Passive magnetic bearing of vacuum pump

Abstract

The invention provides a passive magnetic bearing for a vacuum pump (1), the vacuum pump (1) comprising a stator (2) and a rotor (4), the rotor being configured to rotate relative to the stator (2) about an axis of rotation; the passive magnetic bearing comprises a rotor bearing half (12) comprising one or more substantially annular rotor-side magnets (14) and an opposing and substantially concentric radially arranged stator bearing half (16) comprising one or more substantially annular stator-side magnets (18); a radial gap (g) extending between the rotor and stator bearing halves (12, 16); wherein at least one, preferably each rotor-side magnet (14) has an axial extent that is about 3.5 to about 5.3 times the width of the radial gap (g) and has a radial extent that is less than 1.2 times the axial extent of the respective magnet; and / or wherein at least one, preferably each, stator-side magnet (18) has an axial extent that is about 3.5 to about 5.3 times the width of the radial gap (g) and has a radial extent that is less than 1.2 times the axial extent of the respective magnet.

Description

Technical Field

[0001] This invention relates to passive magnetic bearings for vacuum pumps, vacuum pumps including said passive magnetic bearings, and methods for manufacturing and designing said passive magnetic bearings. Background Technology

[0002] Typically, vacuum pumps use passive magnetic bearings to support the rotor, whose rotor elements (e.g., blades) interact with the stator to transport the gaseous medium from the inlet to the outlet. In turbomolecular vacuum pumps, the stator typically comprises multiple blades configured to interact with multiple rotor blades. Passive magnetic bearings are usually located at least at the higher vacuum end of the turbomolecular vacuum pump.

[0003] Passive magnetic bearings typically consist of an outer bearing half and an inner bearing half. Each bearing half includes one or more magnets, usually in the form of a passive magnetic ring. Depending on the specific arrangement of the passive magnetic bearing, the outer bearing half can be either a rotor bearing half or a stator bearing half, while the inner bearing half is the other of either the rotor or stator bearing half. The bearing halves are placed close to each other with an air gap between them, and are typically configured to repel each other during use.

[0004] For passive magnetic bearings, stiffness is particularly important in order to provide a firm positioning of the rotor relative to the stator.

[0005] Therefore, it is often desirable to determine an optimized design for the required stiffness. For example, once the outer diameter of the bearing and the clearance between the inner and outer bearing halves are determined, the design of the passive magnetic bearing can be optimized to provide the stiffness required for the minimum axial length and / or the stiffness required for the minimum weight of permanent magnet material.

[0006] The paper titled "Optimization of Repulsive Passive Magnetic Bearings" (Moser, Sandtner, et al., in IEEE Transactions on Magnetics, Volume 42, No. 8, August 2006) describes how to determine the optimal magnet size for optimal stiffness using a specific aspect ratio. More specifically, the Moser paper plots the optimal axial and radial ranges of the rotor-side and stator-side magnets as a function of the bearing diameter, given a radial air gap between the rotor and stator-side magnets as a function of diameter.

[0007] Moser is an authority in this field. He deduced that an optimal design can be found for a finite bearing volume and plotted this data so that designers of passive magnetic bearings can select appropriate magnet sizes based on a specific construction space. Moser's design principles provide discrete design solutions for a given number of magnetic rings in a bearing, each solution representing the minimum length of a bearing with a given stiffness. This optimal design is based on continuously stacked layers of permanent magnets for a given combination of air gap and rotor diameter.

[0008] An example of such an implementation of the teaching is described in EP3135932B1, which describes a passive magnetic bearing for a vacuum pump, particularly a turbomolecular pump, wherein the axial height of the inner and / or outer magnetic rings of the bearing is in the range of 3 to 5 times the radial air gap width, and the radial width of the inner and / or outer magnetic rings is greater than or at most equal to 1.2 times the axial height of the respective rings, and less than or at most equal to 1.5 times the axial height of the respective rings.

[0009] However, the applicant has identified a dichotomy between magnet stiffness and the number and size of magnets, which has not yet been resolved or adequately resolved.

[0010] In theory, the assumed optimal radial stiffness can be achieved by producing passive magnetic bearings with magnets having an aspect ratio corresponding to that taught in Moser and EP3135932B1. However, existing technologies, especially Moser, require a relatively large number of bearing magnet layers, each of which must be precisely manufactured, machined, and assembled into a passive magnetic bearing half (rotor bearing half or stator bearing half).

[0011] Furthermore, manufacturing passive magnetic bearings according to existing technology can lead to undesirable waste of magnet material due to machining and / or use of material in the permanent magnet ring that exceeds the optimal range.

[0012] Therefore, the theoretically ideal results described in the prior art cannot help technicians provide suitable real-world improvements to passive magnetic bearings that take into account not only optimal radial stiffness but also more practical factors related to manufacturing and assembly.

[0013] Conversely, in practice, the aspect ratio of the magnets in known passive magnetic bearings is usually much larger than that of the aforementioned prior art, especially the value advocated by Moser. This results in a significantly reduced number of magnets in the bearing, but also leads to suboptimal stiffness and a significantly higher use of magnetic materials.

[0014] Although this practice has been used quite successfully, the pursuit of more rigid bearings, improved pumping performance, and reduced use of magnetic materials has brought about more complex technical requirements for passive magnetic bearings.

[0015] The present invention aims to solve these and other problems of the prior art. Summary of the Invention

[0016] Therefore, in a first aspect, the present invention provides a passive magnetic bearing for a vacuum pump, particularly a passive magnetic bearing for a turbomolecular vacuum pump, the vacuum pump including a stator and a rotor, the rotor being configured to rotate relative to the stator about a rotation axis. The passive magnetic bearing includes a rotor bearing half and opposing, substantially concentric, radially arranged stator bearing halves, the rotor bearing half including one or more substantially annular rotor-side magnets, and the stator bearing half including one or more substantially annular stator-side magnets. A radial clearance extends between the rotor bearing half and the stator bearing half.

[0017] At least one rotor-side magnet (typically, said or each rotor-side magnet) has an axial range of about 3.5 to about 5.3 times the width of the radial clearance; and at least one rotor-side magnet (typically, said or each rotor-side magnet) has a radial range of less than 1.2 times the axial range of the respective magnet.

[0018] Additionally or alternatively, at least one stator-side magnet (typically, said or each stator-side magnet) has an axial range of about 3.5 to about 5.3 times the width of the radial gap; and at least one stator-side magnet (typically, said or each stator-side magnet) has a radial range less than 1.2 times the axial range of the respective magnet.

[0019] As used herein, the term "axial range" refers to the width of the annular magnet in a plane substantially parallel to the axis of rotation of the vacuum pump rotor. The axial range of the rotor-side magnet or stator-side magnet can be plotted as "h / g", that is, the ratio of the axial height to the width as a function of the width of the air gap between the rotor and stator.

[0020] As used herein, the term "radial range" refers to the width of the annular magnet in a plane substantially perpendicular to the axis of rotation of the vacuum pump rotor. The radial range refers to the width of the magnetic material of the annular magnet, not the radius derived from the axis of rotation of the bearing half. The radial range of the rotor-side magnet or stator-side magnet can be plotted as "w / h," that is, the ratio of the radial width to the axial height of the magnet as a function of the axial height.

[0021] Known prior art bearings include magnets that do not have these axial and radial range ratios because the prior art teaches that optimal magnet stiffness cannot be achieved through these ranges. More specifically, as described in Moser, known magnets do not have an axial range that is approximately 3.5 to approximately 5.3 times the radial clearance width, and do not have a radial range that is less than 1.2 times the axial range of the corresponding magnet.

[0022] The known prior art provides teachings that contradict the selection of "this combination of axial and radial ranges of the rotor-side magnets and / or stator-side magnets". As mentioned above, it is generally accepted in the prior art that if the axial range of the rotor-side magnets or stator-side magnets is or greater than about 3.5 times the radial clearance width, then the ratio of the radial range to the axial range should be greater than 1.2 times as a function of the axial range in order to provide optimal stiffness.

[0023] In practice, known bearings typically have a large h / g aspect ratio, usually 6 to 8 or higher, and in some cases just below 6 but above 5.3. In the past, for cost reasons, the focus was on reducing the number of magnets, as optimal stiffness and reducing the amount of material used were not priorities.

[0024] Conversely, the applicant surprisingly discovered that the intermediate axial range, as a function of the radial clearance width, combined with a smaller radial range, provides a short magnetic bearing half that includes fewer magnets than previously taught, while maintaining optimal or near-optimal stiffness and using comparable or less magnetic material. These two properties are crucial in the pursuit of improved performance and sustainability. This is also advantageous because providing optimal stiffness with fewer magnets than previously taught reduces the machining requirements of passive magnetic bearings and thus lowers costs compared to existing technologies.

[0025] By identifying and resolving the dichotomy between optimal magnet stiffness and the number and size of magnets, the applicant now provides, in this invention, a passive magnetic bearing for a vacuum pump that has suitable stiffness while requiring less material than prior art, and with minimal material waste, machining effort, and cost. Specifically, a smaller radial range, combined with a larger axial range within that range, provides a passive magnetic bearing requiring less material. This, in turn, reduces the weight of the passive magnetic bearing, as well as material and machining costs.

[0026] This particular combination of radial and axial ranges of the rotor-side magnets and / or stator-side magnets in the rotor and / or stator-side bearing halves of a passive magnetic bearing provides an unexpected technical advantage, namely, improved stiffness density for a given size of passive magnetic bearing with fewer magnet layers.

[0027] In an embodiment, at least one rotor-side magnet and / or at least one stator-side magnet may have a radial range that is substantially equal to or greater than about 0.8 times the axial range of the respective magnet.

[0028] In an embodiment, the at least one rotor-side magnet and / or the at least one stator-side magnet may have a radial range that is substantially equal to or less than about 1.195 times the axial range of the corresponding magnet; optionally, it may be substantially equal to or less than about 1.19 times the axial range of the corresponding magnet. In an embodiment, the at least one rotor-side magnet and / or the at least one stator-side magnet may have a radial range that is substantially equal to or less than about 1.18 times the axial range of the corresponding magnet.

[0029] In an embodiment, at least one rotor-side magnet and / or at least one stator-side magnet may have a radial range that is about 0.8 to about 1.18 times the axial range of the respective magnet.

[0030] In an embodiment, the at least one rotor-side magnet and / or the at least one stator-side magnet may have an axial range of about 3.5 to about 5 times the width of the radial clearance.

[0031] In an embodiment, the at least one rotor-side magnet and / or the at least one stator-side magnet may have an axial range of about 5 to about 5.3 times the width of the radial clearance.

[0032] Typically, a passive magnetic bearing may include a rotor bearing half and a stator bearing half, which have substantially the same axial extent and include substantially the same, and usually substantially precisely the same, number of magnet layers formed as annular magnetic rings. Typically, each of the inner and outer bearing halves includes multiple magnet layers.

[0033] Therefore, in the embodiments, the inner bearing half and the outer bearing half may each include a corresponding plurality of axially adjacent magnet layers. Although in the embodiments, the inner bearing half and the outer bearing half may have different numbers of magnet layers.

[0034] In an embodiment, each rotor-side magnet and each corresponding stator-side magnet may have a substantially common radial extent. In other words, the corresponding rotor-side magnet and stator-side magnet may have substantially the same radial width.

[0035] In an embodiment, each rotor-side magnet and each corresponding stator-side magnet may have a substantially common axial range. In other words, the corresponding rotor-side magnet and stator-side magnet may have substantially the same axial height.

[0036] In an embodiment, each magnet layer of each bearing half may be in the form of a permanent magnet ring.

[0037] In an embodiment, each permanent magnet ring of the bearing half may have a substantially common axial and radial range.

[0038] In an embodiment, each rotor-side magnet and each stator-side magnet may comprise a neodymium magnet or a neodymium magnet alloy. In another embodiment, each rotor-side magnet and each stator-side magnet may comprise a samarium-cobalt magnet, a neodymium-iron-boron magnet alloy, or any other magnet alloy.

[0039] In embodiments, each rotor-side magnet and / or each stator-side magnet may be axially magnetized or radially magnetized. In embodiments, the rotor bearing half and / or stator bearing half may include a combination of axially and radially magnetized magnets, for example, to form a Halbach array.

[0040] In another aspect, the present invention provides a vacuum pump comprising a passive magnetic bearing according to any of the foregoing aspects. In embodiments, the vacuum pump may include a plurality of the passive magnetic bearings. For example, the vacuum pump may include a first passive magnetic bearing at a higher vacuum end of the vacuum pump and a second passive magnetic bearing at a lower vacuum end of the vacuum pump.

[0041] In this embodiment, the vacuum pump may be a turbomolecular vacuum pump.

[0042] In one embodiment, each rotor-side magnet and each stator-side magnet may comprise a neodymium magnet or a neodymium magnet alloy. In another embodiment, each rotor-side magnet and each stator-side magnet may comprise a samarium-cobalt magnet, a neodymium-iron-boron magnet alloy, or any other alloy.

[0043] In an embodiment, each rotor-side magnet and / or each stator-side magnet may be magnetized axially or radially.

[0044] On the other hand, the present invention provides a method for designing a passive magnetic bearing for a vacuum pump, particularly a turbomolecular vacuum pump, the method comprising the following steps: a) Provides a rotor bearing half and opposing and substantially concentrically arranged stator bearing halves, the rotor bearing half including one or more substantially annular rotor-side magnets, the stator bearing half including one or more annular stator-side magnets, the rotor bearing half and the stator bearing half together forming a passive magnetic bearing having an outer diameter. b) Determine the width of the radial clearance extending between the rotor bearing half and the stator bearing half based on the outer diameter of the passive magnetic bearing; c) At least one rotor-side magnet, typically each rotor-side magnet and / or at least one stator-side magnet, typically each stator-side magnet, are configured to have an axial range of approximately 3.5 to approximately 5.3 times the radial clearance width; and d) At least one rotor-side magnet, typically each rotor-side magnet and / or at least one stator-side magnet, typically each stator-side magnet, are configured to have a radial range less than 1.2 times the axial range of the respective magnet.

[0045] In an embodiment, step d) may include configuring the at least one rotor-side magnet and / or the at least one stator-side magnet to have a radial range that is substantially equal to or greater than about 0.8 times the axial range of the respective magnet.

[0046] In one embodiment, step d) may include configuring the at least one rotor-side magnet and / or the at least one stator-side magnet to have a radial range substantially equal to or less than about 1.195 times the axial range of the corresponding magnet; optionally, substantially equal to or less than about 1.19 times the axial range of the corresponding magnet. In another embodiment, step d) may include configuring the at least one rotor-side magnet and / or the at least one stator-side magnet to have a radial range substantially equal to or less than about 1.18 times the axial range of the corresponding magnet.

[0047] In one embodiment, step d) may include configuring the at least one rotor-side magnet and / or the at least one stator-side magnet to have a radial range that is about 0.8 to about 1.18 times the axial range of the respective magnet. In another embodiment, step d) may include configuring the at least one rotor-side magnet and / or the at least one stator-side magnet to have a radial range that is greater than 0.95 times the axial range of the respective magnet.

[0048] In an embodiment, step c) may include configuring the at least one rotor-side magnet and / or the at least one stator-side magnet to have an axial range of about 3.5 to about 5 times the width of the radial clearance.

[0049] In an embodiment, step c) may include configuring the at least one rotor-side magnet and / or the at least one stator-side magnet to have an axial range of about 5 to about 5.3 times the width of the radial clearance.

[0050] In an embodiment, the method may include the step of configuring the one or each rotor-side magnet and the one or each magnetically corresponding stator-side magnet to have a substantially common radial range.

[0051] In an embodiment, the method may include further steps of configuring the one or each rotor-side magnet and the one or each magnetically corresponding stator-side magnet to have a substantially common axial range.

[0052] In an embodiment, step a) may include providing a plurality of axially adjacent magnet layers for each of the rotor bearing half and the stator bearing half.

[0053] In an embodiment, each magnet layer may be in the form of a permanent magnet ring.

[0054] In an embodiment, the method may further include the step of configuring each permanent magnet ring of each bearing half to have substantially common axial and radial ranges.

[0055] In an embodiment, the method may include the step of axially or radially magnetizing the or each rotor-side magnet and / or the or each stator-side magnet.

[0056] In another aspect, the present invention provides a method for manufacturing a passive magnetic bearing for a vacuum pump, the method comprising the step of manufacturing the passive magnetic bearing according to the design of any of the foregoing aspects.

[0057] In an embodiment, the manufacturing method may include one or more additive manufacturing processes.

[0058] In another aspect, the present invention provides a computer-readable medium for storing data and operating instructions, the data defining a digital representation of a passive magnetic bearing or any suitable vacuum pump of the foregoing aspects, the operating instructions being adapted to control a manufacturing apparatus to manufacture the passive magnetic bearing or vacuum pump using the digital representation of the passive magnetic bearing or vacuum pump when the data is relayed to the manufacturing apparatus.

[0059] In the embodiments, the manufacturing apparatus may be an additive manufacturing apparatus, or may include an additive manufacturing mode or module.

[0060] In another aspect, the present invention provides a rotor bearing half or stator bearing half of a passive magnetic bearing for a vacuum pump, comprising one or more substantially annular magnets configured to operably magnetically engage the magnets of opposing rotor bearing halves or stator bearing halves of the passive magnetic bearing; wherein each magnet of the rotor bearing half or stator bearing half has an axial range that, when the bearing halves are operably magnetically engaged, is about 3.5 to about 5.3 times the width of the radial gap formed between the rotor bearing half or stator bearing half and the opposing rotor bearing half or stator bearing half; and wherein the radial range of each magnet of the rotor bearing half or stator bearing half is less than 1.2 times the axial range of the corresponding magnet.

[0061] In another aspect, the present invention provides a passive magnetic bearing for a compressor, comprising a rotor bearing half and opposing, substantially concentric, radially arranged stator bearing halves, the rotor bearing half comprising one or more substantially annular rotor-side magnets, and the stator bearing half comprising one or more substantially annular stator-side magnets. A radial clearance extends between the rotor bearing half and the stator bearing half.

[0062] At least one rotor-side magnet (typically, said or each rotor-side magnet) has an axial range of about 3.5 to about 5.3 times the width of the radial clearance; and at least one rotor-side magnet (typically, said or each rotor-side magnet) has a radial range of less than 1.2 times the axial range of the respective magnet.

[0063] Additionally or alternatively, at least one stator-side magnet (typically, said or each stator-side magnet) has an axial range of about 3.5 to about 5.3 times the width of the radial gap; and at least one stator-side magnet (typically, said or each stator-side magnet) has a radial range less than 1.2 times the axial range of the respective magnet.

[0064] To avoid confusion, the features of the aspects and embodiments described herein may be combined and still fall within the scope of the invention. Attached Figure Description

[0065] Preferred features of the invention will now be described by way of example with reference to the accompanying drawings, wherein: Figure 1 A cross-sectional view of a passive magnetic bearing used in a vacuum pump is shown.

[0066] Figure 2 The rotor-side bearing half and the stator-side bearing half are shown, each half being fitted with multiple magnetic rings.

[0067] Figure 3 The graph shows the stiffness k of the passive magnetic bearing magnet with different ratios of axial range and radial clearance.

[0068] Figure 4 The graphs show the stiffness and mass of the passive magnetic bearing magnet in the form of different ratios in the axial and radial ranges. Detailed Implementation

[0069] This invention provides a passive magnetic bearing for vacuum pumps, particularly a passive magnetic bearing for turbomolecular vacuum pumps. For example... Figure 1 As shown, the vacuum pump 1 includes a stator 2 and a rotor 4, the rotor being configured to rotate relative to the stator about a rotation axis (“A”) during use.

[0070] The passive magnetic bearing comprises a rotor bearing half 12 and a stator bearing half 16. Typically, in Figure 1 In a vacuum pump, the stator bearing half is the inner bearing half, and the rotor bearing half is the outer bearing half. However, it is conceivable that the stator bearing half can be the outer bearing half, and the rotor bearing half can be the inner bearing half.

[0071] exist Figure 1 and 2 In the rotor bearing half 12, there are a plurality of generally annular rotor-side magnets 14, and the opposing and generally concentrically arranged stator bearing half 16 includes a corresponding plurality of generally annular stator-side magnets 18.

[0072] refer to Figure 2 The radial clearance g extends between the rotor bearing half 12 and the stator bearing half 16.

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

[0074] Additionally or alternatively, at least one stator-side magnet 18 (typically, said or each stator-side magnet) has an axial range that is about 3.5 to about 5.3 times the width of the radial gap; and at least one stator-side magnet 18 (typically, said or each stator-side magnet) has a radial range that is less than 1.2 times the axial range of the corresponding magnet. Figure 1 and 2 The measured dimensions and aspect ratios of the rotor-side magnets and stator-side magnets in the diagram do not need to be precise, depending on their reproduction, etc.; they are provided for illustrative purposes.

[0075] The design of the passive magnetic bearing according to the present invention will now be described by way of example.

[0076] Assuming the outer diameter of the outer bearing half (which is either the rotor bearing half or the stator bearing 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, then the g / D ratio will be approximately 0.025, where g is the width of the air gap between the rotor bearing half and the stator bearing half, and D is the diameter of the bearing.

[0077] Based on the teachings of known existing technologies, including "Moser," and utilizing the above parameters, the optimal design of a passive magnetic bearing will produce the following aspect ratio: h opt / D = 0.065; d opt / D = 0.830; and a opt / D = 0.661, Where h opt The optimal height for a permanent magnet layer, d opt It is the optimal diameter that defines the air gap position between the rotor and stator, a opt D is the optimal diameter of the main rotor shaft, and D is the diameter of the bearing.

[0078] The above aspect ratios can be developed to provide the following aspect ratios: h opt / g = 3.02 w o,opt / g = 1.15 w i,opt / g = 1.15, Where w o,opt It is the optimal radial range of the magnet in the outer bearing half (which is either the stator side or the rotor side), w i,opt is the optimal radial range of the magnet in the inner bearing half, and g is the width of the air gap between the outer bearing half and the inner bearing half.

[0079] Therefore, h opt Equals 1.81, w o It equals 2.08 mm, and w i It equals 2.03 mm.

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

[0081] Table 1 below shows the calculated axial stiffness magnitudes for bearings with different numbers of layers, where the magnet material used is, for example, neodymium. Table 1.

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

[0083] The aforementioned rings have optimal dimensions, including height, to achieve maximum stiffness per unit height. However, the resulting bearings are typically 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 laborious and costly. Furthermore, the resulting rings are thin and not robust, and may be difficult to manufacture and handle. Using fewer and taller magnets as described in this invention is advantageous.

[0084] Figure 3 A graph was plotted showing the relationship between the magnet's stiffness and h / g as the magnet's height increases while maintaining the same outer diameter D, air gap g, and w / h ratio. The graph indicates that for higher h / g values, the stiffness essentially stops increasing.

[0085] in addition, Figure 4 The effect of aspect ratio w / h on the stiffness and weight of magnetic ring stacks is shown.

[0086] Figure 4 The graph shows that for w / h ratios less than 1.2, a local maximum stiffness is obtained, while the stiffness decreases above a w / h ratio greater than 1.2. The weight of the ring increases monotonically with w / h.

[0087] Table 2 below shows possible combinations of stacks with one less magnet layer, which have the same stiffness as described in the prior art including "Moser" and produce minimal increases in stack height and bearing weight. Two sets of results are provided in Table 2: one set with w / h < 1.2 and the other set with w / h ≥ 1.2. Table 2.

[0088] As shown in Table 2, improved results can be obtained when the h / g ratio of higher magnets is smaller, as can be seen from... Figure 3 As expected. Furthermore, when w / h is below 1.2, the weight ratio of a magnet stack with a reduced number of higher magnets to that of a prior art design is much lower compared to when w / h is above 1.2.

[0089] Therefore, compared to existing technologies, using magnets with an h / g ratio less than 5.3 times and a w / h ratio less than 1.2 times minimizes the impact on magnet stack height and weight while maintaining essentially the same stiffness. Using fewer magnets not only reduces machining costs and improves ease of assembly, but also results in less material typically discarded during machining operations. This helps offset any potential increase in material usage while maintaining the same maximum stiffness value.

[0090] When using fewer, taller magnets, the same method can be used to minimize the reduction in stiffness without increasing bearing height and weight. Table 3 below shows the calculation results for w / h less than 1.2 and w / h greater than 1.2. A w / h of 1.3 is used for illustration. When bearing weight does not increase and remains substantially the same, bearing height remains the same or lower, and fewer axially taller magnets are used. 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, for the same given height, the radial width is larger. Therefore, the weight of the ring increases, but the stiffness does not increase accordingly. Shorter rings must be selected, which results in lower stiffness. Therefore, a w / h of less than 1.2 produces the maximum stiffness / weight ratio when using fewer and taller rings than is generally accepted in the prior art, resulting in more cost-effective, robust, and easier-to-assemble bearings.

[0092] In practice, it is possible that the desired stiffness falls between the optimal stiffness determined by prior art principles for two different numbers of layers, N and N+1, where the stiffness with N layers is insufficient, and the stiffness with N+1 layers is excessive. Excessive stiffness can lead to higher-than-desirable vibrations or excessive preloads being applied to the rolling bearing, if any. Therefore, this invention can be used to manufacture bearings with the desired stiffness, wherein N layers are provided and a minimum amount of permanent magnet material is used. In most cases, it is desirable to increase the axial height of the rings and reduce the number of rings, and this invention can be used to achieve this while minimizing the impact on the magnetic materials used.

[0093] However, it should be understood that various modifications may be made to the illustrated embodiments without departing from the spirit and scope of the invention as defined by the appended claims as interpreted by patent law.

[0094] Figure Labels 1 Vacuum pump 2 stators 4 rotors 12 rotor bearing half 14 Rotor-side magnets 16 stator bearing half 18 stator side magnets

Claims

1. A vacuum pump passive magnetic bearing, the vacuum pump comprising a stator and a rotor configured to rotate relative to the stator about an axis of rotation; the passive magnetic bearing comprising a rotor bearing half and an opposite and substantially concentrically radially arranged stator bearing half, the rotor bearing half comprising one or more substantially annular rotor-side magnets, the stator bearing half comprising one or more substantially annular stator-side magnets; a radial gap extending between the rotor bearing half and the stator bearing half; wherein at least one, preferably each, rotor-side magnet has an axial extent that is about 3.5 to about 5.3 times the width of the radial gap, and has a radial extent that is less than 1.2 times the axial extent of the respective magnet; and / or, wherein at least one, preferably each, stator-side magnet has an axial extent that is about 3.5 to about 5.3 times the width of the radial gap, and has a radial extent that is less than 1.2 times the axial extent of the respective magnet. The at least one rotor-side magnet and / or the at least one stator-side magnet has a radial extent that is substantially equal to or greater than about 0.8 times the axial extent of the respective magnet; optionally about 0.8 to about 1.18 times the axial extent of the respective magnet.

2. The vacuum pump passive magnetic bearing of claim 1, wherein, The at least one rotor-side magnet and / or the at least one stator-side magnet has an axial extent that is about 3.5 to about 5 times the width of the radial gap.

3. The vacuum pump passive magnetic bearing of claim 1 or 2, wherein, The at least one rotor-side magnet and / or the at least one stator-side magnet has an axial extent that is about 5 to about 5.3 times the width of the radial gap.

4. The vacuum pump passive magnetic bearing of claim 1 or 2, wherein, The or each rotor-side magnet and the or each magnetically corresponding stator-side magnet has a substantially common radial extent; and / or wherein the or each rotor-side magnet of the rotor bearing half and the or each magnetically corresponding magnet of the stator bearing half has a substantially common axial extent.

5. The vacuum pump passive magnetic bearing of any of the preceding claims, wherein, 6. A vacuum pump, in particular a turbomolecular vacuum pump, comprising a vacuum pump passive magnetic bearing according to any one of claims 1 to 5.

7. The vacuum pump passive magnetic bearing according to any one of claims 1 to 5 or the vacuum pump according to claim 6, wherein the or each rotor-side magnet and / or the or each stator-side magnet is axially or radially magnetized.

8. A method for designing a vacuum pump passive magnetic bearing, the method comprising the steps of: a) providing a rotor bearing half and an opposite and substantially concentrically radially arranged stator bearing half, the rotor bearing half comprising one or more substantially annular rotor-side magnets, the stator bearing half comprising one or more annular stator-side magnets, the rotor bearing half and the stator bearing half together forming a passive magnetic bearing having an outer diameter; b) determining a width of a radial gap extending between the rotor bearing half and the stator bearing half based on the outer diameter of the passive magnetic bearing; ​ c) configuring the at least one, preferably each, rotor-side magnet and / or the at least one, preferably each, stator-side magnet to have an axial extent that is about 3.5 times to about 5.3 times the width of the radial gap; d) configuring the at least one, preferably each, rotor-side magnet and / or the at least one, preferably each, stator-side magnet to have a radial extent that is less than 1.2 times the axial extent of the respective magnet.

9. The method of claim 8, wherein step d) comprises configuring the at least one rotor-side magnet and / or the at least one stator-side magnet to have a radial extent that is substantially equal to or greater than about 0.8 times the axial extent of the respective magnet; optionally, from about 0.8 times to about 1.18 times the axial extent of the respective magnet.

10. The method of 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 extent that is about 3.5 times to about 5 times the width of the radial gap.

11. The method of 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 extent that is about 5 times to about 5.3 times the width of the radial gap.

12. The method of any one of claims 8 to 11, comprising the step of configuring the or each rotor-side magnet and the or each magnetically corresponding stator-side magnet so that they have a substantially common radial extent; and / or wherein the method comprises the further step of configuring the or each rotor-side magnet and the or each magnetically corresponding stator-side magnet so that they have a substantially common axial extent.

13. A method of manufacturing a vacuum pump passive magnetic bearing, the method comprising the step of manufacturing a vacuum pump passive magnetic bearing according to the design of any one of claims 8 to 12.

14. A computer readable medium storing data defining a digital representation of a vacuum pump passive magnetic bearing according to any one of claims 1 to 5 or 7 or a digital representation of a vacuum pump according to claim 6 or 7, and operating instructions adapted to control a manufacturing device to manufacture the passive magnetic bearing or vacuum pump using the digital representation of the vacuum pump passive magnetic bearing or vacuum pump when the data is relayed to the manufacturing device.

15. A rotor bearing half or stator bearing half of a vacuum pump passive magnetic bearing comprising one or more substantially annular magnets configured to operably magnetically engage the magnets of an opposing rotor bearing half or stator bearing half of the passive magnetic bearing; wherein each magnet of the rotor bearing half or stator bearing half has an axial extent that is about 3.5 times to about 5.3 times the width of the radial gap formed between the rotor bearing half or stator bearing half and the opposing rotor bearing half or stator bearing half when the bearing halves are operably magnetically engaged; and Wherein each magnet of the rotor bearing half or stator bearing half has a radial extent that is less than 1.2 times the axial extent of the respective magnet.

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