Aerostatic bearing element

Abstract

An aerostatic bearing element (110) comprises a bearing gas distributing arrangement (112) for distributing a pressurized bearing gas flow (113), and a restrictor (114). The restrictor has a first bearing surface (115) and is configured to receive the bearing gas flow from the bearing gas distributing arrangement and transmit it out of the restrictor through the first bearing surface. The first bearing surface (115) has an electrically conductive first surface section (115a) for serving as a first electrode, and the aerostatic bearing element further comprises a connecting arrangement (117a, 117b, 118a, 118b) for connecting the first electrode to a capacitance measurement circuit (130) to produce a primary measurement signal (131) indicative of a capacitance value of a capacitor formed by the first electrode and a second electrode.

Description

[0001] AEROSTATIC BEARING ELEMENT

[0002] BACKGROUND OF THE INVENTION

[0003] Aerostatic bearings may possess particular advantages over other bearing types in certain applications . For example, being a contactless bearing, an aerostatic bearing may provide very low friction or it may provide high accuracy positioning capability . In comparison to liquid bearings , adverse leakage of the bearing lubricant is avoided .

[0004] Feasibility of aerostatic bearings may be affected by the possibility to monitor and adj ust the bearing gap width or the stiffness of the gas film in the bearing gap in a reliable manner in real time .

[0005] Known solutions for monitoring the bearing gap width comprise utili zation of pressure sensors and / or flow sensors for indirectly measuring the bearing gap width via measurements of the pressure therein . Another possibility is to incorporate additional separate capacitive sensors into the bearing arrangement for measuring the bearing gap width .

[0006] Further developments are needed in the art to further improve the feasibility of aerostatic bearings in various applications .

[0007] SUMMARY

[0008] This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the detailed description . This summary is not intended to identify key features or essential features of the claimed subj ect matter, nor is it intended to be used to limit the scope of the claimed subj ect matter . The scope of protection sought for various embodiments of the present disclosure is set out by the independent claims .

[0009] In a first aspect , an aerostatic bearing element may be implemented, comprising a bearing gas distributing arrangement for distributing a pressuri zed bearing gas flow, and a restrictor, the restrictor having a first bearing surface and being configured to receive the bearing gas flow from the bearing gas distributing arrangement and transmit it out of the restrictor through the first bearing surface .

[0010] The aerostatic bearing element may comprise a body part . In embodiments with a body part , the bearing gas arrangement may be arranged in the body part . The body part may have the bearing gas arrangement .

[0011] In embodiments with a body part , the restrictor may be mounted to the body part .

[0012] The restrictor may be formed of any appropriate restrictor material suitable for said receiving and transmitting the bearing gas . The restrictor material may be porous , thus comprising pores , or it may comprise holes , slots or other voids that allow fluid passage into , within, and out of the restrictor material . One poss ibility for the restrictor material is graphite . Further examples of the restrictor materials include ceramics , additively manufactured metals and metallic foams .

[0013] The first bearing surface has an electrically conductive first surface section for serving as a first electrode , and the aerostatic bearing element further comprises a connecting arrangement for connecting the first electrode to a capacitance measurement circuit to produce a primary measurement signal indicative of a capacitance value of a capacitor formed by the first electrode and a second electrode .

[0014] The restrictor may be formed of an electrically conductive material to form the first bearing surface and the electrical ly conductive first surface section thereof . In another embodiment , the restrictor has a restrictor body formed of an electrically insulating material and an electrically conductive surface layer thereon to form the first bearing surface and the electrically conductive first surface section thereof . In an embodiment , the first bearing surface has a plurality of electrically conductive first surface sections electrically insulated from each other for serving as electrodes , the connecting arrangement being configured for connecting each of the electrodes to a capacitance measurement circuit to measure a capacitance value of a capacitor formed by that electrode as the first and another electrode as the second electrode .

[0015] In an embodiment , the plurality of electrically conductive first surface sections comprise an inner first surface section and at least one outer first surface section surrounding the inner first surface section .

[0016] In an embodiment the plurality of electrically conductive f irst surface sections comprise at least two sectoral first surface sections .

[0017] In an embodiment which may be in accordance with any of the preceding embodiments , the first bearing surface is planar for forming a planar bearing .

[0018] In an alternative embodiment which may be in accordance with any of the embodiments preceding the previous embodiment , the first bearing surface is curved, such as cylindrical , for forming a j ournal bearing .

[0019] In an embodiment which may be in accordance with any of the preceding embodiments , the first bearing surface is conical for forming a conical bearing .

[0020] In an embodiment which may be in accordance with any of the preceding embodiments , the first bearing surface is spherical for forming a spherical bearing .

[0021] A cylindrical first bearing surface may refer to a at least a part of a surface of a cylinder . The cylindrical first bearing surface may thus cover the circumference of a cylinder partially or entirely . On the other hand, an electrically conductive first surface section of a cylindrical first bearing surface may cover the circumference of the cylinder partially or entirely . There may be different electrically conductive first surface sections covering different parts of the circumference . The same applies also to conical and spherical first bearing surfaces . Thus , also then, the first bearing surface or an electrically conductive first surface section thereof may cover the entire circumference , or part of , the circumference of a cone surface or a sphere .

[0022] A cylindrical , conical , or spherical first bearing surface may be configured to form an inner bearing surface of a bearing, at least partially surrounded by a second bearing surface . Alternatively, a cylindrical , conical , or spherical first bearing surface may be configured to form an outer bearing surface of a bearing, at least partially surrounding a second bearing surface .

[0023] In an embodiment which may be in accordance with any of the preceding embodiments , the aerostatic bearing element comprises an electrically insulating coating on the electrically conductive first surface sections ( s ) . The coating may comprise , for example , titanium nitride TiN formed by sputtering .

[0024] In an embodiment which may be in accordance with any of the preceding embodiments , the aerostatic bearing element comprises a body part having an electrically conductive peripheral surface section adj acent to the electrically conductive first surface section, possibly at least partially surrounding it , for serving as a third electrode . Further, the connecting arrangement comprises a third connector for connecting the third electrode to the capacitance measurement circuit to produce a shielding electrical field adj acent to , pos sibly at least partially surrounding the electrical ly conductive first surface section . The third electrode and connector may be called a shielding electrode and connector, respectively .

[0025] In a second aspect , an aerostatic bearing may be implemented, comprising an aerostatic bearing element in accordance with the first aspect of any embodiment thereof , and a second bearing surface opposite to the first bearing surface , separated therefrom by a bearing gap having a bearing gap width . The gap width may lie , for example , in the range of 1 to 25 pm under operating conditions . The second bearing surface may comprise an electrically conductive second surface section for serving as the second electrode , wherein the connecting arrangement may be configured for connecting the second electrode to the capacitance measurement circuit .

[0026] In an embodiment , an aerostatic bearing or an aerostatic bearing arrangement comprises one or more aerostatic bearing elements comprising at least two of a planar, curved, such as cylindrical , conical , and spherical first bearing surfaces . Different aerostatic bearing elements may have different first bearing surface types or geometries .

[0027] In an embodiment , an aerostatic sealing comprises an aerostatic bearing in accordance with any of the preceding aerostatic bearing embodiments , the first bearing surface serving as a first sealing surface , the second bearing surface serving as a second sealing surface , and the bearing gap serving as a sealing gap, for forming a sealing in the sealing gap .

[0028] In a third aspect , an aerostatic bearing or sealing control arrangement may be implemented, comprising an aerostatic bearing or sealing in accordance with the second aspect or any embodiment thereof , and the capacitance measurement circuit connected to the first electrode ( s ) and the second electrode ( s ) . The aerostatic bearing or sealing control arrangement may comprise a bearing or sealing control unit configured to determine a secondary measurement signal indicative of the bearing or sealing gap width on the basis of the primary measurement signal .

[0029] In an embodiment , the aerostatic bearing or seal ing control arrangement comprises a plurality of capacitors formed by the first and the second electrodes , wherein the capacitance measurement circuit is configured to produce a primary measurement signal indicative of a capacitance value of each of the capacitors , and the bearing control unit is configured to determine a tertiary measurement signal indicative of a mutual tilt of the first and the second bearing surfaces .

[0030] In an embodiment, which may be in accordance with the previous embodiment , the aerostatic bearing control arrangement further comprises a bearing gas source connected to the bearing gas distribution arrangement to supply the pressuri zed bearing gas flow therein, wherein bearing gas source is configured to be control led to adj ust , on the basis of the first or the secondary measurement signal , the pressure of the pressuri zed bearing gas flow for adj usting the bearing gap width .

[0031] In a fourth aspect , a device may be implemented comprising an aerostatic bearing or sealing in accordance with the second aspect or an aerostatic bearing or sealing control arrangement in accordance with the third aspect, or any embodiment thereof . The device may be implemented as a process pump, turbomachinery, a turbo compressor, a coordinate-measuring machine , a lithography machine , a turbo machine , a spindle , or an high-precision or ultra-precision machining device such as a milling or turning machine .

[0032] In a fifth aspect , a method may be disclosed for measuring a width of a bearing or seal ing gap of an aerostatic bearing or seal ing between a first bearing or seal ing surface of a restrictor and a second bearing or sealing surface , respectively, opposite to the first bearing surface , separated therefrom by the bearing or sealing gap . The method comprises : measuring a capacitance formed by an electrically conductive f irst surface section of the f irst bearing or sealing surface forming a first electrode , and a second electrode ; and determining the width of the bearing or sealing gap on the basis of the measured capacitance .

[0033] "On the basis of" the measured capacitance refers to the measured value of the capacitance being used in the determination such that the determined width of the bearing or sealing gap is dependent on and / or proportional to the measured value of the capacitance .

[0034] In an embodiment , the first bearing surface comprises a plurality of electrically conductive first surface sections , and the second electrode is formed by an electrically conductive first surface section different from that forming the first electrode .

[0035] In an embodiment , the second bearing surface comprises an electrical ly conductive second surface section forming the second electrode .

[0036] Further embodiments of the above aspects may be implemented within the scope of the claims .

[0037] BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The present disclosure will be better understood from the following detailed description read in view of the accompanying drawings , wherein :

[0039] FIG . 1 shows a cross sectional view A) of an aerostatic bearing, and a bottom view B) of the aerostatic bearing element thereof ;

[0040] FIG . 2 shows a cros s sectional view of another aerostatic bearing element ;

[0041] FIGs . 3 and 4 show bottom views of yet other aerostatic bearing elements , especially the restrictors thereof ; and

[0042] FIG . 5 shows a cross sectional view of an aerostatic bearing in the form of a j ournal bearing .

[0043] Unless specifically stated to the contrary, any of the aforementioned drawings may be schematic and drawn not to scale such that any element in said drawing may be drawn with inaccurate proportions with respect to other elements in said drawing in order to emphasi ze certain structural aspects of the embodiment of said drawing . Moreover, corresponding elements in the embodiments of any two drawings of the aforementioned drawings may be disproportionate to each other in said two drawings in order to emphas i ze certain structural aspects of the embodiments of said two drawings .

[0044] DETAILED DESCRIPTION

[0045] Reference will now be made in detail to example embodiments , examples of which are illustrated in the accompanying drawings . It is apparent to a person skilled in the art that with the advancement of technology, the basic idea of the invention may be implemented in various ways . The invention and its embodiments are thus not limited to the examples described above , instead they may vary within the scope of the claims .

[0046] The aerostatic bearing 100 of FIG . 1 comprises an aerostatic bearing element 110 .

[0047] A "bearing element" refers to an element capable of serving as a part of an aerostatic bearing .

[0048] The bearing element comprises a body part 111 . Flow channel s 112 are formed in the body part for di stributing a pres suri zed bearing gas flow 113 of a bearing gas , such as air or nitrogen . There may be any appropriate gas connectors connected to the flow channels for enabling connection of a bearing gas source to the flow channels . The flow channels together with possible gas connectors serve as a bearing gas distributing arrangement .

[0049] A restrictor 114 is mounted to the body part . The restrictor has a first bearing surface 115 . The restrictor may be made of any appropriate porous material capable of receiving the bearing gas flow 113 and transmitting it out of the restrictor through the first bearing surface 115 .

[0050] In the example of FIG . 1 , the aerostatic bearing 100 comprises , in addition to the aerostatic bearing element 110 , a bearing counterpart 120 having a second bearing surface 121 opposite to the first bearing surface . The first and the second bearing surfaces define therebetween by, and define, a bearing gap 101 having a bearing gap width W . The bearing gap width may alternatively be called a bearing gap height .

[0051] In the example of FIG . 1 , the restrictor is formed of an electrically conductive material , for example , graphite . Thereby, the first bearing surface 115 is electrically conductive . Another example of providing an electrically conductive first bearing surface is discussed below with reference to FIG . 2 .

[0052] The example restrictor 114 of FIG 1 , and thereby also the first bearing surface 115 have a circular shape . In other embodiments , different shapes may be used .

[0053] The restrictor 114 is divided into two parts : an inner restrictor part 114a and an outer restrictor part 114b surrounding the inner restrictor part . The two parts are separated and electrically insulated from each other by a circumferential insulator member 116 , which in the circular geometry of the example of FIG . 1 is circular, i . e . in the form of an annular ring . The insulator may comprise or be formed of , for example, some polymer material such as an epoxy or some other plastics material .

[0054] The first bearing surface 115 is thereby divided into electrically conductive inner and outer surface sections 115a, 115b defined by the inner and outer restrictor parts , respectively .

[0055] The aerostatic bearing element 110 comprises first electrical conductors 117a, 117b electrically connecting the electrically conductive inner and outer surface sections 115a, 115b to two first connectors 118a, 118b . The two first connectors are configured to enable connecting each of the electrically conductive surface sections to an electrical circuit with, for example , electrical cables such as the first connecting cables 119a, 119b illustrated in Fig . 1 . The electrical conductors 117a, 117b and the connectors 118 a, 118b are illustrated in the drawing of FIG . 1 schemati cally, not showing any detai led configuration thereof . The electrical conductors 117a, 117b may be implemented in any appropriate manner and form . They may comprise various wires or cables , which may be electrically connected to the electrically conductive surface sections in any appropriate manner . The body part 111 of the bearing element 110 may comprise any appropriate channels of holes formed therein for leading the conductors therein . Correspondingly, the connectors 118a, 118b may be implemented in any appropriate manner and form . For example , any appropriate commonly available types of connectors may be utili zed .

[0056] Thereby, each of the electrically conductive inner and outer surface sections may serve as an electrode . Especially, such electrode can be used as one of the two electrodes of a capacitor . Each electrically conductive surface section is connected, by a connector cable, to a capacitive measurement circuit 130 configured to produce a primary measurement signal 131 indicative of , i . e . being dependent on or affected by a capacitance value of such capacitor . Thereby, the conductors 117a, 117b, and the connectors 118a, 118b form a connecting arrangement for connecting the electrodes to the capacitive measurement circuit .

[0057] An arrangement comprising both the bearing 100 and the capacitive measurement circuit 130 connected to the connecting arrangement may form at least a part of an aerostatic bearing control arrangement .

[0058] An electrically conductive surface section may be considered as an electrically conductive first surface section forming or serving as a first electrode of a capacitor . The other, i . e . second electrode may then be formed by another electrically conductive surface section, which may be considered as an electrically conductive second surface section . For example , any one of the inner and outer electrically conductive surface sections may serve as a first electrode , and the other one may serve as the second electrode . In the example of FIG . 1 , the bearing counterpart 120 provides another option as explained below .

[0059] The bearing counterpart 120 of FIG . 1 is formed of an electrically conductive material and is thus electrically conductive . Thereby, the second bearing surface 121 forms or serves as an electrically conductive second surface section 121a which may serve as the second electrode of a capacitor, the first electrode of which i s formed by one of the electrically conductive inner and outer surface sections 115a, 115b .

[0060] Corresponding to the electrically conductive inner and outer surface sections 115a, 115b, al so the electrically conductive second surface section 121a is connectable , via a second connector 118c, to an external circuit . In the example of FIG . 1 , the electrically conductive second surface section 121a and the second connector 118c is electrically connected to the capacitance measurement circuit 130 by a second connecting cable 119c .

[0061] In the case of the first and the second electrodes lying at opposite sides of the bearing gap 101 , the capacitance is proportional to the bearing gap width . Also in the case of the first and the second electrodes lying at the same side of the bearing gap 101 , the distance between the first and the second bearing surfaces affects the capacitance . The bearing gap width thus affects in each case the capacitance of a capacitor formed by two electrodes formed by electrically conductive surface sections . Then, the bearing gap width or height W can be measured by measuring the capacitance of the capacitor . This may be carried out by the capacitance measurement circuit 130 being configured to produce a primary measurement signal 131 indicative of a capacitance value of a capacitor formed by the first electrode and a second electrode .

[0062] Such primary measurement signal 131 may then be used to determine , for example , by an appropriate control unit , a secondary measurement signal indicative of the bearing gap width on the basis of the primary measurement signal . Such secondary signal may then be used, for example , to control a bearing gas supply to adj ust the pressure of the pressuri zed bearing gas flow to adj ust the bearing gas width W .

[0063] Such control unit , possibly compri sing the capacitive measurement circuit, may be part of an aerostatic bearing control arrangement .

[0064] The electrodes being formed by or at the first and / or second bearing surfaces itself may advantageously enable an accurate and reliable way of determining the bearing gap width W . An integrated configuration without any need for additional electrodes may provide a simple and cost-efficient way to implement a bearing gap width measurement arrangement .

[0065] In other embodiments , a bearing element may have a plurality of any other number of electrically conductive first surface sections .

[0066] In the example of Fig . 1 , the body part 111 is formed of an electrically conductive material , such as a metal . Its lower surface surrounding the restrictor 114 thereby forms an electrically conductive peripheral surface section 111 ' adj acent to the electrically conductive first surface sections 115a, b . In other embodiments , a body part may be formed of an electrically insulating material , such as a plastic . Then, an electrically conductive peripheral surface section may be formed by an electrically conductive coating on peripheral surface section of the body part . An electrically conductive peripheral surface section may serve as a third electrode .

[0067] Due to the electrically conductive material of the body part 111 , the first electrical conductors 117a, 117b may be insulated from the body part material by any appropriate manner (not illustrated in the drawing of Fig . 1 ) .

[0068] Further, the connecting arrangement comprises a third connector 118d and a third connecting cable 119d for connecting the electrically conductive peripheral surface section 111 ' , capable of serving as a serving third electrode , to the capacitance measurement circuit 130 . By supplying a suitable voltage to such shielding electrode , a shielding electrical field may be produced adj acent to, possibly at least partially surrounding the electrically conductive first surface section . For example , in the case of an electrical f ield coupled between a first electrode on the first bearing surface 115 and a second electrode on the second bearing surface 121 , a shielding electrical field may be coupled between the electrically conductive peripheral surface section 111 ' serving as a third or shielding electrode and the second electrode . Such shielding electrical field may serve for minimi zing or reducing the stray electrical field between the first and the second electrodes which might otherwise extend outside the bearing gap 101 .

[0069] In other embodiments where there is no need for a third electrode , implementations without any third connector and third connecting cable may be possible . In such embodiments , a bearing element may comprise an electrically insulating body part 111 . In the example of FIG . 1 , both the bearing element and 110 and the bearing counterpart 120 comprise parts of the connecting arrangement . In other embodiments , a plurality of electrically conductive surface sections in a bearing element may provide an easy way to accomplish a bearing gap width measurement arrangement as all the electrodes can be provided by the bearing element , thus without any need for arranging conductors or connectors in the bearing counterpart .

[0070] Another advantage of a plurality of electrically conductive first surface section may be resulted from the possibility to measure capacitance values of several capacitors at different locations of the first bearing surface . Then, the measurement circuit may be configured to produce a primary measurement signal indicative of a capacitance value of each of the capacitors . A tertiary measurement signal may then be determined, for example , by a control unit , indicative of a mutual tilt , i . e . an inclination, between the first and the second bearing surfaces . Further examples of bearing elements with a plurality of electrically conductive first surface sections are discussed below with reference to FIGs . 2 to 6 . It is also possible to have a bearing element with one electrically conductive first surface section only, wherein the bearing counterpart may provide the second electrode of the capacitor .

[0071] The bearing element 210 of FIG . 2 distinguishes from that of FIG . 1 in that the restrictor 214 thereof is formed of an electrically insulating material , such as aluminium oxide . There is an electrically conductive surface layer 219 on the restrictor 214 to form the first bearing surface 215 and the electrically conductive first surface sections 215a, 215b thereof separated from each other by a gap 216 which may be empty or filled with an insulator material forming an insulator element . The surface layer may be formed of some metal , conductive ceramics , such as titanium nitride TiN, or graphite , for example .

[0072] The connecting arrangement 217a, 217b, 218a, 218b may be substantially similar to that of the embodiment discussed above with reference to FIG . 1 . The conductors 271a, 271b are connected to the electrically conductive surface layer 219 and to the connectors 218a, 218b .

[0073] In various embodiments discussed above with reference to FIGs . 1 and 2 and below with reference to FIGs . 3 to 5 , thecon- ductive electrode ( s ) of the first bearing surface may be coated by an electrically insulating coating comprising, for example , aluminium oxide A1O . Such coating may protect the electrodes from wearing . Further, the first bearing surface may be coated with a plurality of insulating and conductive coatings to , for example , construct layered electrodes . Thereby, the electrical properties of the electrodes may be adj usted .

[0074] The restrictor 314 of the bearing element 300 of FIG . 3 distinguishes from that of FIG . 1 in that instead of an inner and an outer electrically conductive inner and outer restrictor parts , the restrictor 314 is divided by insulator member ( s ) 316 into a plurality of sectoral restrictor parts . Thereby, the and the first bearing surface 315 is divided into a plural ity of sectoral electrically conductive first surface sections 315a, 315b, ..., 315h . In the example of FIG . 3 , there are eight such sectoral surface sections . In other embodiments , any other number of sectoral surface sections may be used .

[0075] "Sectoral" refers to the plurality of the electrically conductive first surface sections being located around and surrounding a fictitious centre point C . Then, observed from the centre point , each first surface section may cover an angular sector not overlapping with the angular sector of any other first surface section .

[0076] Yet another example of a plurality of electrically conductive first surface sections is illustrated in FIG . 4 . The first bearing surface 415 of the circular restrictor 414 of the bearing element 400 of FIG . 4 comprises three smaller electrically conductive first surface sections 415a, 415b, 415c separated from the remaining part of the first bearing surface by annular insulator members 416 . The remaining part of the first bearing surface forms a larger electrically conductive first surface section 415d . There are thus four surface sectors capable of serving as first and / or second electrodes for the capacitance measurements .

[0077] The configuration of FIG . 4 may be particularly useful in measuring a tilt between the bearing element 410 and a bearing counterpart .

[0078] In the examples of FIGs . 1 to 4 , the first bearing surfaces are planar . They may thus be used to form planar bearings . Such bearings

[0079] In other embodiments , a first bearing surface may be curved . For example , it may be cylindrical . A cylindrical or other type of curved first bearing surface may be used to form, for example , a j ournal bearing, such as that of FIG . 5 .

[0080] A "j ournal bearing" refers to a bearing arrangement of two bodies , were one of the bodies at least partially surrounds or encircles the other body . The mutual movement between the two bodies may comprise linear or translational movement , or rotational movement . In the case of rotational movement , for example , in axels , the rotating part may be the inner part . In other embodiments , the inner part may be stationary, and the outer part rotatable .

[0081] The j ournal bearing 500 of FIG . 5 compri ses bearing element 510 having a tubular body part 511 to which a tubular restrictor 514 is mounted . The restrictor is divided into four sectoral restrictor parts 514a, 514b, 514c, 514d by radially positioned insulator members 516 . The cylindrical first bearing surface 515 is thereby divided into four electrically conductive first surface sections 515a, 515b, 515c, 515d . Axial flow channels 512 are formed in the body part 511 for forming a bearing gas distributing arrangement . A connecting arrangement comprises conductors 517b, connecting the electrically conductive first surface sections to connectors 518b ( for the sake of clarity of the drawing of FIG . 5 , reference numbers of only one conductor and one connector are marked in the drawing) .

[0082] A bearing counterpart 520 having a circular cross-section is located in the inner volume of the tubular restrictor 514 . The outer surface of the bearing counterpart forming a second bearing surface 521 is separated from the first bearing surface 515 by a bearing gap 501 .

[0083] In other embodiments , a j ournal bearing for translational relative movement between two bodies may be implemented with non-circular cross-sectional geometry .

[0084] In other embodiments , a j ournal bearing may comprise an inner restrictor surrounded by a bearing counterpart surrounding or encircling it .

[0085] In the examples of FIGs . 3 to 5 , the restrictors are made of an electrically conductive material , such as graphite . In other embodiments , corresponding restrictor geometries and configurations may be implemented in accordance with the example of FIG . 2 , i . e . using an electrically insulating restrictor body with an electrically conductive surface layer thereon .

[0086] In the examples of FIGs . 1 to 5 , all the aerostatic bearing elements compri se a body part . Other embodiments are pos sible without a body part . Then, the restrictor may also form, or serve as , a body or support element . A bearing gas distributing arrangement may comprise flow channel ( s ) and / or connector ( s ) arranged in another appropriate manner instead of being arranged in a body part .

[0087] Bearing elements and bearings can be used in various devices where accurately controllable aerostatic bearings are used . Examples of such devices comprises various process pumps , turbo compressors , coordinate-measuring machines , a l ithography machines , and an high-preci sion or ultra-precision machining devices such as a turning machines .

[0088] In the above, specific examples and embodiments have been discussed . However, other implementations are possible where any embodiment of one or more features of such is be combined with another embodiment unless explicitly disallowed .

[0089] Although the subj ect matter has been described in language specific to structural features and / or acts , it is to be understood that the subj ect matter defined in the appended claims is not necessarily limited to the specific features or acts described above . Rather, the specific features and acts described above are disclosed as examples of implementing the claims and other equivalent features and acts are intended to be within the scope of the claims .

[0090] It will be understood that the benef its and advantages described above may relate to one embodiment or may relate to several embodiments . The embodiments are not limited to those that solve any or all of the stated problems or those that have any or all of the stated benef its and advantages . It will further be understood that reference to ' an ' item may refer to one or more of those items . The steps or operations of the methods described herein may be carried out in any suitable order, or simultaneously where appropriate . Additional ly, individual blocks may be deleted from any of the methods without departing from the scope of the subj ect matter described herein . Aspects of any of the embodiments described above may be combined with aspects of any of the other embodiments described to form further embodiments without losing the effect sought .

[0091] The term ' comprising ' is used herein to mean including the method, blocks , or elements identified, but that such blocks or elements do not comprise an exclusive list and a method or apparatus may contain additional blocks or elements .

[0092] It will be understood that the above description is given by way of example only and that various modifications may be made by those skilled in the art . The above specification, examples and data provide a complete description of the structure and use of exemplary embodiments . Although various embodiments have been described above with a certain degree of particularity, or with reference to one or more individual embodiments , those s killed in the art could make numerous alterations to the disclosed embodiments without departing from scope of this specification .

Claims

CLAIMS1. An aerostatic bearing element (110) comprising a bearing gas distributing arrangement (112) for distributing a pressurized bearing gas flow (113) , and a restrictor(114) , the restrictor having a first bearing surface (115) and being configured to receive the bearing gas flow from the bearing gas distributing arrangement and transmit it out of the restrictor through the first bearing surface, c h a r a c t e r i z e d in that the first bearing surface(115) has an electrically conductive first surface section (115a) for serving as a first electrode, and the aerostatic bearing element further comprises a connecting arrangement (117a, 117b, 118a, 118b) for connecting the first electrode to a capacitance measurement circuit (130) to produce a primary measurement signal (131) indicative of a capacitance value of a capacitor formed by the first electrode and a second electrode.

2. An aerostatic bearing element (110) as defined in claim 1, wherein the restrictor (114) is formed of an electrically conductive material to form the first bearing surface (115) and the electrically conductive first surface section (115a) thereof.

3. An aerostatic bearing element (210) as defined in claim 1, wherein the restrictor (214) has a restrictor body (214' ) formed of an electrically insulating material and an electrically conductive surface layer (219) thereon to form the first bearing surface (215, 215a) and the electrically conductive first surface section thereof.

4. An aerostatic bearing element (110) as defined in any of claims 1 to 3, wherein the first bearing surface (115) has a plurality of electrically conductive first surfacesections (115a, 115b) electrically insulated from each other for serving as electrodes, the connecting arrangement (117a, 117b, 118a, 118b) being configured for connecting each of the electrodes to a capacitance measurement circuit (130) to measure a capacitance value of a capacitor formed by that electrode as the first and another electrode as the second electrode.

5. An aerostatic bearing element (110) as defined in claim 4, wherein the plurality of electrically conductive first surface sections comprise an inner first surface section (115a) and at least one outer first surface section (115b) surrounding the inner first surface section.

6. An aerostatic bearing element (310) as defined in claim 4 or 5, wherein the plurality of electrically conductive first surface sections comprise at least two sectoral first surface sections (315a, 315b, ..., 315h) .

7. An aerostatic bearing element (110) as defined in any of claims 1 to 6, wherein the first bearing surface (115) is planar for forming a planar bearing (100) .

8. An aerostatic bearing element (510) as defined in any of claims 1 to 6, wherein the first bearing surface (515) is curved, such as cylindrical, for forming a journal bearing (500) .

9. An aerostatic bearing element as defined in any of claims 1 to 6, wherein the first bearing surface is conical for forming a conical bearing.

10. An aerostatic bearing element as defined in any of claims 1 to 6, wherein the first bearing surface is spherical for forming a spherical bearing.

11. An aerostatic bearing element as defined in any of claims 1 to 10, comprising an electrically insulating coating on the electrically conductive first surface sections (s) .

12. An aerostatic bearing element as defined in any of claims 1 to 11, comprising a body part (111) having an electrically conductive peripheral surface section (111' ) adjacent to the electrically conductive first surface section (115a) , possibly at least partially surrounding it, for serving as a third electrode, and the connecting arrangement comprising a third connector (118d) for connecting the third electrode to the capacitance measurement circuit (130) for producing a shielding electrical field adjacent to, possibly at least partially surrounding, the electrically conductive first surface section (115a) .

13. An aerostatic bearing (100) comprising an aerostatic bearing element (110) as defined in any of claims 1 to 12 and a second bearing surface (121) opposite to the first bearing surface (115) , separated therefrom by a bearing gap (101) having a bearing gap width W.

14. An aerostatic bearing (100) as defined in claim 13, wherein the second bearing surface (121) comprises an electrically conductive second surface section (121a) for serving as the second electrode, and the connecting arrangement (118c) is configured for connecting the second electrode to the capacitance measurement circuit (130) .

15. An aerostatic sealing comprising an aerostatic bearing as defined in claim 13 or 14, the first bearing surface serving as a first sealing surface, the second bearing surface serving as a second sealing surface, andthe bearing gap serving as a sealing gap, for forming a sealing in the sealing gap .16 . An aerostatic bearing or sealing control arrangement comprising an aerostatic bearing ( 100 ) as defined in claim 13 or 14 or an aerostatic sealing as defined in claim 15 , and the capacitance measurement circuit ( 130 ) connected to the first electrode ( s ) and the second electrode ( s ) .17 . A method for measuring a width of a bearing or sealing gap of an aerostatic bearing or sealing between a first bearing or sealing surface of a restrictor and a second bearing or sealing surface , respectively, opposite to the first bearing surface , separated therefrom by the bearing or sealing gap, the method comprising : measuring a capacitance formed by an electrically conductive first surface section of the first bearing or sealing surface forming a first electrode , and a second electrode ; and determining the width of the bearing or sealing gap on the basis of the measured capacitance .18 . A method as defined in claim 17 , wherein the first bearing or sealing surface comprises a plurality of electrically conductive first surface sections , and the second electrode is formed by an electrically conductive first surface section different from that forming the first electrode .19 . A method as defined in claim 17 , wherein the second bearing surface comprises an electrically conductive second surface section forming the second electrode .

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