Technical domain

[0001] The present invention concerns a magnetic bearing with high efficiency, stability and reduced wear.

Related art

[0002] It is known from literature that kinetic friction as expressed by the basic formula Fk=/Jk F _n is dependent upon two parameters, i.e., the coefficient of kinetic friction /Jk between the two materials in contact and the normal force applied between the two surfaces F _n . Defined as the friction arising between bodies in motion with respect to each other, this kinetic friction is the main limiting factor for the efficiency of classical bearings. Even though bearings are subject to rolling rather than sliding resistance, the conclusions would still hold as the same formula expresses them.

[0003] Most research has been focused on structural engineering and materials with the goal of trying to decrease the coefficient of friction /Jk- Little attempts have been made to decrease the second parameter of kinetic friction, namely the normal force between the two contact surfaces.

[0004] One promising attempt lies in magnetic bearings, as they remove contact between stator and rotor altogether. However, their intricacy and inherent lack of stability make them rather complex to use in a wide array of settings. Such bearings with a lack of stability are not reliable, which prevents them from being applied in various applications. Short disclosure of the invention

[0005] An aim of the present invention is the provision of a magnetic bearing that overcomes the shortcomings and limitations of the state of the art.

[0006] Another aim of the invention is the provision to provide a bearing with reduced wear properties and high efficiency.

[0007] A further aim of the invention is the provision of a bearing that is less complex and provide a stable and reliable operation at the same time.

[0008] According to the invention, these aims are attained by the object of the attached claims, and especially by a magnetic bearing comprising a fixated base element with a first surface, a rotatable element having a second surface oppositely disposed to the first surface and being rotatable around an axis of rotation and being movable along said axis of rotation, wherein the first surface is separated from the second surface forming a variable gap and an elastic element with a third surface being disposed in said variable gap and a magnetic field generating element for generating a magnetic field in said variable gap, wherein the position of the rotatable element along said axis of rotation is controlled by a magnetic force generated by said magnetic field and/or by the force of gravity attracting the rotatable element, such that the third surface is in contact with the first and/or the second surface.

[0009] Advantageous embodiments of the invention are the object of the dependent claims and include variants the magnetic bearing which may be provided with a variable airgap and with a contact area between the first or second surface and the third surface can be at least 10 times, preferably at least 100 times smaller than the area of the first and/or second surface and in which the contact area between the third surface on one side the first or second surface on the other side can be resumed to a point when the rotatable element is in a neutral position. The surfaces on the other hand may be configured with a coefficient of kinetic friction (COF), wherein the COF of the first and/or second surface can be smaller or greater than the COF of the third surface by a factor two or more.

[0010] Alternatively, the contact area in a neutral position could be resumed to a plurality of discrete points of contact not necessarily being centred (similar to classical rolling bearings). Such an arrangement would necessarily increase friction, but it would also improve stability. In another embodiment, Alternatively, the contact area in a neutral position could be resumed to one or a plurality of lines or curves or segments of curves.

[0011] Variants of the elastic element of the magnetic bearing may be mechanically fixated to and extending from the first or second surface and can be disposed in a centre portion of the first and/or second surface. The modulus of elasticity of the elastic element might be at least two times, preferably five times, most preferably ten times greater than a modulus of elasticity of the fixated base element and/or of the rotatable element. In addition the elastic element may be configured to apply a force to the first and/or second surface that is greater than the magnetic force or force of gravity attracting the rotatable element, when a distance between the first surface and the second surface dips below a limit, wherein the force causes the rotatable element to move into an opposing direction.

[0012] Elasticity is understood in the present disclosure as the ability of a deformed material body to return to its original shape and size when the forces causing the deformation are removed. Compression is a special type of deformation.

[0013] The rotatable element of the magnetic bearing may comprise a shaft element extending to an end opposed to the second surface for transmission of motive power. The magnetic force or the force of gravity attracting the rotatable element may extend in an axial direction with reference to the axis of rotation of the rotating element. The rotatable element can be configured to persist in a neutral position, such that the third surface of the elastic element can be in contact with the first and/or second surface without being deformed. The rotatable element may be further configured with a mass, wherein the absolute value of the force of gravity attracting the rotatable element may be equal to the absolute value of the magnetic force attracting or repelling the rotatable element but with opposite directions, when the elastic element is in contact with the first and/or second surface without being deformed. The rotatable element can be further arranged with a diamagnetic element configured to stabilise the rotating element when rotating. Alternatively, or in addition, might the rotating element be stabilised using a classical rolling bearing. The shaft element might therefore extend via the inner ring of said classical bearing.

[0014] The field generating element of the magnetic bearing can be configured as electromagnet or permanent magnet and may be arranged as an integral part of the fixated base element and/or rotatable element. Alternatively or in addition the fixated base element or rotatable element can comprise a material that is attractable by a magnetic field, preferably a ferromagnetic material.

[0015] With respect to what is known in the art the invention provides a reduced wear and an improved efficiency as the normal force and the coefficient of friction between the first and/or second surface and the third surface is reduced by configuration the magnetic bearing as disclosed herein.

[0016] The invention may yield a superior stable and reliable operation since the rotating element can remain in a neutral position and the elastic element facilitates to stabilize the operation when the rotating element is moved outside its neutral position.

[0017] The invention is useful for many kinds of applications, where vertical bearings are required, such as bearing for supporting fan assemblies, turntables, work piece in machine tool, etc. Short description of the drawings

[0018] Exemplar embodiments of the invention are disclosed in the description and illustrated by the drawings in which:

Figure 1 illustrates a magnetic bearing schematically according to a first preferred embodiment of the invention.

Figure 2 illustrates a magnetic bearing schematically according to a second embodiment of the invention.

Figure 3a -3d illustrate schematically variants of elastic elements disposed in a variable gap.

Figure 4 illustrates a magnetic bearing schematically according to a third embodiment of the invention.

Figure 5 illustrates a magnetic bearing schematically according to a fourth embodiment of the invention.

Examples of embodiments of the present invention

[0019] Fig. 1 illustrates a magnetic bearing 1 according to a first preferred embodiment of the invention. The magnetic bearing 1 comprises a fixated base element 10. The fixated base element 10 preferably is configured in a shape of a right circular cylinder, with a diameter and a height. The diameter in this example is greater than the height. The fixated base element 10 alternatively may be configured in any other shape. The fixated base element 10 in this example is made of a ferromagnetic material, such as iron. [0020] The fixated base element 10 is fixated on an upper end, namely on a fixation end 12 with a torque proof connection and is configured with a first surface 11 being almost horizontally arranged. The first surface 11 is facing in this example downwards.

[0021] The fixated base element 10 incorporates or is made of a magnetic field generating element 40 in the form of a permanent magnet 40. One pole, in this example the north pole of the permanent magnet 40, is facing in the same direction as the first surface 11.

[0022] The magnetic bearing 1 comprises in this preferred embodiment a rotatable element 30 that is provided with a second surface 31 on an upper end. The second surface 31 is facing the first surface 11. The rotatable element 30 is rotatable around a fixed axis of rotation R. The axis of rotation R is preferably aligned with the centre portion of the second surface 31 of the rotatable element 30. The rotatable element 30 is furthermore configured to move in a vertical direction, such that the first surface 11 and the second surface 31 can get closer or more distanced to each other. The fixated base element 10, on the contrary, is fixed and not movable relative to the upper end.

[0023] The rotatable element 30 is configured in a shape of a right circular cylinder, with a diameter and a height. The diameter in this example is greater than the height. The rotatable element 30 alternatively may be configured in any other shape.

[0024] A shaft element 32 is attached and mechanically fixed to the rotatable element 30 and extends to an end, opposing the second surface 31. The shaft element 32 is configured for transmission of motive power to an element external to the magnetic bearing 1. The shaft element 32 can also be made integral with the rotatable element, and form one single component. [0025] The rotatable element 30 and the shaft element 32 can be made of a magnetically permeable material, such as plastic. The shaft element 32 preferably is formed integrally with the rotatable element 30 and may be made of the same material.

[0026] The rotatable element 30 incorporates or is made of a magnetic field generating element 40 arranged as a permanent magnet 40. The south pole of the permanent magnet 40 is facing in the same direction as the second surface 31.

[0027] The first surface 11 and the second surface 31 are distanced by a variable gap G formed by a variable distance between the first surface 11 and the second surface 31 . In this embodiment the variable gap G is filled with air to form a variable airgap GA. Alternatively, a vacuum might be formed in the variable gap to reduce friction even further.

[0028] An elastic element 20 is fixated to the fixated base element 10 and extends from the first surface 11 into the direction of the second surface 31. The elastic element 20 therefore is disposed in said variable airgap GA. The elastic element 20 preferably is made of an elastic material, such as rubber and is placed in a centre portion of the first surface 11. The elastic element 20, as shown in Fig. 1 in this example, is not in contact with the second surface 31 but can get into contact. The elastic element 20 comprises a third surface 21.

[0029] A magnetic field (indicated in Fig. 1 by dotted lines) is generated by the two permanent magnets 40, arranged with opposing poles and extending through the variable airgap GA. The magnetic field is configurated as a uniform magnetic field. The magnetic field extending in an axial direction with reference to the axis of rotation R of the rotatable element 30, generates a magnetic force FM that attracts the rotatable element 30. As the rotatable element 30 is movable on a vertical axis with respect to the fixated base element 10 the second surface 31 can move closer to the first surface 11. By moving the second surface 31 closer to the first surface 11 gets the second surface 31 into contact with the third surface 21 of the elastic element 20, so that the elastic element 20 is compressed. In this moment act at least three forces on the rotatable element 30, namely the magnetic force FM pulling the rotatable element 30 into an upward direction, the force of gravity FG, pulling the rotatable element into a downward direction and a force FE (not shown) originating from elastic element 20 pushing the rotatable element 30 into a direction opposed to the magnetic force FM.

[0030] When the rotatable element 30 is rotating, a friction force (not shown) acts between the third surface 21 and the second surface 31, which can slow the rotatable element 30 down.

[0031] The contact area ac (not shown) between the third surface 21 and the second surface 31 is minimised to reduce the friction force and consequently the wear of the elastic element 20 and/or second surface 31 of the rotatable element 30. This is achieved by shrinking or shaping the elastic element 20 such that the contact area ac between the second surface 31 and the third surface 21 is at least 10 times, preferably at least 100 times smaller than the area of the second surface 31. In other words, the contact area ac between the third surface 21 and the second surface 31 is at least 10 times, preferably at least 100 times greater than the area of the second surface 31.

[0032] The friction force is also reduced by configuring the kinetic friction (COF) of second surface 31 to a value that is smaller than the COF of the third surface 21 by a factor two or more. Alternatively, the COF of the third surface 21 is configured to be smaller than the COF of second surface 31 by a factor two or more. At least one of the surfaces interacting with each other has a reduced COF.

[0033] The rotatable element 30 is configurated to remain in a neutral position. The neutral position is where the first surface 11 and the second surface 31 are distanced from each other so that the second surface 31 is in contact with the third surface 21 without compressing the elastic element 20. In other words, the third surface 21 of the elastic element 20 is in contact with the second surface 31 without deforming the elastic element 20. In this neutral position, the contact surface is reduced to a single point, or at least to surface much smaller than the maximal section of the elastic element 20. The neutral position can be set or engaged when the rotatable element 30 rotates and/or when the rotatable element 30 is in standstill.

[0034] For this sake, the rotatable element 30 is configured with a mass M, wherein the absolute value of the force of gravity FG is equal to the absolute value of the magnetic force FM attracting the rotatable element 30 but with opposite directions when the third surface 21 of the elastic element 20 is in contact with the first surface 11 without deforming the elastic element 20. In other words, the sum of the forces acting on the rotatable element 30 is zero when the rotatable element 30 remains in a neutral position.

[0035] When the elastic element 30 is pushed out of the neutral position, such that the first surface 11 and the second surface 31 get closer to each other, the elastic element 20 can apply a force to the second surface 31 and finally to the rotating element 30 along a direction opposite to that of the magnetic force FM. Said force is greater than the magnetic force FM and it will push the rotating element 30 into an opposing direction as the rotating element 30 is configured to be movable along the axis of rotation R. In other words, the elastic element 20 is configured to apply a force FE to the second surface 31 that is greater than the magnetic force FM attracting the rotatable element 30, when a distance between the first surface 11 and the second surface 31 dips below a limit, wherein the force FE causes the rotatable element 30 to move into an opposing direction. The limit may be the distance between the first surface 11 and the second surface 31 before the force generated by the magnetic field becomes nonlinear. [0036] It is important to note that the distance between the first surface 11 and the second surface 31 needs to be kept in a range, where the magnetic force FM acts linearly onto the rotatable element 30, such that the magnetic bearing 1 is operated in a stable manner.

[0037] For this sake, the rotatable element 30 and the elastic element 20 are configured with a modulus of elasticity, wherein the modulus of elasticity of the elastic element 20 is at least two times, preferably five times, most preferably ten times greater than the modulus of elasticity of the rotatable element 30. In other words, the elastic element 20 has a higher modulus of elasticity compared to the elasticity of the rotatable element 30 in particular compared to the modulus of elasticity of the second surface 31 of the rotatable element 30. Alternatively, but not preferably, the modulus of elasticity of the elastic element 20 can be smaller than the modulus of rotatable element 30.

[0038] Fig. 2 illustrates a magnetic bearing 1 according to a second preferred embodiment of the invention. The magnetic bearing 1 comprises a fixated base element 10. The fixated base element 10 is configured in a shape of a right circular cylinder, with a diameter and a height. The diameter in this example is greater than the height. The fixated base element 10 alternatively may be configured in any other shape. The fixated base element 10 in this example is made of a magnetically transparent material, such as plastic.

[0039] The fixated base element 10 is fixated on its fixation end 12 with a torque proof connection. The fixated base element 10 is configured with a first surface 11 being almost horizontally arranged. The first surface 11 is facing in this example downwards.

[0040] The fixated base element 10 incorporates a magnetic field generating element 40 in the form of an electromagnet 40 or, alternatively, a permanent magnet. The north pole of the electromagnet 40 is facing in the same direction as the first surface 11. The magnetic bearing 1 comprises in this second embodiment a rotatable element 33 that is provided with a second surface 31 on an upper end. The second surface 31 is facing the first surface 11. The rotatable element 33 is rotatable around a fixed axis of rotation R. The axis of rotation R preferably is aligned with the centre portion of the second surface 31 of the rotatable element 33. The rotatable element 33 furthermore is configured to move in a vertical direction, such that the first surface 11 and the second surface 31 can get closer or more distanced to each other. The fixated base element 10, on the contrary, is fixed and not movable.

[0041] The rotatable element 33 is configured in a shape of a right circular cylinder, with a diameter and a height. The diameter in this example is greater than the height. The rotatable element 33 alternatively may be configured in any other shape.

[0042] A shaft element 32 is attached and mechanically fixed to the rotatable element 33 and extends to an end, opposing the second surface 31. The shaft element 32 is configured for transmission of motive power to an element external to the magnetic bearing 1.

[0043] The rotatable element 33 and the shaft element 32 is made of a material that is attractable by magnetic fields, such as a ferromagnetic material. The shaft element 32 preferably is formed in one-piece with the rotatable element 33 and may be made of the same material. In this example and contrary to the embodiment set out in Fig. 1, the rotatable element 33 does not incorporate a magnetic field generating element 40.

[0044] The first surface 11 and the second surface 31 are distanced by a variable gap G formed by a variable distance between the first surface 11 and the second surface 31. In this embodiment, the variable gap G is filled with a liquid lubricant, such as oil. An enclosure (not shown) encloses the volume formed by the first and second surface 11, 31 to contain the liquid lubricant. [0045] An elastic element 20 is fixated to the rotatable element 33 and extends from the second surface 31 into the direction of the first surface 11. The elastic element 20 therefore is disposed in said variable gap G. The elastic element 20 preferably is made of an elastic material, such as a plastic material and is placed in a centre portion of the second surface 31. The elastic element 20, as shown in Fig. 2 in this example, is in contact with the first surface 11. The elastic element 20 comprises a third surface 21.

[0046] A magnetic field (indicated in Fig. 2 by dotted lines) is generated by the electromagnet 40 and extends through the variable gap G. The magnetic field is configurated in this example as a uniform magnetic field with a time-invariant magnetic field strength. The magnetic field extending in an axial direction with reference to the axis of rotation R of the rotatable element 32, generates a magnetic force FM that attracts the rotatable element 33. As the rotatable element 33 is movable on a vertical axis with respect to the fixated base element 10 the second surface 31 can move closer to the first surface 11. Moving the second surface 31 closer to the first surface 11 gets the second surface 31 into contact with the third surface 21 of the elastic element 20, so that the elastic element 20 is compressed. In this moment act at least three forces on the rotatable element 33, namely the magnetic force FM pulling the rotatable element 33 into an upward direction, the force of gravity FG, pulling the rotatable element into a downward direction and a force FE (not shown) originating from elastic element 20 pushing the rotatable element 33 into a direction opposed to the magnetic force FM.

[0047] When the rotatable element 33 is rotating, a friction force (not shown) acts between the first surface 11 and the third surface 21, which can slow the rotatable element 30 down.

[0048] The contact area ac between the third surface 21 and the first surface 11 is minimised to reduce the friction force and consequently the wear of the elastic element 20 and/or first surface 11 of the fixated base element 10. This is achieved by shrinking or shaping the elastic element 20 such that the contact area ac between the first surface 11 and the third surface 21 is at least 10 times, preferably at least 100 times smaller than the area of the second surface 31. In other words, the contact area ac between the third surface 21 and the first surface 11 is at least 10 times, preferably at least 100 times greater than the area of the first surface 11.

[0049] The friction force is also reduced by configuring the COF of first surface 11, to a value that is smaller than the COF of the third surface 21 by a factor two or more. Alternatively, the COF of the third surface 21 is configured to be smaller than the COF of first surface 11 by a factor two or more. At least one of the surfaces interacting with each other has a reduced COF. Alternatively, the surfaces interacting with each other might be arranged with the same COF, as the lubricant in the gap G reduces the friction.

[0050] The remaining properties, with respect to the neutral position and/or the properties of the elastic element 20 of the rotatable element 33, is comparable with the first embodiment.

[0051] In one alternative to this embodiment, the magnetic force FM attracting the rotatable element 33 varies by varying the magnetic field strength over time. The magnetic field strength can be varied by changing or controlling an electric current flowing through the electromagnet 40. The electric current might also generate a rotating magnetic field that forces the rotatable element 33 to rotate around its axis of rotation R.

[0052] Figure 3a -3d illustrate schematically variants of elastic elements disposed in a variable gap G or in a variable airgap GA. The following disclosure might be applied to all embodiment herein disclosed. Thus, the fixated base element 10 and/or the rotatable element 30 may be configured with a magnetic field generating element 40. The rotatable element 30 may be arranged with a shaft element 32. [0053] Fig. 3a illustrates a fixated base element 10 arranged at the bottom and a rotatable element 30 arranged above the fixated base element 10. An elastic element 20 is fixated to the rotatable element 30 and extending from the second surface 31 into the direction of the first surface 11. The elastic element 20 is in a hemispherical shape, whereas the lower end of the hemisphere is in contact with the first surface of the fixated base element 10 forming a contact area ac.

[0054] Fig. 3b illustrates a rotatable element 30 arranged at the bottom and fixated base element 10 arranged above the rotatable element 30. The rotatable element 30 comprises a cavity that is arranged in a centre portion of the second surface 31. An elastic element 20 is fixated to the fixated element 10 and extending from the first surface 11 into the direction of the second surface 31.

[0055] The elastic element 20 is in a hemispherical shape, whereas the lower end of the hemisphere extends into the cavity 22 whereas large parts of the third surface 21 is in contact with the surface of the cavity forming a contact area acwith enlarged size. By configuration the rotatable element 30 with a cavity 22 it is possible to bring the first surface 11 closer to the second surface 31 without the need for a material of the elastic element 20 with a greater elasticity. The engagement of the hemisphere shaped elastic element 20 within the cavity 22 also maintains the lateral stability of the rotatable element 30 and associated shaft 32.

[0056] Fig. 3c illustrates a fixated base element 10 arranged at the bottom and a rotatable element 30 arranged above the fixated base element 10. An elastic element 20 is fixated to the rotatable element 30 and extending from the second surface 31 into the direction of the first surface 11. The elastic element 20 is in a conical frustum shape, whereas the lower end of the frustum shape is in contact with the first surface of the fixated base element 10 forming a contact area ac. It can be seen that the contact area ac is larger compared to the example in Fig. 3a. The friction value can be controlled by enlarging or reducing the size of the contact area ac.

[0057] Fig. 3d illustrates a rotatable element 30 arranged at the bottom and fixated base element 10 arranged above the rotatable element 30. The fixated base element 10 is configured with an upper cavity 24 and the rotatable element 30 is configured with a lower cavity 23. The cavities 23, 24 are arranged in a centre portion of the first and second surface 11, 31. An elastic element 20 in a sphere shape is arranged in the lower and upper cavity 23, 24. The sphere-shaped elastic element 20 is not fixated to first and second surface 11, 31, and therefore movable in all dimensional directions. The engagement of the sphere-shaped elastic element 20 within the cavities 23, 24 also maintains the lateral stability of the rotatable element 30 and associated shaft 32.

[0058] The elastic element 20 of all examples illustrated in Fig. 3a - 3d is made of a material with a greater elastic modulus compared to the surface 11, 31 to which the elastic elements 20 might get into contact. The shape of the elastic element 20 is exemplarily and may have any other shape that is compatible with the magnetic bearing 1.

[0059] Fig. 4 illustrates a magnetic bearing 1 according to a third embodiment of the invention. The magnetic bearing 1 comprises a fixated base element 10 similarly configurated as in the first preferred embodiment, but with a first surface 11 that is facing upwards.

[0060] The elastic element 20 is similarly configurated and placed as in the first preferred embodiment, whereas the third surface 21 of the elastic element 20 is in contact with the second surface 31.

[0061] The magnetic bearing 1 comprises in this embodiment a rotatable element 30 that is provided with a second surface 31 on a lower end. Otherwise, the rotatable element 30 is similarly configurated as in the first preferred embodiment, except that the permanent magnet 40 is arranged differently. The north pole of the permanent magnet 40 is facing in the same direction as the second surface 31.

[0062] A shaft element 32 is attached and mechanically fixed to the rotatable element 30 and extends to an end, opposing the second surface 31 and the first surface 11 and the second surface 31 are distanced by a variable airgap GA.

[0063] A magnetic field (indicated in Fig. 4 by dotted lines) is generated by the two permanent magnets 40, arranged with like poles and extending through the variable airgap GA. The magnetic field is configurated as a uniform magnetic field. The magnetic field extending in an axial direction with reference to the axis of rotation R of the rotatable element 30, which generates a magnetic force FM that repels the rotatable element 30. As the rotatable element 30 is movable on a vertical axis with respect to the fixated base element 10 the second surface 31 can move closer to the first surface 11. Moving the second surface 31 closer to the first surface 11 gets the second surface 31 into contact with the third surface 21 of the elastic element 20, so that the elastic element 20 is compressed. In this moment act at least three forces on the rotatable element 30, namely the magnetic force FM pushing the rotatable element 30 into an upward direction, the force of gravity FG, pulling the rotatable element into a downward direction and a force FE (not shown) originating from elastic element 20 pushing the rotatable element 30 into the same direction as the magnetic force FM.

[0064] The rotatable element 30 is also configurated to remain in a neutral position. When the elastic element 30 is rotation and/or is pushed out of the neutral position, such that the first surface 11 and the second surface 31 get closer to each other, the elastic element 20 can apply a force to the second surface 31 and finally to the rotating element 30 that has the same direction with regard to the magnetic force FM. Said force is greater than the force of gravity FG and it will push the rotating element 30 into an opposing direction as the rotating element 30 is configured to be movable along a vertical axis. In other words, the elastic element 20 is configured to apply a force FE to the second surface 31 that is greater than the force of gravity FG attracting the rotatable element 30, when a distance between the first surface 11 and the second surface 31 dips below a limit, wherein the force FE causes the rotatable element 30 to move into an opposing direction. The limit may be the distance between the first surface 11 and the second surface 31 before the force generated by the magnetic field becomes non-linear.

[0065] It is important to note that the distance between the first surface 11 and the second surface 31 needs to be kept in a range, where the magnetic force FM acts linearly onto the rotatable element 30, such that the magnetic bearing 1 is operated in a stable manner.

[0066] Fig. 5 illustrates a magnetic bearing 1 according to a fourth preferred embodiment of the invention. The magnetic bearing 1 comprises a fixated base element 10, an elastic element 20 and a rotatable element 33 similarly configurated as in the second embodiment.

[0067] A shaft element 32 is attached to the rotatable element 33 and extends into an opposing direction to the second surface 31. The shaft element 32 is configured with a diamagnetic element 50 on a lower end. The diamagnetic element 50 comprises a diamagnetic material, such as Pyrolytic Carbon or Bismuth.

[0068] The diamagnetic element 50 immerses into a magnetic field (indicated in Fig. 5 by dotted lines) generated by a magnetic field generator 60. The magnetic field is radially symmetric to the axis of rotation R. The magnetic field generator 60 can be configured as a permanent magnet or an electromagnet.

[0069] Diamagnetic materials are repelled by magnetic fields. The interaction between the magnetic field and the diamagnetic element 50 forces the rotatable element 33 to stay aligned with the axis of rotation R when rotating. A slight deviation from the axis of rotation R would lead to an imbalance and thus to unwanted vibrations. This magnetic stabilization system may be applied to all of the before disclosed embodiments.

[0070] The movability of the rotating element 30 in all of the before disclosed embodiments is limited in a vertical direction. A minimum distance between the first surface 11 and the second surface 31 is kept, as the elastic element 20 acts as a spacer. The vertical movability in the opposing direction may also be limited by a technical means, such that the gap G does not become too large. The movability in a horizontal direction might also be limited, such that the rotatable element 30 keeps its axis of rotation R. These measures avoid the rotatable element 30 losing the interaction with the magnetic field, attracting or repelling said rotatable element 30.

Reference signs magnetic bearing

10 fixated base element

I I first surface

12 fixation end

20 elastic element

21 third surface

22 cavity

23 lower cavity

24 upper cavity

30, 33 rotatable element

31 second surface

32 shaft element

40 magnetic field generating element, permanent- or electromagnet

50 diamagnetic element

60 magnetic field generator ac contact area

FE force originating from elastic element

FG force of gravity FM magnetic force

G variable gap

GA variable airgap

M mass

R axis of rotation