuum pump according to any of claims 1 to 3, wherein the cartridge is made from a ferromagnetic material.

5. Vacuum pump according to any of claims 1 to 4, wherein active thrust-bearing assembly comprises a static yoke extending in an axial direction.

6. Vacuum pump according to claim 5, wherein a static coil is arranged radially between the cartridge and the static yoke to generate a magnetic field.

7. Vacuum pump according to claim 5 or 6, wherein a rotated yoke is connected to the rotor shaft and extending in a radial direction, wherein the rotated yoke is at least partially arranged axially between the cartridge and an axial end of the static yoke to be affected by the magnetic field.

8. Vacuum pump according to any of claims 5 to 7, wherein the static yoke is clamped between the cap element and the cartridge.

9. Vacuum pump according to any of claims 1 to 8, wherein the eddy current damper comprises a first rotated ring magnet connected to the rotor shaft and rotated together with the rotor shaft and a static damper element, wherein the static damper element is connected to the static yoke.

10. Vacuum pump according to any of claims 1 to 9, wherein the active thrust-bearing assembly comprises a positioning ring, wherein a pressing force of the cap element is transferred to the cartridge and preferably the static yoke by the positioning ring.

11. Method for providing a preassembled active thrust-bearing assembly including: providing a static yoke;connecting a static damper element to the static yoke;inserting from a first side a first rotated ring magnet into the static damper element; connecting a rotated yoke from the first side to the rotated ring magnet; surrounding the static yoke by a coil; andinserting the static yoke, the static damper element, the first rotated ring magnet, the rotated yoke, and the coil into a cartridge.

12. Method according to claim 11, wherein the method further comprising inserting a second rotated ring magnet from a second side, opposite to the first side, into the static damper element.

13. Method for assembly of a vacuum pump, in particular a turbomolecular pump, including:providing a housing defining a pump chamber;providing a rotor assembly and inserting the rotor assembly into the pump chamber; the rotor assembly comprising a rotor shaft having a first end and an opposite second end; andinserting a preassembled active thrust-bearing assembly into the housing.

14. Method according to claim 13, wherein the second end of the rotor shaft is inserted into the preassembled active thrust-bearing assembly upon inserting the preassembled active thrust-bearing assembly into the housing, the method further comprises: Fixing at least a first rotated ring magnet and a rotated yoke of the preassembled active thrust-bearing assembly to the rotor shaft.

15. Method according to claim 13 or 14, wherein the preassembled active thrust-bearing assembly is fixed to the housing.

16. Method according to any of claims 13 to 15, wherein a positioning ring is inserted into the preassembled active thrust-bearing assembly to transfer a clamping force from the cap element onto the preassembled active thrust-bearing assembly.

17. Method according to any of claims 13 to 16, wherein a cover element is inserted between the cap element and the preassembled active thrust-bearing assembly.

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