Arrangement with a vacuum pump and method of compensating magnetic field produced by magnetic interference field of at least one vacuum pump component

Abstract

An arrangement includes a vacuum pump having a rotor, and a drive unit for driving the rotor and having at least one magnetic interference field-generating component and at least one compensation coil for compensating the magnetic interference field generated by the at least one component.

Claims

1. An arrangement, comprising a vacuum pump including a rotor, and drive means for driving the rotor, at least one magnetic interference field-generating component; and at least one compensation coil for compensating a magnetic interference field generated by the at least one component of the vacuum pump and arranged on a vacuum pump housing or in a vacuum pump housing remotely from the at least one magnetic interference field-generating component.

2. An arrangement according to claim 1, comprising altogether three compensation coils for compensating the magnetic interference field generated by the at least one component of the vacuum pump.

3. An arrangement according to claim 2, wherein magnetic fields of the three compensation coils are oriented in three spatial directions.

4. An arrangement according to claim 3, wherein the magnetic fields of the three compensation coils are oriented at an angle of 90° to each other.

5. An arrangement according to claim 1, wherein the at least one compensation coil is formed of at least one winding of an electrical conductor.

6. An arrangement according to claim 1, further comprising at least one sensor for at least one sizing and measuring the magnetic interference field or phase reference of the at least one component.

7. An arrangement according to claim 6, further comprising a current source for the at least one compensation coil; and a compensation device for controlling current in the at least one compensation coil dependent on the at least one of sizing and measuring the magnetic interference field of the at least one component.

8. An arrangement according to claim 7, wherein the compensation device and the at least one compensation coil are formed as separately controlled components.

9. An arrangement according to claim 1, wherein the drive means comprises an electric motor for rotating the rotor, and at least one magnetic bearing for supporting the rotor, and wherein the at least one magnetic interference field generating component is one of the magnetic bearing and the electric motor.

10. An arrangement according to claim 9, wherein the magnetic bearing is formed as one of permanent magnetic bearing and active magnetic bearing.

11. An arrangement according to claim 1, wherein the vacuum pump housing has an attachment, and wherein the at least one compensation coil is arranged on or in the attachment.

12. An arrangement according to claim 1, wherein the vacuum pump includes a plurality of magnetic interference field-generating components, and the at least one compensation coil is adapted to compensate magnetic interference fields generated by the plurality of the magnetic interference field-generating components.

13. A method of compensating a magnetic interference field generated by at least one component arranged in a vacuum pump, comprising the step of providing at least one compensation coil for compensating a magnetic interference field of the at least one component of the vacuum pump, and arranging the compensation coil on a vacuum pump housing or in the vacuum pump housing remotely from the at least one magnetic interference field-generating component.

14. A method according to claim 13, comprising the step of providing a compensation device for controlling current in the at least one compensation coil dependent on one of sizing and measuring the magnetic interference field.

15. A method according to claim 13, wherein the at least one compensation coil generates a field vector having adjustable amplitude and direction.

16. A method according to claim 14, wherein the compensation device derives a rotationally-synchronous compensation principal frequency and first to n harmonic components with n≧2 from drive electronics of the vacuum pump.

17. A method according to claim 13, comprising the step of providing a sensor for determining the phase reference of the vacuum pump.

18. A method according to claim 13, wherein the at least one component is formed as one of at least one magnetic bearing and at least one electric motor.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The drawings show:

(2) FIG. 1 a longitudinal cross-sectional view of a turbomolecular pump; and

(3) FIG. 2 a schematic view of orientation of compensation coils.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(4) FIG. 1 shows a cross-sectional view of a turbomolecular pump 1 having a flange 4 releasably securable to a flange of a to-be-discharged chamber (not shown). The gas is aspirated through a suction opening 6 into the pump 1 and is discharged through an outlet 8. A rotor 10 and a stator 20 are located in a housing 2 of the pump. The cooperation of the rotor and stator provides for gas delivery. The rotor 10 includes a shaft 12 on which a forevacuum side rotor disc 14, an intermediate rotor disc 16, and a high vacuum side rotor disc 18 are provided. Each of the rotor discs 14, 16, 18 has several blade assemblies formed of separate blades.

(5) The shaft 12 is rotatably supported, at its high vacuum side, by a permanent magnetic bearing 40 and at its forevacuum side, by a roller bearing 42. A drive 44 rapidly rotates the rotor with a speed of 10,000 revolutions per minute. The stator has a forevacuum side stator disc 24, an intermediate stator disc 26, and a high vacuum side stator disc 28. The stator discs 24, 26, 28 are axially spaced from each other with respect to the shaft 12 by spacer rings 30, 32, 34 and are alternatively arranged with the rotor discs 14, 16, 18. The stator discs 24, 26, 28 likewise each is provided with blade assemblies. The number of the rotor and stator discs depends on desired vacuum-technical parameters such as suction capacity, pressure ratio between the suction opening and the outlet.

(6) On a pump attachment 36, three coils 46, 48, 50 are located. The coils 46, 48, 50 are arranged at a 90° degree angle with respect to each other. In addition, a compensation device 52 controls, via conductors, not shown, the current in the coils 46, 48, 50. A sensor 54 determines the magnetic interference field {right arrow over (B)}.sub.St. The coils 46, 48, 50 generate a compensation field {right arrow over (B)}.sub.K so that a resulting field {right arrow over (B)}.sub.Res={right arrow over (B)}.sub.St−{right arrow over (B)}.sub.K(i.sub.X,Y,Z) is produced. The resulting field is minimized by the compensation device 52 so that the magnetic field {right arrow over (B)}.sub.St generated by the magnetic bearing 40 and/or the motor 44 does not influence any other apparatus such s, e.g., an electronic microscope, with which the vacuum pump is connected.

(7) The compensation device 52 minimizes, by varying amplitudes and phases of the current in the coils 46, 48, 50, the resulting field {right arrow over (B)}.sub.Res, while the drive electronic produces, via an induction coil, the rotation-synchronous compensation principal frequency and first to n harmonic component with n≧2.

(8) The amplitude and phase variation of the current in the coils 46, 48, 50 is carried out according to the following equation:
i.sub.z=i.sub.zo.Math.sin(ω.sub.o.Math.t+φ.sub.o)+i.sub.z1.Math.sin(2ω.sub.o.Math.t+φ.sub.1)+i.sub.z2.Math.sin(3ω.sub.o.Math.t+φ.sub.2)+ . . .
which is the same in X- and Y-directions.

(9) The field vector {right arrow over (B)}.sub.K with adjustable amplitude and direction is generated by the current in the coils 46, 48, 50. The field vector {right arrow over (B)}.sub.K compensates the magnetic interference field {right arrow over (B)}.sub.st which is generated by the magnetic bearing 40 and the drive motor 44 of the turbomolecular pump. The a.c. interference field naturally has the same frequency as the turbomolecular pump 1 and is slightly non-sinusoidal.

(10) The zero or minimal tuning of the interference field is carried out either automatically by a specific variation of the above-mentioned parameters and detection of the magnetic interference field {right arrow over (B)}.sub.Res with the magnetic sensor 54. The tuning can also be carried out by monitoring the dispersal degree of the apparatus with which the turbomolecular pump is connected. The tuning can also be carried out in an electronic microscope (note shown).

(11) FIG. 2 shows an advantageous orientation of the coils 46, 48, 50 with respect to each other. The coil windings are oriented along X-, Y- and Z-axes so that the coils are arranged to each other at an angle of 90°.

(12) Thereby, an optimal compensation of the magnetic interference field becomes possible.

(13) Though the present invention was shown and described with references to the preferred embodiment, such is merely illustrative of the present invention and is not to be construed as a limitation thereof and various modifications of the present invention will be apparent to those skilled in the art. It is, therefore, not intended that the present invention be limited to the disclosed embodiment or details thereof, and the present invention includes all variations and/or alternative embodiments within the spirit and scope of the present invention as defined by the appended claims.