Rotary vacuum pump, structure and method for the balancing thereof

Abstract

A rotary vacuum pump ( 101; 201 ) comprising displacement sensors ( 121 A- 121 F; 221 A- 221 F), variously coupled to the pump basement ( 103; 203 ) and arranged close to the pump rotor ( 113; 213 ) and/or to the rotating shaft ( 105; 205 ) thereof, the sensors being turned towards it (them) and being perpendicular thereto, in order to detect non-homogeneous distributions, if any, of masses of said rotor ( 113; 213 ) with respect to its rotation axis. The invention also relates to a structure for and a method of balancing a rotary pump.

1 . A rotary vacuum pump ( 101 ;  201 ) comprising a stationary portion ( 103 ;  203 ) and a portion rotating relative to said stationary portion, the rotating portion comprising a rotating shaft ( 105 ;  205 ) equipped with a rotor assembly ( 113 ;  213 ), driven by an electric motor ( 111 ;  211 ) and supported by at least one rolling mechanical bearing ( 107 ;  207 ) relative to said stationary portion, the rotary pump comprising: 
 at least two displacement sensors ( 121 A- 121 D;  221 A- 221 B) positioned between said stationary portion and said rotating portion for generating an electrical signal varying with a distance variation between said stationary portion and said rotating portion during the rotation of said shaft and said rotor assembly.    
   
   
       2 . The rotary vacuum pump as claimed in  claim 1 , wherein the pump ( 101 ) further comprises: 
 a basement ( 103 ) with the rotating shaft ( 105 ) supported by a pair of rolling bearings ( 107 ) and mounted theron;    a rotor ( 109 ) of the electric motor ( 111 ), which is mounted on the rotating shaft ( 105 ) for rotating said shaft ( 105 ) and the rotor assembly ( 113 ); and    the rotor assembly( 113 ) comprises a bell-shaped cavity ( 117 ) housing the rotating shaft ( 105 ) and the electric motor ( 111 ).    
   
   
       3 . The rotary vacuum pump as claimed in  claim 2 , wherein said pump comprises at least one pair of displacement sensors ( 121 A- 121 D) mounted in the basement ( 103 ) of the pump ( 101 ), close to the rotor ( 113 ) and/or to the rotating shaft ( 105 ) thereof, each sensor facing said shaft ( 105 ) or said rotor ( 113 ) so that the possible variations in the distance between the rotor and the sensor during rotation of the rotor is measured.  
   
   
       4 . The rotary vacuum pump as claimed in  claim 3 , further comprising a first pair of sensors ( 121 A,  121 B) facing the rotating shaft ( 105 ) and turned towards it, and a second pair of sensors ( 121 C,  121 D) facing the internal wall ( 113   a ) of the rotor assembly ( 113 ) and turned towards the wall.  
   
   
       5 . The rotary vacuum pump as claimed in  claim 1 , wherein said rotor assembly ( 113 ) comprises at least one threaded cylindrical bore ( 123 ) having an axis lying in a plane orthogonal to a rotation axis of the rotor ( 113 ) and tangentially relative to said rotor, wherein additional masses of the bore consisting of threaded dowels can be located and displaced for reducing the unbalance of the rotating portion.  
   
   
       6 . The rotary vacuum pump as claimed in  claim 1 , wherein said rotor assembly ( 113 ) comprises at least one threaded cylindrical bore ( 123 ) having an axis lying in a plane orthogonal to a rotation axis of the rotor ( 113 ) and radially relative to said rotor, wherein additional masses of the bore consisting of threaded dowels can be located and displaced for reducing the unbalance of the rotating portion.  
   
   
       7 . The rotary vacuum pump as claimed in  claim 1 , wherein: 
 the rotating shaft ( 205 ) is supported by a pair of rolling bearings ( 207 ) and is driven by the electric motor ( 211 ), the bearings and the motor are located in a pump region that is axially separated from the pumping region housing the rotor assembly ( 213 ); and    a pair of displacement sensors ( 221 A,  221 B) is positioned in a basement ( 203 ) of the pump ( 201 ), opposite to the rotating shaft ( 205 ) and at opposite sides of the rotor ( 209 ) of the electric motor ( 211 ).    
   
   
       8 . The rotary vacuum pump as claimed in  claim 1 , wherein said displacement sensors are eddy current displacement sensors, which comprise a coil ( 53 ) in which a high frequency AC current generating a variable magnetic field flows.  
   
   
       9 . The rotary vacuum pump as claimed in  claim 8 , wherein said sensors comprise an impedance-to-voltage converter ( 61 ), wherein a variation in the voltage level of an output signal of said converter ( 61 ) corresponds to an impedance variation in the coil of said sensor.  
   
   
       10 . The rotary vacuum as claimed in  claim 12 , wherein said sensors ( 121 A- 121 D;  221 A- 221 B) provide a signal representative of the displacement of the rotating portion relative to the stationary portions during the pump's operation.  
   
   
       11 . The rotary vacuum as claimed in  claim 1 , wherein said pump is a turbomolecular pump.  
   
   
       12 . A structure for balancing a rotary vacuum pump comprising a stationary portion ( 103 ;  203 ) and a portion rotating relative to said stationary portion having a rotating shaft ( 105 ;  205 ) equipped with a rotor assembly ( 113 ;  213 ), driven by an electric motor ( 111 ;  211 ) and supported by at least one rolling mechanical bearing ( 107 ;  207 ) relative to said stationary portion, and a vacuum-tight bell ( 119 ;  219 ) in which the pump can be housed during balancing, said structure comprising: 
 at least two displacement sensors ( 121 A- 121 D;  221 A- 221 B), generating an electrical signal varying with the distance variation between said bell and said rotating portion during the rotation of said shaft and said rotor assembly, and being positioned between said bell and said rotating portion.    
   
   
       13 . The structure as claimed in  claim 12 , wherein: 
 the pump ( 101 ;  201 ) comprises a basement ( 103 ;  203 ) on which the rotating shaft ( 105 ;  205 ) supported by a pair of rolling bearings ( 107 ;  207 ) is mounted, the rotor ( 109 ;  209 ) of the pump electric motor ( 111 ;  211 ) for rotating the shaft ( 105 ;  205 ) and the rotor assembly ( 113 ;  213 ) being mounted on said rotating shaft ( 105 ;  205 ); and    the rotor assembly ( 113 ;  213 ) has a bell-shaped cavity ( 117 ) where the rotating shaft ( 105 ;  205 ) and the electric motor ( 111 ;  211 ) are housed.    
   
   
       14 . The structure as claimed in  claim 13 , wherein said pump comprises a plurality of displacement sensors ( 121 A- 121 D;  221 A,  221 B) mounted in the basement ( 103 ;  203 ), in proximity to the rotor assembly ( 113 ;  213 ) and/or to the rotating shaft ( 105 ;  205 ) thereof, each sensor facing said shaft ( 105 ;  205 ) or said rotor ( 113 ;  213 ) for detecting a variation in the distance between the rotor and the sensor during rotation of the rotor.  
   
   
       15 . The structure as claimed in  claim 14 , wherein said pump comprises a first sensor pair ( 121 A,  121 B;  221 A,  221 B) facing the rotating shaft ( 105 ;  205 ) and turned towards it, and a second sensor pair ( 121 C,  121 D;  221 C,  221 D) facing the internal wall ( 113   a ;  213   a ) of the rotor assembly ( 113 ;  213 ) and turned towards internal wall.  
   
   
       16 . The structure as claimed in  claim 15 , wherein, the bell ( 219 ) is equipped with a central cylindrical projection ( 219   a ) penetrating into the rotor assembly ( 213 ) for positioning the second sensor pair ( 221 C,  221 D).  
   
   
       17 . The structure as claimed in  claim 15 , wherein a third pair of displacement sensors ( 121 E,  121 F;  221 E,  221 F) is provided, said displacement sensors are arranged in proximity to the external wall ( 113   b ;  213   b ) of the rotor assembly ( 113 ;  213 ), between a pair of rotor discs ( 115 ;  215 ), and are turned towards said external wall.  
   
   
       18 . The structure as claimed in  claim 17 , wherein said sensors ( 121 E,  121 F;  221 E,  221 F) of said third pair of displacement sensors are cantilevered on a vertical support ( 120 ;  220 ) adjacent to one of the walls of the bell ( 119 ;  219 ).  
   
   
       19 . The structure as claimed in  claim 18 , wherein said sensors are eddy current displacement sensors.  
   
   
       20 . A method of balancing a rotary vacuum pump comprising a stationary portion ( 103 ;  203 ) and a rotating portion wiht a rotating shaft ( 105 ;  205 ) equipped with a rotor assembly ( 113 ;  213 ) co-operating with a stator assembly for gas pumping, said rotating shaft being driven by an electric motor ( 111 ;  211 ) and supported by at least one rolling mechanical bearing ( 107 ;  207 ) relative to said stationary portion, the method comprising the steps of: 
 a) providing a vacuum-tight bell ( 119 ;  219 ) in which the pump is housed during balancing operation;    b) coupling the pump, without the stator assembly, to the bell;    c) making vacuum in the bell;    d) driving the rotating portion into rotation;    e) measuring the displacement, at the rotation frequency, of the rotating portion relative to the stationary portion;    f) stopping the rotating portion;    g) balancing the rotating portion by means of additional masses;    h) repeating, if necessary, steps b) through g); and    i) obtaining displacement measurement by means of at least two displacement sensors ( 121 A- 121  F;  221 A- 221  F), capable of generating an electrical signal varying with the distance between said stationary portion or the bell and the rotating portion during the rotation of the shaft ( 105 ;  205 ) and said rotor assembly ( 113 ;  213 ).