Vacuum Pump

Abstract

A dry pump comprises a stator housing a rotor assembly comprising intermeshing rotor components defining a running clearance with a surface of the stator, means for applying a transient magnetic force to at least one magnetic member of the rotor assembly to move the rotor components away from the stator surface and increase the size of the running clearance to reduce a frictional force applied to the rotor components by particulates accumulated within the running clearance, and means for moving the rotor components back towards the stator surface upon reduction of the magnetic force.

1 . A dry pump comprising a stator housing a rotor assembly comprising: intermeshing rotor components; and means for applying a transient magnetic force to at least one magnetic member of the rotor assembly to effect axial movement of the rotor components within the stator to vary at least one clearance between the rotor components and the stator. 
   
   
       2 . The pump according to  claim 1 , wherein the magnetic force applying means is arranged to move the rotor assembly to increase the distance between a surface of the rotor components and a surface of the stator. 
   
   
       3 . The pump according to  claim 2 , wherein the magnetic force applying means is arranged to move the rotor components away from a location proximate the surface of the stator, the pump comprising means for returning the rotor components to said location upon cessation or reduction of the magnetic force. 
   
   
       4 . A dry pump having a stator housing a rotor assembly comprising: intermeshing rotor components defining a running clearance with a surface of the stator; means for applying a transient magnetic force to at least one magnetic member of the rotor assembly to move the rotor components away from the stator surface and increase the size of the running clearance to reduce a frictional force applied to the rotor components by particulates accumulated within the running clearance; and means for moving the rotor components back towards the stator surface upon reduction of the magnetic force. 
   
   
       5 . The pump according to  claim 3  wherein the returning means comprises means for biasing the rotor components towards the stator surface. 
   
   
       6 . The pump according to  claim 5  wherein the rotor assembly comprises a bearing assembly for supporting the rotor assembly within the housing, and wherein the biasing means is arranged to apply a biasing force to the bearing assembly. 
   
   
       7 . The pump according to  claim 6  wherein the biasing means comprises a resilient member located between the bearing assembly and a fixed member mounted on or integral with the stator. 
   
   
       8 . The pump according to  claim 6  wherein the mean value of the magnetic force applied to the rotor assembly is approximately equal to the biasing force applied to the rotor assembly. 
   
   
       9 . The pump according  claim 1  wherein the magnetic force applying means is arranged to apply a pulsed magnetic field to said at least one magnetic member of the rotor assembly. 
   
   
       10 . The pump according to  claim 9  wherein the magnetic force applying means comprises an electromagnet and means for supplying a time variant current to the electromagnet to generate the pulsed magnetic field. 
   
   
       11 . The pump according to  claim 1  wherein the magnetic force applying means comprises at least one permanent magnet, and means for moving said at least one permanent magnet relative to said at least one magnetic member of the rotor assembly. 
   
   
       12 . The pump according to  claim 11  wherein said at least one magnetic member of the rotor assembly comprises a gear assembly for transmitting torque between shafts of the rotor assembly. 
   
   
       13 . The pump according to  claim 11  wherein said at least one magnetic member of the rotor assembly comprises at least one disc mounted on the rotor assembly. 
   
   
       14 . The pump according to  claim 13  comprising control means for actuating said magnetic force applying means. 
   
   
       15 . The pump according to  claim 14  wherein the control means is arranged to actuate said magnetic force applying means in dependence on an operating characteristic of the pump. 
   
   
       16 . The pump according to  claim 15  wherein the control means is arranged to actuate said magnetic force applying means periodically during use of the pump. 
   
   
       17 . The pump according to  claim 3  further comprising additional means for applying a transient magnetic force to at least one magnetic member of the rotor assembly to effect radial movement of the rotor components within the stator. 
   
   
       18 . A vacuum pump comprising: a stator housing a rotor assembly defining a running clearance with a surface of the stator; means for applying a transient magnetic force to at least one magnetic member of the rotor assembly to move the rotor assembly away from the stator surface and increase the size of the running clearance to reduce a frictional force applied to the rotor assembly by particulates accumulated within the running clearance; and means for moving the rotor assembly back towards the stator surface upon reduction of the magnetic force. 
   
   
       19 . (canceled) 
   
   
       20 . A vacuum pump comprising: a stator housing a rotor assembly defining a running clearance with a surface of the stator; means for applying a magnetic force to at least one magnetic member of the rotor assembly for a period of time to heat the rotor assembly and increase the size of the running clearance to reduce a frictional force applied to the rotor assembly by particulates accumulated within the running clearance. 
   
   
       21 . A method of starting a pump, the pump comprising a stator housing a rotor assembly defining a running clearance with a surface of the stator, the method comprising the steps of: applying a magnetic force to at least one magnetic member of the rotor assembly to heat the rotor assembly to increase the size of the running clearance and reduce a frictional force applied to the rotor assembly by particulates accumulated within the running clearance; and subsequently rotating the rotor assembly. 
   
   
       22 . The method according to  claim 21  wherein the step of applying a magnetic force is applied for a period of time, and after the period of time has elapsed, applying a transient magnetic force to the at least one magnetic member of the rotor assembly to move the rotor assembly away from the stator surface and increase the size of the running clearance, and subsequently moving the rotor assembly back towards the stator surface upon a reduction of the transient magnetic force. 
   
   
       23 . The pump according to  claim 4  wherein the returning means comprises means for biasing the rotor components towards the stator surface. 
   
   
       24 . The pump according  claim 4  wherein the magnetic force applying means is arranged to apply a pulsed magnetic field to said at least one magnetic member of the rotor assembly. 
   
   
       25 . The pump according to  claim 23  wherein the magnetic force applying means comprises at least one permanent magnet, and means for moving said at least one permanent magnet relative to said at least one magnetic member of the rotor assembly.