WO2009060230A1

WO2009060230A1 - Improvements in and relating to reflectors

Info

Publication number: WO2009060230A1
Application number: PCT/GB2008/051006
Authority: WO
Inventors: Michael John Hanney
Original assignee: Polymer Optics Limited
Priority date: 2007-11-06
Filing date: 2008-10-28
Publication date: 2009-05-14
Also published as: GB0721740D0

Abstract

The present invention relates to reflectors, to methods of manufacturing reflectors, and to templates for use in the manufacture of reflectors. A planar reflector template (20) of metallic sheet material is formed with edge portions (21,22) that when brought together, e.g. by pressing the template in a mould, form a curved reflective surface.

Description

Improvements in and Relating to Reflectors

Field of the Invention

The present invention relates to reflectors, to methods of manufacturing reflectors, and to templates for use in the manufacture of reflectors.

Background to the Invention

Figure 1 shows a reflector 10. The reflector comprises a former 12 onto which a reflective layer 14 is applied. However, for some former shapes, such as deeply curved shapes is typically difficult to coat the surfaces of the former with an optically consistent reflective layer. A deeply curved reflector shape such as that shown in Figure 1 makes it difficult to ensure the reflective layer reliably reaches all surfaces inside the reflector with controllable coating thickness and uniformity.

Some lower quality reflectors can be made by pressing a ductile material, such as aluminium sheet, into the former. However, problems with material stretch and possible splitting mean this technique is not suitable for deeply curved formers. Furthermore, the ductile materials used in this technique typically have poor surface finishes, and any surface finish applied to the material before pressing into the former is easily damaged by the pressing process.

In volume manufacturing techniques, to try to reduce the coating cost, large numbers of formers are placed into a coating chamber for application of the reflective layer using evaporative vacuum coating or plasma assisted deposition techniques, for example. However, mounting and dismounting the reflectors onto jigging inside the coating chamber is labour intensive.

Example embodiments of the present invention aim to address one of more disadvantages of the prior art, whether identified herein, or otherwise.

Summary of the Invention

In a first aspect, the present invention provides a method of manufacturing a reflector, the method comprising: providing a reflector template including first and second edge portions; and bringing the first and second edge portions towards one another to shape the reflector template in three dimensions.

Suitably, the method comprises bringing the first and second edge portions alongside one another. Suitably, the method comprises bringing the first and second edge portions alongside one another along their whole lengths.

Suitably, the method comprises bringing the first and second edge portions into contact with one another, such that the first and second edge portions remain in contact with one another along their whole lengths.

Suitably, the template comprises sheet material. Suitably the template comprises a planar sheet. Suitably, the template comprises a reflective surface finish provided by coating or otherwise processing a surface thereof. Suitably, the template comprises a chemically polished reflective surface. Suitably, the template comprises a metallic material with a hard-anodised surface finish. Suitably, the template is provided with a removable protective covering to the reflective surface. Suitably, the template comprises an aluminium sheet of thickness 0.5mm. Suitably, the method comprises the step of removing the protective covering from the template. Suitably, the method comprises removing the protective covering after the step of bringing the first and second end portions towards one another.

Suitably, the first and second edge portions comprise linear edges. Suitably, the first and second edge portions intersect one another at an angle. Suitably, the first and second edge portions comprise curved edges.

Suitably, the first and second edge portions intersect one another to form an interior corner. Suitably, the first and second edge portions comprise the sides of a substantially V-shaped recess. Suitably, the first and second edges are formed by cutting material from a material sheet. Suitably, the first and second edge portions are formed by die cutting.

Suitably, the step of bringing the first and second edge portions towards one another involves pressing the template into a three dimensional shape.

Suitably, the first and second edge portions are brought towards one another by pressing the template into a three dimensional shape, and are then supported by moulding the template with a support structure. Suitably, the support structure comprises features thereon for subsequent location or fixing of the reflector in an optical apparatus. Suitably, the support structure is formed by injection moulding.

Suitably, the template is plastically deformed in the process of bringing the first and second edge portions towards one another.

Suitably, the template further comprises coupling portions associated with the first and second edge portions, said coupling portions used to assist in holding the first and second edge portions in position alongside one another.

Suitably, the first and second edge portions are coupled to one another to shape the reflector in three dimensions. Suitably, the first and second edge portions are brought alongside one another to form a concave reflective surface .

Suitably, the template has rotational symmetry about a central point. Suitably, the template comprises a first set of first and second edge portions, and a second set of first and second edge portions. Suitably, the template comprises a plurality of sets of first and second edge portions. Suitably, the template comprises a plurality of webs projecting between first and second edge portions.

Suitably, the template comprises six webs projecting between six pairs of opposed first and second edge portions. Suitably, the step of bringing each of the sets of first and second edge portions towards one another occurs simultaneously.

Suitably, the template further comprises one or more strengthening portions, arranged to reinforce an area of the template between the first and second edge portions. Suitably, the template comprises a strengthening portions are arranged at an outer edge of a web. Suitably, the template comprises a strengthening portion associated with each web, or with alternate webs. Suitably, the strengthening portion or portions is folded at an angle to the webs in the finished reflector. Suitably the strengthening portions may comprise the coupling portions, and/or may be further supported by the support structure.

Suitably, the method may further comprise pre-processing steps performed prior to bringing the first and second edge portions towards one another. Suitably, the preprocessing steps may comprise one or more of: folding one or more of the webs; defining points or lines of weakness in one or more of the webs; and forming one or more relieving cuts. Suitably, relieving cuts are provided in one or more or the webs, and/or in one or more of the strengthening portions. Suitably, relieving cuts are provided at the intersection of the first and second edge portions. Suitably, the relieving cuts run approximately transverse to the first and second edge portions.

In a second aspect, the present invention provides a reflector manufactured according to the method of the first aspect of the present invention.

In a third aspect the present invention provides a template for use in the manufacture of an optical reflector, the template comprising first and second edge portions arranged to be brought towards one another to shape the template in three dimensions. In a fourth aspect, the present invention provides an reflector manufactured from a template as described in the first or third aspect of the invention.

According to the present invention there are provided apparatus and methods as set forth in the appended claims. Other features of the invention will be apparent from the dependent claims, and the description which follows.

Brief Introduction to the Drawings

For a better understanding of the invention, and to show how embodiments of the same may be carried into effect, reference will now be made, by way of example, to the accompanying diagrammatic drawings in which:

Figure 1 shows an example reflector manufactured by a known technique;

Figure 2 shows a template according to an example embodiment of the present invention;

Figure 3 shows a reflector according to an example embodiment of the present invention, formed using the template of Figure 2;

Figures 4A-4C show a method of manufacturing a reflector according to an example embodiment of the present invention; Figures 5A and 5B show a reflector according to another example embodiment of the present invention;

Figure 6 shows a reflector according to another example embodiment of the present invention; and

Figures 7A and 7B show a reflector according to another example embodiment of the present invention.

Description of Example Embodiments

Figure 2 shows a template 20 comprising a flat sheet of aluminium of around 0.5mm thickness, which is hard- anodised on the front surface and chemically polished to provide a highly reflective surface R. This material is available under the trade name Alanod from ALANOD Aluminium-Veredlung GmbH & Co. KG of Ennepetal, Germany, and from other sources. Due to the surface hardness of anodised materials of this type, it is very difficult to form a reflector by pressing. The hard surface will crack when pressed onto a former with anything other than a very shallow curvature. This restricts the freedom of product designers in using this type of material in reflectors.

To reduce these problems, the template 20 is provided with first and second edge portions 21,22 adjacent to recesses 23. Between the recesses 23 are webs 25 which will form reflector segments. The template 20 is pressed into an intended three dimensional shape to form a reflector 30 as shown in Figure 3. This approach still has some restriction in the possible steepness of curve that can be formed, due to the hardness of the sheet material, but more freedom in design is achieved by providing the first and second edge portions 21,22 and then bringing these towards and then alongside one another to shape the reflector in three dimensions.

The template 20 is easily formed into a three dimensional shape of the reflector 30 shown in Figure 3. However, the reflector 30 is relatively weak, due to the weakness of the thin sheet material used for the template 20. Also, in the pressing process, the sheet material exhibits a degree of elasticity and tends to spring back, trying to return to its original flat form. The elasticity is such that the curvature of surfaces present in the reflector 30 may become slightly flatter than intended. These effects are reduced in the reflector 30 by providing strengthening portions 24 into the template 20. The strengthening portions 24 reinforce an edge of the webs 25 and may be coupled to one another and fix each reflector segment 35 to the adjacent segments. This improves stability and strength of the reflector 30 and constrains the reflector segments 35 closer to the required form by reducing the tendency to spring back.

The pressing of the template 20 into the three dimensional reflector 30 will be further explained with reference to Figure 4. Figure 4A shows the template 20 sheet as it is loaded into a mould tool 41,42. As the mould tool 41,42 is closed the reflector 30 is press-formed to the required shape, then held in place in the mould tool 41,42.

In one example embodiment the template 20 is provided with a removable protective layer on top of the reflective surface. This protective layer is suitably a sheet of plastics material. The protective layer may suitably remain in place for the cutting and forming processes, to protect the reflective surface. The presence of a protective layer during press-forming as described above may advantageously reduce the level of smoothness required of the pressing tool - the protective layer means that the reflective surface is less likely to be damaged by contact from the tool during pressing. This reduces the manufacturing cost associated with polishing or otherwise finishing the pressing surfaces of the tool.

In the example embodiment shown in Figure 4B, plastic P is then injected into a cavity (shown in dashed lines) in the mould tool 41,42. The plastic P flows around the reflector 30 to produce a support structure around the reflector 30 to retain it in shape.

Also in this process, mechanical features for location and fixing of the reflector 30 can be formed in the support structure, so the final part that is removed from the mould tool 41, 42 is a finished component, as shown in Figure 4C. Figures 5A and 5B show a reflector 50 which has been formed using the process of Figure 4 to comprise a support structure 51,52,53. The support structure 51,52,53 comprises features thereon intended to locate or fix the reflector 50 in an optical apparatus, as well as strengthen and reinforce the reflector 30.

In order to produce precision reflector parts using this technique, conforming closer to a more optically desirable circular symmetry, the template can be die cut so that the pressed reflector comprises a parabolic, or some other mathematical form. To aid this process, relieving cuts are made around the edges and centre of the reflector to reduce the amount of metal stretch and deformation in the pressing process. Figures 6 shows a reflector 60 with relieving cuts 61 in a strengthening portion 24, and relieving cuts 62 at the junction of the first and second edge portions 21,22. Figures 7A and 7B show a reflector 70 with relieving cuts 74 and a support structure 71, 72, 73.

As will be appreciated, by initially working with reflective sheet materials in planar form, coating the sheet material to a high level of uniformity is simplified. The bringing together of first and second edge portions when shaping reflectors in three dimensions reduces the risk of cracking, and offers an increase in the designer's freedom to use curved reflector shapes. The example embodiments described herein simplify manufacturing of reflectors, and subsequent handling of reflectors .

Some possible modifications

Other higher specification variants of the hard anodised and polished aluminium sheet material are also available, with the surface of the polished aluminium sheet is coated with a thin layer of silver to improve its broad band reflection efficiency and angular reflection efficiency. These higher specification variants are suitable for use in forming templates and reflectors as described herein.

The flat metal sheet can be substituted for a suitable plastic sheet or sheet of some other material, which can be optically finished and provided with an optically reflective surface. In addition to the simple reflective coatings described above, coatings with other optical properties can be applied to the material sheet. The embodiments described herein simplify the design and manufacture of reflectors with more exotic reflective coatings, since the coating is applied to the planar sheet material before it is shaped. Coatings can be applied to the material sheet to enhance reflectivity of certain wavelengths, improve durability, etc. Similarly, the sheet material can be provided with a surface finish other than by provision of a coating, such as a textured surface to scatter the reflected light into to a wide range of angles and provide a smoother more diffuse projected beam from a reflector into which the sheet is incorporated.

The reflectors described herein and shown in the Figures have curved reflecting surfaces. However, in other embodiments the reflector is be made up from a series of flats. Folds or predetermined lines/points of weakness in the template may help in allowing the template to be formed into the required reflector shape in such embodiments .

Although the reflectors described herein comprise generally concave shapes, it will be appreciated that the principles described herein may be applied to generally convex shapes and/or other more complex shapes. Furthermore, the term reflectors described used herein are not limited to use with radiation in the visible range of the electromagnetic spectrum, for example, the reflectors described herein are suitable for use with sources operating in the infra-red and ultraviolet parts of the spectrum.

Die cutting the templates from sheet material is described, but in alternative embodiments the templates may be formed by other methods, such as laser cutting.

Attention is directed to all papers and documents which are filed concurrently with or previous to this specification in connection with this application and which are open to public inspection with this specification, and the contents of all such papers and documents are incorporated herein by reference.

All of the features disclosed in this specification (including any accompanying claims, abstract and drawings), and/or all of the steps of any method or process so disclosed, may be combined in any combination, except combinations where at least some of such features and/or steps are mutually exclusive.

Each feature disclosed in this specification (including any accompanying claims, abstract and drawings) may be replaced by alternative features serving the same, equivalent or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated otherwise, each feature disclosed is one example only of a generic series of equivalent or similar features.

The invention is not restricted to the details of the foregoing embodiment (s) . The invention extends to any novel one, or any novel combination, of the features disclosed in this specification (including any accompanying claims, abstract and drawings), or to any novel one, or any novel combination, of the steps of any method or process so disclosed.

Claims

CLAIMS :

1. A method of manufacturing a reflector, the method comprising: providing a reflector template including first and second edge portions; and bringing the first and second edge portions towards one another to shape the reflector template in three dimensions, wherein the step of bringing the first and second edge portions towards one another involves pressing the template into a three dimensional shape.

2. The method of claim 1, wherein the first and second edge portions are brought towards one another by pressing the template into a three dimensional shape using a tool, and further comprising the step of supporting the first and second edge portions by moulding the template with a support structure.

3. The method of claim 2, wherein the step of supporting the first and second edge portions comprises providing a support structure formed by injection moulding.

4. The method of claim 2 or 3, wherein the support structure comprises features thereon for subsequent location or fixing of the reflector in an optical apparatus .

5. The method of claim 2, 3 or 4, wherein the step of supporting the first and second edge portions is performed in the same tool as used for the pressing step.

6. The method of any preceding claim, wherein the template is plastically deformed in the process of bringing the first and second edge portions towards one another .

7. The method of any preceding claim, wherein the template provided comprises a metallic material with a hard-anodised surface finish.

8. The method of any preceding claim, wherein the template provided comprises a removable protective covering .

9. The method of claim 8, wherein the method comprises the step of removing the protective covering from the template, performed after the step of bringing the first and second edge portions towards one another.

10. The method of any preceding claim, wherein the template provided comprises first and second edge portions in the form of curved edges that intersect one another to form an interior corner.

11. The method of any preceding claim, comprising an initial step of cutting material from a material sheet to form the first and second edge portions.

12. The method of any preceding claim, further comprising coupling the first and second edge portions to one another .

13. The method of any preceding claim, comprising bringing the first and second edge portions alongside one another to form a concave reflective surface.

14. The method of any preceding claim, wherein the template provided comprises a plurality of webs, each projecting between corresponding pluralities of sets of first and second edge portions.

15. The method of any one of claim 14, comprising simultaneously bringing each of the sets of first and second edge portions towards one another.

16. The method of any preceding claim, wherein the template provided further comprises one or more strengthening portions, arranged to reinforce an area of the template between the first and second edge portions.

17. The method of any preceding claim, wherein the template provided comprises a strengthening portion arranged at an outer edge of a web of material, the web of material projecting between the first and second edge portions.

18. The method of claim 17, wherein the template provided comprises a plurality of webs, and a strengthening portion associated with each web.

19. The method of claim 17, wherein the template provided comprises a plurality of webs, and a strengthening portion associated with alternate webs.

20. The method of any one of claims 17-19, further comprising the step of folding the or each strengthening portion such that the or each strengthening portion is at an angle to the webs in the finished reflector.

21. The method of any one of claims 17-20, wherein the template provided comprises strengthening portions including coupling portions.

22. The method of any one of claims 17-21, wherein the template comprises strengthening portions, arranged to be further supported by a support structure.

23. The method of any preceding claim, further comprising a pre-processing step performed prior to bringing the first and second edge portions toward one another, the pre-processing step including one or more of: folding of one or more webs of material between the first and second edge portions; defining points or lines of weakness in one or more webs of material between the first and second edge portions .

24. The method of any preceding claim, further comprising a pre-processing step performed prior to bringing the first and second edge portions toward one another, the pre-processing step including forming one or more relieving cuts in the template.

25. The method of claim 24, where the step of forming one or more relieving cuts in the template comprises: providing one or more relieving cuts in one or more web of material between the first and second edge portions, and/or in one or more strengthening portions.

26. The method of claim 24 or 25, wherein the step of forming one or more relieving cuts comprises providing one or more reliving cuts at the intersection of the first and second edge portions.

27. The method of any one of claims 24-26, wherein the step of forming one or more relieving cuts comprises providing one or more relieving cuts running approximately transverse to the first and second edge portions.

28. A reflector manufactured according to the method of the any one of claims 1-27.

29. A method, reflector, or template substantially as herein described, with particular reference to the accompanying drawings .