Multiple pumping mechanism vacuum pump

Abstract

A vacuum pump having multiple pumping mechanisms mounted on at least two shafts is disclosed. The vacuum pump comprises a combined electric machine, which may be a motor, and magnetic gearing mechanis

Description

FIELD OF THE INVENTION The field of the invention relates to vacuum pumps and in particular, to vacuum 5 pumps with multiple pumping mechanisms. BACKGROUND Different types of vacuum pumps with different types of pumping mechanism are known. These include entrapment type pumps, where a gas is trapped in a solid 10 or liquid state; momentum transfer pumps such as turbomolecular pumps where the molecules of the gas are accelerated from the inlet side towards the outlet or exhaust side, and positive displacement pumps, where a gas is trapped and moved. 15 These different types of vacuum pump may operate most effectively at different pressures and at different rotational speeds. Thus, for example positive displacement pumps, such as a scroll pump may operate well at lower vacuums and a lower rotational speed, while a turbomolecular pump operates effectively at high vacuums and requires a high rotational speed. A drag pump for example 20 operates well between the two pressures. Thus, when evacuating a chamber, multiple pumps with different types of pumping mechanisms may be arranged in series to attain the desired pressures. In some cases, rather than having multiple pumps a multi-stage pump may be 25 used whereby different pumping mechanisms such as a turbomolecular stage and drag stage may be mounted on a same shaft. Although such an arrangement may be compact and require less hardware than multiple pumps, it may be problematic to mount different pumping mechanism on the same shaft, where the different pumping mechanisms have different configurations or do not 30 operate well at the same rotational speeds. SUMMARY An aspect provides a vacuum pump comprising a plurality of pumping mechanisms mounted on at least two shafts, said vacuum pump comprising: a 5 combined electric machine and magnetic gearing mechanism comprising a first magnetic gear member and a second magnetic gear member for rotating said at least two shafts at two different speeds; wherein at least one component of said magnetic gearing mechanism comprises a rotor of said electric machine or a stator of said electric machine. 10 It was recognised that there might be advantages in having a vacuum pump with several pumping mechanisms with magnetic gears allowing the pumping mechanisms to be driven at different speeds. This would allow a flexible effective and efficient vacuum pump to be provided that is both compact and hardware 15 efficient. Furthermore, sharing components between and co-locating the electrical machine and the magnetic gear member provides for additional part savings and a compact arrangement. The electrical machine may be a motor driving the gears and thus, the shafts of the different pumping mechanism. 20 The several pumping mechanisms may be pumping mechanisms of different types using different pumping principles or be of a same or similar type but with different volumetric configurations, in each case they may operate effectively at different rotational speeds, and the provision of a gearing mechanism allows them to be driven by a single motor at or close to each of their optimum speeds. 25 The pumping mechanisms are mounted on different shafts. In some cases, these shafts may be coaxial shafts. In some embodiments, said plurality of pumping mechanisms comprise a lower pressure pumping mechanism and a higher pressure mechanism, said lower 30 pressure mechanism being configured to pump down to a lower pressure when operational than a pressure that said higher pressure pumping mechanism pumps down to. ln some embodiments, said gearing mechanism is configured such that said lower pressure pumping mechanism is driven at a higher rotational speed than said higher pressure pumping mechanism. 5 An alternative aspect provides an electric motor and magnetic gearing mechanism for driving two shafts at different rotational speeds comprising: a first magnetic gear member and a second magnetic gear member for rotating said at least two shafts at two different speeds; wherein at least one component of said 10 magnetic gearing mechanism comprises a rotor of said motor or a stator of said motor. In some embodiments, said magnetic gearing mechanism comprises: said first magnetic gear member, said second magnetic gear member and a modulator 15 arranged between said first and second magnetic gear members, said at least one component of said magnetic gearing mechanism comprising at least one of said first magnetic gear member, said second magnetic gear member and said modulator. 20 In some embodiments, said first and said second magnetic gear members and said modulator are concentrically mounted nested cylinders. In other embodiments, said first and said second magnetic gear members are concentrically mounted and axially displaced from each other. Having 25 concentrically mounted nested cylinders may provide for a particularly compact arrangement, however, concentrically mounted axially displaced gear members which may be in the form of discs is also a possible arrangement. In some embodiments, said first magnetic gear member comprises an outer 30 cylindrical and said second magnetic gear member comprises an inner cylindrical member. ln some embodiments, said second magnetic gear member is mounted on one of said shafts that is configured to be driven at a faster one of said two different speeds. The second magnetic gear member is the inner member where the gear members are cylinders and is configured for faster rotation. 5 In some embodiments, said electrical machine comprises an electric motor. In some embodiments, said combined electric motor and magnetic gearing mechanism comprises an outer cylindrical member comprising motor windings 10 and magnets said outer cylindrical member forming said motor stator and said first magnetic gear member. In some embodiments, said combined electric motor and magnetic gearing mechanism comprises an inner cylindrical member comprising magnets, said 15 inner cylindrical member forming said motor rotor and said second magnetic gear member. In some embodiments, said combined electric motor and magnetic gearing mechanism comprises a modulator, said modulator being mounted on one of said 20 shafts that is configured to be driven at a slower one of said two different speeds. In some cases the first magnetic gear member may be stationary and part of the motor stator, while the modulator rotates at the slower speed and drives the slower shaft of the higher pressure pumping mechanism, and the second gear 25 member is mounted on the shaft of the lower pressure pumping mechanism and is driven at a higher speed. In some embodiments, there is a partition separating a lower pressure region of said vacuum pump housing said second magnetic gear member from a higher pressure region housing said first magnetic gear member. 30 In some embodiments, said partition comprises a cylindrical portion said cylindrical portion forming a support surface for bearings mounting said shaft configured to rotate at said faster of said two different speeds. Where the gears, modulators and motor parts are nested cylinders then a partition between the modulator cylinder and the second gear member cylinder may also have a cylindrical form and could be used to mount the bearings supporting the faster 5 shaft and thereby lead to a more compact arrangement. In some embodiments, said first magnetic gear member comprises a cylindrical member comprising magnets and forming said motor rotor, said first magnetic gear member being mounted on one of said shafts configured to be driven at a 10 slower one of said two different speeds. In some embodiments, said combined electric motor and magnetic gearing mechanism comprises an inner cylindrical member comprising magnets, said inner cylindrical member forming said second magnetic gear member and being 15 mounted on one of said shafts configured to be driven at a faster one of said two different speeds. In some embodiments, said first magnetic gear member comprises a cylindrical member comprising magnets, said first magnetic gear member being mounted on 20 one of said shafts configured to be driven at a slower one of said two different speeds. In some embodiments, said combined electric motor and magnetic gearing mechanism comprises an inner cylindrical member comprising magnets, said 25 inner cylindrical member forming said second magnetic gear member and said motor rotor and being mounted on one of said shafts configured to be driven at a faster one of said two different speeds. In some embodiments, said modulator comprises said motor windings and forms 30 said motor stator. Whi 1st the modulator could drive either the outer or the cylindrical member comprising magnets, it may be preferable to drive the inner cylindrical member so that this forms the motor rotor as this rotates faster and allows the arrangement to be smaller. 5 In other embodiments, said combined electric motor and magnetic gearing mechanism comprises a cylindrical outer member surrounding said magnetic gear members and comprising motor windings, said cylindrical outer member forming said motor stator. 10 In some embodiments, said combined electric motor and magnetic gearing mechanism comprises a cylindrical modulator between said first and second magnetic gear members, said cylindrical modulator forming at least a part of a partition separating a lower pressure region of said vacuum pump housing said 15 second magnetic gear member from a higher pressure region housing said first magnetic gear member. In some embodiments, a cylindrical portion of said partition comprising said modulator forms a support surface for bearings mounting said shaft configured to 20 rotate at said faster of said two different speeds and being within said lower pressure region of said vacuum pump. Where the modulator is fixed and not rotating, it may be used to form a partition separating the higher and lower pressure regions of the multiple mechanism 25 vacuum pump. It may also be used to support the bearings of the faster shaft. This allows the modulator to have several functions, reducing the number of pump components and providing a more compact machine. In some embodiments, said combined electrical machine and magnetic gearing 30 mechanism comprises an outer cylindrical member comprising motor windings said outer cylindrical member forming said electrical machine stator and said first magnetic gear member, and an inner cylindrical member comprising magnets, said inner cylindrical member forming said electrical machine rotor and said second magnetic gear member and being mounted on one of said two shafts, said shaft being said shaft of said lower pressure pumping mechanism. 5 In some embodiments, the vacuum pump further comprises drive circuitry configured to supply said electrical machine windings with power to create a rotating magnetic field of a required speed. In some cases, rather than acting as an electric motor to drive both shafts, the 10 electrical machine may be used to create a magnetic field that may be a rotating magnetic field rotating at a certain speed, the speed being selected according to the desired speed of rotation of the inner rotor. This allows the inner rotor to be driven at a variable speed and provides what may be seen as a variable ratio magnetic gear. It may be advantageous to drive pumping mechanisms at 15 different speeds during different phases of their operation and thus, such an arrangement may have advantages particularly during pump down, for example. In some embodiments, said combined electrical machine and magnetic gearing mechanism comprises a modulator, said modulator being mounted on said shaft 20 of said higher pressure pumping mechanism. In some embodiments, said vacuum pump comprises a further motor configured to drive said shaft of said higher pressure pumping mechanism at a slower speed than said shaft of said lower pressure pumping mechanism, in others the further 25 motor could be configured to drive said shaft of lower pressure pumping mechanism at a faster speed. The electrical machine acts to allow a variation in the gear ratio of the magnetic gear, by providing a braking effect or a driving effect on, in the example above, 30 the faster shaft, however, this means that a separate motor to drive the other shaft may be required. ln some embodiments, the vacuum pump comprises a partition separating a lower pressure region of said vacuum pump housing said second magnetic gear member from a higher pressure region housing said first magnetic gear member. 5 In some embodiments, said partition comprises a cylindrical portion, said cylindrical portion forming a support surface for bearings mounting said shaft configured to rotate at said faster of said two different speeds. The electrical machine forms the active part of the magnetic gear and the control 10 circuitry driving the motor windings of the separate motor and the stator windings of the magnetic gear may be combined to control the speed of rotation of the rotating magnetic field produced by the windings in conjunction with controlling the speed of the separate motor. 15 Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims. 20 Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function. BRIEF DESCRIPTION OF THE DRAWINGS 25 Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which: Figure 1 shows a first embodiment of a combined electrical motor and magnetic gear for a vacuum pump; Figure 2 shows a second embodiment of a combined electrical motor and 30 magnetic gear for a vacuum pump; Figure 3 schematically shows a pump with two pumping mechanisms according to an embodiment; and Figure 4 schematically shows a variable ratio magnetic gear, according to an embodiment. DESCRIPTION OF THE EMBODIMENTS 5 Before discussing the embodiments in any more detail, first an overview will be provided. Embodiments co-locate the magnetic gears and the electrical machine that may be an electrical motor. io Embodiments with split magnetically geared machines. Split magnetically geared machines combine the electrical machine rotor with a magnetic gear component. Examples may provide a separate electric motor stator nested inside the inner rotor of the magnetic gear. Magnets mounted 15 inside the inner rotor magnetically couple with the motor stator windings, thus such a magnetic gear inner rotor is also the electrical motor rotor. The magnetic gear outer ring or the modulator are then couped to one shaft running at a lower speed than the electrical motor, therefore providing a combined high speed motor and speed-down magnetic gearbox unit. 20 Such an arrangement, however, is an issue for a multi- mechanism pump where the combined electrical magnetic and magnetic gear needs to drive at least two separate shafts at different speeds, as it would be difficult to support such an inner mounted motor stator. 25 Embodiments provide a multi-mechanism vacuum pump that uses an adapted spit magnetically geared machine to drive two rotors of the pump. In this embodiment the motor stator is located outside the magnetic gear (MG) outer ring or first magnetic member. Embodiments may have a decoupled 30 configuration where the number of the motor poles is different (lower) than the number of magnetic poles of the MG outer ring, which is typically high in order to provide an adequate gearing ratio. This is more easily implemented than a design with a coupled configuration. The faster lower pressure mechanism is coupled to the MG inner rotor or second 5 magnetic gear member whereas the slow mechanism is coupled to the MG outer ring or first magnetic gear mechanism. Where the two mechanisms operate at two different pressures, the modulator in the can also be used as a pressure boundary, and the inboard bearing of the high-speed mechanism can be nested in the modulator, which will act also as a bearing support. Such a design is 10 shown in Figure 1 and described in more detail below. In other embodiments, the pressure boundary could be provided by a separate ‘can’ and the bearing could be supported by a separate bracket if more convenient for a specific design. Benefits of the embodiment include: increased further integration (with smaller 15 pump footprint and simplified user interface) and a reduction in the number of components. Magnetically, the design is relatively simple because the motor and the gear are not coupled. 20 Figure 1 shows such an embodiment and in this embodiment, shaft 10 of the slow higher pressure pumping mechanism is attached to and driven by the motor rotor 40, which also acts as the magnetic gear outer ring or first magnetic gear member 22. The motor stator 30 and motor windings 32 are in this embodiment 25 mounted on the pump stator 60 outside of the motor rotor 40. The magnetic gear inner ring or second member 42 is mounted to shaft 20 of the faster lower pressure pumping mechanism. The magnetic gear inner ring 42 comprises a number of magnetic elements 44 of alternating polarity arranged around a circumference. The magnetic gear outer ring 22 and motor rotor 40 also have a 30 number of magnetic elements 23, 24 of alternating polarity arranged around its circumference. The magnetic gear inner ring 42 has fewer magnetic elements 44 than the magnetic gear outer ring 22 such that it rotates at a higher speed in response to rotation of magnetic gear member 22 and motor rotor 40. In this embodiment, modulator 70 for the magnetic gear is within partition 80 that partitions the lower pressure region 90 from the higher pressure region 92. Modulator 70 may comprise ferro-magnetic elements arranged around its 5 circumference which help channel the magnetic field between the two magnetic gear members 42, 22. There are bearings 50 for mounting shaft 20 within the partition 80, these may be magnetic bearings. These bearings 50 are in the higher pressure region 92. io Embodiments with Ring Stator magnetic geared machines. In ring stator electrical geared machines, a further degree of integration can be obtained by combining an electric motor stator and its windings with the outer ring of the magnetic gear. The electric motor stator drives the magnetic gear inner rotor, which is therefore combined with the electric motor rotor, which in 15 examples is not coupled to any shaft. The modulator is coupled to the slower output shaft therefore providing a highly integrated combined high speed motor and speed-down magnetic gearbox unit. In this embodiment for multi mechanism vacuum pumps, the motor stator 30 and 20 magnetic outer ring 22 of Figure 1 are merged and are mounted on the stator 60. The modulator 70 is mounted within the rotor 40 of the slow mechanism and this also drives shaft 10. In summary the windings 32 in the outer ring 30 drive the inner rotor 40 - this can 25 be achieved with a motor having a number of poles that is equal to the number of magnetic poles in the inner rotor 40, so that the two fields can interact. The field generated by the permanent magnets 34 in the outer ring interact with the modulated field of the magnetic field of the inner rotor 40. The field is formed by the pole pieces and this interaction sets the modulator in motion with a defined 30 gear ratio. ln summary: the motor stator 30 drives the inner rotor 40, which is coupled to the fast lower pressure pumping mechanism and shaft 20 and induces rotation in the modulator 70 by interacting with the magnetic gear. 5 A possible embodiment of this is presented in Figure 2. The MG inner ring 42 is coupled to the fast mechanism, via shaft 20. As the MG outer ring 22 (merged with the motor stator 30) is static, the MG modulator 70 will have to rotate and provide output to the slow mechanism via shaft 10. io In the embodiment of Figure 2 pressure segregation is required. A rotating MG modulator 70 coupled to the slow mechanism or shaft 10, cannot provide this and a separate can is used as the partition 80. The bearing 50 is, in this embodiment, mounted outboard of the MG resulting in a less compact design - it could be 15 mounted to the can, in an alternative, if this were designed to be robust enough, but this may not be easy as the thickness of the can is constrained by the requirement to keep the airgap small. Wound modulator magnetically geared machine. 20 In the embodiment of Figure 3, the motor stator 30 is merged with the MG modulator 70, by fitting windings thereto. The MG outer ring 22 drives the slow mechanism via shaft 10, whilst the MG inner ring 42 drives the fast mechanism via shaft 20. This design provides 25 excellent integration especially if the modulator 70 supports some of the bearings 50 and provides pressure segregation (if this is needed). Figure 3 illustrates an example of this embodiment, with the magnets 24 of inner ring 42 being mounted on shaft 20 within the bearings 50. The magnetic gear 30 outer ring 22 is mounted on the motor rotor 30 attached to slow shaft 10 and has permanent magnets 24 on its inner surface. The windings of the motor stator 30 are within the modulator 70, which is within the partition 80 dividing the higher and lower pressure regions. In the context of an implementation for a geared pump, for the embodiments 5 presented one slower pumping mechanism for pump 97 is mounted on shaft 10 which in turn is driven by MG outer ring 22 (or alternatively, by a rotating MG modulator) and the other faster pumping mechanism for pump 98 is mounted on shaft 20 and is driven by the MG inner ring 42. That is the shaft 20 would be the fast mechanism and the other shaft 10 the slow mechanism. io Embodiments can be used for any combination of high-speed booster and slower speed backing pump to provide a highly integrated solution with a reduced footprint and interface requirements. 15 Variable Ratio Magnetic Gear In an alternative embodiment the flux modulated electrical machine is used to provide a variable gear ratio magnetic gear, which is used to drive two shafts bearing vacuum mechanisms running at different speeds. A separate electrical motor is used to drive one of the two shaft, and the flux modulated electrical 20 machine provides the gearing function. Figure 4 shows an embodiment with an electrical machine, where the slow shaft 10 is driven by a separate electrical motor 92 and a ring stator magnetically geared machine where MG outer ring 22 is combined with the electrical machine 25 stator and comprises stator windings 32. No magnetic gear magnets are mounted on the outer ring 22 but a magnetic field with a number of poles is generated by the electric machine stator; this field can be static or rotating with a selected frequency. The magnetic field generated by the first magnetic gear member, MG outer ring 22, interacts with the field generated by the second 30 magnetic gear member, MG inner ring 42, through the field modulation provided by the modulator 70. The MG inner ring 42 is coupled to the fast shaft and the modulator 70 is coupled to the slow shaft. If the magnetic field created by the magnetic field stator is static, the gear ratio between the gear members is the same as a corresponding magnetic gear with the same number of magnetic poles. However, if the field is rotating, a different gear ratio is generated. In this way a variable ratio gear can be provided. 5 The drive 94 for the outer ring stator windings 32 can be merged with the drive of the main motor 92, this could be two completely separate drives in the same enclosure or, at the other extreme, one single integrated drive and control for both of them. io Speed sensing, for the commutation of the stator windings 32, can be provided by suitable speed sensors measuring for example the speed of the fast shaft; additional signals like for example pressure can be combined with the speed to provide a control signal. 15 Whilst this alternative embodiment does not result in further integration, the flexibility in setting the speeds for the two or more shafts can be used advantageously. 20 For example: 1. if a fast air inrush occurs, the rotational speed of a fast inlet mechanism (for example a booster) could be altered, for example decreased, to alter (for example reduce) the resistance torque decreasing the occurrence of synchronisation loss between the shafts - one of the main risks when operating 25 magnetic gears. The air inrush could be sensed by pressure readings, torque required to keep the speed constant and / or its rate of change. Alternatively an external signal from plant (i.e. ‘start pumping’) could be sent to the control system in advance. 30 The ability of running at different gear ratios should help to gain control if synchronisation between the two shafts is lost. 2. If the fast-running mechanism is running as a booster for the slow primary mechanism, but there is little or no inlet flow in it, then its speed can be reduced to reduce power losses in the mechanism and in the magnetic gear and increase bearing life, the speed can be increased when the pumping requirements 5 thereafter; In general the relative speeds of the different mechanisms can be altered so that the machine train can provide the required pumping with the lowest power. When the stator windings generate power, this can be returned to the grid, io used in the main motor, or stored in a battery which can be shared between the two of them and used when speed changes are required. 3. With a variable speed range, there is more flexibility during ramp up - for example the gear ratio could be set to minimum first to allow fast ramp up of the slow mechanism if this is a primary pump, providing a first evacuation, followed 15 by a speed increase of the fast mechanism once rough vacuum has been attained. This could also reduce the maximum torque requirements on the magnetic gear and also on the motor since the acceleration load will be lower. Although illustrative embodiments of the invention have been disclosed in detail 20 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. REFERENCE SIGNS 10 slower shaft 20 faster shaft 22 first magnetic gear member or outer magnetic gear ring 5 23, 24 magnets 30 stator 32 motor windings 40 rotor 42 second magnetic gear member or inner magnetic gear ring I rotor io 44 magnets 50 bearings 70 modulator 80 partition 90 lower pressure region 15 92 higher pressure region 94 drive circuitry 95 motor 97 slower pump 98 faster pump 20

Claims

1. A vacuum pump comprising:a plurality of pumping mechanisms mounted on at least two shafts; and5 a combined electric machine and magnetic gearing mechanism comprisinga first magnetic gear member and a second magnetic gear member for rotating said at least two shafts at two different speeds;wherein at least one component of said magnetic gearing mechanism comprises a rotor of said electric machine or a stator of said electric machine.io2. A vacuum pump according to claim 1, wherein said magnetic gearing mechanism comprises: said first magnetic gear member, said second magnetic gear member and a modulator arranged between said first and second magnetic gear members, said at least one component of said magnetic gearing mechanism 15 comprising at least one of said first magnetic gear member, said secondmagnetic gear member and said modulator.

3. A vacuum pump according to claim 2, wherein said first magnetic gear member comprises an outer cylindrical and said second magnetic gear member 20 comprises an inner cylindrical member4. A vacuum pump according to claim 2 or 3, wherein said second magnetic gear member is mounted on one of said shafts that is configured to be driven at a faster one of said two different speeds.

255. A vacuum pump according to any preceding claim, wherein said electrical machine comprises an electric motor.

6. A vacuum pump according to claim 5, wherein said combined electric 30 motor and magnetic gearing mechanism comprises an outer cylindrical member comprising motor windings and magnets, said outer cylindrical member forming said motor stator and said first magnetic gear member.

7. A vacuum pump according to claim 6, wherein said combined electric motor and magnetic gearing mechanism comprises an inner cylindrical member comprising magnets, said inner cylindrical member forming said motor rotor and 5 said second magnetic gear member.

8. A vacuum pump according to claim 6 or 7, wherein said combined electric motor and magnetic gearing mechanism comprises a modulator, said modulator being mounted on one of said shafts that is configured to be driven at a slower io one of said two different speeds.

9. A vacuum pump according to claim 5, wherein said first magnetic gear member comprises a cylindrical member comprising magnets and forming said motor rotor, said first magnetic gear member being mounted on one of said 15 shafts configured to be driven at a slower one of said two different speeds.

10. A vacuum pump according to claim 9, wherein said combined electric motor and magnetic gearing mechanism comprises an inner cylindrical member comprising magnets, said inner cylindrical member forming said second magnetic 20 gear member and being mounted on one of said shafts configured to be driven ata faster one of said two different speeds.

11. A vacuum pump according to claim 5, wherein said first magnetic gear member comprises a cylindrical member comprising magnets, said first magnetic 25 gear member being mounted on one of said shafts configured to be driven at aslower one of said two different speeds; said vacuum pump further comprising an inner cylindrical member comprising magnets, said inner cylindrical member forming said second magnetic gear member and said motor rotor and being mounted on one of said shafts configured to be driven at a faster one of said two 30 different speeds.

12. A vacuum pump according to any of claims 9 to 11, wherein saidmodulator comprises said motor windings and forms said motor stator13. A vacuum pump according to claim 9 or 10, where said combined electric5 motor and magnetic gearing mechanism comprises a cylindrical outer member surrounding said magnetic gear members and comprising motor windings said cylindrical outer member forming said motor stator.

14. A vacuum pump according to any one of claims 5, or 9 to 13, wherein saidio combined electric motor and magnetic gearing mechanism comprises acylindrical modulator between said first and second magnetic gear members, said cylindrical modulator forming at least a part of a partition separating a lower pressure region of said vacuum pump housing said second magnetic gear member from a higher pressure region housing said first magnetic gear member.1515. A vacuum pump according to any one of claims 9 to 14, wherein acylindrical portion of said partition comprising said modulator forms a support surface for bearings mounting said shaft configured to rotate at said faster of said two different speeds and being within said lower pressure region of said vacuum20 pump.

16. A vacuum pump according to any one of claims 1 to 4, wherein said combined electrical machine and magnetic gearing mechanism comprises an outer cylindrical member comprising stator windings, said outer cylindrical25 member forming said electrical machine stator and said first magnetic gear member, and an inner cylindrical member comprising magnets, said inner cylindrical member forming said electrical machine rotor and said second magnetic gear member and being mounted on one of said two shafts, said shaft being said shaft of said lower pressure pumping mechanism.

17. A vacuum pump according to claim 16, further comprising drive circuitry configured to supply said stator windings with power to create a rotating magnetic field of a selected speed.5 18. A vacuum pump according to claim 16 or 17, wherein said combinedelectrical machine and magnetic gearing mechanism comprises a modulator, said modulator being mounted on said shaft of said higher pressure pumping mechanism.io 19. A vacuum pump according to claim 18, further comprising a further motor configured to drive said shaft of said higher pressure pumping mechanism at a slower speed than said shaft of said lower pressure pumping mechanism.

20. A vacuum pump according to any one of claims 6 to 8, or 16 to 19,15 comprising a partition separating a lower pressure region of said vacuum pump housing said second magnetic gear member from a higher pressure region housing said first magnetic gear member.

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