FIELD OF THE INVENTION

The field of the invention relates to turbomolecular pumps and their method of operation.

BACKGROUND

Turbomolecular pumps are high speed pumps used to generate a high vacuum. They are high cost machines generally operated in highly controlled

environments such as clean rooms in semiconductor processing plants.

Smaller, lower cost machines are currently being developed which may have application in more diverse situations.

It would be desirable to provide turbomolecular pumps which could be operated effectively in different environments without unduly increasing their servicing requirements or damaging their components.

SUMMARY

A first aspect of the present invention provides a turbomolecular pump comprising: a stator and a rotor; said rotor being supported for rotation by bearings; a motor for rotating said rotor; wherein said turbomolecular pump is configured to perform a warm-up cycle for warming up at least one pump component prior to operation of said pump said turbomolecular pump

comprising control circuitry, said control circuitry being operable to trigger said warm-up cycle; said control circuitry being configured to supply power to at least one winding of said motor during said warm-up cycle to raise a temperature of said at least one pump component.

Turbomolecular pumps are high cost, high speed machines manufactured to close tolerances which tend to be operated in controlled benign conditions. The tolerance, or distance, between the tip of the rotor blade and the inner wall of the pump casing for example, must be small in order for the pump to achieve the required pumping performance. If the pump operates above a desired temperature the resulting expansion of the rotor blades can be such that a catastrophic failure can occur due to the rotor blades colliding with stationary parts of the internal mechanism, such as the stator blades. Thus, the temperature of operation of a turbomolecular pump is generally controlled with a view to avoid it rising too high. Indeed efforts to date regarding temperature control of such pumps have been directed towards providing sufficient cooling of the pumps. However, operating a pump at low temperatures can also lead to problems, due to variations in distances between components, condensation of water vapour within the pump, and any lubricants being less effective at these lower temperatures. The inventor recognised not only that this was a potential problem, but also that a simple, elegant and low cost solution would be to configure the pump to perform a warm-up cycle prior to pumping operations, thereby avoiding operation at unsuitably low temperatures and protecting the components from the stresses and strains associated with such operation. In this regard, turbomolecular pumps have particular high stress start-up operations where they are accelerated rapidly to reach their high operational speed. The present invention seeks to ensure that at least one of the components of the pump that might be sensitive to lower temperature operations is protected from such lower temperature operations thereby avoiding or at least mitigating potential damage of components due to lower temperature conditions.

In some embodiments, said turbomolecular pump is configured to perform said warm-up cycle to raise a temperature of said at least one of said pump components to a predetermined operational temperature prior to operation of said pump.

Attempting to operate a turbomolecular pump in an environment where temperature is low may cause damage to the pump. In order to avoid such a situation it may be advantageous to raise the temperature to a pre-determ ined operational temperature where it is deemed safe and effective to operate the pump prior to such operation. ln some embodiments, said at least one of said pump components comprise said bearings.

One component of the pumps which is particularly sensitive to operation at low temperatures is the bearings. In this regard, where they are lubricated bearings then where grease is used the grease needs to be above a certain temperature to operate as an effective lubricant and to effectively cover the bearings. Where there is no lubricant and the bearings are magnetically levitated bearings for example, then the rotor may seize on start-up at lower temperatures due to deposits on the mechanism when the pump cools down. Providing some heating prior to starting rotation of the rotor can alleviate this.

The warm-up cycle is triggered by control circuitry either as a default condition on start-up or in response to detected conditions. Automatic control of the warm-up cycle reduces operator error and provides an effective and simple way to operate the pump.

In some embodiments, said control circuitry is operable to detect a temperature of said pump and to trigger said warm-up cycle where said temperature is below a predetermined value and operation of said pump is requested.

The control circuitry may be configured such that when operation of the pump is requested, either by it being switched on or by a“start pumping” signal, it will check the temperature of the pump and where it is below a predetermined value will trigger the warm-up cycle. In other embodiments it may simply run the warm-up cycle and when a certain temperature is reached stop the warm-up cycle. Where the pump is already warm then this may be a very short warm-up cycle.

The windings of the motor are used as the warming circuitry, current being passed through one or more of these to provide warming of at least one of the pump components. This is an effective and economic way of warming up the pump particularly where the components to be warmed are close to the motor, for example where it is important to warm the bearings. ln some embodiments, said control circuitry is configured to control said motor to rotate said rotor at a low initial speed during said warm up cycle.

In addition to sending current through the windings to provide warming the warm-up cycle may also comprise rotation of the rotor at a low speed, this may occur once the temperature has reached a predetermined intermediate temperature. This initial slow spinning of the rotor may help to distribute the heat and warm components such as the bearings gradually. Where the bearings are lubricated such spinning will also help to warm and distribute the lubricant. It may also aid in any outgassing of the pump at start up.

In some embodiments, said control circuitry is configured to control said motor to rotate said rotor in response to detecting a temperature of said pump rising above an intermediate predetermined value.

Although it may be advantageous if the pump is rotated during the warm-up cycle perhaps at a lower speed, it may be preferred for the temperature of the pump to be above a certain value prior to this rotation. This value is lower than the operational temperature which is suitable for high speed operation but above a value where spinning is deemed acceptable.

In some embodiments, said control circuitry is configured to rotate said rotor at a single low speed during said warm up cycle. In other embodiments, said control circuitry is configured to rotate said rotor at a low initial speed and then subsequently to gradually increase the speed of rotation during said warm up cycle.

Providing some rotation of the rotor during the warm-up cycle may be effective for outgassing and distribution of the lubricant. A low initial speed may be advantageous as the stresses and strains on the pump at the lowest speed are themselves lower and thus, where the temperature is not yet at operational temperature this may be an effective way of warming the pump up while protecting it. ln some embodiments, the pump is a dry pump whilst in others it comprises a lubricant supply for lubricating said bearings.

In some embodiments the lubricant comprises grease.

Turbo pumps are high speed pumps and their method of lubrication and its effectiveness dictates their service life and reliability. In some cases the operational parameters of the pump may mean that a dry pump is required and in such case magnetic bearings may be used. These are expensive and also require careful operation in order to avoid or at least reduce the chances of seizing. Thus, operation in a preferred temperature range helps protect them from damage. Where the pump is lubricated using grease or oil then this is an effective way of lubricating bearings allowing the use of bearings that are less expensive than magnetic bearings.

Grease is the simplest and cheapest lubricant to use, it comes in a sealed pot and is thus less susceptible to contamination and is suitable for operation in a portable pump which may be tilted. However, the effectiveness of grease is particularly sensitive to operating conditions and it is more difficult to achieve the right operating conditions where grease is an effective lubricant than it is for oil. Furthermore, as grease is generally provided in a sealed reservoir the quantity of grease is limited by the size of this reservoir. In particular, cold grease is not a good lubricant so for grease lubricated bearings it is particularly advantageous to prepare the lubricant during a warm-up cycle such that it is effective prior to operation of the pump. In this regard, a new pump that uses grease as a lubricant will generally have a run in process which takes 24-48 hours and uses closed loop control to distribute the grease effectively.

However, where the grease becomes cold then for it to be effective again it is advantageous if it is warmed up and indeed if the motor is run to some extent prior to use. Thus, the warm-up cycle of embodiments is particularly effective for grease lubricated pump. Furthermore, grease is a particularly effective lubricant for portable pumps and such pumps may be operated at a range of temperatures. Operating at different temperatures for grease lubricated pump produces its own issues and these can be mitigated by the use of a warm-up cycle.

Where the lubricant is oil then this has the advantage of being a better lubricant and allowing faster operation with high loads than grease. It can also have a bigger reservoir with a filter to remove debris. However, it again operates better within a certain temperature zone and thus, an oil lubricated pump may also profit from a warm-up cycle. In this regard, during the start-up of a turbomolecular pump there may be rapid acceleration and at this point it is important that the lubricant is effective. Thus, a warm-up cycle to provide optimal or least preferred operating conditions for the lubricant of the pump prior to the rapid acceleration will make its operation more effective and increase its lifetime.

A second aspect of the present invention provides a method of operating a turbomolecular pump, said method comprising performing an initial warm-up cycle for warming up components of said pump prior to operating said pump; said initial warm-up cycle comprising supplying power to at least one winding of said motor prior to rotating said rotor.

In some embodiments, the method comprises an initial step of detecting a temperature of said pump and performing said warm-up cycle where said temperature is below a predetermined value.

In some embodiments, the method comprises performing said warm-up cycle until a temperature of said at least one of said pump components reaches a predetermined operational temperature and then operating said turbomolecular pump to evacuate a chamber.

In some embodiments, said warm-up cycle comprises rotating a rotor of said pump at a low speed once a predetermined intermediate temperature has been reached. ln some embodiments, said rotating step comprises a single speed rotation.

In some embodiments, said rotating step in said warm-up cycle comprises passing current through at least one winding of said motor to raise a

temperature of said bearings followed by rotation at an initial lower speed and a subsequent gradual increase in speed of rotation.

In some embodiments, said pump comprises a lubricant supply for lubricating said bearings, said lubricant comprising grease.

In some embodiments, said pump is a portable pump.

Further particular and preferred aspects are set out in the accompanying independent and dependent claims. Features of the dependent claims may be combined with features of the independent claims as appropriate, and in combinations other than those explicitly set out in the claims.

Where an apparatus feature is described as being operable to provide a function, it will be appreciated that this includes an apparatus feature which provides that function or which is adapted or configured to provide that function.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present invention will now be described further, with reference to the accompanying drawings, in which:

Figure 1 illustrates a turbomolecular pump and control circuitry according to an embodiment; and

Figure 2 illustrates a flow diagram illustrating a method of operating a

turbomolecular pump according to an embodiment.

DESCRIPTION OF THE EMBODIMENTS

Before discussing the embodiments in any more detail, first an overview will be provided. Turbomolecular pumps are normally operated under quite benign conditions (e.g. air-conditioned labs). Newer pumps suitable as point-of-use equipment may present much tougher conditions and steps may be required to protect such pumps.

In embodiments, prior to start-up of a turbomolecular pump and in particular, one with grease-lubricated bearings, the bearings (and by extension the lubricant within) are warmed by passing current through one or more of the coils in the motor stator. Furthermore, a gradual warm-up may be provided by an initial phase of low-speed operation, before accelerating to full speed.

For high-speed operation of grease-lubricated bearings, distribution and conditioning of the grease is the key to achieving long service life. On first build, this is achieved by careful and time-consuming running-in procedures. Grease lubrication is under consideration for a small turbomolecular pump for point-of-use mass spectrometers where the grease will have advantages due to potential tipping of the pump. Such use however, implies exposure to difficult operating conditions, including any-orientation and outdoor use. Outside, the pump may be expected to start up from low ambient temperature, with the risk that grease distribution might be affected. Embodiments provide a more controlled start-up that is beneficial to grease service life. This is achieved by pre-warming, and/or by a gradual or stepped acceleration to reduce stress on the grease and bearings.

Current could be passed through the motor stator windings whose primary purpose is to spin the rotor, resulting in a temperature rise in the motor and then the adjoining parts; the bearing is typically close to the motor to make the overall layout compact. A single phase could be used, or multiple phases simultaneously; or all phases in turn, but at low frequency so that the pump initially spins slowly to warm the bearing gradually. In an alternative technique a dedicated heater winding separate from the motor windings could be used for providing additional heating during a warm-up process. The pump controller could have a default start-up routine, or more usefully, one that is triggered by a thermal sensor; most turbomolecular pumps have at least a thermocouple embedded in the motor stator. The warm-up could be for a fixed time period or until a given temperature is reached.

Although the above is particularly advantageous for grease lubricated bearings a warm-up cycle may have advantages for both oil lubricated and dry pumps where the pump operates in non-controlled ambient conditions. In particular, where deposits in the pump are a problem and may causes seizing of the pump at low temperature start up, an initial warming of the pump in the region of the motor, perhaps followed by a slow rotation may alleviate these problems. This is particularly the case where deposits are particularly problematic in the lower vacuum regions of the pump close to the motor, such as in the drag stage.

Figure 1 shows a cross section of a turbomolecular pump 1 according to an embodiment. The pump 1 comprises a housing or casing 19 with an inlet 3 for receiving gas and an outlet 5 for exhausting the gas conveyed through the pump 1. Within the casing 19 there is provided a rotor 100, which comprises a number of radially outwardly extending rotor blade stages 9. The casing 19 defines a stator component comprising a series of stator blade stages 11 extending radially inwardly and located between each of the rotor blade stages 9 in a manner well known to those skilled in the art of turbomolecular pump design. The rotor 100 also comprises, proximate to the outlet 5, a series of molecular drag, or Holweck, stages 13.

In this embodiment, the rotor 100 is supported for rotation with bearings 15 which comprise a ball type bearing arrangement lubricated by grease. The rotor 100 is driven by motor 26. In the example shown the motor 26 is a synchronous two-pole, three-phase brushless DC motor contained in a stator 28. The motor 26 comprises three sets of motor coil windings 44 that are evenly distributed around the motor stator 28.

There is also control circuitry 16 for controlling operation of the turbomolecular pump. The control circuitry controls both the driving of motor 26 during normal operation and the warm-up cycle. In this embodiment there is a temperature sensor 2 located close to the motor windings and to the bearings, for detecting the temperature of the pump and in particular the temperature of the bearings. In other embodiments the

temperature sensor may be located elsewhere to detect the temperature of other components of the pump.

The control circuitry 16 controls both start up and operation of the pump and is responsive to the readings of the temperature sensor.

The control circuitry 16 will initiate a warm-up cycle either automatically on start- up or when a reading from the temperature sensor indicates a warm-up cycle is required by feeding current to one or more motor windings. Additionally it may drive the motor to rotate at a slow speed during the warm up cycle. When a temperature at or above an operation temperature is detected the control circuitry 16 will control the motor 26 to accelerate to operational speeds.

Figure 2 shows a flow diagram illustrating steps in a method for operating a turbomolecular pump according to an embodiment.

In response to a request to initiate pumping operations, the control circuitry determines whether the temperature is below a given value or not. If it is then the control circuitry triggers a current to pass through at least one of the windings of the motor to warm up the area around the motor.

Once the warm-up cycle is started, then the temperature of the sensor is monitored until the temperature sensor detects the temperature has risen to an intermediate temperature, rotation of the rotor at a slow speed is then

commenced. When the temperature is detected as having risen to an operational temperature, pumping operations are started and the rotor is accelerated to operational speeds.

If the initially detected temperature is higher than the predetermined value, then the control circuitry may immediately initiate pumping operations without triggering a warm-up cycle. In some embodiments, where the initially detected temperature is at or above a predetermined temperature but below an operational temperature then an initial slow rotation of the rotor and some heating of the pump by the motor windings may be triggered to raise the temperature to the operational temperature prior to normal operation

commencing.

Although illustrative embodiments of the invention have been disclosed in detail herein, with reference to the accompanying drawings, it is understood that the invention is not limited to the precise embodiment and that various changes and modifications can be effected therein by one skilled in the art without departing from the scope of the invention as defined by the appended claims and their equivalents.

REFERENCE SIGNS

1 turbomolecular pump

2 temperature sensor

3 inlet

5 exhaust

9 rotor blades

11 stator blades

13 drag stage

15 bearings

16 control circuitry

19 pump casing

26 motor

28 motor stator

44 motor windings

100 rotor