WO2000037981A1

WO2000037981A1 - Mount element

Info

Publication number: WO2000037981A1
Application number: PCT/GB1999/004301
Authority: WO
Inventors: Roy Edward Powell
Original assignee: The Secretary Of State For Defence
Priority date: 1998-12-21
Filing date: 1999-12-17
Publication date: 2000-06-29
Also published as: AU1872300A; GB9828095D0

Abstract

A mount element, or KINEBUTTON, for accurately positioning a component on a base. The mount element comprises a flat surface arranged to provide a sliding contact with a surface on the component, a fully or partially spherical portion arranged so as to allow the flat surface to change orientation in relation to the component and means for maintaining the centre of the fully or partially spherical portion in a fixed position with respect to the base.

Description

MOUNT ELEMENT

The present invention relates to mounts for the accurate positioning and alignment of components such as those used in optical systems. Such systems are increasingly being built in modular form with some individual components being removable to facilitate maintenance, re-alignment, comparison, etc. These removable components often need to be returned accurately to their original position and this can be achieved using specialist mounts.

A component can be accurately relocated if its position is controlled at six suitably chosen points. Known mounts exist for this purpose such as the classic kinematic "Cone, Grove and Flat". Typically, such mounts consist of three ball bearings arranged in a triangular pattern, resting in conical seatings in the upper surface of the system base. These locate against specially prepared surfaces below the component. The first locates in a conical seating, the second in a grove running radially to the base. In the classic Cone, Grove and flat mount the cone essentially provides three of these points of contact the groove two and the flat one. In practice, hardened metal inserts are provided at each of these points to support the loading of the component .

As technology evolves, the weight of components is increasing and a disadvantage of existing mounts is that they fail under the increased point contact pressures involved. This loading can result in indentation of the ball bearings into the flats and cones. It can also result in "cold welding" when the component is settling into position and there is a sliding motion of ball on flat.

It is an aim of the present invention to provide an improved mount element for mounting a component in relation to another component/base surface which will reduce the above problems.

Accordingly, the present invention provides a mount element for accurately positioning first and second surfaces (one of which is located on the component and one on the other component/base surface) , relative to each other wherein the mount element comprises a flat surface, arranged to provide a sliding contact with the first surface, a fully or partially spherical portion arranged so as to allow the flat surface to change orientation in relation to the first surface and means for maintaining the centre of the fully or partially spherical portion in a fixed position with respect to the second surface.

Three mount elements are described as different embodiments of this invention. The first uses a spherical portion of up to half a sphere, the second uses between half and a full sphere and the third uses a complete sphere. The sphere, in many cases, would probably be a conventional ball bearing modified as required.

The mount element of the invitation, herein also referred to as a KINEBUTTON, uses two known types of contact, "ball in cone" and

"flat on flat" . In the KINEBUTTON these two types of contact have been combined in such a way that they overcome each others weaknesses. When a component is settling down into its required position the KINEBUTTON will commonly experience high transverse loading while guiding the component into its final position. This high transverse loading on the "ball in cone" can result in damage to the circular seating area of the cone which quickly changes to point loading if the ball rides up the cone. In the KINEBUTTON this transverse loading is limited to acceptable levels by a sliding motion of the "flat on flat". The "flat on flat" is capable of supporting high loads but is prone to damage if the two flats are not parallel when they come into contact with each other. Such alignment is improbable during location of a component with fixed flats. With the KINEBUTTON this alignment is facilitated by the ability of the fully or partially spherical portion, referred to as the button, to rotate in its seating and constantly adjust its flat to the required orientation throughout the location of the component. Thus the KINEBUTTON ensures that the conditions required by the two types of contact are satisfied before any potentially damaging load is supported. The "button" providing the "ball in cone" contact may be provided by a fully or partially spherical portion which is free to rotate preferably within a cone recess (albeit with limited rotation in the case of a partial sphere) . The flat surface can rotate about the centre of the fully or partially spherical portion of the

KINEBUTTON to ensure that it is parallel with the first surface, before any potentially damaging load is supported by the KINEBUTTON. This has the advantage of increasing the load carrying capacity of the KINEBUTTON. Hence the mount element according to the invention provides a practical mounting system capable of accurate positioning with increased load carrying capacity and extended life.

In the mount element comprising a partially spherical portion, in some embodiments the partially spherical portion may be in the form of a hemisphere and may be arranged in two configurations.

The flat surface, or flat, may be provided as a flat plane surface on the partially spherical portion with the partially spherical portion free to rotate. Alternatively, the flat may be provided on a support with the fully or partially spherical portion in a fixed position such that the support is free to rotate about the fully or partially spherical portion. In the later configuration the fully or partially spherical portion may be integral with the second surface, using any means which allows the support to rotate sufficiently about its spherical surface.

The centre of the fully or partially spherical portion of the mount element should be maintained in a fixed position with respect to the second surface (either on the base or the component) , so as to set the distance between the first and second surfaces and to provide stability for the mount. In order to maintain the centre of the fully or partially spherical portion in a fixed position with respect to the second surface the second surface may be provided with a recess formed therein. Alternatively, so as to avoid directly mounting into the second surface, the second surface can be provided with a support mounted therein the support having a recess formed therein for maintaining the partially spherical portion in position with respect to the second surface. The above recesses can be of any configuration which provides sufficient support for the fully or partially spherical portion of the mount element and allows the fully or partially spherical portion to rotate freely within it. However, with embodiments of the type shown in figure 5 the full sphere does not have to be free to rotate in its lower recess, 34, and may even be prevented by mechanical means .

The man skilled in the art will appreciate that although a cone recess for the portion described above is conventional, in the KINEBUTTON the recess may usefully be pyramidical, pyra idoidal conical or spherical. A disadvantage of pyramidal or pyramidoidal recesses are that rather than a circular line of contact (as with the "ball in cone") the button will have multi -point contact within the seating (dependant upon the number of sides to the pyramid) and therefore lower load carrying capability. A disadvantage of the spherical recess is the increased size of the "land", the contact areas, which increases the risk of foreign matter being trapped between the surfaces of the fully or partially spherical portion and the recess with an adverse effect on positioning accuracy.

In the mount elements, or KINEBUTTONs, of the invention, each of the six points of contact, required to accurately position a component, are provided by a separate mount element or KINEBUTTON. Each KINNEBUTTON essentially having the properties of the "ball on flat" combination of the classic kinematic mount.

The KINEBUTTON allows flexibility when designing a mounting system. A set of KINEBUTTONs can be used in a variety of arrangements to match the positioning requirements of a component. It will be appreciated that the orientation of the KINEBUTTON, is reversible and may be used either with the section containing the button fixed to the base, as described, or fixed to the component. The KINEBUTTON may be used singly, in groups of two or in groups of three, which in use, resemble the conventional flat, groove and cone of the classic mount respectively. Other groupings can of course also be used. To ensure sliding contact between the flat surface of the mount and the first surface (either on the base or the component) , both surfaces should have a good surface finish. Rather than polishing an area of the first surface to provide a suitable surface and making it from a hard material it is preferable to provide a separate polished hard flat assembly which can be fixed to the first surface in a suitable position.

The flat surface provided on the mount element may usefully have an area which is recessed. This reduces the contact area between the flat surface and the first surface and reduces the chance of 'wringing' i.e. sticking together.

As stated above polished surfaces can assist in seating as can the provision of a recess in the flat surface but where a number of mounts are used or when all the load is being concentrated on one mount these means may not be sufficient on their own to ensure correct seating. Either the flat surface of the mount and/or the first surface could therefore be advantageously provided with an air bearing to assist in seating the first surface and the flat surface.

Such an air bearing could usefully be provided by feeding air between the flat surface of the mount and the first surface. In a preferred embodiment an air bearing is provided by feeding compressed air down a conduit which is in communication with the flat surface of the mount and/or the first surface. This conduit could usefully be provided by a hole through the flat surface of the mount and/or the first surface. A valve can usefully be provided in the conduit so as to be able to control the flow of air onto the flat surface of the mount and/or the first surface. Such a valve can be provided by using a ball seated in the end of the conduit such that the ball partially protrudes through the flat surface. In operation air pressure will maintain the ball in position in the conduit preventing air escaping from the conduit over the flat surface of the mount and/or the first surface. When the surfaces come close together the ball is configured so as to be pushed away from the end of the conduit allowing the compressed air to escape from the conduit and pass over the flat surface of the mount and/or the first surface. Initially the air released will blow away any contamination between the flat surface of the mount and the first surface which is a further advantage. As the location progresses the air flow will generate an air bearing. This will reduce friction to an insignificant level and provide improved seating. Once the seating has been achieved the air supply can be turned off and as the pressure drops the flat surface of the mount and the first surface will come into contact.

An air bearing can also assist in removal of components as an air bearing can be used to separate components by providing an initial force. This is particularly useful where the components are particularly heavy or have been in position for some time both of which can lead to the components sticking.

Air bearings along the above lines can usefully be used in the present invention at any point where two surfaces move against each other.

Air bearings can therefore offer four advantages; they can assist in accurate seating; they can assist in the removal of contamination prior to seating; they can overcome 'wringing' problems and they can assist in the separation of the components.

In a preferred embodiment of the invention, the KINEBUTTON comprises a ball mounted between two supports in recesses provided therein. One support capable of being fixed to the component or base and the other support providing the flat surface. In this arrangement, during location and when fully seated, the component load is well distributed around the three active lines of contact in the KINEBUTTON (two "ball in cone" and one "flat on flat")

The KINEBUTTON may be "aged" to improve its positioning reproducibility and load carrying capacity. For this the KINEBUTTON may be loaded with the rated or higher than rated load after final assembly to "seat" the spherical surface of the button into the cone. This seating will have a finite width and therefore greater load carrying capacity than the initial contact which would have been close to the theoretical line contact. As this "ageing" may damage the spherical surface of the button a ball bearing with the same radius will probably be used for this purpose and discarded. It should be noted that while this "ageing" will be beneficial in the KINEBUTTON it would be damaging to the classic kinematic mount.

If the KINEBUTTON is not artificially "aged" this process may occur naturally when the mount is first used. If this "natural ageing" proves satisfactory the spherical surface of the button should be significantly harder than that of the recess.

The fully or partially spherical portion and support assembly of the KINEBUTTON may be fitted inside a flexible gaiter. The gaiter improves the robustness of the KINEBUTTON by holding the component parts together and also prevents dirt from entering the assembly and causing pitting on the contact surfaces or ceasing the button within its seatings.

The connection of the KINEBUTTON to the component/base or component and, if used, the flat assembly to the other surface can be achieved using any known fixing or joining technology, for example gluing, screwing or using a spigot and socket or spring arrangement. As the KINEBUTTON is effectively defining a distance between the component and base, the spigots should be a loose fit in the sockets to allow the "flat on flat" contact to define this distance.

When using a recess to maintain the centre of the fully or partially spherical portion in a fixed position with respect to the second surface an "0" ring or circlip can be used to limit movement of the fully or partially spherical portion within the recess. The use of an "0" ring provides the additional advantage of assisting in the retention of any oil or other lubricant used in the KINEBUTTON between the recess and fully or partially spherical portion. However, the circlip solution is more applicable if a Kinebutton is to be used inside a vacuum system.

Whilst the KINEBUTTON may lack some of the simplicity of the classic kinematic mount it is a far more practical design. Not only is it capable of carrying far greater loads using the same size of ball bearing as in conventional mounts but a single mount element can be manufactured and then used to build up the different types of conventional mounts.

Several embodiments of the present invention will now be described, by way of example only, with reference to the accompanying figures, wherein

Figure 1 shows a cross section view of a mount element according to the invention showing the basic concept.

Figure 2 shows a cross section view of a preferred mount element or KINEBUTTON according to the invention.

Figure 3a shows a partial cross section of a typical arrangement using two KINEBUTTONS to replicate a 'ball in groove mount' .

Figure 3b shows a partial cross section of an alternative arrangement also using two KINEBUTTONS to replicate a 'ball in groove mount' this time in a single mount.

Figure 4 shows a cross section view of a further embodiment of the invention comprising a flattened sphere within a support.

Figure 5 shows a cross section view of a mount element or KINEBUTTON according to the invention, comprising a sphere interposed between two supports.

The basic concept of a mount element according to the present invention, the KINEBUTTON, is shown in fig. 1. The KINEBUTTON provides for the accurate positioning a first surface 1, with respect to a second surface 2. The KINEBUTTON comprises a button, 3, with a partially spherical surface, which is free to rotate, albeit with limited range, within a recess in insert, 4, mounted within the base, 6. The button, 3, also provides a flat surface, 5. Within the component, 7, is mounted an insert, 8, which provides a flat surface, 9.

As the component, 7, is brought towards the base, 6, the flat surface, 5 of the button, 3, will come into contact with the surface, 9, of the insert, 8. The button, 3, will rotate within the recess in insert, 4, to make surface, 5, and surface, 9, parallel correcting for small angular errors which occur between the component and the base in practice. Also the two flat surfaces, 5 and 9, will slide to accommodate small translation errors between the component, 7, and the base, 6. This compensation for angular and translation errors continues throughout the location of the component until it is finally seated.

Accordingly, the present invention provides a mount element for accurately controlling the position of a component at a point. When the component is fully seated this control is established in five stages, starting at the base: -

1. The insert, 4, is fixed to the base.

2. The centre of the spherical surface of the button, 3, is retained in a fixed position with respect to insert, 4 , as a consequence of the spherical surface of the button, 3, being seated in the recess of insert, 4.

3. The flat surface, 5, on the button, 3, is at a fixed distance from the centre of the spherical surface of the button, 3, as a consequence of machining.

4. The flat surface on the insert, 9, is at a fixed distance from the centre of the spherical surface of the button as a result of it being in contact with surface, 5, on the button, 3.

5. Surface, 9, of the insert, 8, is fixed to the component.

Therefore the position of the component with respect to the base is being controlled by defining the distance of the component from the centre of the spherical surface of the button which, as a result of its mounting, is a fixed point relative to the base. In this respect it serves the same purpose as the "ball on flat" combination of the classic kinematic mount which controls the position of the component by defining the distance of the component from the centre of a ball which also, as a result of the mounting of the ball, is a fixed point relative to its base. However, with the KINEBUTTON the distance is the perpendicular distance between the centre of the spherical face of the button and the flat on the button, whereas, with the ball on flat this equivalent distance is the radius of the ball.

Figure 2 shows a preferred embodiment of the invention the KINEBUTTON.

In this embodiment the principal element is a button, 10, bounded by a partial spherical surface, 11 and a flat surface 12, relieved over its central area. A tension spring, 13, holds the spherical surface, 11, of button, 10, against a conical seating, 14, in insert, 15, which is screwed into the base, 16. Insert, 17, has a flat surface, 18, and is screwed into the component, 19. A conduit, 50, is provided in the insert, 17, through which compressed air can be fed. The flow of the compressed air over the flat surface, 18, is controlled by a valve in the form of a ball, 51.

As with the classic kinematic mount, the first and second surfaces make use of hardened inserts, 15 and 17, locally to obviate the need for the component and the base to be made from suitably hard materials with specially machined surfaces. These inserts resemble countersunk screws and will be screwed into suitably machined holes in the component and base. However, other traditional methods of fixing are not excluded. The contact areas between the button, 10, and its contacting surfaces with the two inserts, 15 and 17, have been reduced consistent with still being sufficient to support the load of the component without unacceptable deformation. This lowers the probability of foreign matter being trapped between these surfaces with an adverse affect on positioning capability. Of all of the possible configurations for the contact area between the button, 10, and the recess in insert 15, the KINEBUTTON uses a conical surface, 14, making this contact that of the traditional "ball in cone" . It should be noted that though other configurations are unlikely to be used but they are not excluded from this invention. The flat surface 12, on button, 10, has been relieved over its central area to leave a narrow circular land. Small radial groves (not shown) have been included to vent the volume enclosed between the two surfaces. This relief also helps to prevent surfaces 12 and 18 from wringing together and becoming difficult to separate. However, other traditional methods of achieving this are not excluded.

An air bearing is produced by the provision of compressed air onto the surface, 18, via the conduit, 50, and valve in the form of a ball, 51. In operation air pressure will maintain the ball, 51, in position in the conduit, 50,preventing air escaping from the conduit, 50, over the flat surface of the mount, 18. When the surfaces, 18 and 12, come close together the ball, 51, is configured so as to be pushed away from the end of the conduit, 50, allowing the compressed air to escape from the conduit, 50, and pass over the flat surface, 18.

A further air bearing, not shown, could optionally be provided between the spherical surface, 11, of button, 10, and the conical seating, 14, in insert, 15.

For practical convenience a tension spring, 13, has been included to retain the button, 10, in the insert, 15, when the component is removed from the base. However, other traditional forms of retention are not excluded from this invention.

Figure 3A shows a side elevation of a typical arrangement using two of the KINEBUTTONs shown in figure 2. They are mounted so as to replicate the traditional "ball in groove" mount which thus controls the position of the component at two points. In this arrangement two KINEBUTTONs have been screwed into two projections from the base and one projection from the component. A similar arrangement can be made using three KINEBUTTONs to replicate the traditional "ball in cone" mount which thus controls the position of the component at three points. In this arrangement they would normally be in an equi- spaced triangular pattern when viewed perpendicular to the plane of the base.

Figure 3B shows a side elevation of a typical arrangement integrating two KINEBUTTONs into a single mount which also replicates the traditional "ball in groove" mount. Two button assemblies have been set into the faces of a block, similar to an engineers "V" Block, which is screwed to the component. The two flats which would normally abut the buttons have been combined into a single block which is screwed to the base. A similar arrangement can be made using three buttons in a triangular pattern to replicate the traditional "ball in cone" mount which thus controls the position of the component at three points. In this arrangement they would normally be equi -spaced when viewed perpendicular to the plane of the base and would abut a three sided pyramidal block.

Figures 3A and 3B also demonstrate that the KINEBUTTON is reversible by incorporating the button in the base and the component respectively.

Figure 4 shows a further embodiment according to the present invention similar to that shown in Figure 1 and operating in the same way. In figure 4 a flattened sphere, 20, is rotatably mounted within a support, 21, fixed in the base, 22. The support, 21, has a conical recess, 23, in which the flattened sphere, 20, sits. The flattened surface of the sphere, 24, provides one of the "flat on flat" mount surfaces. The second of the "flat on flat" mount surfaces, 26, is provided on a support, 25, fixed to the component 27. The flattened surface of the sphere, 24, also has a recessed area, 28, within its boundary, so as to reduce the contact area between the surfaces 24 and 26 and thereby reduces the chances of the surfaces wringing together. Also provided in the support 21, is an "0" ring, 29, which acts to assist in retaining the flattened sphere, 20, in the support, 21, and also to retain any oil, grease or other lubricant used in the KINEBUTTON.

Figure 5 shows a further embodiment of the invention. In this embodiment a ball, 30, is mounted between two supports, 35 and 31, in recesses, 34 and 36, respectively provided therein. The support 35 is fixed to the base, 37, and the support 31 is free to rotate about the ball. The support 31 also provides a flat surface, 38, to form one of the "flat on flat" mount surfaces. The second of the "flat on flat" mount surfaces, 39, is provided on a support, 40, fixed to the component 41. In order to improve the robustness of the KINEBUTTON and to hold the components together, the KINEBUTTON is also provided with an '0' ring, 42, which can also retain a lubricant, not shown.

Again, as the component 41 is brought towards the base, 37, the flat surface, 38, of the support, 31, will come into contact with the surface, 39, of the support, 40. As the support, 31, is able to rotate about the ball, 30, any angular errors between the flat surface, 38, and the flat surface, 39, will be corrected before any load is taken by the KINEBUTTON. Also as the two flat surfaces 38 and 39 provide a "flat on flat" mount any translational errors between the component , 41, and base, 37, will be accommodated by the sliding of the two flat surfaces. Thus any loads taken by the KINEBUTTON throughout the above operation will be well distributed over the contact points and point loadings will be minimised.

Other means, in addition to the spring, 13, the recessed support, 4, and/or "0" ring, 29, can be used to maintain the centre of the fully or partially spherical portion of the mount element in a fixed position with respect to the second surface such as a Circlip.

Claims

1. A mount element for accurately positioning first and second surfaces relative to each other wherein the mount element comprises a flat surface arranged to provide a sliding contact with the first surface, a fully or partially spherical portion arranged so as to allow the flat surface to change orientation in relation to the first surface and means for maintaining the centre of the fully or partially spherical portion in a fixed position with respect to the second surface.

2. A mount element according to claim 1 wherein the partially spherical portion is hemispherical.

3. A mount element according to claim 1 wherein the flat surface is provided as a flat plane of the partially spherical portion.

4. A mount element according to any of claims 1 to 3 wherein the second surface has a recess formed therein for maintaining the spherical portion in a fixed position with respect to the second surface.

5. A mount element according to any of claims 1 to 3 wherein the second surface has a support mounted therein the support having a recess formed therein for maintaining the centre of the partially spherical portion in a fixed position with respect to the second surface.

6. A mount element according to claims 4 or 5 further comprising an additional support having a recess formed therein for mounting the additional support on the spherical portion, the additional support also providing the flat surface of the mount element.

7. A mount element according to any of claims 4 to 6 wherein at least one recess is pyramidical.

8. A mount element according to any of claims 4 to 6 wherein at least one recess is conical.

9. A mount element according to any of claims 4 to 6 wherein at least one recess has at least one spherical surface for seating the spherical portion therein.

10. A mount element according to any of the preceding claims further comprising a component to be attached to the first surface, the component forming a flat on the first surface for providing a sliding contact with the flat surface of the mount element.

11. A mount element according to any of the preceding claims wherein the means for maintaining the centre of the fully of partially spherical portion in a fixed position with respect to the second surface comprises a spigot and socket arrangement.

12. A mount element according to any of claims 1 to 10 wherein the means for maintaining the centre of the fully of partially spherical portion in a fixed position with respect to the second surface comprises a spring.

13. A mount element according to any of claims 1 to 10 wherein the means for maintaining the centre of the spherical portion in a fixed position with respect to the second surface comprises a circlip.

14. A mount element according to any of claims 1 to 13 wherein the means for maintaining the centre of the spherical portion in a fixed position with respect to the second surface further comprises an 'O' ring.

15. A mount element according to claim 1 or 2 wherein the partially spherical portion is integral with the second surface.

16. A mount element according to any of the preceding claims further comprising a flexible gaiter arranged around the spherical portion, between the flat surface and the second surface.

17. A mount element according to any of the preceding claims wherein the flat surface comprises a recessed area.

18. A kinematic mount comprising a plurality of mount elements according to any of the preceding claims, arranged such that the position of a component is controlled at 2 or more defined points.

19. A mount element as hereinbefore described with reference to any of figures 1, 2, 3a, 3b, 4 or 5.

20. A mount element according to any of the preceding claims further comprising an air bearing provided between the flat surface and the first surface.