EP3441617A1 - Method for heating a rotor of a vacuum pump - Google Patents

Abstract

A method is provided for heating a rotor of a vacuum pump, in particular a turbomolecular pump. The vacuum pump has a rotor drivable by means of an electric motor, the temperature of which is in the range of an ambient temperature during a first operating phase of the vacuum pump. According to the method, eddy currents are generated within the rotor during a second operating phase, which cause heating of the rotor to a desired temperature above the ambient temperature.

Description

The present invention relates to a method for heating a rotor of a vacuum pump, in particular a turbomolecular pump, wherein the rotor is drivable by means of an electric motor.

In some scientific studies and manufacturing processes, for example in semiconductor technology, it is necessary that an ultra-high vacuum is present in a recipient, ie a pressure of less than 10 ^-10 mbar. In order to achieve such a pressure in the recipient, the recipient and also a flange and optionally a housing of a vacuum pump connected to the recipient must be baked to remove water molecules for reducing the residual gas pressure in the recipient from the inside surfaces of the recipient and the flange Vacuum pump to remove.

Due to its mounting, for example a magnetic bearing, the rotor of a vacuum pump is usually thermally insulated from corresponding stator parts of the vacuum pump and thus with respect to the pump flange and the recipient. Heating elements, which are provided for heating the recipient and the pump flange, therefore can not heat the rotor.

When the rotor heats up during operation of the vacuum pump, for example, in an application requiring a gas load or an increased backing pressure, the rotor will outgas due to its lack of bakeout. As a result, the pressure in the recipient rises due to the heating of the rotor. This can have the consequence that the desired final pressure in the recipient, for example a pressure in the ultra-high vacuum range, not or only with great difficulty can be achieved.

The rotor of the vacuum pump should therefore also be heated during the evacuation of the recipient. For this purpose, it has been proposed to increase the gas friction within the rotor by either increasing the fore-vacuum pressure or providing an additional gas load near the outlet of the vacuum pump. Due to the increased gas friction, the temperature of the rotor increases, causing it to heat up. However, such an approach is time consuming and therefore incurs additional costs.

In addition, due to the limited pumping speed of the vacuum pump, when additional gas is admitted at the outlet of the vacuum pump, an unavoidable backflow takes place in the direction of its inlet and into the recipient. Molecules of the admitted gas can therefore additionally accumulate on the inner surfaces of the recipient. As a result, the maximum realizable end pressure in the recipient can increase in such a way that the ultra-high vacuum region may no longer be reached. At least, the additional gas inlet increases the time until an acceptable final pressure in the recipient is achieved. Furthermore, the admission of additional gas in the high vacuum or ultra-high vacuum range of a vacuum system is problematic insofar as impurities can enter the recipient via the additional gas.

Therefore, it is an object of the invention to provide a method for heating a rotor of a vacuum pump, with which the rotor can be heated to a temperature sufficient for heating, without additional gas must be introduced into the vacuum system.

This object is achieved by a method having the features of claim 1 and in particular by virtue of the fact that, within the rotor of a vacuum pump, which is drivable by means of an electric motor and whose temperature during a first operating phase of the vacuum pump is in the range of an ambient temperature, during a second operating phase eddy currents are generated, which cause heating of the rotor to a desired temperature above ambient temperature.

To generate the eddy currents, the electromagnetic properties of the rotor are changed, for example, directly by means of a magnetic field or indirectly by a manipulation of the control of the electric motor. The heating of the rotor thus requires no additional gas load, so that neither a device for the additional gas inlet is necessary, nor there is the risk of contamination by additional gas. Since the eddy currents within the rotor can be generated directly by changing the electromagnetic properties of the rotor, the temperature required for heating the rotor can be reached faster than in a method in which the heating of the rotor takes place by means of additional gas friction due to a gas load.

The inventive method can also be carried out simultaneously with the conventional heating of a recipient and a housing of the vacuum pump described above. The simultaneous heating of the recipient and the housing as well as the rotor of the vacuum pump reduces the likelihood that molecules released from the surfaces of the rotor due to heating will re-attach to surfaces of the recipient or static parts of the vacuum pump and vice versa. As a result, a lower end pressure in the recipient can be achieved, and the time is shortened until this final pressure is reached.

Advantageous embodiments of the invention are set forth in the subclaims, the description and in the figures.

According to one embodiment, the eddy currents are generated by an efficiency reduction of the electric motor. Compared to a normal operation in which eddy current losses in the rotor are undesirable, the electric motor is temporarily operated at a reduced efficiency in driving the rotor. This contributes to a simple and cost-effective heating of the rotor, in which it requires no additional components compared to the normal operation of the vacuum pump, but only a special control of existing components.

The eddy currents are preferably generated by a change in the power supply for the electric motor, in particular by a change, preferably displacement, a commutation for a stator of the electric motor. One part of a commutation phase can be used, for example, to accelerate the electric motor, while in another part of the commutation phase, a deceleration of the electric motor takes place. In electronics for controlling the vacuum pump, therefore, only a separate setting mode is required for heating the rotor, which leads to the displacement of the commutation for the stator of the electric motor compared to the normal operation of the vacuum pump. The heating of the rotor can thus be carried out with a particularly low cost.

Alternatively or additionally, the eddy currents can be generated by an external magnetic field. This has the advantage that optimum control of the electric motor for driving the rotor during heating or heating of the rotor can be maintained. Furthermore, no change or expansion of the electronics for driving the vacuum pump or the electric motor for the drive is required because the external magnetic field is generated by a separate device.

Advantageously, the temperature of the rotor is measured by means of a temperature sensor and kept at the desired temperature for a predetermined period of time. By means of the temperature sensor can be ensured that the desired temperature of the rotor is actually achieved and the desired temperature for the predetermined period of time is maintained. The predetermined period of time can be determined empirically, for example, on the basis of the pressure rise during the heating of the rotor.

The desired temperature is preferably a temperature at which outgassing of the rotor occurs, and is in particular in a range between 90 ° C and 120 ° C. The desired temperature is thus a compromise between a minimum temperature at which, for example, water molecules and other impurities still separate from the rotor, and a temperature of well above 120 ° C, which would be more suitable for heating the rotor, but the operation of the rotor and thus the vacuum pump would affect overall. In principle, however, it is also conceivable to increase the temperature of the rotor for a limited, comparatively short, period of time above 120.degree. This can improve the effectiveness of bakeout. However, the time period should be selected such that impairment of the operability of the vacuum pump is precluded.

According to a further embodiment, the generation of the eddy currents for heating the rotor is stopped when a predetermined pressure at an inlet of the vacuum pump is exceeded. The heating of the rotor can thus be additionally controlled by means of a measurement of the pressure in the high-vacuum or ultra-high vacuum range. The predetermined pressure is then undershot when the outgassing of the rotor stops and the rotor is sufficiently baked. By stopping the heating of the rotor falls below the predetermined pressure, the generation of the eddy currents to an effective period of time limited. This can reduce the energy consumption and the cost of heating the rotor.

The invention further relates to a vacuum pump, in particular a turbomolecular pump having a rotor, an electric motor for driving the rotor and a control device for the electric motor, which is designed to carry out one of the methods described above.

Fig. 1

eine schematische Darstellung einer Anordnung zum erfindungsgemäßen Erwärmen eines Rotors einer Vakuumpumpe,

Fig. 2

zeitliche Verläufe des Drucks an verschiedenen Positionen einer Vakuumanlage, bei welcher ein Rotor einer Vakuumpumpe nicht mit dem erfindungsgemäßen Verfahren erwärmt wurde, und

Fig. 3

zeitliche Verläufe des Drucks an verschiedenen Positionen einer Vakuumanlage, bei welcher der Rotor der Vakuumpumpe zuvor mit dem erfindungsgemäßen Verfahren erwärmt wurde.

The invention is explained below purely by way of example with reference to possible embodiments of the invention with reference to the accompanying figures. Show it:

Fig. 1

a schematic representation of an arrangement for heating according to the invention of a rotor of a vacuum pump,

Fig. 2

time profiles of the pressure at various positions of a vacuum system in which a rotor of a vacuum pump has not been heated by the method according to the invention, and

Fig. 3

time profiles of the pressure at various positions of a vacuum system, in which the rotor of the vacuum pump was previously heated by the method according to the invention.

Fig. 1 schematically shows an arrangement with which a method according to the invention for heating or heating a rotor of a vacuum pump can be performed. In the case of the vacuum pump, this is a turbomolecular pump 11, more precisely a so-called split-flow pump, which operates between a not shown inlet and an outlet 12 of the pump has a total of six ports H1 to H6 at which the pressure can be measured and via which a gas inlet into the pump is possible. Of these ports H1 to H6 are in Fig. 1 only ports H1, H3 and H5 are shown.

The turbomolecular pump 11 has a turbomolecular pumping stage 13 and a Holweckpumpstufe 15 and a rotor 17 for both pumping stages 13, 15 which is drivable by means of an electric motor 19. Further, a control device 21 is provided, which includes a power supply and an electronics for controlling the electric motor 19 and is connected by means of connecting lines 23 to the electric motor 19 of the turbomolecular pump 11.

At the inlet of the turbomolecular pump 11, an ultra-high vacuum can be generated, ie a pressure in the range of less than 10 ^-10 mbar. The turbomolecular pump 11 has, within the turbomolecular pumping stage 13, a port H1 at which the pressure in the vicinity of the inlet can be measured, and a port H3 at which the pressure in a central region of the turbomolecular pumping stage 13 can be measured. Further, the turbomolecular pump 11 within the Holweckpumpstufe 17 a port H5, which is intended to measure the pressure in the vicinity of the outlet of the pump and for the admission of a gas load.

The outlet 12 of the turbomolecular pump 11 is connected by means of a vacuum line 25 to a backing pump 27.

Furthermore, the arrangement comprises a device 29 for generating an external magnetic field. In addition, a temperature sensor 28 is provided, through which the temperature of the rotor 17 can be measured and which is arranged for example on a lower part of the turbomolecular pump 11.

For the operation of the arrangement, a first operating phase is provided which corresponds to a normal operation of the turbomolecular pump 11 and in which the temperature of the rotor 17 is in the range of the ambient temperature. The electric motor 19 is controlled during the first phase of operation such that leakage currents, such as eddy currents, are minimized in the rotor 17.

For the first operating phase, a warning threshold for the signal of the temperature sensor 28 is also provided, which corresponds to a predetermined temperature of the rotor 17, above which the turbomolecular pump 11 should not be operated in the first phase of operation. Consequently, if the signal of the temperature sensor 28 during the first operating phase exceeds the warning threshold, a warning is issued to the control device 21.

During a second operating phase of the turbomolecular pump 11, which may also be referred to as a "bake-out phase", a changed control of the electric motor 19 is provided in comparison to normal operation. Specifically, a commutation for a stator of the electric motor 19 is shifted compared to the normal operation during the second operating phase, so that eddy currents in the rotor 17 arise. These eddy currents lead to a heating of the rotor 17 and thus to outgassing the same, without an additional gas load, for example via the port H5, is admitted into the turbomolecular pump 11.

During the second operating phase, the warning threshold of the temperature sensor 28, ie for the temperature of the rotor 17, is further increased or deactivated in order to avoid unintentional termination of the heating and of the heating of the rotor 17. The signal of the temperature sensor 28 is used in the second phase of operation not only for control purposes, but it is used to control the temperature of the rotor 17 to a desired temperature, which is for example in a range between 90 ° C and 120 ° C. The temperature of the Rotor 17 may also be raised above 120 ° C for a limited, comparatively short, period of time to improve the efficiency of bakeout. Since the temperature sensor 28 is already present in the turbomolecular pump 11 anyway, the method according to the invention thus requires no additional device for regulating the temperature of the rotor 17, but merely an adaptation of the control device 21 which is likewise present.

The second operating phase can be ended when a predetermined pressure at an inlet of the turbomolecular pump 11 is exceeded, because the outgassing of the rotor 17 has stopped and the rotor 17 is thus sufficiently baked. The turbomolecular pump 11 is then operated again under the conditions of the first operating phase described above.

Alternatively, or in addition to changing the commutation of the electric motor 19, the device 29 generates an external magnetic field in the region of the rotor 17, which also generates eddy currents in the rotor 17. Thus, the rotor 17 can also be heated and baked by means of the external magnetic field generating device 29.

In order to heat the rotor of the turbomolecular pump 11 by means of the method according to the invention using the arrangement of Fig. 1 To demonstrate, pressure measurements were made on the turbomolecular pump 11 with two different preconditions. The results of the pressure measurements are in Fig. 2 and 3 shown. At the curves of Fig. 2 was the rotor 17 of the turbomolecular pump 11 previously not heated or annealed, while in the curves of Fig. 3 previously the inventive method for heating and heating of the rotor 17 was used.

Furthermore, for test purposes both the pressure measurements of Fig. 2 as well as those of Fig. 3 such a gas in the area of the outlet 12 of the

Turbomolekularpumpe 11 admitted that at the outlet 12 each had approximately the same pressure as the upper curves 31 and 41 in Fig. 2 or 3 show. The increased pressure due to the additional gas led to an increased gas friction in the rotor 17 and thereby to its heating, which in turn a degassing of the rotor 17 was triggered.

In Fig. 2 and 3 is the pressure at various positions of a vacuum system, such as schematically in Fig. 1 is illustrated over time. The pressure measurement was carried out in each case at the outlet 12 of the turbomolecular pump 11, ie in the fore-vacuum region (curves 31 and 41), at the port H5 (cf. Fig. 1 , Curve 42 in Fig. 3 ), at port H3 (curves 33 and 43), at port H1 (curves 35 and 45) and at the inlet of the turbomolecular pump 11, ie in the ultra-high vacuum range (curves 37, 39, 47 and 49). To improve the measurement reliability, the pressure measurement in the ultra-high vacuum range was carried out at two different positions in the region of the inlet of the turbomolecular pump 11.

Both in the pressure measurement of Fig. 2 as well as in the pressure measurement of Fig. 3 For example, the pressure in the pre-vacuum region of the assembly was increased to about 3 mbar by introducing a gas via port H5 as compared to normal operation (see curves 31 and 41 in FIG Fig. 2 or 3). As a result, an increase in pressure occurred at the ports H3 and H1 as well as in the ultra-high vacuum region at the inlet of the turbomolecular pump 11. The pressure increase is most evident in Fig. 2 in the time course of the curves 31, 33 and 35 can be seen.

As further in Fig. 2 can be seen, the pressure in the ultra-high vacuum region of the assembly increased due to the outgassing of the previously not heated rotor 17 of about 10 ^-10 mbar to almost 10 ^-9 mbar, ie by about one order of magnitude. Further, operation over several hours with additional gas load was required until the ultra high vacuum pressure of the assembly did not increase and a saturation pressure was reached. Besides, it was even after several hours the operation with additional gas load no further drop in pressure to observe, which would have indicated a reduction in the outgassing of the rotor 17.

However, when the rotor 17 of the turbomolecular pump 11 has previously been heated and baked by the method according to the invention (see Fig. 3 ), although in operation with additional gas load initially likewise an increase in pressure in the ultra-high vacuum region of the arrangement occurred, but after a much shorter time reached a saturation value, which was still well below 10 ^-10 mbar (see the curves 47 and 49 in Fig. 3 ). Even with an additional gas load in the pre-vacuum region of the arrangement, the pressure in the recipient was thus still within the desired ultra-high vacuum range. In this case, a comparatively small rise in pressure in the curves 47 and 49 results above all from an unavoidable backflow of the additionally admitted gas in the direction of the inlet of the turbomolecular pump 11, ie into the ultra-high vacuum range, and less from outgassing of the rotor 17.

The test result of Fig. 3 shows thus that the rotor 17 was efficiently heated and baked by the method according to the invention and the pressure increase in the ultra-high vacuum despite additional gas load in Vorvakuumbereich was at least an order of magnitude lower than without previous heating of the rotor 17. In other words, the curves 47 and 49 of Fig. 3 in that the rotor 17 was able to sufficiently outgas beforehand by the method according to the invention, so that even with additional gas load and the resulting additional heating of the rotor 17 in comparison with the curves 37 and 39 of FIG Fig. 2 only a slight increase in pressure occurred in the ultra-high vacuum range. The successful heating of the rotor 17 by means of the method according to the invention can also be recognized from the fact that the pressure increase in the curves 47 and 49 of FIG Fig. 3 after a short time reached the saturation value below 10 ^-10 mbar.

LIST OF REFERENCE NUMBERS

11

Turbo molecular pump

12

outlet

13

Turbo molecular pump stage

15

Holweckpumpstufe

17

rotor

19

electric motor

21

control device

23

interconnectors

25

vacuum line

27

backing pump

28

temperature sensor

29

Device for generating an external magnetic field

H1

Port in the area of the pump inlet

H3

Port in the middle area of the turbomolecular pumping stage

H5

Port in the area of Holweckpumpstufe

31.41

backing pressure

42

Pressure at port H5

33, 43

Pressure at port H3

35.45

Pressure at port H1

37, 47, 39, 49

Pressure in the ultra-high vacuum range

Claims (10)

Method for heating a rotor (17) of a vacuum pump (11), in particular a turbomolecular pump (11), which has a rotor (17) which can be driven by means of an electric motor (19) whose temperature is within the range of a first operating phase of the vacuum pump (11) Ambient temperature is,
characterized in that
during a second phase of operation eddy currents are generated within the rotor (17), which cause a heating of the rotor (17) to a desired temperature above the ambient temperature. Method according to claim 1,
characterized in that
the eddy currents are generated by an efficiency reduction of the electric motor (19). Method according to claim 1 or 2,
the eddy currents are generated by a change in the power supply to the electric motor (19). Method according to claim 3,
characterized in that
the eddy currents are generated by a change, in particular displacement, of a commutation for a stator of the electric motor (19). Method according to one of the preceding claims,
characterized in that
the eddy currents are generated by an external magnetic field. Method according to one of the preceding claims,
characterized in that
the temperature of the rotor (17) is measured by means of a temperature sensor (28) and maintained at the desired temperature for a predetermined period of time. Method according to one of the preceding claims,
characterized in that
the desired temperature is a temperature at which outgassing of the rotor (17) occurs. Method according to one of the preceding claims,
characterized in that
the desired temperature is in a range between 90 ° C and 120 ° C. Method according to one of the preceding claims,
characterized in that
the generation of the eddy currents for heating the rotor (17) is stopped when a predetermined pressure at an inlet of the vacuum pump (11) is exceeded. Vacuum pump (11), in particular turbomolecular pump (11), with: a rotor (17), an electric motor (19) for driving the rotor (17) and a control device (21) for the electric motor (19), which is designed to carry out a method according to one of the preceding claims.

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