Method for controlling the drive motor of a positive displacement vaccum pump

Abstract

Method for controlling a drive motor of a positive displacement vacuum pump A method for controlling a drive motor of a positive displacement vacuum pump comprises the following method steps: storing a curve ( 32 ) indicating a respective speed value n of the drive motor for inlet pressure values p, wherein the curve ( 32 ) comprises: an upper range ( 34 ) for inlet pressure values p larger than or equal to an upper limit pressure p 1 , with a single constant upper speed value n 1 being associated with said upper range ( 34 ), and an alteration range ( 36 ) for inlet pressure values p smaller than the upper limit pressure p 1 , wherein in the alteration range different speed values n v are associated with the inlet pressure values p; determining the inlet pressure value p; determining the speed n associated with the inlet pressure value p in the curve ( 32 ); and operating the drive motor ( 20 ) at the determined speed n. By providing an alteration range the vacuum pump can always be operated at a speed which allows maximum effective suction capacity of the positive displacement pump.

1 . A method for controlling a drive motor of a positive displacement vacuum pump, the method: 
 storing a curve indicating a respective speed n of the drive motor for inlet pressure values p, the curve comprising: 
 an upper range for inlet pressure values p larger than or equal to an upper limit pressure p 1 , a single constant upper speed value n 1  being associated with said upper range, and  
 an alteration range for inlet pressure values p smaller than the upper limit pressure p 1 , in the alteration range different speed values n v  being associated with the inlet pressure values p;  
   determining the inlet pressure value p;    determining the speed n associated with the determined inlet pressure value p in the curve; and    operating the drive motor at the determined speed n.    
   
   
       2 . The method according to  claim 1 , wherein the curve comprises a lower range for inlet pressure values p smaller than or equal to a lower limit pressure p 2 , a single constant lower speed value n 2  being associated with the lower range, and the alteration range being limited to inlet pressure values p larger than the lower limit pressure p 2 .  
   
   
       3 . A method for controlling a drive motor of a positive displacement vacuum pump, the method comprising: 
 storing a curve indicating a respective speed n of the drive motor for inlet pressure values p, the curve comprising: 
 a lower range for inlet pressure values p smaller than or equal to a lower limit pressure p 2 , a single constant lower speed value n 2  being associated with said lower range,  
 an alteration range for inlet pressure values p larger than the lower limit pressure p 2 , in the alteration range different speed values n v  being associated with the inlet pressure values p;  
   determining the inlet pressure value p;    determining the speed n associated with the determined inlet pressure value p in the curve; and    operating the drive motor at the determined speed n.    
   
   
       4 . The method according to  claim 1 , wherein in the alteration range decreasing speeds n v  are associated with decreasing inlet pressure values p.  
   
   
       5 . The method according to  claim 2 , wherein the upper limit value p 1  ranges between 20 mbar and 1 mbar, and the lower limit value p 2  ranges between 1.0 mbar and 0.005 mbar.  
   
   
       6 . The method according to  claim 2 , wherein the upper constant speed value n 1  ranges between 2,200 and 1,000 rpm, and the lower constant speed value n 2  ranges between 300 and 1,300 rpm.  
   
   
       7 . The method according to  claim 1 , wherein the positive displacement vacuum pump is a fore vacuum pump arranged upstream of a high vacuum pump, and the inlet pressure p is a suction-side pressure of the high vacuum pump.  
   
   
       8 . The method according to  claim 1 , wherein the curve is saved in a characteristic diagram storage.  
   
   
       9 . The method according to  claim 1 , wherein the drive motor is an asynchronous motor.  
   
   
       10 . A positive displacement vacuum pump comprising: 
 a drive motor, an inlet pressure sensor and a drive motor control for controlling a speed n of the drive motor in dependence on the inlet pressure value p determined by the inlet pressure sensor,    the drive motor control comprising a storage for storing a curve which indicates a respective speed n of the drive motor for inlet pressure values p of the inlet pressure sensor, the curve comprising: 
 at least one of (a) an upper range for inlet pressure values p larger than or equal to an upper limit pressure p 1 , a single constant upper speed value n 1  being associated with said upper range and (b) a lower range for the inlet pressure values p lower than or equal to a lower pressure limit p s , a single constant lower speed value n 2  being associated with the lower range: and  
 an alteration range for inlet pressure values p smaller than the upper limit pressure p 1  or larger than the lower limit pressure p s , in the alteration range different speed values n v  being associated with the inlet pressure values p.  
   
   
   
       11 . The positive displacement vacuum pump according to  claim 10 , wherein the drive motor control comprises a processor which has connected therewith the inlet pressure sensor and which evaluates signals from the inlet pressure sensor.  
   
   
       12 . The method according to  claim 3 , wherein in the alteration range decreasing speeds n v  are associated with decreasing inlet pressure values p.  
   
   
       13 . The method according to  claim 3 , wherein the positive displacement vacuum pump is a fore vacuum pump arranged upstream of a high vacuum pump, and the inlet pressure p is a suction-side pressure of the high vacuum pump.  
   
   
       14 . The method according to  claim 3 , wherein the curve is saved in a characteristic diagram storage.  
   
   
       15 . The method according to  claim 3 , wherein the drive motor is an asynchronous motor.