WO1984000231A1

WO1984000231A1 - Temperature sensitive light reflector particularly ice warning device for road traffic

Info

Publication number: WO1984000231A1
Application number: PCT/DE1982/000233
Authority: WO
Inventors: Walter Ries; Gerhard Meier
Original assignee: Meier Hans Ulrich; Walter Ries; Gerhard Meier
Priority date: 1982-06-30
Filing date: 1982-12-22
Publication date: 1984-01-19
Also published as: EP0113350A1

Abstract

A temperature sensitive light reflector is comprised of a reflecting element (4) for example a retroreflector before which there is arranged a Mauguin-type liquid crystal cell (2) located between two polarisers (1, 3). Between the cell (2) and either of the polarisers a birefringent element (5) may also be incorporated. The reflector modifies the intensity or color of the light which is reflected as a function of the temperature and is particularly appropriate as an ice warning device. The reflector may be associated with a sign post, a sign panel or a traffic indicator for example, situated directly in the ground or at the vicinity of the road. To indicate three temperature depending states, a double cell comprised of two adjacent Mauguin cells (2', 2'') may be provided with a polariser in between (3' respectively 5, 3') or a temperature sensitive optical element (sol-gel filter or dispersion filter) may be added.

Description

Temperature-dependent light reflector, especially for warning of slippage in road traffic

The invention relates to a temperature-dependent reflector light ^10, in particular for roads! Such and light signs according to the preamble of claim 1. Such a light reflector changes the intensity or the color of the light reflected by the arrangement depending on the temperature. 15

The European patent application 80103061.0, publication number 22 917, has disclosed a street pole for carrying one or more reflectors, which discloses the idea that the reflectors should be made from one

Choose material that has at least two different colors depending on the outside temperature. In this way, the light reflected from the reflectors (e.g. from car headlights) should be clearly distinguishable from that at higher ° temperatures when the outside temperature is slippery.

The invention is based on the object of realizing the above idea of temperature-dependent light reflectors, in particular for warning of black ice in road traffic, on the basis of liquid crystals which have the property that their optical behavior, depending on the material, is strongly temperature-dependent is and changes suddenly, especially at the clearing point. The invention is therefore intended to show a simple and economically practicable route which, by means of 5 liquid crystals, leads to a temperature-dependent light reflector which can also be easily produced as a mass article,

OMPI 1 which causes a change in the color and / or the intensity of the light reflected by the reflectors at a certain temperature. , The light reflector should thus assume at least two different states

₅ can. However, there should also be the possibility that the light reflector can assume more than two states, in particular three states.

The object is achieved with the characterizing Q features of claim 1.

Advantageous designs and / or further developments of the invention result from the features of the subclaims and / or the following description. 5

The optical liquid crystal 1 cell 1 e was already described by C. Mauguin in 1911 (Bull. Soc. Franc. Miner. Vol. 34, P. 71, 1911). It consists of two transparent plates, between which there is a liquid crystal layer such that the liquid crystal has a helical structure (e.g. rotation by 90) with respect to the layer plane. Such twisting is achieved by suitable pretreatment of the plate surfaces. The liquid crystal consists, for example, of a nematic phase which, when heated above a certain temperature T, changes into a normal (isotropic) liquid phase. Nematic liquid crystals have a parallel structure, i.e. In the unaffected state, their molecules are parallel to a preferred direction. The twisting in the cell arises in that the molecules assume the preferred orientation given on the surface of the plate parallel to the surface. The liquid crystal stall can also be of the cholesteric type, which has a natural twist. They are also electrically switchable liquid crystals! known, e.g. be used when displaying digits in electronic watches. Such electrically switchable liquid

OMPI - Crystals do not play a role here, since the temperature change should be displayed without any auxiliary energy.

Now polarized light falls on an optical cell

Mauguin, the polarization vector of light follows the

Screw structure so that the light in terms of

Direction of polarization by a certain angle (e.g.

Exits 90 °). However, this only applies as long as the cell is at a temperature below the clearing temperature

T of the liquid crystal. Above the Kl r- c ³ temperature T is the Fl üssi gkri is stal -Zel 1 1 e in the isotropic state, and the polarization state of the preceding durch¬ L ^'othing remains unchanged.

By combining such an optical cell according to Mauguin with polarizing and reflecting elements, possibly also with the inclusion of birefringent elements, reflectors can be constructed according to the invention which change their reflection properties (color, intensity) at a certain clarification temperature T, i.e. two can assume different states. By switching two Maugui n cells 1 or by combining a temperature-dependent optical filter (eg sol-gel filter or dispersion filter) with a Maugui n cell 1 e, a light reflector according to the invention can also be built up can assume three different states depending on the temperature, which can be particularly advantageous for black ice warning in road traffic.

The invention is described below for exemplary embodiments which are shown schematically in a drawing. Here shows 1 shows a cross section through a reflector according to the invention with intensity switching at the clarification temperature T for two different states;

FIG. 2 shows a cross section through a reflector according to the invention with color switching at the clarification temperature T, also for Z-Vei different states;

3 shows a cross section through a reflector according to the invention similar to that of FIG. 1 for three different states;

FIG. 4 shows a cross section through a reflector according to the invention similar to that according to FIG. 2 for three different states; and

Figure 5 shows another reflector according to the invention for three different states.

1 shows a combination of the Mauguin cell 1 e with two polarizers 1, 3 (e.g. polarizing foils) and a reflective element 4 (e.g. retroreflector). The light (e.g. from a car headlight) is first linearly polarized by a polarizer 1. When passing through the Maugui n cell 1 e 2, depending on the temperature T, the plane of polarization of the light either remains unchanged (T y T) or it is rotated by 90 ° (TT). A second polarizer 3, whose polarization direction is perpendicular to that of the first, absorbs the unchanged light while letting the light through 90 ° pass. The continuous light strikes the reflecting element 4, is reflected there, passes through the polarizer-cell combination a second time and steps in the direction of the

* ^ RE

O PI - Light source off again. This reflector arrangement thus reflects light when the temperature is below the temperature r T, while at temperatures above 1 no light is reflected. A color filter can be switched on at any suitable point in the beam path of the layer combination according to FIG. 1. The reflector 4 can also be specially colored in order to reflect a colored light.

Fig. 2 differs from that just described

Arrangement by an additional birefringent element 5, which is either in front or - as shown - behind the Maugui n-Zel 1 e. Element 5 will generally be a birefringent plate or sheet oriented so that the optical axis forms an angle of 45 ° with the vertical. This element acts as an optical delay element in that the light is split into two mutually perpendicularly polarized partial beams which suffer different delays due to the birefringence of the element. These partial beams are reassembled in polarizer 3. Since the optical path length difference of the two beams strongly depends on the wavelength of the light, the light emerging from the polarizer 3 and striking the reflecting element 4 is colored. The color can be selected by the thickness and birefringence of the element 5. The transmitted color for temperatures T "T is complementary to the color for ^ T. After reflection on element 4, the light passes through the arrangement a second time and emerges again in the direction of the light source. This reflector arrangement thus reflects the light in different ways colors, depending on whether the temperature is above or below T. the element 5 either before or after the Flüssigk istallschich ^'t lying birefringent may together with the adjacent thereto lying polarizer 1 and 3 by a known per se pl eochroi table selectively absorbing element (selective polarizer) to be replaced.

The light reflector according to the invention is particularly suitable, for example, for warning of black ice in road traffic. For example, a carrier can be provided with one or more of the light reflectors according to the invention. To warn against black ice, especially in the dark, it is advantageous to design the reflective element 4 as a retroreflector so that the incident light from a car headlight is reflected back again with high intensity in the same direction. The carrier can be, for example, a road pole. Here, a erfi ndungsgemä ^'SSER reflector in addition to the reflector or reflectors herköm¬ mlichen in the immediate soil ^näh * s angeo dnet are. , The carrier can also be, for example, a relatively short rubber elastic lobe, which is used for

Marking of road guidance lines is arranged in a plurality at short intervals along road guidance lines directly on the roadway and thus carries at least one light reflector according to the invention in the immediate vicinity of the ground. Such rubber-elastic rags are known as carriers for conventional cat eyes and can be run over by a vehicle without damaging it. However, the carrier can also be, for example, a half-shell-shaped or hemispherical component which is firmly connected to the roadway and rises only slightly above the roadway level, so that a vehicle can drive over it without damage. At least one light reflector according to the invention is located on a free visible surface of the half-shell shaped carrier facing the road user. It is clear that the invention is not limited to attachment to certain supports. If the reflector according to the invention for warning of black ice cannot be attached in the immediate vicinity of the ground of a roadway in order to indicate floor temperatures which are dangerous for ice, it is advantageous to use a metallic reflector Connect ladder to the floor. It is preferably a metal strip or metal strip with good thermal conductivity, for example copper. It can be the metal band or the metal ^¬ fen strei also forms excluded foil-like thin. In this way, the reflectors according to the invention can also be used in addition to or instead of the conventional reflectors on roads! be attached, taking into account the road surface temperature.

The present invention has compared to other methods for ice warning in road traffic, among others. above all the following advantages:

1. No additional temperature sensor, no power supply and no electrical cables are required.

2. There are no moving parts.

3. Depending on the type, the warning can be switched from non-reflective to reflective or from one

Color done to another. It is also possible to specify reflectors according to the invention which have three or more states depending on the temperature.

4. The switchover is not gradual, but at a sharply defined temperature T (within a few tenths of a degree), which can be set by selecting the liquid crystal material.

5. The layer thickness of the liquid crystal between thin parallel glass or f! üssigkri stal 1 -resistant plastic sheets can be freely selected within wide limits.

6. The light reflector according to the invention is advantageously sandwich-like. On the front and back * On the side of the cover layers of the liquid crystal made of thin glass or liquid crystal-resistant plastic plates, the polarizers 1 and 3 made of thin film sections can be glued on, for example, so that the liquid crystal forms a structural unit with the two polarizers according to FIG. 1. The polarizer 1 coming to the outside can be coated on its outer layer with a translucent protective film or the like. The light reflector unit can, for example, be glued to a thin reflector plate or the like. On the other hand, the light reflector assembly can also be supplemented by a birefringent element 5 in the form of a thin plate or film according to FIG. 2. It is clear that the light reflector assemblies can also have two liquid crystals according to FIGS. 3 and 4 or, according to FIG. 5, are provided with a temperature-dependent filter in the form of a thin plate or film.

As a black ice warning device, the light reflector according to the invention is advantageously arranged in the immediate vicinity of the road surface. To this end, a multitude of refector carriers are available to the person skilled in the art. If the light reflector according to the invention cannot be attached in the immediate vicinity of the road surface, it may be advantageous to connect the light reflector to the driver via a temperature bridge (metallic conductor in the form of a metal strc! -Rd ../ a5 or metal 1 strip) ¬ to connect the floor. A copper foil is preferably used as the temperature bridge.

If one replaces the Maugui n cell 1 e 2 in the arrangement according to FIG. 1 or 2 with two such cells, between which a polarizer 1 or 3 is located, it can be achieved that the overall arrangement depends on the prevailing temperature can assume three different states. For this purpose, liquid crystal materials with different phase transition temperatures, which may be referred to as T - or c2, are used in the two cells. If one selects T ^ T «» one of the states is included

Temperatures above T,, in the range between T, and T _ - and below T. The c_ optical behavior of the arrangement is different in each of these three states. By suitably orienting the two cells and the other optical elements to one another, it can be determined in which of the three areas the arrangement in which color (also white) should or should not reflect.

Fig. 3 shows an embodiment with two Maugui n cell 1 s 2 ¹ and 2 ", between which a polarizer 3 'is arranged .- Dami t - ^■ is the Mauguin cell 2 in Fig. 1 by the two Mauguin¬ Cells 2 'and 2 "and an intermediate polarizer 3' replaced. FIG. 4 shows a further embodiment with two Maugui n cells 1 '2' and 2 ", between which a birefringent element 5 'and a polarizer 3' are arranged. As a result, the Mauguin cell 2 in FIG. 2 is through replaced the two Mauguin cells 2 'and 2 "with the interposed birefringent element 5' and polarizer 3 '. The latter can also be replaced by a selective polarizer.

Another possibility of generating a third Temperatur¬ range with different optical properties sheep en consists in the addition of a temperaturabhä ^'NCI gen optical element to the arrangement of FIG. 1 or FIG. 2. The temperature-dependent optical elements such filters are also suitable. Such filters are known in the literature. For example, a sol-gel filter is described in German patent specification 939 595, which becomes opaque when cooled to the gel state. Another example is dispersion filters as described in German Patent 1,573,140. Such filters, also called Christiansen filters after their discoverer, take advantage of the fact that the dependence of the refractive index on the wavelength of the light, the dispersion, depends on the temperature. If you now combine two suitable substances (for example by embedding one as a fine-grained powder in the other), you can achieve that the color or the intensity of the transmitted light changes with the temperature. By adding such a temperature dependent

Filters to the arrangement according to FIG. 1 or FIG. 2 overlap the transmission properties of the filter and the reflection properties of the arrangement, so that - similar to the arrangement with a double cell just described - there are three different areas when the point of change of the filter is at a temperature different from T.

FIG. 5 shows an embodiment in which an optical filter 6 (sol-gel filter or dispersion filter) is arranged in front of the polarizer 1 according to FIG. 2. Correspondingly, the optical filter 6 can also be connected upstream of the polarizer 1 in FIG. 1.

If, for special applications, the light reflector indicates more than three color or intensity states, several Maugui n cells can be provided, each with an interposed polarizer. In addition, a temperature-sensitive optical

Filters can be added.

Claims

Expectations

1. Temperature-dependent light reflector, in particular for black ice warning in road traffic, characterized in that in front of a reflecting element (4) is a between two polarizers (1, 3) arranged ﬂ i gkri s al 1 cell 1 e (2) according to Mauguin .

2. Light reflector according to claim 1 or 2, characterized gekenn¬ characterized in that there is a color filter in the beam path of the reflector.

3. Light reflector according to claim 1, characterized in that the reflecting element (4) is colored.

4. Light reflector according to claim 1, characterized in that between the Fl üssi gkri stal 1 cell 1 e (2) and the rear polarizer (3) acting as an optical delay element, birefringent element (5) for Auf¬ splitting the light in two mutually perpendicular polarized partial beams.

5. Light reflector according to claim 4, characterized in that between the Fl üss i gkri stal 1 cell 1 e (2) and the front polarizer (1) acting as an optical delay element, birefringent element (5) for splitting the light located in two mutually perpendicularly polarized partial beams.

6. Light reflector according to claim 4, characterized in

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OMPI

SK, WI_Ό ^' that the rear polarizer (3) and the double computing element (5) are replaced together by a pl eochroitically selectively absorbing element (selective polarizer).

7. Light reflector according to claim 5, characterized in that the front polarizer (1) and the birefringent element (5) are replaced together by a pl eochroitically selectively absorbing element. .

8. Light reflector according to one of claims 4 to 7, characterized in that the color of the light passing through the birefringent element (5) is set by the choice of the strength of the birefringent element (5).

9. Light reflector according to one of claims 1 to 8, da¬ characterized in that the reflective element (4) is a Retroref1 ektor.

10. Light reflector according to one of claims 1 to 9, da¬ characterized in that the Mauguin cell (2) by a double cell from two series-connected Mauguin cells (2 ', 2 ") with intervening polarizer (3' or 5 ', 3') is replaced.

11. Light reflector according to one of claims 1 to 9, da¬ characterized in that a temperature-dependent optical element (6) is added.

12. Light reflector according to claim 11, characterized gekenn¬ characterized in that the optical element (6) is a sol-gel filter or a dispersion filter (Christiansen.-Fi 1 ter).

13. Light reflector according to one of claims 1 to 12, characterized in that it is held by a reflector carrier in contact with the road surface or in its immediate vicinity.

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OMPI - 1 ^* 3 - 14. Light reflector according to one of claims 1 to 13, characterized in that it is held on a reflector carrier at a distance from the roadway and that the light reflector is connected to the roadway floor via a temperature bridge.

15. Lfchtref1 ektor according to claim 14, characterized in that the temperature bridge is formed by a copper foil or copper tape.

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