Dual-interface air-bearing joint and payload mount

Abstract

A dual-interface air-bearing joint and payload mount utilizing at least three support structures at locations defining a triangle and at least three, dual-interface air bearings is disclosed herein. One or more of the support structures may be actively actuated. Each air bearing provides a planar interface and a spherical interface that together provide five degrees of freedom. In some embodiments, a support-structure-side interface is spherical and a payload-side interface is planar, although this arrangement may be reversed. The spherical interface provides rotational articulation about axes intersecting a center of curvature of the spherical interface, while the planar interface provides translational accommodation between the payload and the support structures. The air bearings may be preloaded mechanically, magnetically, by gravity, or by vacuum. In optical embodiments, the payload may comprise a mirror, and motion of the support structures may be translated into piston, tip, and tilt positioning of the mirror.

Description

LUMV001-PCT-MJCDUAL-INTERFACE AIR-BEARING JOINT AND PAYLOAD MOUNTRELATED APPLICATIONS

[0001] This application is filed under the Patent Cooperation Treaty and claims the benefit of US Provisional Patent Application No. 63 / 780,124, filed March 28, 2025. This application is herein incorporated by reference, in its entirety, for all purposes.FIELD OF INVENTION

[0002] The present invention generally relates to mounting, positioning, and actuation of a payload, in particular to a dual-interface air-bearing and use thereof in mounting and actuation of an optical component, such as a flat optical mirror.BACKGROUND

[0003] Many optical applications require steering of a laser beam or a sensor line of sight to fulfil their function. This is accomplished using optical scanners, many of which are mechanical systems. There are several typical implementations of mechanical optical scanners, each having non-trivial drawbacks.

[0004] A first implementation is generally known as a galvanometer scanner. It comprises two mirrors, each with a single rotational degree of freedom. When mounted orthogonally to each other, such arrangement results in a system that can scan in two directions. In many such arrangements, the second mirror may be larger and / or have a higher moment of inertia because the first mirror scans across the second mirror. This can produce uneven system performance in each axis and limit the size of the optical system aperture that can be scanned using this implementation.

[0005] A second implementation involves mounting a mirror in a frame having the first rotational degree of freedom between the mirror and the frame and then mounting the frame into a housing having the second rotational degree of freedom perpendicular to the first rotational degree of freedom. This arrangement, generally known as a gimbal mount, offers tiptilt mirror actuation but suffers from uneven performance in these orthogonal axes and does not scale well with mirror size.

[0006] A third implementation is generally known as a fast-steering mirror. It typically employs mechanical flexures for enabling the degrees of freedom required for mirror actuation. ThisLUMV001-PCT-MJCapproach typically limits the actuation range to a few degrees off nominal and limits the maximum size and weight of the mirror.

[0007] A fourth implementation was disclosed in U.S. Pat. No. 10,685,771 (Krylov), issued June 16, 2020. That patent describes an apparatus having three linear actuators coupling a mirror or other payload to an actuator using laterally unconstrained magnetic joints. Reliance on sliding point-contact interfaces, however, results in tradeoffs relating to wear, particle generation, acoustic noise, load capacity, and / or long-term durability. Also, the hardness of materials in point contact fundamentally limits the attraction force, which in turn limits the size and weight of the mirror that can be mounted using this method.

[0008] What is needed, therefore, is a support structure arrangement and way of coupling a payload, such as a mirror, that eliminates, or at least mitigates, the disadvantages of the above- mentioned approaches.SUMMARY OF THE INVENTION

[0009] According to one aspect of the present invention, there is provided a payload mount comprising at least three support structures, at least three of which are disposed at locations that define a triangle, and at least three dual-interface air bearings configured to couple a payload and each of the at least three support structures, wherein one or more of the support structures may be configured to actuate along respective axes that are nominally parallel to each other. In optical embodiments, the payload may comprise a mirror assembly and the mount may provide piston, tip, and tilt motion of the mirror assembly.

[0010] Each support structure may comprise a mechanical body and one or more of a linear motion bearing, a position measurement system, and, in embodiments in which a given support structure includes powered actuation, a motor, as well as other components that may assist in actuation and / or reducing friction during actuation. By way of non-limiting example, a support structure may be implemented as, or include, any of the following actuator types or technologies: electric actuators (e.g., ball-screw or lead-screw linear actuators; belt-driven linear actuators; rack-and-pinion actuators; linear motors / voice-coil actuators; rotary servomotors driving linkages; stepper-motor actuators; brushed or brushless DC motor actuators; AC motor actuators; geared motor actuators including planetary, harmonic, cycloidal, or worm gear drives; direct-drive torque motors); fluid-power actuators (e.g., hydraulic cylinders; pneumatic cylinders; rotary hydraulic or pneumatic vane actuators; diaphragm actuators); piezoelectricLUMV001-PCT-MJCactuators (e.g., stack actuators, bimorph actuators); shape-memory alloy actuators; electroactive polymer actuators; magneto-strictive actuators; electromagnetic solenoid actuators; thermal actuators (e.g., bimetal or wax-motor actuators); and / or manual or spring- biased actuators (e.g., spring return mechanisms) optionally combined with a powered drive.

[0011] The support structure may provide linear and / or rotary output and may be configured as a single-axis or multi-axis actuator, including parallel and / or serial arrangements. The linear motion bearing may include, for example, ball bearings, roller bearings, crossed-roller bearings, bushings / sleeve bearings, linear guides / rails, air bearings, magnetic bearings, flexure bearings, and / or plain bearing surfaces with lubricants or low-friction liners. The position measurement system may include, for example, optical, magnetic, inductive, capacitive, Hall-effect, or resistive encoders; linear scales; potentiometers; LVDTs; resolvers; strain gauges; and / or inertial sensors, and may be used for open-loop and / or closed-loop control.

[0012] Other components that may assist a support structure in actuation and / or friction reduction may include, by way of example, gears, belts, pulleys, chains, couplings, clutches, brakes, springs, dampers, counterbalances, lubrication systems, seals, wipers, preloads, compliant elements, flexures, vibration isolators, and / or thermal management components (e.g., heat sinks or fluid cooling).

[0013] In embodiments, a support structure terminates with a tip defining an interface surface.In illustrated embodiments, the tip interface surface is spherical. In a first, non-limiting embodiment, the locations of the support structures form an equilateral triangle. In other embodiments the locations of the support structures form any type of triangle. One, two, or all three of the support structures may be actively actuated depending on the desired degrees of freedom of the payload mount.

[0014] In embodiments, the payload comprises corresponding payload-side interface surfaces.In optical embodiments, a mirror assembly may incorporate three planar interface surfaces all parallel to the reflective surface of the mirror and co-located, but not necessarily aligned, with the locations of the support structures. The parallelism between the reflective surface and the three interface surfaces enables lateral motion of the mirror assembly without affecting pointing of the piston-tip-tilt mirror mount disclosed herein.

[0015] Air bearings each have two opposing interface surfaces, one spherical and another planar. In illustrated embodiments, the spherical surface of the air bearing interfaces with theLUMV001-PCT-MJCspherical surface of the support-structure tip, and the planar surface of the air bearing interfaces the corresponding payload-side interface surface.

[0016] In alternative embodiments, the planar interface may be disposed on the supportstructure side and the spherical interface may be disposed on the payload side, while achieving the same fundamental functionality as the embodiments described above, although such embodiments may be less preferred in practice.

[0017] In a first, non-limiting embodiment, the air bearing is preloaded magnetically. Nonlimiting embodiments for magnetic preloading include several magnets, such as three permanent magnets incorporated into the payload and one or more magnets within each dualinterface air bearing assembly, with two or more used to enable independent preloading of each side. Support-structure tips may comprise either a magnet or a ferromagnetic material. The outcome of such embodiments is a force acting against the compressed air film, ensuring the integrity of the air bearing joint and improving its performance. Non-limiting embodiments for payload-side planar interfaces include the use of discrete components attached to the payload, a rear payload surface itself, or the faces of permanent magnets incorporated into the payload.

[0018] In another, non-limiting embodiment, air bearings are preloaded mechanically by means of a spring connecting the payload to the tip of a support structure. Other methods of preloading air bearings, such as vacuum or gravity, are also within the scope of the present invention.

[0019] Embodiments of the dual-interface air bearing provide up to five degrees of freedom.The planar interface provides up to two translational and one rotational degree of freedom and the spherical interface provides up to three rotational degrees of freedom. In some applications, one or more of these degrees of freedom may be limited to better define the position of the payload without affecting the fundamental functionality of the solution. This accommodates the change in the distance between the intersections of the support -structure axes with a payload reference surface over the payload angular actuation range.

[0020] In embodiments, each dual-interface air bearing of the present invention includes a preloading means that creates a force acting perpendicular to the air film interface, which is an axial force in the embodiments depicted in the figures. When the planar interface of the air bearing is misaligned, the preloading means also produces a radial centering force, which is helpful in practical applications of the described scanning solution. Some embodiments of the dual-interface air bearing of the present invention also incorporate a method for restricting theLUMV001-PCT-MJCrange of lateral motion of the planar interface - a desired feature for payload mounts that operate when subjected to external acceleration, shock, and / or vibration.

[0021] Each air bearing interface may utilize one or more existing aerostatic air bearing technologies. Examples of suitable aerostatic air bearing technologies include, but are not limited to, porous media air bearings, micro-nozzle air bearings, and orifice type air bearings.

[0022] The apparatus described herein addresses drawbacks of existing mechanical optical scanners by translating linear motion of the support structures into controlled positioning of the payload while eliminating physical contact between moving parts, wear of bearing components, and debris associated with component wear, rending embodiments of the present disclosure suitable for use in clean room applications. In optical embodiments in which the payload is a mirror assembly, such controlled positioning may include piston, tip, and tilt positioning of the mirror assembly.BRIEF DESCRIPTION OF DRAWINGS

[0023] Embodiments of the present invention are illustrated in the accompanying Figures, which are exemplary and non-limiting. Like reference numbers are used to indicate similar elements.

[0024] FIG. 1 is a sectioned perspective view illustrating a piston-tip-tilt mirror mount utilizing mechanical means of air bearing preloading and a concave spherical surface of the actuator tip, in accordance with embodiments of the present disclosure.

[0025] FIG. 2 is a sectioned perspective view illustrating a piston-tip-tilt mirror mount made in accordance with an embodiment of the present disclosure which utilizes magnetic means of air bearing preloading and a convex spherical surface of the actuator tip.

[0026] FIG. 3 is a sectioned perspective view illustrating a piston-tip-tilt mirror mount made in accordance with an embodiment of the present disclosure which utilizes magnetic means of air bearing preloading using two magnets and a concave spherical surface of the actuator tip.

[0027] FIG. 4 is a cross-section of individual magnetically preloaded dual-interface air bearing showing an exaggerated air gap to aid the clarity of the air flow description.

[0028] FIGs. 5A and 5B are cross-sections of an individual magnetically preloaded dual-interface air bearing, with FIG. 5A showing the air bearing in a nominal, or centered, orientation and FIG.5B showing the air bearing with the supported payload actuated to an arbitrary angular offsetLUMV001-PCT-MJCfrom nominal, schematically illustrating a center of curvature of the spherical interface and a corresponding articulation axis.

[0029] FIG. 6 is a cross-section of individual magnetically preloaded dual-interface air bearings made in accordance with another non-limiting embodiment of the present disclosure.

[0030] In the Figures, terms referencing direction, such as upward, downward, vertical, horizontal, left, right, top, bottom, etc., are used for convenience. The present disclosure is not limited by these directional references, and it is contemplated that the mount disclosed herein can be used in any orientation.

[0031] Furthermore, the present disclosure is not limited by the axial symmetry of the components depicted in the drawings, and it is contemplated that some embodiments of the mount disclosed herein may use more complex component shapes.DETAILED DESCRIPTION OF THE INVENTION

[0032] The following detailed description is merely exemplary in nature and is not intended to limit the invention or the application and uses of the invention. Furthermore, there is no intention to be bound by any theory presented in the preceding sections or the following detailed description.

[0033] A dual-interface air bearing design is disclosed. The design is particularly well-suited for mounting, positioning, and actuation of a payload, such as an optical component, e.g. a flat optical mirror, although other payloads can benefit from the joint design, as will be appreciated in light of this disclosure.

[0034] A payload mount that utilizes the dual-interface air bearing is also disclosed herein. Such a mount, in embodiments, is configured to actuate a payload in three degrees of freedom. In optical embodiments in which the payload is a mirror, these degrees of freedom may be referred to as piston, tip, and tilt. The tip and tilt degrees of freedom may be utilized for pointing of an optical system line of sight in a desired direction while the piston degree of freedom may have utility for some, but not all applications. These three degrees of motion may be achieved, in embodiments, using at least three support structures, at least three of which are arranged at locations defining a triangle, wherein one or more of the support structures may comprise linear actuators traveling along respective axes, the axes of the support structures configured to travel linearly being generally parallel to each other and also generally parallel toLUMV001-PCT-MJCthe nominal normal of the payload in a nominal position. The coupling of the payload to these support structures is achieved, in embodiments, using the dual-interface air bearings.

[0035] Such embodiments may comprise dual interface air bearings having a first air bearing interface, the first air bearing interface being a spherical interface between a support-side structure and a first, dual interface air bearing. In embodiments, a support structure tip has a convex surface that matches, or is complementary to, a concave surface associated with the first, dual interface air bearing. In other embodiments, the tip has a concave surface that matches, or is complementary to, a convex surface associated with the first, dual interface air bearing. Any suitable air bearing preloading method, either described herein or otherwise, can be used with either spherical interface surface orientation.

[0036] The spherical interface of the air bearing provides three rotational degrees of freedom about axes intersecting the center of curvature of the spherical interface. Two of these rotational degrees of freedom may represent tip and tilt articulation of the joint. An angular actuation range of the air bearing, expressed as the maximum angular deflection from a nominal orientation, primarily depends on the geometrical properties of the two interfacing surfaces and secondarily may depend on other design elements of the payload mount disclosed herein.

[0037] In some embodiments, convex and concave spherical-interface arrangements may present different tradeoffs with respect to achievable angular range, packaging envelope, preload force path, stiffness, air-flow routing, contamination tolerance, manufacturability, startup / shutdown robustness, and / or suitability for particular applications. Selection between such geometries may therefore depend on the requirements of a particular application.

[0038] Furthermore, as used herein, an articulation axis of the dual-interface air bearing may be defined with reference to the spherical interface. In some embodiments, an articulation axis passes through the center of curvature of the spherical interface and, in a nominal orientation, may be nominally collinear with an axis of the corresponding support structure. Tip and tilt articulation of the dual-interface air bearing may therefore be understood as rotation about axes intersecting the center of curvature of the spherical interface. In embodiments having the reversed interface allocation described herein, articulation may likewise be defined with reference to the spherical interface.

[0039] Embodiments may further comprise a second air bearing interface, the second air bearing interface being a planar interface between a payload-side structure and a second, dual interface air bearing. In optical embodiments, a back surface of the mirror may be finished to aLUMV001-PCT-MJCrequired surface roughness and flatness and be rendered parallel to a front surface of the mirror. Embodiments may also include a discrete component that implements the planar, second air bearing interface and is attached to the payload. Alternatively, the second air bearing may be magnetically preloaded and utilize a flat face of a magnet used to provide magnetic preload, which may be a permanent magnet, as the planar interface.

[0040] The planar interface of the second air bearing may have two translational and one rotational degree of freedom. The two translational degrees of freedom laterally decouple the payload from the support structures as the distance between spherical-interface centers changes for each support-structure position. The position of the support structures relative to each other defines the orientation of a plane defined by a surface of the payload. The location of the center of curvature of the spherical interface relative to the planar interface may influence achievable angular range, packaging envelope, stiffness, and motion relationships between the support structure and the payload.

[0041] In alternative embodiments, the relative placement of the planar and spherical interfaces may be reversed such that the support structure side interface is planar and the payload-side interface is spherical, while preserving the functional relationship described herein. In such embodiments, the spherical interface continues to provide three rotational degrees of freedom and the planar interface continues to provide two translational degrees of freedom and one rotational degree of freedom.

[0042] In embodiments, one or both of the planar and spherical interface surfaces may be formed integrally with their supporting components or may be provided by discrete components attached thereto. Suitable interface-forming materials may include metals, ceramics, glasses, silicon-based materials, carbides, nitrides, coated metals, and combinations thereof. One or both interfaces may include a hard and / or low-friction coating selected to improve surface finish, contamination tolerance, startup / shutdown robustness, wear resistance, and / or damage resistance.

[0043] Additionally, there are several aerostatic air bearing technologies that can be incorporated into embodiments of the present disclosure, including porous media air bearings, micro-nozzle air bearings, and orifice type air bearings. Any new developments in air bearing technology would also likely be suitable for incorporation into embodiments of the present disclosure. While compressed air is used in illustrated embodiments, other gases may be used asLUMV001-PCT-MJCthe working fluid, including clean dry air, nitrogen, inert gases, and / or other filtered gases compatible with the intended application environment.

[0044] In embodiments, the air bearings are preloaded to achieve a design air gap and stiffness.The dual-interface air bearings may be preloaded mechanically, such as by the means of a spring. Alternatively, the dual-interface air bearing may be preloaded magnetically. Vacuum and gravity preloading may also be suitable for some applications.

[0045] The combination of air bearing interfaces and preloading methods creates a payload mount suitable for a variety of positioning and scanning applications, including, by way of nonlimiting example, single-mirror scanning and two-dimensional optical scanning. Such a mount eliminates the drawbacks of existing mounts used with mechanical optical scanning technologies.

[0046] Embodiments may use one, two, or three moving actuators together with fixed or passive supports, depending on the desired degrees of freedom. For example, embodiments may only use two moving actuators and one fixed support, limiting scanning degrees of freedom to two axes, e.g. tip and tilt. Other embodiments may use one moving actuator and two fixed supports, limiting any scanning to a single axis.

[0047] FIGS. 1 and 2 illustrate a piston-tip-tilt mirror mount comprising a mirror 10 having a reflective front surface 51 and planar air bearing interface surface 55 connected to three linear actuators 40, which terminate with tips 22 comprising a spherical air bearing interface surface 54. The planar air bearing interface surface 55 is connected to the three linear actuators 40 by means of three, dual-interface air bearings. Each dual-interface air bearing comprises an element 20 having two interface surfaces, one spherical 52 and one planar 53 and a manifold 21 capable of receiving and distributing an air input 23.

[0048] The depiction of element 20 of the dual-interface air bearing in all the drawings (FIGS. 1- 6) is schematic. In embodiments that utilize porous media air bearing technology, the element 20 may be a single part made from porous material, which may have additional air routing features, or it may be implemented as having separate porous material parts, one for a spherical interface 54 and another for a planar interface 53. In embodiments that utilize micro-nozzle or orifice-type air bearing technology, the element 20 may be a single-part or multi-part subassembly that incorporates features for air exhaust (orifices or micro-nozzles) on spherical interface surface 52 and planar interface surface 53, as well as air routing to the air exhaust features.LUMV001-PCT-MJC

[0049] In all the drawings (FIGS. 1-6), the manifold 21 of the dual-interface air bearing is represented as a functional element whose purpose is to deliver pressurized air from a single input to the air bearing element 20 in a manner that promotes uniformity of air pressure and therefore uniformity of the air film thickness between spherical interface surfaces 52 and 54 and planar interface surfaces 53 and 55. In some embodiments of the present disclosure, the manifold 21 may be implemented as an integral part of the air bearing element 20.

[0050] Figure 1 depicts an example of mechanical preloading of the dual-interface air bearing using an extension spring 31. The extension spring 31 exerts a force between the mirror assembly 10 and the actuator tip 22 and is attached to the mirror assembly by means of a spring anchor 30. Other approaches to extension spring anchoring may be used. The spring force creates preload forces on the spherical interface between surfaces 52 and 54 and the planar interface between surfaces 53 and 55 of the dual-interface air bearing.

[0051] Figure 2 depicts an example of magnetic preloading of the dual-interface air bearing, using a permanent magnet 35. The permanent magnet 35 is embedded into the mirror assembly 10 and the actuator tip 22 comprises a ferromagnetic material. The attraction force between these two elements creates preload forces on the spherical interface between surfaces 52 and 54 and the planar interface between surfaces 53 and 55 of the dual-interface air bearing. The actuator tip 22 may also comprise a permanent magnet. The permanent magnet 35 and actuator tip 22 may be placed in close proximity to maximize the attraction force, but without making physical contact.

[0052] Figure 3 provides another example of magnetic preloading of the dual-interface air bearing. In this example, the dual-interface air bearing has a discrete planar interface component 24 attached to the back surface of the mirror and the assembly comprises two permanent magnets. The first permanent magnet 35 is integrated with the planar interface component 24. The second permanent magnet 36 is integrated with the air bearing element 20. The attraction force between these two permanent magnets preloads the planar interface of the dual-interface air bearing. The combined field of these two permanent magnets interacts with the spherical tip 22 made of the ferromagnetic material and produces an attractive force that preloads the spherical interface of the dual-interface air bearing.

[0053] FIGs. 1 and 3 depict embodiments of the dual-interface air bearing in which the air bearing 20 has a convex spherical surface 52 and the actuator tip 22 has a concave spherical surface 54. In contrast, FIG. 2 depicts an embodiment of the dual-interface air bearing in whichLUMV001-PCT-MJCthe air bearing 20 has a concave spherical surface 52 and the actuator tip 22 has a convex spherical surface 54. Each design approach can be used with either air bearing preloading method, and the pairings depicted in FIG. 1, FIG. 2, and FIG. 3 are only for illustrative purposes.

[0054] Likewise, the illustrated placement of the planar and spherical interface surfaces on the payload-side and actuator-side structures is exemplary only. In alternative embodiments, as described herein, that placement may be reversed while preserving the same functional relationship and fundamental functionality.

[0055] FIG. 4 shows a cross-section of a single dual-interface air bearing utilizing the magnetic preloading method. The air bearing is shown with exaggerated air film thickness (distance or gap between interface surfaces 52 and 54 or interface surfaces 53 and 55) to aid illustration of the air flow. High pressure air 60, as required for air bearing operation, is delivered to an input 23 of the air bearing manifold 21. The air then enters the air bearing 20 at the surface 52 or features on the surface 52, depending on air bearing type.

[0056] Air bearing element 20 then delivers air to the spherical interface surface 52 and planar interface surface 53. The delivery method depends on the type of air bearing and is outside of the scope of this disclosure. When the air exits the air bearing through the features on surfaces 52 and 53 a pressurized air film is created between the surfaces 52 and 54 and between the surfaces 53 and 55. The air then exits radially 61 and 62 from the spherical and planar interfaces of the dual-interface air bearing respectively.

[0057] The specific airflow configuration of FIG. 4 should be considered exemplary; other ways of routing air to these interfaces and exhausting air therefrom would be apparent to one of ordinary skill in the art.

[0058] FIGs. 5A and 5B show a cross-section of a single, dual-interface air bearing utilizing a magnetic preload method in a nominal (aligned) orientation (FIG. 5A) and when the supported payload is actuated to an arbitrary angular offset from nominal (FIG. 5B). The figures schematically illustrate a center of curvature of the spherical interface and a corresponding articulation axis.

[0059] Lastly, FIG. 6 depicts an embodiment of the dual-interface air bearing that utilizes the magnetic preload method and the face 56 of the magnet 35 as a planar interface surface of the air bearing. The three magnets 35 are integrated into the mirror assembly 10 so that their planar faces 56 are parallel to the front mirror face and to each other. In most practical applications, the three planar faces 56 will be coplanar, but this is not a required constraint.LUMV001-PCT-MJC

[0060] The foregoing description of example embodiments has been presented for the purposes of illustration and description. It is not intended to be exhaustive or to limit the present disclosure to precise forms disclosed. Many modifications and variations are possible in light of this disclosure. It is intended that the scope of the present disclosure be limited not by this detailed description, but rather by the claims appended hereto. Future-filed applications claiming priority to this application may claim the disclosed subject matter in a different manner and generally may include any set of one or more limitations as variously disclosed or otherwise demonstrated herein.

Claims

LUMV001-PCT-MJCClaimsWhat is claimed is1. A system comprising:a payload comprising at least three interface surfaces associated therewith;at least three support structures, at least three of which are disposed at locations defining a triangle, each support structure having a tip comprising a corresponding tip interface surface; andat least three dual-interface air bearings, each dual-interface air bearing having a planar interface surface and a spherical interface surface,wherein, for each dual-interface air bearing, the planar interface surface forms a bearing interface with a corresponding planar interface surface on one of the payload and the tip of a corresponding one of the support structures,wherein, for each dual-interface air bearing, the spherical interface surface forms a bearing interface with a corresponding spherical interface surface on the other of the payload and the tip of the corresponding one of the support structures, and wherein one or more of the support structures are configured to travel linearly along respective axes, andwherein if two or more of the support structures are configured to travel linearly along respective axes, the axes of the support structures configured to travel linearly are nominally parallel to each other.

2. The system of claim 1, wherein exactly one of the support structures is actively actuated and the remaining support structures are fixed or passive supports.

3. The system of claim 1, wherein exactly two of the support structures are actively actuated and a remaining one of the support structures is a fixed or passive support.

4. The system of claim 1, wherein all three support structures are actively actuated.

5. The system of claim 1, wherein each actively actuated support structure comprises a motor, a linear motion bearing, and a position measurement system.LUMV001-PCT-MJC6. The system of claim 1, wherein at least one of the support structures comprises a single-axis actuator.

7. The system of claim 1, wherein at least one of the support structures comprises a multi-axis actuator configured to provide linear and rotary output.

8. The system of claim 1, wherein at least one of the support structures comprises one or more components selected from the group consisting of gears, belts, pulleys, chains, couplings, clutches, brakes, springs, dampers, counterbalances, linkages, cams, screws, gearboxes, and fluidpressure components configured to assist actuation and / or friction reduction.

9. The system of claim 1, wherein at least one dual-interface air bearing is mechanically preloaded, such that a force is produced between the payload and the tip of a corresponding support structure, and wherein at least one dual-interface air bearing is magnetically preloaded, such that a magnetic attractive force is produced between the payload and the tip of a corresponding support structure.

10. The system of claim 1, wherein each dual -interface air bearing is either: magnetically preloaded, such that a magnetic attractive force is produced between the payload and the tip of each support structure, or mechanically preloaded, such that a force is produced between the payload and the tip of each support structure.

11. The system of claim 1, wherein the system is oriented, during use, such that a weight of the payload preloads each dual-interface air bearing.

12. The system of claim 1, wherein rotation at each spherical bearing interface occurs about axes intersecting a center of curvature of the corresponding spherical interface.

13. The system of claim 1, wherein the corresponding interface surfaces of the payload are planar and the corresponding interface surfaces of the tips of the support structures are spherical.

14. The system of claim 1, wherein the corresponding interface surfaces of the payload are spherical and the corresponding tip interface surfaces are planar.LUMV001-PCT-MJC15. The system of claim 1, wherein the payload comprises an optical component.

16. The system of claim 15, wherein the optical component comprises a mirror.

17. The system of claim 16, wherein the corresponding interface surfaces of the payload are planar and are parallel to a reflective surface of the mirror.

18. A dual-interface air-bearing joint assembly comprising:a bearing element having a planar interface surface and a spherical interface surface; a manifold configured to deliver pressurized gas to the planar interface surface and the spherical interface surface;a first structure having a corresponding planar interface surface configured to form a planar bearing interface with the planar interface surface of the bearing element; and a second structure having a corresponding spherical interface surface configured to form a spherical bearing interface with the spherical interface surface of the bearing element,wherein the spherical bearing interface permits rotational articulation about axes intersecting a center of curvature of the spherical interface surface, and wherein the planar bearing interface permits translational accommodation between the first structure and the second structure during articulation of the joint assembly.

19. The joint assembly of claim 18, wherein the first structure comprises a payloadside structure and the second structure comprises a support-structure tip.

20. A method of positioning a payload, the method comprising:coupling the payload to at least three support structures, at least three of which are disposed at locations defining a triangle, by at least three dual -interface air bearings, each dual-interface air bearing having a planar interface and an opposing, spherical interface;actuating one or more of the support structures along respective axes, wherein if two or more of the support structures are actuated along respective axes, those axes are nominally parallel to each other; andLUMV001-PCT-MJCpositioning the payload by rotational articulation at spherical bearing interfaces about axes intersecting centers of curvature of corresponding spherical interfaces and by translational accommodation at corresponding planar bearing interfaces.

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