Method and apparatus for controlling vacuum pump to stop

Abstract

A vacuum pump has an oil housing, which defines a pump chamber and an oil zone adjacent to the pump chamber. A rotary shaft extends from the pump chamber through the oil housing and projects to the oil zone. A stopper is attached to the rotary shaft to integrally rotate with the rotary shaft. The stopper prevents oil from entering the pump chamber. The vacuum pump draws gas by operating a gas conveying body in the pump chamber through rotation of the rotary shaft. When the rotary shaft shifts from an operation state to a stopped state, the pressure difference occurs between the pump chamber and the oil zone. Rotation of the rotary shaft is controlled such that the pressure difference becomes maximum before the rotary shaft completely stops.

What is claimed is:  
     
         1 . A vacuum pump that draws gas by operating a gas conveying body in a pump chamber through rotation of a rotary shaft, the vacuum pump comprising: 
 an oil housing defining an oil zone adjacent to the pump chamber, wherein the rotary shaft extends from the pump chamber through the oil housing and projects to the oil zone, and wherein, when the rotary shaft shifts from an operation state to a stopped state, the differential pressure raises between the pump chamber and the oil zone; and    a non-contact seal means for preventing oil from entering the pump chamber;    wherein rotation of the rotary shaft is controlled to maximize the differential pressure between the pump chamber and the oil zone before the complete stop of the rotary shaft.    
     
     
         2 . The vacuum pump according to  claim 1 , wherein the rotary shaft is initially decelerated at greater deceleration than a constant deceleration and subsequently decelerated at smaller deceleration than the constant deceleration within a period required for the rotary shaft to be completely stopped when decelerated at the constant deceleration.  
     
     
         3 . The vacuum pump according to  claim 2 , wherein the deceleration of the rotary shaft is indicated by an exponential curve represented by a formula a×e −bt .  
     
     
         4 . The vacuum pump according to  claim 2 , wherein the deceleration of the rotary shaft is represented by a deceleration line including at least two straight lines.  
     
     
         5 . The vacuum pump according to  claim 1 , wherein the rotary shaft is one of a plurality of rotary shafts located parallel to each other, wherein the rotary shafts are coupled to each other by a gear mechanism such that the rotary shafts integrally rotate, and wherein the gear mechanism is accommodated in the oil zone.  
     
     
         6 . The vacuum pump according to  claim 1 , wherein a bearing for rotatably supporting the rotary shaft is accommodated in the oil zone.  
     
     
         7 . The vacuum pump according to  claim 1 , wherein said non-contact seal means includes a labyrinth seal disposed between the rotary shaft and the oil housing.  
     
     
         8 . The vacuum pump according to  claim 1 , further comprising a first receptacle and a second receptacle respectively having bottoms, and a first shaft seal and second shaft seal respectively fitted to the first shaft and the second shaft, wherein first annular projections and second annular projections respectively project from the bottoms of the receptacles, and wherein the first shaft seal and the second shaft seal respectively have annular grooves facing the associated projection forming a first labyrinth seal and a second labyrinth seal, wherein said non-contact seal means includes the first labyrinth seal and the second labyrinth seal.  
     
     
         9 . The vacuum pump according to  claim 1 , further comprising a first shaft seal and a second shaft seal fitted to the first shaft and the second shaft, wherein said non-contact seal means includes a pumping means having helical grooves respectively formed in outer circumferential surfaces of the shaft seals to urge the lubricant oil between the shaft seal and the associated receptacle.  
     
     
         10 . The vacuum pump according to  claim 1 , wherein said non-contact seal means includes seals respectively having end faces.  
     
     
         11 . A vacuum pump comprising: 
 a housing, which has a pump chamber and an oil zone, wherein the housing has a partition wall, which separates the pump chamber from the oil zone;    a pair of rotary shafts, which are parallel to each other, wherein the rotary shafts extend from the pump chamber through the partition wall into the oil zone, and wherein, when the rotary shafts shift from an operation state to a stopped state, the pressure difference occurs between the pump chamber and the oil zone;    a pair of rotors arranged in the pump chamber, wherein each rotor is attached to one of the rotary shafts, and wherein the rotor on one of the rotary shafts meshes with the rotor on the other one of the rotary shafts;    a gear mechanism arranged in the oil zone, wherein the gear mechanism couples the rotary shafts with each other such that the rotary shafts integrally rotate with each other; and    a controller for controlling rotation of the rotary shafts such that the pressure difference between the pump chamber and the oil zone becomes maximum before the rotary shafts completely stop.    
     
     
         12 . The vacuum pump according to  claim 11 , wherein the rotary shafts are first decelerated at greater deceleration than a constant deceleration and subsequently decelerated at smaller deceleration than the constant deceleration within period required for the rotary shafts to be completely stopped when decelerated at the constant deceleration.  
     
     
         13 . The vacuum pump according to  claim 12 , wherein the deceleration of the rotary shafts is indicated by an exponential curve represented by a formula a×e −bt .  
     
     
         14 . The vacuum pump according to  claim 12 , wherein the deceleration of the rotary shafts is represented by a deceleration line including at least two straight lines.  
     
     
         15 . The vacuum pump according to  claim 11 , wherein the rotary shafts are arranged parallel to each other, wherein the rotary shafts are coupled to each other by a gear mechanism such that the rotary shafts integrally rotate, and wherein the gear mechanism is accommodated in the oil zone.  
     
     
         16 . The vacuum pump according to  claim 11 , wherein bearings for rotatably supporting the rotary shafts are accommodated in the oil zone.