METHOD FOR OPERATING A VACUUM PUMP SYSTEM

Abstract

A processing chamber is connected to a lock chamber. For evacuating the lock chamber and/or the processing chamber a vacuum pump system is provided. The latter comprises a vacuum pump equipment having at least one vacuum pump. Further, the vacuum pump system comprises a valve device for connection to the lock chamber as well as a controller. For noise reduction, a cyclically occurring operating parameter is determined by means of the controller. From said parameter it is determined at which point in time the valve is opened such that temporally before the opening of the valve the rotational speed of at least one of the vacuum pumps can be reduced. This results in a considerable noise reduction at continuing good pump-out times.

Claims

1. A method for operating a vacuum pump system for evacuating a chamber connected to a processing chamber. wherein said vacuum pump system comprises a vacuum pump equipment including at least one vacuum pump, a valve device arranged between said vacuum pump equipment and said chamber, and a controller, wherein the method comprises: determining at least one cyclically occurring operating parameter of said vacuum pump system via a controller, and reducing temporally a rotational speed of a least one of said vacuum pumps of said vacuum pump equipment before said valve device is opened.

2. The method according to claim 1, wherein an operating parameter significantly changes when the opened valve device is selected as the operating parameter.

3. The method according to claim 1, wherein a motor current of a motor driving a vacuum pump of the vacuum pump equipment is determined as the operating parameter, wherein in particular a significant increase of the motor current is associated with opening the valve device.

4. The method according to claim 1, wherein an inlet pressure of the vacuum pump equipment and/or an inlet pressure of at least one of the vacuum pumps of said vacuum pump equipment and/or a temperature of at least one of said vacuum pumps and/or a travelling path of a pressure relief valve between the inlet and the outlet of at least one of said vacuum pumps of said vacuum pump equipment are determined as the operating parameter.

5. The method according to claim 1, wherein a cycle length is determined as a period of time between two identical changes of an operating parameter.

6. The method according to claim 5, wherein, at or before the end of a cycle length, the rotational speed of one of the vacuum pumps of the vacuum pump equipment is reduced.

7. The method according to claim 1, wherein, after the valve device has been opened, the rotational speed of at least one of the vacuum pumps is increased.

8. The method according to claim 1, wherein on the basis of at least one operating parameter a load duration is determined during which the chamber is evacuated to a predetermined vacuum.

9. The method according to claim 8, wherein, at a point in time after the load duration, the pump rotational speed is reduced, and the pump rotational speed remains reduced for the remaining cycle length.

10. The method according to claim 6, wherein the electrical braking energy generated during the reduction of the rotational speed of at least one of the vacuum pumps of the vacuum pump equipment is stored in an energy storage unit or fed back into the supply network by means of an energy feedback unit.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Hereunder the disclosure is explained in detail on the basis of an exemplary embodiment with reference to the drawings and graphs in which:

[0025] FIG. 1 shows a schematic representation of a vacuum pump system as well as a lock chamber,

[0026] FIG. 2 shows a graph of a motor current as well as a motor rotational speed versus time in known processes,

[0027] FIG. 3 shows a graph of a motor current as well as a motor rotational speed versus time in the method according to the disclosure, and

[0028] FIGS. 4 and 5 shows a schematic representation of a vacuum pump comprising an energy feedback unit.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0029] In a schematically depicted processing chamber 10 a product is processed, e.g., coated. For this purpose, a vacuum is generated in the processing chamber 10. For feeding products, materials and the like to be processed into the processing chamber, a lock chamber 12 is connected to the processing chamber 10. The lock chamber 12 comprises a lock inlet 14 for feeding a product or the like into the lock chamber 12 as well as a lock outlet 16 for transferring the product or the like from the lock chamber 12 into the processing chamber 10.

[0030] For evacuating the lock chamber 12 the latter is connected to a vacuum pump system. The vacuum pump system comprises a vacuum pump equipment 18. In the illustrated exemplary embodiment, the vacuum pump equipment 18 comprises a main vacuum pump 20 and a prevacuum pump 22 arranged in series downstream of the main vacuum pump 20. The main vacuum pump 20 is in particular a Roots or screw pump. The main vacuum pump 20 is connected to the lock chamber 12 via a pipe 24, wherein in the pipe 24 a valve device 26 is arranged. The outlet of the main vacuum pump 20 is connected to the inlet of the prevacuum pump via a pipe 28.

[0031] Further, the vacuum pump system comprises a controller 30. In the illustrated exemplary embodiment, the controller 30 is connected to the main vacuum pump 20 as well as the prevacuum pump 22 via electric lines 32, 34. Via the lines 32, 34, on the one hand, an electric motor driving the corresponding pump can be controlled, and, on the other hand, operating parameters measured in or at the corresponding pump can be transmitted to the controller 30.

[0032] The measured operating parameter is in particular the motor current. Furthermore, as illustrated by an arrow 36, further data can be transmitted to the controller, and of course the controller can also perform other controlling tasks. In particular, the controller 30 can open and close the valve 26.

[0033] Hereunder the disclosure is explained with reference to FIGS. 2 and 3 on the basis of a possible evaluation of a motor current of in particular an electric motor of the main vacuum pump 20.

[0034] Here, FIG. 2 shows a cyclical profile of a motor current as well as the rotational speed of the vacuum pump according to prior art, and FIG. 3 shows the corresponding graphs according to the disclosure.

[0035] In conventional applications, the curve of the motor current I illustrated by a thick line indicates at a point in time t.sub.1, when the valve is open, a strong current increase from I.sub.min to I.sub.max. The same current increase occurs again after a cycle length t.sub.z at another point in time t.sub.1. From the graph or the current profile, the controller 30 can thus determine the cycle length t.sub.z on the basis of the current increase occurring in cyclical intervals at the points in time t.sub.1. This determination is independent of the knowledge when the valve 26 is actually opened. This is of interest since frequently no signal is generated or issued which informs the controller that the valve is opened or when it is opened. The controller according to the disclosure is of the self-learning type since even in the case of changing processes it can automatically determine the new cycle length.

[0036] The curve of the current profile illustrated by a thick line further shows that after the current increase at the point in time t.sub.1, it first decreases slowly and then relatively rapidly such that at a point in time t.sub.2 the electric motor receives again the minimum current I.sub.min.

[0037] The period of time t.sub.1 to t.sub.2 is the load duration, i.e. that period of time during which the lock chamber 12 is evacuated.

[0038] The further current profile after the point in time t.sub.2 is then constantly at a low current I.sub.min until the valve is opened again at the next point in time t.sub.1.

[0039] The thin line illustrates the rotational speed profile of the corresponding vacuum pump. At the point in time t.sub.1, that is when the valve 26 is opened, the pressure at the pump inlet increases abruptly such that the rotational speed of the pump decreases. During the load duration t.sub.L the pump rotational speed then increases to a maximum value and remains at this maximum rotational speed until the valve is opened again at the further point in time t.sub.1.

[0040] With the aid of the controller according to the disclosure it is thus possible, even without actually knowing when the valve 26 is opened, to determine a point in time for opening the valve. According to the disclosure, the rotational speed of the pump can thus be reduced before or, at the latest, when the valve 26 is opened. Thereby, considerable noise reductions can be achieved.

[0041] As illustrated in FIG. 3, the motor rotational speed is considerably reduced already before the point in time t.sub.1 at which the valve 26 is opened. At a point in time t.sub.3 the motor rotational speed is reduced from the maximum rotational speed, which is reached during the evacuation of the lock chamber 12, to a considerably lower rotational speed. Here, the point in time t.sub.3 is later than a point in time t.sub.2 such that at the point in time t.sub.3 the evacuation of the lock chamber has already been performed or the load duration 4 is terminated.

[0042] Preferably, again with the aid of the controller 30, a defined braking up to a point in time t.sub.4 takes place. During the braking between the points in time t.sub.3 and t.sub.4 the current increases for a short time and decreases again to the minimum value at the point in time t.sub.4.

[0043] As from the point in time t.sub.4, the rotational speed of the motor is thus considerably lower than the maximum rotational speed. When the valve is opened at the subsequent point in time t.sub.1, the motor does not have the maximum rotational speed as in prior art but a considerably reduced rotational speed. Hence, after the valve has been opened (point in time t.sub.1) the rotational speed is further reduced only to a small extend, as can be seen in FIG. 3.

[0044] The kinetic energy released during braking between t.sub.3 and t.sub.4 can be fed back to the supply network via a feedback unit. Thereby, the energy efficiency of a vacuum pump can be increased which results in saving of costs at the operator's end.

[0045] In FIGS. 4 and 5 examples of an energy feedback unit are illustrated. In a particularly preferred embodiment, these are used for pumps which are employed in the method described above. However, it is also possible to employ such energy feedback units for vacuum pumps which are used in other methods.

[0046] FIG. 4 schematically shows a vacuum pump 40 which may be the vacuum pump 20 or 22 (FIG. 1), for example. The vacuum pump 40 comprises an electric motor 42 by means of which a pump rotor 44 is driven. In the illustrated exemplary embodiment, the electric motor 42 is driven or controlled via a frequency converter 46. The frequency converter 46 is connected to the supply network 48.

[0047] When the rotor 44 of the vacuum pump 40 is braked, the electric motor 42 is used as a generator due to the considerable kinetic energy. The electrical energy produced is fed to an energy feedback unit 50 via the frequency converter and can then be fed again into the supply network 48 via the illustrated lines.

[0048] In an alternative embodiment according to FIG. 5, the connection of the frequency converter 56 to the supply network 48 via the energy feedback unit 50 is provided. The energy feedback unit 50 thus also serves as a feeding unit.