Method for stopping a vacuum pump

Abstract

A method of stopping rotation of a rotor of a vacuum pump is provided. The method includes the steps of rotating the rotor at an intermediate RPM for a dwell time sufficient to bring the vacuum pump to or below a threshold temperature at which there is substantially no likelihood of rotor-stator collisions; and subsequently coasting the rotation of the rotor down to a stop.

Description

Technical Field

[0001] The present invention relates to vacuum pumps, and more particularly to a method for stopping (i.e., stopping) the rotation of a vacuum pump rotor. Background Technology

[0002] When manufacturing components for vacuum or compressor pumps, much like with all manufactured parts, minute variations in the physical dimensions may exist between individual units of the same component. These manufacturing tolerances are often inherent and unavoidable; however, they are typically minimized as much as possible. Manufacturers can balance the production costs and efficiency of providing components with minimal manufacturing tolerances with the benefits this provides to the final assembled pump or compressor. Acceptable manufacturing tolerances can vary depending on the component and its intended use.

[0003] When pumps or compressors are in use, reducing manufacturing tolerances is particularly important for components that move relative to other parts, such as the pump rotor blades or vanes. Reduced tolerances allow moving parts to be arranged with smaller distances between them, thereby improving pump efficiency.

[0004] This is particularly important in dry vacuum pumps such as screw pumps, roots pumps, or claw pumps, because there is no lubrication in the main pump chamber between the rotor and stator. The lack of lubrication can help reduce contamination of the vacuum system; however, the lack of lubrication necessitates further reduction of the clearance between the rotor and stator to improve pumping efficiency.

[0005] As the clearance decreases, the chances of the rotor colliding with the stator or another rotor may increase. Such rotor collisions can not only stop the pump, but also damage the rotor and / or stator involved.

[0006] The inventors have discovered that in many pumps, such as multistage Roots pumps, additional spacing may be required between components in relative motion due to the thermal cycling experienced by the pump during operation. The heat generated by the pump causes thermal expansion of the pump components. Different components within the pump comprise different materials, and therefore their rates of thermal expansion may differ. The effect of this varying thermal expansion of the components within the pump is that the spacing between adjacent components can change with temperature, thereby allowing for effective movement of the components relative to each other.

[0007] When the pump is "cold-started," that is, when the vacuum pump starts rotating at ambient temperature (e.g., 25°C), the rotor shifts approximately upstream in the pump direction. This shift is partly due to the rotor's dynamic effects and the settling of the bearings on which the rotor shaft is rotatably mounted. The shift is also partly due to the internal pressure gradient generated in the pump chamber along the pump direction. Typically, this shift can be less than about 100 micrometers, preferably less than about 50 micrometers, for example, 20 micrometers.

[0008] Therefore, to prevent the rotor of each stage from colliding with the adjacent upstream partition wall (i.e., the stator), the upstream axial clearance can be greater than the clearance required for optimal pump efficiency. Thus, typically, the increased upstream axial clearance is greater than the rotor displacement during a "cold start".

[0009] As discussed above, when a pump is in use, its temperature may rise, causing thermal expansion of the components within the pump. The inventors have discovered that as the pump temperature rises, the rotor can be effectively displaced relative to the stator in a generally downstream pump direction. This may be partly due to the different thermal expansion of the pump components caused by their different geometries. Furthermore, it may be partly due to the inclusion of different components made of different materials with different coefficients of thermal expansion. Typically, the rotor and stator comprise different materials; for example, the stator may comprise aluminum, and the rotor may comprise iron. Therefore, the coefficient of thermal expansion of an aluminum stator can be greater than that of an iron rotor.

[0010] For example, the inventors have discovered that in some pumps operating near their thermal limits, the rotor can be displaced by up to about 150 μm or even up to about 250 μm in the pumping direction approximately downstream of the stator.

[0011] When the pump is shut off, the rotor's rotational speed can be reduced until it stops rotating. This reduction to a standstill can be called coasting (or inertial coasting, coasting down). Typically, the rotors rotate freely until they stop, although braking (e.g., motor braking) can be applied. Coasting can take less than about 120 seconds, preferably less than about 60 seconds, for example, about 20 seconds.

[0012] When the pump coasts, the decrease in rotor speed can be non-linear. Immediately after the pump stops, the rate of change of rotor speed may be small because the pressure gradient still exists within the pump and the rotor's rotational inertia remains relatively high. However, as the pressure gradient decreases, the rate of decrease in rotor speed may increase due to increased resistance on the rotor. Finally, as the rotor nears a stop, the rate of decrease in rotor speed decreases again.

[0013] As the pressure gradient inside the pump chamber decreases, the rotor can be displaced in the approximate downstream pumping direction.

[0014] If the pump has already been operated to the point that its temperature has caused the rotor to shift relative to the stator in the generally downstream pumping direction, then as the rotor coasts, it may shift further downstream due to the reduced pressure gradient. This further downstream shift may result in the rotor colliding with the downstream stator. A collision between the rotor and stator can be defined as direct contact between the rotor and stator, which can cause damage to the rotor and / or stator. One or more components of the pump may require repair and / or replacement, and therefore, the collision prevents further rotation of the rotor until such repair / replacement has occurred.

[0015] When used in certain applications, such as semiconductor manufacturing processes, some pumps may experience particulate matter buildup within the pump chamber during operation. When the pump stops and components thermally shrink, this particulate matter can be compressed between the rotor and the adjacent stator within the pump chamber. During a "cold start," the increased friction between the compressed particulate matter and the rotor can increase the torque required to start the rotor rotating. In some cases, the required torque may exceed the pump's operating torque, leading to start-up failure.

[0016] To overcome this startup problem, various mechanisms for removing particulate matter during pump shutdown are known. For example, WO 2004 / 038222 discloses an automatic shutdown procedure that includes: stopping the operation of the pumping mechanism, monitoring the temperature of the pumping mechanism, starting the operation of the pumping mechanism at pre-selected temperature intervals to remove contaminating particulate matter from the pump chamber, and finally stopping the operation of the pumping mechanism.

[0017] This method of shutdown allows for the removal of deposited particulate matter from the pump chamber, ensuring that such particulate matter is not compressed between the rotor and stator of the pump mechanism. This avoids startup problems.

[0018] EP 1900943(A1) discloses an alternative method for removing particulate matter from a pump chamber. The method includes: reducing the rotational speed of the pumping mechanism to below a preset threshold speed, maintaining the rotational speed for a period of time to remove any accumulated particulate matter between the rotor and the adjacent stator, and then stopping the rotation of the pumping mechanism. Similarly, this method prevents the accumulation and compaction of particulate matter in the gap between the rotor and stator. Therefore, the increased torque demand during cold starts of the pump mechanism is avoided.

[0019] EP 2048365(A2) discloses a mechanism for rotating a pump rotor in a forward and / or reverse direction according to a predetermined timing pattern before stopping the pump rotation after a pump stop operation has been performed. Similarly, the mechanism removes particulate matter in the gap between the rotor and stator and prevents the compaction of particulate matter in the gap between the rotor and stator.

[0020] Each of these disclosures addresses the problem of increased torque during vacuum pump startup caused by the compaction of particulate matter in the gap between the rotor and stator. However, none of these disclosures reveal a more serious problem of the rotor colliding with the stator during rotational stops.

[0021] Currently, to reduce the risk of collisions during use, the nominal spacing between components takes into account both tolerance superposition and thermal cycling / expansion. However, increasing the spacing between components, especially between the rotor and stator, significantly reduces pump efficiency. These issues are particularly relevant when reducing the size of vacuum pumps, as the efficiency loss has a significant impact on the overall pump performance. This can be detrimental to pumping performance and reduce the final pumping pressure that the pump can achieve.

[0022] Therefore, there is a continued need to address the impact of thermal expansion on pump efficiency.

[0023] The present invention aims to solve these and other problems of the prior art. Summary of the Invention

[0024] Therefore, in a first aspect, the present invention provides a method for stopping (i.e., halting) the rotation of the rotor of a vacuum pump. The vacuum pump includes a pump chamber, which includes a rotor and a stator.

[0025] Before starting the method, the rotor rotates at an operating RPM (revolutions per minute). The operating RPM is greater than a threshold RPM such that the rotor cannot coast from the operating RPM to a stop (i.e., stand still) without a relatively high probability of a rotor colliding with the stator.

[0026] The method includes the step of rotating the rotor at an intermediate RPM, at which it is substantially impossible for the rotor to collide with the stator for a residence time sufficient to bring the vacuum pump to or below a threshold temperature. Then, the rotor coasts until rotation stops.

[0027] The intermediate RPM is equal to or lower than the threshold RPM.

[0028] Advantageously, the inventors have discovered that the method according to the invention significantly reduces the risk of rotor-stator collision when the vacuum pump is subsequently shut down. Rotating the rotor at an intermediate RPM for a sustained residence time according to this method ensures a sufficient pressure gradient is maintained within the pump, while simultaneously reducing the pump temperature, thereby preventing significant downstream displacement of the rotor during component thermal displacement, which could potentially lead to collision. Furthermore, because the effects of such a temperature-dependent collision mechanism are substantially avoided, the gap between each rotor and the adjacent downstream stator can be reduced, thereby improving pumping efficiency.

[0029] Preferably, the method according to the invention allows the rotor and stator of the vacuum pump to be arranged such that the minimum distance (i.e., gap) between them is such that if the rotor rotates above a threshold RPM during operation and coasts to a stop, there is a relatively high probability of rotor-stator collision.

[0030] For the purposes of this invention, the threshold RPM is the maximum rotational speed under thermally stable conditions, where the rotor can coast until rotation stops with virtually no possibility of rotor-stator collision. Those skilled in the art will understand that the threshold RPM can depend on many factors, such as the specific type of vacuum pump, the rotor-stator arrangement, the minimum clearance between the rotor and stator, the materials of the vacuum pump components, and the cooling rate of the vacuum pump components.

[0031] The threshold temperature is the temperature of the vacuum pump when the rotor is rotating at the threshold RPM in a thermally stable state.

[0032] For the purposes of this invention, stopping the rotation of the vacuum pump rotor means reducing the rotor's rotational speed until it comes to a substantial stop, i.e., rotating at approximately 0 RPM. At approximately 0 RPM, rotation is considered to have stopped. This cessation of rotation is typically associated with purposes such as maintenance or shutting down the pump between uses.

[0033] Typically, during coasting, the rotors rotate freely until they come to a stop, although braking can be applied. Normally, during coasting, the motor will no longer drive the rotors.

[0034] For the purposes of this invention, "rotor colliding with the stator" can be defined as direct contact between the rotor and the stator. Typically, when colliding with the stator, the rotor can rotate. During the collision, friction and impact between the rotor and stator stop the rotor's rotation. A rotor colliding with the stator can result in damage to the rotor and / or the stator. The collision may require repair and / or replacement of one or more components of the pump.

[0035] A collision between the rotor and stator can result in a locking engagement between them. This locking engagement can occur due to the rotor contacting and engaging with the stator, causing the rotor's rotation to become stuck. If locking engagement occurs during a collision, it can lead to irreparable damage to the rotor and / or stator and may result in significant downtime for the vacuum pump. Rotors and / or stators made of aluminum or aluminum alloys may be particularly prone to locking engagement during a collision.

[0036] For the purposes of this invention, a "relatively high probability of rotor-stator collision" can be defined as a greater than about 1% chance of rotor-stator collision during coasting from a particular RPM, preferably greater than about 5%, more preferably greater than about 10%, more preferably greater than about 20%, more preferably greater than about 30%, more preferably greater than about 40%, more preferably greater than about 50%, more preferably greater than about 60%, more preferably greater than about 70%, more preferably greater than about 80%, and more preferably greater than about 90%. Most preferably, during coasting from a particular RPM, there is a greater than about 99% chance of rotor-stator collision.

[0037] "Rotors that collide with the stator" can exclude rotors that come into contact with particulate matter deposited on the stator.

[0038] For the purposes of this invention, "the possibility of substantially no rotor-stator collision" can be defined as a less than approximately 0.1% chance of rotor-stator collision during coasting from that particular RPM, more preferably a less than approximately 0.01% chance of rotor-stator collision. Preferably, the rotor will not collide with the stator during the life of the vacuum pump or between maintenance.

[0039] Due to the potentially serious consequences associated with collisions between the rotor and stator, those skilled in the art will understand that a “relatively high probability of rotor-stator collision” can be determined compared to the “potentially no probability of rotor-stator collision” when the rotor’s rotation is coasted from the intermediate RPM. A collision between the rotor and stator can damage the vacuum pump and also the processing equipment to which the vacuum pump is attached. Therefore, prior art vacuum pumps are operated such that there is virtually no possibility of rotor-stator collision. Even a 1% probability of collision occurring when the rotor coasts from the operating RPM to a stop is considered unacceptable. Of course, a higher probability of collision is even more unacceptable. The present invention allows the rotor to rotate at an operating RPM exceeding a threshold RPM, which is avoided in prior art methods. Furthermore, the method of the present invention allows the gap between the rotor and stator to be reduced to a size at which a relatively high probability of collision exists between the rotor and stator if the rotor coasts from the operating RPM to a stop.

[0040] Furthermore, the "relatively high probability of rotor-stator collision" can be broadly defined to include variations in the probability of a collision occurring based on the magnitude by which the operating RPM exceeds a threshold RPM. The greater the amount by which the operating RPM exceeds the threshold RPM, the higher the probability of a collision occurring between the rotor and stator.

[0041] For the purposes of this invention, the thermally stable state can be defined as the temperature of the vacuum pump when the rotor rotation is maintained at a specific rotational speed (RPM) until the rotor temperature becomes substantially constant (e.g., the change is less than about + / - 0.1°C for at least 1 minute).

[0042] The vacuum pump can be a dry vacuum pump. Preferably, the dry vacuum pump can be a Roots pump, and more preferably a multi-stage Roots pump. For example, the vacuum pump can be an nXRi dry multi-stage Roots pump or an nXLi dry multi-stage Roots pump manufactured by Edwards Vacuum.

[0043] The pump chamber may house one or more rotors and / or stators. Preferably, the pump chamber may be defined by an outer wall substantially surrounding one or more rotors and / or stators.

[0044] A vacuum pump may include multiple rotors. Preferably, one or more rotors are arranged on one or more rotor shafts. Each rotor may include a multi-lobe piston arranged to rotate with the rotor shaft. Preferably, each rotor may include a two-lobe, three-lobe, four-lobe, or five-lobe piston. Preferably, each rotor of the vacuum pump has substantially the same dimensions.

[0045] Preferably, the rotor of the vacuum pump can be configured as a rotor stage. Each rotor stage may include a first rotor arranged on a first rotor shaft and a corresponding second rotor arranged on a second rotor shaft. The first and second rotor shafts may be substantially parallel. In use, the first and second rotor shafts may be configured to rotate in opposite directions. The rotation paths of the blades of the first and second rotors overlap, while the first or second rotor does not contact.

[0046] Typically, the outer wall of the pump chamber may include an inlet through which fluid enters the pump chamber. The outer wall of the pump chamber may also include an outlet through which fluid exits the pump chamber. Typically, the pump inlet may be located at or towards the first end of the pump chamber, and / or the pump outlet may be located at or towards the second end of the pump chamber. Typically, when the pump is in use, the pump inlet may be connected to the chamber to be evacuated, and / or connected to another vacuum pump.

[0047] Pump direction can be defined as the direction in which most of the fluid flowing through the vacuum pump can flow when the pump is in use. Typically, the outlet is located downstream of the inlet along the pump direction.

[0048] Without departing from the above, the pump inlet can be configured such that, during operation, fluid enters the main chamber in a direction substantially perpendicular to the pump direction. Alternatively, the pump outlet can be configured such that, during operation, fluid exits the main chamber in a direction substantially perpendicular to the pump direction. Advantageously, this allows for a reduction in pump size.

[0049] Typically, a vacuum pump may also include a motor, usually an electric motor, configured to drive the rotation of one or more rotors during use. The motor is usually located outside the pump chamber. The motor may be coupled to each rotor shaft. Alternatively, each rotor shaft may be coupled to a separate motor.

[0050] Preferably, the pump may include multiple rotor stages. The multiple rotor stages may be arranged along the length of a first rotor shaft and / or a second rotor shaft. The rotor stages may be separated by partition walls (i.e., stators). The partition walls may include connecting pipes that allow fluid connection between adjacent rotor stages.

[0051] Typically, a pump may include from about 1 to about 10 rotor stages, preferably from about 2 to about 8 rotor stages. The number of rotor stages may depend on the type of pump.

[0052] Typically, one or more rotors are metallic, for example, made of iron or its alloys.

[0053] Typically, one or more stators are made of metal, such as aluminum or aluminum alloys.

[0054] One or more stators may be in the form of partition walls, preferably, each stator may be a partition wall. Typically, partition walls may be located between each rotor of an adjacent rotor stage.

[0055] When the pump is in operation, the operating RPM of the rotor can be from about 5,000 RPM to about 16,000 RPM, preferably from 6,000 RPM to about 16,000 RPM, and more preferably from about 12,000 RPM to about 15,000 RPM.

[0056] Typically, the intermediate RPM is equal to or lower than the threshold RPM. Preferably, the intermediate RPM is about half the rotational speed of the operating RPM, preferably from about 25% to about 75% of the operating RPM, and preferably from about 40% to about 60% of the operating RPM.

[0057] Typically, a vacuum pump includes a temperature sensor configured to measure the temperature of the vacuum pump. The method may also include the steps of measuring the temperature of the vacuum pump via the temperature sensor during a residence time and determining whether the temperature is at or below a threshold temperature. Typically, the temperature of the vacuum pump refers to the temperature of the vacuum pump's rotor.

[0058] Typically, temperature sensors are configured to directly measure the temperature of the rotor; however, they can also be configured to measure the temperature of a component of the vacuum pump from which the rotor temperature can be inferred, such as the stator and / or rotor shaft. Preferably, the temperature sensor can be configured to measure the temperature of the stator.

[0059] When the pump is in operation, the temperature of the pump (e.g., the rotor) can be from about 50°C to about 150°C, preferably from about 70°C to about 120°C. This can be referred to as the operating temperature. The operating temperature is usually stable. Technicians will understand that the temperature of a vacuum pump during operation can depend on factors such as ambient temperature and the rotor's rotational speed.

[0060] The operating temperature can be the temperature of the pump (e.g., rotor or stator) when the rotor is in a thermally stable state and rotating at operating RPM. Preferably, when the pump temperature is at the operating temperature, the rotor cannot coast from operating RPM to a stop without a relatively high probability of rotor-stator collision. To avoid confusion, the relatively high probability of rotor-stator collision is as mentioned above.

[0061] Typically, the threshold temperature is about 10°C to about 70°C lower than the operating temperature, preferably about 20°C to about 50°C lower.

[0062] In this embodiment, the pump may include multiple temperature sensors. Each temperature sensor may be configured to measure the temperature of different components of the vacuum pump. Preferably, each temperature sensor may be configured to measure the temperature of different stages of the vacuum pump. More preferably, each temperature sensor may be configured to measure the temperature of the stator of different stages of the vacuum pump.

[0063] Alternatively or concurrently, the pump may include a temperature sensor configured to measure the temperature of the motor or its components.

[0064] Typically, a temperature sensor can be a thermistor.

[0065] Advantageously, measuring the temperature of the vacuum pump (rotor) via a temperature sensor can improve the efficiency of the method, because once the pump is at or below a threshold temperature, it can begin to coast until rotation stops.

[0066] In this embodiment, the temperature of the vacuum pump (rotor) can be measured via a temperature sensor at predetermined time intervals throughout the residence time. Preferably, the predetermined time interval is one second or less. Preferably, the predetermined time interval is less than about 0.5 seconds, more preferably less than about 0.1 seconds. Alternatively, the temperature of the vacuum pump (rotor) can be measured substantially continuously.

[0067] Advantageously, measuring the vacuum pump temperature via a temperature sensor at predetermined time intervals or substantially continuously reduces the time between the vacuum pump temperature being at or below a threshold temperature and the rotor's rotation coasting down to a stop. This can further improve the efficiency of the method.

[0068] The method may also include the following steps: once the temperature of the vacuum pump measured by the temperature sensor is less than or equal to the threshold temperature, only the rotation of the rotor is started from the intermediate RPM to coasting to stop.

[0069] Advantageously, by initiating rotor rotation from an intermediate RPM to a coasting state where rotation stops only when the vacuum pump temperature is less than or equal to a threshold temperature, the possibility of rotor-stator collision can be virtually eliminated, while providing a time- and energy-efficient coasting process. Furthermore, this method ensures that there is virtually no possibility of rotor-stator collision during the rotation stop, regardless of the operating RPM at which the rotor rotates during use. Therefore, this method offers versatility adaptable to the pump's operating conditions.

[0070] Advantageously, measuring the temperature of the vacuum pump, preferably the rotor temperature, or via the stator, most preferably via the stator, allows for a more accurate determination of whether to avoid a collision between the rotor and stator. This is because the collision during rotational cessation is primarily caused by the different thermal expansion of the rotor and stator.

[0071] Alternatively, the rotor can rotate at an intermediate RPM for a predetermined residence time. The predetermined residence time can be selected based on the specific pump configuration. Preferably, the predetermined residence time can be determined to ensure that the temperature of the vacuum pump is below a threshold temperature at the end of the predetermined residence time.

[0072] This method can be executed automatically when the vacuum pump is turned off. Therefore, the user may not be aware that the process is being used. The same applies to other methods according to the present invention.

[0073] Technicians will understand that the threshold temperature and / or threshold RPM and / or predetermined residence time can be determined through finite element analysis and / or experiments.

[0074] Rotating the rotor at an intermediate RPM for a predetermined residence time can advantageously simplify the method. Furthermore, operating at the predetermined residence time eliminates the need for a temperature sensor, thereby reducing the cost of the vacuum pump.

[0075] Typically, the planned stay time can be from about 0 to about 600 seconds, preferably from about 30 to about 480 seconds.

[0076] Typically, a vacuum pump includes a controller. A method for coasting the rotor from the operating RPM until it stops rotating can be initiated by a single operator input to the controller. Preferably, once initiated, the controller can automatically execute the method of the present invention.

[0077] Typically, the controller can be coupled to the motor. The controller can be configured to control the rotational speed of the rotor. Preferably, the controller can be coupled to one or more temperature sensors of the vacuum pump.

[0078] The controller can be configured to control the rotational speed of the rotor in response to a signal generated by a temperature sensor. The controller can be configured to compare the temperature measured by the temperature sensor with a predetermined temperature value (e.g., a threshold temperature) and adjust the rotor's rotational speed accordingly by sending a signal to the motor.

[0079] Preferably, once the method according to the invention has been started, the temperature sensor can transmit a signal indicating the temperature of the vacuum pump to the controller. The signal can be transmitted substantially continuously or at predetermined time intervals.

[0080] Preferably, the controller is coupled to a display device. The display device may include a screen.

[0081] Preferably, the controller can be configured to allow a user to input commands. Command input can occur via a switch, touchscreen, or other device. Preferably, the method according to the invention can be initiated by a single user input to the controller, such as a switch. Advantageously, this allows the method to be fully automated after the initial user input. This reduces the possibility of user error and improves the efficiency of the method.

[0082] Typically, a vacuum pump includes a cooling system configured to reduce the temperature of the vacuum pump (e.g., the rotor and / or stator). The method may include the step of operating the cooling system to reduce the temperature of the vacuum pump. Preferably, the method may also include activating the cooling system when the rotor is rotating at an intermediate RPM, or improving the cooling performance of the cooling system.

[0083] During the operation of a vacuum pump, the motor that drives the rotor generates heat. This heat can cause thermal expansion of the vacuum pump's components.

[0084] The cooling system may include a cooling fan and / or a fluid cooling system. The fluid cooling system may be a water cooling system.

[0085] The cooling system can be configured to cool the motor during operation. Alternatively, the cooling system can be configured to reduce the temperature of one or more rotors of the vacuum pump.

[0086] In embodiments where the cooling system includes a cooling fan, increasing the cooling rate of the cooling system may involve increasing the rotational speed of the cooling fan. In embodiments where the cooling system includes a fluid cooling system, increasing the cooling rate of the cooling system may involve increasing the fluid flow rate.

[0087] Typically, during the method according to the invention, the cooling rate of the cooling system can be increased as the rotor's rotational speed decreases. Advantageously, reducing the temperature of the vacuum pump through the cooling system can reduce the residence time required for the vacuum pump temperature to fall below the threshold temperature. This can reduce the time required to bring the rotor to a complete stop using the method of the invention.

[0088] Typically, the cooling system can be connected to a controller, allowing its operation to be controlled by the controller. Advantageously, this enables the operation of the cooling system to be automated, requiring no user input other than via a controller-based start-up method.

[0089] In one embodiment, when the rotor rotates at a speed greater than the threshold RPM, the cooling effect of the cooling system can be increased, thereby reducing the temperature of the vacuum pump below the threshold temperature, wherein the rotation of the rotor can be slowed down to stop.

[0090] By reducing the rotor's rotational speed to an intermediate RPM equal to or below the threshold RPM, the cooling rate of the vacuum pump can be increased, preferably while operating the cooling system. Therefore, the method according to the invention allows for a faster and more energy-efficient stopping of the vacuum pump's rotor rotation.

[0091] Typically, the threshold RPM is approximately 30% to approximately 70% of the rotor's maximum rotational speed, preferably approximately 40% to approximately 50%. For example, the threshold RPM can be from approximately 5000 RPM to approximately 8000 RPM, preferably from approximately 6000 RPM to approximately 7500 RPM. Those skilled in the art will understand that the threshold RPM can depend on the specific pump to which the method is applied and / or the specific application using that pump. Furthermore, those skilled in the art will understand that the operating RPM can be equal to or lower than the rotor's maximum rotational speed.

[0092] In another aspect, the present invention provides a method for stopping the rotation of a vacuum pump rotor. The vacuum pump includes a pump chamber, which includes a rotor and a stator. The rotor rotates at an operating RPM and in a thermally stable state.

[0093] The method includes the following steps: measuring the temperature of the vacuum pump (rotor); and determining, based on the temperature of the vacuum pump, whether the rotor is rotating at an operating RPM greater than a threshold RPM. If the operating RPM is greater than the threshold RPM, the rotor rotation is stopped according to the method defined in the foregoing aspect; or if not, the rotor coasts from the operating RPM until it stops, without any dwell time at an intermediate RPM.

[0094] Threshold RPM is the maximum rotational speed under thermally stable conditions, in which the rotor can coast until it stops rotating, with virtually no possibility of the rotor colliding with the stator.

[0095] Advantageously, this method ensures that the method according to the foregoing aspects is used only when the rotor rotates at an operating RPM greater than the threshold RPM. If the rotor rotates at an operating RPM less than the threshold RPM, there is essentially no possibility of the rotor colliding with the stator. Therefore, the method described in the foregoing aspects is unnecessary, and the rotor rotation can be stopped without allowing the rotor to rotate at an intermediate RPM for a dwell time. Advantageously, this ensures that the stopping of the rotation of the vacuum pump rotor occurs as effectively as possible. As mentioned above, a cooling system can be used to bring the temperature of the vacuum pump (e.g., the rotor) to or below the threshold temperature.

[0096] Preferably, one or more temperature sensors are used to measure the temperature of the vacuum pump (e.g., the rotor).

[0097] In another aspect, the present invention provides a vacuum pump. The vacuum pump includes a pump chamber comprising a rotor, a stator, and a controller configured to control the rotational speed of the rotor.

[0098] The rotor and stator are arranged such that the distance between them ensures that if the rotor rotates above a threshold RPM during operation and coasts to a stop, the probability of the rotor colliding with the stator is relatively high. The threshold RPM is the maximum rotational speed under thermally stable conditions, wherein the rotor can coast until it stops rotating with virtually no possibility of collision with the stator.

[0099] During operation where the rotor coasts from an operating RPM greater than a threshold RPM, the controller is configured to reduce the rotor's rotational speed to an intermediate RPM and maintain that intermediate RPM for a residence time sufficient to keep the vacuum pump at or below a threshold temperature, at which point the rotor has virtually no possibility of colliding with the stator. The intermediate RPM is equal to or below the threshold RPM. After the residence time, the controller is configured to coast the rotor's rotation until it stops.

[0100] Threshold temperature is the temperature of a vacuum pump (e.g., the rotor) when the rotor is rotating at a threshold RPM in a thermally stable state.

[0101] The vacuum pump may also include a cooling system configured to reduce the temperature of the vacuum pump.

[0102] The cooling system may include a cooling fan and / or a fluid cooling system. The fluid cooling system may be a water cooling system. Preferably, the cooling system includes a cooling fan.

[0103] The cooling system can be configured to cool the motor during operation. Advantageously, using a cooling system to lower the temperature of the vacuum pump reduces the residence time required for the vacuum pump temperature to fall below a threshold temperature. This, in turn, reduces the time required to bring the rotor to a complete stop.

[0104] Typically, the cooling system can be connected to a controller, allowing the controller to control the operation of the cooling system. Advantageously, this can automate the operation of the cooling fan, requiring no user input other than starting its rotation to stop via the controller (e.g., pressing a "shutdown" command).

[0105] Typically, the pump is a multi-stage vacuum pump. Preferably, the pump is a multi-stage Roots pump. For example, the pump can be an nXLi dry multi-stage Roots pump or an nXRi dry multi-stage Roots pump manufactured by Edwards Vacuum.

[0106] On the other hand, the present invention provides a vacuum pump comprising a pump chamber having a rotor and a stator, and a controller configured to control the rotational speed of the rotor. The rotor and stator are arranged such that the minimum distance between them is such that if the rotor rotates above a threshold RPM during operation and coasts to a stop, there is a relatively high probability of the rotor colliding with the stator.

[0107] Threshold RPM is the maximum rotational speed under thermally stable conditions, where the rotor can coast until it stops rotating with virtually no possibility of rotor-stator collision. The pump may include a temperature sensor configured to measure the temperature of the vacuum pump. A controller may be coupled to the temperature sensor.

[0108] During the operation of the rotor coasting from an operating RPM greater than a threshold, the controller is configured to reduce the rotor's rotational speed at a certain rate, making it virtually impossible for the rotor to collide with the stator. This can be achieved by a temperature sensor sending temperature signals to the controller at predetermined intervals or substantially continuously.

[0109] To avoid confusion, “a relatively high probability of the rotor colliding with the stator” and “the rotor has virtually no chance of colliding with the stator” are defined above.

[0110] The controller can compare the temperature signal received from the temperature sensor with the relationship between a predetermined rotor rotation speed and a pump threshold temperature. The relationship between the maximum rotor rotation speed and the temperature threshold determines the maximum permissible thermally stable pump temperature at each rotor rotation speed, from which the rotor rotation speed can coast down to a complete stop with virtually no possibility of rotor-stator collision. Preferably, if the measured temperature of the vacuum pump is higher than the predetermined rotor rotation speed versus pump temperature threshold, the controller will slow down the rate of rotor rotation reduction.

[0111] To avoid confusion, the features of the aspects and embodiments described herein may be combined and still fall within the scope of the invention. Attached Figure Description

[0112] Preferred features of the invention will now be described by way of example with reference to the accompanying drawings, in which:

[0113] Figures 1(a)-1(d) (Figure 1) show schematic diagrams of the operation of a pump according to the prior art.

[0114] Figure 2 (a)- Figure 2 (d)( Figure 2 The diagram shows a schematic of the operation of the pump according to the present invention.

[0115] Figure 3 A flowchart of the pump operation method according to the present invention is shown. Detailed Implementation

[0116] Figures 1(a)-1(d) show schematic diagrams of pumps according to the prior art. The figures show cross-sectional views of the rotor stage (1) of the vacuum pump.

[0117] The rotor stage (1) includes a rotor (2) mounted on a rotor shaft (3). The rotor shaft (3) may be substantially parallel to the pump direction (A). The pump direction (A) defines the direction of flow of a large volume of fluid during pump operation. The pump direction (A) may define the direction between a pump inlet (not shown) and a pump outlet (not shown). The rotor stage (1) also includes a pair of stators (4, 5). The pair of stators includes an upstream stator (4) and a downstream stator (5). The terms “upstream” and “downstream” define the position of each stator relative to a particular rotor. The upstream stator (4) and the downstream stator (5) may each be in the form of an interstage partition wall.

[0118] Figure 1(a) shows the arrangement of the rotor stage (1) when the pump is off (i.e., when the rotor (2) does not rotate relative to the pair of stators (4, 5). This shows the configuration of the rotor (2) within the rotor stage (1) and the clearance within the pump when the pump is stationary.

[0119] Between the rotor (2) and the upstream stator (4), there exists an upstream rotor clearance (x), which defines the minimum distance between the rotor (2) and the upstream stator (4). Between the rotor (2) and the downstream stator (5), there exists a downstream rotor clearance (y), which defines the minimum distance between the rotor (2) and the downstream stator (5). Typically, when the rotor (2) is not rotating relative to the pair of stators (4, 5), the upstream rotor clearance (x) is smaller than the downstream rotor clearance (y).

[0120] To accommodate manufacturing tolerances, the pump is configured such that the upstream rotor clearance (x) and downstream rotor clearance (y) are relatively small, while ensuring that the rotors do not contact the stator. This reduces fluid leakage between the stages of the vacuum pump.

[0121] When the rotor (2) is stationary, the fluid pressure within the rotor stage is in equilibrium, meaning there is essentially no difference in fluid pressure between the upstream end and the downstream end of the rotor stage (1). The upstream end of the rotor stage (1) can be defined as being between the upstream stator (4) and the rotor (2). The downstream end of the rotor stage (1) can be defined as being between the rotor (2) and the downstream stator (5).

[0122] Figure 1(b) shows the rotor stage when the pump has been turned on (i.e., during the first 20 seconds of use). When the pump is turned on, the rotor (2) rotates about its axis of rotation (Z) relative to the stator (4, 5).

[0123] As the rotor (2) rotates, a pressure gradient is established between the upstream and downstream ends of the rotor stage (1). The fluid pressure can be lower at the upstream end of the stage and higher at the downstream end. This can thus bias the position of the rotor (2) towards the upstream end of the stage (1).

[0124] Furthermore, the rotor dynamics and the settling of the bearing (not shown) on which the rotor shaft (3) is rotatably mounted contribute to the displacement of the rotor toward the upstream end of the rotor stage (1).

[0125] Compared to Figure 1(a), the displacement of the rotor (2) toward the upstream end of the rotor stage (1) can reduce the upstream clearance (x) and increase the downstream clearance (y).

[0126] This upstream displacement of the rotor is also a factor that can be considered when designing the pump to minimize the risk of collision between the rotor (2) and the stator (4).

[0127] Figure 1(c) shows the rotor stage (1) when the pump is already running and the pump (rotor) temperature has increased to the operating temperature (e.g., 85°C). The operating temperature is above the threshold temperature.

[0128] The temperature of the vacuum pump has risen, and due to the different materials used in the rotor and stator, different thermal expansions occur in the rotor (2) and stator (4, 5), respectively. This effectively causes the rotor (2) to shift towards the downstream end of the rotor stage (1).

[0129] Compared to Figure 1(b), the displacement of the rotor (2) toward the downstream end of the rotor stage (1) can increase the upstream clearance (X) and decrease the downstream clearance (y).

[0130] Figure 1(d) shows the rotor stage (1) when the rotor (2) stops rotating at a temperature above 70°C. The temperature of the vacuum pump is above the threshold temperature.

[0131] When the rotation of rotor (2) stops, the pressure gradient between the upstream and downstream ends of rotor stage (1) decreases. This eliminates the offset of rotor (2) towards the upstream end of rotor stage (1), resulting in a further displacement of rotor (2) towards the downstream end of rotor stage (1). As shown, this further displacement causes rotor (2) to collide with the downstream stator (5). The collision occurs because the downstream clearance (y) becomes virtually zero, resulting in direct contact between rotor (2) and stator (5).

[0132] Such an impact may cause damage to the rotor (2) and / or stator (5), as well as machine downtime.

[0133] Figure 2 (a)- Figure 2 (d) shows a schematic diagram of the operation of the pump according to the invention. The accompanying drawing shows a cross-sectional view of the rotor stage (6) of the pump according to the invention.

[0134] Figure 2 (a) and Figure 2 (b) is essentially the same as those in Figures 1(a) and 1(b), as are the conditions and processes within the pump, and therefore will not be described again. The rotor stage (6) includes a controller (10) configured to control the rotational speed of the rotor (7).

[0135] Figure 2 (c) shows the rotor stage (6) when the pump has been running and the pump temperature has increased above the ambient temperature (e.g., 20°C) to the operating temperature (e.g., 85°C). The operating temperature is above the threshold temperature. Since the rotor and stator are made of different materials with different coefficients of thermal expansion, their heating effectively causes the rotor to shift towards the downstream end of the rotor stage (6).

[0136] When the pump is shut down using the method according to the invention, the rotational speed of the rotor (7) decreases from the operating RPM to the intermediate RPM. The intermediate RPM is less than the threshold RPM.

[0137] The rotor stage (6) also includes a temperature sensor (11) configured to measure the temperature of the stator (8, 9) during operation. The temperature of the rotor can be inferred from the temperature of the stator.

[0138] The rotational speed of the rotor (7) is maintained at an intermediate RPM for a period of time. During this time, the temperature sensor (11) continuously measures the temperature of the stator (8, 9). The controller (10) can compare the temperature signal received from the temperature sensor (11) with a threshold temperature. When the temperature of the stator (8, 9) indicates that the rotor has dropped to or below the threshold temperature (e.g., at or below 70°C), the drive on the rotor (7) can be removed, causing the rotor to slow down to a standstill (e.g., coast).

[0139] Figure 2 (d) shows the rotor stage (6) when the rotation of the rotor (7) stops. As shown, there is no collision between the rotor (7) and the stator (8, 9) during the coasting deceleration of the rotor (7) until it stops rotating.

[0140] Figure 2 (c) and Figure 2 There is a small decrease in the downstream gap (y) between (d), but it is not enough to cause a collision between the rotor (7) and the stator (9).

[0141] As the pump cools further, the pump will move towards Figure 2 The configuration shown in (a) returns to the initial configuration at approximately ambient temperature (e.g., 20°C).

[0142] Figure 3 A flowchart of the pump operation method according to the present invention is shown. Initially, before the method of stopping the rotation of the vacuum pump rotor begins, the rotor rotates at an operating RPM (12). The operating RPM is greater than a threshold RPM, such that the rotor cannot coast from the operating RPM to a stop rotating in the absence of a relatively high probability of rotor-stator collision.

[0143] The method then includes the step of rotating the rotor at an intermediate RPM (13). When rotating at an intermediate RPM, there is essentially no possibility of the rotor colliding with the stator. The intermediate RPM is equal to or below the threshold RPM. The threshold temperature is the temperature of the vacuum pump when the rotor is rotated at the threshold RPM in a thermally stable state. The rotor is rotated at an intermediate RPM for a sufficient residence time to keep the vacuum pump at or below the threshold temperature.

[0144] The method may also include the step of activating a cooling system (14). The cooling system may be configured to reduce the temperature of the vacuum pump. Preferably, a temperature sensor may be configured to measure the temperature of the rotor or stator.

[0145] The method may also include a step (15) of measuring the temperature of the vacuum pump via a temperature sensor during the residence time. The temperature can be measured via the temperature sensor at predetermined time intervals throughout the residence time. Preferably, the predetermined time interval can be one second or less.

[0146] The method includes the step of coasting the rotation of the rotor until it stops rotating (16).

[0147] However, it will be understood that various modifications may be made to the illustrated embodiments without departing from the spirit and scope of the invention as defined by the appended claims as interpreted by patent law.

[0148] Figure Labels

[0149] 1. Rotor stage (existing technology)

[0150] 2. Rotor (Prior Art)

[0151] 3. Rotor shaft (existing technology)

[0152] 4. Stator (existing technology)

[0153] 5. Stator (Prior Art)

[0154] 6. Rotor stage

[0155] 7. Rotor

[0156] 8. Stator

[0157] 9. Stator

[0158] 10. Controller

[0159] 11. Temperature sensor

[0160] 12. A rotor that rotates at an operating RPM

[0161] 13. Rotor rotating at intermediate RPM

[0162] 14. Start the cooling system

[0163] 15. The temperature of the vacuum pump is measured using a temperature sensor.

[0164] 16. Reduce the rotor speed by coasting until it stops rotating.

Claims

1. A method of stopping rotation of a rotor of a vacuum pump, the vacuum pump comprising a pump chamber, the pump chamber comprising a rotor and a stator, wherein, the rotor is rotating and is in a thermally stable state; the method comprises the steps of: a) measuring a temperature of the vacuum pump; b) determining from the temperature of the vacuum pump whether the rotor is rotating at an operating RPM greater than a threshold RPM such that the rotor cannot coast down from the operating RPM to a stop without a relatively high likelihood of the rotor colliding with the stator, c) if so, then: i) causing the rotor to rotate at an intermediate RPM for a dwell time sufficient to bring the vacuum pump to or below a threshold temperature, at which intermediate RPM there is substantially no likelihood of the rotor colliding with the stator, wherein the intermediate RPM is at or below the threshold RPM; ii) subsequently causing rotation of the rotor to coast down until a stop; wherein the threshold RPM is a maximum rotational speed in a thermally stable state at which the rotor can coast down to a stop without substantially any likelihood of the rotor colliding with the stator; and wherein the threshold temperature is a temperature of the vacuum pump when the rotor is rotating at the threshold RPM in a thermally stable state.

2. The method of claim 1, wherein, Step a) comprises measuring a temperature of the rotor and / or stator.

3. The method of claim 1, wherein, The vacuum pump comprises a temperature sensor configured to measure a 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.

4. The method of claim 3, comprising measuring the temperature of the vacuum pump via the temperature sensor at predetermined time intervals throughout the dwell time.

5. The method of claim 4, wherein the predetermined time intervals are per second or less.

6. The method of claim 3, comprising initiating the step of causing rotation of the rotor to coast down from the intermediate RPM to a stop only once the temperature of the vacuum pump measured by the temperature sensor is less than or equal to the threshold temperature.

7. The method of claim 3, wherein, The temperature sensor is configured to measure a temperature of the rotor.

8. The method of claim 3, wherein, The temperature sensor is configured to measure a temperature of the stator.

9. The method of claim 1, wherein, During step (i), the rotor rotates at an intermediate RPM for a predetermined dwell time.

10. The method of claim 9, wherein, The predetermined dwell time is less than or equal to 600 seconds.

11. The method of claim 10, wherein, The predetermined dwell time is from 30 seconds to 480 seconds.

12. The method of claim 1, wherein, The vacuum pump comprises a controller, and wherein the method is initiated by a single user input to the controller.

13. The method of claim 1, wherein, The vacuum pump comprises a cooling system configured to reduce a temperature of the vacuum pump, wherein the method comprises the step of operating the cooling system to reduce the temperature of the vacuum pump.

14. The method of claim 13, further comprising increasing a cooling performance of the cooling system when the rotor is rotating at the intermediate RPM.

15. The method of any preceding claim, wherein, The threshold RPM is from 5000 RPM to 8000 RPM.

16. The method of claim 15, wherein, The threshold RPM is from 6000 RPM to 7500 RPM.

17. A vacuum pump comprising: a pump chamber comprising a rotor, a stator; and a controller configured to control a rotational speed of the rotor; wherein the rotor and the stator are arranged such that a minimum distance therebetween is such that if, during operation, the rotor is rotating above a threshold RPM and freewheeling down to a rotational stop, there is a relatively high likelihood of the rotor colliding with the stator; wherein the threshold RPM is a maximum rotational speed in a thermal steady state in which the rotor can freewheel down to a stop rotation without substantially likelihood of the rotor colliding with the stator, wherein, during operation, when it is determined from a temperature of the vacuum pump that the rotor is rotating at an operating RPM greater than a threshold RPM and the rotational speed of the rotor is decreasing from the operating RPM, the controller is configured to reduce the rotational speed of the rotor to an intermediate RPM at which there is substantially no likelihood of the rotor colliding with the stator, and to hold the rotational speed at the 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 is configured to, after the dwell time, cause rotation of the rotor to freewheel down to a stop rotation; wherein the threshold temperature is a temperature of the vacuum pump when the rotor is rotating at the threshold RPM in a thermal steady state.

18. The vacuum pump of claim 17, further comprising a temperature sensor configured to measure a temperature of the rotor and / or stator.

19. The vacuum pump of claim 17, further comprising a cooling system configured to reduce a temperature of the rotor.

20. The vacuum pump of claim 19, wherein the cooling system comprises a fan.

21. The vacuum pump of any of claims 17 to 20, wherein, the pump is a multi-stage vacuum pump.

22. The vacuum pump of claim 21, wherein, the pump is a multi-stage Roots pump.

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