GB2155580A

GB2155580A - Rotary motion drive

Info

Publication number: GB2155580A
Application number: GB08502913A
Authority: GB
Inventors: Peter Vincent Head; Brian John Stevens
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-03-08
Filing date: 1985-02-05
Publication date: 1985-09-25
Also published as: GB2155580B; GB8406143D0; GB8502913D0

Abstract

A rotary motion drive for transmitting rotary motion across a barrier, typically across the wall of a chamber such as a vacuum chamber, comprises a housing (10) sealably securable to an aperture in the barrier; an end cap (20) rotatably mounted on the housing and accessible, in use, from one side of the barrier; a drive tube (32) eccentrically mounted with respect to the end cap; a first drive shaft (44) extending axially through the drive tube, the drive tube and/or first drive shaft being mounted for relative rotation with respect to the end cap; a second, final, drive shaft (50) extending axially relative to the end cap and terminating, in use, on the other side of the barrier, the first and second drive shafts being linked by an eccentric mounting arrangement (52) for producing rotation of the second drive shaft on circular movement of the first drive shaft; and a bellows seal (58) sealed relative to the housing and also relative to a component mounted for relative rotation with respect to the end cap. In use, rotation of the end cap causes rotary movement of the drive tube and first drive shaft, causing rotation of the second drive shaft via the eccentric link. <IMAGE>

Description

SPECIFICATION Rotary motion drive Field of invention This invention relates to a rotary motion drive for transmitting a rotary motion across a barrier, typically across the wall of a chamber such as a vacuum chamber.

Background to the invention There are various circumstances in which it is required to transmit a rotary motion across a barrier, for example for manipulation of a specimen or other object isolated from normal atmospheric conditions in a chamber such as a vacuum chamber, presssure chamber or environmental chamber. In some cases it is possible to use a direct drive passing through the barrier for this purpose. However, this is not possible where there is a high pressure differential across the barrier, for example with a vacuum chamber, because a direct drive arrangement cannot be adequately sealed to prevent leakage of gas across the barrier. Indirect rotary drives have been developed for use in such circumstances, using a bent shaft (known as a wobble shaft) passing through the barrier, e.g. a vacuum chamber wall, and sealed with a correspondingly bent tubular bellows seal.One end of the bellows seal is sealed relative to the interior of the chamber and the other end is sealed to an element received eccentrically and rotatably in a rotatable cap (known as a thimble) accessible from the exterior of the chamber. The wobble shaft extends axially through the bellows seal, with one end received in the element. On rotation of the thimble the element moves with the thimble because of its eccentric location. However, because the element is not fixed in rotation to the thimble and because of the constraining action of the bellows the element "slips" relative to the thimble and describes a circular path while remaining in the same orientation. The outer end of the bellows seal moves in a similar manner, with the inner end being fixed, such movement being permitted by deformation of the bellows.The wobble shaft rotates with the thimble, within the bellows, transmitting a rotary motion to the interior of the chamber.

Certain disadvantages arise with such known arrangements, including the following: 1. Only comparatively low torque ratings are possible.

2. It is difficult to produce an accurately bent wobble shaft, and inaccuracies lead to bearing wear and reduce operating speeds.

3. The wobble shaft tends to straighten out during the heating process known as baking which is necessary in preparing equipment for use in very high vacuum applications, reducing operating speeds and producing additional forces on the bearings which then tend to sieze.

4. The convolutions of the bent bellows tend to work harden in use, leading to cracking.

3 is accordingly an aim of the present invention to provide an improved rotary motion drive.

The invention.

According to the present invention there is provided a rotary motion drive comprising: a housing sealably securable to an aperture in a barrier; an end cap rotatably mounted on the housing and accessible, in use, from one side of the barrier; a drive tube eccentrically mounted with respect to the end cap; a first drive shaft extending axially through the drive tube, the drive tube and/or first drive shaft being mounted for relative rotation with respect to the end cap; a second, final, drive shaft extending axially relative to the end cap and terminating, in use, on the other side of the barrier, the first and second drive shafts being linked by an eccentric mounting arrangement for producing rotation of the second drive shaft on circular movement of the first drive shaft; and a bellows seal sealed relative to the housing and also relative to a component mounted for relative rotation with respect to the end cap.

In use, the drive housing is appropriately secured in position to an aperture in a barrier, e.g. being sealed in position passing through a hole in the wall of a chamber such as a vacuum chamber.

Rotation of the end cap causes rotary movement of the drive tube and first drive shaft, causing rotation of tne second drive shaft via the eccentric link. During such movement the component or components mounted for relative rotation with respect to the end cap (the drive tube and/or first drive shaft) "slips" or "floats" relative to the end cap and describes a circular path while remaining in the same orientation. The bellows seal is sealed to such a component, constraining the component to move in this way. Further, the bellows seal where sealed to the component describes a similar circular path while remaining in the same orientation, with the seal where sealed relative to the housing remaining stationary.

The bellows seal can deform to accommodate such movement, while preventing leakage across the barrier.

Of the three connections between: i) the end cap and the drive tube; ii) the drive tube and the first drive shaft; and iii) the first drive shaft and the second drive shaft, two of these connections must be such as to permit relative rotation between the components connected thereby, while the third connection may be either rigid or so as to permit relative rotation. A number of different combinations is thus possible, all of which produce the same effect in use. Each combination results in the drive tube or the first drive shaft being rotatable relative to the end cap, and the bellows seal should be sealed to the relevant component which is relatively rotatable in this way.

For constructional reasons it is preferred that the eccentric link between the first and second drive shafts is rigid, with the drive tube being mounted for rotation relative to the end cap and the drive shaft mounted for rotation relative to the drive tube. In this case, the bellows seal should be sealed relative to the drive tube.

With such an arrangement, in use, rotation of the end cap causes the drive tube to move therewith, but because the drive tube is not fixed in rotation to the end cap and because of the constraining effect of the bellows seal, the drive tube "slips" or "floats" relative to the end cap and describes a circular path while remaining in the same orientation. The first drive shaft moves with the drive tube, but because the first drive shaft is not fixed in rotation to the drive tube and because of the constraining effect of the rigid eccentric link with the second drive shaft, the first drive shaft "slips" or "floats" relative to the drive tube and moves as if fixed in rotation relative to the end cap. This movement causes rotation of the second drive shaft via the eccentric link.

The bellows seal where sealed relative to the drive tube describes a similar circular path to that of the drive tube while remaining in the same orientation, with the sealed relative to the housing remaining stationary.

As a further example consider an embodiment in which the drive tube is fixed in rotation to the end cap, with the first drive shaft being mounted for relative rotation with respect to the drive tube, and the eccentric link permitting relative rotation between the first and second drive shafts. In this case, the bellows seal should be sealed relative to the first drive shaft.

In use, rotation of the end cap causes the drive tube to rotate therewith. The first drive shaft moves with the drive tube but because the first drive shaft is not fixed in rotation to the drive tube and because of the constraining effect of the bellows seal, the first drive shaft "slips" or "floats" relative to the drive tube and describes a circular path while remaining in the same orientation. This movement causes rotation of the final drive shaft via the eccentric link.

The bellows seal where sealed relative to the first drive shaft describes a similar circular path while remaining in the same orientation, with the seal where sealed relative to the housing remaining stationary.

The housing is preferably of generally tubular configuration, conveniently having a narrower portion comprising a support tube for the second drive shaft and a wider portion for the remaining components. A shoulder region between the narrower and wider portions is conveniently extended outwardly to form an annular flange which abuts against the barrier in use. The shoulder and/or flange may carry suitable sealing means e.g. a copper ring seal.

The end cap is conveniently cup-shaped, extending over the end of the wider portion of the tubular housing.

Bearings are conveniently provided to promote smooth running between the various relatively rotatable components, for example between the housing and end cap, between the end cap and drive tube in appropriate embodiments, between the drive tube and first drive shaft in appropriate embodiments, between the first drive shaft and eccentric mounting with the second drive shaft in appropriate embodiments, and between the second drive shaft and its associated support tube.

One end of the bellows seal is conveniently sealed to an annular flange extending inwardly from the housing, with the other end sealed to the first drive shaft or drive tube, as appropriate.

The components such as housing, drive tube, drive shafts, bellows and bearings are preferably of stainless steel, with the end cap desirably of aluminium alloy.

The first and second drive shafts may be generally solid. Alternatively, the drive shafts may be of tubular configuration with a push rod extending therethrough for axial movement. In this case, the end of the push rod adjacent the end cap may be linked to an arrangement for causing axial movement, conveniently a micrometer linked to the push rod via an arrangement for transmitting axial movement without rotation. A bush and bearing arrangement are conveniently used for this purpose. With such embodiments a further bellows seal is provided, sealed relative to the first drive shaft or drive tube, as appropriate, and also relative to the push rod for preventing gas leakage while permitting axial movement.

The present invention also includes within its scope a barrier, particularly the wall of a vacuum chamber, with the housing of a rotary motion drive in accordance with the invention sealingly secured to an aperture in the barrier.

Various advantages result from using an eccentric link in place of a wobble shaft of the prior art arrangements.

Higher torque ratings are possible. Use of ratings below maximum increases working life.

The eccentric link can be machined more precisely which results in greater precision of operation, prolongs bearing life and also per mits higher operating speeds.

The bellows seal can be straight rather than bent, reducing wear.

Problems with straightening of bends on baking do not arise.

The displacement of the bellows in use can be smaller than in prior art arrangements, prolonging bellows life.

Further, embodiments having a push rod are superior to comparable prior art arrangements which have a rod extending through a bent tubular wobble shaft: such prior art arrangements use balls and slugs in the bend region to permit axial movement of the rod around the bends. In contrast, with the present invention the rod can be straight, providing a much simpler more effective arrangement. Further, with the prior art arrangements it was necessary to use a spring loaded push rod, biased to its retracted position, and in practice the spring tended to stick, particularly after baking. With the present invention, because the push rod can be straight it can be positively displaced in both directions.

Embodiments of the invention will now be described, by way of example, with reference to the accompanying drawings.

In the drawings Figure 1 is a sectional view of one embodiment of a rotary motion drive in accordance with the invention; and Figure 2 is a sectional view of another embodiment of rotary motion drive in accordance with the invention.

Detailed description of the drawings Referring to the drawings, Figure 1 illustrates a rotary motion drive for transmitting a rotary motion from ambient atmospheric conditions into a vacuum chamber. The illustrated drive comprises a tubular housing 10 of generally stepped configuration, comprising an outer, larger diameter portion 1 2 and an inner, smaller diameter portion 1 4. An outwardly extending annular flange 1 8 is located at the junction between portions 1 2 and 1 4.

An end cap 20 is located at the free end of the housing portion 12. Cap 20 comprises an end disc with an outer, cylindrical flange portion 22 extending around the adjacent end of housing portion 12, and an attached cylindrical portion 24 extending axially within housing portion 1 2. Cap 20 is mounted for rotation relative to the housing 10 via bearings 26 and 28 located between portion 24 and housing portion 1 2. A locking screw 30 extends outwardly from the end cap, for locking the drive against rotary motion.

A drive tube 32 is mounted in an eccentric recess 34 in cylindrical portion 24, the tube having a closed outer end 36 and an open inner end 38. The tube 32 is mounted for rotation relative to the cap 20 via bearings 40 and 42.

A first drive shaft 44 extends axially through tube 32, mounted in bearings 46 and 48 to permit relative rotation between the shaft 44 and tube 32.

The inner end of drive shaft 44 is eccentrically mounted relative to a second drive shaft 50 via a rigid eccentric link 52, the two drive shafts and eccentric link being integrally formed and constituted by a single component in this embodiment. The second drive shaft 50 extends axially through housing portion 14, supported via bearings 54 and 56, the housing portion acting as a support tube. The second drive shaft is also axially located with respect to housing portion 1 2 and end cap 20.

An adjuster 57 is provided adjacent to the end of drive shaft 50 for location adjustment.

The adjuster is appropriately adjusted prior to use to prevent axial movement of the drive shaft 50 in use.

A bellows seal 58 is sealed at one end to a flange 60 extending rearwardly from the outer end of housing portion 14, the other end of the bellows seal being secured to the inner end of drive tube 32. The bellows seal 58 acts to prevent leakage of gas, generally air, from the surrounding atmosphere into the vacuum chamber during use, conditions of vacuum existing within the bellows seal as a result of leakage past bearings such as bearings 54, with conditions of atmospheric pressure existing surrounding the bellows seal as a result of leakage past bearings including bearings 26, 28, 40 and 42.

End cap 20 is made of aluminium alloy, with all other components being of stainless steel.

In use, housing is is secured to an aperture in the wall of a vacuum chamber, with portion 14 extending into the chamber and portion 1 2 located on the outside, and with flange 1 8 abutting the chamber wall surrounding the aperture. The housing is sealed and secured in position, for example with a copper ring seal (not shown) located between the flange 18 and wall.

On rotation of end cap 20, tube 32 moves therewith, but because the drive tube is not fixed in rotation to the end cap and because of the constraining effect of the bellows seal 58, the drive tube "slips" or "floats" relative to the end cap and describes a circular path while remaining in the same orientation. The first drive shaft 44 moves with the drive tube, but because the first drive shaft is not fixed in rotation to the drive tube and because of the constraining effect of the rigid eccentric link 52 with the second drive shaft 50, the first drive shaft "slips" or "floats" relative to the drive tube and moves as if fixed in rotation with respect to the end cap 20. This movement causes rotation of the second drive shaft 50 via the eccentric link 52.

The bellows seal 58 where sealed to the drive tube 32 describe a similar circular path while remaining in the same orientation, with the bellows where sealed relative to the housing interior remaining stationary. The bellows can deform to accommodate such movement, while preventing leakage of gas.

In the illustrated embodiment, the housing and end cap together have an overall length of approximately 1 70mm, with portion 14 up to flange 1 8 being approximately 54mm long and having an external diameter of approximately 25mm. Portion 12 and end cap 20 are together about 1 03mm long, with the internal diameter of the housing portion being approximately 38mm.

Figure 2 illustrates a further embodiment of rotary motion drive for use with a vacuum chamber, which is generally similar to the Figure 1 embodiment and like components are indicated by like reference numerals. However, the Figure 2 embodiment additionally includes a push rod 70 passing axially through the housing 10 and arranged for axial movement. The first and second drive shafts 44 and 50 are of hollow, tubular configuration to permit the push rod to pass therethrough.

A micrometer of conventional construction is mounted in end cap 20, with the micrometer spindle 74 linked to the rear end of push rod 70 via assembly 76. Assembly 76 includes a stub shaft 78 and bearing 80 mounted in a support 82 and is arranged to transmit axial movement of the spindle 74 to rod 70 without transmitting rotation. Assembly 76 also permits rotation of end cap 20 without causing rotation of the push rod 70.

A locking ring 72 is provided for locking the micrometer and hence rod 70 against linear motion.

A further stainless steel bellows seal 84 is provided, with one end sealed relative to the drive tube 32 and the other end sealed relative to the support 82 of assembly 76. Bellows seal 84 isolates the conditions of vacuum prevailing inside the bellows from atmospheric conditions existing outside.

The push rod 70 extends the full length of the first and second drive shafts 44 and 50, being supported in the latter via bushes 86 and 88.

In use, rotation of the second drive shaft 50 is caused in exactly the same way as with the Figure 1 embodiment. On such rotation push rod 70 remains stationary due to bushes 86 and 88. Push rod 70 can be independently moved in an axial direction by use of micrometer 72. The push rod has a maximum axial travel of 25mm and is movable between a fully retracted position as illustrated in which it protrudes by about 1 2mm from the end of the second drive shaft 50 and a fully extended position in it which protrudes by a further 25mm, i.e. by about 37mm. The push rod 70 may be positively withdrawn by reverse rotation of micrometer 72.

This embodiment is approximately 250mm long measured between the front of flange 1 8 and the rear of micrometer 72.

The illustrated rotary motion drives may be used for high precision manipulation of specimens in vacuum chambers, for example for use in surface physics and chemical applications. The illustrated embodiments are suitable for use with vacuum chambers at pressures down to about 10 -12 m.bar. Such low pressures require baking of the vacuum chamber to a temperature of about 250"C, but higher pressures, say down to about 10-8 m.bar, can be readily obtained without baking of the chamber.

The illustrated drives can also be used in conjunction with environmental chambers, for example for manipulation of radioactive specimens, and also with pressure vessels. In the latter case the bellows seal or seals must be arranged to withstand a pressure differential in the appropriate sense.

Claims

1. A rotary motion drive comprising: a housing sealably securable to an aperture in a barrier; an end cap rotatably mounted on the housing and accessible, in use, from one side of the barrier; a drive tube eccentrically mounted with respect to the end cap; a first drive shaft extending axially through the drive tube, the drive tube and/or first drive shaft being mounted for relative rotation with respect to the end cap; a second, final, drive shaft extending axially relative to the end cap and terminating, in use, on the other side of the barrier, the first and second drive shafts being linked by an eccentric mounting arrangement for producing rotation of the second drive shaft on circular movement of the first drive shaft; and a bellows seal sealed relative to the housing and also relative to a component mounted for relative rotation with respect to the end cap.

2. A drive according to claim 1, wherein the drive tube is mounted for rotation relative to the end cap and the drive shaft is mounted for rotation relative to the drive tube, with the bellows seal being sealed relative to the drive tube.

3. A drive according to claim 2, wherein the eccentric link between the first and second drive shafts is rigid.

4. A drive according to claim 1, wherein the drive tube is fixed in rotation to the end cap, the first drive shaft is mounted for relative rotation with respect to the drive tube, and the eccentric link is arranged to permit relative rotation between the first and second drive shafts, with the bellows seal being sealed relative to the first drive shaft.

5. A drive according to any one of the preceding claims, wherein the housing is of generally tubular configuration.

6. A drive according to claim 5, whrein the housing includes a narrower portion comprising a support tube for the second drive shaft and a wider portion for the remaining components.

7. A drive according to claim 6, wherein a shoulder region between the narrower and wider portions is extended outwardly to form an annular flange.

8. A drive according to claim 7, wherein the shoulder and/or flange carries sealing means.

9. A drive according to any one of claims 6 to 8, wherein the end cap is cup-shaped, extending over the end of the wider portion of the tubular housing.

1 0. A drive according to any one of the preceding claims, wherein bearings are provided between relatively rotatable components.

11. A drive according to any one of the preceding claims, wherein one end of the bellows seal is sealed to an annular flange extending inwardly from the housing, with the other end sealed to the first drive shaft or drive tube, as appropriate.

1 2. A drive according to any one of the preceding claims, wherein the housing, drive tube, drive shafts, bellows and bearings are of stainless steel, with the end cap being of aluminium alloy.

1 3. A drive according to any one of the preceding claims, wherein the first and second drive shafts are generally solid.

14. A drive according to any one of claims 1 to 12, wherein the first and second drive shafts are of tubular configuration with a push rod extending therethrough for axial movement, a further bellows seal being sealed relative to the push rod and also being sealed relative to the component to which first bellows seal is sealed.

15. A drive according to claim 14, wherein the end of the push rod adjacent the end cap is linked to an arrangement for causing axial movement.

1 6. A drive according to claim 1 5, wherein a micrometer is linked to the push rod via an arrangement for transmitting axial movement without rotation.

1 7. A rotary motion drive substantially as herein described with reference to, and as shown in, Figure 1 of the accompanying drawings.

1 8. A rotary motion drive substantially as herein described with reference to, and as shown in, Figure 2 of the accompanying drawings.

1 9. A barrier with the housing of a rotary motion drive in accordance with any one of the preceding claims sealingly secured to an aperture in the barrier.

20. A vacuum chamber with the housing of a rotary motion drive in accordance with any one of claims 1 to 1 8 sealingly secured to an aperture in the a thereof.