Passive magnetic bearings for vacuum pumps

Abstract

The present invention provides a passive magnetic bearing for a vacuum pump (1), the vacuum pump (1) comprising a stator (2) and a rotor (4) configured to rotate around a rotation axis relative to the stator (2), the passive magnetic bearing comprising a rotor bearing half (12) comprising one or more substantially annular rotor-side magnets (14) and a stator bearing half (16) comprising one or more substantially annular stator-side magnets (18) facing each other and arranged radially in a substantially concentric manner, wherein the radial clearance (g) between the rotor bearing half (14) and the stator Spreading between the bearing half (16), at least one, preferably each rotor-side magnet (14) has an axial dimension of about 3.5 to about 5.3 times the width of the radial clearance (g) and a radial dimension of less than 1.2 times the axial dimension of each rotor-side magnet, and / or at least one, preferably each stator-side magnet (18) has an axial dimension of about 3.5 to about 5.3 times the width of the radial clearance (g) and a radial dimension of less than 1.2 times the axial dimension of each stator-side magnet.

Description

[Technical Field]

[0001] The present invention relates to a passive magnetic bearing for a vacuum pump, a vacuum pump equipped with a passive magnetic bearing, and a method for manufacturing and designing a passive magnetic bearing. [Background technology]

[0002] Generally, vacuum pumps use passive magnetic bearings to support the rotor, and its rotor elements (e.g., vanes) interact with the stator to transport a gaseous medium from inlet to outlet. In turbomolecular vacuum pumps, the stator typically includes multiple vanes configured to interact with multiple rotor vanes. Passive magnetic bearings are generally provided at least on the higher vacuum side of the turbomolecular vacuum pump.

[0003] A passive magnetic bearing generally comprises an outer bearing half and an inner bearing half, each containing one or more magnets, generally in the form of a passive magnetic ring. Depending on the specific arrangement of the passive magnetic bearing, the outer bearing half may be a rotor bearing half or a stator bearing half, and the inner bearing half may be the other half of the rotor bearing half or stator bearing half. The bearing halves are positioned close to each other with a gap between them and are generally configured to repel each other during use.

[0004] Regarding passive magnetic bearings, the rigidity of the passive magnetic bearing is particularly important in order to ensure reliable positioning of the rotor relative to the stator.

[0005] Therefore, it is generally desirable to determine a design that is optimized with respect to the required rigidity. For example, the design of a passive magnetic bearing can be optimized to provide the required rigidity with respect to the minimum axial length and / or the minimum weight of the permanent magnet material by determining the outer diameter of the bearing and the clearance between the inner and outer bearing halves.

[0006] In this specification, the paper referred to as "Moser," "Optimisation of repulsive passive magnetic bearings" (Moser, Sandtner, et al, IEEE Transactions on Magnetics, Vol. 42, No. 8, August 2006), describes a method for determining the magnet size that achieves optimal stiffness using a specific aspect ratio. Specifically, in Moser's paper, the optimal axial and radial dimensions of the rotor and stator magnets are plotted as a function of the bearing diameter, with the predetermined radial gap between the rotor and stator magnets as a function of the diameter.

[0007] Moser, an authority in this field, concluded that an optimal design can be found for limited bearing volumes and plotted this data so that designers of passive magnetic bearings can select appropriate magnet sizes based on specific structural spaces. Moser's design principle provides discrete design solutions for a given set of magnet rings in a bearing, each solution representing the minimum length of the bearing at a given stiffness. This optimal design is based on continuously stacking permanent magnet layers for a given combination of air gap and rotor diameter.

[0008] An example of such an embodiment of this teaching is described in European Patent No. 3135932, which describes a passive magnetic bearing for a vacuum pump, more specifically a turbomolecular pump, where the axial height of the inner and / or outer magnetic rings of the bearing is in the range of 3 to 5 times the width of the radial gap, and the radial width of the inner and / or outer magnetic rings is at most 1.2 times and not more than 1.5 times the axial height of each ring.

[0009] However, the applicant has identified a dichotomy (a conflict) between the rigidity of the magnet and the number and size of the magnets, which has not been addressed and has not been adequately resolved.

[0010] Theoretically, the assumed optimal radial stiffness can be achieved by manufacturing a passive magnetic bearing with magnets corresponding to the aspect ratios taught by Moser and European Patent No. 3135932. However, the prior art, specifically Moser's, requires a relatively large number of bearing magnet layers, each of which must be precisely manufactured, machined, and assembled as half of the passive magnetic bearing (rotor half or stator half).

[0011] Furthermore, the manufacturing of passive magnetic bearings using prior art may lead to waste of magnetic material due to machining and / or material usage exceeding the optimal value for the permanent magnet ring.

[0012] Therefore, the theoretical ideals described in the prior art are not helpful to those skilled in the art in providing improved passive magnetic bearings for the real world that take into account not only optimal radial stiffness but also practical factors in manufacturing and assembly.

[0013] Conversely, the aspect ratio of magnets in actual, known passive magnetic bearings is usually much larger than the aforementioned prior art, specifically the value proposed by Moser. This leads to a significant reduction in the number of magnets, but results in bearings with suboptimal rigidity and a considerably increased amount of magnetic material.

[0014] While these methods have been moderately successful, the technical requirements for passive magnetic bearings are becoming more complex as we pursue higher rigidity in bearings, improved pump performance, and a reduction in the amount of magnetic material used. [Prior art documents] [Patent Documents]

[0015] [Patent Document 1] European Patent No. 3135932 [Non-patent literature]

[0016] [Non-Patent Document 1] 「Optimisation of repulsive passive magnetic bearings」(Moser, Sandtner, et al, IEEE Transactions on Magnetics, Vol. 42, No. 8, August 2006)

Summary of the Invention

Problems to be Solved by the Invention

[0017] The present invention aims to solve the above and other problems of the prior art.

Means for Solving the Problems

[0018] Thus, in a first aspect, the present invention provides a passive magnetic bearing for a vacuum pump, particularly a turbomolecular vacuum pump, the vacuum pump including a stator and a rotor configured to rotate about a rotation axis relative to the stator. The passive magnetic bearing includes a rotor bearing half including one or more substantially annular rotor-side magnets, and a stator bearing half including one or more substantially annular stator-side magnets arranged substantially concentrically and radially opposite. A radial gap extends between the rotor bearing half and the stator bearing half.

[0019] At least one, typically the above or each, rotor-side magnet has an axial dimension of about 3.5 times to about 5.3 times the width of the radial gap, and at least one, typically the above or each, rotor-side magnet has a radial dimension of less than 1.2 times the respective axial dimension of the magnet.

[0020] Additionally or alternatively, at least one, typically the above or each, stator-side magnet has an axial dimension of about 3.5 times to about 5.3 times the width of the radial gap, and at least one, typically the above or each, stator-side magnet has a radial dimension of less than 1.2 times the respective axial dimension of the magnet.

[0021] As used herein, "axial dimension" refers to the width of the annular magnet in a plane substantially parallel to the rotation axis of the vacuum pump rotor. The axial dimension of the rotor-side magnet or the stator-side magnet can be plotted as "h / g", i.e., the axial height as a function of the width of the gap between the rotor and the stator.

[0022] As used herein, "radial dimension" refers to the width of the annular magnet in a plane substantially perpendicular to the rotation axis of the vacuum pump rotor. The radial dimension refers to the width of the magnetic material of the annular magnet, rather than the radius from the rotation axis of the bearing half. The radial dimension of the rotor-side magnet or the stator-side magnet can be plotted as "w / h", i.e., the radial width as a function of the axial height of the magnet.

[0023] Known prior art bearings include magnets that do not have these ratios of axial and radial dimensions, because the prior art teaches that optimal magnetic rigidity is not achieved within these ranges. More specifically, as described by Moser, known magnets do not have an axial dimension that is about 3.5 to about 5.3 times the width of the radial gap, and further, do not have a radial dimension that is less than 1.2 times the axial dimension of each magnet.

[0024] The known prior art teaches to avoid the selection of such combinations of axial and radial dimensions of the rotor-side magnet and / or the stator-side magnet. As described above, in the prior art, generally, when the axial dimension of the rotor-side magnet or the stator-side magnet is more than about 3.5 times the width of the radial gap, it is recognized that the radial dimension as a function of the axial dimension should be greater than 1.2 times in order to provide optimal rigidity.

[0025] In fact, known bearings generally have a large h / g aspect ratio of 6 to 8 or more, and in some cases, more than 5.3 and less than 6. Conventionally, optimization of rigidity and reduction of material usage have not been prioritized, and reduction of the number of magnets has been emphasized for cost reasons.

[0026] In contrast, the applicant has surprisingly discovered that combining an intermediate axial dimension as a function of the radial clearance width with a smaller radial dimension allows for shorter magnetic bearing halves composed of fewer magnets than taught in the prior art, using equivalent or fewer magnetic materials while maintaining optimal or near-optimal rigidity. Both properties are crucial in the pursuit of improved performance and sustainability. This is also advantageous because achieving optimal rigidity with fewer magnets than in the prior art reduces the machining requirements for passive magnetic bearings, and therefore the cost is lower compared to the prior art.

[0027] By identifying and addressing the dichotomy between optimal magnet stiffness and the number and size of magnets, the applicant provides a passive magnetic bearing for vacuum pumps that has adequate stiffness with less material than the prior art, minimizing material waste and machining labor and costs. More specifically, within this range, providing smaller radial dimensions in combination with larger axial dimensions enables a passive magnetic bearing that requires less material. This reduces the weight of the passive magnetic bearing, as well as the material and machining costs.

[0028] The selection of this particular combination of radial and axial dimensions for the rotor-side and / or stator-side magnets in the rotor-side and / or stator-side bearing halves of a passive magnetic bearing results in an unexpected technical advantage: it provides improved rigidity density for a given size passive magnetic bearing with fewer magnet layers.

[0029] In the embodiment, at least one rotor-side magnet and / or at least one stator-side magnet may have a radial dimension substantially about 0.8 times or more the axial dimension of each magnet.

[0030] In the embodiment, at least one rotor-side magnet and / or at least one stator-side magnet may optionally have a radial dimension of substantially about 1.19 times or less substantially than the axial dimension of each magnet, and substantially about 1.19 times or less substantially than the axial dimension of each magnet. In the embodiment, at least one rotor-side magnet and / or at least one stator-side magnet may have a radial dimension of substantially about 1.18 times or less substantially than the axial dimension of each magnet.

[0031] In the embodiment, at least one rotor-side magnet and / or at least one stator-side magnet may have a radial dimension that is approximately 0.8 to approximately 1.18 times the axial dimension of each magnet.

[0032] In the embodiment, at least one rotor-side magnet and / or at least one stator-side magnet may have an axial dimension of about 3.5 to about 5 times the width of the radial clearance.

[0033] In the embodiment, at least one rotor-side magnet and / or at least one stator-side magnet may have an axial dimension of about 5 to 5.3 times the width of the radial clearance.

[0034] Generally, a passive magnetic bearing may include a rotor bearing half and a stator bearing half having substantially the same axial dimensions and having substantially the same, substantially the same number, typically exactly the same number of magnetic layers formed as annular magnetic rings. Typically, each of the inner bearing half and the outer bearing half has multiple magnetic layers.

[0035] Accordingly, in the embodiment, each of the inner and outer bearing halves may include a corresponding number of axially adjacent magnet layers. However, in the embodiment, the inner and outer bearing halves may have different numbers of magnet layers.

[0036] In the embodiment, the rotor-side magnets and the magnetically corresponding stator-side magnets may have substantially common radial dimensions. In other words, the corresponding rotor-side magnets and stator-side magnets may have substantially the same radial width.

[0037] In this embodiment, the rotor-side magnets and the magnetically corresponding stator-side magnets may have substantially common axial dimensions. In other words, the corresponding rotor-side magnets and stator-side magnets may have substantially the same axial height.

[0038] In this embodiment, each magnet layer in each bearing half can be in the form of a permanent magnet ring.

[0039] In this embodiment, each permanent magnet ring in the bearing half may have substantially common axial and radial dimensions.

[0040] In the embodiment, the rotor-side magnets and stator-side magnets may include neodymium magnets or neodymium magnet alloys. In the embodiment, the rotor-side magnets and stator-side magnets may include samarium-cobalt magnets, neodymium-iron-boron magnet alloys, or any other magnet alloys.

[0041] In embodiments, the rotor-side magnets and / or stator-side magnets can be magnetized axially or radially. In embodiments, the rotor bearing halves and / or stator bearing halves may include combinations of magnets magnetized axially and radially to form, for example, a Halbach arrangement.

[0042] In a further embodiment, the present invention provides a vacuum pump comprising a passive magnetic bearing according to any of the above embodiments. In the embodiment, the vacuum pump may be provided with a plurality of the passive magnetic bearings. For example, the vacuum pump may be provided with a first passive magnetic bearing at the high vacuum end of the vacuum pump and a second passive magnetic bearing at the low vacuum end of the vacuum pump.

[0043] In this embodiment, the vacuum pump may be a turbomolecular vacuum pump.

[0044] In the embodiment, the rotor-side magnets and stator-side magnets may include neodymium magnets or neodymium magnet alloys. In the embodiment, the rotor-side magnets and stator-side magnets may include samarium-cobalt magnets, neodymium-iron-boron magnet alloys, or any other alloys.

[0045] In this embodiment, the rotor-side magnet and / or stator-side magnet can be magnetized in the axial or radial direction.

[0046] In a further embodiment, the present invention provides a method for designing a passive magnetic bearing for a vacuum pump, more particularly for a turbomolecular vacuum pump, the method of which a) A step of preparing a rotor bearing half including one or more substantially annular rotor-side magnets and opposing stator bearing halves substantially concentrically arranged radially, each including one or more annular stator-side magnets, wherein the rotor bearing half and the stator bearing half together form a passive magnetic bearing having an outer diameter, b) A step of determining the width of the radial clearance between the rotor bearing half and the stator bearing half based on the outer diameter of the passive magnetic bearing, c) The step of configuring at least one, typically each rotor-side magnet and / or at least one, typically each stator-side magnet, to have an axial dimension that is approximately 3.5 to approximately 5.3 times the width of the radial gap, d) The step of configuring at least one, typically each rotor-side magnet and / or at least one, typically each stator-side magnet, to have a radial dimension less than 1.2 times the axial dimension of each of the magnets, Includes.

[0047] In an embodiment, step d) may include configuring at least one rotor-side magnet and / or at least one stator-side magnet to have a radial dimension substantially about 0.8 times or more the axial dimension of each magnet.

[0048] In an embodiment, step d) may include configuring at least one rotor-side magnet and / or at least one stator-side magnet to have a radial dimension of substantially about 1.195 times or less the axial dimension of each magnet, and optionally substantially about 1.19 times or less the axial dimension of each magnet. In an embodiment, step d) may include configuring at least one rotor-side magnet and / or at least one stator-side magnet to have a radial dimension of substantially about 1.18 times or less the axial dimension of each magnet.

[0049] In an embodiment, step d) may include configuring at least one rotor-side magnet and / or at least one stator-side magnet to have a radial dimension of about 0.8 to about 1.18 times the axial dimension of each magnet. In an embodiment, step d) may include configuring at least one rotor-side magnet and / or at least one stator-side magnet to have a radial dimension greater than 0.95 times the axial dimension of each magnet.

[0050] In an embodiment, step c) may include configuring at least one rotor-side magnet and / or at least one stator-side magnet to have an axial dimension of about 3.5 to about 5 times the width of the radial clearance.

[0051] In an embodiment, step c) may include configuring at least one rotor-side magnet and / or at least one stator-side magnet to have an axial dimension of about 5 to 5.3 times the width of the radial clearance.

[0052] In embodiments, the method may include the step of configuring the above-mentioned rotor-side magnets and the above-mentioned magnetically corresponding stator-side magnets to have substantially common radial dimensions.

[0053] In embodiments, the method may include a further step of configuring the above-mentioned rotor-side magnets and the above-mentioned magnetically corresponding stator-side magnets to have substantially common axial dimensions.

[0054] In the embodiment, step a) may include preparing a plurality of axially adjacent magnet layers in each of the rotor bearing half and the stator bearing half.

[0055] In this embodiment, each magnet layer can be in the form of a permanent magnet ring.

[0056] In embodiments, the method may further include the step of configuring each permanent magnet ring in each bearing half to have substantially common axial and radial dimensions.

[0057] In this embodiment, the method may include the step of magnetizing the above-mentioned rotor-side magnets and / or the above-mentioned stator-side magnets in the axial or radial direction.

[0058] In a further embodiment, the present invention provides a method for manufacturing a passive magnetic bearing for a vacuum pump, the method comprising the step of manufacturing a passive magnetic bearing according to some design of the above embodiment.

[0059] In the embodiment, the manufacturing method may include one or more additive manufacturing processes.

[0060] In a further embodiment, the present invention provides a computer-readable medium for storing data that defines both a digital representation of a passive magnetic bearing or vacuum pump of some suitable embodiment described above, and an operation instruction, when transmitted to a manufacturing apparatus, which controls the manufacturing apparatus to manufacture the passive magnetic bearing or vacuum pump using the digital representation of the passive magnetic bearing or vacuum pump.

[0061] In the embodiment, this may include a manufacturing apparatus, an additive manufacturing apparatus, or an additive manufacturing mode or module.

[0062] In a further embodiment, the present invention provides a rotor-side bearing half or stator-side bearing half of a passive magnetic bearing for a vacuum pump, comprising one or more substantially annular magnets configured to operatively magnetically engage with magnets of opposing rotor-side bearing half or stator-side bearing half of a passive magnetic bearing, wherein each magnet of the rotor-side bearing half or stator-side bearing half has an axial dimension of about 3.5 to about 5.3 times the width of the radial clearance formed between the rotor-side bearing half or stator-side bearing half and the opposing rotor-side bearing half or stator-side bearing half when the bearing half is operatively magnetically engaged, and each magnet of the rotor-side bearing half or stator-side bearing half has a radial dimension of less than 1.2 times the axial dimension of the respective magnet.

[0063] In a further embodiment, the present invention provides a passive magnetic bearing for a compressor, comprising a rotor bearing half including one or more substantially annular rotor-side magnets, and opposing, substantially concentrically radially arranged stator bearing halves including one or more substantially annular stator-side magnets. A radial clearance is provided between the rotor bearing half and the stator bearing half.

[0064] At least one, typically the rotor-side magnet described above or each of them, has an axial dimension of approximately 3.5 to 5.3 times the width of the radial clearance, and at least one, typically the rotor-side magnet described above or each of them, has a radial dimension of less than 1.2 times the axial dimension of each magnet.

[0065] Additionally or alternatively, at least one, typically the above-mentioned or each stator-side magnet, has an axial dimension of approximately 3.5 to 5.3 times the width of the radial gap, and at least one, typically the above-mentioned or each stator-side magnet, has a radial dimension of less than 1.2 times the axial dimension of each magnet.

[0066] To avoid misunderstanding, the features of the embodiments and models described herein can be combined and still fall within the scope of the present invention.

[0067] Preferred features of the present invention are described below with reference to the accompanying drawings. [Brief explanation of the drawing]

[0068] [Figure 1] A cross-sectional view of a passive magnetic bearing for a vacuum pump is shown. [Figure 2] The rotor-side bearing half and stator-side bearing half, each incorporating multiple magnet rings, are shown. [Figure 3] This graph shows the stiffness k of a passive magnetic bearing magnet for various ratios of axial dimension to radial clearance. [Figure 4] This graph shows the stiffness and weight of passive magnetic bearing magnets for various ratios of axial and radial dimensions. [Modes for carrying out the invention]

[0069] The present invention provides a passive magnetic bearing for a vacuum pump, more particularly for a turbomolecular vacuum pump. As shown in Figure 1, the vacuum pump 1 includes a stator 2 and a rotor 4 configured to rotate relative to the stator around a rotation axis (A) when in use.

[0070] A passive magnetic bearing comprises a rotor bearing half 12 and a stator bearing half 16. Typically, in the vacuum pump shown in Figure 1, the stator bearing half is the inner bearing half and the rotor bearing half is the outer bearing half, but it is also conceivable that the stator bearing half is the outer bearing half and the rotor bearing half is the inner bearing half.

[0071] In Figures 1 and 2, the rotor bearing half 12 includes a plurality of substantially annular rotor-side magnets 14, and the opposing stator bearing half 16, which is substantially concentrically arranged radially, includes a corresponding plurality of substantially annular stator-side magnets 18.

[0072] Referring to Figure 2, the radial gap g widens between the rotor bearing half 12 and the stator bearing half 16.

[0073] At least one, typically the above or each rotor-side magnet 14, has an axial dimension h that is about 3.5 to about 5.3 times the width of the radial gap g, and at least one, typically the above or each rotor-side magnet 14, has a radial dimension w that is less than 1.2 times the axial dimension of the corresponding magnet.

[0074] Additionally or alternatively, at least one, typically the above-described or each stator-side magnet 18, has an axial dimension of approximately 3.5 to 5.3 times the width of the radial gap, and at least one, typically the above-described or each stator-side magnet 18, has a radial dimension of less than 1.2 times the axial dimension of the corresponding magnet. The measured dimensions and aspect ratios of the rotor-side and stator-side magnets in Figures 1 and 2 are not necessarily accurate due to reproducibility issues, etc., and are presented for illustrative purposes only.

[0075] As an example, the design of a passive magnetic bearing according to the present invention is described below.

[0076] Assuming that the outer diameter of the outer bearing half (rotor or stator half) of the passive magnetic bearing, or the inner diameter of the rotor cavity housing, is approximately 28 mm and the radial clearance between the inner bearing half and the outer bearing half is approximately 0.6 mm, the g / D ratio is approximately 0.025, where g is the width of the gap between the rotor half and the stator half and D is the diameter of the bearing.

[0077] According to the teachings of the known prior art including "Moser", when performing an optimal design of a passive magnetic bearing with the above parameters, the following aspect ratios, h

[0079] / D = 0.065 d opt / D = 0.830 a opt / D = 0.661 are obtained, where h opt is the optimal height of one permanent magnet layer, d opt is the optimal diameter defining the position of the gap between the rotor and the stator, a opt is the optimal diameter of the main rotor shaft, and D is the diameter of the bearing.

[0078] The above aspect ratios are h opt / g = 3.02 w o,opt / g = 1.15 w i,opt / g = 1.15 that can be developed to give an aspect ratio of o,opt where w i,opt is the optimal radial dimension of the magnet on the outer bearing half (stator side or rotor side), w opt is the optimal radial dimension of the magnet on the inner bearing half, and g is the width of the gap between the outer bearing half and the inner bearing half.

[0079] Therefore, h o is equal to 1.81, w i is equal to 2.08 mm, and w

[0080] The bearing stiffness of a passive magnetic bearing design, formed by increasing the number of magnet layers, can be calculated, for example, using finite element analysis (FEA). Once the required stiffness is known, the required number of layers N can be determined.

[0081] Table 1 shows the calculated axial stiffness of bearings formed with different numbers of layers, for example, when using neodymium magnets. [Table 1]

[0082] The radial stiffness value of a bearing can be calculated by dividing the value in Table 1 by 2.

[0083] The ring described above has optimal dimensions, including height, and consequently possesses maximum rigidity per unit height. However, the resulting bearing is generally formed from a relatively large number of rings. Therefore, assembly becomes more difficult and expensive, especially since machining the rings to the required tolerances is more time-consuming and costly. In addition, the resulting rings may be thin and not very robust, making them difficult to manufacture and handle. As described in this invention, it is advantageous to use fewer, taller magnets.

[0084] Figure 3 plots the stiffness of the magnet as h / g increases while keeping the outer diameter D, air gap g, and w / h ratio constant. The plot shows that the increase in stiffness practically stops as the h / g value increases.

[0085] In addition, Figure 4 shows the effect of the aspect ratio w / h on the rigidity and weight of the magnet ring stack.

[0086] The plot in Figure 4 shows that the local stiffness is maximized when the w / h ratio is less than 1.2, and that the stiffness decreases when the w / h ratio exceeds 1.2. The weight of the ring increases monotonically with w / h.

[0087] Table 2 shows possible combinations of laminates with one fewer magnet layer that have the same rigidity as prior art (including "Moser") and result in the minimum increase in laminate height and bearing weight. Table 2 presents two sets of results: one for w / h less than 1.2 and one for w / h 1.2 or greater. [Table 2]

[0088] As shown in Table 2, better results are obtained when the h / g ratio of taller magnets is small (as can be predicted from Figure 3). Furthermore, when w / h is less than 1.2, the ratio of the weight of the magnet stack with fewer taller magnets to the weight of the conventional design is significantly lower than when w / h is greater than 1.2.

[0089] Therefore, by using magnets with an h / g ratio of less than 5.3 times and a w / h ratio of less than 1.2 times, it is possible to maintain substantially the same stiffness while minimizing the impact on the height and weight of the magnet stack compared to prior art. Using fewer magnets reduces not only machining costs and ease of assembly, but also generally reduces material waste during machining. This helps to offset any potential increase in material usage that may occur while maintaining the same maximum stiffness.

[0090] Using a similar method, the reduction in stiffness when using fewer taller magnets can be minimized without increasing the bearing height and weight. Table 3 shows the calculation results for w / h less than 1.2 and greater than 1.2. w / h = 1.3 is used as an example. If the bearing weight is kept substantially the same without increasing it, the bearing height remains the same or decreases, and the number of axially taller magnets used decreases. [Table 3]

[0091] Table 3 shows that for the same bearing weight, the stiffness ratio is higher when w / h is less than 1.2 than when w / h is greater than 1.2. This is because the radial width is larger for the same appropriate height. Consequently, the ring weight increases without a corresponding increase in stiffness. A shorter ring must be selected, which results in a decrease in stiffness. Therefore, when w / h is less than 1.2, the maximum stiffness / weight ratio is achieved by using fewer taller rings than is generally accepted in the prior art, resulting in a more cost-effective, more robust, and easier-to-assemble bearing.

[0092] In practice, the desired stiffness may lie between two different optimal stiffnesses for different number of layers, N and N+1, determined by the principles of the prior art. In this case, the stiffness of the N layer is insufficient, and the stiffness of the N+1 layer is excessive. Excessive stiffness can lead to higher vibrations than desired, or to excessive preload on the roller bearing (if present). Therefore, the present invention can be used to manufacture bearings with the required stiffness while minimizing the amount of permanent magnet material used by providing N layers. Often, it is desirable to reduce the number of rings by increasing the axial height of the rings, and the present invention can be used to achieve this while minimizing the impact on the magnetic material used.

[0093] It should be understood that various modifications are possible to the embodiments shown without departing from the spirit and scope of the invention as defined by the attached claims, as interpreted in accordance with patent law. [Explanation of Symbols]

[0094] 1. Vacuum pump 2 staters 4 rotors 12 Rotor bearing half 14. Rotor-side magnet 16 Stator bearing half 18 Stator-side magnet

Claims

1. A passive magnetic bearing for a vacuum pump, wherein the vacuum pump includes a stator and a rotor configured to rotate around a rotation axis relative to the stator, and the passive magnetic bearing includes a rotor bearing half including one or more substantially annular rotor-side magnets and a stator bearing half including one or more substantially annular stator-side magnets facing each other and arranged radially in a substantially concentric manner, wherein a radial clearance extends between the rotor bearing half and the stator bearing half. At least one, preferably each rotor-side magnet, has an axial dimension of approximately 3.5 to 5.3 times the width of the radial gap, and a radial dimension of less than 1.2 times the axial dimension of each of the magnets. and / or, A passive magnetic bearing for a vacuum pump, wherein at least one, preferably each stator-side magnet, has an axial dimension of about 3.5 to about 5.3 times the width of the radial gap, and each of the magnets has a radial dimension of less than 1.2 times the axial dimension.

2. The passive magnetic bearing for a vacuum pump according to claim 1, wherein the at least one rotor-side magnet and / or the at least one stator-side magnet have a radial dimension that is substantially about 0.8 times or more the axial dimension of each magnet, and optionally about 0.8 to about 1.18 times the axial dimension of each magnet.

3. The passive magnetic bearing for a vacuum pump according to claim 1 or 2, wherein the at least one rotor-side magnet and / or the at least one stator-side magnet have an axial dimension of about 3.5 to about 5 times the width of the radial clearance.

4. The passive magnetic bearing for a vacuum pump according to claim 1 or 2, wherein the at least one rotor-side magnet and / or the at least one stator-side magnet have an axial dimension of about 5 to about 5.3 times the width of the radial clearance.

5. A passive magnetic bearing for a vacuum pump according to any one of claims 1 to 4, wherein the rotor-side magnets and the magnetically corresponding stator-side magnets have substantially common radial dimensions, and / or the rotor-side magnets of the rotor bearing half and the magnetically corresponding magnets of the stator bearing half have substantially common axial dimensions.

6. A vacuum pump comprising a passive magnetic bearing according to any one of claims 1 to 5, more particularly a turbomolecular vacuum pump.

7. A vacuum pump passive magnetic bearing according to any one of claims 1 to 5, wherein the rotor-side magnet and / or stator-side magnet are magnetized in the axial or radial direction, or a vacuum pump according to claim 6.

8. A method for designing a passive magnetic bearing for a vacuum pump, a) A step of preparing a rotor bearing half including one or more substantially annular rotor-side magnets and opposing stator bearing halves arranged substantially concentrically in the radial direction and including one or more annular stator-side magnets, wherein the rotor bearing half and the stator bearing half together form a passive magnetic bearing having an outer diameter, b) A step of determining the width of the radial clearance between the rotor bearing half and the stator bearing half based on the outer diameter of the passive magnetic bearing, c) The step of configuring at least one, preferably each rotor-side magnet and / or at least one, preferably each stator-side magnet, to have an axial dimension of about 3.5 to about 5.3 times the width of the radial gap, d) The step of configuring at least one, preferably each rotor-side magnet and / or at least one, preferably each stator-side magnet, to have a radial dimension of less than 1.2 times the axial dimension of each of the magnets, A method that includes this.

9. The method of claim 8, step d) comprising configuring the at least one rotor-side magnet and / or the at least one stator-side magnet to have a radial dimension of at least substantially 0.8 times the axial dimension of each magnet, and optionally ranging from about 0.8 times to about 1.18 times the axial dimension of each magnet.

10. The method according to claim 8 or 9, step c) comprising configuring the at least one rotor-side magnet and / or the at least one stator-side magnet to have an axial dimension of about 3.5 to about 5 times the width of the radial gap.

11. The method according to claim 8 or 9, wherein step c) comprises configuring the at least one rotor-side magnet and / or the at least one stator-side magnet to have an axial dimension of about 5 to about 5.3 times the width of the radial gap.

12. The method according to any one of claims 8 to 11, comprising the steps of configuring the rotor-side magnets and the magnetically corresponding stator-side magnets to have substantially common radial dimensions, and / or the rotor-side magnets and the magnetically corresponding stator-side magnets to have substantially common axial dimensions.

13. A method for manufacturing a passive magnetic bearing for a vacuum pump, comprising the step of manufacturing a passive magnetic bearing for a vacuum pump in accordance with a design described in any one of claims 8 to 12.

14. A computer-readable medium for storing data that defines both a digital representation of a passive magnetic bearing for a vacuum pump according to any one of claims 1 to 5 or 7, or a vacuum pump according to claim 6 or 7, and an operation instruction that, when transmitted to a manufacturing apparatus, controls the manufacturing apparatus to manufacture the passive magnetic bearing for the vacuum pump or the vacuum pump using the digital representation of the vacuum pump.

15. A rotor bearing half or stator bearing half of a passive magnetic bearing of a vacuum pump, comprising one or more substantially annular magnets configured to operatively magnetically engage with the magnets of the opposing rotor bearing half or stator bearing half of the passive magnetic bearing, Each magnet in the rotor bearing half or the stator bearing half has an axial dimension of approximately 3.5 to 5.3 times the width of the radial clearance formed between the rotor bearing half or the stator bearing half and the rotor bearing half or the stator bearing half facing it when the bearing half is operably magnetically engaged. A rotor bearing half or stator bearing half of a vacuum pump, wherein each magnet in the rotor bearing half or stator bearing half has a radial dimension less than 1.2 times the axial dimension of each of the magnets.

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