ADJUSTABLE SCROLL PUMP

Abstract

The invention provides a scroll pump comprising an orbiting scroll and a fixed scroll, wherein the orbital axis of the orbiting scroll is movable in a radial direction relative to the fixed scroll while the orbiting scroll is orbiting about its orbital axis, or wherein the fixed scroll is movable relative to the orbiting scroll in a radial direction while the orbiting scroll is orbiting about its orbital axis.

Claims

1. A scroll pump comprising an orbiting scroll and a fixed scroll, wherein the orbital axis of the orbiting scroll is movable in a radial direction relative to the fixed scroll while the orbiting scroll is orbiting about its orbital axis, or wherein fixed scroll is movable relative to the orbiting scroll in a radial direction while the orbiting scroll is orbiting about its orbital axis.

2. The scroll pump according to claim 1 wherein the scroll pump further comprises a first bearing coupled to a drive shaft for driving the orbiting scroll, wherein the first bearing is movable with drive shaft in a direction substantially perpendicular to a rotational axis of the drive shaft.

3. The scroll pump according to claim 2 wherein the first bearing is coupled to a housing element of the scroll pump, the housing element being movable relative to the fixed scroll while the drive shaft is rotating.

4. The scroll pump according to claim 3 wherein the movable housing element may have its position relative to the fixed scroll selectively fixed.

5. The scroll pump according to claim 2 further comprising a second bearing, the second bearing being coupled to the drive shaft and to a bearing carrier which is flexible in an axial direction.

6. The scroll pump according to claim 2 wherein the first bearing is located in a position from a substantially distal end of the drive shaft to substantially adjacent the fixed scroll.

7. A scroll chamber for a scroll pump, the scroll chamber containing an orbiting scroll and a fixed scroll each comprising an axially extending scroll wall, wherein the scroll chamber has a capacity below 5 m.sup.3/h and wherein the minimum radial clearance between the axially extending scroll wall of the orbiting scroll and the axially extending scroll wall of the fixed roll whilst the orbiting scroll is orbiting is less than about 0.06 mm, preferably from about 0.01 mm to about 0.05 mm.

8. An orbiting scroll and fixed scroll of a scroll pump, the orbiting scroll having an orbital axis and the fixed scroll having a longitudinal axis, wherein said orbital axis and longitudinal axis are coaxially aligned with a variation of less than about ±0.03 mm, preferably less than about ±0.01 mm.

9. A method for centring an orbiting scroll and fixed scroll of a scroll pump, the scroll pump comprising an orbiting scroll and a fixed scroll which maintain a radial separation during pumping, the orbiting scroll being coupled to a drive shaft via an eccentric member, the drive shaft having an axis of rotation, the method comprising the steps of: a. rotating the eccentric member about the axis of rotation of the drive shaft to impart an orbiting action upon the orbiting scroll; b. while the orbiting scroll is orbiting moving the orbital axis of the orbiting scroll or longitudinal axis of the fixed scroll relative to the other in a first direction substantially perpendicular to the axis of rotation of the drive shaft until the orbiting scroll engages the fixed scroll, upon said engagement whichever has moved of the orbital axis of the orbiting scroll or the longitudinal axis of the fixed scroll being in a first engagement position, c. moving whichever has moved of the orbital axis of the orbiting scroll or longitudinal axis of the fixed scroll relative to the other in a second direction opposite the first direction until the orbiting scroll again engages the fixed scroll, upon said engagement whichever has moved of the orbital axis of the orbiting scroll or the longitudinal axis of the fixed scroll being in a second engagement position, and d. positioning whichever has moved of the orbital axis of the orbiting scroll or the longitudinal axis of the fixed scroll in a first centred position substantially halfway between the first engagement position and the second engagement position and substantially in a first plane containing the first engagement position, second engagement position and the first centred position of whichever has moved of the orbital axis of the orbiting scroll or the longitudinal axis of the fixed scroll.

10. The method according to claim 9 further comprising the subsequent steps of: e. rotating the eccentric member about the axis of rotation of the drive shaft to impart an orbiting action upon the orbiting scroll; f. while the orbiting scroll is orbiting moving the orbital axis of the orbiting scroll or the longitudinal axis of the fixed scroll relative to the other in a third direction substantially perpendicular to the axis of rotation of the crank and substantially perpendicular to the first direction until the orbiting scroll engages the fixed scroll, upon said engagement whichever has moved of the orbital axis of the orbiting scroll or the longitudinal axis of the fixed scroll being in a third engagement position, g. moving whichever has moved of the orbital axis of the orbiting scroll or the longitudinal axis of the fixed scroll relative to the other in a fourth direction substantially opposite the third direction until the orbiting scroll engages the fixed scroll, upon said engagement whichever has moved of the orbital axis of the orbiting scroll or the longitudinal axis of the fixed scroll being in a fourth engagement position, and h. positioning whichever has moved of the orbital axis of the orbiting scroll or the longitudinal axis of the fixed scroll in a second centred position substantially halfway between the third engagement position and the fourth engagement position substantially in a second plane containing the third engagement position, fourth engagement position and the second centred position of whichever has moved of the orbital axis of the orbiting scroll or the longitudinal axis of the fixed scroll.

11. The method according to claim 10 wherein second centred position is additionally substantially halfway between the first engagement position and the second engagement position substantially in a third plane containing the first engagement position, second engagement position and the second centred position of whichever has moved of the orbital axis of the orbiting scroll or the longitudinal axis of the fixed scroll.

12. The method according to claim 9 wherein the orbiting scroll is moved relative to the fixed scroll.

13. The method according to claim 9 wherein the engagement between the fixed scroll and the orbiting scroll is detected by monitoring for the drive shaft ceasing to rotate.

14. The method according to claim 9 wherein the drive shaft is rotated at a low speed, preferably less than about 5 Hz, preferably from about 0.01 Hz to about 4 Hz.

15. The method according to claim 9 wherein the drive shaft is rotated by directing an airflow through the scroll pump, preferably wherein the airflow is introduced via an exhaust duct of the scroll pump.

16. The method according to claim 9 wherein the drive shaft is rotated in a direction opposite to its pumping direction.

17. The method according to claim 9 wherein the orbiting scroll is moved relative to the fixed scroll by pivoting or translating the drive shaft.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0030] In the following disclosure, which is given by way of example only, reference will be made to the drawings, in which:

[0031] FIG. 1 is a schematic representation of a prior art scroll pump; and

[0032] FIG. 2 is a schematic representation of a scroll pump according to the invention.

DETAILED DESCRIPTION

[0033] The present invention provides a scroll pump, preferably a vacuum scroll pump, as well as methods for centring an orbiting scroll and a fixed scroll of a scroll pump.

[0034] FIG. 1 shows a typical small capacity scroll pump (1). The orbiting scroll (2) is mounted on a rotating crank or drive shaft (3). The crank offset is provided by a sleeve (4). The central and rear crank bearings (5, 6) are held in fixed positions. In the illustrated example, the rear bearing (6) is held by a fixed bearing housing (15) integrally formed with the scroll pump housing (16). In the illustrated example, the radial clearance between the two scrolls (2, 17) is determined by nine components. The inventors have found that the combination of the manufacturing tolerances on these parts may create a total variation of approximately +/−0.2 mm.

[0035] As the capacity of vacuum pumps is reduced, internal leakage becomes an increasing issue for pump performance. This leakage impacts negatively on the ultimate pressure. In the illustrated configuration, it may be impossible to have a minimum clearance that will not seize and to also have an average or maximum radial clearance that delivers acceptable performance in a small capacity pump. For instance, a pump with a capacity below 5 m.sup.3/h.

[0036] FIG. 2 shows a scroll pump (7) according to the invention. The illustrated scroll pump (7) has a rear shaft bearing (8) which is moveable to enable the radial position of the orbiting scroll (9) to be changed. This adjustment enables the orbiting scroll (9) to be placed in a substantially optimum radial location to deliver a radial clearance between the scrolls (9, 10) that is near constant in all crank (11) orientations. The optimised positioning of the orbiting scroll (9) permits a smaller radial clearance to be realised than is otherwise achievable, which in turn leads to improved performance, including lower ultimate pressure and power. The invention thereby facilitates the provision of smaller capacity scroll pumps. However, the skilled person will appreciate that the method and pump configuration may be successfully used in pumps of all sizes.

[0037] In the illustrated scroll pump (7), the rear bearing (8) is mounted in a slidable carrier (12) forming part of the scroll pump (7) housing (18). The carrier (12) is mounted on the motor body (18) and has drive screws (not shown) for moving the bearing housing (8) in ‘X’ and ‘Y’ directions. The pump (7) is run at low speed in reverse by applying 350 mbar of air to the pump's exhaust (not shown). The pump's rotation stops when the scrolls (9, 10) are pushed to the point of contact. In this way, the extreme positions at which the pump (7) will run can be found and the rear bearing (8) then set to a substantially central position. This may be done in both ‘X’ and ‘Y’ directions. Then the rear bearing's position is locked, e.g. by tightening the screws (13, 14) on the bearing carrier (12). The relatively low air pressure applied to the exhaust ensures that only a light contact is required to stop rotation, avoiding damage to the scrolls (9, 10). The illustrated bearings (8, 20) are ball bearings.

[0038] In an alternative arrangement the pump motor may be run in a forward or a reverse direction at a low speed (e.g. less than about 5 Hz) and contact may be determined using a torque meter; the pump motor being cut when the torque meter determines an increase in torque attributable the scrolls contacting.

[0039] In the embodiment shown in FIG. 2, the central bearing (20) is held in a flexible bearing carrier (19). The flexible bearing carrier (19) may flex in an axial direction but, in use, substantially eliminates radial movement of the drive shaft (11). The flexible bearing carrier (19) combined with the adjustable rear bearing (8) may deliver a high degree of control over the position of the orbiting scroll (9) relative to the fixed scroll (10). Typically, the flexible bearing carrier is metallic, typically the flexible bearing carrier is made from an aluminium alloy or steel. Typically, in use, the flexible bearing carrier enables the bearing to move from about −0.5 to about +0.5 mm in an axial direction.

[0040] Unless stated otherwise, for the purpose of the invention, axial and longitudinal directions relate to a direction substantially parallel to the axis of rotation (A) of the drive shaft (11) of the pump. Radially refers to a direction extending out from the axis of rotation (A) of the drive shaft (11) transverse to the longitudinal direction.

[0041] In alternative arrangements, the position of the rear bearing may be fixed and the middle (or central) bearing may be movable. Both arrangements enable the movement of the orbital axis of the orbiting scroll relative to the fixed scroll. In still further alternative arrangements, the fixed scroll may be movable relative to the orbital axis of the orbiting scroll. Orbiting scroll is a term of art and refers to the scroll that orbits during use of the scroll. It will be appreciated that the orbiting scroll may itself be stationary when the pump is not in use.

[0042] It shall be appreciated that various modifications may be made to the embodiments shown without departing from the spirit and scope of the invention as defined by the accompanying claims as interpreted under patent law.

[0043] Although elements have been shown or described as separate embodiments above, portions of each embodiment may be combined with all or part of other embodiments described above.

[0044] Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are described as example forms of implementing the claims.