WO1998053231A1

WO1998053231A1 - Sealed drive system

Info

Publication number: WO1998053231A1
Application number: PCT/GB1998/001376
Authority: WO
Inventors: Douglas Alan Brooks; Vadim Boguslavskiy
Original assignee: Advanced Fluid Systems Limited
Priority date: 1997-05-16
Filing date: 1998-05-14
Publication date: 1998-11-26
Also published as: GB9710050D0

Abstract

A sealed drive system for transferring rotary motion into a vacuum chamber is disclosed. The system has a housing (14) with a flange secured to a wall (10) of the chamber around an aperture (12) in the wall. The housing (14) houses at least one bearing (18, 20), and a rotary shaft (24) having an end (26) which passes through the aperture (12) in the chamber wall (10). The housing (14) further houses at least one magnetic circuit including a magnetic fluid (38) which forms a seal around the rotary shaft (24). In order to provide a particularly compact arrangement, the housing (14) also houses an electric motor (44) which is arranged to rotate the shaft (24).

Description

SEALED DRIVE SYSTEM

This invention relates to a sealed drive system and is more particularly concerned with a sealed drive system for transferring rotary motion into a sealed chamber such as a vacuum chamber using a rotary shaft sealed using a magnetic fluid.

Sealed drive systems incorporating a magnetic fluid are known for transmitting rotary motion into a vacuum chamber. These systems are commonly referred to as magnetic fluid feedthroughs and consist of a magnetic circuit using a magnetic fluid to form a standing liquid ring around a rotary shaft which runs within a stationary housing secured to the vacuum chamber. The required conditions within the vacuum chamber being sealed can be met by varying the number of these rings and their strength, through the use of different magnetic fluids and different magnetic circuits. To achieve rotary motion of the shaft, it is common practice to use an electric motor which is coupled to the shaft of the feedthrough by a belt or by gears. These arrangements impose large side loads on bearings in the feedthrough, thus reducing bearing life. As an alternative, the electric motor can be coupled with the drive shaft of the motor axial ly aligned with the rotary shaft and connected therewith using a flexible coupling. However, this latter arrangements results in a long and cumbersome assembly requiring additional support work to support the motor, and furthermore it is thus impossible to insert anything through the shaft itself.

According to the present invention, these and other objects have now been realised by the provision of a sealed drive system for transferring rotary motion into a chamber having a wall including an aperture, the drive system comprising a housing adapted to be secured to the wall around the aperture, at least one bearing in the housing, a rotary shaft mounted in the at least one bearing within the housing, the rotary shaft having an end which is adapted to pass through the aperture into the chamber, at least one magnetic circuit including a magnetic fluid in the housing adapted to form a seal around the rotary shaft, and a motor mounted within the housing for rotating the rotary shaft.

In one embodiment, the motor has a hollow rotor, which is mounted on the shaft, which in turn can have an opening to permit insertion of a desired material, part or device into the chamber through the seal.

In accordance with one embodiment of the sealed drive system of the present invention, the motor includes a rotor mounted on the rotary shaft and a stator which is mounted in the housing so as to surround the motor. In a preferred embodiment, the motor is an electric motor.

In accordance with another embodiment of the sealed drive system of the present invention, the housing includes a first end adapted to be secured to the end wall and a second end, the at least one magnetic circuit being mounted adjacent to the first end of the housing and the motor being mounted adjacent to the second end of the housing.

In accordance with another embodiment of the sealed drive system of the present invention, the at least one bearing is disposed between the motor and the magnetic circuit.

In accordance with another embodiment of the sealed drive system of the present invention, the system is adapted to transfer rotary motion into an additional chamber having a wall including an aperture, and the end of the rotary shaft comprises a first end and the rotary shaft includes a second end which is adapted to pass through the aperture in the wall of the additional chamber, and the motor is disposed in the housing between the ends of the rotary shaft. Preferably, the at least one magnetic circuit comprises a first magnetic circuit mounted adjacent to the first end of the rotary shaft and the system includes a second magnetic circuit including a magnetic fluid mounted adjacent to the second end of the rotary shaft. In a highly preferred embodiment, the at least one bearing comprises a pair of bearings, each of the pair of bearings being disposed between the motor and a respective one of the first and second magnetic circuits.

In accordance with another embodiment of the sealed drive system of the present invention, the housing includes a first end adapted to be secured to the end wall, and a second end, the at least one magnetic circuit comprising a first magnetic circuit including a magnetic fluid and a second magnetic circuit including a magnetic fluid in the housing adapted to form a seal around the rotary shaft, the motor being mounted between the first and second magnetic circuits. In a preferred embodiment, the second end of the housing comprises a closed end. In another preferred embodiment, the at least one bearing comprises a first bearing and a second bearing in the housing, the motor being mounted between the first and second bearings.

Such a sealed drive system can be relatively compact and also can enable undue side loads on the bearing means to be eliminated. Additionally, it will be appreciated that, in the system according to the present invention, the housing can be completely sealed when mounted on the chamber. This is of considerable benefit from a cleanliness point of view, making the system particularly useful in clean facilities. Additionally, a completely sealed housing has the safety advantage that there are no exposed moving parts so that items cannot be trapped or caught up in the moving parts. Most significantly, the present invention can permit both the bearings and the motor to be on the non-vacuum or air side of the seal, particularly since these units generally do not operate well in a vacuum, such as that which may be present within the chamber.

Most preferably, the motor includes a rotor mounted on the rotary shaft and a stator which is mounted in the housing so as to surround the motor. Most preferably, the motor is an electric motor, but it can also be a hydraulic, pneumatic or other type of motor.

In one convenient embodiment, the at least one magnetic circuit is provided adjacent an end of the housing which is adapted to be secured to said wall, and the motor is provided adjacent an opposite end of the housing. The at least one bearing may be disposed between the motor and the magnetic circuit.

In another convenient embodiment, the sealed drive system is adapted to transfer rotary motion into an additional chamber; the rotary shaft has an opposite end which is adapted to pass through an aperture in a wall of the additional chamber; and the motor is disposed in the housing between the ends of the shaft.

Preferably, the at least one magnetic circuit comprises a respective magnetic circuit provided adjacent each end of the shaft. Preferably, the at least one bearing comprises a pair of bearings in which each bearing is disposed between the motor and a respective one of the magnetic circuits.

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings, in which:-

Fig 1 is a schematic axial section through a first embodiment of sealed drive system according to the present invention,

Fig 2 is a schematic axial section through a second embodiment of sealed drive system according to the present invention,

Fig 3 is a partly cut-away end view of a third embodiment of sealed drive system according to the present invention,

Fig 4 is an axial section on the line X-X of Fig 3,

Fig 5 is an axial section through a fourth embodiment of sealed drive system according to the present invention,

Fig 6 is an end view of the sealed drive system illustrated in Fig 5, and

Fig 7 is a schematic axial section through a fifth embodiment of a sealed drive system according to the present invention.

Referring now to Fig 1 of the drawings, the sealed drive system is for transferring rotary motion into a vacuum chamber having a wall 10 with an aperture 12 therein. The system comprises a generally cylindrical housing 14 having an annular end flange 16 secured by bolts (not shown) to the chamber wall 10 around the aperture 12. Disposed within the housing 14 are axially spaced inner and outer bearings 18 and 20, respectively located adjacent the end flange 16 and adjacent an outer end 22 of the housing 14. A rotary shaft 24 extends axially within the cylindrical housing 14 and is mounted in the bearings 18 and 20. The rotary shaft 24 has an inner end 26 which projects through the aperture 12 in the chamber wall 10 so as to be operably connected with a rotary device (not shown) in the chamber 10.

Disposed within the housing 14 adjacent the bearings 18 and 20 is a magnetic circuit indicated generally by arrow 28. Such magnetic circuit includes inner and outer annular pole pieces 30 and 32 which are disposed adjacent the bearings 18 and 20, respectively, and which surround the shaft 24. The magnetic circuit 28 further includes an annular magnet 34 which is disposed within the housing 14 so as to extend between the pole pieces 30 and 32. The magnet 34 is disposed adjacent the wall of the cylindrical housing 14. A magnetic fluid 38 forms a radial ring between the top of each of sets of annular teeth 40 and 42 forming a rotary seal between the shaft 24 and the pole pieces 30 and 32 in a manner well known per se. The sets of teeth 40 and 42 are provided around the shaft 24 inwardly of the respective pole pieces 30 and 32.

In accordance with the present invention, an electric motor 44 is coaxially mounted within the cylindrical housing 14 and, in this embodiment, is disposed between the outer bearing 20 and the outer end 22 of the housing 14. The motor 44 comprises a rotor 46 which is mounted on the rotary shaft 24, and a stator 48 which surrounds the rotor 46 and which is fixed to the housing 14.

It will be understood that, when the motor 44 is supplied with an electrical current through electrical leads (not shown), the rotor 46 is caused to rotate, thereby rotating the shaft 24, and driving the rotary device within the vacuum chamber. Because of the concentration of the lines of magnetic force across the gaps between the tops of the teeth 40 and 42 and the adjacent inner surfaces of the respective pole pieces 30 and 32, the magnetic fluid 38 is concentrated in such gaps and form standing liquid rings around the shaft 24, thereby effecting a seal with the shaft 24.

Referring now to Fig 2, parts of the system which are similar to those of Fig 1 are accorded the same reference numerals. In this embodiment, the outer bearing 20 is moved outboard of the motor 44 which is disposed between the outer bearing 20 and the pole piece 32. Also, shaft 24 has an outer end which is disposed wholly within the housing 14 which has its outer end 22 sealed by end plate 50.

Referring now to the embodiment of sealed drive system il lustrated in Figs 3 and 4, parts of the system which are similar to those of the previously-described embodiments are accorded the same reference numerals. In this embodiment, the sealed drive system is designed to transfer rotary motion into two vacuum chambers which are spaced apart with the sealed drive system being disposed between the two vacuum chambers. For this purpose, housing 14 of the drive system is provided with opposite annular end flanges 16a and 16b each of which is adapted to be bolted, clamped or otherwise attached to the chamber wall of a respective one of the vacuum chambers.

Electric motor 44 is disposed centrally of rotary shaft 24 and between bearings 18 and 20. To permit the motor 44 to be mounted at this location, the housing 14 is split into a housing portion 14a on which the end flange 16a is provided and a portion 14b on which the end flange 16b is provided. The housing portion 14a has a cup-shaped region 14c of enlarged cross-sectional area which accommodates the motor 44. The housing portion 14b has a flange 14d which is secured to (and thereby closes) the cup-shaped region 14c by means of a series of securing and locating studs 60. The motor 44 is brushless and has a stator 44a which is mounted within the portion 14c and secured in place by grub screws 62. Electrical terminals 64 and 66 enable an electrical supply connection to be made to the motor 44. The terminals 64 and 66 are secured to the portion 14d of the housing 14. The motor 44 also includes a rotor 44b which is secured to the central region of the shaft 24.

Pairs of annular polepieces 30a, 32a and 30b, 32b of respective magnetic circuits 28a and 28b are disposed adjacent the end flanges 16a and 16b, respectively. Each magnetic circuit 28a, 28b also includes an annular rare earth magnet 34a, 34b disposed between the respective pair of polepieces.

Because the sealed drive system is exposed to elevated temperatures in use, the pole pieces 30 and 32 and the motor 44 are water-cooled, with coolant water being provided via respective pairs of coolant connections 70, 72 and 74. Because of the sections taken in the drawings, only one connection of each pair of connections 70 and 72 can be seen in Figs 3 and 4. The bearings 18 and 20 are retained in place by respective lock nuts 80 and 82.

The sealed drive system according to Figs 3 and 4 operates in a manner analogous to that described above for Figs 1 and 2. Thus, in use, magnetic fluid 38a forms a standing liquid ring around the rotary shaft 24 and between the pair of annular pole pieces 30a and 32a and the annular magnet 34a. The pair of annular pole pieces 30b and 32b, annular magnet 34b and magnetic fluid 38b at the opposite end of the shaft 24 act in a similar way to provide a magnetic seal around the rotary shaft 24.

Referring now to Figs 5 and 6, the sealed drive system illustrated therein is similar to that of Figs 3 and 4 and similar parts are accorded the same reference numerals. However, in this embodiment, the sealed drive system is designed to transfer rotary motion into only a single vacuum chamber, and the motor 44 is provided at the opposite end of housing 14 to the flange 16. Instead of accommodating a second magnetic circuit, housing portion 14b is constituted by an end cap upon which is mounted a plug box 90 carrying the electrical terminals 64 and 66. In this embodiment, the bearings 18 and 20 are separated by a spacer 94.

Referring finally to Fig 7, a sealed drive system is illustrated therein which is again similar to the sealed drive systems shown in Figs 1 and 2, and similar parts are therefore accorded the same reference numerals. In this embodiment, however, the motor 44 is mounted between the inner bearing 18 and the outer bearing 20, and between the magnetic circuits 28. Also, the shaft 24 with inner end 26 is hollow and is defined by a cylindrical sleeve through which a stationary part 96 supported by end plate 50 can extend so that the part 96 can be inserted into the vacuum chamber. The end plate 50 is sealed with the housing 14 to maintain the vacuum in use. Reference numerals 30, 32 and 34 illustrate an assembly of pole pieces 30 and 32 and magnet 34 arranged in a similar way to those illustrated in Figs 3 and 4. Although the invention herein has been described with reference to particular embodiments, it is to be understood that these embodiments are merely illustrative of the principles and applications of the present invention. It is therefore to be understood that numerous modifications may be made to the illustrative embodiments and that other arrangements may be devised without departing from the spirit and scope of the present invention as defined by the appended claims.

Claims

1 . A sealed drive system for transferring rotary motion into a chamber having a wall including an aperture, said drive system comprising a housing adapted to be secured to said wall around said aperture; at least one bearing in said housing; a rotary shaft mounted in said at least one bearing within said housing, said rotary shaft having an end which is adapted to pass through said aperture into said chamber; at least one magnetic circuit including a magnetic fluid in said housing adapted to form a seal around said rotary shaft; and a motor mounted within said housing for rotating said rotary shaft.

2. A sealed drive system as claimed in claim 1 , wherein said motor includes a rotor mounted on said rotary shaft and a stator which is mounted in said housing so as to surround said motor.

3. A sealed drive system as claimed in claim 1 or 2, wherein said motor comprises an electric motor.

4. A sealed drive system as claimed in any preceding claim, wherein said housing includes a first end adapted to be secured to said wall and a second end, said at least one magnetic circuit being mounted adjacent to said first end of said housing, and said motor being mounted adjacent to said second end of said housing.

5. A sealed drive system as claimed in any preceding claim, wherein said at least one bearing is disposed between said motor and said magnetic circuit.

6. A sealed drive system as claimed in any one of claims 1 to 3, adapted to transfer rotary motion into an additional chamber having a wall including an aperture, wherein said end of each rotary shaft comprises a first end and wherein said rotary shaft includes a second end which is adapted to pass through said aperture in said wall of said additional chamber, and wherein said motor is disposed in said housing between said ends of said rotary shaft.

7. A sealed drive system as claimed in claim 6, wherein said at least one magnetic circuit comprises a first magnetic circuit mounted adjacent to said first end of said rotary shaft, and a second magnetic circuit including a magnetic fluid mounted adjacent to said second end of said rotary shaft.

8. A sealed drive system as claimed in claim 7, wherein said at least one bearing comprises a pair of bearings, each of said pair of bearings being disposed between said motor and a respective one of said first and second magnetic circuits.

9. A sealed drive system as claimed in Claim 1 , wherein said housing includes a first end adapted to be secured to said wall and a second end, said at least one magnetic circuit comprising a first magnetic circuit including a magnetic fluid and a second magnetic circuit including a magnetic fluid in said housing, each of said circuits being adapted to form a seal around said rotary shaft, and said motor being mounted between said first and second magnetic circuits.

10. A sealed drive system as claimed in Claim 9, wherein said second end of said housing comprises a closed end.

1 1 . A sealed drive system as claimed in Claim 9, wherein said at least one bearing comprises a first bearing and a second bearing in said housing, said motor being mounted between said first and second bearings.

12. A sealed drive system as claimed in Claim 1 , wherein the motor has a hollow rotor which is mounted on the shaft.

13. A sealed drive system as claimed in Claim 1 or 12, wherein the shaft has an opening therein to permit insertion of a desired material, part or device into the chamber through the seal.