Magnetic bearings and vacuum pumps

Abstract

A magnetic bearing for a vacuum pump, particularly a turbomolecular pump, comprising: a permanent magnet radial bearing having stationary and rotating magnetic elements arranged radially adjacent to one another and mutually repelling to provide radial support; an end ring mounted axially adjacent to the rotating magnetic elements; and a magnetic axial bearing including an electromagnet, the end ring having a radially extending protrusion arranged adjacent to the electromagnet so that the electromagnet can apply an axial magnetic force to the protrusion of the end ring.

Description

[Technical Field]

[0001] The present invention relates to a magnetic bearing for a vacuum pump, in particular a turbomolecular pump.Furthermore, the present invention relates to a vacuum pump, in particular a turbomolecular pump, equipped with such a magnetic bearing. [Background technology]

[0002] A vacuum pump includes a housing having an inlet and an outlet. A rotor including a rotor shaft is disposed within the housing, and at least one rotor element is coupled to the rotor shaft and rotated by an electric motor. In the case of a turbomolecular pump, a plurality of vanes are coupled to the rotor shaft as pumping elements that interact with a plurality of vanes of a stator coupled to the housing. Rotation of the rotor transports a gaseous medium from the inlet to the outlet. At this point, the rotor shaft is rotatably supported by one or more bearings.

[0003] It is known to use permanent magnetic bearings, which are contactless and not subject to wear. However, permanent magnetic bearings are typically used for radial support, and these bearings must be complemented by axial bearings that axially support the rotor shaft. In particular, if both or all of the bearings supporting the rotor shaft are constructed as permanent magnetic radial bearings, axial support of the rotor shaft is essential. However, the additional axial bearings increase the space required and the overall size of the vacuum pump. Summary of the Invention [Problem to be solved by the invention]

[0004] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a compactly constructed magnetic bearing and a vacuum pump equipped with such a magnetic bearing. [Means for solving the problem]

[0005] This problem is solved by a magnetic bearing according to claim 1 and a vacuum pump according to claim 8.

[0006] In a first aspect, a magnetic bearing for a vacuum pump, particularly a turbomolecular pump, is provided. The magnetic bearing comprises a permanent magnet radial bearing having a stationary magnetic element coupled to the vacuum pump housing and a rotating magnetic element coupled to the vacuum pump rotor, disposed radially adjacent to one another and mutually repelling one another to provide radial support. An end ring is attached axially adjacent to the rotating magnetic element. The end ring, typically made of a hard metal such as steel, must protect the fragile permanent magnet ring of the rotating magnetic element during insertion of the rotor shaft into the vacuum pump housing. While the end ring does not contribute to radial support of the rotor shaft, in addition to providing protection, it also maintains the axial position of the rotating magnetic element of the permanent magnet bearing.

[0007] According to the present invention, the magnetic bearing comprises a magnetic axial bearing including an electromagnet or coil for generating an adjustable magnetic field. Furthermore, the end ring has a radially extending protrusion and is positioned adjacent to the electromagnet, which can apply an axial magnetic force to the end ring protrusion. Thus, the adjustable axial force applied to the end ring protrusion provides axial support for the rotor shaft. Thus, the end ring protrusion integrates the radial bearing and the axial bearing, thereby reducing the space requirements of the magnetic bearing and, consequently, the minimum space requirements of a vacuum pump including such a magnetic bearing.

[0008] Preferably, the protrusions and more preferably the end rings are made from a ferrite material, and since the end rings are in direct contact with the outermost ring magnet of the rotating magnetic element, the ferrite material allows the magnetic field to penetrate the protrusions, increasing the magnetic field at the electromagnets and improving the efficiency of the axial bearing.

[0009] Preferably, the electromagnet is coupled to a yoke element that extends radially and is positioned axially adjacent to the end ring protrusion to generate a magnetic field at the protrusion. Preferably, the yoke is U-shaped, with yoke components positioned axially on either side of the end ring protrusion. The yoke thus forms a gap within which the end ring protrusion is positioned to enhance the magnetic field generated by the electromagnet.

[0010] Preferably, the projection and the end ring are constructed as a single piece, i.e., are integrally molded.

[0011] Preferably, a sensor coil is disposed axially adjacent to the protrusion and is coupled to the housing, i.e., non-rotating or stationary. The sensor coil allows the axial position of the protrusion to be measured directly. Preferably, the sensor coil is used as an eddy current sensor and is able to detect the axial position of the rotor shaft over the entire circumference. This design has the advantage that it does not detect possible rotor tilt vibrations and therefore does not cause any harmful coupling or interference between the radial and axial movements of the rotor shaft. In particular, the sensor coil is part of a resonant circuit, and a shift in the resonant frequency is related to changes in axial position.

[0012] Preferably, a bias magnet is coupled to the housing and positioned at least partially axially adjacent to the protrusion for applying a bias force to the magnetic axial bearing. Thus, an axial bias force is applied to the protrusion and the rotor shaft by the bias magnet configured as a magnetic ring. Additionally, this bias allows electromagnets to apply attractive and repulsive magnetic forces to the protrusions of the end ring to precisely adjust the axial position of the rotor shaft. Specifically, the bias magnet has a magnetic polarity orientation opposite to that of the outermost ring magnet of the rotating magnetic element adjacent to the end ring. With this configuration, the bias effect of the bias magnet is enhanced by the additional magnetic field of the last magnet ring of the rotating magnetic element adjacent to the end ring, transmitted by the protrusion.

[0013] Preferably, the sensor coil is located within the bias magnet. This arrangement reduces space requirements and simplifies assembly. Furthermore, detection is close to the location of the force acting on the rotor. Because the sensor coil is located outside the main magnetic flux of the magnetic field, it is less susceptible to the influence of magnetic bearings located adjacent to the sensor coil.

[0014] Preferably, the stationary end ring is disposed axially adjacent to the stationary magnetic element, particularly immediately adjacent to the outermost magnetic ring of the stationary magnetic element, in that it is disposed on the same side as the end ring mounted axially adjacent to the rotating magnetic element.

[0015] Preferably, a conductive disk is coupled to the stationary end ring and is positioned at least partially axially adjacent to the rotating magnetic element so that eddy currents are induced in the conductive disk by the magnetic field of the rotating magnetic element. Thus, a conductive disk made of a conductive material such as copper or aluminum creates an eddy current damper that utilizes the magnetic field provided by the outermost rotating magnetic element of the permanent magnet bearing. Specifically, the disk extends radially so as to be positioned axially adjacent to the rotating magnetic element.

[0016] In another aspect of the present invention, there is provided a vacuum pump, in particular a turbomolecular pump, comprising a housing and a rotor shaft disposed within the housing and rotatably supported by the at least one permanent magnet bearing as described above.

[0017] Preferably, the vacuum pump comprises two bearings, the second bearing being constructed as a conventional permanent magnet bearing or roller bearing, or alternatively the second bearing being constructed as a permanent magnet bearing as described above including an additional / second axial bearing to provide combined axial support for the rotor shaft.

[0018] Preferably, the permanent magnetic bearing according to the invention is arranged on the exhaust side of the rotor shaft, alternatively or additionally, the permanent magnetic bearing according to the invention is provided on the suction side of the rotor shaft.

[0019] Preferably, the stationary magnetic element is coupled to a trunnion that extends into a recess in the rotor shaft, and the rotating magnetic element is coupled to an inner surface of the recess radially opposite the stationary magnetic element.

[0020] The present invention will now be described in more detail with reference to the accompanying drawings. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a first embodiment of a vacuum pump according to the present invention. [Figure 2] FIG. 2 is a detailed view of a magnetic bearing according to the present invention. [Figure 3] 3 is a detailed view of a further embodiment of a magnetic bearing according to the invention; [Figure 4] 3 is a detailed view of a further embodiment of a magnetic bearing according to the invention; [Figure 5] 3 is a detailed view of a further embodiment of a magnetic bearing according to the invention; DETAILED DESCRIPTION OF THE INVENTION

[0022] Referring to FIG. 1, a vacuum pump constructed as a turbomolecular pump is shown. The vacuum pump includes a housing 10 including an inlet 12 and an outlet 14. A rotor 16 is disposed within the housing and supported by a first radial bearing 18, constructed as a permanent magnetic bearing, and a second radial bearing 100, also constructed as a permanent magnetic bearing. The first radial bearing 18 includes a plurality of magnet rings 22, 23. The stationary magnet ring 23 of the first radial bearing 18 is mounted on a trunnion 24 extending into a recess 26 in the rotor shaft 16. The rotating magnet ring 22 is disposed radially adjacent to the stationary magnet ring 23 on the inner surface of the recess. In the second radial bearing 100, a rotating magnet ring 106 is mounted inside a bell-shaped element 28, radially adjacent to a stationary magnet ring 105 coupled to the housing. In that respect, the stationary magnet ring 23 of the first radial bearing 18 repels each of the rotating magnet rings 22 of the first radial bearing 18, and similarly, the stationary magnet ring 105 of the second radial bearing 100 repels each of the rotating magnet rings 106 of the second radial bearing 100, thereby rotatably supporting the rotor 16 within the housing 10.

[0023] Furthermore, the first radial bearing 18 and the second radial bearing 100 comprise an emergency run bearing 30 constructed as a ball bearing. The rotor shaft 16 is driven by an electric motor 32. A plurality of pump elements 34 are attached to the rotor shaft 16, which are connected to the vacuum pump housing 10 and constructed as vanes interacting with stator elements 36 arranged alternately with the pump elements 34. In addition, the vacuum pump of Fig. 1 comprises a Holweck stage 38 comprising a rotating cylinder 40 interacting with a threaded stator 42 connected to the housing. Rotation of the rotor shaft 16 transports the gaseous medium from the inlet 12 towards the outlet 14 of the vacuum pump.

[0024] Reference will now be made to the lower magnetic bearing 100 shown in Figure 1 and in more detail in Figure 2. In that regard, reference is made to an axial direction coinciding with the axis of rotation of the vacuum pump and a radial direction perpendicular to the axial direction.

[0025] A magnetic bearing 100 according to the present invention includes a first or rotating magnetic element 102 and a stationary magnetic element 104. The rotating magnetic element is coupled to the rotor shaft 16 via the bell element 28. The stationary magnetic element 104 is coupled to a trunnion 118 of the housing 10. The rotating magnetic element 102 and the stationary magnetic element 104 include radially adjacent, mutually repelling ring magnets 106, 105 for radially supporting the rotor shaft 16. An end ring 108 is coupled to the rotating magnetic element 102 and is directly coupled to the outermost ring magnet 107 of the rotating magnetic element 102. The end ring 108 is typically made of steel and is provided to protect the relatively fragile ring magnets 107, 106 from damage when the rotor shaft 116 is inserted into the housing 10 or when a cap element 120 of the housing 10 is inserted, thereby introducing the trunnion 118 into the recess formed by the bell element 28. Additionally, the stationary end ring 122 may be mounted radially adjacent to the end ring 108 of the rotating magnetic element 102. The stationary end ring 122 maintains / fixes the axial position of the ring magnet 106 of the stationary magnetic element 104. Preferably, the stationary end ring 122 is made of plastic.

[0026] In accordance with the present invention, end ring 108 includes a radial protrusion 110 that, in certain embodiments, extends outwardly of bell element 28. Magnetic bearing 100 further includes an axial bearing 112. Axial bearing 112 includes an electromagnet 114 or coil for generating an adjustable magnetic field. Yoke elements 116A, 116B are coupled to electromagnet 114, positioned axially on opposite sides of the radial protrusion. Yoke elements 116A, 116B thus define a radially extending gap within which radial protrusion 110 is positioned. The yoke elements therefore apply the magnetic field generated by electromagnet 114 to radial protrusion 110, thereby applying an axial force to protrusion 110 and, consequently, rotor shaft 16. The radial and axial magnetic bearings are thus integrated, reducing space requirements and providing effective axial and radial support for the rotor shaft.

[0027] Although the end ring 108 and the radial protrusions 110 are shown as two separate elements in Figure 2, they may be constructed as a single, integrally formed piece. In particular, the end ring 108 and / or the protrusions 110 are formed from a ferritic material such that the magnetic field of the outermost ring magnet 107 is transmitted by the ferritic material of the end ring 108 and the protrusions 116, enhancing the axial force applied to the protrusions 110 by the axial bearings 112.

[0028] Reference is now made to Figure 3, which illustrates another embodiment of the present invention, in which the same or similar elements are designated with the same reference numerals, and in which the description is limited to the differences between the embodiment of Figure 2 and the embodiment of Figure 3.

[0029] Specifically, in the embodiment shown in FIG. 3 , a bias magnet 124 is coupled to the cap element 120 of the housing 110. The bias magnet 124, constructed as a ring magnet, generates a bias magnetic flux in an axial air gap 200 between the protrusion 110 and one of the yoke elements 106B and an axial air gap 201 between the protrusion 110 and the other of the yoke elements 106A. Additionally, the magnetic field of the bias magnet 124 penetrates the protrusion 110, enhancing the magnetic interaction between the protrusion 110 and the magnetic field generated by the electromagnet 114. The bias magnet 124, constructed as a permanent magnet, is positioned adjacent to the protrusion 110. At that point, the bias magnet 112 is magnetically coupled to the yoke elements 106A and 106B to create a magnetic circuit. As shown in FIG. 3 , the bias magnet 124 generates a magnetic flux 113. Based on the magnetic orientation of the bias magnet 124, the magnetic flux of the electromagnet 110 or coil weakens the magnetic flux in one air gap 200 (or air gap 201) and strengthens the magnetic flux in the respective other air gap 201 (or 200). Thus, the force applied to the protrusion 110 can be exerted in both axial directions, depending on the direction of current in the electromagnet 114 or coil. In that regard, preferably, the magnetic poles of the bias magnet 124 and the outermost ring magnet 107 of the rotating magnetic element 102 are oriented in opposite directions, thereby enhancing the bias effect. As a result, the bias magnet 124 can be constructed smaller while still maintaining sufficient axial bias of the bias magnet 124.

[0030] Referring to FIG. 4 , a sensor coil 126 is provided along the entire circumference of the trunnion 118. The sensor coil 126 is disposed axially adjacent to the protrusion 110, and a sensor element 127 is coupled to the protrusion 110. The sensor element can be a permanent magnet to induce eddy currents in the sensor coil 126. Alternatively, the sensor element 127 is made of a conductive material such as copper or aluminum, and a magnetic field is induced in the sensor element by the sensor coil 126 itself. The sensor coil 126 functions as an eddy current sensor to detect the axial distance between the sensor coil 126 and the rotor shaft 16, which is used to control the magnetic field created by the electromagnet 114 to apply an axial force to the protrusion 110 and the rotor shaft 16. This allows the axial position of the rotor shaft 16 to be controlled / maintained. Because the sensor coil 126 is constructed in a ring shape, the tiling of the rotor shaft has no or little effect on the sensor signal, as it is averaged from the sensor signal detected along the entire circumference. Furthermore, a compact design can be achieved due to the placement of the sensor coil radially inward of the bias magnet 124, but the sensor coil is outside the main magnetic flux of the axial bearing 112. Therefore, interaction between the position sensor and the axial bearing is reduced.

[0031] Referring to FIG. 5 , the end rings 122 of the stationary magnetic element 104 are directly coupled to radially extending conductive disks 128. The conductive disks 128 are made of a conductive material such as copper, aluminum, or the like. The disks 128 provide an eddy current damper that acts directly on the end of the rotor shaft 16 to damp radial vibrations of the rotor shaft 16. At that point, the magnetic field of the outermost ring magnet 107 induces eddy currents in the disks 128, creating a restoring magnetic force that damps radial vibrations of the rotor shaft 16. Thus, the outermost ring magnet 107 has the dual function of radial support for the rotor shaft 16 and as an eddy current damper.

[0032] 5 shows the magnetic bearing 100 with an eddy current damper, a sensor coil 126, and a bias magnet 124, although different combinations of these features are possible in different embodiments. Thus, in one embodiment, only the eddy current damper 128 is implemented with the sensor coil 126, and not the bias magnet 124. In another embodiment, the eddy current damper 128 is implemented with the bias magnet 124 without the sensor coil 126. In another embodiment, the eddy current damper is implemented without the sensor coil 126 and the bias magnet 124. In another embodiment, the bearing 100 according to the present invention includes only a sensor coil, without the eddy current damper and the bias magnet 124. Thus, in addition to the illustrated embodiment, any combination of the eddy current damper 128, the sensor coil 126, and the bias magnet 124 can be implemented in the magnetic bearing 100 according to the present invention to provide a compact and efficient magnetic bearing that simultaneously provides radial and axial support. [Explanation of symbols]

[0033] 16 rotors 28 Bell-shaped element 100 Radial bearing 102 Rotating Magnetic Element 104 Stationary Magnetic Elements 105 Stationary Magnet Ring 106 Rotating Magnet Ring 107 Ring Magnet 108 End Ring 110 Protrusion 112 Axial bearing 114 Electromagnet 116A Yoke element 116B Yoke element 118 Trunnion 120 Cap Elements 122 Stationary End Ring

Claims

1. A magnetic bearing for a vacuum pump, more specifically for a turbomolecular pump, A permanent magnet radial bearing having stationary magnetic elements and rotating magnetic elements arranged radially adjacent to each other and repelling each other to provide radial support, An end ring attached adjacent to the aforementioned rotating magnetic element in the axial direction, A magnetic axial bearing including an electromagnet, Equipped with, A magnetic bearing wherein the end ring has a radially extending projection and is positioned adjacent to the electromagnet, and the electromagnet can apply an axial magnetic force to the projection of the end ring.

2. The aforementioned protrusion and preferably the terminal ring are made of a ferrite-based material. The magnetic bearing according to claim 1.

3. The magnetic bearing according to claim 1, wherein the protruding portion and the end ring are integral parts.

4. The magnetic bearing according to claim 1, wherein a sensor coil is arranged adjacent to the protrusion in the axial direction in order to detect the radial position of the protrusion.

5. The magnetic bearing according to claim 1, comprising a bias magnet positioned at least partially adjacent to the protrusion in the axial direction to apply a bias force to the magnetic axial bearing.

6. The magnetic bearing according to claim 1, wherein a stationary end ring is mounted axially adjacent to the stationary magnetic element.

7. The magnetic bearing according to claim 6, wherein a conductive disk is coupled to the stationary end ring, and the conductive disk is positioned at least partially adjacent to the rotating magnetic element in the axial direction, such that eddy currents are induced in the conductive disk by the magnetic field of the rotating magnetic element.

8. Housing and A rotor shaft disposed within the housing and rotatably supported by at least one permanent magnet bearing according to any one of claims 1 to 7, A vacuum pump that, in detail, is a turbomolecular vacuum pump.

9. The vacuum pump according to claim 8, comprising a second bearing constructed as a permanent magnet bearing or a roller bearing.

10. The vacuum pump according to claim 8, wherein the magnetic bearing is located on the exhaust side and / or the intake side of the rotor shaft.

11. The vacuum pump according to claim 8, wherein the stationary magnetic element is coupled to a trunnion extending into a recess in the rotor shaft, and the rotating magnetic element is coupled to the inner surface of the recess.

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