ROTOR SUPPORT AND VACUUM PUMP WITH SUCH A ROTOR SUPPORT

Abstract

A rotor support configured to rotatably mount a rotor shaft in a vacuum pump is disclosed. The rotor support comprises: a rolling bearing for rotatably supporting the shaft; an insert and at least one resilient damping member, the insert and the at least one resilient damping member surrounding the rolling bearing. The insert comprises inner and outer annular portions connected by a plurality of flexible members, the plurality of flexible members being configured to flex in a radial plane and resist movement in an axial plane, thereby absorbing radial movement of the shaft. The at least one resilient damping member is formed of an elastomeric material configured to flex in both a radial and axial direction.

Claims

1. A rotor support configured to rotatably mount a rotor shaft in a vacuum pump, said rotor support comprising: a rolling bearing for rotatably supporting said shaft; an insert and at least one resilient damping member, said insert and said at least one resilient damping member surrounding said rolling bearing; wherein said insert comprises inner and outer annular portions connected by a plurality of flexible members, said plurality of flexible members being configured to flex in a radial plane and resist movement in an axial plane, thereby absorbing radial movement of said shaft; and said at least one resilient damping member is formed of an elastomeric material configured to flex in both a radial and axial direction; wherein said at least one resilient damping member is configured to support said insert and is arranged in series with said insert.

2. The rotor support according to claim 1, wherein said at least one resilient damping member is arranged in series with said insert at least one of the following configurations: at least one of said at least one resilient damping member is located between said inner annular portion of said insert and said rolling bearing; and said outer annular portion of said insert is located between at least one of said at least one resilient damping member and said rolling bearing.

3. The rotor support according to claim 1, wherein said insert is formed of a stiff material and said flexible members are longer axially than they are wide, thereby providing axial stiffness and radial flexibility.

4. The rotor support according to claim 3, wherein said stiff material comprises a metallic material or a plastic material.

5. The rotor support according to claim 1, wherein each of the flexible members comprises an elongate, arcuate member substantially concentric with the inner and outer annular portions.

6. The rotor support according to claim 1, wherein the flexible members provide a plurality of integral leaf springs providing radial flexibility.

7. The rotor support according to claim 1, wherein said rolling bearing comprises an inner race, an outer race and a plurality of rolling elements located between the races, said outer race being bonded to said insert.

8. The rotor support according to claim 1, wherein at least one of said at least one resilient damping member is located between said insert and said rolling bearing.

9. The rotor support according to claim 1, wherein said insert is located between said rolling bearing and at least one of said at least one resilient damping member.

10.The rotor support according to claim 1, further comprising at least one resilient axial damping member formed of an elastomeric material and mounted such that axial movement of said rolling bearing changes a compression of said at least one resilient axial damping movement.

11. The rotor support according to claim 8, wherein at least one of said at least one resilient damping member is located between said insert and said rolling bearing and wherein at least one of said at least one resilient axial damping member is mounted on an outer surface of said rotor support extending in a radial plane.

12. The rotor support according to claim 9, wherein said insert is located between said rolling bearing and at least one of said at least one resilient damping member and wherein said insert comprises an extension extending radially inwardly from an end of said inner annular member, said surface extending over said rolling bearing, at least one of said at least one resilient axial member being mounted between a surface of said rolling bearing facing said extension and a surface of said extension facing said rolling bearing.

13. The rotor support according to claim 10, wherein said at least one resilient damping member is axially more flexible than said resilient axial damping means.

14. (canceled)

15. The rotor support according to claim 10, wherein said resilient axial damping member and said resilient damping member comprise a single member.

16. The rotor support according to claim 15, wherein said single member comprises an L-shaped member.

17. The rotor support according to claim 1, wherein said at least one resilient damping member comprises at least one O-ring.

18. A vacuum pump comprising: a rotor comprising a shaft rotatably mounted within a pump body on a rotor support, said rotor support comprising a rotor support according to any preceding claim.

19. The vacuum pump according to claim 18, wherein an outer one of said at least one resilient damping member or said insert are bonded to said pump body.

20. The vacuum pump according to claim 18, wherein said at least one resilient damping member comprises at least one O-ring and wherein said at least one O-ring is mounted in at least one recess in said pump body.

21. The vacuum pump according to claim 18, wherein said vacuum pump comprises a turbomolecular pump.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0053] Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

[0054] FIG. 1 shows a cross section through a rotor support means according to a first embodiment;

[0055] FIG. 2 shows the insert of the rotor support means of FIG. 1; and

[0056] FIG. 3 shows a cross section through one side of a rotor support means according to a further embodiment.

DETAILED DESCRIPTION

[0057] Before discussing the embodiments in any more detail, first an overview will be provided.

[0058] To improve the vibration levels of a vacuum pump and in particular, a turbo pump with an insert in the form of a compact metal or plastic spring damper, an elastomeric element is added in series with the compact metal spring damper CMSD or insert.

[0059] In applications such as pumping electron microscopes the level of vibration caused by the turbo pump is very critical to the microscope resolution. To reduce the level of vibration caused by the pump a compact metal spring damper may be used to mount the ball bearings. This uses circumferential spring elements to give a low radial stiffness, but high axial stiffness, thus absorbing radial movement of the shaft due to imbalance, but maintaining a good axial location of the rotor. This achieves a high level of isolation and a good vibration performance, however there is still room for improvement in the most demanding applications.

[0060] Embodiments seek to enhance the performance of such an insert by using an elastomeric element to support the insert, giving a degree of axial and radial compliance and further isolating the bearing noise and vibration from the main pump housing.

[0061] The compliant element may be made up of one or more components, such as one or more O-rings for radial location and a flat elastomeric ‘washer’ for axial location. Alternatively an ‘L’ shaped elastomeric component could provide both axial and radial location.

[0062] In one embodiment, the elastomeric element(s) is/are mounted between the insert and pump housing, alternatively, or additionally, they are mounted between the bearing and insert.

[0063] This arrangement is used in pumps with a single ball bearing and a passive magnetic bearing or in pumps with two ball bearings supporting the shaft.

[0064] FIG. 1 shows a cross section through a rotor shaft 20 that is supported by a rotor shaft support 5 according to an embodiment. The rotor shaft support 5 comprises rolling bearings 10 which are held in position by a compact metal spring damper or insert 70. Insert 70 is in this embodiment bonded to the bearing 10 with adhesive. Insert 70 provides axial stiffness and some radial flexibility for the bearing 10, helping to maintain them in position while allowing some radial movement to absorb vibrations. The rotor shaft 20 is the shaft of a turbomolecular pump.

[0065] Insert 70 is mounted to pump body 30 via a resilient damping member 40 formed of elastomeric material mounted between the insert 70 and the pump body 30. This resilient damping member 40 has some axial and radial flexibility and helps reduce vibrations still further. In some embodiments, the shaft is held in position by adhering the rotor support to the pump body 30, however, in this embodiment, the rotor support is held in position by a further resilient damping member in this case an axial resilient damping member 42.

[0066] Axial resilient damping member 42 is mounted between a projecting portion of the pump housing 30 and the upper surface of the insert 70. In this embodiment axial resilient damping member 42 is a ring shaped gasket. The resilient damping member 40 has an annular form and is thicker than the flat gasket 42 allowing more axial movement. Gasket 42 is arranged such that axial movement of the bearing compresses the gasket and thus, axial movement is resisted.

[0067] Shaft 20 is mounted on a rolling bearing 10 located towards the outlet end of the pump and on magnetic bearings (not shown) located towards the inlet end of the pump. These magnetic bearing provide the biasing force to hold the insert 70 against gasket 42. In this way gasket 42 helps provide axial alignment of the rotor shaft 20, while its elasticity helps reduce vibration transmission from the rolling bearing 10 to the pump body 30 along the axial path. The elasticity of gasket 42 is selected to be relatively low such that axial movement is restricted and axial alignment is maintained within acceptable limits. The elasticity of resilient member 40 is selected to be higher providing more flexibility and reducing vibration transmission particularly in the radial path between the insert 70 and pump body 30.

[0068] FIG. 2 shows the insert 70 in more detail. The insert 70 is provided to mount the shaft within the rolling bearing in a way that is axially stiff and radially flexible. In this embodiment insert 70 is formed of a metallic material, although in other embodiments it may be formed of a plastic. Insert 70 has integral inner and outer annular portions 54, 56 connected together by a plurality of flexible members 58. In this embodiment they are formed by machining slots 60 in the insert 70. Each flexible member 58 is connected by a first resilient hinge 62 to the inner portion 54, and by a second resilient hinge 64 to the outer portion 56. Each flexible member 58 is in the form of an elongate, arcuate member substantially concentric with the inner and outer annular portions 54, 56, and, as illustrated in FIG. 2., the flexible members 58 are preferably circumferentially aligned. The flexible members 58 of the resilient support 52 thus provide integral leaf springs of the resilient support or insert 70. As can be appreciated the elasticity of the insert 70 in each of the radial and axial directions is dependent upon the material of the insert and the thickness and shape of the flexible members 58 and on their hinged portions 64, 62. Thus, the insert can be designed according to requirements, with desired axial and radial properties.

[0069] FIG. 3 shows an alternative embodiment of a cross section through one side of a rotor support 5 configured to support shaft 20 of a vacuum pump rotor within pump body 30. Rotor support 5 comprises insert 70, rolling bearing 10 and resilient members 40, 42 and 43.

[0070] In this embodiment, shaft 20 is mounted via the rotor support 5 towards the outlet end of the pump and on magnetic bearings (not shown) towards the inlet end of the pump. The magnetic bearings provide a biasing force 80 on shaft 20 which biases it against axial resilient member 42 and a portion of resilient member 43.

[0071] It should be appreciated that the flexible resilient members may be located either between the rolling bearing 10 and insert 70 and/or between the insert 70 and pump body 30. In this embodiment they are mounted between both, but in some embodiments there are only flexible resilient members 40 and 42 or flexible resilient member 43.

[0072] The resilient members may be bonded to the rolling bearing 10 and insert 70 and to the pump body wall 30, however, generally they are held in position by their elasticity.

[0073] In the embodiment of FIG. 3 rolling bearing 10 is adhered to shaft 20. Insert 70 lies between pump body 30 and rolling bearing 10 and there is an L-shaped resilient member 43 between the rolling bearing 10 and insert 70. The L-shaped resilient member is formed of an elastomeric material and has a narrower cross sectional width along the radially extending portion than along the axially extending portion. There are further resilient members between the insert 70 and the pump body 30. These comprise O-ring 40 located in recess 32 in the pump body wall and axial resilient member 42. In other embodiments L-shaped resilient member 43 may be replaced by two separate resilient members, a ring gasket arranged to lie on the upper surface of rolling bearing 10 and an annular elastomeric damping member arranged to lie around the outer surface of bearing 10 and adjacent to the inner surface of insert 70.

[0074] Insert 70 has an inner annular member 54 with a radially inwardly extending portion at one axial end that extends over the rolling bearing 10 and provides a surface for a portion of the L-shaped resilient member 43 that extends over the axial end surface of rolling bearing 10 to abut with and provide additional axial stability. The insert further has a central flexible member 58 extending from the outer annular member 56 to the inner annular member 54 and providing radial flexibility while also biasing the rolling bearings towards a central position. The outer annular member 56 has a radially outwardly extending portion at the other axial end to the radially inwardly extending portion that provides a surface parallel to a protruding portion 34 of the pump wall body 30. Axial resilient member 42 which is in the form of a gasket is located between the two parallel radially extending surfaces and provides additional axial stability. In this embodiment biasing force 80 biases the bearing against L-shaped member 43 and the insert 70 against resilient member 42 holding the support axially in place, the biasing force 80 resisting axial movement in the downward direction and the two resilient members 42, 43 resisting it in the upwards direction and acting to damp any axial vibrations.

[0075] O-ring 40 and the axially extending portion of L-shaped resilient member 43 provide damping of vibrations travelling radially from the shaft and bearings towards the pump body 30. The O-ring 40 is mounted in a recess 32 of pump body wall 30 and this allows it to be held in place while the insert, shaft and bearing are slid into position.

[0076] Were the rolling bearing 10 to need to be replaced, then the arrangement of the rotor support 5 will help to accurately position the shaft both radially and axially allowing the bearings to be changed in the field without the need for rebalancing.

[0077] Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiment and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.

[0078] Although elements have been shown or described as separate embodiments above, portions of each embodiment may be combined with all or part of other embodiments described above.

[0079] Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are described as example forms of implementing the claims.