Scroll pump

Abstract

A scroll pump 100, comprising an orbiting scroll 130; a fixed scroll 120; a drive shaft 140 coupled to the orbiting scroll, wherein the drive shaft is movable relative to the fixed scroll in an axial

Description

FIELD OF THE INVENTION The present invention relates to scroll pumps. BACKGROUND Scroll pumps are a known type of pump used in various different industries to pump fluid. Scroll pumps operate by using the relative motion of two intermeshed scrolls (known as a fixed scroll and an orbiting scroll) to pump fluid. Each of the fixed and orbiting scrolls includes a spiral wall extending from a base. In one type of scroll pump, the end of the spiral wall of each of the scrolls is in contact with an axial seal located on the base of the other scroll in order to seal the space used for pumping. SUMMARY OF INVENTION In an aspect of the invention there is provided a scroll pump comprising: an orbiting scroll; a fixed scroll; a drive shaft coupled to the orbiting scroll, wherein the drive shaft is movable relative to the fixed scroll in an axial direction; an annular bearing coupled to the drive shaft for supporting and facilitating rotation of the drive shaft; a biasing mechanism arranged to provide a biasing force on the annular bearing which acts via the annular bearing and the drive shaft to axially bias the orbiting scroll and the fixed scroll together; and a diaphragm attached to the annular bearing to support the annular bearing, wherein the diaphragm is flexible in the axial direction to allow the annular bearing to move in the axial direction, thereby facilitating the movability of the drive shaft relative to the fixed scroll in the axial direction. The diaphragm may be stiff in a radial direction to oppose movement of the annular bearing in the radial direction. The diaphragm may mechanically couple the annular bearing to the fixed scroll. The diaphragm may mechanically couple the annular bearing to a housing portion of the scroll pump. The scroll pump may comprise a first annular bearing and a second annular bearing, wherein both the first and second annular bearings extend around the drive shaft to support and facilitate rotation of the drive shaft. The diaphragm mechanically may couple the first annular bearing to the fixed scroll. The second annular bearing may be mechanically coupled to a housing portion of the scroll pump such that the second annular bearing is able to slide in the axial direction relative to the housing portion, thereby facilitating the movability of the drive shaft relative to the fixed scroll in the axial direction. The diaphragm may mechanically couple the first annular bearing to the fixed scroll. The second annular bearing may be mechanically coupled to a housing portion of the scroll pump by a further diaphragm attached to the second annular bearing to support the second annular bearing, wherein the further diaphragm is flexible in the axial direction to allow the second annular bearing to move in the axial direction, thereby facilitating the movability of the drive shaft relative to the fixed scroll in the axial direction. The biasing mechanism may comprise a preload spring. In another aspect of the invention, there is provided a scroll pump comprising: a fixed scroll; an orbiting scroll; an annular bearing coupled to the orbiting scroll; a crank sleeve coupled to the annular bearing; and a drive shaft coupled to the crank sleeve, wherein the drive shaft is arranged to drive orbiting of the orbiting scroll via the crank sleeve and the annular bearing, wherein the crank sleeve is axially movable relative to the drive shaft to allow axial movement of the orbiting scroll relative to the fixed scroll; and a biasing mechanism arranged to provide a biasing force on the crank sleeve which acts via the crank sleeve and the annular bearing to axially bias the orbiting scroll and the fixed scroll together. In yet another aspect of the invention, there is provided a scroll pump comprising: a fixed scroll; an orbiting scroll; an annular bearing coupled to the orbiting scroll; a crank sleeve coupled to the annular bearing; a drive shaft coupled to the crank sleeve, wherein the drive shaft is arranged to drive orbiting of the orbiting scroll via the crank sleeve and the annular bearing, wherein the annular bearing is axially movable relative to the crank sleeve to allow axial movement of the orbiting scroll relative to the fixed scroll; and a biasing mechanism arranged to provide a biasing force on the annular bearing to axially bias the orbiting scroll and the fixed scroll together. In yet another aspect of the invention, there is provided a scroll pump, comprising: a fixed scroll; an orbiting scroll; an annular bearing coupled to the orbiting scroll; a drive shaft coupled to the annular bearing, wherein the drive shaft is arranged to drive orbiting of the orbiting scroll via the annular bearing, wherein the orbiting scroll is axially movable relative to the annular bearing to allow axial movement of the orbiting scroll relative to the fixed scroll; and a biasing mechanism arranged to provide a biasing force on the orbiting scroll to axially bias the orbiting scroll and the fixed scroll together. In yet another aspect of the invention, there is provided a scroll pump comprising: a fixed scroll; an orbiting scroll; a drive shaft coupled to the orbiting scroll, wherein the drive shaft is arranged to drive orbiting of the orbiting scroll; wherein the fixed scroll is axially movable relative to the drive shaft and the orbiting scroll is axially fixed relative to the drive shaft, thereby to allow axial movement of the fixed scroll relative to the orbiting scroll; and a biasing mechanism arranged to provide a biasing force on the fixed scroll to axially bias the orbiting scroll and the fixed scroll together. In yet another aspect of the invention, there is provided a vacuum pumping system comprising a scroll pump according to any of the above aspects. In yet another aspect of the invention, there is provided use of the scroll pump of any of the above aspects to pump fluid. BRIEF DESCRIPTION OF DRAWINGS Figure 1 is a schematic illustration (not to scale) showing a cross-sectional view of a first scroll pump; Figure 2 is a schematic illustration (not to scale) showing a cross-sectional view of a second scroll pump; Figure 3 is a schematic illustration (not to scale) showing a cross-sectional view of a third scroll pump; Figure 4 is a schematic illustration (not to scale) showing a cross-sectional view of a fourth scroll pump; and Figure 5 is a schematic illustration (not to scale) showing a cross-sectional view of a fifth scroll pump. DETAILED DESCRIPTION Figure 1 is a schematic illustration (not to scale) showing a cross-sectional view of a first scroll pump 100. The first scroll pump 100 comprises housing portions 110, a fixed scroll 120, an orbiting scroll 130, a drive shaft 140, an actuator 150, a first bearing assembly 160a, a second bearing assembly 160b, a third bearing assembly 160c, a diaphragm 170, a first channel seal 180a, a second channel seal 180b, a first preload spring 190a, and a second preload spring 190b. In this embodiment, the housing portions 110 and the fixed scroll 120 together define an overall housing of the scroll pump 100 within which other components of the scroll pump 100 are located. However, it will be appreciated that, in other embodiments, the fixed scroll 120 may not define any of the overall housing of the scroll pump 100 and instead may be located entirely within an overall housing. In this embodiment, the orbiting scroll 130 is located within the overall housing of the scroll pump 100. The orbiting scroll 130 is intermeshed with the fixed scroll 120 to define a space (or channel) which is used by the scroll pump 100 during operation to pump fluid (e.g. a gas). The orbiting scroll 130 is configured to orbit relative to the fixed scroll 120 to pump fluid from an inlet (not shown) of the scroll pump 100 to an outlet (not shown) of the scroll pump 100. The precise physical mechanism by which fluid is pumped by the orbiting of the orbiting scroll 130 relative to the fixed scroll 120 is well understood and will not be described herein. The fixed scroll 120 comprises a first base 122 and a first spiral wall 124. The orbiting scroll 130 comprises a second base 132 and a second spiral wall 134. The first spiral wall 124 and second spiral wall 134 are intermeshed with each other. Furthermore, the first spiral wall 124 extends perpendicularly from the first base 122 towards the second base 132 such that an end surface (also known as the tip) of the first spiral wall 124 is in contact with the first channel seal 180a. The second spiral wall 134 extends perpendicularly from the second base 132 towards the first base 122 such that an end surface (or tip) of the second spiral wall 134 is in contact with the second channel seal 180b. In this way, the space between the spiral walls 124, 134 used for pumping fluid is sealed to prevent radial leakage of fluid across the spiral walls 124, 134. In this embodiment, the first base 122 and first spiral wall 124 are integrally formed with each other, and the second base 132 and second spiral wall 134 are integrally formed with each other. However, in other embodiments, one or both of the spiral walls 124, 134 are not integrally formed with their respective bases 122, 132. The drive shaft 140 is coupled to the orbiting scroll 130 and configured to rotate to drive the orbiting of the orbiting scroll 130. The drive shaft 140 is located within the overall housing of the scroll pump 100 and mounted via the main bearing assembly 160 which facilitates rotation of the drive shaft 140. In this embodiment, the drive shaft 140 extends through both the fixed scroll 120 and the orbiting scroll 130, and the orbiting scroll 130 is mounted at an end of the drive shaft 140. The actuator 150 (e.g. an electric motor) is coupled to the drive shaft 140 and configured to actuate the drive shaft 140 to cause the drive shaft 140 to rotate to drive the orbiting of the orbiting scroll 130. The actuator 150 is located within the overall housing of the scroll pump 100 and mounted around the drive shaft 140. The first bearing 160a is an annular bearing mounted at a first end of the drive shaft 140. The second bearing 160b is an annular bearing mounted at a location on the drive shaft 140 between the first end of the drive shaft 140 and a second end of the drive shaft 140. In other words, the second bearing 160b is located between the first bearing 160a and the third bearing 160c in the axial direction. The third bearing 160c is an annular bearing mounted at the second end of the drive shaft 140. The first bearing 160a mechanically couples the orbiting scroll 130 to the first end of the drive shaft 140. The second bearing 160b mechanically couples the fixed scroll 120 to the drive shaft 140. More specifically, the second bearing 160b mechanically couples the fixed scroll 120 to the drive shaft 140 via the diaphragm 170. The third bearing 160c mechanically couples the second end of the drive shaft 140 to the overall housing of the scroll pump 100. The diaphragm 170 is attached to and surrounds the second bearing 160b to mechanically couple the second bearing 160b to the fixed scroll 120. The diaphragm 170 is attached to the fixed scroll 120 at a radially outer periphery of the diaphragm 170. The diaphragm 170 extends circumferentially around the second bearing 160b to support the second bearing 160b in its position. In other words, the diaphragm 170 comprises a hole and the second bearing 160b is located within the hole, whilst being attached to the diaphragm 170 via an edge of the diaphragm 170 defining the hole. The diaphragm 170 supports the second bearing 160b whilst being flexible in the axial direction to allow the second bearing 160b to move axially relative to the fixed scroll 120. The diaphragm 170 also has a high radial stiffness in order to oppose and / or prevent the second bearing 160b from moving in the radial direction. The radial to axial stiffness ratio may be at least 10:1, preferably 100:1 or greater. The diaphragm 170 may be formed from, for example, steel or aluminium. The first channel seal 180a is spiral shaped seal located on the second base 132 of the orbiting scroll 130. The first channel seal 180a is sandwiched between the second base 132 and the end of the first spiral wall 124 in order to seal the space used for pumping fluid. The second channel seal 180b is a spiral shaped seal located on the first base 122 of the fixed scroll 120. In a similar manner to the first channel seal 180a, the second channel seal 180b is sandwiched between the first base 122 and the end of the second spiral wall 134 in order to seal the space used for pumping fluid. In this embodiment, the third bearing 160c is mounted to a housing portion 110 in a bore in the housing portion 110 such that the third bearing 160c is slidable in the axial direction relative to the housing portion 110. This allows the third bearing 160c to move axially in the bore relative to the housing portion 110 and the fixed scroll 120. An O-ring is located in the bore around the third bearing 160c between the third bearing 160c and the housing portion 110 in order to centralise the third bearing 160c in the bore and to reduce noise from movement of the third bearing 160c. Since both the second bearing 160b and the third bearing 160c are axially movable, this allows the drive shaft 140 to move axially, which in turn allows the orbiting scroll 130 to move axially. In this embodiment, the scroll pump 100 further comprises a first preload spring 190a and a second preload spring 190b. The first preload spring 190a is arranged to cause a preloading force to act on the second bearing 160b which pulls the orbiting scroll 130 in the axial direction towards the fixed scroll 120. The second preload spring 190b is arranged to cause a preloading force to act on the third bearing 160c which pulls the orbiting scroll 130 in the axial direction towards the fixed scroll 120. In this embodiment, the first preload spring 190a is located in the axial direction between the fixed scroll 120 and the second bearing 160b, and the second preload spring 190b is located in the axial direction between a housing portion 110 and the third bearing 160c. This preloading force, in combination with the axially movability of the drive shaft 140, enables the orbiting scroll 130 and the fixed scroll 120 to be biased together precisely to maintain a tight seal. Advantageously, the use of the above-described diaphragm 180 tends to avoid the issue of fretting which occurs in other mechanisms which allow bearings to move axially, e.g. the sliding mechanism described for the third bearing 160c. Advantageously, the use of the above-described diaphragm 180 tends to enable a very precise radial location to be maintained for the orbiting scroll 130, due to the high radial stiffness of the diaphragm 180. The diaphragm 180 eliminates radial movement of the drive shaft 140 in the plane of the second bearing 160b, which in turn reduces variation in the radial clearance between the scrolls and allows a smaller radial clearance to be used. Advantageously, the flexibility of the diaphragm 180 allows the second bearing 160b to tilt and fully align with the drive shaft 140. Hence, the third bearing 160c and the housing portion 200 can be repositioned by moving them radially, without stressing the second bearing 160b. In a further embodiment (not shown), instead of being supported via the sliding mechanism described above, the third bearing 160c is supported by a diaphragm in the same way as the second bearing 160b. In other words, in this embodiment, the scroll pump 100 comprises a further diaphragm located between the third bearing 160c and the housing portion 110. The further diaphragm is attached to and surrounds the third bearing 160c to mechanically couple the third bearing 160c to the housing portion 110. The further diaphragm supports the third bearing 160c whilst being flexible in the axial direction to allow the third bearing 160c to move axially relative to the housing portion 110. The further diaphragm also has a high radial stiffness in order to oppose and / or prevent the third bearing 160c from moving in the radial direction. Figure 2 is a schematic illustration (not to scale) showing a cross-sectional view of a second scroll pump 200. The second scroll pump 200 comprises housing portions 210, a fixed scroll 220, an orbiting scroll 230, a drive shaft 240, an actuator 250, a first bearing assembly 260a, a second bearing assembly 260b, a third bearing assembly 260c, a slidable crank sleeve 270, a first channel seal 280a, a second channel seal 280b, a first preload spring 290a, and a second preload spring 290b. The embodiment of Figure 2 is the same as the embodiment of Figure 1, except that instead of having a diaphragm 170 the second scroll pump 200 comprises an axially movable crank sleeve 270, and the first preload spring 290a of Figure 2 is in a different location to the location of the first preload spring 190a of Figure 1. It will be appreciated that the housing portions 210, fixed scroll 220, orbiting scroll 230, drive shaft 240, actuator 250, first bearing assembly 260a, second bearing assembly 260b, third bearing assembly 260c, first channel seal 280a, second channel seal 280b, and second preload spring 290b respectively correspond to the elements labelled 110, 120, 130, 140, 150, 160a, 160b, 160c, 180a, 180b and 190b in the embodiment of Figure 1, and so have the same or similar structure and / or function to said respective corresponding elements in Figure 1. The crank sleeve 270 is an element present in scroll pumps which provides a crank offset for imparting an orbital path on the orbital scroll 230 of the scroll pump 200. The crank sleeve 270 extends around the drive shaft 240 and is coupled to the orbiting scroll 230 via the first bearing 260a. The crank sleeve 270 is an eccentric member with a centre of rotation parallel to, but radially offset from, the axis of rotation of the drive shaft 240 in order to provide the crank offset for the orbiting of the orbiting scroll 230. In this embodiment, the crank sleeve 270 is axially movable (or slidable) relative to the drive shaft 240 to allow for axial movement of the orbiting scroll 230 relative to the fixed scroll 220. Specifically, the crank sleeve 270 is attached to the first bearing 260a and the first bearing 260a is attached to the orbiting scroll 230. Thus, axial movement of the crank sleeve 270 causes axial movement of the orbiting scroll 230 via the attachment of the orbiting scroll 230 to the first bearing 260a and the attachment of the first bearing 260a to the crank sleeve 270. In this embodiment, the second bearing 260b is fixed and the first bearing 260a is movable. The first preload spring 290a is arranged to provide an axial biasing force on the crank sleeve 270 which acts through the crank sleeve 270 and the first bearing 260a to bias the orbiting scroll 230 towards the fixed scroll 220. In this embodiment, the first preload spring 290a extends axially between a shoulder portion (e.g. a clamp disc at the end of the drive shaft 240) of the drive shaft 240 and the crank sleeve 270. Since the crank sleeve 270 is axially movable relative to the drive shaft 240, a particular biasing force provided by the first preload spring 290a can be chosen in order to maintain stability of the orbiting scroll 230 and provide a tight seal between the fixed and orbiting scrolls 220, 230. Figure 3 is a schematic illustration (not to scale) showing a cross-sectional view of a third scroll pump 300. The third scroll pump 300 comprises housing portions 310, a fixed scroll 320, an orbiting scroll 330, a drive shaft 340, an actuator 350, a first bearing assembly 360a, a second bearing assembly 360b, a third bearing assembly 360c, a crank sleeve 370, a first channel seal 380a, a second channel seal 380b, a first preload spring 390a, and a second preload spring 390b. The embodiment of Figure 3 is the same as the embodiment of Figure 2, except that instead of the crank sleeve being slidable relative to the drive shaft, the first bearing 360a is slidable relative to the crank sleeve 370. Also, the first preload spring 390a is in a different location compared to the first preload spring of Figure 2. It will be appreciated that the housing portions 310, fixed scroll 320, orbiting scroll 330, drive shaft 340, actuator 350, first bearing assembly 360a, second bearing assembly 360b, third bearing assembly 360c, first channel seal 380a, second channel seal 380b, and second preload spring 390b respectively correspond to the elements labelled 110, 120, 130, 140, 150, 160a, 160b, 160c, 180a, 180b and 190b in the embodiment of Figure 1, and so have the same or similar structure and / or function to said respective corresponding elements in Figure 1. In the embodiment of Figure 3, the crank sleeve 370 is fixed relative to the drive shaft 340 and the first bearing 360a is movable (or slidable) axially relative to the crank sleeve 370. More specifically, the first bearing 360a may be axially movable on a crank pin of the crank sleeve 370. The first bearing 360a is attached to the orbiting scroll 330. Thus, axial movement of the first bearing 360a on the crank sleeve 370 causes axial movement of the orbiting scroll 330 via the attachment of the orbiting scroll 330 to the first bearing 260a. The first preload spring 390a is arranged to provide an axial biasing force on the first bearing 360a which acts through the first bearing 360a to bias the orbiting scroll 330 towards the fixed scroll 320. In this embodiment, the first preload spring 390a extends axially between a shoulder portion of the crank sleeve 370 and the first bearing 360a. Since the first bearing 360a is axially movable relative to the crank sleeve 370, a particular biasing force provided by the first preload spring 390a can be chosen in order to maintain stability of the orbiting scroll 330 and provide a tight seal between the fixed and orbiting scrolls 320, 330. Figure 4 is a schematic illustration (not to scale) showing a cross-sectional view of a fourth scroll pump 400. The fourth scroll pump 400 comprises housing portions 410, a fixed scroll 420, an orbiting scroll 430, a drive shaft 440, an actuator 450, a first bearing assembly 460a, a second bearing assembly 460b, a third bearing assembly 460c, a crank sleeve 470, a first channel seal 480a, a second channel seal 480b, a first preload spring 490a, and a second preload spring 490b. The embodiment of Figure 4 is the same as the embodiment of Figure 3, except that instead of the first bearing being slidable relative to the crank sleeve, the orbiting scroll 430 is slidable relative to the first bearing 460a. Also, the first preload spring 490a is in a different location compared to the first preload spring of Figure 3. It will be appreciated that the housing portions 410, fixed scroll 420, orbiting scroll 430, drive shaft 440, actuator 450, first bearing assembly 460a, second bearing assembly 460b, third bearing assembly 460c, first channel seal 480a, second channel seal 480b, and second preload spring 490b respectively correspond to the elements labelled 110, 120, 130, 140, 150, 160a, 160b, 160c, 180a, 180b and 190b in the embodiment of Figure 1, and so have the same or similar structure and / or function to said respective corresponding elements in Figure 1. In the embodiment of Figure 4, the first bearing 460a is fixed relative to the crank sleeve 470 and the orbiting scroll 430 is movable (or slidable) axially relative to the first bearing 360a. Thus, axial movement of the orbiting scroll 430 on the first bearing 460a causes axial movement of the orbiting scroll 430 relative to the fixed scroll 420. The first preload spring 490a is arranged to provide an axial biasing force on the orbiting scroll 430 which acts on the base 432 of the orbiting scroll 430 to bias the orbiting scroll 430 towards the fixed scroll 420. In this embodiment, the first preload spring 490a extends axially between the first bearing 460a and the base 432 of the orbiting scroll 430. Since the orbiting scroll 430 is axially movable relative to the first bearing 460a, a particular biasing force provided by the first preload spring 490a can be chosen in order to maintain stability of the orbiting scroll 430 and provide a tight seal between the fixed and orbiting scrolls 420, 430. Figure 5 is a schematic illustration (not to scale) showing a cross-sectional view of a fifth scroll pump 500. The fifth scroll pump 500 comprises housing portions 510, a fixed scroll 520, an orbiting scroll 530, a drive shaft 540, an actuator 550, a first bearing assembly 560a, a second bearing assembly 560b, a third bearing assembly 560c, a crank sleeve 570, a first channel seal 580a, a second channel seal 580b, a first preload spring 590a, and a second preload spring 590b. The embodiment of Figure 5 is the same as the embodiment of Figure 4, except that instead of the orbiting scroll being slidable relative to the first bearing, the fixed scroll 520 is slidable relative to the housing portions 510. More specifically, the fixed scroll 520 is slidable relative to a housing portion 510 constituting a motor body of the scroll pump 100 (i.e. a part of the overall housing containing the actuator 550 which may be a motor). Also, the first preload spring 590a is in a different location compared to the first preload spring of Figure 4. It will be appreciated that the housing portions 510, fixed scroll 520, orbiting scroll 530, drive shaft 540, actuator 550, first bearing assembly 560a, second bearing assembly 560b, third bearing assembly 560c, first channel seal 580a, second channel seal 580b, and second preload spring 590b respectively correspond to the elements labelled 110, 120, 130, 140, 150, 160a, 160b, 160c, 180a, 180b and 190b in the embodiment of Figure 1, and so have the same or similar structure and / or function to said respective corresponding elements in Figure 1. In the embodiment of Figure 5, the fixed scroll 520 is movable (or slidable) axially relative to the motor body 510 and the orbiting scroll 530 is fixed relative to the drive shaft 540, such that the fixed scroll 520 is movable axially relative to the orbiting scroll 530. The first preload spring 590a is arranged to provide an axial biasing force on the fixed scroll 520 which acts through the base 522 of the fixed scroll 520 to bias the fixed scroll 520 towards the orbiting scroll 530. In this embodiment, the first preload spring 590a extends axially between a housing portion 510 and the base 522 of the fixed scroll 520. Since the fixed scroll 520 is axially movable relative to the drive shaft 540, a particular biasing force provided by the first preload spring 590a can be chosen in order to maintain stability of the orbiting scroll 530 and provide a tight seal between the fixed and orbiting scrolls 520, 530. Advantageously, the embodiment of Figure 5 tends to avoid fretting on the orbiting scroll bearing as the axial movement is performed on the fixed scroll side rather than the orbiting scroll side. Advantageously, it will be appreciated that all of the scroll pumps described herein provide different alternative ways of biasing the fixed and orbiting scrolls together in order to provide a tight seal between the fixed and orbiting scrolls, whilst maintaining radial stability. The above-described scroll pumps 100 may be used as part of a vacuum pumping system including multiple pumps and / or other components. It will be appreciated that various modifications / deviations may be made to the above described embodiments without departing from the scope of the invention. For example, the locations of the fixed and orbiting scrolls in the embodiments of Figures 1 to 5 are all in a so-called “reverse” design for scroll pumps in which the orbiting scroll is on the end of the drive shaft and the drive shaft extends through the fixed scroll to reach the orbiting scroll. However, it will be appreciated that a so-called “forward” design may be used instead where the fixed scroll is on the other side of the orbiting scroll and the drive shaft does not extend through the fixed scroll. Furthermore, in the embodiments of Figures 1 to 5, preload springs are used to provide axial biasing force(s), but it will be appreciated that in general any appropriate biasing mechanism may be used to provide the axial biasing force (s). Furthermore, in the embodiments of Figures 1, 3, 4 and 5, the crank sleeve on which the first bearing (orbiting scroll bearing) 5 is mounted may or may not be integrally formed with the drive shaft. REFERENCE NUMERAL LIST 100, 200, 300, 400, 500: scroll pump 110, 210, 310, 410, 510: housing 120,220, 320, 420, 520: fixed scroll 122, 222, 322, 422, 522: base of fixed scroll 124, 224, 324, 424, 524: spiral wall of fixed scroll 130, 230, 330, 430, 530: orbiting scroll 132, 232, 332, 432, 532: base of orbiting scroll 134, 234, 334, 434, 534: spiral wall of orbiting scroll 140, 240, 340, 440, 540: drive shaft 150. 250, 350, 450, 550: actuator 160, 260, 360, 460, 560: main bearing assembly 160a. 260a, 360a, 460a, 560a: first bearing 160b, 260b, 360b, 460b, 560b: second bearing 160c, 260c, 360c, 460c, 560c: third bearing 170: diaphragm 270, 370, 470, 570: crank sleeve 04 09 25

Claims

1. A scroll pump, comprising:a fixed scroll;5 an orbiting scroll;an annular bearing coupled to the orbiting scroll;a crank sleeve coupled to the annular bearing; anda drive shaft coupled to the crank sleeve, wherein the drive shaft is arranged to drive orbiting of the orbiting scroll via the crank sleeve and the10 annular bearing, wherein the crank sleeve is axially movable relative to the drive shaft to allow axial movement of the orbiting scroll relative to the fixed scroll;anda biasing mechanism arranged to provide a biasing force on the crank sleeve which acts via the crank sleeve and the annular bearing to axially bias15 the orbiting scroll and the fixed scroll together, wherein the biasing mechanism comprises a preload spring.

2. A scroll pump according to claim 1, wherein the biasing mechanism extends between the crank sleeve and a shoulder portion of the drive shaft.

203. A vacuum pumping system comprising the scroll pump of claim 1 or 2.

4. Use of the scroll pump of claim 1 or 2 to pump fluid.25

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