GB2592657A

GB2592657A - Scroll pump apparatus and method

Info

Publication number: GB2592657A
Application number: GB2003220.7A
Authority: GB
Inventors: Ernest Kinnaird Holbrook Alan
Original assignee: Edwards Ltd
Current assignee: Edwards Ltd
Priority date: 2020-03-05
Filing date: 2020-03-05
Publication date: 2021-09-08
Also published as: WO2021176222A1; GB202003220D0; EP4115084A1

Abstract

A scroll pump 101 with drive shaft 115, fixed scroll 105, orbiting scroll 103, has at least one actuator 129-n for adjusting the axial position of the orbiting scroll or the fixed scroll (fig.7). Each of the scrolls has a wrap, or involute scroll wall 107, 111 which extends axially towards the base 109,113 of the opposing scroll, the actuator can open a gap or spacing between the scroll and the opposing wall reducing the throughput of the pump without altering the motor 116 driving speed. Spacing can be sensed by a [capacitive] sensor 127-n on either scroll to actively target a specific spacing. Target spacings of 5, 10, 15, 20 microns are given, chosen by operating temperature and pressure. A baseline zero spacing may be found by driving the pump and sensing the slowing of rotation. Scroll walls may be PTFE coated. Also disclosed is positioning an actuator on the shaft distal to the orbiting scroll (fig.1), and having several angularly spaced actuators which operate to alter the 2D/3D orientation between the bases of the scrolls, for example to ensure the base plates are substantially parallel. Application: vacuum pump.

Description

SCROLL PUMP APPARATUS AND METHOD

TECHNICAL FIELD

The present disclosure relates to a scroll pump apparatus and method. Aspects of the invention relate to a scroll pump and a method of configuring a scroll pump.

BACKGROUND

Scroll pumps comprise a fixed scroll and an orbiting scroll which, in use, follows an orbiting path. Known scroll pumps have scrolls with fixed axial positions. In some cases, the pump design and materials are chosen to minimise thermal variation in the axial clearances.

However, this cannot address the variation from part tolerances, assembly and wear. In typical scroll pumps each of the scroll walls has a tip seal for sealing against the opposing scroll plate (or base) to provide an axial seal. A problem with this arrangement is that tip seals are abraded in use because of surface friction and generate contaminating tip seal dust, and may require replacement periodically. The requirement for tip seals is derived in part from the difficulty of setting accurately the spacing between the orbiting and fixed scrolls.

It is an aim of the present invention to address one or more of the disadvantages associated with the prior art.

SUMMARY OF THE INVENTION

Aspects and embodiments of the invention provide a scroll pump and a method of actively configuring a scroll pump as claimed in the appended claims.

According to an aspect of the present invention there is provided a scroll pump comprising: an axially extending drive shaft having an eccentric shaft portion; a fixed scroll having a fixed scroll wall extending axially from a fixed scroll base; an orbiting scroll having an orbiting scroll wall extending axially from an orbiting scroll base towards the fixed scroll, the orbiting scroll being disposed on the eccentric shaft portion of the drive shaft; and at least one actuator for adjusting the axial position of the orbiting scroll and/or the fixed scroll in dependence on a determined spacing between the orbiting scroll and the fixed scroll. The spacing between the orbiting scroll and the fixed scroll may comprise or consist of a scroll-to-scroll gap, typically defined in an axial direction. The at least one actuator can be operated controllably to adjust the axial position of the orbiting scroll and/or the fixed scroll.

The actuator can thereby control the spacing (clearance) between the fixed scroll and the orbiting scroll, for example to achieve a target spacing. At least in certain embodiments, the actuator may provide active control of the axial position of the orbiting scroll and/or the fixed scroll. The clearance between the fixed scroll and the orbiting scroll may be actively controlled. The adjustment in the axial position of the orbiting scroll and/or the fixed scroll may selectively increase or decrease the spacing between the fixed scroll and the orbiting scroll. The axial position of the orbiting scroll and/or the fixed scroll may be controllably adjusted, for example to compensate for one or more of the following: varying operational loads (such as changing operating pressure); dynamic effects; thermal variation; and wear (such as lifetime component wear). At least in certain embodiments, the present invention may improve the manufacture, operation and life of existing scroll pumps and enable the creation of small non-contacting scroll pumps, for example scroll pumps having a capacity in the range from 3 to 15 m3/h.

The at least one actuator may be configured to adjust the axial position of the orbiting scroll and/or the axial position of the fixed scroll. The at least one actuator may thereby adjust the spacing between the orbiting scroll and the fixed scroll. The spacing is the axial spacing between the orbiting scroll and the fixed scroll along a longitudinal axis. The at least one actuator may be configured to adjust the spacing between the scroll wall of one of the orbiting scroll and the fixed scroll, and the scroll base of the other one of the orbiting scroll and the fixed scroll. For example, the spacing may be between the orbiting scroll wall and the fixed scroll base. Alternatively, the spacing may be between the orbiting scroll base and the fixed scroll wall. The at least one actuator may be operated to achieve a target spacing between the orbiting scroll and the fixed scroll. The target spacing may be predetermined. The target spacing may be less than 20 microns, for example. The target spacing may be defined as 5 microns, 10 microns, 15 microns or 20 microns. In certain embodiments, the target spacing may be controlled dynamically, for example in dependence on operating parameters of the scroll pump; and/or in dependence on operating conditions, such as operating temperature and/or operating pressure. The target spacing may be set depending on the process fluids to be pumped by the scroll pump.

Determining the spacing between the orbiting scroll and the fixed scroll may comprise operating the at least one actuator to axially displace one of the orbiting scroll and the fixed scroll relative to the other one of the orbiting scroll and the fixed scroll. An axial position where the orbiting scroll and the fixed scroll contact each other may be identified. For example, the scroll pump may be activated and the orbiting scroll displaced along an orbital path. Alternatively, low pressure air may be admitted to an exhaust of the scroll pump to drive the scroll pump in the reverse direction. The at least one actuator may be actuated to displace the orbiting scroll and/or the fixed scroll in an axial direction. The orbital motion of the orbiting scroll may stop or slow when the orbiting scroll and the fixed scroll contact each other. The change in the movement of the orbiting scroll may be identified, for example by monitoring a rotational speed of the drive shaft. A (axial) contact position between the orbiting scroll and the fixed scroll may thereby be determined. Alternatively, a load on the at least one actuator may be monitored to determine when contact occurs. The contact position may be considered as representing zero (0) clearance between the orbiting scroll and the fixed scroll. The contact position may be used as a datum or reference point. The at least one actuator may be operated to adjust the axial position of the orbiting scroll and/or the fixed scroll in dependence on the identified contact position. For example, the at least one actuator may be operated to set a target clearance between the orbiting scroll and the fixed scroll in dependence on the identified contact position The spacing between the orbiting scroll and the fixed scroll may be determined with reference to an operative position of the or each actuator. For example, the spacing may be determined in dependence on the operative position of the or each actuator. The operative position may indicate an extension position or state of the or each actuator.

Alternatively, or in addition, the scroll pump may comprise at least one sensor for determining the spacing between the orbiting scroll and the fixed scroll.

The at least one sensor and the at least one actuator may both be associated with the orbiting scroll. At least one first sensor may determine the axial position of the orbiting scroll; and at least one first actuator may adjust the axial position of the orbiting scroll. Alternatively, or in addition, the at least one sensor and the at least one actuator may both be associated with the fixed scroll. At least one second sensor may determine the axial position of the fixed scroll; and at least one second actuator may adjust the axial position of the fixed scroll.

The at least one sensor may be configured to determine an axial position of the orbiting scroll and/or the fixed scroll. The spacing between the orbiting scroll and the fixed scroll may be determined in dependence on the determined axial position of the orbiting scroll and/or the determined axial position of the fixed scroll.

Alternatively, or in addition, the at least one sensor may directly measure a scroll-to-scroll gap between the orbiting scroll and the fixed scroll. The at least one sensor may measure: a first gap between the orbiting scroll wall and the fixed scroll base; and/or a second gap between the fixed scroll wall and the orbiting scroll base. The axial position of the orbiting scroll and/or the fixed scroll may be adjusted in dependence on said first gap and/or said second gap.

The orbiting scroll is disposed on the eccentric shaft portion of the drive shaft. The rotation of the eccentric shaft portion imparts an orbiting motion to the orbiting scroll relative to the fixed scroll. The at least one actuator may be disposed at an end of the drive shaft distal from the orbiting scroll.

The or each sensor may be configured to determine an axial displacement of the orbiting scroll and the fixed scroll relative to each other. Alternatively, the or each sensor may be configured to determine an axial displacement of the orbiting scroll and/or the fixed scroll relative to a datum. The datum may have a predefined position, for example a predefined position on a longitudinal axis of the scroll pump. Alternatively, the datum may define an axial position of the orbiting scroll corresponding to the contact position of the orbiting scroll and the fixed scroll. The datum may be determined by displacing the orbiting scroll until the scroll wall of one of the orbiting scroll and the fixed scroll contacts a base of the other one of the orbiting scroll and the fixed scroll.

The or each sensor may be in the form of a displacement sensor. For example, the or each sensor may comprise a capacitive displacement sensor. The or each sensor may comprise a contact sensor or a non-contact sensor.

The scroll pump may comprise a control unit for controlling the at least one actuator. The control unit may be configured to determine the spacing between the orbiting scroll and the fixed scroll. The control unit may comprise one or more electronic processor and a system memory. The electronic processor may have at least one input for receiving a sensor signal from at least one sensor. The control unit may control the at least one actuator in dependence on a displacement signal(s) output by the or each sensor. Alternatively, or in addition, the electronic processor may be configured to determine an operative position of the or each actuator to determine the relative position of the orbiting scroll and the fixed scroll. The electronic processor may have at least one output for outputting a control signal to the at least one actuator. The control unit may be configured to implement the method(s) described herein.

The control unit may be configured to determine a datum corresponding to the contact position of the fixed scroll and the orbiting scroll. The control unit may be operated to adjust the axial location of the orbiting scroll and/or the fixed scroll such that the orbiting scroll and the fixed scroll contact each other. The control unit may be configured to determine the datum in one or more of the following operating conditions: start-up of the scroll pump; during a calibration process for the scroll pump; at predefined time intervals; in dependence on a request from an operator or service engineer. In a variant, the datum could be predefined, for example based on a geometry or technical specification of the scroll pump.

The control unit may be configured to control the at least one actuator to adjust the axial position of the orbiting scroll and/or the fixed scroll. The control unit may be configured to control the at least one actuator to adjust the axial position of the orbiting scroll and/or the fixed scroll relative to the determined datum. The control unit may be configured to control the at least one actuator to set a pre-defined operating clearance (spacing) between the fixed scroll and the orbiting scroll. The control unit may be configured to control the at least one actuator to set a clearance between the fixed scroll and the orbiting scroll to set an inlet pressure or a power of the scroll pump.

The or each sensor may be configured to measure the axial displacement of the orbiting scroll base or the drive shaft relative to the datum. The axial displacement of the orbiting scroll may be measured directly by determining the position of the orbiting scroll, for example the position of the orbiting scroll base. Alternatively, the axial displacement of the orbiting scroll may be measured indirectly by determining the position of the drive shaft.

The scroll pump may comprise a biasing means for biasing the orbiting shaft in a first direction.

The biasing means may generate a first force for biasing the orbiting scroll away from the fixed scroll. The biasing means may comprise one or more spring members.

The at least one actuator may be configured to generate a force for displacing the orbiting scroll towards the fixed scroll; or for displacing the fixed scroll towards the orbiting scroll. The at least one actuator may be configured to generate a second force. The second force may comprise a thrust force which is applied to one or more of the following: the orbiting scroll (for example to the orbiting scroll base); the fixed scroll (for example to the fixed scroll base); or the drive shaft (on which the orbiting scroll is mounted).

The at least one actuator and the biasing means may be configured to operate in opposition to each other. The first force generated by the biasing means may act in a first direction. The second force generated by the at least one actuator may act in a second direction. The first and second directions may be opposite to each other.

The scroll pump may comprise an axial thrust bearing assembly for transmitting the second force to the orbiting scroll. The axial thrust bearing assembly may be configured to transmit an axial force to the drive shaft or the orbiting scroll.

According to a further aspect of the present invention there is provided a scroll pump cornprising: an axially extending drive shaft having an eccentric shaft portion; a fixed scroll having a fixed scroll wall extending axially from a fixed scroll base; an orbiting scroll having an orbiting scroll wall extending axially from an orbiting scroll base towards the fixed scroll, the orbiting scroll being disposed on the eccentric shaft portion of the drive shaft; and at least one actuator for adjusting the orientation of the orbiting scroll and/or the fixed scroll in dependence on a determined orientation of the orbiting scroll relative to the fixed scroll. The orientation of the orbiting scroll or the fixed scroll may, for example, be determined in relation to a reference plane. The reference plane may, for example, correspond to a front face of the fixed scroll or the fixed scroll. The at least one actuator can be operated controllably to adjust the orientation of the orbiting scroll and/or the fixed scroll. At least in certain embodiments, the at least one actuator may provide active control of the orientation of the orbiting scroll and/or the fixed scroll. The at least one actuator may actively control the orientation of the fixed scroll and the orbiting scroll relative to each. The orientation of the orbiting scroll and/or the fixed scroll may be adjusted such that the orbiting scroll and the fixed scroll are at least substantially parallel with each other.

In use, the axial position of the orbiting scroll and/or the fixed scroll may be controlled to adjust the clearance between the fixed scroll and the orbiting scroll to control an inlet pressure of the scroll pump, for example to achieve a target or specified inlet pressure. The scroll pump may comprise a pressure sensor for sensing the inlet pressure. Alternatively, or in addition, the axial position of the orbiting scroll may be controlled to adjust the clearance between the fixed scroll and the orbiting scroll to reduce or minimise power or to achieve a target or specified power.

The scroll pump may comprise a control unit for controlling the at least one actuator. The control unit may control the at least one actuator in dependence on the determined orientation of the orbiting scroll relative to the fixed scroll. The control unit may comprise one or more electronic processors and a system memory. The control unit may be configured to determine the orientation of the orbiting scroll relative to the fixed scroll. The electronic processor may have at least one input for receiving a sensor signal from at least one sensor. The control unit may control the at least one actuator in dependence on a displacement signal(s) output by the or each sensor. Alternatively, or in addition, the electronic processor may be configured to determine an operative position of the or each actuator to determine the orientation of the orbiting scroll relative to the fixed scroll. The electronic processor may have at least one output for outputting a control signal to the at least one actuator. The control unit may be configured to implement the method(s) described herein.

The scroll pump may comprise at least one sensor for determining an orientation of the orbiting scroll and/or the fixed scroll. The at least one sensor may determine the orientation of the fixed scroll in relation to the orbiting scroll.

The at least one sensor and the at least one actuator may both be associated with the orbiting scroll or may both be associated with the fixed scroll. At least one first sensor may determine the axial position and/or the orientation of the orbiting scroll; and at least one first actuator may adjust the axial position and/or the orientation of the orbiting scroll. Alternatively, or in addition, at least one second sensor may determine the axial position and/or the orientation of the fixed scroll; and at least one second actuator may adjust the axial position and/or the orientation of the fixed scroll.

The orientation of the orbiting scroll and/or the fixed scroll may be determined in two dimensions. Alternatively, the orientation of the orbiting scroll and/or the fixed scroll may be determined in three dimensions.

The scroll pump may comprise or consist of two or more sensors. The scroll pump may comprise first and second sensors for determining the orientation of the orbiting scroll and/or the fixed scroll in two dimensions. At least in certain embodiments, the scroll pump may comprise or consist of three sensors. The scroll pump may comprise first, second and third sensors for determining the orientation of the orbiting scroll and/or the fixed scroll in three dimensions. The scroll pump may comprise more than three sensors. The sensors may be angularly separated from each other. There may be a uniform angular separation (angular pitch) between the sensors. The sensors may, for example, be arranged in an annular configuration.

The scroll pump may comprise or consist of two or more actuators. At least in certain embodiments, the scroll pump may comprise or consist of three actuators. The scroll pump may comprise more than three actuators. The actuators may be angularly separated from each other. There may be a uniform angular separation (angular pitch) between the actuators.

The actuators may, for example, be arranged in an annular configuration.

Each sensor may be associated with one or more actuators. The sensors and the actuators may be angularly aligned with each other (for example disposed on a radius extending perpendicular from a longitudinal axis of the scroll pump). By way of example, a first sensor and a first actuator may be disposed on a first radius; a second sensor and a second actuator may be disposed on a second radius; and a third sensor and a third actuator may be disposed on a third radius. The first, second and third radii may be angularly offset from each other. The radii may have equal angular separation.

The or each sensor may comprise a displacement sensor, such as a capacitive displacement sensor. The scroll pump may comprise a plurality of the sensors. Each sensor may be configured to determine an axial displacement of the orbiting scroll relative to a respective datum. The sensors may be spaced apart angularly from each other. For example, the sensors may be angularly spaced about a rotational axis of the drive shaft.

The or each sensor may be configured to output a displacement signal. The control unit may be configured to control the at least one actuator in dependence on the displacement signal(s).

The scroll pump may comprise a plurality of the actuators. The actuators may be spaced apart angularly from each other about a rotational axis of the drive shaft. The sensors and the actuators may be angularly aligned with each other.

The or each actuator may be configured to apply a force to a thrust bearing assembly associated with the orbiting scroll wall. The thrust bearing assembly may comprise an array of ball bearings for bearing against the orbiting scroll base. The thrust bearing assembly may comprise at least one thrust surface for bearing against the array of ball bearings.

The control unit may be configured to determine the orientation of the orbiting scroll relative to the fixed scroll by sequentially operating each of the actuators to adjust the orientation of one of the orbiting scroll and the fixed scroll. Operating each actuator in turn may adjust the orientation of the orbiting scroll relative to the fixed scroll. The orientation of the orbiting scroll relative to the fixed scroll which results in contact may be determined by operating each actuator in turn. For example, the scroll pump may be activated and the orbiting scroll displaced along an orbital path. Alternatively, low pressure air may be admitted to an exhaust of the scroll pump to drive the scroll pump in the reverse direction. The orbital motion of the orbiting scroll may stop or slow when the orbiting scroll and the fixed scroll contact each other.

The actuators may be operated sequentially to identify respective contact positions. The change in the movement of the orbiting scroll may be identified, for example by monitoring a rotational speed of the drive shaft. The contact position between the orbiting scroll and the fixed scroll may thereby be determined. Alternatively, a load on the at least one actuator may be monitored to determine when contact occurs. This process may be repeated for each of the actuators. The orientation of the orbiting scroll relative to the fixed scroll may be determined in dependence on the contact positions identified for the respective actuators.

The at least one sensor may be configured to determine a spacing between the orbiting scroll and the fixed scroll. The spacing may comprise or consist of a scroll-to-scroll gap, typically measured in an axial direction. The at least one sensor may be configured to determine an axial position of the orbiting scroll and/or the fixed scroll. The at least one actuator may be configured to adjust the axial position of the orbiting scroll and/or the fixed scroll to achieve a target spacing between the orbiting scroll and the fixed scroll.

The or each sensor may be configured to output a displacement signal. The control unit may determine the spacing between the orbiting scroll and/or the fixed scroll in dependence on the displacement signal(s). The control unit may be configured to control the or each actuator to adjust the axial position of the orbiting scroll and/or the fixed scroll. At least in certain embodiments, the at least one actuator may be operable to adjust the axial position of the orbiting scroll and/or the fixed scroll; and/or the orientation of the orbiting scroll and/or the fixed scroll According to a further aspect of the present invention there is provided a method of actively configuring a scroll pump, the scroll pump comprising a drive shaft, a fixed scroll and an orbiting scroll; wherein the method comprises: determining a spacing between the orbiting scroll and the fixed scroll; and controlling at least one actuator to adjust the axial position of the orbiting scroll and/or the fixed scroll to achieve a target spacing between the orbiting scroll and the fixed scroll.

The spacing between the orbiting scroll and the fixed scroll may be determined by measuring an axial position of the orbiting scroll and/or the fixed scroll. The axial position of the orbiting scroll and/or the fixed scroll may be determined by measuring axial displacement relative to a datum. The datum may correspond to a contact position of the fixed scroll and the orbiting scroll. The datum may thereby represent zero or substantially zero clearance between the orbiting scroll and the fixed scroll.

The method may comprise operating the or each actuator to axially displace one of the orbiting scroll and the fixed scroll relative to the other one of the orbiting scroll and the fixed scroll. An axial position where the orbiting scroll and the fixed scroll contact each other may be identified. The method may comprise activating the scroll pump and displacing the orbiting scroll displaced along an orbital path. The at least one actuator may be actuated to displace the orbiting scroll and/or the fixed scroll in an axial direction. The orbital motion of the orbiting scroll may stop or slow when the orbiting scroll and the fixed scroll contact each other. The method may comprise identifying a change in the movement of the orbiting scroll, for example by identifying a reduction in a rotational speed of the drive shaft. A (axial) contact position between the orbiting scroll and the fixed scroll may thereby be determined. The contact position may be considered as representing zero (0) clearance between the orbiting scroll and the fixed scroll.

Alternatively, or in addition, a gap between the orbiting scroll and the fixed scroll may be measured directly. For example, at least one sensor may measure: a first gap between the orbiting scroll wall and the fixed scroll base; and/or a second gap between the fixed scroll wall and the orbiting scroll base. The axial position of the orbiting scroll and/or the fixed scroll may be adjusted in dependence on said first gap and/or said second gap.

The method may comprise controlling the at least one actuator to adjust the axial position of the orbiting scroll and/or the fixed scroll to set a pre-defined operating clearance (target spacing) between the orbiting scroll and the fixed scroll. Determining the datum and/or adjusting the axial position of the orbiting scroll and/or the fixed scroll may be performed continuously, for example to compensate for component wear. Alternatively, or in addition, determining the datum and/or adjusting the axial position of the orbiting scroll and/or the fixed scroll may be performed in one or more of the following circumstances: during a start-up procedure of the scroll pump; during a calibration process for the scroll pump; at a predefined time interval; and in dependence on a request from an operator or service engineer.

Alternatively, or in addition, the axial position of the orbiting scroll and/or the fixed scroll may be controlled to adjust the clearance between the fixed scroll and the orbiting scroll to control an inlet pressure of the scroll pump, for example to achieve a target or specified inlet pressure.

This may enable the inlet pressure to be optimised. The method may comprise sensing an inlet pressure of the scroll pump.

Alternatively, or in addition, the axial position of the orbiting scroll may be controlled to adjust the clearance between the fixed scroll and the orbiting scroll to reduce or minimise power or to achieve a target or specified power.

According to a further aspect of the present invention there is provided a method of actively configuring a scroll pump, the scroll pump comprising a drive shaft, a fixed scroll and an orbiting scroll; wherein the method comprises: controlling at least one actuator to adjust an axial position of the orbiting scroll and/or the fixed scroll to identify a contact position where the orbiting scroll contacts the fixed scroll; and controlling the at least one actuator in dependence on the identified contact position to adjust a separation between the fixed scroll and the scroll pump.

The method may comprise controlling a plurality of actuators to determine contact positions at a plurality of discrete positions in order to determine the relative orientation of the orbiting scroll and the fixed scroll. The contact position at each of the discrete positions may be determined by monitoring a localized load and/or a load on the respective actuators. The method may comprise controlling the actuators in dependence on the determined relative orientation of the orbiting scroll and the fixed scroll to adjust a relative orientation of the fixed scroll and the scroll pump. The method may comprise controlling the actuators such that the orbiting scroll and the fixed scroll are substantially parallel to each other.

According to a further aspect of the present invention there is provided a method of actively configuring a scroll pump, wherein the scroll pump comprises a drive shaft, a fixed scroll and an orbiting scroll; the method comprising: determining an orientation of the orbiting scroll relative to the fixed scroll; controlling at least one actuator to adjust the orientation of the orbiting scroll and/or the orientation of the fixed scroll such that the orbiting scroll and the fixed scroll are substantially parallel to each other.

The scroll pump may comprise a plurality of the actuators. The method may comprise operating the actuators in turn (i.e. one at a time) to identify a contact position where the orbiting scroll and the fixed scroll contact each other. The scroll pump may be activated and the orbiting scroll displaced along an orbital path. Alternatively, low pressure air may be admitted to an exhaust of the scroll pump to drive the scroll pump in the reverse direction. The actuators may be operated to identify respective contact positions. The orbital motion of the orbiting scroll may stop or slow when the orbiting scroll and the fixed scroll contact each other. The change in the movement of the orbiting scroll may be identified, for example by monitoring a rotational speed of the drive shaft. The contact position between the orbiting scroll and the fixed scroll may thereby be determined. This process may be repeated for each of the actuators. The orientation of the orbiting scroll relative to the fixed scroll may be determined in dependence on the contact positions identified for the respective actuators.

According to a still further aspect of the present invention, there is provided a control unit for controlling a scroll pump to implement the method(s) described herein. The control unit may comprise one or more electronic processors for executing a set of computational instructions to implement the method(s).

Within the scope of this application it is expressly intended that the various aspects, embodiments, examples and alternatives set out in the preceding paragraphs, in the claims and/or in the following description and drawings, and in particular the individual features thereof, may be taken independently or in any combination. That is, all embodiments and/or features of any embodiment can be combined in any way and/or combination, unless such features are incompatible. The applicant reserves the right to change any originally filed claim or file any new claim accordingly, including the right to amend any originally filed claim to depend from and/or incorporate any feature of any other claim although not originally claimed in that manner.

BRIEF DESCRIPTION OF THE DRAWINGS

One or more embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawings, in which: Figure 1 shows a scroll pump in accordance with a first embodiment of the present invention; Figure 2 shows a first flow chart illustrating operation of the scroll pump shown in Figure 1 Figure 3 shows a variant of the scroll pump shown in Figure 1; Figure 4 shows a scroll pump in accordance with a second embodiment of the present invention; Figure 5 shows an end elevation of the orbiting scroll of the scroll pump shown in Figure 4; Figure 6 shows a second flow chart illustrating operation of the scroll pump shown in Figure 4; and Figure 7 shows a variant of the scroll pump shown in Figure 4.

DETAILED DESCRIPTION

A scroll pump 1 in accordance with an embodiment of the present invention is described herein with reference to the Figures 1 and 2. The scroll pump 1 in the present embodiment is a scroll vacuum pump. The scroll pump 1 may, for example, be used in industrial and high vacuum processes The scroll pump 1 is described herein with reference to a longitudinal axis X. References herein to a component or feature extending axially or in an axial direction are to be understood as referring to a direction which is at least substantially coincident with or parallel to the longitudinal axis X. As shown in Figure 1, the scroll pump 1 comprises an orbiting scroll 3 and a fixed scroll 5 disposed in a housing 6. The orbiting scroll 3 and the fixed scroll 5 are configured to cooperate with each other. The orbiting scroll 3 has an orbiting scroll wall 7 extending axially from an orbiting scroll base 9 towards the fixed scroll 5. The orbiting scroll base 9 is generally in the form of a plate or a disc; and has a front face 9a and a rear face 9b. The orbiting scroll wall 7 extends from the front face 9a of the orbiting scroll base 9. The fixed scroll 5 is mounted in a fixed position in the scroll pump 1. The fixed scroll 5 has a fixed scroll wall 11 extending axially from a fixed scroll base 13 towards the orbiting scroll 3. The fixed scroll base 13 has a front face 13a which opposes the front face 9a of the orbiting scroll base 9. The fixed scroll wall 11 extends from the front face 13a of the fixed scroll base 13. The orbiting scroll 3 and the fixed scroll 5 cooperate with each other to form axial seals. In particular, the orbiting scroll wall 7 cooperates with the fixed scroll base 13; and the fixed scroll wall 11 cooperates with the orbiting scroll base 9. The orbiting scroll wall 7 may optionally have a tip seal for sealing against the fixed scroll base 13 to provide an axial seal. The fixed scroll wall 11 may optionally have a tip seal for sealing against the orbiting scroll base 9 to provide an axial seal. In use, the tip seal(s) may be abraded as a result of surface friction. The abrasion of the tip seal(s) may generate contaminating tip seal dust, and when they become too worn require replacement. The requirement for tip seals may be derived in part from the difficulty of setting accurately the spacing between the orbiting scroll 3 and the fixed scroll 5 (i.e. the scroll-toscroll gap). The scroll pump 1 in accordance with the present embodiment does not include tip seals.

The scroll pump 1 comprises a drive shaft 15 and an electric motor 16. The motor 16 is configured to rotate the drive shaft 15. The drive shaft 15 comprises a concentric shaft portion 17 and an eccentric shaft portion 19. The orbiting scroll 3 is fixedly mounted to the drive shaft 15. In particular, the orbiting scroll 3 is fixedly mounted to the eccentric shaft portion 19 of the drive shaft 15. The rotation of the eccentric shaft portion 19 imparts an orbiting motion to the orbiting scroll 3 relative to the fixed scroll 5. The relative motion of the orbiting scroll 3 and the fixed scroll 5 pumps fluid from an inlet disposed in a radially outer position to an outlet disposed at a radially inner position. The drive shaft 15 is supported for rotation by first and second bearings 21, 22. The first and second bearings 21, 22 each comprise a single row bearing. A third bearing 23 supports the orbiting scroll 3. The third bearing 23 in the present embodiment comprises a double row bearing. The first and second bearings 21, 22 constrain the drive shaft 15 to rotate about a rotational axis coincident with the longitudinal axis X. Axial displacement of the drive shaft 15 causes the orbiting scroll 3 (which is mounted on the drive shaft 15) to be displaced relative to the fixed scroll 5. The scroll pump 1 is configured to reduce any such axial movement of the drive shaft 15. It will be understood, however, that axial displacement of the drive shaft 15 still occurs.

An axial spring 25 is provided to apply a first axial force Fl to the concentric shaft portion 17 of the drive shaft 15. The axial spring 25 acts on the second bearing 22 such that the first axial force Fl is applied to the drive shaft 15. The first axial force Fl is applied to the drive shaft 15 in a first direction (to the left in the arrangement shown in Figure 1). The first axial force Fl biases the drive shaft 15 (and the orbiting scroll 3) in said first direction. The first axial force Fl thereby biases the orbiting scroll 3 in an axial direction away from the fixed scroll 5. The axial spring 25 helps to reduce or avoid clashing between the orbiting scroll 3 and the fixed scroll 5, for example during pump start-up when there is insufficient gas pressure to displace the orbiting scroll 3 away from the fixed scroll 5. Alternatively, or in addition, the drive shaft 15 may be biased in an axial direction by pre-loading at least one of the first and second bearings 21, 22, for example with a spring or other biasing means.

The scroll pump 1 comprises a sensor 27 for determining a spacing between the orbiting scroll 3 and the fixed scroll 5. In the present embodiment, the sensor 27 is configured to determine an axial position (or axial displacement) of the orbiting scroll 3. The sensor 27 is configured directly to measure the axial position of the orbiting scroll 3. Specifically, the sensor 27 is configured to measure the axial position of the front face 9a of the orbiting scroll base 9. In a variant, the sensor 27 could be configured to determine the axial position of the orbiting scroll 3 by measuring the axial position of the rear face 9b of the orbiting scroll base 9. In a further variant, the sensor 27 could be configured to determine the axial position of the orbiting scroll 3 indirectly, for example by measuring the axial position of the drive shaft 15. As shown in Figure 1, the sensor 27 is disposed in a central position (proximal to or coincident with the rotational axis of the drive shaft 15). In the present embodiment, the sensor 27 is a displacement sensor, such as a capacitive displacement sensor. The sensor 27 measures the axial displacement of the front face 9a of the orbiting scroll base 9 relative to a datum. Other types of non-contacting displacement sensor may be used, such as an eddy current sensor or an optical sensor. The datum may have a predefined axial position, for example a predefined position on the longitudinal axis X. Alternatively, the datum may define an axial position where the orbiting scroll 3 and the fixed scroll 5 contact each other. The datum may be determined by displacing the orbiting scroll 3 until the scroll wall of one of the orbiting scroll 3 and the fixed scroll 5 contacts a base of the other one of the orbiting scroll 3 and the fixed scroll 5. The sensor 27 is configured to output a displacement signal 'SIN' indicating the axial displacement of the orbiting scroll 3. In a variant, the scroll pump 1 may comprise more than one of the sensors 27.

An actuator 29 is provided for adjusting the axial position of the drive shaft 15, thereby modifying the axial position of the orbiting scroll 3. The actuator 29 in the present embodiment is disposed at a first end of the drive shaft 15 distal from the eccentric shaft portion 19. The actuator 29 in the present embodiment is an electromechanical actuator, such as a solenoid. Other types of actuator are contemplated, such as a hydraulic actuator or a pneumatic actuator. The actuator 29 comprises a drive member 31 operable to generate a second axial force F2 in a second direction (to the right in the arrangement shown in Figure 1). The first bearing 21 transmits the second axial force F2 to the drive shaft 15. The second axial force F2 is applied to the drive shaft 15 to adjust the spacing between the orbiting scroll 3 and the fixed scroll 19. In the present embodiment, the first axial force Fl applied by the axial spring 25 is in opposition to the second axial force F2 applied by the actuator 29. The drive shaft 15 is displaced in the first direction (to the left in the arrangement shown in Figure 1) when the axial force applied by the actuator 29 is less than the first axial force Fl applied by the axial spring 25. The drive shaft 15 is displaced in the second direction (to the right in the arrangement shown in Figure 1) when the axial force applied by the actuator 29 is greater than the first axial force Fl applied by the axial spring 25. The drive shaft 15 is held in a fixed axial position when the axial force applied by the actuator 29 is substantially equal to the first axial force Fl applied by the axial spring 25. Thus, the axial position of the drive shaft 15 (and the orbiting scroll 3) can be adjusted by varying the magnitude of the second axial force F2 applied by the actuator 29. It will be understood that the sensor 27 can monitor the axial position of the drive shaft 15, for example to provide feedback to control operation of the actuator 29. In a variant, a second actuator (not shown) could be provided to generate the first axial force Fl in said first direction. The second actuator could be used in conjunction with, or instead of the axial spring 25. The second actuator could be controlled to adjust the magnitude of the first axial force Fl. In a further variant, an actuator could be provided selectively to apply an axial force in said first and second directions. The magnitude and direction of the axial force could be controlled to displace the drive shaft 15 in either said first direction or said second direction.

In a variant, the actuator 29 could be configured controllably to displace the drive shaft 15 in said first direction to increase a spacing between the orbiting scroll 3 and the fixed scroll 5. In this arrangement, the axial spring 25 could be omitted. The actuator 29 could be controlled to increase or decrease the space between the orbiting scroll 3 and the fixed scroll 5 during a start-up procedure, for example prior to rotation of the drive shaft 15. The actuator 29 could, for example, comprise a pre-loaded bearing that could selectively apply a first axial force Fl in said first direction and a second axial force F2 in said second direction.

A control unit 39 is provided for controlling operation of the actuator 29. The control unit 39 comprises at least one electronic processor 41 and system memory 43. A set of computational instructions is stored in the system memory 43. When executed, the set of computational instructions cause the electronic processor 41 to perform the method(s) described herein. The electronic processor 41 comprises at least one input 45 for receiving the displacement signal SIN output by the sensor 27. The electronic processor 41 comprises at least one output 47 for outputting a control signal SOUT to the actuator 29. As outlined above, the datum represents the position where the orbiting scroll 3 and the fixed scroll 5 are in contact each other. The electronic processor 41 is configured to control a spacing (i.e. an axial gap or an axial separation) between the orbiting scroll 3 and the fixed scroll 5. The electronic processor 41 may, for example, control the axial displacement of the orbiting scroll 3 from the datum (which corresponds to the axial position of the orbiting scroll 3 in contact with the fixed scroll 5). The electronic processor 41 generates the control signal SOUT to adjust the position of the drive shaft 15 to achieve a target spacing (along the longitudinal axis X) between the orbiting scroll 3 and the fixed scroll 5. The target spacing can be achieved by displacing the orbiting scroll 103 a predetermined distance from the identified position where the orbiting scroll 103 and the fixed scroll 105 contact each other. In particular, the control signal SOUT is generated to control the actuator 29 to displace the drive shaft 15 selectively to increase or decrease the spacing. Since the orbiting scroll 3 is mounted on the drive shaft 15, adjusting the position of the drive shaft 15 adjusts the spacing between the orbiting scroll 3 and the fixed scroll 5. The control signal SOUT controls the actuator 29 to adjust the position of the drive shaft 15, thereby selectively increasing or decreasing the spacing between the orbiting scroll 3 and the fixed scroll 5. The control unit 39 thereby controls the spacing between the orbiting scroll 3 and the fixed scroll 5. The clearance between the orbiting scroll 3 and the fixed scroll 5 may thereby be actively controlled. The operating gas pressure in the scroll pump 1 produces a net force that separates the orbiting scroll 3 and the fixed scroll 5. The resulting force can displace the drive shaft 15 on to the actuator 29. The axial spring 25 maintains a load on the second bearing 22 which helps to ensure correct orientation of the drive shaft 15. The axial spring 25 may reduce or prevent radial movement of the drive shaft 15, for example caused by the rotating and orbiting masses being unbalanced.

The operation of the vacuum scroll pump 10 in accordance with the present embodiment will now be described with reference to a first flow chart 100 shown in Figure 2. The scroll pump 1 is activated (BLOCK 105). The drive shaft 15 is displaced in said first direction by the first axial force Fl (applied by the axial spring 25), thereby reducing or avoiding clashing of the orbiting scroll 3 and the fixed scroll 5. The control of the actuator 29 during start-up is appropriate since the working pressures in the scroll pump 1 may not be sufficient to displace the orbiting scroll 3 away from the fixed scroll 5. The electric motor 16 is energized to rotate the drive shaft 15 (BLOCK 110). The sensor 27 measures the axial displacement of the orbiting scroll base 9 and determines the axial position of the orbiting scroll 3 (BLOCK 115). The sensor 27 outputs the displacement signal SIN to the control unit 39 (BLOCK 120). The control unit 39 determines if the axial position of the drive shaft 15 should be adjusted to increase or decrease the spacing between the orbiting scroll 3 and the fixed scroll 5 (BLOCK 125). The control unit 39 may, for example, determine if the axial displacement of the drive shaft 15 is greater than or less than a predetermined value (BLOCK 130). The control unit 39 generates and outputs the control signal SOUT to control operation of the actuator 29 (BLOCK 135). The control signal SOUT may, for example, cause the actuator 29 to increase or decrease the second axial force F2 applied to the drive shaft 14. The sensor 27 continues to measure the axial displacement of the orbiting scroll base 9 and output the displacement signal SIN to the control unit 39. The sensor 27 provides feedback which allows active control of the space between the orbiting scroll 3 and the fixed scroll 5. The process continues until the scroll pump 1 is deactivated (BLOCK 140). During the shut-down procedure, the control unit 39 may optionally generate a control signal SOUT to control the actuator 29 to reduce or remove the second axial force F2, such that the drive shaft 15 is displaced axially by the axial spring to increase the space between the orbiting scroll 3 and the fixed scroll 5.

The scroll pump 1 described herein may be referred to as having a forward scroll arrangement.

In particular, the drive shaft is connected to the orbiting scroll without passing through the fixed scroll. In a reverse scroll arrangement, the drive shaft extends through a central opening or aperture formed in the fixed scroll and is connected to the orbiting scroll on an opposing or distal side of the fixed scroll from the motor. The present invention(s) is applicable also in a reverse scroll arrangement.

The scroll pump 1 has been described with reference to adjusting the axial position of the orbiting scroll 3. Alternatively, or in addition, the axial position of the fixed scroll 5 can be adjusted. In this variant, the fixed scroll 5 may be fixed to the extent that it does not rotate or follow an orbiting path. However, the axial position of the fixed scroll 5 is adjustable, for example by one or more actuators. A schematic representation of this variant is shown in Figure 3. Like reference numerals are used for like components.

The scroll pump 1 in this variant is configured such that the axial position of the fixed scroll 5 can be adjusted. The actuator 29 is configured controllably to apply the second force F2 to the fixed scroll 5 to adjust the axial position of the fixed scroll 5. The sensor 27 is configured to measure the axial position of the orbiting scroll 3 and/or the fixed scroll 5. The control unit 39 generates and outputs the control signal SOUT to control operation of the actuator 29. The spacing between the orbiting scroll 3 and the fixed scroll 5 can be adjusted. For example, the axial position of the fixed scroll 5 can be adjusted to provide a target spacing between the orbiting scroll 3 and the fixed scroll 5. The control unit 39 is configured to output the control signal SOUT to control operation of the actuator 29 so as to adjust the axial position of the fixed scroll 5.

The actuator 29 in the variant shown in Figure 3 may be configured to advance and retract the fixed scroll 5. Alternatively, or in addition, a biasing means (not shown) may be provided to apply a biasing force in the opposite direction to the second force F2. The biasing means may, for example, comprise one or more spring member for applying a biasing force to the fixed scroll 5.

In a further variant, the sensor 27 may be a first sensor which directly measures a first gap between the orbiting scroll wall 7 and the fixed scroll base 13; and/or a second sensor (not shown) may directly measure a second gap between the fixed scroll wall 11 and the orbiting scroll base 9. The first sensor 27 may output a first gap signal indicating the first gap; and/or the second sensor may output a second gap signal indicating the second gap. The axial displacement of the orbiting scroll 3 and/or the fixed scroll 5 in dependence on one or both of the measured gaps. For example, the axial displacement may be controlled in dependence on an average of the first and second gaps. The control unit 39 may be configured to control operation of the actuator 29 in dependence on said first gap signal and/or said second gap signal. Alternatively, the axial displacement may be controlled in dependence on a minimum of the first gap and/or the second gap.

A scroll pump 101 in accordance with a further embodiment of the present invention will now be described with reference to Figures 4, 5 and 6. The scroll pump 101 comprises a reverse scroll arrangement. Like reference numerals are used for like components, albeit incremented by 100 to aid clarity.

As shown in Figure 4, the scroll pump 101 comprises an orbiting scroll 103 and a fixed scroll 105 disposed in a housing 106. As described herein, the orientation of the orbiting scroll 103 can be adjusted such that the orbiting scroll 103 and the fixed scroll 105 are disposed at least substantially parallel to each other. Thus, in the present embodiment, the orbiting scroll 103 can be levelled with respect to the fixed scroll 105 (i.e. made parallel to the fixed scroll 105). The orbiting scroll 103 and the fixed scroll 105 are configured to cooperate with each other.

The orbiting scroll 103 has an orbiting scroll wall 107 extending axially from an orbiting scroll base 109 towards the fixed scroll 105. The orbiting scroll base 109 is generally in the form a plate or a disc; and has a front face 109a and a rear face 109b. The orbiting scroll wall 107 extends from the front face 109a of the orbiting scroll base 109. The fixed scroll 105 has a fixed scroll wall 111 extending axially from a fixed scroll base 113 towards the orbiting scroll 103. The fixed scroll base 113 has a front face 113a which opposes the front face 109a of the orbiting scroll base 109. The fixed scroll wall 111 extends from the front face 113a of the fixed scroll base 113.

The orbiting scroll 103 is mounted on a drive shaft 115 which is driven by an electric motor 116. The drive shaft 115 comprises a concentric shaft portion 117 and an eccentric shaft portion 119. The concentric shaft portion 117 has a rotational axis which is substantially coincident with the longitudinal axis X of the scroll pump 101. The orbiting scroll 103 is mounted on the eccentric shaft portion 119 and follows an orbital path around the longitudinal axis X. As shown in Figure 4, the positioning and orientation of the orbiting scroll 103 and the fixed scroll 105 in relation to the electric motor 116 is reversed compared to that of the scroll pump 1 in the previous embodiment. The fixed scroll 105 is mounted in a fixed position. The fixed scroll 105 is disposed proximal to the electric motor 116 and the drive shaft 115 extends through a central aperture 149. The drive shaft 115 is supported for rotation by first and second bearings 121, 122. The first and second bearings 121, 122 each comprise a single row bearing. The first and second bearings 121, 122 support the concentric shaft portion 117. A third bearing 123 is located on the eccentric shaft portion 119 to support the orbiting scroll 105. The third bearing 123 is located concentrically on the eccentric shaft portion 119 and supports the orbiting scroll 103.

An axial spring assembly 125 is provided to apply a first axial force Fl to a first end of the drive shaft 15. The axial spring assembly 125 acts on an outer ring of the first (rear) bearing 121 which does not rotate. The axial spring assembly 125 comprises one or more springs for generating the first axial force Fl. The first axial force Fl is applied to the drive shaft 15 in a first direction (to the right in the arrangement shown in Figure 4). The first axial force Fl biases the drive shaft 15 (and the orbiting scroll 3) in said first direction to bias the orbiting scroll 3 away from the fixed scroll 5.

The scroll pump 101 comprises a plurality of sensors 127-n for determining a spacing between the orbiting scroll 3 and the fixed scroll 5. The sensors 127-n are configured to determine an axial position of the orbiting scroll 3. The sensors 127-n are also operable to determine an orientation of the orbiting scroll 103. The orientation of the orbiting scroll 103 may be determined in relation to the fixed scroll 105. For example, the orientation of the orbiting scroll 103 may be determined in relation to a reference plane extending perpendicular to the longitudinal axis X of the scroll pump 101. The reference plane may, for example, correspond to a plane of a front face 113a of the fixed scroll 105. In the present embodiment, the sensors 127-n each measure an axial displacement of the orbiting scroll 103 at a fixed location. The measurements performed by each sensor 127-n may be referred to as a local axial displacement. By comparing the local axial displacement at a plurality of locations, preferably two (2), three (3) or more locations, the orientation and/or the axial position of the orbiting scroll 103 can be determined. The orbiting scroll 103 is at least substantially aligned with the reference plane when the sensors 127-n measure the same axial displacement. The orbiting scroll 103 can be actively aligned with the reference plane. Alternatively, or in addition, the sensors 127-n may determine an axial position (or axial displacement) of the orbiting scroll 103.

As shown in Figure 5, the sensors 127-n are angularly spaced apart from each other around the longitudinal axis X. In the present embodiment, there are three (3) sensors 127-1, 127-2, 127-3 having a uniform angular spacing (corresponding to a pitch of 1200 in the present embodiment). It will be understood that there may be one (1) sensor 127-n, two (2) sensors 127-n or more than three (3) of the sensors 127-n. Each of the sensors 127-n is configured to measure the axial position (or axial displacement) of the rear face 109b of the orbiting scroll base 109. By determining the axial position at different locations on the rear face 109b of the orbiting scroll base 109, the orientation of the orbiting scroll 103 can be determined in two dimensions or three dimensions. In the present embodiment, the local axial displacement of the orbiting scroll 103 is measured at three (3) locations to enable determination of the orientation of the orbiting scroll 103 in three dimensions. In the present embodiment, the sensors 127-n are displacement sensors which measure the local axial displacement of the rear face 9b of the orbiting scroll base 9 relative to a predetermined datum. The sensors 127n may be contact sensors, but preferably they are non-contacting sensors, such as capacitive displacement sensors. Other types of sensor are also contemplated, such as eddy current sensors or optical sensors. The number of sensors 127-n required to determine the orientation of the orbiting scroll 103 may be reduced, for example using one or more scanning sensors (such as an optical scanning sensor) to measure axial displacement. The scroll pump 101 may optionally comprise one or more sensor for measuring the orientation of the orbiting scroll base 109.

The scroll pump 101 comprises a plurality of actuators 129-n for selectively adjusting the axial position of the drive shaft 115, thereby modifying the axial position of the orbiting scroll 103.

In the present embodiment, there are three (3) actuators 129-1, 129-2, 129-3 having a uniform angular spacing (corresponding to a pitch of 120° in the present embodiment). Each of the actuators 129-n is associated with a respective one of the sensors 127-n. The sensors 127-n and the actuators 129-n have at least substantially the same angular spacing. As shown in Figure 5, the sensors 127-n and the actuators 129-n are angularly aligned with each other. As described herein, the actuators 129-n are controlled such that at least substantially the same axial displacement is measured by each of the sensors 127-n. It will be understood that the sensors 127-n and the actuators 129-n could be radially offset from each other, and/or angularly offset from each other (i.e. separated in a circumferential direction). A transform may be applied to determine appropriate control parameters for the actuators 129-n to adjust the axial position of the orbiting scroll 103 to achieve a target separation between the orbiting scroll 103 and the fixed scroll 105.

As shown in Figure 4, the actuators 129-n are configured to co-operate with the rear face 109b of the orbiting scroll base 109. Each of the actuators 129-n is configured to apply a second axial force F2-n in a second direction (to the left in the arrangement shown in Figure 4) to the rear face 109b of the orbiting scroll base 109. The second axial force F2-n is applied in opposition to the first axial force Fl applied by the axial spring assembly 125. The actuators 129-n in the present embodiment each comprise an electromechanical actuator, such as a solenoid. Other types of actuator are contemplated, such as a hydraulic actuator or a pneumatic actuator. The actuators 129-n each comprise a drive member 131 operable to generate the second axial forces F2-n. A thrust bearing assembly 135 is provided to transmit the second axial forces F2-n generated by the actuators 129-n to the orbiting scroll base 109. The thrust bearing assembly 135 comprises a plurality of axial thrust bearings 137-n each associated with one of the actuators 129-n. The axial thrust bearings 137-n may be incorporated into the actuators 129-n or may be a separate component. In the present embodiment, the axial thrust bearings 137-n each comprise a ball bearing which rolls over the rear face 109b of the orbiting scroll base 109 whilst applying a thrust force. The ball bearings in the present embodiment are spherical, but other geometric shapes may be used to perform this function. The second axial forces F2-n are applied to the orbiting scroll base 109 to adjust the orientation and/or the axial position of the orbiting scroll 103. To adjust the axial position of the orbiting scroll 103, the actuators 129-n are controlled to apply substantially equal second axial forces F2-n to the orbiting scroll base 109. The application of substantially equal forces F2-n to the orbiting scroll base 109 displaces the orbiting scroll 103 in a substantially axial direction. It will be understood that the second axial forces F2-n can be controlled to adjust one or both of the orientation and the axial position of the orbiting scroll 103.

The axial thrust bearings 137-n are provided to transmit the second axial forces F2-n generated by the actuators 129-n to the orbiting scroll base 109. The axial thrust bearings 137-n comprise ball bearings which are retained in position relative to the orbiting scroll 103. A retainer may be provided to retain the ball bearings in position. The retainer in the present embodiment comprises a retaining ring 151. The retaining ring 151 is annular and comprises a plurality of retaining portions for at least partially receiving respective ball bearings. The retaining portions each comprise a cup or a recess formed in a surface of the retaining ring 151 and facing towards the orbiting scroll 103. The back face 113b of the orbiting scroll 103 comprises a substantially planar surface over which the ball bearings describe a circular path and are retained by the retaining ring 138. Other types of axial thrust bearings 137-n are contemplated for transmitting the second axial forces F2-n to the orbiting scroll base 109.

A control unit 139 is provided for controlling operation of the actuators 129-n. The control unit 139 has the same composition as the control unit 39 described in respect of the previous embodiment. The control unit 139 comprises an electronic processor 141 and system memory 143. The electronic processor 41 comprises a plurality of inputs 145 for receiving displacement signals SIN-n output by the respective sensors 127-n. The electronic processor 141 comprises at least one output 147 for outputting control signals SOUT-n to the respective actuators 129n. The electronic processor 141 is configured to determine the orientation of the orbiting scroll 103; and/or the axial position of the orbiting scroll 103 relative to the fixed scroll 105. The electronic processor 41 generates the control signals SOUT-n to adjust the orientation and/or the position of the orbiting scroll 103. The control signals SOUT-n controls one or more of the actuators 129-n to adjust the orientation and/or the axial position of the orbiting scroll 103. The axial clearance between the orbiting scroll 103 and the fixed scroll 105 and/or the orientation of the orbiting scroll 3 and the fixed scroll 5 may be actively controlled.

The operation of the vacuum scroll pump 101 in accordance with the present embodiment will now be described with reference to a second flow chart 200 shown in Figure 6. The scroll pump 101 is activated (BLOCK 205). The drive shaft 115 is displaced in said first direction by the first axial force Fl (applied by the axial spring assembly 125), thereby reducing or avoiding clashing of the orbiting scroll 103 and the fixed scroll 105. The electric motor 116 is energized to rotate the drive shaft 115 (BLOCK 210). The sensors 127-n measure the axial displacement of the orbiting scroll base 109 at different circumferential locations (BLOCK 215). The control unit 139 determines the orientation of the orbiting scroll 103 and/or the axial position of the orbiting scroll 103 (BLOCK 220). The control unit 139 determines if the actuators 129-n should be operated to adjust the orientation of the orbiting scroll 103 and/or adjust the spacing between the orbiting scroll 103 and the fixed scroll 105 (BLOCK 225). The control unit 139 may, for example, compare the axial displacement measured by each sensor 127-n to the predetermined datum(s) (BLOCK 230). The control unit 39 outputs control signals SOUT-n to control operation of each actuator 129-n (BLOCK 235). One or more of the actuators 129 may be operated to adjust the axial position of the orbiting scroll 103 and/or the orientation of the orbiting scroll 103. The control signals SOUT-n may cause the actuators 129-n to increase or decrease the second axial force F2-n applied at the respective locations on the orbiting scroll base 109. The process continues until the scroll pump 101 is deactivated (BLOCK 240). During the shut-down procedure, the control unit 139 may optionally generate a control signal SOUT-n to control the actuators 129 to reduce or remove the second axial force F2-n, such that the drive shaft 115 is displaced axially by the axial spring assembly 125 to increase the space between the orbiting scroll 3 and the fixed scroll 5.

The control unit 139 controls the actuators 129-n to adjust the spacing between the orbiting scroll 103 and the fixed scroll 105. The control unit 139 compares the axial displacement measured by each sensor 127-n to a datum (or reference position). The datum may be predefined, for example in dependence on a known position of the sensors 127-n within the scroll pump 101. Alternatively, the control unit 139 may determine the datum, for example during a calibration process. The control unit 139 may be configured to determine a contact relationship between the orbiting scroll 103 and the fixed scroll 105. The control unit 139 may determine the datum by controlling the actuators 129-n to adjust the axial position of the orbiting scroll 103 until the scroll wall of at least one of the orbiting scroll 103 and the fixed scroll 105 contacts the scroll base of the other of said orbiting scroll 103 and the fixed scroll 105. A load on each actuator 129-n may be monitored to determine when contact occurs. For example, an increase in the electrical load on each actuator 129-n may indicate that the orbiting scroll 103 and the fixed scroll 105 are in contact with each other. Alternatively, or in addition, one or more load sensors may be provided to determine when contact occurs. The datum may be defined in dependence on the determined contact relationship. The control unit 139 may determine the datum following installation of the scroll pump 101. Alternatively, or in addition, the control unit 139 may determine the datum during a start-up procedure.

The actuators 129-n may be controlled with reference to the datum. The control unit 139 may control one or more of the actuators 129-n to displace the orbiting scroll 103 relative to the fixed scroll 104 to control the spacing between the orbiting scroll 103 and the fixed scroll 105. The control unit 139 may thereby control the axial position of the orbiting scroll 103 to set or maintain a target spacing between the orbiting scroll 103 and the fixed scroll 105. The target spacing can be achieved by displacing the orbiting scroll 103 a predetermined distance from the identified position where the orbiting scroll 103 contacts the fixed scroll 105. The spacing between the orbiting scroll 103 and the fixed scroll 105 may be less than 20 microns and preferably between about five (5) and fifteen (15) microns. The spacing between the scrolls is selected so that the running clearance is as small as possible to reduce leakage across the scroll walls (between the scroll walls and the opposing scroll base) but sufficient to avoid clashing when the orbiting scroll deflects and to allow for thermal expansion. In one example, the end surface of one or both scroll walls has a PTFE or filled PTFE coating. The coating may have a thickness in the region of 25pm. Such a coating protects the scrolls if there is any contact in use and also reduces friction during any such contact. In another example, the ends of the scroll walls are not coated. By way of example, an aluminium scroll may be hard anodised.

When in use there is thermal expansion of components of the pump with increased operating temperature, particularly the orbiting scroll, even though the materials of the components are chosen for low thermal expansion. For example, the scrolls may be made of aluminium. The spacing selected between the scrolls takes account of thermal expansion so that the scrolls do not clash, or contact, in use. However, it is desirable as discussed above to maintain this spacing to minimum practical. Initially therefore, prior to thermal expansion, there is a gap between the scrolls allowing some leakage across the scroll walls. After thermal expansion the gap between scrolls is reduced. The control unit 139 in the present embodiment may adjust the axial position of the orbiting scroll 103 actively to adjust the scroll-to-scroll spacing between the orbiting scroll 103 and the fixed scroll 105. The control unit 139 may, for example, adjust the spacing in dependence on an operating temperature of the scroll pump 101. It will be understood that this form of active control may also be employed in the scroll pump 1 according the above embodiment.

The scroll pump 101 has been described herein as comprising three sensors 127-n and three actuators 129-n. It will be understood that the scroll pump 101 could utilise three or more sensors 127-n and actuators 129-n. In a further variant, the scroll pump 101 may comprise different numbers of sensors 127-n and actuators 129-n. There may be more sensors 127-n than actuators 129-n or fewer sensors 127-n than actuators 129-n The scroll pump 101 has been described with reference to adjusting the axial position and/or the orientation of the orbiting scroll 103. In a variant, the axial position and/or the orientation of the fixed scroll 105 can be adjusted. In this variant, the fixed scroll 105 is fixed to the extent that it does not rotate or follow an orbiting path. However, the axial position and/or the orientation of the fixed scroll 105 can be controllably adjusted, for example by one or more actuators 129. A schematic representation of this variant is shown in Figure 7. Like reference numerals are used for like components.

The scroll pump 101 in this variant is configured such that the axial position and the orientation of the fixed scroll 105 can be adjusted. The actuators 129 are configured controllably to apply the second forces F2-n to the fixed scroll 105 to adjust the axial position and/or the orientation of the fixed scroll 105. The sensors 127 are configured to measure the axial position of the fixed scroll 5. The control unit 139 generates and outputs the control signals SOUT-n to control operation of the respective actuators 129. The spacing between the orbiting scroll 103 and the fixed scroll 105 can be adjusted. For example, the axial position of the fixed scroll 5 can be adjusted to provide a target spacing between the orbiting scroll 3 and the fixed scroll 5.

Alternatively, or in addition, the orientation of the fixed scroll 105 can be adjusted. For example, the orientation of the fixed scroll 105 can be adjusted such that the orbiting scroll 103 and the fixed scroll 105 are substantially parallel to each other. The control unit 139 is configured to output the control signal SOUT-n to control operation of the actuators 129-n so as to adjust the axial position and/or the orientation of the fixed scroll 105.

The actuators 129 in the variant shown in Figure 7 may be configured to advance and retract the fixed scroll 105. Alternatively, or in addition, a biasing means (not shown) may be provided to apply a biasing force in the opposite direction to the second forces F2-n. The biasing means may, for example, comprise one or more spring member for applying a biasing force to the fixed scroll 105.

It will be appreciated that various changes and modifications can be made to the present invention without departing from the scope of the present application.

Reference Numerals 1 Scroll Pump 101 Scroll Pump 3 Orbiting Scroll 103 Orbiting Scroll Fixed Scroll 105 Fixed Scroll 6 Housing 106 Housing 7 Orbiting Scroll Wall 107 Orbiting Scroll Wall 9 Orbiting Scroll Base 109 Orbiting Scroll Base 9a Orbiting Scroll Base Front Face 109a Orbiting Scroll Base Front Face 9b Orbiting Scroll Base Rear Face 109b Orbiting Scroll Base Rear Face 11 Fixed Scroll Wall 111 Fixed Scroll Wall 13 Fixed Scroll Base 113 Fixed Scroll Base 13a Fixed Scroll Base Front Face 113a Fixed Scroll Base Front Face Drive Shaft 115 Drive Shaft 16 Electric Motor 116 Electric Motor 17 Concentric Shaft Portion 117 Concentric Shaft Portion 19 Eccentric Shaft Portion 119 Eccentric Shaft Portion 21 First Bearing 121 First Bearing 22 Second Bearing 122 Second Bearing 123 Third Bearing Axial Spring 125 Axial Spring Assembly 27 Displacement Sensor 127-n Displacement Sensor 29 Actuator 129-n Actuator 31 Drive Member 131 Drive Member Thrust bearing assembly 137-n Axial thrust bearing 39 Control Unit 139 Control Unit 41 Electronic Processor(s) 141 Electronic Processor(s) 43 System Memory 143 System Memory Input 145-n Input 47 Output 147-n Output 149 Central Aperture 151 Retaining Ring

FLOW CHART LABELS

First Flow Chart (100) Activate scroll pump Rotate drive shaft Measure axial displacement of drive shaft Determine axial position of orbiting scroll Determine if adjustment of axial displacement appropriate Compare determined axial displacement to predetermined datum Output actuator control signal Deactivate scroll pump Second Flow Chart (200) 205 Activate scroll pump 210 Rotate drive shaft 215 Measure axial displacement of the orbiting scroll at different locations 220 Determine orientation and/or axial position of orbiting scroll 225 Determine if adjustment of orientation and/or axial displacement appropriate 230 Compare determined axial displacements to predetermined datum 235 Output actuator control signals 240 Deactivate scroll pump

Claims

CLAIMS1. A scroll pump (1; 101) comprising: an axially extending drive shaft (15; 115) having an eccentric shaft portion (19; 119); a fixed scroll (5; 105) having a fixed scroll wall (11; 111) extending axially from a fixed scroll base (13; 113); an orbiting scroll (3; 103) having an orbiting scroll wall (7; 107) extending axially from an orbiting scroll base (9; 109) towards the fixed scroll (5; 105), the orbiting scroll (3; 103) being disposed on the eccentric shaft portion (119) of the drive shaft (15; 115); and at least one actuator (29; 129-n) for adjusting the axial position of the orbiting scroll (3; 103) and/or the fixed scroll (5; 105) in dependence on a determined spacing between the orbiting scroll (3; 103) and the fixed scroll (5; 105).
2. A scroll pump (1; 101) as claimed in claim 1, wherein the at least one actuator (29; 129-n) is configured to adjust the axial position of the orbiting scroll (3; 103) and/or the axial position of the fixed scroll (5; 105) to achieve a target spacing between the orbiting scroll (3; 103) and the fixed scroll (5; 105).
3. A scroll pump (1; 101) as claimed in claim 1 or claim 2, wherein determining the spacing between the orbiting scroll (3; 103) and the fixed scroll (5;105) comprises: operating the at least one actuator (29-n; 129-n) to axially displace one of the orbiting scroll (3; 103) and the fixed scroll (5; 105) relative to the other one of the orbiting scroll (3; 103) and the fixed scroll (5; 105); and determining a position where the orbiting scroll (3; 103) and the fixed scroll (5; 105) contact each other.
4. A scroll pump (1; 101) as claimed in any one of claims 1, 2 or 3 comprising at least one sensor (27; 127-n) for determining the spacing between the orbiting scroll (3; 103) and the fixed scroll (5; 105); wherein the or each sensor (27; 127-n) is configured to determine: an axial position of the orbiting scroll (3; 103); and/or an axial position of the fixed scroll (5; 105).
5. A scroll pump (1; 101) as claimed in claim 4 comprising a control unit (39; 139) for controlling the at least one actuator (29; 129-n); wherein the or each sensor (27; 127-n) is configured to output at least one displacement signal (SIN) and the control unit (39; 139) is configured to control the at least one actuator (29; 129-n) in dependence on the at least one displacement signal (SIN).
6. A scroll pump (1; 101) as claimed in any one of the preceding claims, wherein the at least one actuator (29; 129-n) is configured to act on the orbiting scroll (3; 103) or the fixed scroll (5; 105).
7. A scroll pump (1; 101) as claimed in claim 6 comprising an axial thrust bearing assembly (137-n) for transmitting an axial force (F2-n) generated by the at least one actuator (129-n) to the orbiting scroll (103).
8. A scroll pump (101) comprising: an axially extending drive shaft (115) having an eccentric shaft portion (119); a fixed scroll (105) having a fixed scroll wall (111) extending axially from a fixed scroll base (113); an orbiting scroll (103) having an orbiting scroll wall (107) extending axially from an orbiting scroll base (109) towards the fixed scroll (105), the orbiting scroll (103) being disposed on the eccentric shaft portion (119) of the drive shaft (115); and at least one actuator (129-n) for adjusting the orientation of the orbiting scroll (103) and/or the fixed scroll (105) in dependence on a determined orientation of the orbiting scroll (103) relative to the fixed scroll (105).
9. A scroll pump (101) as claimed in claim 8, wherein the at least one actuator (129-n) is configured to adjust the orientation of the orbiting scroll (103) and/or the orientation of the fixed scroll (5; 105) such that the orbiting scroll (3; 103) and the fixed scroll (5; 105) are substantially parallel to each other.
10. A scroll pump (101) as claimed in claim 8 or claim 9 comprising at least one sensor (127-n) for determining an orientation of the orbiting scroll (103) and/or an orientation of the fixed scroll (105).
11. A scroll pump (101) as claimed in claim 10 comprising a control unit (139) for controlling the at least one actuator (129-n), wherein the or each sensor (127-n) is configured to output a displacement signal (SIN-n), the control unit (139) being configured to control the at least one actuator (129-n) in dependence on the displacement signal(s) (SIN-n).
12. A scroll pump (101) as claimed in any one of claims 8 to 11 comprising a plurality of the actuators (129-n), the actuators (129-n) being spaced apart angularly from each other about a rotational axis of the drive shaft (115).
13. A scroll pump (101) as claimed in claim 12, wherein determining the orientation of the orbiting scroll (103) relative to the fixed scroll (105) comprises: sequentially operating each of the actuators (129-n) to adjust the orientation of one of the orbiting scroll (103) and the fixed scroll (105), and determining an axial position where the orbiting scroll (103) and the fixed scroll (105) contact each other as each actuator (129-n) is operated.
14. A scroll pump (101) as claimed in any one of claims 8 to 13, wherein the or each actuator (129-n) is configured to apply a force (F2-n) to a thrust bearing assembly (135) associated with the orbiting scroll wall (107).
15. A method of actively configuring a scroll pump (1; 101), the scroll pump (1; 101) comprising a drive shaft (15; 115), a fixed scroll (5; 105) and an orbiting scroll (3; 103); wherein the method comprises: determining a spacing between the orbiting scroll (3; 103) and the fixed scroll (5; 105); and controlling at least one actuator (29; 129-n) to adjust the axial position of the orbiting scroll (3; 103) and/or the fixed scroll (5; 105) to achieve a target spacing between the orbiting scroll (3; 103) and the fixed scroll (5; 105).
16. A method of actively configuring a scroll pump (101), wherein the scroll pump (101) comprises a drive shaft (115), a fixed scroll (105) and an orbiting scroll (103); the method comprising: determining an orientation of the orbiting scroll (103) relative to the fixed scroll (105); controlling at least one actuator (129-n) to adjust the orientation of the orbiting scroll (103) and/or the orientation of the fixed scroll (5; 105) such that the orbiting scroll (3; 103) and the fixed scroll (5; 105) are substantially parallel to each other.