GB2488140A

GB2488140A - Reflector

Info

Publication number: GB2488140A
Application number: GB1102754.7A
Authority: GB
Inventors: Tim Williams; Dirk Landheer
Original assignee: SIMPACT ENGINEERING Ltd
Current assignee: SIMPACT ENGINEERING Ltd
Priority date: 2011-02-17
Filing date: 2011-02-17
Publication date: 2012-08-22
Also published as: GB201102754D0

Abstract

A reflector e.g. for sunlight has a reflecting surface 22 formed on a flexible material, the flexible material being preformed into a concave shape and being held in its preformed shape by a pressure difference across the flexible material. The reflector may be parabolic and formed in a single piece on elastic supporting means such as an elastic rod or hoop 16, 18or on an airtight bag 14. Also provided are a method of collapsing the reflector and a kit of parts for the reflector.

Description

A Reflector The present invention relates to a reflector. In one fonTn, the reflector could reflect S light, in particular sunlight.

EP0212034 shows a radiation collector with an elastomeric reflecting material which is initially stretched flat and then is stretched to a concave shape to create the required radiation collecting shape.

US5O 16998 shows a focused control system for a stretched membrane mirror module.

In this case the minor surface is initially stretched flat and is then deformed into either a concave or convex shape by stretching of the minor surface.

US4422723 shows an adjustable reflector wherein the reflecting surface is initially stretched flat and then deformed to a concave shape by application of a partial vacuum behind reflecting surface.

In all three examples above, because the reflecting surface is initially stretched flat, then a relatively large pressure difference across the surface is required to deform the surface to the required concave or convex degree. This relatively large pressure difference requires a suitably strong supporting structure at the outside of the reflecting surface. Due to the required strength requirements this supporting structure is relatively heavy and expensive and is relatively cumbersome and difficult to transport.

Thus, an object of the present invention is to provide a reflector which is cheaper and/or lighter and/or more easily transportable.

Thus, according to the present invention there is provided a reflector having a reflecting surface formed on a flexible material, flexible material being preformed into a concave shape, the flexible material being held in its preformed shape by at least a pressure difference across the flexible material.

Advantageously, by preforming the reflecting surface then a relatively lower pressure difference across the flexible material is required to hold the reflecting surface in its preformed shape. In the prior art the pressure difference (in some cases the partial S vacuum) must be sufficient to elastically deform the reflecting surface and therefore must necessarily be higher than the pressure difference (or partial vacuum) required in the present invention to merely hold the reflecting surface in its preformed shape.

With a lower pressure difference, then the supporting structure need be less strong and therefore can be made lighter and cheaper. By making the supporting structure lighter, it necessarily becomes more transportable.

The invention will now be described, by way of example only, with reference to the accompanying drawings in which: Figure 1 is a cross section of a reflector assembly according to the present invention, Figure 2 is an isometric view of the reflector assembly of Figure 1, Figure 3 is a cross section view of the flexible material on which the reflecting surface of the reflector assembly of Figure 1 is formed prior to this flexible material being manufactured into the reflector assembly of Figure 1, Figure 4 shows a kit of parts used to assemble the reflector assembly of figure 1, Figure 5 shows the subassembly of figure 4 in a stowed condition, Figure 6 shows a sub assembly of a further reflector assembly according to the present invention in a stowed condition, and Figure 7 shows the sub assembly of figure 6 in a partially deployed condition.

With reference to figures 1 to 5, there is shown a reflector assembly 10 having a reflector 12. The reflector assembly 10 is made from a bag 14, hoops 16 and 18, and a series of spacing rods 20 in this case eight spacing rods. Bag 14 is made from four panels namely a reflecting panel 22, first panel 24, second panel 26 and third panel 28.

Reflecting panel 22 is preformed to a concave shape as shown in Figure 3. The reflecting panel 22 may be made from a polyethylene composite with an aluminium coating. The polyethylene composite may be 0.1 mm thick. The material of the reflecting panel 22 is a thermoplastic material and as such it is possible to preform it to the shape shown in figure 3 by laying it over an appropriately shaped former and then heating the material so that it plastically deforms to the shape of the former. The material and former are then cooled following which the reflecting panel 22 can be removed from the former. Since it is cool, the reflecting panel once removed from the former will maintain the concave shape as shown in Figure 3. A reflective material can then be applied to the concave surface 22A of the reflecting panel 22 (however the step of applying a reflective material is not necessary if the reflecting panel is made of a reflecting material).

The first panel 24 is frustoconical. The second panel 26 is frustoconical. The third panel 28 is flat and circular.

As will be appreciated, frustoconical surfaces do not contain compound curves, i.e. they can be formed from a flat blank of flexible material. Typically the material of the first panel, second panel, and third panel is ripstop nylon fabric with a fluid barrier.

The rip stop nylon fabric may be 0.1 mm thick.

The reflecting panel 22, first, second, and third panels are sewn, stitched, glued or otherwise attached together to form the bag 14. In particular the bag 14 once assembled is an airtight bag containing a fixed amount of a gas, typically air.

Hoop 16 is formed from an elastomeric rod 17 which, in its unstressed form is straight. The hoop itself is formed by elastically deforming the rod into a circular shape and attaching opposite ends of the rod together. As such, the rod 17 is under tension and naturally forms a circle.

Hoop 18 is similarly formed from an elastomeric rod 19 which in its unstressed state is straight. Hoop 18 is formed by bending the rod to form a circle and attaching the ends of the rod together. As such the rod naturally forms the hoop 18.

Rods 17 and 18 may be rectangular in cross-section, having cross section sides 1.2 mm by 6 mm and having a length to give a diameter of hoops 16 and 18 of approximately 1.2 m. Rods 17 and 18 may be made from carbon fibre which is a relatively strong but is also relatively elastic.

Hoop 16 is attached to the periphery of the reflecting panel 22 by any suitably method such as gluing or stitching. Hoop 18 is attached to the periphery of the third panel by any suitable method such as gluing or stitching.

Hoop 16 is held in spaced apart relationship from hoop 18 by the spacer rods 20. As shown in figure 1 the spacing between hoops 16 and 18 is distance D. The volume of air fixed in the bag 14 is such that in order to assemble the spacer rods in place they are under compression, i.e. in the absence of spacer rods 20 the hoop 16 would be spaced slightly less than distance D from hoop 18 (see figure 4 and distance d). The spacer rods 20 may be 8 mm in diameter and may be 200 mm in length.

The reflector assembly is assembly as follows:-Figure 4 shows the kit of parts required to assemble the reflector assembly 10. The kit comprises sub assembly 30 and eight rods 20. The sub assembly 30 includes hoops 16 and 18 and bag 14 containing the fixed amount of gas. As can be seen from figure 4, the reflecting panel 22 and the first and second panels 24 and 26 are shown as being crumpled, i.e. they are not under tension. Hoops 16 and 18 are spaced apart by distance d which is smaller than distance D. To assembly the reflector assembly, spacer rods 20 are selectively clipped into place (using suitable clips or other fixing devices) so as to space apart hoop 16 from hoop 18. Once the final spacer rod 20 has been put in place the hoop 16 will be spaced apart from hoop 18 by distance D and the spacer rods 20 will all be in compression and the reflecting panel, first panel and second panel will all be under a relatively small tension as determined by the initial volume of fixed gas and the final (slightly larger) volume of the bag in the fully assembled form.

Figure 5 shows the sub assembly 30 of figure 4 wherein the circular hoops 16 and 18 have been "coiled" around on top of each other to form a more compact arrangement with each hoop defining three coils or loops. h order for the sub assembly 32 remain in this stowed condition a retainer strap 36 must be provided. The rods 32 and 34 are stressed such that upon release of the retainer strap 36 the sub assembly 30 automatically springs from the figure 5 position to the position shown in figure 4.

This is somewhat similar to the manner in which known "pop-up tents" spring from a collapsed state to a deployed state.

S

As mentioned above, the reflecting panel 22, first panel 24, second panel 26 and third panel 28 are made from a flexible material in order to allow the subassembly 30 to be stored as shown in figure 5. However, it is not necessary for the reflecting panel, first panel, second panel and third panel to be elastic in nature. Because the reflecting panel 22 is preformed to the concave shape it is not necessary to elastically deform the reflecting panel 22 (since, by definition, it is already in the appropriate concave shape). As such, it is often preferable to make reflecting panel, the first panel, the second panel and the third panel out of relatively inelastic material. By making these panels out of relatively inelastic material the rigidity of the reflector assembly 10 is improved. Thus, as mentioned above, the diameter of hoops 16 and 18 may be 1.2 m.

Typically when the reflectors are used to reflect sunlight they will be used outside and subject to the prevailing wind conditions. By making the reflecting panel 22, first panel 24, second panel 26 and third panel 28 out of relatively inelastic material, wind forces acting on the reflector assembly will not stretch any of these panels and they will therefore maintain their as assembled shape and in particular the preformed shape of the reflecting panel 22 will be maintained which results in the focal point of the reflecting panel staying unchanged. Typically the reflector assembly will be used to focus the suns rays on an article to be heated, such as a water container for boiling water. By making the reflecting panel, first panel, second panel and third panel out of relatively inelastic material results in the focal point of the reflecting panel remaining on the article to be heated even in windy or blustery conditions.

Typically, the preformed shape of the reflecting panel 22 will be a parabola with a focal point F ananged on the axis A of reflector assembly 10. However, in further embodiments the focal point of the parabola may be offset from axis A, for example the focal point may be at Fl, or F2, or F3, or at any other point. The focal length may be within an order of magnitude of the diameter of the reflector for example the focal length may be between 0.5 of the diameter of the reflector and two times the diameter of the reflector.

In further embodiments it may be required to have a concave shape other than a parabola. By performing the reflecting panel 22 to an appropriate shape, this shape will be the shape of the reflector in the finally assembled reflector assembly 10. This can be contrasted with the prior art wherein the shape of the concave or convex reflecting surface is simply that shape that results in applying the appropriate pressure difference across the reflecting surface and this will not necessarily be a parabola. In other words, the present invention allows the manufacturer to tailor the specific shape of reflecting surface in a way not possible with the prior art reflecting surfaces which rely on being stretched.

As mentioned above, by providing the reflecting panel, first panel, second panel and third panel as relatively inelastic material this then stiffens the reflector assembly.

Furthermore, the first and second panels being frustoconical panels also, by virtue of their geometry, stiffen the assembly when compared with the anangement which has the second and third panels replaced by a single cylindrical panel. Thus, the Diablo shape as shown in figure 1 inherently stiffens the reflector assembly by virtue of its shape.

As mentioned above, the bag 14 contains a fixed amount of gas. In further embodiments a valve or tap can be fitted to the bag to allow air in and out and then to selectively fix an amount of air in the bag. Thus, figure 6 shows a collapsed sub assembly 130 held in this condition by returning strap 136. Sub assembly 130 is identical to sub assembly 30 except that it includes air tap 138 (shown schematically).

As shown in figure 6 the air tap 138 is open. When the retaining strap 136 is released the sub assembly 130 springs to the position shown in figure 7. At this stage the reflecting panel 122 is in contact with the third panel 128 since there is no air in the bag 114. As the spacer rods 20 are selectively inserted, the volume inside the bag 114 will increase thereby sucking air through the air tap 138. Once a predetermined amount of air has been allowed into the bag 114 the air tap 138 can be closed. For example in one embodiment once four of the eight spacer rods 20 have been inserted around half of the subassembly 130 the air tap 138 can be closed. The remaining spacer rods can then be assembled thereby creating a relatively low partial vacuum in the bag 114 causing the reflecting panel 122 to be held more rigidly so as to retain its preformed shape.

S

Whilst the reflector 12 is circular, other shapes could be used, for example, ellipsoid, ovals, etc. The elastomeric rods 17 and 19 and the spacer rods 20 could be made from alternative materials, such as aluminium, steel, wood etc. They could be solid rods or they could be hollow rods. The cross-section shape of the rod could be other circular or rectangular, for example ellipsoid or oval etc. The reflective coating could be any type of reflective coating. Where the reflective coating is an aluminium coating, the aluminium coating may be created by sputtering.

The focal length may be between 0.5 m and 2.0 m.

As described above, in the collapsed state as shown in figure 5 each hoop 16 and 18 has been folded to create three loops each. In further embodiments each hoop could be folded to create more or less loops than three, in particular each hoop could be folded to create at least two hoops.

As will be appreciated, polyethylene composite material which is 0.1 mm thick whilst being relatively flexible (so that it may be collapsed and stored) nevertheless is relatively inelastic. Because the reflecting surface is preformed, then there is no need for the reflecting surface to be elastic. Where the reflecting surface is to be stored, such as is shown in figures 5 and 6, then it must be flexible enough to be folded. As will be appreciated, a distinction must be drawn between the flexibility of a material and the elasticity (or inelasticity) of a material.

Claims

Claims 1. A reflector having a reflecting surface formed on a flexible material, the flexible material being preformed into a concave shape, the flexible material being held in its preformed shape by at least a pressure difference across the flexible material.
2. A reflector assembly as defined in claim 1 wherein the preformed concave shape is substantially parabolic.
3. A reflector as defined in any preceding claim in which the pressure difference is less than 0.3 bar, alternatively less than 0.2 bar, alternatively less than 0.1 bar.
4. A reflector as defined in any preceding claim wherein the reflecting surface is formed on a single piece of flexible material.
5. A reflector as defined in any preceding claim wherein a periphery of the reflecting surface is supported by an elastic supporting means.
6. A reflector as defined in claim 5 wherein the elastic supporting means is an elastic rod.
7. A reflector as defined in any preceding claim wherein the flexible material forms part of an airtight bag.
8. A reflector as defined in claim 7 wherein the airtight bag contains a fixed amount of gas.
9. A reflector as defined in claim 7 wherein the airtight bag contains a selectively fixable amount of gas.
10. A reflector as defined in any preceding claim wherein the reflecting surface formed on the flexible material is in the form of a circular panel.
11. A reflector as defined in claim 10 when dependent upon claim 7 wherein the airtight bag contains a further circular panel.
12. A reflector as defined in claim 11 wherein the circular panel is spaced from the further circular panel by a spacing panel.
13. A reflector as defined in claim 12 wherein the spacing panel is formed as a first frustoconical panel and a second frustoconical panel.
14. A reflector as defined in any preceding claim in which a periphery of the flexible material is supported by an elastomeric rod.
15. A reflector as defined in any preceding claim in which a rod is formed into a hoop.
16. A method of collapsing a reflector as defined in claim 15 including the step of folding the hoop to create at least two loops.
17. A reflector kit including a reflector as defined in claim 15 in which the hoop is folded to create at least two ioops.