Magnetic bearing and vacuum pump

Abstract

Magnetic bearing for a vacuum pump, in particular a turbo molecular pump, comprising: a radial permanent magnet bearing having a static magnetic element and a rotating magnetic element arranged radially adjacent to each other and mutually exclusive to provide radial support; a terminal ring attached axially proximate to the rotating magnetic element; a magnetic axial bearing includes an electromagnet, where the terminal ring includes a protrusion extending in a radial direction and disposed proximate to the electromagnet such that an axial magnetic force can be applied by the electromagnet to the protrusion of the terminal ring.

Description

Technical Field

[0001] The invention relates to a magnetic bearing for a vacuum pump and in particular for a turbomolecular pump. The invention also relates to a vacuum pump and in particular to a turbomolecular pump having such a magnetic bearing. Background Art

[0002] The vacuum pump comprises a housing with an inlet and an outlet. A rotor comprising a rotor shaft is arranged in the housing, wherein at least one rotor element is connected to the rotor shaft and rotated by an electric motor. In the case of a turbomolecular pump, a plurality of blades are connected to the rotor shaft as pump elements, thereby interacting with a plurality of blades of a stator connected to the housing. When the rotor rotates, a gaseous medium is conveyed from the inlet to the outlet. The rotor shaft is rotatably supported by one or more bearings.

[0003] It is known to use permanent magnetic bearings, which are contactless and therefore not subject to wear. However, permanent magnetic bearings are usually used for radial support, wherein these bearings must be supplemented by axial bearings that support the rotor shaft in the axial direction. In particular, if two or all bearings supporting the rotor shaft are constructed as permanent magnetic radial bearings, axial support of the rotor shaft is required. However, due to the additional axial bearings, the space requirement increases, thereby increasing the overall size of the vacuum pump.

[0004] It is therefore an object to provide a compactly constructed magnetic bearing and a vacuum pump having such a magnetic bearing. Summary of the invention

[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 and in particular for a turbomolecular pump is provided. The magnetic bearing comprises a radial permanent magnetic bearing having a static magnetic element to be connected to the housing of the vacuum pump and a rotating magnetic element to be connected to the rotor of the vacuum pump, the static magnetic element and the rotating magnetic element being arranged radially adjacent to each other and magnetically repelling each other to provide radial support. Wherein, a terminal ring is attached axially adjacent to the rotating magnetic element. By means of the terminal ring, which is usually made of a hard metal such as steel, the fragile permanent magnetic ring of the rotating magnetic element will be protected during the process of inserting the rotor shaft into the housing of the vacuum pump. The terminal ring does not contribute to the radial support of the rotor shaft, and in addition to providing protection, maintains the axial position of the rotating magnetic element of the permanent magnetic bearing.

[0007] According to the invention, the magnetic bearing comprises a magnetic axial bearing comprising an electromagnet or a coil in order to generate an adjustable magnetic field. In addition, the terminal ring comprises a protrusion extending in the radial direction and arranged adjacent to the electromagnet, so that an axial magnetic force can be applied by the electromagnet to the protrusion of the terminal ring. Therefore, by the adjustable axial force applied to the protrusion of the terminal ring, axial support of the rotor shaft is provided. Therefore, by the protrusion of the terminal ring, the radial bearing and the axial bearing are integrated, thereby reducing the space requirement of the magnetic bearing and thus reducing the minimum space requirement of a vacuum pump comprising such a magnetic bearing.

[0008] Preferably, the protrusion is made of ferrite material, and even more preferably, the terminal ring is also made of ferrite material. Since the terminal ring is in direct contact with the outermost annular magnet of the rotating magnetic element, the magnetic field penetrates the protrusion through the ferrite material and increases the magnetic field at the electromagnet, thereby improving the efficiency of the axial bearing.

[0009] Preferably, the electromagnet is connected to a yoke element extending in the radial direction and arranged axially adjacent to the protrusion of the terminal ring, so as to generate a magnetic field at the location of the protrusion. Preferably, the yoke has a U-shape. Thus, a portion of the yoke is arranged on both sides of the protrusion of the terminal ring in the axial direction. Thus, by means of the yoke, a gap is created in which the protrusion of the terminal ring is arranged, so as to enhance the magnetic field generated by the electromagnet.

[0010] Preferably, the projection and the terminal ring are constructed as one piece, ie are integrally formed.

[0011] Preferably, the sensor coil is arranged axially next to the protrusion and connected to the housing, i.e. not rotating or stationary. By means of the sensor coil, the axial position of the protrusion can be measured directly. Preferably, the sensor coil is used as an eddy current sensor and can detect the axial position of the rotor shaft over the entire circumference. This design offers the advantage that possible tilting vibrations of the rotor are not detected and therefore no destructive coupling or interference occurs between radial and axial movements of the rotor shaft. In particular, the sensor coil is part of a resonant circuit, wherein a shift in the resonant frequency is correlated to a change in the axial position.

[0012] Preferably, a bias magnet is connected to the housing and is at least partially arranged axially adjacent to the protrusion to apply a bias force to the magnetic axial bearing. In this way, by means of the bias magnet constructed as a magnetic ring, a bias force in the axial direction is applied to the protrusion and the rotor shaft. In addition, by means of the bias, attractive magnetic forces and repulsive magnetic forces can be applied by the electromagnet to the protrusion of the terminal ring so as to reliably adjust the axial position of the rotor shaft. In particular, the bias magnet includes a magnetic pole orientation opposite to that of the outermost annular magnet of the rotating magnetic element adjacent to the terminal ring. By means of this construction, the bias effect of the bias magnet is enhanced due to the additional magnetic field of the last magnetic ring of the rotating magnetic element adjacent to the terminal ring that penetrates through the protrusion.

[0013] Preferably, the sensor coil is arranged inside the bias magnet. Thus, the space requirement can be reduced by such an arrangement and at the same time it can be easily assembled. Furthermore, a position close to the forces acting on the rotor is detected. Therein, the sensor coil is located outside the main flux of the magnetic field and is therefore less affected by a magnetic axial bearing located in the immediate vicinity of the sensor coil.

[0014] Preferably, the static terminal ring is arranged axially adjacent to the static magnetic element, in particular, directly adjacent to the outermost magnetic ring of the static magnetic element, wherein the static terminal ring is arranged at the same side as the terminal ring attached axially adjacent to the rotating magnetic element.

[0015] Preferably, the conductive disk is connected to the static terminal ring, and the disk is at least partially arranged axially adjacent to the rotating magnetic element, so that the magnetic field passing through the rotating magnetic element induces eddy currents in the conductive disk. Therefore, an eddy current damper is formed by the conductive disk made of a conductive material such as copper, aluminum, etc., using the magnetic field provided by the outermost rotating magnetic element of the permanent magnetic bearing. In particular, the disk extends in a radial direction to be arranged axially adjacent to the rotating magnetic element.

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

[0017] Preferably, the vacuum pump comprises two bearings, wherein the second bearing can be constructed as a conventional permanent magnetic bearing or a roller bearing. Alternatively, the second bearing is also constructed as a permanent magnetic bearing as described above, which comprises an additional / second axial bearing to provide axial support for the rotor shaft in combination.

[0018] Preferably, the permanent magnetic bearing according to the invention is arranged at the discharge side of the rotor shaft.Alternatively or additionally, the permanent magnetic bearing according to the invention is provided at the inlet side of the rotor shaft.

[0019] Preferably, the static magnetic element is connected to a trunnion extending into a recess in the rotor shaft, wherein the rotating magnetic element is connected to an inner surface of the recess diametrically opposite the static magnetic element. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention is described in more detail hereinafter with reference to the accompanying drawings.

[0021] The accompanying drawings show:

[0022] Figure 1 is a first embodiment of a vacuum pump according to the present invention,

[0023] Figure 2 is a detailed view of a magnetic bearing according to the present invention,

[0024] Figure 3 is a detailed view of another embodiment of a magnetic bearing according to the present invention,

[0025] Figure 4 is a detailed view of another embodiment of a magnetic bearing according to the present invention,

[0026] Figure 5 is a detailed view of another embodiment of a magnetic bearing according to the present invention. DETAILED DESCRIPTION

[0027] refer to Figure 1 , which shows a vacuum pump constructed as a turbomolecular pump. The vacuum pump includes a housing 10, which includes an inlet 12 and an outlet 14. The rotor 16 is arranged in 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 magnetic rings 22, 23. Among them, the static magnetic ring 23 of the first radial bearing 18 is attached to the trunnion 24 extending into the recess 26 of the rotor shaft 16. The rotating magnetic ring 22 is arranged at the inner surface of the recess radially adjacent to the static magnetic ring 23. For the second radial bearing 100, the rotating magnetic ring 106 is attached in the bell-shaped element 28 radially adjacent to the static magnetic ring 105 connected to the housing. Among them, the static magnetic ring 23 of the first radial bearing 18 and each of the rotating magnetic rings 22 of the first radial bearing 18 repel each other. Similarly, the static magnetic ring 105 of the second radial bearing 100 correspondingly repel each of the rotating magnetic rings 106 of the second radial bearing 100, thereby providing rotatable support for the rotor 16 in the housing 10.

[0028] Furthermore, the first radial bearing 18 and the second radial bearing 100 comprise an emergency running bearing 30 which is 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 constructed as blades interacting with stator elements 36 which are connected to the housing 10 of the vacuum pump and are arranged alternately with the pump elements 34. In addition, Figure 1 The vacuum pump of comprises a Holweck stage 38, which comprises a rotating cylinder 40 interacting with a threaded stator 42 connected to the housing. By the rotation of the rotor shaft 16, the gaseous medium is conveyed from the inlet 12 towards the outlet 14 of the vacuum pump.

[0029] Reference now Figure 1 shown in and Figure 2 The lower magnetic bearing 100 is shown in detail in FIG. The direction coinciding with the rotation axis of the vacuum pump is called the axial direction, and the radial direction is perpendicular to the axial direction.

[0030] The magnetic bearing 100 according to the present invention comprises a first or rotating magnetic element 102 and a static magnetic element 104. The rotating magnetic element is connected to the rotor shaft 16 via a bell-shaped element 28. The static magnetic element 104 is connected to the trunnion 118 of the housing 10. Both the rotating magnetic element 102 and the static magnetic element 104 comprise annular magnets 106, 105 which are arranged radially adjacent to each other and repel each other so as to provide radial support of the rotor shaft 16. A terminal ring 108 is connected to the rotating magnetic element 102 and directly connected to the outermost annular magnet 107 of the rotating magnetic element 102. The terminal ring 108 is typically made of steel and is provided to protect the relatively fragile annular magnets 107, 106 from damage when the rotor shaft 116 is inserted into the housing 10, or alternatively when the cap element 120 of the housing 10 is inserted so as to introduce the trunnion 118 into the recess formed by the bell-shaped element 28. In addition, a static terminal ring 122 may be implemented radially adjacent to the terminal ring 108 of the rotating magnetic element 102. The axial position of the annular magnet 106 and the static magnetic element 104 is maintained / fixed by the static terminal ring 122. Preferably, the static terminal ring 122 is made of plastic.

[0031] According to the invention, the terminal ring 108 comprises a radial protrusion 110, which in the given example extends beyond the bell-shaped element 28. In addition, the magnetic bearing 100 comprises an axial bearing 112. The axial bearing 112 comprises an electromagnet 114 or a coil in order to generate an adjustable magnetic field. Yoke elements 116A, 116B are connected to the electromagnet 114, which are arranged on both sides of the radial protrusion in the axial direction. Therefore, by means of the yoke elements 116A, 116B, a radially extending gap is formed, in which the radially extending protrusion 110 is arranged. Therefore, by means of the yoke elements, the magnetic field generated by the electromagnet 114 is applied to the radial protrusion 110, thereby applying an axial force to the protrusion 110 and, therefore, to the rotor shaft 16. Therefore, the radial magnetic bearing and the axial magnetic bearing are integrated, thereby reducing the space requirements and providing effective axial and radial support of the rotor shaft.

[0032] Despite Figure 2 108 and the radial protrusion 110 are shown as two elements, but the terminal ring 108 and the radial protrusion 110 can be constructed as a single piece formed integrally. In particular, the terminal ring 108 and / or the protrusion 110 are formed of a ferrite material so that the magnetic field of the outermost annular magnet 107 is transmitted through the ferrite material of the terminal ring 108 and the protrusion 116, thereby enhancing the axial force applied to the protrusion 110 by the axial bearing 112.

[0033] Reference now Figure 3 , which shows another embodiment of the present invention. In which the same or similar elements are represented by the same reference numerals. In which the description is limited to Figure 2 and Figure 3 The differences between the embodiments.

[0034] In particular, Figure 3 In the embodiment shown in , the bias magnet 124 is connected to the cap element 120 of the housing 110. By the bias magnet 124 constructed as an annular magnet, a bias magnetic flux is generated in the axial air gap 200 between the protrusion 110 and one yoke element 106B and in the axial air gap 201 between the protrusion 110 and the other yoke element 106A. In addition, the magnetic field of the bias magnet 124 penetrates the protrusion 110 and enhances 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 arranged adjacent to the protrusion 110. Therein, the bias magnet 112 is magnetically connected to the yoke elements 106A, 106B to generate a magnetic circuit. As Figure 3As shown in , the magnetic flux 113 is provided by the bias magnet 124. According to the magnetic orientation of the bias magnet 124, the magnetic flux of the electromagnet 110 or the coil weakens the magnetic flux in one air gap 200 (or air gap 201) and enhances the magnetic flux in the corresponding other air gap 201 (or 200). Therefore, according to the direction of the current in the electromagnet 114 or the coil, the force applied to the protrusion 110 can be provided in two axial directions. Among them, preferably, the bias magnet 124 is oriented in the opposite direction to the magnetic pole of the outermost annular magnet 107 of the rotating magnetic element 102, 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.

[0035] refer to Figure 4 , the sensor coil 126 is arranged along the entire circumference of the trunnion 118. The sensor coil 126 is arranged axially adjacent to the protrusion 110, wherein a sensor element 127 is connected to the protrusion 110. The sensor element may be a permanent magnet so as to induce eddy current into the sensor coil 126. Alternatively, the sensor element 127 is made of a conductive material such as copper or aluminum, and the magnetic field is induced into the sensor element by the sensor coil 126 itself. The sensor coil 126 is used as an eddy current sensor for detecting the axial distance between the sensor coil 126 and the rotor shaft 16, which is used to control the magnetic field generated by the electromagnet 114 so as to apply an axial force to the protrusion 110 and the rotor shaft 16. Thereby, the axial position of the rotor shaft 16 can be controlled / maintained. Since the sensor coil 126 is constructed as a ring, the tilting of the rotor shaft has no effect or only a small effect on the sensor signal, because it is obtained by averaging the sensor signal detected along the entire circumference. Furthermore, by positioning the sensor coil radially within the bias magnet 124, a compact design can be achieved while the sensor coil is outside the main magnetic flux of the axial bearing 112. Thus, the interaction between the position sensor and the axial bearing is reduced.

[0036] refer to Figure 5 , the terminal ring 122 of the static magnetic element 104 is directly connected to a radially extending conductive disk 128. The conductive disk 128 is made of a conductive material such as copper, aluminum, or the like. Through the disk 128, the eddy current damper is configured to act directly on the end of the rotor shaft 16 to damp the radial vibration of the rotor shaft 16. Therein, the magnetic field of the outermost annular magnet 107 generates eddy current into the disk 128, thereby generating a magnetic force as a restoring force to damp the radial vibration of the rotor shaft 16. Therefore, the outermost annular magnet 107 has a dual function, namely, for radial support of the rotor shaft 16 and for the eddy current damper.

[0037] although Figure 5A magnetic bearing 100 with an eddy current damper, a sensor coil 126 and a bias magnet 124 is shown, but different combinations of these features are possible in different embodiments. Thus, in one embodiment, only an eddy current damper 128 and a sensor coil 126 are implemented without a bias magnet 124. In another embodiment, an eddy current damper 128 is implemented together with a bias magnet 124 without a sensor coil 126. In another embodiment, an eddy current damper is implemented without a sensor coil 126 and without a bias magnet 124. In another embodiment, a bearing 100 according to the present invention includes only a sensor coil without an eddy current damper and without a bias magnet 124. Thus, in addition to the embodiments shown in the drawings, all different combinations of eddy current dampers 128, sensor coils 126 and bias magnets 124 can be implemented into a magnetic bearing 100 according to the present invention to provide a compact and efficient magnetic bearing that provides both radial and axial support.

Claims

1. A magnetic bearing for a vacuum pump, in particular a turbomolecular pump, comprising: a radial permanent magnetic bearing having a static magnetic element and a rotating magnetic element, the static magnetic element and the rotating magnetic element being arranged radially adjacent to each other and repelling each other to provide radial support; a terminal ring which is attached axially adjacent to the rotating magnetic element, A magnetic axial bearing comprising an electromagnet, The terminal ring includes a protrusion extending in a radial direction and arranged adjacent to the electromagnet, so that an axial magnetic force can be applied by the electromagnet to the protrusion of the terminal ring.

2. The magnetic bearing according to claim 1, wherein: The protrusion is made of a ferrite material, and preferably the terminal ring is also made of a ferrite material.

3. The magnetic bearing according to any one of claims 1 or 2, wherein: The protrusion and the terminal ring are in one piece.

4. The magnetic bearing according to any one of claims 1 to 3, wherein: The sensor coil is arranged axially adjacent to the protrusion to detect the radial position of the protrusion.

5. A magnetic bearing according to any one of claims 1 to 4, comprising a biasing magnet arranged at least partially axially adjacent to the protrusion to apply a biasing force to the magnetic axial bearing.

6. The magnetic bearing according to any one of claims 1 to 5, wherein: A static terminal ring is attached axially adjacent to the static magnetic element.

7. The magnetic bearing according to claim 6, wherein: A conductive disk is connected to the static terminal ring, and the disk is at least partially disposed in close axial proximity to the rotating magnetic element such that eddy currents are induced into the conductive disk by the magnetic field of the rotating magnetic element.

8. A vacuum pump, in particular a turbomolecular vacuum pump, comprising a housing and a rotor shaft, the rotor shaft being arranged in the housing and rotatably supported by at least one permanent magnetic bearing according to any one of claims 1 to 7. 9 . The vacuum pump according to claim 8 , comprising a second bearing configured as a permanent magnetic bearing or a roller bearing.

10. The vacuum pump according to claim 8 or 9, wherein: The magnetic bearing is arranged at the discharge side of the rotor shaft and / or at the inlet side of the rotor shaft.

11. The vacuum pump according to claim 8 or 9, wherein: A static magnetic element is connected to a trunnion extending into a recess in the rotor shaft, wherein a rotating magnetic element is connected to an inner surface of the recess.

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