SCROLL PUMP AND SCROLL PUMP ANTI-ROTATION DEVICE

Abstract

A scroll pump anti-rotation device for resisting relative rotational movement between two scrolls and a scroll pump comprising such a device is disclosed. The anti-rotation device comprises: an elongate member forming an inner ring; an elongate member forming an outer ring surrounding the inner ring; a plurality of connecting members extending between adjacent elongate members; and at least one fixing point for fixing the outer ring to the scroll pump in a fixed relation to one of the scrolls and at least one further fixing point for fixing the inner ring to the scroll pump in a fixed relation to the other of the scrolls.

Claims

1. A scroll pump anti-rotation device configured to resist relative rotational movement between two scrolls, the anti-rotation device comprising: a first elongate member forming an inner ring; a second elongate member forming an outer ring surrounding the inner ring; a plurality of connecting members extending between adjacent first and second elongate members; and at least one fixing point configured to fix the outer ring to the scroll pump in a fixed relation to one of the two scrolls and at least one further fixing point for fixing the inner ring to the scroll pump in a fixed relation to the other of the two scrolls.

2. The scroll pump anti-rotation device according to claim 1, further comprising at least one further elongate member extending around the inner ring and located between the inner and outer rings.

3. The scroll pump anti-rotation device according to claim 1, further comprising a plurality of further elongate members each extending around the inner ring and located at different positions between the inner and outer rings.

4. The scroll pump anti-rotation device according to claim 1, wherein at least one of the first or second elongate members has a circular ring form.

5. The scroll pump anti-rotation device according to claim 1, wherein at least one of the first or second elongate members has a polygonal ring form.

6. The scroll pump anti-rotation device according to claim 5, wherein the polygonal ring form comprises a ring with curved arcs between angles of the polygon ring form.

7. The scroll pump anti-rotation device according to claim 5, wherein the polygonal ring form comprises a ring with straight edges between angles of the polygon ring form.

8. The scroll pump anti-rotation device according claim 5, wherein the first and second elongate members comprise rings of a same polygonal shape.

9. The scroll pump anti-rotation device according to claim 5, wherein the plurality of connecting members join to the first and second elongate members at nodes.

10. The scroll pump anti-rotation device according to claim 9, wherein the nodes are located on the elongate members at the angles of the polygon ring form.

11. The scroll pump according to claim 9, wherein the first and second elongate members are configured between the nodes to deform under a radial force and to resist a tangential force.

12. The scroll pump according to claim 9, wherein the plurality of connecting members at adjacent nodes are angled alternately by obtuse and acute angles with respect to the first or second elongate member from which the plurality of connecting members extend.

13. The scroll pump anti-rotation device according to claim 1, wherein the plurality of connecting members are radially extending connecting members and connecting members extending from adjacent elongate members are offset with respect to each other on any radius.

14. The scroll pump anti-rotation device according to claim 1, wherein the first and second elongate members when not under stress comprise concentric rings.

15. The scroll pump anti-rotation device according to claim 1, comprising six or fewer connecting members connecting the first and second elongate members.

16. The scroll pump anti-rotation device according to claim 15, comprising four or fewer connecting members connecting the first and second elongate members.

17. The scroll pump anti-rotation device according to claim 15, the scroll pump anti-rotation device having a planar disk form.

18. The scroll pump anti-rotation device according to claim 15, wherein the scroll pump anti-rotation device is formed of plastic.

19. The scroll pump anti-rotation device according to claim 15, comprising an outer support ring, the outer support ring being thicker and less flexible than the elongate members, and comprising at least one of the fixing points.

20. The scroll pump anti-rotation device according to claim 15, comprising an inner portion, an intermediate portion and the outer ring, the inner portion being formed of at least one member and the intermediate portion being formed of a plurality of elongate and connecting members, the plurality of elongate and connecting members being narrower and more flexible than the at least one member of the inner portion.

21. The scroll pump anti-rotation device according to claim 20, wherein the inner portion comprises a circular disk.

22. The scroll pump anti-rotation device according to claim 20, wherein the inner portion comprises a plurality of radially extending members.

23. A scroll pump comprising: a pump housing; an orbiting scroll; and a fixed scroll; a central drive shaft having an eccentric shaft portion connected to the orbiting scroll for driving the orbiting scroll in an orbiting motion relative to the fixed scroll; and the anti-rotation device according to claim 1 connected in a fixed relation to the fixed and orbiting scrolls for resisting rotation of the orbiting scroll while allowing the orbiting motion.

24. A scroll pump comprising: a pump housing; two rotating scrolls mounted on offset parallel axes; a drive shaft for driving one of the two rotating scrolls; and the anti-rotation device according to claim 1 connected in a fixed relation to the one of the two rotating scrolls and to the other of the two rotating scrolls, such that the two scrolls rotate in synchronization with each other.

25. The scroll pump according to claim 24, wherein the anti-rotation device is operable to transmit torque from the one scroll to the other scroll and to resist relative angular rotation of the two scrolls.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0045] Embodiments of the present disclosure will now be described further, with reference to the accompanying drawings.

[0046] FIGS. 1 to 3 illustrate different examples of anti-rotation devices according to different embodiments.

[0047] FIG. 4 shows a scroll pump comprising an anti-rotation device according to an embodiment.

DETAILED DESCRIPTION

[0048] Before discussing the embodiments in any more detail, first an overview will be provided.

[0049] An anti-rotation device for a scroll pump is provided having elongate members in the form of bands which loop round such that the band comprises two opposing continuous surfaces and two edge surfaces connecting the two opposing surfaces. In use, the elongate members are arranged around the centre of rotation of the scroll(s) and any rotational forces between the scrolls, or at least the major component of these rotational forces act along the material forming the elongate members and thus, act as compression or tension forces on the material, which forces can thereby be effectively resisted by the material. Radial forces due to translational movement of one of the scrolls relative to the other act in a perpendicular direction to the material of the elongate member, or at least a major component of such forces do. Resistance to these forces is low compared to the resistance to the rotational forces, as the forces do not act along the material and the elongate material is able to move and flex in response to these forces.

[0050] In this way a device operating on similar principles to the device of WO2011/135324 is provided which in some embodiments has a plurality of elongate members to share the loads, thereby increasing robustness. Furthermore, the device does not require the same rigid framework required in WO2011/135324 to support the flexible elongate members, thus, the device can be lighter, and therefore easier to balance. In this regard, as the rigid framework reciprocates rather than following an orbit it does not have a spinning weight counterbalance.

[0051] There are a number of different designs for such an anti-rotation device, FIGS. 1 to 3, providing just three examples. The important principle is that several generally annular concentric rings (which may be circular, may be polygonal, or may be a combination of both) are connected by staggered radial or angled spokes.

[0052] Torque is transmitted from the inner hub to the outer rim through tension in the annular parts, and the radial parts (being in some embodiments only short sections between adjacent annular parts) resist bending. Therefore, the angular displacement per unit torque is low. Under radial force, the longer annular parts are subject to bending forces, and the shorter radial elements are in tension or compression. The design is flexible allowing linear displacement of the inner and outer elongate members in the plane of the device.

[0053] The underlying principle is that elongated features are stiff when pulled but are easy to bend, to provide torsional stiffness but lateral compliance.

[0054] Such a device thereby provides an effective anti-rotation device. This device may be used to provide stability and control of the radial clearances between scrolls of a scroll pump with fixed and orbiting scrolls. It may also be used in scroll pumps where both scrolls rotate about offset axes as a torque transmission device. In such a case, one of the scrolls may be mounted on a drive shaft and the other may mounted to rotate about a shaft that is not driven. Driving of the non-driven scroll may be provided via the anti-rotation device which acts to transmit torque from one scroll to the other. The properties of high resistance to relative rotational movement but low resistance to relative orbital motion makes this device particularly effective in this role. Furthermore, it is a more cost effective solution that requires less maintenance than the alternative solution of providing gears to drive the second shaft, or providing two drive motors.

[0055] FIG. 1 shows an example of an anti-rotation device 10 according to an embodiment. The anti-rotation device 10 comprises an outer support ring 11, which comprises fixing points (not shown) to fix the device to one of the scrolls. The fixing points may comprise apertures through which a bolt may be mounted, or they may comprise some other means which may be used in association with other attaching means to attach the outer support ring and thereby the outer elongate member 12 of the anti-rotation device to one of the scrolls.

[0056] Outer elongate member 12 has a ring form arranged around the centre of rotation 9. It is attached to the outer support ring 11 at four points, and is connected to an inner elongate member 18, via four connecting members 19. The connecting members 19 meet the elongate members 12, 18 at nodes 15. In this embodiment the connecting members 19 are angled such that a line perpendicular to a radius of the device, the radius passing through the centre of rotation 9, bisects the angle between the elongate member and connecting member.

[0057] In this embodiment the inner elongate member, is formed of elongate portions and a section of the inner portion 13 of the anti-rotation device 10. This inner portion 13 comprises fixing points 17 in the form of holes for receiving bolts to attach the anti-rotation device to the other of the scrolls. In this way the outer elongate member 12 is fixed via the outer support ring 11 to one of the scrolls and the inner elongate member 18 is fixed via the inner portion 13 to the other of the scrolls when mounted on the scroll pump. Thus, relative movement of the scrolls will be transmitted through the inner and outer elongate members of the anti-rotation device, and its configuration is such that relative rotational forces which will act substantially along the elongate members and will be resisted, while translational forces acting substantially at right angles to the elongate members will experience a much lower resistance.

[0058] FIG. 2 shows an alternative embodiment, wherein the inner portion 13 comprises an inner support ring, concentric to the outer support ring 11. In this embodiment there are three elongate members, 12, 14 and 18 and these are joined via connecting members 19, which extend from the elongate members at nodes 15. The elongate members form concentric hexagonal polygons with straight sides between nodes 15. There are six connecting members angled such that a tangent to a circle around the centre of rotation bisects the angle between connecting members and elongate members. At alternate nodes, the connecting members extend in opposite directions. In this way a device is provided where the inner ring 13 can move within the outer ring 11 by flexing of the elongate members, but cannot rotate with respect to it.

[0059] FIG. 3 shows a further embodiment, comprising inner and outer support rings, 13, 11 between which eight concentric rings forming eight elongate members are located. Each elongate member is connected to at least one adjacent elongate member and the inner and outer elongate members are connected to the inner and outer support rings, via five radial spokes. The radial spokes extending from adjacent elongate members are offset with respect to each other. In this way radial motion of the inner ring with respect to the outer ring is allowed as there is no continuous radial spoke, while relative rotational motion is resisted.

[0060] FIG. 4 schematically shows a scroll pump 20 according to an embodiment, comprising anti-rotation device 10 mounted with the inner elongate member connected to orbiting scroll 31 and the outer elongate member connected to fixed scroll 30.

[0061] It would be clear to a skilled person that this is simply an example embodiment and the inner elongate member could be connected to the fixed scroll and the outer elongate members to the orbiting scroll. Furthermore, in a further embodiment, the scroll pump may comprise two rotating scrolls with offset axes and in such a case the anti-rotation device would be mounted in a similar manner to the above, but with the inner and outer elongate members being fixed to respective ones of the two rotating scrolls. In each case forces due to relative motion of the two scrolls are transmitted from the inner to outer elongate members of the anti-rotation device via intermediate elongate and connecting members.

[0062] Scroll pump 20 comprises a pump housing 22 and a drive shaft 24 having an eccentric cam 26. The drive shaft 24 is driven by a motor 40 and the eccentric cam 26 is connected to an orbiting scroll 31 so that during use rotation of the drive shaft imparts an orbiting motion to the orbiting scroll relative to a fixed scroll 30. The orbiting motion pumps fluid along a fluid flow path between a pump inlet 25 and pump outlet 27. The fixed scroll 30 is shown generally on the left and the orbiting scroll 31 is shown generally on the right in FIG. 4.

[0063] In this arrangement, the fixed scroll comprises an opening through which the shaft 24 extends. The shaft is connected to the orbiting scroll 31 on an opposing side of the fixed scroll to the motor 40. A high vacuum region is located at the inlet 25 and a low vacuum, or atmospheric, region is located at the outlet 27.

[0064] A counter-weight 28 balances the weight of the orbiting components of the pump, including the orbiting scroll 31, and the eccentric portion of the drive shaft. The orbiting scroll 31 constitutes the majority of the weight of the orbiting components and its centre of mass is located relatively close to the scroll plate of the orbiting scroll.

[0065] An anti-rotation device 10 according to an embodiment, such as is shown in FIGS. 1 to 3, is located in the high vacuum region of the pump and in this embodiment, the inner portion is connected to the orbiting scroll 31 via bolts 42 which pass through holes on the inner portion of the anti-rotation device. The outer support ring is connected to the pump housing 22, which is in a fixed relation to the fixed scroll. Thus, the outer support ring and the fixed scroll stay fixed together while the inner portion moves with the orbiting scroll. The anti-rotation device 10 provides high resistance to relative rotational movement between the two scrolls and significantly lower resistance to the orbiting motion.

[0066] The anti-rotation device is lubricant free and in this example is made from a plastics material, and may be a one-piece polymer component.

[0067] Although illustrative embodiments of the disclosure have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the disclosure 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 disclosure as defined by the appended claims and their equivalents.