Structures

The present invention relates to prism slats as in accordance with the preamble of the main claim.

From WO/2001/000958 and from US 6,367,937 B2 and DE 44134213870, it has been known to produce reflective slats and to shape them prismatic on their upper sides. The whole prior art is characterized in that the prisms are preferably made pointed and sharp-edged.

While prisms effect a deflection of the sun, this might lead to an undesired darkening of the interior space since sufficient daylight is no longer guided into the room.

It is therefore the task of the invention to shape prismatic slat contours so that by retro reflection of the sun a passive cooling effect is obtained, on one hand, at the same time, however, defined improved room illumination in the room depth is obtained, on the other. Direct sun supplies an illumination intensity of about 100,000 Ix. In order to illuminate the interior space, a small percentage would be sufficient. The task consists now in defining the contrasting requirements of passive cooling and of simultaneous room illumination by the precision of the prism contours. The aim is to define the total energy transmission, or energy reflection, on one hand, and to ensure glare free room illumination, on the other, while the task consists furthermore in providing a method of glare free deflecting a particular section of the sky, for instance zenith radiation, into the depth of an interior space. The point is the quantitative definition of total energy transmission, on one hand, and the directional definition of light deflection, on the other.

This task is solved as in accordance with the characterizing clause of the main claim. It is the advantage of the present invention that sun energy can be deflected at the catheti of the prisms while at the same time, in view of the precise shaping of the prism tips, a small portion of the light radiation may be guided in a defined direction into the interior space to support natural, glare free day light illumination in the interior while no overheating, on one hand, nor glare when looking at the sun-illuminated slats, on the other, will occur.

By precise flattening of the prism tips which preferably occurs in a separate rolling process, the slat is given a light guidance exactly to be calculated which ensures a forecast-able optical behaviour or defined optical properties, and hence glare freedom.

The advantage of the invention is to be seen in light engineering, on one hand, and in building physics, on the other. In view of the prismatic shape, the energy input into the building and in that way the cooling charge is reduced as a result of the retro-reflection of the sun radiation; by the flattened prism tips, light introduction for improved room illumination is obtained which should not, however, glare the user. Directionally guided light radiation follows the law "angle of incidence = angle of reflection" and should exactly be defined in view of the precise shaping of the tips in the direction of the deflection to avoid that unaimed glare effects occur at the tips.

It is irrelevant from which direction the sun light impinges onto the slat. The advantages as shown may be realized independently on whether the sun incides from direction A or direction B into the prism structure. The illumination intensity in the exterior space in the direct sun amounts up to 100,000 Ix. Only 1 ,000 Ix to 2,000 Ix in the window are sufficient to illuminate a room with 500 Ix. The advantage of the slat is, therefore, to be seen in the simultaneity of deflecting the overheating sun via prismatic surface shaping (primary reflector) and guiding-in the sun light for an improved natural room illumination via the tooth tips (secondary reflec- tor). In order to avoid overheating and over-illumination, the relation of prism width x ₂ to flattening should be x-i > 5:1 . Of particular advantage is a relation of > 20:1 und larger, wherein the flattening over a slat cross section may also vary to realize specific light guiding effects. Flattening may for instance continuously increase from the irradiation side of a slat in order to deflect more flat winter sun more effectively into the interior space.

Further advantages will be explained based on the figures, wherein Figure 1 shows a micro-structured slat with light deflection.

Figure 2 shows the formation of a prism edge

Figure 3 shows a typical shape of the prism edges over a slat contour

Figure 4 shows two Venetian blind slats disposed one upon the other with the light deflection on the prism and prism edges.

Figures 5 and 6 show the analysis of the individual reflective systems of Figure 4

super-imposing each other.

Figure 7 shows a w-shaped guided slat.

Figure 1 shows a typical micro-structured slat 10 with light incidence 1 1 to 13 on the fragments of a Fresnel reflector (primary reflector system) and light incidence 14 to 16 on the flattened tips (secondary reflector system). On the prisms, the sun is reflected in the direction of radiation incidence A. On the flattened prism edges, the light is deflected into the interior space in direction B. The flattening of the tips to constitute a secondary light guiding system occurs for instance in parallel to the curvature 17 of the slat. As can be taken from Figure 4, 5 and 6, this results in a superposition of two optical structures:

1 . a primary reflector with a Fresnel optical system with a focus F-i on the sun irradiation side,

2. a parabolic secondary reflector with a focus F ₂ on the room interior side which results from fragments of prism flattening. Depending on the relations of Xi to x ₂ of Figure 2, the structural-physical and light- technological properties of a slat may be defined and modulated. The total energy transmission of the slats is defined via the relation of Xi/x ₂ . The direction of the light guided in, or room depth illumination of the interior space, respectively, is determined by the contour of the superimposed secondary light guiding system.

Figure 2 shows a detail of a tooth tip transformation. The tips of the reflector faces 31 , 32 are flattened so that a third reflector face 32 results. The latter is broader by the bulges 35, 36 and results in a total width of x-i . The size of these teeth x ₂ is almost op- tional and may be made significantly larger than 1 mm but also significantly smaller than 0.1 mm. The slat may be exposed to direct sun incidence either on the long prism side y-ι or on the short prism side y ₂ , or the prisms are symmetrical having an identical cathetus. These surfaces are for instance produced by a process of embossing into a thin aluminium strap or another metallic material or in plastic layers or coatings exhibiting plastic behaviour under pressure and/or heat. In this case, as can be taken from Figure 2, material displacement and broadening of reflector fragment x-i occurs by the bulges being formed. A further possibility consists in pasting embossed foils onto a slat or thin tape.

As embossing tools, embossing rollers bearing the exact prism structure are preferably employed. A particularly interesting manufacturing process consists of two steps: In the first step, the metal strip is prismatically embossed the embossing process being performed either to produce a flat strip or one in concave-convex shape. In a second operational step, when roll shaping into a concave-convex shape, the edges are pressed flat. Depending on the gap width between top roller and bottom roller, the reflection behaviour of the slat is defined by the contact pressure, or the flattening, of the relation of Xi to x ₂ . By using this procedure, it is also possible to shape the slat surface to show a different characteristic. For instance, the prisms according to Figure 3 in the first portion A facing sun incidence may be rather sharp-edged, and in the second portion B facing the interior space may be rolled out more flat in order to design the slat surfaces in the op- tical behaviour thereof depending on light and climatic requirements. The embodiments shown in Figures 1 to 3 constitute mere examples only. The process may be used for varied designs.

Figure 4 shows the optical system of the penetration of a prismatic slat with a so-called reflective flat slat. Figures 5 and 6 show the decomposition of these two optical systems penetrating each other, as single representations each.

The advantage of the two-step manufacturing process can also be experienced in connection with logistics: In the workshops of the strip manufacturer, the material is pro- duced sharp-edged. The subsequent processing plant passing the slat material between the rollers in the roll shaping process will then produce, depending on the requirements of the order and by means of particular top rollers for flattening, aimed surface contours or secondary reflectors. A secondary reflector in the sky light of a window, for instance, calls for completely different requirements than in the middle window or in the lower railing area.

For such a two or more step rolling procedure, material composites such as for instance plated steel band or plated aluminium are particularly suitable. In this case, a tempered base material is selected onto which a thin high-purity aluminium layer is rolled on. High-purity aluminium is a very soft material that is easily to be embossed and which in the second working step according to the invention may easily be transformed into the secondarily superimposed contour.

The upper side may also be coated with a clear varnish, whereby in view of light refrac- tion in an optically denser medium, additional prism effects will result. Consequently, superimposition of the light guidance via the prism catheti will follow together with the prismatic effects in the optically denser medium.

In the present examples, all slats include uniformly non-symmetric single prisms. The innovation includes of course other prism shapes as well, particularly symmetrically shaped single prisms.

Instead of prismatically shaping the slat surfaces, the slats may be embossed with holograms having light guiding properties according to patent claim 1 . Alternatively, the slats may be coated with foils into which either the prisms have been embossed or the holograms have been inscribed.

Figure 5 shows a further example of the invention. The slat 50 includes two parts, a retro reflector 51 as a primary light guiding system and a light guiding sword 52. The retro reflector 51 is penetrated by retro reflector fragments 53, 54 as secondary light guidance so that beams 55, 56 which incide in the area of retro reflector 51 onto fragments 53, 54 are deflected to the interior. The advantage is that in case of high summer sun, re-deflection is primarily effected to the outside to promote passive cooling while nonetheless improved room illumination by radiation from the sky is provided. Depending on the requirements of room illumination, fragments 53, 54 may be declined to the outside or to the inside. These inclinations of the angles are indicated by dotted lines 57, 58.

To improve the room illumination by redirected sun light, the flattened mirrors 32 may be superimposed by one more micro structure to distribute the redirected light in several directions. This can be done by embossing u- or v-shaped indents into the secondary reflector system. Those u- or v-shaped mirrors are preferably rectangular to the prisms or diagonal. The u- or v-shaped mirrors may form crossed patterns or wavy lines.