SCROLL PUMP, ANTI-ROTATION DEVICE FOR A SCROLL PUMP AND METHOD OF REDUCING VIBRATIONS IN A SCROLL PUMP

Abstract

 A scroll pump (10), anti-rotation device and method are disclosed. The scroll pump has: a motor (18); two interleaving scrolls (22, 20) mounted such that rotation of the motor imparts an orbital motion to one scroll with respect to the other; and an anti-rotation device (50) mounted to at least one of the two scrolls and configured to impede relative rotational movement between the two scrolls, the anti-rotation device comprising a body portion (53) configured to move in a substantially linearly reciprocating motion in response to the relative orbiting motion of the scrolls. The scroll pump comprises at least one counterweight (46) mounted such that movement of the at least one counterweight is constrained to a same substantially linear direction as the reciprocating motion of the body portion of the anti-rotation device and configured such the at least one counterweight (46) moves in a reciprocating motion that is out of phase with, and at least partially compensates for, movement of the body portion (53) in response to rotation of the rotor.

Description

FIELD OF THE INVENTION

[0001] The field of the invention relates to scroll pumps and to scroll pump anti-rotation devices.

BACKGROUND

[0002] A scroll pump comprises two interleaving scrolls one of which has an orbital motion with respect to the other thereby trapping and pumping or compressing pockets of fluid between the scrolls. In some cases, one of the scrolls is fixed, while the other is mounted on a drive shaft with an eccentric cam such that it orbits eccentrically without rotating. Another method for producing the relative orbiting motion is by co-rotating the scrolls, in synchronous motion, but with offset axes of rotation. Thus, the two scrolls are mounted on parallel shafts and the relative motion is the same as if one were orbiting and the other stationary.

[0003] In the case of fixed and orbiting scrolls an anti-rotation device may be used connected to the scrolls to resist relative rotation between them and thereby allowing the radial clearances to be accurately maintained as the scrolls pump. The anti-rotation device should resist rotational movement but also allow the relative orbiting motion required for the pumping. In the case of co-rotating scrolls, such a device can be used to transmit a drive force from one scroll to the other, in a similar way to a pair of gears or a drive belt and pulleys.

[0004] A bellows arrangement formed from a crimped pipe has been used as an anti-rotation device in a fixed and orbiting scroll pump. This arrangement is located on the orbiting scroll side of the pump and resists rotation of the orbiting scroll but is sufficiently flexible to allow the orbiting motion.

[0005] A drawback of such a device is that the bellows need to be quite long to limit stress in the bellows below fatigue limits, and thus, pumps with bellows are physically quite big for their displacement. An alternative more compact anti-rotation arrangement is disclosed in WO2011/135324. The anti-rotation device here comprises a body portion from which two perpendicular pairs of arms extend, a first pair being connected in a fixed relation to the fixed scroll and a second pair in a fixed relation to the orbiting scroll, the first pair flexing to allow movement of the orbiting scroll relative to the fixed scroll in a first direction and the second pair flexing to allow movement of the orbiting scroll in a second orthogonal direction. This provides a more compact arrangement than the bellows, however the flexing arrangement provides an unbalanced mass associated with the movement of the body portion of the anti-rotation devices which introduces vibration to the pump.

[0006] It would be desirable to provide a scroll pump with a scroll pump anti-rotation device where the unbalanced mass is compensated for to at least some extent.

SUMMARY

[0007] One aspect provides a scroll pump comprising: a motor; two interleaving scrolls mounted such that rotation of said motor imparts an orbital motion to one scroll with respect to the other; an anti-rotation device mounted to at least one of said two scrolls and configured to impede relative rotational movement between said two scrolls, said anti-rotation device comprising a body portion configured to move in a substantially linearly reciprocating motion in response to the relative orbiting motion of the scrolls; wherein said scroll pump comprises at least one counterweight mounted such that movement of said at least one counterweight is constrained to a same substantially linear direction as said reciprocating motion of said body portion of said anti-rotation device and configured such said at least one counterweight moves in a reciprocating motion that is out of phase with, and at least partially compensates for, movement of said body portion in response to rotation of said motor.

[0008] It was recognised that where an anti-rotation device is formed such that the orbiting motion of the pump causes a substantially linearly reciprocating movement of the body portion of the anti-rotation device as the pump motor rotates, then this will provide an unbalanced mass within the pump that will lead to vibrations. It was also recognised that this unbalanced mass could be compensated for and the vibrations reduced with the use of a counterweight were that counterweight to be constrained to also move in a substantially linear direction in response to rotation of the motor. In particular, if it could be configured to reciprocate in a similar way to the body portion but out of phase with it, then it could at least partially compensate for the body portion movement and vibrations would be reduced.

[0009] The directional movement of the counterweight may be constrained in a number of ways, and in some embodiments, the scroll pump comprises at least one linear guide for constraining movement of said at least one counterweight in said substantially linear direction.

[0010] The linear guide may take a number of forms, in some embodiments, said at least one linear guide comprises at least one rod on which is mounted said at least one counterweight

[0011] In other embodiments, said at least one linear guide comprises at least one set of guide rails.

[0012] In some embodiments, said scroll pump comprises a protrusion mounted to execute circular motion on rotation of said motor; and said at least one counterweight comprises a linear cavity, said at least one counterweight being mounted such that said protrusion extends into said linear cavity, said protrusion being configured to move along said linear cavity as said protrusion performs said circular motion, said counterweight moving in said linear direction perpendicular to said linear cavity in response to said protrusion performing said circular motion.

[0013] One way in which the circular motion generated by rotation of the motor may be translated into linear motion may be by the use of a protrusion on a rotating part of the pump that extends into a linear elongate cavity on a counterweight, such that the rotating motion of the protrusion drives the counterweight in a linearly reciprocating movement. The rotating part on which the protrusion is mounted may be any part that rotates with the motor such as the rotating counterbalance. The linear elongate cavity may be a groove or an aperture within the counterweight. The cavity allows movement of the protrusion in one direction along the length cavity as the protrusion executes circular motion, but resists movement in the direction perpendicular to the length of the cavity. In this way rotation of the protrusion will move the counterweight in a linear reciprocating manner in a direction that is perpendicular to the length of the cavity. By suitable arrangement of the counterweight and cavity with respect to the protrusion, the counterweight may move in an opposite direction to the body portion of the anti-rotation device, that is 180° out of phase with it and thereby at least partially compensate for the imbalance that movement of this body portion would otherwise produce.

[0014] In other embodiments, said at least one counterweight is mounted via a resilient means to said body portion of said anti-rotation device, a stiffness of said resilient means and a weight of said at least one counterweight being selected to provide said out of phase reciprocal motion.

[0015] An alternative way of generating the out of phase linear motion of the counterweight is to mount it to the body portion via a resilient means. By appropriate selection of the mass and stiffness of the resilient means, the natural frequency of the reciprocal motion of the counterweight that is triggered by the reciprocating motion of the body portion can be selected to be such that the counterweight movement is out of phase with, but at substantially the same frequency as, the reciprocal motion of the body, thereby allowing it to compensate for the motion of the body.

[0016] In some embodiments, said body portion comprises said at least one linear guide, said at least one linear guide being symmetrical about an axis through a centre of said scrolls in a direction of said linear guide and said at least one counterweight being mounted on said body portion for movement along said at least one linear guide.

[0017] In order for the counterweight not to generate its own imbalance it is desirable if it is mounted symmetrically to an axis running in the linear direction of the reciprocating motion through a central axis of rotation of the pump. For example, where the body portion is a frame and there is one counterweight, the counterweight should be mounted towards the centre of one strut of the frame that is perpendicular to the direction of linear reciprocating movement, while where there are two counterweights they may be mounted on the strut symmetrically about this central axis. In some embodiments there are two linear guides and two counterweights mounted on said body portion
In some embodiments, said anti-rotation device comprises said body portion and two pairs of opposing arms extending from said body portion, a first pair being connected in a fixed relation to one of said two scrolls and a second pair being connected in a fixed relation to the other of said two scrolls, said first and second pair being configured to flex to allow movement in two generally orthogonal directions.

[0018] The arms of the anti-rotation device may comprise elongate members, that are configured to flex in a direction perpendicular to their length and resist movement along their length. In some embodiments the pairs of arms are arranged on opposite sides of a body portion, arms within a pair being substantially parallel to each other, and arms of the different pairs being substantially perpendicular to each other. One pair allows movement of the orbiting scroll relative to the housing in a first direction and the other pair allows movement of the orbiting scroll relative to the housing in a second direction generally orthogonal to the first direction.

[0019] In some embodiments, said scrolls comprise a fixed scroll and an orbiting scroll, said pair of arms attached in a fixed relation to said fixed scroll being configured to flex and allow movement in said substantially linear direction, said body portion following said movement in said substantially linear direction.

[0020] As the orbiting scroll orbits the arms attached to orbiting scroll flex in one direction but resist movement in a direction perpendicular to this, so the body portion does not follow the movement of the orbiting scroll in the linear direction that the arms attached to the orbiting scroll flex in, but does follow it in the perpendicular direction to this, which is the direction that the other arms flex in.

[0021] In some embodiments the at least one counterweight has substantially the same mass as the portion of the anti-rotation device that performs the reciprocating motion. In order to provide effective compensation, the masses of the bodies reciprocating in different directions should be similar to each other, preferable within 25% of each other.

[0022] A further aspect provides a method of reducing vibrations of a scroll pump comprising an anti-rotation device configured to impede relative rotational movement between two scrolls of said scroll pump, said anti-rotation device comprising a body portion configured to move in a substantially linearly reciprocating motion in response to the relative orbiting motion of the scrolls; said method comprising mounting at least one counterweight to said scroll pump such that movement of said at least one counterweight is constrained to a same substantially linear direction as said body portion of said anti-rotation device, said at least one counterweight being configured such that said at least one counterweight moves in a reciprocating motion that is out of phase with, and at least partially compensates for, movement of said body portion.

[0023] A scroll pump with an unbalanced anti-rotation device can have the lack of balance due to this anti-rotation device corrected for by the mounting of a counterweight on the pump that is constrained to move linearly and is configured to move in a reciprocating motion that is out of phase with, and at least partially compensates for, movement of the body portion in response to rotation of the motor.

[0024] In some embodiments said scroll pump comprises a vacuum pump.

[0025] A yet further aspect provides a scroll pump anti-rotation device for resisting relative rotational movement between two scrolls, said anti-rotation device comprising: a body portion; two pairs of opposing arms extending from said body portion, said two pairs of arms comprising fixing points for fixing to said scroll pump, a first pair being configured to be fixed to said scroll pump in a fixed relation to one of said scrolls and a second pair being configured to be fixed to said scroll pump in a fixed relation to the other of said scrolls; wherein said first pair are configured to flex to allow relative movement of one of said two scrolls to the other of said two scrolls in a first direction and said second pair are configured to flex to allow relative movement of said one of said two scrolls to the other in a second direction substantially orthogonal to said first direction; wherein said anti-rotation device comprises at least one linear guide extending substantially parallel to said first direction and at least one counterweight mounted via resilient means to said body portion and constrained by said linear guide such that any movement of said counterweight is in a direction substantially parallel to said first direction.

[0026] In some embodiments, said body portion comprises a frame type arrangement comprising struts, at least one strut extending substantially parallel to said first pair of arms and comprising said at least one linear guide extending substantially perpendicularly to said at least one strut, said at least one counterweight being mounted via said resilient means to said at least one strut and constrained by said at least one guide linear guide such that any movement of said at least one counterweight is in a direction substantially perpendicularly to said strut.

[0027] In some embodiments, said at least one linear guide comprises at least one rod on which is mounted said at least one counterweight.

[0028] In some embodiments, said at least one linear guide comprises at least one set of guide rails.

[0029] 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.

[0030] 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

[0031] Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

Figure 1 shows a scroll pump having an anti-rotation device according to an embodiment;

Figure 2 shows the counter weight for compensating for the unbalanced mass of the anti-rotation device according to an embodiment;

Figure 3 shows the anti-rotation device according to a further embodiment;

Figure 4 shows the anti-rotation device according to yet a further embodiment; and

Figure 5 shows a flow diagram illustrating steps in a method of reducing vibrations in a scroll pump according to an embodiment.

DESCRIPTION OF THE EMBODIMENTS

[0032] Before discussing the embodiments in any more detail, first an overview will be provided.

[0033] Embodiments relate to a counterweight to at least partially compensate for the linear reciprocal motion of an anti-rotation device within a scroll pump.

[0034] In some embodiments the scroll pump has one fixed (stationary) scroll and its counterpart the so-called orbital scroll which can move in a plane so that there are 3 degrees of freedom (DoF). The rotational degree of freedom is removed by the anti-rotation device so two translational DoF remain, which is how the orbiting movement of the orbital or orbiting scroll is achieved. In some embodiments the anti-rotation device comprises a frog having a pair of outer legs or arms which are connected to the fixed scroll and another pair of legs or arms (inner legs) which connects the frog to the orbiting scroll and the frame which represents the rigid part of the frog. The frame is the heaviest part of the frog and because of the frog's design moves linearly. Oscillation of the frame in a linear direction cannot be reduced or cancelled by rotating forces and thus, a counterweight constrained to move linearly can, if it has a similar inertia force and an opposite phase, be used to compensate for this movement.

[0035] The premise is to reduce non-rotating force present within the pump and thus reduces the vibration.

[0036] Figure 1 shows a scroll pump 10 according to an embodiment. Scroll pump 10 comprises a pump housing 12 from which the fixed scroll 22 extends and which has a cap portion 18. Scroll pump 10 has a drive shaft 14 driven by a motor 18 and having an eccentric shaft portion 16 which may be in the form of a cam sleeve. The drive shaft 14 is and the eccentric shaft portion 16 are connected to an orbiting scroll 20 so that rotation of the shaft imparts an orbiting motion to the orbiting scroll 20 relative to the fixed scroll 22 for pumping fluid along a fluid flow path between a pump inlet 24 and a pump outlet 26. The fixed scroll is shown generally on the left and the orbiting scroll on the right.

[0037] In this arrangement the fixed scroll comprises an opening through which the shaft 14, 16 extends. The shaft is connected to the orbiting scroll 20 on an opposing side of the fixed scroll to the motor 18. A high vacuum region 30 is located at the inlet 24 and a low vacuum or atmospheric region is located adjacent to the outlet 26. A first bearing 34 supports a concentric portion of the drive shaft for rotation. A second bearing 36 supports the eccentric portion 16 of the drive shaft relative to the orbiting scroll 20 allowing angular movement of the orbiting scroll relative to the eccentric portion.

[0038] A counterbalance 44 balances the weight of the orbiting components of the pump including the orbiting scroll, the second bearing 36 and the eccentric portion of the drive shaft. An anti-rotation device 50 in the form of a "frog" is located in the high vacuum region 30 of the pump. The anti-rotation device 50 comprises arms connected to the orbiting scroll and other arms connected in a fixed relation to the fixed scroll. The anti-rotation device 50 of an embodiment is shown in more detail in Figures 3 and 4 but essentially has a body portion and a plurality of arms extending from the body. The arms are arranged in two opposing pairs, one of the pairs being connected in a fixed relation to the fixed scroll and one of the pairs being connected in a fixed relation to the orbiting scroll. Rotation of the motor causes the orbiting scroll to orbit and the arms connected in a fixed relation to the fixed scroll resist movement in a direction along the length of the arms and allow it in a direction perpendicular to the arms, the arms flexing to move substantially in this direction, such that the body portion of the anti-rotation device moves in a linear reciprocating manner in phase with the rotation of the motor.

[0039] Embodiments provide one or more counterweights mounted to move in a similar linear reciprocating manner to the body portion of the anti-rotation device but out of phase with it, so that the imbalance that might arise due to this movement is reduced. The mounting of the one or more counterweights on the pump may be done in a number of different ways, three examples of which are shown in Figures 2 to 4.

[0040] Figure 2 shows a counterweight 46 configured to compensate for the weight of the body of the anti-rotation device 50. In this embodiment counterweight 46 is mounted on the rotational counterbalance 44, that is configured to compensate for unbalances due to the orbiting components. The counterweight 46 comprises an elongate linear notch 48 that is arranged to extend perpendicularly to the linear motion of the body portion of the anti-rotation device 50 (not shown in Figure 2). A pin 42 from the counterbalance 44 extends into the notch and on rotation of the motor the rotational counterbalance 44 will rotate in the direction denoted by arrow B and the pin 42 extending into the notch 48 on counterweight 46 will drive the counterweight 46 in this arrangement vertically up and down in the direction denoted by arrow A. The horizontal component of the pin's rotational movement will be translated to movement of the pin 42 along notch 48, while the vertical component drives the counterweight 46 in the vertical up and down directions denoted by arrow A. Although in this embodiment the motion of the pin 42 is shown as horizontal and the motion of the counterweight 46 is shown as vertical, these directions may be different depending on the configuration of the pump, however, these two directions of motion will be perpendicular to each other.

[0041] The movement of the counterweight 46 is constrained by linear groove 49 within cap 18 that fits on the end of housing 12. By suitable mounting of the counterweight 46 the linear motion of the counterweight can be set to be out of phase with the linear motion of the body portion of the anti-rotation device 50 and in this way the movement of the body portion of the anti-rotation device 50 can be compensated for and any imbalance and vibrations due to this movement reduced.

[0042] In summary, the counterweight 46 has a specific weight and is arranged at a specific distance from a centre of rotation and has a notch perpendicular to its intended movement and is fitted in a groove forming a linear guide in the cap 18, such that only one DoF remains free. Motion in this remaining direction is driven by the rotation of rotating counterbalance 44. Rotating counterbalance 44 is connected to the counterweight by pin 42, which is inserted into counterweight's notch. The pin forces the counterweight to move in one direction and leaves the second direction free. The mass is selected to create the same force as due to the frog's frame inertia but with opposite phase which results in reducing resulting force and thus vibration.

[0043] Figure 3 shows an alternative embodiment where there are two counterweights 46A and 46B and these are mounted within linear guides 49 on anti-rotation device 50. Although there are two counterweights in this embodiment a different number could be used provided that they are arranged symmetrically about a axis of movement passing through the centre of gravity of said anti-rotation device. Anti-rotation device 50 comprises a body portion 53, outer arms 56 which are mounted to the fixed scroll and inner arms 58 mounted to the orbiting scroll. Rotational movement of the motor causes orbiting motion of the orbiting scroll and arms 56 are resistant to horizonal movement parallel to the arms but flex in a direction perpendicular to their length, vertically in Figure 3. Inner arms 58 connected to the orbiting scroll flex horizontally and thus, follow the horizontal movement of the orbiting scroll but resist vertical movement and the body portion 53 of frog 50 follows the vertical movement of the orbiting scroll that the arms 58 resists.

[0044] The counterweights 46A and 46B are attached to the body portion 53 of frog 50 by springs 60. By suitable choice of resilience of the springs 60 and weights of counterweights 46A and 46B the resonant frequency of the movement of the counterweights 46A, 46B can be selected such that they oscillate at substantially the same frequency as the frequency of rotation of the shaft but out of phase with it and thus in an opposite direction to the movement of the body portion 53. They are mounted such that they are symmetrical about an axis between the arms 58 and thus, do not provide further imbalances to the frog.

[0045] Figure 4 shows an alternative embodiment of frog 50 wherein counterweights 46a and 46b are mounted via resilient members 60 to a strut 53A of frog body 53. The weights are hollow and are mounted on rods 62 in a way that they can slide up and down the rods to provide the reciprocal motion, the rods acting as linear guides. Again the weights of the counterweights 46A and 46B and the resilience of springs 60 are selected such that the movement of the counterweights is out of phase with the movement of the body portion 53 of the anti-rotation device or frog 50 and thereby provides at least some compensation for the reciprocal movement of the body and reduces vibrations. The frog 50 in this embodiment comprises a frame type body 53 comprising struts 53A extending substantially parallel to arms 56 and struts 53B extending substantially parallel to arms 58.

[0046] Figure 5 shows a flow diagram illustrating steps in a method of reducing vibrations in a scroll pump according to an embodiment. In an initial step S10 the scroll pump is provided with a linear guide extending substantially parallel to the arms of the frog that are connected in a fixed relation to the orbiting scroll. This is substantially parallel to the direction of reciprocal motion that the anti-rotation body will move in, on rotation of the motor. One or more counterweights that in total have substantially the same mass as the frame of the frog are then mounted to the scroll pump in step S20 such that their movement is constrained by the linear guide. Rotation of the motor of the scroll pump then causes the frame of the frog to reciprocate in a direction substantially parallel to the arms of the orbiting scroll and the at least one counterweight moves in a similar linear reciprocating manner but out of phase with the frame of the frog.

[0047] Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiment and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.

REFERENCE SIGNS

[0048] 

10

scroll pump

12

housing

14

shaft

16

crank sleeve

18

cap

19

motor

20

oribiting scroll

22

fixed scroll

24

inlet

26

outlet

30

high vacuum region

34, 36

bearings

42

pin

44

rotational counterbalance

46

counterweight

46A, 46B

counterweight

48

notch

49

linear guide

50

frog, anti-rotation device

53

body

53A, 53B

struts

56

arms for connection to fixed scroll

58

arms for connection to orbiting scroll

60

spring

62

rod

Claims

1. A scroll pump comprising:

a motor;

two interleaving scrolls mounted such that rotation of said motor imparts an orbital motion to one scroll with respect to the other;

an anti-rotation device mounted to at least one of said two scrolls and configured to impede relative rotational movement between said two scrolls, said anti-rotation device comprising a body portion configured to move in a substantially linearly reciprocating motion in response to the relative orbiting motion of the scrolls; wherein

said scroll pump comprises at least one counterweight mounted such that movement of said at least one counterweight is constrained to a same substantially linear direction as said reciprocating motion of said body portion of said anti-rotation device and configured such said at least one counterweight moves in a reciprocating motion that is out of phase with, and at least partially compensates for, movement of said body portion in response to rotation of said rotor.

2. A scroll pump according to claim 1, wherein said scroll pump comprises at least one linear guide for constraining movement of said at least one counterweight in said substantially linear direction.

3. A scroll pump according to claim 1 or 2, wherein said at least one linear guide comprises at least one rod on which is mounted said at least one counterweight.

4. A scroll pump according to claim 1 or 2, wherein said at least one linear guide comprises at least one set of guide rails.

5. A scroll pump according to any one of claims 1, 2 or 4, wherein said scroll pump comprises a protrusion mounted to execute circular motion on rotation of said motor; and
said at least one counterweight comprises a linear cavity, said at least one counterweight being mounted such that said protrusion extends into said linear cavity, said protrusion being configured to move along said linear cavity as said protrusion performs said circular motion, said counterweight moving in said linear direction perpendicular to said linear cavity in response to said protrusion performing said circular motion.

6. A scroll pump according to any one of claims 1 to 4, wherein said at least one counterweight is mounted via a resilient means to said body portion of said anti-rotation device, a stiffness of said resilient means and a weight of said at least one counterweight being selected to provide said out of phase reciprocal motion.

7. A scroll pump according to claim 6 when dependent upon any one of claims 2 to 4, wherein said body portion comprises said at least one linear guide, said at least one linear guide being symmetrical about an axis through a centre of said scrolls in a direction of said linear guide and said at least one counterweight is mounted on said body portion for movement along said at least one linear guide.

8. A scroll pump according to claim 7, comprising two linear guides and two counterweights mounted on said body portion.

9. A scroll pump according to any preceding claim, wherein said anti-rotation device comprises said body portion and two pairs of opposing arms extending from said body portion, a first pair being connected in a fixed relation to one of said two scrolls and a second pair being connected in a fixed relation to the other of said scrolls, said first and second pair being configured to flex to allow movement in two generally orthogonal directions.

10. A scroll pump according to claim 9, wherein said scrolls comprise a fixed scroll and an orbiting scroll, said pair of arms attached to said fixed scroll being configured to flex and allow movement in said substantially linear direction, said body portion following said movement in said substantially linear direction.

11. A method of reducing vibrations of a scroll pump comprising an anti-rotation device configured to impede relative rotational movement between two scrolls of said scroll pump, said anti-rotation device comprising a body portion configured to move in a substantially linearly reciprocating motion in response to the relative orbiting motion of the scrolls; said method comprising
mounting at least one counterweight to said scroll pump such that movement of said at least one counterweight is constrained to a same substantially linear direction as said body portion of said anti-rotation device, said at least one counterweight being configured such that said at least one counterweight moves in a reciprocating motion that is out of phase with, and at least partially compensates for, movement of said body portion.

12. A scroll pump anti-rotation device for resisting relative rotational movement between two scrolls, said anti-rotation device comprising:

a body portion;

two pairs of opposing arms extending from said body portion, said two pairs of arms comprising fixing points for fixing to said scroll pump, a first pair being configured to be fixed to said scroll pump in a fixed relation to one of said scrolls and a second pair being configured to be fixed to said scroll pump in a fixed relation to the other of said scrolls; wherein

said first pair are configured to flex to allow relative movement of one of said two scrolls to the other of said two scrolls in a first direction and said second pair are configured to flex to allow relative movement of said one of said two scrolls to the other in a second direction substantially orthogonal to said first direction; wherein

said anti-rotation device comprises at least one linear guide extending substantially parallel to said first direction and at least one counterweight mounted via resilient means to said body portion and constrained by said linear guide such that any movement of said counterweight is in a direction substantially parallel to said first direction.

13. A scroll pump anti-rotation device according to claim 12, wherein
said body portion comprises a frame type arrangement comprising struts, at least one strut extending substantially parallel to said first pair of arms and comprising said at least one linear guide extending substantially perpendicularly to said at least one strut, said at least one counterweight being mounted via said resilient means to said at least one strut and constrained by said at least one guide linear guide such that any movement of said at least one counterweight is in a direction substantially perpendicularly to said strut.

14. A scroll pump anti-rotation device according to claim 12 or 13, wherein said at least one linear guide comprises at least one rod on which is mounted said at least one counterweight.

15. A scroll pump anti-rotation device according to claim 12 or 13, wherein said at least one linear guide comprises at least one set of guide rails.

Drawing