DE102015218158A1 - Fail-safe symbol displays with LED light source and light guide - Google Patents

Abstract

The invention relates to an LED symbol display with color mixing collection optics, especially for safety-related applications. The color-mixing property of the light source is used on the one hand to completely hide the failure of one LED and to apply the corresponding power to the remaining LEDs if necessary, on the other hand to implement symbols in several standard colors in a common design. As a light source high-power LEDs (R, G) are used with a flat light emission and separate interconnection, and electrical and / or optical monitoring in a compact arrangement, the light mixed in the optical fiber rod (2) and after the flat exit surface (4) in a Fiber optic bundle (6) or a Lichtaufteilendes element is passed, there divided into individual light guide arms and their exit surfaces (8a, 8b ...) is directed to individual, forming a symbol collecting lenses (5) whose focal points (F) in the respective exit surfaces lie. The light distribution can be further adapted to the field of application by reflecting surfaces and / or a structure (S) on the converging lens (5).

Description

The application relates to an optic with LED light source and light guide, according to the WO2012 / 068603A1 (Swarco).

The mixed color collection optics disclosed in this document is not well suited for a fail-safe symbol display. Symbols are constructed of individual luminous points, which according to their arrangement in a known manner digits, letters or simple graphic representations, such as arrows, crosses, bars or lines.

In the above application is already pointed to the use as a redundant light source with multiple LED crystals for security tasks when can be switched to another in case of failure of an LED crystal, no apparent change in the light emission. Likewise, it is also possible to switch back and forth between differently colored LED crystals without any noticeable change in the light emission. These characteristics of the above application are now to be used for symbol representations in safety equipment, in particular in rail, shipping, aviation or road traffic. In this case, the possibility of a color change can additionally be used, in that symbols in several colors can be realized by the color-switchable light source.

Safety equipment is a redundant system designed so that failure of any component will under no circumstances lead to failure of the system. If a component fails, a replacement system must maintain its function, reporting the presence of an error so that the system can be quickly repaired. In a simpler variant, the system must enter or shut down to a stable predetermined state for each fault, so that behavior rules for failed symbols come into effect.

So far, symbols have been implemented in security applications using optical fiber bundles. Two reflector incandescent lamps illuminate the same optical fiber bundle via divider or deflecting mirrors whose arms lead to the individual optics forming the symbol in the device front, which is referred to as the matrix plate, and where each optic forms a point of light. If the first lamp blows, this leads to a switch to the second lamp due to a lack of current flow in the electrical controller. A warning signal is activated. If only one lamp is provided, then the symbol shown is safely switched off after the lamp has blown through, in the controller the detection is effected by the absence of a current flow. For highest security requirements, each symbol can only be operated by means of a single circle of light, because splitting it into several circles of light can, in the event of a fault, lead to a mutilated symbol representation.

The technical development of the LEDs meant that the variable traffic signs, which were previously equipped with fiber optic bundles, were quickly converted to individual optics with one LED per optic for cost reasons. As a result, it was also possible for the first time to produce graphics-capable devices through raster arrangement and modular design, the representations of which can be freely programmed. However, low safety requirements apply, meaning that these devices are not suitable for safety-relevant environments.

Today, optical fibers are mainly used for signal transmission. There remain only a few photometric edge areas, where the use of LED light sources together with optical fiber bundles makes sense, for example, in endoscopes or in medical technology as in the US 2014 / 126233A1 (Sunoptic). However, only a single high-power LED directly illuminates an (exchangeable) fiber optic bundle.

The manufacturers of symbol displays for security-relevant applications are here in the dilemma, if they want to equip their displays with the particularly durable LED technology. If high demands are placed on safety, all LEDs must be individually monitored in order to guarantee an unflamed symbol representation. This would require special electronic controllers, which work together with the controls in the highest security level, which causes immense costs, because the existing older system controllers are not compatible and would also need to be changed. However, the electronic imitation of a light bulb behavior in safety equipment is also very complex and does not offer the technical possibilities of an electronic connection of the devices, such as bus line, as already provided in the control systems of the latest generations, such as integrated control, brightness control, operating hours count, function monitoring and logging the operating circumstances and disturbances.

Even if such developments are made, the susceptibility to failure of such complex systems because of the use of a variety of individual components is also relatively high and is contrary to the idea of reliability. Previously presented systems are inconclusive recognizable as a system of the future.

The arrangement of individual LEDs in each look encounters various difficulties, as desired brightness and light distribution sometimes can not be achieved with individual LEDs. Often low-power LEDs are too faint, alternatively high-power LEDs would have to be operated outside their specifications with too little power. So-called mid-power LEDs are not yet available in all signal colors. With optical fiber bundles, however, the light point brightness could be realized within wide limits, especially in the brightness range of interest. Added to this is the system-immanent safety of a complete symbol representation, because one or more fancy points of light are only possible with LED light points.

Therefore, it was also thought to maintain the light guide design and equip it with extra-durable LED bulbs. However, the production of lamp-compatible LED light sources still encounters difficulties, in particular with regard to the thermal problems, but also with regard to the required light bundling on optical fiber bundles. In addition, both single and multi-LED light sources have neither incandescent-compatible electrical behavior nor safe failure mode. In any case, new approaches would have to be developed for this.

An optical signaling system requires only a relatively few high-power LEDs for sufficient brightness, which can be operated with much less effort and monitored electrically, such as the many light points of a symbol. It would therefore be a common LED light source in symbol displays of considerable advantage. If an LED fails, the LED current for the functional LEDs could be raised to keep the brightness of the signaling constant, without interfering with individual points of light.

Unfortunately, in known optical systems due to failure of an LED but to the formation of dark spots and changes in the light distribution, so often the lighting specifications are no longer met. These phenomena become all the more conspicuous the closer the light has to be bundled, since in this case the method of light scattering for equalization is out of the question. A spatially curved arrangement of LEDs with single optics, which focus their light overlapping on a fiber optic bundle, manufacturing technology is very complex and lighting technology not very efficient, apart from this results in different bright areas on the light guide entry, balancing expensive fiber optic bundles with mixed optical fibers requires.

So far, no optical systems were known that could accomplish a balancing mixing of the light of individual LEDs without loss of light and bundling and without considerable technical effort. The aforementioned WO2012 / 068603A1 now shows a solution for it. However, it treats only small optics for individual pixels of variable traffic signs with very small and faint multicolor LEDs, which act only in the associated optics, but are quite sufficient because of the high optical efficiency of the system.

The object of the invention is therefore to develop a mixing-out light source with high-power LEDs and light point optics, with which LED symbol displays can be implemented in optical fiber technology. This is achieved in accordance with the invention in such a way that an optical fiber rod with a flat, closely dimensioned, rectangular, triangular or hexagonal light entry surface and a similar cross section is arranged directly in front of the light source board composed of a plurality of high-power LEDs with a planar encapsulation in a dense packing flared and has a flat light exit surface perpendicular to its axis, to which the light entrance surface of a Lichtaufteilenden element immediately adjoins, which divides the incoming light over a plurality of light bundles and each light bundle separately to each exit surface passes, which is in focus one before is located in a matrix plate mounted collecting lens.

Because each individual LED produces the same light distribution through this optical system, the remaining intact LEDs can be energized higher on the one hand in case of failure of one or more LEDs, on the other hand, LEDs in different colors of light can be switched on separately, whereby both a failure compensation, and a symbol in different Color representation is possible.

Signaling systems have to emit certain standardized light colors depending on their importance. These are not produced in RGB color mixing, but must use for safety reasons LEDs in the respective signal color, because to keep a mixture obtained by mixing light color under all operating circumstances and incidents constant, would be a highly insoluble problem under high security conditions, its solution reliability Availability undermines, is costly and otherwise brings no advantage. Regardless, of course, the version with LEDs in RGB colors is technically possible.

The light-dividing element is in most cases a commercially available optical fiber bundle whose individual arms consist of a plurality of fine glass fibers, which can be easily guided around curves and even a fraction of some individual fibers only a minimal effect on the appearance and light distribution of the affected individual optics would have. Likewise, though also cheaper, standard single cores made of transparent, elastic plastic are provided, but here falls in the case of a wire break the associated light point completely, so tight bends of the arms, high temperatures and vibrations are to be avoided. The arms are brought together in both cases in a common light entry of the optical fiber bundle. For special cases and larger quantities, a transparent, one-part distribution light guide is also possible as a light-dividing element.

The invention will now be explained with reference to drawings. It shows or shows:

the 1 a partial section and an illustrative representation of the invention,

the 2 a schematic longitudinal section through the invention and

the 3 a variant in longitudinal section.

The 1 shows the invention partly in cross section, partly in an illustrative form. The light source board 1 carries several high-power LEDs of the same or different color R, G, shown here in so-called chip-LED design, each LED chip sits on a slightly larger, very good heat conducting ceramic support and a level casting from environmental influences and mechanical damage. Such LEDs, which are also called chip LEDs, can be arranged close together and have a similar energy and light density, such as LED chips applied directly to a printed circuit board in COB (chip-on-board) technology and just encapsulated. The COB design as identical in effect light source design is more cost-effective, especially for large quantities. Preferably, the light source board 1 made of thermally conductive ceramic in order to best distribute and dissipate the very concentrated heat loss incurred.

The two electrical connections of each LED chip R, G are via tracks on the light source board 1 led out individually to allow any interconnections, especially in terms of electrical parameter monitoring and safety requirements, which is best possible with double row LED arrays. These interconnections together with the complete supply electronics can also be wholly or partially on the light source board 1 be arranged.

The level potting allows a fiber optic rod 2 with its flat entrance area 3 immediately before the LED chips R, G is set, taking its entrance surface 3 only slightly larger than the outline of the LED array, and yet capture most of the light generated. Because of the rectangular LEDs and mostly square LED chips, a dense arrangement is usually also rectangular, as is the optical fiber cross section. But it can also be square, triangular or hexagonal according to the invention, if this results in the achievement of the desired light distribution.

The entrance area 3 has a tolerance-related safety distance to the LED chips R, G, the surfaces of which must not be touched, whereby light rays, which the entrance surface 3 miss or be superficially reflected, emerge laterally. These unusable edge light beams can be picked up by means of unillustrated light-conducting elements and directed to optical sensors for monitoring the functional status.

The lateral surface of the optical fiber rod 2 consists of flat, highly polished surfaces for total reflection of the light and widens according to the invention conically towards a flat exit surface 4 perpendicular to its longitudinal axis. The drawing shows the course of some light rays r, starting from the LED chip R. The conical enlargement leads in a known manner to a bundling of the radiated light rays r within the light guide rod 2 , which also affects the angular range of the light after its exit.

The adjacent fiber optic bundle 6 , but also every other fixed light guide has a so-called "aperture angle", so that the critical angle of the incoming and outgoing light is meant under which there is a further transmission by total reflection. Light outside this angle exits through the sidewalls and is lost to the system. The conical shape of the fiber optic rod 2 is therefore such that the generated light exit angle A is less than or equal to the aperture angle of the adjacent fiber optic bundle 6 is. This means about a doubling to tripling of length and width of the light exit surface 4 to the light entry surface 3 , at about five to ten times the length of the optical fiber rod 2 regarding the diagonal of its entrance surface 3 , The aspect ratio of the fiber optic rod 2 Also determines the number of reflections of the light rays in its interior, hence the number of mirror images of each LED chip and thus the mixing quality.

Immediately to the exit surface 4 adjoining the flat light entry surface extends 7 of the fiber optic bundle 6 Preferably, it is exactly the same size and contour so that no light is lost, but each fiber of light is fully exposed to light.

The light in each fiber optic arm 6a . 6b ... comes out at its end and in the collection optics 5 a, which is fixed in the matrix plate M and forms a light spot of the symbol, and whose focus is in the light exit of the respective light guide arm, as in 2 shown in more detail.

In 2 only the mirror images of the single LED chip R are out 2 considered in the cross section photometrically. The curved arrangement of the mirror images Ra, Rb, Rc .., results from the weak conicity of the optical fiber rod 2 , For explanation, only the center light beams of the LED chip R and its mirror images through the center of the exit surface will be described here 4 considered. The emanating from each mirror image light rays are shown by dashed lines, since they actually go out from the only existing LED chip R and after several lossless reflections on the fiber optic rod walls the continuous drawn light rays r, ra, rb, rc ... result. The irregular angle values of the light rays correlate with the arrangement of the mirror images.

As the aforementioned WO2012 / 068603A1 it can be seen, is the exit surface 4 of the fiber optic rod 2 of each individual LED R, G illuminated substantially uniformly bright because it is illuminated at each point of its surface only by directly from the LED chip and its mirror images originating light rays, which are emitted by the LED with a continuous course in so-called cosine distribution. It is therefore not necessary to use optical fiber bundles with mixed optical fibers, which is compensated in incandescent lamp systems, the uneven brightness of the collimated light spot. However, the light emission takes place from the exit surface 4 irregular in the form of divergent light beams in different directions, corresponding to the offset positions of the mirror images Ra, Rb, Rc .., the LED R with respect to the exit surface 4 , This irregularity of the light emission angle is largely retained in the subdivision and propagation of the light as shown in the illustration D, so that each exit surface 8a . 8b ... of the fiber optic bundle 6 Although also has a uniform brightness, but preferred light exit angle of the light.

If not only the center light beams, but all the light rays are taken into account, then this phenomenon remains in principle, the preferred light exit angle, however, appear washed out and running.

In analogy to the multiple mentioned WO2012 / 068603A1 This phenomenon is neutralized if any exit surface 8a . 8b ... in the focus F of the associated, in the matrix plate M attached subsequent collection optics 5 is located, whereby all the light rays of each point of the exit surface are switched by parallel alignment. This creates the collection optics 5 according to optical laws a light distribution in the form of the upside-down, uniformly bright emitting exit surface 8a of the fiber optic arm 6a as a projection into the infinite. The condenser lens 5 captures as far as possible all exiting light rays up to the aperture angle A for maximum efficiency. Advantageously, their light entry surface extends 10 directly to the exit surface 8a of the fiber optic arm 6a approach and is at least so large that all emerging light rays are detected.

The geometry of the exit surfaces 8a . 8b ... the fiber optic arms 6a . 6b ... is customizable in particular when using optical fibers, but also through the targeted shaping of massive light guide arms. As is known, this light distribution geometry can be achieved by superposed optical structures S approximately on the entrance surface 10 or the light exit surface 11 the condenser lens 5 modify within limits. It can also subsets of light through about in the convergent lens 5 integrated reflection surfaces are reflected in other distribution areas. Here, a wide field of design offers itself in order to adapt the light distribution to the specifications.

Indicates the fiber optic bundle 6 very long arms, it is already within the arms caused by manufacturing tolerances and curvatures statistical compensation of the inhomogeneous light directions, so that in this case the converging lenses no focus at the exit surfaces 8a . 8b ... must have the light guide arms and thus can be freely designed.

The light cross section of the light guide arms and their number is freely selectable within wide limits and can be easily determined by those skilled in the knowledge of the invention. Of course, in the overall optical system, the number and mode of operation of the LEDs, the size of the light exit surface, the taper of the light guide rod, the geometry of the exit surfaces of the light guide arms and the number, size and design of the optics with the desired light distribution and brightness to vote. This is usually done by means of photometric simulation. Refractive indices, absorptions, surfaces, reflections and structures as well as non-linear influences and distortions are considered.

Of course, the elements of the optical system can also form a modular system, which is tuned so that existing components can be accessed for every customary application, at the expense of certain losses, in particular at the entrance and exit surfaces of the light.

3 shows a Lichtaufteilendes element in solid fiber optic design. To the conical fiber optic rod 2 immediately closes the substantially flat distribution light guide 9 with to the exit surface 4 congruent entrance surface 7 at. From him branch to each condenser lens 5 in the matrix plate M photoconductive arms ( 9a . 9b ...) with large radii, which are exactly in focus F of the respective convergent lens 5 end up. The light rays r of an LED R initially distribute evenly over all light-conducting arms 9a . 9b ... without changing their angle of inclination. Only through the curves is a relatively small change in these angles, so at the exit surfaces 8a . 8b ... still a very similar directional dependence of the light rays as at the entrance surface 7 exists and the exit surfaces are therefore in focus F of the converging lenses 5 must be located.

This design is recommended especially for the separately switchable straight segments of a so-called seven-segment alphanumeric display, but also for the bars of a signal position indicator, whose components are located substantially in one plane. Because in the illustrated arrangement, fiber optic rod 2 and split light guide 9 be easily merged into a single component. For simple lighting requirements such as concentric light bundling even the converging lenses 5 even in one piece to the light-conducting arms 9a . 9b ... be connected. Thus, a common, one-piece and thus cost-effective production of fiber optic rod, distributor and optics made of transparent plastic in a relatively simple injection mold is possible.

Such a design is also particularly bright, because both the interface losses, as well as the gusset losses between the glass fibers of a fiber optic bundle 6 be avoided. The filigree fiber optic geometry is preferably held and protected in position by a housing, not shown, which also includes the converging lenses 5 includes and is built into the matrix plate M from behind.

In an embodiment of the invention, integrally connected star-shaped distribution light guide can also be made relatively easy with the light guide rod.

If the same LED light source is also used in signal lights, for example, their operation can in principle be carried out with the same control. This saves the development of a further safety electronics.

Of course, the light source board 1 Well cooled, in order to dissipate the heat loss of the high-power LEDs, in particular by direct and full-surface contact with housing walls, heat sinks, signs or other components, preferably made of aluminum.

Terms such as "uniform", "in focus", "even", "highly polished", "immediately before" and many others are to be understood or interpreted in the technical context and not in the mathematical or ideal / idealistic. Terms like "about", unless otherwise stated, mean ranges with deviations of ± 10%.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• WO 2012/068603 A1 [0001, 0014, 0032, 0034]
• US 2014/126233 A1 [0007]

Claims (18)

LED symbol display for safety-related use, in particular in rail, marine, aviation and traffic signaling based on optical fibers, comprising a light-mixing LED light source, a light-dividing light guide element and light emission optics in a matrix plate (M) in arrangement of the symbol to be represented, characterized that directly in front of the light source circuit board (7) arranged in a sealed package of several high-power LEDs (R, G) 1 ) a light guide rod ( 2 ) with planar, preferably tightly dimensioned, polygonal, in particular rectangular, triangular or hexagonal light entry surface ( 3 ) and is arranged in the same cross section, which gradually widens conically and a flat light exit surface ( 4 ) perpendicular to its axis, to which the light entry surface ( 7 ) of a light-dividing element preferably immediately adjoins, which divides the incoming light into a plurality of light bundles and each light bundle separately to each exit surface ( 8a ), which is focused in the focus (F) of a collection optics (FIG. 5 ) is located. LED symbol display according to claim 1, characterized in that the light-dividing element is an optical fiber bundle ( 6 ), which, as is known, from optical fiber arms ( 8a . 8b ...) with a plurality of light-conducting glass fibers, which in the light entry surface ( 7 ) are summarized. LED symbol display according to claim 1, characterized in that the light-dividing element is an optical fiber bundle ( 6 ), which as known consists of elastic plastic light guide arms, which in the light entry surface ( 7 ) are summarized. LED symbol display according to claim 1, characterized in that the light-dividing element is a one-part distribution light guide ( 9 ), which consists of transparent material and which in its entrance surface ( 7 ) entering light by means of branching light-conducting arms ( 9a . 9b ...) and to the collecting lenses ( 5 ). LED symbol display according to claim 4, characterized in that distribution light guides ( 9 ) and optical fiber rod ( 2 ) are made in one piece of the same material, in particular a highly transparent plastic. LED symbol display according to claim 4, characterized in that distribution light guides ( 9 ) and converging lenses ( 5 ) are made in one piece of the same material, in particular a highly transparent plastic. LED symbol display according to claim 4, characterized in that the light guide rod ( 2 ), Distribution light guide ( 9 ) and converging lenses ( 5 ) are made in one piece of the same material, in particular a highly transparent plastic. LED symbol display according to at least one of claims 1 to 7, characterized in that the exit surface ( 4 ) of the optical fiber rod ( 2 ) and the entrance surface ( 7 ) of the light-dividing element have congruent size and shape. LED symbol display according to at least one of claims 1 to 8, characterized in that from each exit surface ( 8a . 8b ...) of the light guide arm ( 6a . 6b ...) exiting light completely from the subsequent convergent lens ( 5 ) is detected and directed. LED symbol display according to at least one of claims 1 to 9, characterized in that the exit surfaces ( 8a . 8b ...) of the light guide arms ( 6a . 6b ...) have such a shape, which already corresponds to the intended light distribution or at least comes close and their shape by the focus position with respect to the converging lens ( 5 ) is projected to infinity. LED symbol display according to at least one of claims 1 to 10, characterized in that the light entry surface ( 10 ) and / or light exit surface ( 11 ) of the condenser lens ( 5 ) has a superimposed scattering structure (S) or other optically active surfaces which correspond to the shape of the light guide exit surfaces (S). 8a . 8b ...) corresponding light distribution more closely matches the requirements. LED symbol display according to at least one of claims 1 to 11, characterized in that the entrance surface ( 10 ) of the condenser lens ( 5 ) directly to the exit surface ( 8a . 8b ...) of the respective light guide arm ( 6a . 6b ...) borders and has at least congruent or prominent outline. LED symbol display according to at least one of claims 1 to 12, characterized in that by the conicity of the optical fiber rod ( 2 ) is less than or at most equal to the aperture angle of the adjacent light-dividing element. LED symbol display according to at least one of claims 1 to 13, characterized in that the symbol of a single optical unit consisting of light source board ( 1 ), Optical fiber rod ( 2 ) and lichtaufteilendem element is illuminated. LED symbol display according to at least one of claims 1 to 13, characterized in that the symbol is represented by means of a seven-segment display and with seven optical units consisting of light source board ( 1 ), Optical fiber rod ( 2 ) and lichtaufteilendem element is illuminated. LED symbol display according to at least one of claims 1 to 15, characterized in that the LED chips in COB technology directly to the light source board ( 1 ) are applied and together just shed. LED symbol display according to at least one of claims 1 to 16, characterized in that the light source board ( 1 ) made of electrically insulating, thermally conductive ceramic and thermally well connected to cooling surfaces is connected. LED symbol display according to at least one of claims 1 to 17, characterized in that the light guide rod ( 2 ) Missing edge light beams of the high-power LEDs are preferably collected by means of light-conducting elements, bundled and directed to optical sensors.

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