Method for stopping a vacuum pump

Abstract

The present invention provides a method of ceasing rotation of a rotor of a vacuum pump. The method comprises the steps of rotating the rotor at an intermediate RPM, at which there is substantially no probability of the rotor clashing with the stator, for a dwell time sufficient for the vacuum pump to be at or below a threshold temperature, and subsequently coasting down the rotation of the rotor until cessation of rotation.

1 . A method of ceasing rotation of a rotor of a vacuum pump, the vacuum pump comprising a pump chamber including the rotor and a stator;
 wherein prior to initiation of the method the rotor is rotating at an operational RPM, wherein the operational RPM is greater than a threshold RPM, such that the rotor cannot be coasted down from the operational RPM to cessation of rotation without a relatively high probability of the rotor clashing with the stator;   the method comprising the steps of:   a) rotating the rotor at an intermediate RPM, at which there is substantially no probability of the rotor clashing with the stator, for a dwell time sufficient for the vacuum pump to be at or below a threshold temperature, wherein the intermediate RPM is at or below the threshold RPM;   b) subsequently coasting down the rotation of the rotor until cessation of rotation;   wherein the threshold RPM is the maximum speed of rotation at a thermal steady state wherein the rotor can be coasted down until cessation of rotation with substantially no probability of the rotor clashing with the stator; and   wherein the threshold temperature is the temperature of the vacuum pump when the rotor is rotating at the threshold RPM at a thermal steady state.   
     
     
         2 . The method according to  claim 1 , wherein the vacuum pump comprises a temperature sensor configured to measure the temperature of the vacuum pump, the method further comprising the step of measuring the temperature of the vacuum pump via the temperature sensor during the dwell time and determining whether the temperature is at or below the threshold temperature. 
     
     
         3 . The method according to  claim 2 , comprising measuring the temperature of the vacuum pump via the temperature sensor at predetermined time intervals throughout the dwell time, preferably wherein the predetermined time interval is every second or less. 
     
     
         4 . The method according to  claim 2 , comprising the step of only initiating coast down of the rotation of the rotor from the intermediate RPM until cessation of rotation once the temperature of the vacuum pump as measured by the temperature sensor is less than or equal to the threshold temperature. 
     
     
         5 . The method according to  claim 2 , wherein the temperature sensor is configured to measure the temperature of the rotor or the stator, preferably the rotor. 
     
     
         6 . The method according to  claim 1 , wherein during step (a), the rotor is rotated at an intermediate RPM for a predetermined dwell time. 
     
     
         7 . The method according to  claim 6 , wherein the predetermined dwell time is less than or equal to about 600 seconds, preferably from about 30 seconds to about 480 seconds. 
     
     
         8 . The method according to  claim 1 , wherein the vacuum pump comprises a controller, and wherein the method is initiated by a single user input to the controller. 
     
     
         9 . The method according to  claim 1 , wherein the vacuum pump comprises a cooling system configured to reduce the temperature of the vacuum pump, wherein the method comprises the step of operating the cooling system to reduce the temperature of the vacuum pump, preferably further comprising increasing the cooling performance of the cooling system when the rotor is rotating at the intermediate RPM. 
     
     
         10 . The method according to  claim 1 , wherein the threshold RPM is from about 5000 RPM to about 8000 RPM, preferably from about 6000 RPM to about 7500 RPM. 
     
     
         11 . A method of ceasing rotation of a rotor of a vacuum pump, the vacuum pump comprising a pump chamber including the rotor and a stator, wherein the rotor is rotating and at a thermal steady state;
 the method comprising the steps of:   a) measuring the temperature of the vacuum pump, preferably the temperature of the rotor and/or the stator;   b) determining whether the rotor is rotating at an operational RPM greater than a threshold RPM;   c) if so, ceasing rotation of the rotor according to the method defined in  claim 1 ;   wherein the threshold RPM is the maximum speed of rotation at a thermal steady state wherein the rotor can be coasted down until cessation of rotation with substantially no probability of the rotor clashing with the stator.   
     
     
         12 . A vacuum pump comprising a pump chamber including a rotor, a stator, and a controller configured to control the rotational speed of the rotor;
 wherein the rotor and stator are arranged such that the minimum distance therebetween is such that if during operation the rotor is rotating above a threshold RPM and coasted down to cessation of rotation, there is a relatively high probability of the rotor clashing with the stator;   wherein the threshold RPM is the maximum speed of rotation at a thermal steady state wherein the rotor can be coasted down until cessation of rotation with substantially no probability of the rotor clashing with the stator,   wherein during operation when the rotational speed of the rotor is reduced from an operational RPM that is greater than the threshold RPM, the controller is configured to reduce the rotational speed of the rotor to an intermediate RPM, at which there is substantially no probability of the rotor clashing with the stator, and retain the rotation speed at said intermediate RPM for a dwell time sufficient for the vacuum pump to be at or below a threshold temperature, wherein the intermediate RPM is at or below the threshold RPM;   the controller being configured to, after the dwell time, coast down the rotation of the rotor until cessation of rotation;   wherein the threshold temperature is the temperature of the vacuum pump when the rotor is rotating at the threshold RPM at a thermal steady state.   
     
     
         13 . The vacuum pump according to  claim 12 , further comprising a temperature sensor configured to measure the temperature of the rotor and/or stator. 
     
     
         14 . The vacuum pump according to any of  claim 12 , further comprising a cooling system configured to reduce the temperature of the rotor, preferably wherein the cooling system comprises a fan. 
     
     
         15 . The vacuum pump according to  claim 12 , wherein the pump is a multi-stage vacuum pump, preferably a multi-stage roots pump.