WO2000022462A1

WO2000022462A1 - Improved curved mirror

Info

Publication number: WO2000022462A1
Application number: PCT/NZ1999/000170
Authority: WO
Inventors: Robert Ian Dolby; Alastair William Bennett
Original assignee: Bennett Mirror & Glass Co. Limited
Priority date: 1998-10-13
Filing date: 1999-10-12
Publication date: 2000-04-20
Also published as: AU1083800A; CA2346981A1

Abstract

A convex or spherical mirror is formed by securing a sheet of flexible reflective material to one side of a base sheet at least as large as the reflective surface of the mirror; the curvature of the mirror is achieved by a tensioning system secured across the other side of the base sheet; the tensioning system consists of means such as tensioning bars for curving the base about either or both of two mutually perpendicular axes in the plane of the base.

Description

Title: IMPROVED CURVED MIRROR

Technical Field

The present invention relates to a curved mirror, and to a method of making such a mirror. As used herein, the terms "curved mirror" is used to mean a convex or a cylindrical mirror, and does not include a concave mirror.

Curved mirrors are used in applications where, for a given mirror size, a very much larger field of view is required than is given by a plane mirror. Typical applications are for security mirrors, vehicle rear view mirrors, safety mirrors at traffic junctions and in railway stations, and positioning mirrors for docking aircraft. The mirror of the present invention has been designed especially as a positioning mirror for docking aircraft, to enable the pilot of an aircraft entering a docking bay to see the nose wheel of the aircraft and the guide markings on the ground of the bay, so that the aircraft can be positioned very accurately relative to an air bridge or similar installation. However, it will be appreciated that the mirror of the present invention is also suitable for a wide variety of other applications.

Background Art

Curved mirrors made of glass by conventional methods are both heavy and expensive to produce. A typical airport docking mirror is approximately 1200 x 2400 mm in size; this would be prohibitively expensive to produce in glass, and extremely heavy. It is known to overcome this problem by making a curved mirror from a flexible plastics reflective material supported by a suitable backing. Such a mirror is described in UK Patent 2152701 , which discloses a cylindrical mirror consisting of a framework, two opposite sides of which are curved to the required curvature of the mirror, and a sheet of flexible plastics reflective material which is secured to the framework by securing strips which overlie the reflective material around its edges.

However, the design described in UK patent 2152701 has a number of drawbacks:- firstly, the curvature of the mirror is preset by the framework, and cannot be varied or corrected. Thus, if the framework is not manufactured accurately, or the reflective material is not held onto the framework with a uniform pressure, the mirror will be distorted. Secondly, since the reflective material is flexible and is supported only by the pressure of the securing strips, over time there are problems with the reflective material sagging and/or distorting. WO 97/15847 is an attempt to overcome the problems of UK Patent 2152701, by providing a frame for the mirror, the curvature of which can be adjusted along either of two mutually perpendicular axes. However, although the curvature of the concave mirror disclosed in WO 97/15847 certainly can be adjusted after manufacture, the design still has the drawback that the reflective material is supported by a frame and thus is supported only around its periphery. As described above, for reasons of cost the preferred reflective material is flexible plastics reflective material which is both thin and flexible and therefore is prone to sagging and distortion over time.

It is therefore an object of the present invention to provide a curved mirror which overcomes the above drawbacks.

Disclosure of Invention

The present invention provides a curved mirror comprising: a base formed from stable, slightly flexible, material, one side of said base providing a supporting surface at least as large as the reflective surface of the mirror; a sheet of flexible reflective material secured to and supported by said one side of said base, with the reflective surface of said material outermost from said base to form the reflective surface of the mirror; and a tensioning system secured to the other side of said base, said tensioning system comprising means for curving said base about either or both of two mutually perpendicular axes in the plane of the base.

Preferably, the reflective material is a plastics material such as an acrylic or a polycarbonate or a polyvinylchloride material.

Preferably, a cushioning layer (for example closed-cell foam) is secured between the base and the sheet of reflective material.

Preferably also, adhesive is used to secure the various layers (i.e. reflective material/base/cushioning material) together.

Preferably, said tensioning system comprises two mutually parallel sets of tensioning rods, each rod being mounted at or adjacent each end in a bracket secured to said base adjacent the corresponding edge of said base, such that the length of each rod between the corresponding set of brackets may be lengthened or shortened by moving said rod relative to said brackets. The brackets may be individual brackets i.e. one bracket for each end of each rod, but preferably each bracket extends for substantially the full length of the corresponding side of said base, and one end of all the rods of one set is mounted in one bracket.

Brief Description of Drawings

By way of example only, preferred embodiments of the present invention are described in detail, with reference to the accompanying drawings, in which:-

Fig. 1 is a vertical section through part of a mirror in accordance with a first embodiment of the present invention, on an enlarged scale, with the tensioning system omitted;

Fig. 2 is a vertical section through the mirror of Fig. 1 on a smaller scale than that of Fig. 1, but with the tensioning system included;

Fig. 3 is an isometric view of the underside (i.e. the non- reflective side) of a mirror of Fig. 1, on a reduced scale;

Fig. 4 is a view similar to Fig. 1 , but of a second embodiment of the invention; and

Fig. 5 is a view similar to Fig. 3, but of an alternative tensioning system.

Best Mode of Carrying Out the Invention

Referring to Fig. 1-3 of the drawings, a mirror 2 comprises a base 3 the top surface of which supports a reflective material 4 and the underside of which supports a tensioning system 5. (Fig. 2 and 3 only).

The base 3 may be made of any tough, stable, but slightly flexible material, for example medium density fiberboard. The reflective material 4 is a thin flexible sheet of plastics material (e.g. acrylic material) the outer surface 6 of which is reflective. Reflective material of this type is a known product. Because the reflective material 4 is both very thin and very flexible, any irregularities in the surface underlying the material 4 will show up as distortions of the mirror surface 6, it is therefore important that the whole reflective area of the reflective material 4 is evenly supported upon the base 3, preferably with a cushioning layer between the reflective material 4 and the base 3 to accommodate any irregularities, rough areas, or foreign bodies in the upper surface of the base 3. The cushioning layer consists of a sheet of closed cell foam 7, (typically about 0.8-1.5 mm thick), one face of which is secured to the base 3 by a layer of adhesive 8, and the other face of which is secured to a thin sheet of metal foil 9 by a second layer of adhesive 10. A third layer of adhesive 11 secures the metal foil 9 to the underside of the reflective material 4.

The closed cell foam 7 may be of the type provided with an adhesive layer on each face, or a separate adhesive may be used. For clarity, the adhesive layers 8, 9, 11 are greatly enlarged in thickness in Fig. 1.

A series of connected grooves 12 is formed in the top surface of the base 3 (shown in Fig. 1 only) and an electrical heating cable (12a) is mounted in the grooves 12 and connected to a thermostatically controlled electrical heating system (not shown) for heating the mirror when the temperature drops below a predetermined temperature, to prevent misting of the reflective surface 6. The metal foil 9 helps to disperse the heat from the heating cable evenly over the whole mirror surface.

The metal foil 9 may be made of any suitable metal which forms a foil readily, is a good conductor of heat, and is chemically compatible with the adhesive and with the plastics of the reflective material 4. Typically, aluminum foil will be used.

The base 3 is curved to the required degree of curvature about its longitudinal axis A and/or its horizontal axis B. The axes are indicated in broken lines in Fig. 3 only.

The curvature is achieved by the tensioning system 5 which comprises two sets of mutually perpendicular spaced tensioning bars 13, 14. The tensioning bars 13 extend parallel to the axis A and the tensioning bars 14 extend parallel to the axis B. Each bar of each set of tensioning bars 13, 14 is formed with a screw thread 15 at one or both ends.

Each tensioning bar is mounted at each end in a bracket 16. Each bracket 16 consists of two mutually perpendicular plates 16a, 16b; each plate 16a is mounted adjacent the corresponding edge of the base 3 by means of a counter sunk bolt 17 to the underside of the base 3 and each plate 16b extends perpendicular to the base 3.

As shown in Fig. 3, the plates 16b upon which the set of tensioning rods 14 is mounted are longer than those upon which the set 13 is mounted, so that the set 13 lie beneath the set 14 and the two sets of tensioning rods do not foul each other.

The screw threaded portion(s) 15 on each tensioning bar are engaged with screw threaded apertures formed in the corresponding plates 16b. The length of each bar

15 extending between two opposed brackets 16 can be lengthened or shortened by screwing the screw threaded portion 15 of the bar relative to the plate 16b; a nut 18 is rigidly secured on said portion 15 to facilitate rotation of the bar.

When the bars in the set 13 are shortened, the base 3 and the reflective material 4 are curved about the axis B. When the bars in the set 14 are shortened, the base 3 and the reflective material 4 are curved about the axis A. Since each bar can be adjusted individually, a very accurate curvature of the reflective material 4 can be achieved, since the individual adjustment of the bars 13, 14 can compensate for any irregularities in stiffness of the base 3.

A second embodiment of the invention is shown in Fig. 4. In this embodiment, the base 23 is formed from sheet aluminium (typically 3.5 mm thick). A layer of adhesive coated closed cell foam 24 is secured over one side of the base 23, and a sheet of flexible plastics reflective material 25 is secured over the foam 24. As in the first embodiment, the reflective surface of the reflective material 25 is outermost, and reflective material is completely supported by the base 23. In the event that the mirror requires a heating circuit, electrical heating cables 26 are secured directly to the other side of the base 23; since the sheet aluminium is a good conductor of heat, it is not necessary to include a layer of foil and the heating cables operate effectively even though they are secured to the side of the base opposite to the reflective surface.

The embodiment of Fig. 4 may be provided with a tensioning system of the type shown in Fig. 3 or as shown in Fig. 5. The tensioning system shown in Fig. 5 is the same as that of Fig. 3 except that the separate brackets 16 are replaced by a continuous bracket 28, 29, 30, 31 along each edge of the other side of the base. The continuous mounting brackets 28, 29, 30, 31 tend to stiffen the base and it therefore is preferred to pre-curve these brackets at least partially towards the desired final curvature of the mirror.

Each of the continuous brackets has the same cross-sectional shape as the separate brackets and is bolted to the base at spaced intervals. Each of the tensioning bars 14 is engaged at one end with the bracket 28 and at the other end with the bracket 30. Each of the tensioning bars 13 is engaged at one end with the bracket 29 and that the other end with the bracket 31. As in the Fig. 3 embodiment, the portions of the brackets 28, 30 lying in a plane at right angles to the plane of the base are longer than the corresponding portion of the brackets 29, 31 , so that the set of tensioning rods 14 lies above the set 13. The manner in which the brackets 28, 29, 30, 31 are secured to the base, and the manner in which the tensioning rods are adjusted relative to the brackets, are as shown in Fig. 2.

It will be appreciated that the first and second embodiments of the invention of both may be provided with either the tensioning system of Fig. 3 or that of Fig. 5. Both tensioning systems operate in the same manner to adjust the curvature of the mirror.

The use of a layer of foam between the base and the reflective material is optional:- if the adjacent surface of the base is completely smooth and regular, then the cushioning layer of foam could be omitted.

As shown in Fig. 2 only, the mirror may be completed by an outer frame 19 which may be of any suitable type and provides a protective surrounding for the mirror. A plastics glazing strip 20 of known type extends around the joint between the edge of the mirror surface 4 and the frame 19, to give a waterproof seal and protect the base 3 from moisture. However, the outer frame 19 does not bear upon the mirror surface 4 in any way, so that there is no distorting pressure upon the mirror surface 4.

Claims

Claims:-

1. A curved mirror comprising: a base formed from stable, slightly flexible, material, one side of said base providing a supporting surface βt least as large as the reflective surface of the mirror; a sheet of flexible reflective material secured to and supported by said one side of said base, with the reflective surface of said material outermost from said base to form the reflective surface of the mirror; and a tensioning system secured to the other side of said base, said tensioning system comprising means for curving said base about either or both of two mutually perpendicular axes in the plane of the base.

2. The mirror as claimed in claim 1, further comprising a layer of cushioning material secured between said one side of the base and the sheet of reflective material.

3. The mirror as claimed in claim 2 wherein said cushioning material is a closed cell foam.

4. The mirror as claimed in claim 1 , wherein said sheet of reflective material is secured to said base by means of adhesive.

5. The mirror as claimed in claim 2 or claim 3, wherein said layer of cushioning material is secured to both said sheet of reflective material and said one side of said base by means of adhesive.

6. The mirror as claimed in any one of the preceding claims wherein said reflective material comprises plastics material.

7. The mirror as claimed in any one of the preceding claims further comprising electrical heating elements connected to said base.

8. The mirror as claimed in claim 7 wherein said base is made of sheet metal and said heating elements are secured to said other side of said base.

9. The mirror as claimed in claim 2 or claim 3 wherein said base is made of a non-metallic material and electrical heating elements are mounted on said one side of said base, in grooves formed in the base.

10. The mirror as claimed in claim 8 or claim 9 wherein said heating elements are connected to a thermostatically controlled heating system.

11. The mirror as claimed in any one of the preceding claims wherein said tensioning system comprises two mutually parallel sets of tensioning rods, each rod being mounted at or adjacent each end in a bracket secured to said other side of said base adjacent the corresponding edge of said base, such that the length of each rod between the corresponding set of brackets may be lengthened or shortened by moving said rod relative to said brackets.

12. The mirror as claimed in claim 1 wherein each bracket extends for substantially the full length of the corresponding side of said base, and one end of all the rods of one set is mounted in one bracket.

13. The mirror as claimed in claim 12 wherein each bracket is pre-curved at least partially towards the desired final curvature of the mirror.

14. The mirror as claimed in claim 11 wherein each bracket comprises an individual bracket in which one end of one rod is mounted.

15. The mirror as claimed in any one of claims 11-14 wherein one set of tensioning rods lies in a plane above the plane of the other set of tensioning rods.

16. The mirror as claimed in any one of claims 11-15 wherein at least one end of each rod is in screw threaded engagement with the corresponding bracket.