Fail-safe symbol displays with LED light source and light guide

Abstract

LED symbol display for safety-relevant applications, particularly in railway, maritime, aviation, and traffic signaling, based on fiber optics, comprising a light-mixing LED light source, a light-dividing light guide element, and light-exit optics in a matrix plate (M) arranged to display a symbol, characterized in that the light-mixing LED light source comprises several high-power LEDs arranged in a dense packing with a flat encapsulation (R, G) on a light source circuit board (1), and immediately in front of the light source circuit board (1) is a light guide rod (2) with a flat, preferably narrowly dimensioned, polygonal, in particular rectangular, triangular, or hexagonal, light-entry surface (3) and the same cross-section, which gradually widens conically and has a flat light-exit surface (4) perpendicular to its axis, to which a light-entry surface (7) of the light-dividing light guide element is attached.preferably directly, which divides the incoming light into a plurality of light beams and directs each light beam separately to an exit surface (8a), each of which is located in the focus (F) of a collecting optic (5) attached in front of it in the matrix plate (M).

Description

[0001] The application concerns an optic with LED light source and light guide, in accordance with WO2012 / 068603A1 (Swarco).

[0002] The color-mixing optical system revealed in this printed material is not well suited for reliable symbol representation. Symbols are composed of individual luminous dots which, according to their arrangement, form numbers, letters, or simple graphic representations such as arrows, crosses, bars, or lines in the usual manner.

[0003] The above application already mentions its use as a redundant light source with multiple LED crystals for safety applications, where, in the event of one LED crystal failure, switching to another is possible without any perceptible change in light emission. Similarly, switching between different colored LED crystals is also possible without any perceptible change in light emission. These properties of the above application are now to be used for symbol displays in safety equipment, particularly in railway, maritime, aviation, or road traffic. In this context, the possibility of color switching can also be utilized, enabling symbols to be displayed in multiple colors using the color-switchable light source.

[0004] Safety equipment refers to a redundant system designed so that the failure of any single component will under no circumstances lead to the failure of the entire system. If a component fails, a backup system must maintain functionality, reporting the fault so that the system can be quickly repaired. In a simpler version, the system must enter a stable, predetermined state or shut down upon any fault, triggering predefined procedures for malfunctioning symbols.

[0005] Previously, symbols in safety applications were implemented using fiber optic bundles. Two reflector lamps illuminate the same fiber optic bundle via splitter or deflecting mirrors. The arms of this bundle lead to the individual optics forming the symbol in the front panel of the device, known as the matrix panel, with each optic creating a point of light. If the first lamp burns out, the electrical controller switches to the second lamp due to the lack of current flow. This activates a warning signal. If only one lamp is used, the displayed symbol is safely switched off after the lamp burns out; the controller detects this by the absence of current flow. For the highest safety requirements, each symbol must be operated using only a single light circuit, as splitting the symbol across multiple circuits can lead to a distorted symbol representation in the event of a malfunction.

[0006] The technological development of LEDs meant that variable message signs, previously equipped with fiber optic bundles, were very quickly converted to individual optics with one LED per optic for cost reasons. This also made it possible, for the first time, to produce graphics-capable devices using grid arrangements and modular construction, whose displays can be freely programmed. However, these devices are subject to low safety standards, meaning they are not suitable for safety-critical environments.

[0007] Today, optical fibers are primarily used for signal transmission. Only a few niche areas of lighting technology remain where the use of LED light sources in conjunction with optical fiber bundles is practical, for example, in endoscopes or medical technology, as described in US 2014 / 126233A1 (Sunoptic). However, in this application, only a single high-power LED directly illuminates a (replaceable) optical fiber bundle.

[0008] Manufacturers of symbol displays for safety-critical applications face a dilemma when they want to equip their displays with the particularly durable LED technology. If high safety standards are required, each LED must be individually monitored to guarantee an unaltered symbol display. This would necessitate special electronic controllers that operate at the highest safety level in conjunction with the control systems, incurring immense costs because existing, older control systems are incompatible and would also need to be modified.However, electronically imitating the behavior of an incandescent lamp in safety equipment is also very complex and does not offer the technical possibilities of electronically connecting the devices, for example via bus lines, as already provided for in the latest generations of control systems, with integrated control, brightness regulation, operating hour counting, function monitoring and logging of operating conditions and faults.

[0009] Even if such developments are undertaken, the susceptibility to failure of such complex systems is relatively high due to the use of numerous individual components, thus contradicting the principle of functional reliability. Systems presented so far are not clearly identifiable as systems of the future.

[0010] The arrangement of individual LEDs in each optic presents various difficulties, as the desired brightness and light distribution are sometimes unattainable with single LEDs. Low-power LEDs are often too dim, while high-power LEDs would have to be operated outside their specifications with insufficient current. So-called mid-power LEDs are not yet available in all signal colors. However, light guide bundles would allow for a wide range of brightness levels to be achieved, particularly within the relevant brightness range. Furthermore, the system offers the inherent reliability of complete symbol representation, as one or more failed light points are only possible with LED light points.

[0011] Therefore, consideration was given to retaining the light guide design and equipping it with particularly durable LED bulbs. However, the production of bulb-compatible LED light sources continues to encounter difficulties, especially regarding thermal issues, but also concerning the necessary light focusing onto light guide bundles. Furthermore, neither single nor multi-LED light sources exhibit incandescent-compatible electrical behavior or a safe failure mode. In any case, new control systems would have to be developed.

[0012] An optical signaling system requires only a relatively small number of high-power LEDs for sufficient brightness. These LEDs can be operated and electrically monitored with far less effort than, for example, the many light points of a symbol. Therefore, a single LED light source in symbol displays would be significantly advantageous. If one LED fails, the current to the functioning LEDs could be increased to maintain a constant signaling brightness without affecting individual light points.

[0013] Unfortunately, in known optical systems, the failure of an LED leads to the formation of dark spots and changes in light distribution, often resulting in a failure to meet the photometric specifications. These phenomena become more noticeable the more tightly the light must be focused, as the method of light diffusion for uniformity is not suitable in such cases. A spatially curved arrangement of LEDs with individual optics, which focus their light onto a fiber optic bundle in an overlapping manner, is very complex to manufacture and not particularly efficient from an optical perspective. Furthermore, this results in areas of varying brightness at the fiber optic entry point, the compensation for which requires expensive fiber optic bundles with mixed optical fibers.

[0014] Until now, no optical systems were known that could achieve a balanced blending of the light from individual LEDs without loss of light intensity or focusing, and without significant technical effort. The aforementioned WO2012 / 068603A1 now presents a solution. However, it only addresses small optics for individual pixels of variable message signs with similarly small and low-luminosity multicolor LEDs, which are only effective within their respective optics, but are entirely sufficient due to the system's high optical efficiency.

[0015] The object of the invention is therefore to develop a blending light source with high-power LEDs and optical elements, with which LED symbol displays can be implemented using light guide technology. According to the invention, this is achieved by arranging a light guide rod with a flat, compact, rectangular, triangular, or hexagonal light entry surface and cross-section directly in front of the light source circuit board, which consists of several high-power LEDs with flat encapsulation arranged in a dense pack. This light guide rod gradually widens conically and has a flat light exit surface perpendicular to its axis. The light entry surface of a light-dividing element is directly connected to this light entry surface. This element divides the incoming light into a plurality of light beams and directs each light beam separately to an exit surface located at the focus of a converging lens mounted in a matrix plate in front of it.

[0016] Because this optical system ensures that each individual LED produces the same light distribution, if one or more LEDs fail, the remaining intact LEDs can be supplied with a higher current, and LEDs in different light colors can also be switched on separately, thus enabling both failure compensation and a symbol in different color representation.

[0017] Signaling systems must emit specific, standardized light colors depending on their meaning. These colors are not generated using RGB color mixing, but rather, for safety reasons, must utilize LEDs in the respective signal color. Maintaining a consistent light color obtained through mixing under all operating conditions and malfunctions would be a virtually insurmountable problem under stringent safety regulations. Such a solution would undermine reliability and availability, increase costs, and offer no other advantages. Of course, implementation using RGB LEDs is technically feasible.

[0018] The light-splitter element is, in most cases, a standard optical fiber bundle whose individual arms consist of numerous fine glass fibers. These fibers are particularly easy to bend, and even a break in a few individual fibers would have only a minimal impact on the appearance and light distribution of the affected optical element. Alternatively, more cost-effective, standard single fibers made of transparent, flexible plastic can be used. However, in the event of a fiber break, the corresponding light source is completely lost, which is why tight bends in the arms, high temperatures, and vibrations must be avoided. In both cases, the arms are joined at a common light entrance of the optical fiber bundle. For special applications and larger production runs, a transparent, one-piece splitting optical fiber is also possible as the light-splitter element.

[0019] The invention will now be explained with the aid of drawings. It shows(s):

[0020] the Fig. 1 a partial section and a clear illustration of the invention,

[0021] the Fig. 2 a schematic longitudinal section through the invention and

[0022] the Fig. 3. A variant design in longitudinal section.

[0023] The Fig. Figure 1 shows the invention partly in cross-section and partly in a more illustrative form. The light source circuit board 1It incorporates several high-power LEDs of the same or different colors (R, G), shown here in a so-called chip LED design, where each LED chip sits on a slightly larger, highly thermally conductive ceramic substrate and is protected from environmental influences and mechanical damage by a flat encapsulation. These LEDs, also known as chip LEDs, can be arranged close together and exhibit a similar energy and luminous intensity to LED chips mounted directly onto a circuit board using COB (chip-on-board) technology and encapsulated flat. The COB design, as an identical light source configuration in terms of effect, is particularly cost-effective for large production runs. Preferably, the light source board is... 1 Made of thermally conductive ceramic to distribute and dissipate the highly concentrated waste heat in the best possible way.

[0024] The two electrical connections of each LED chip, R and G, are connected via circuit traces on the light source board. 1 Individually routed to allow for any desired circuit configuration, particularly with regard to electrical parameter monitoring and safety requirements, which is best achieved with dual-row LED arrangements. These circuits, along with all the necessary power supply electronics, can also be mounted wholly or partially on the light source board. 1 be arranged.

[0025] The flat potting allows a fiber optic rod to be inserted. 2 with its flat entrance surface 3 is placed directly in front of the LED chips R, G, with its entry surface 3The light guide is only slightly larger than the outline of the LED array, yet it captures most of the generated light. Because of the rectangular LEDs and mostly square LED chips, a dense array is generally also rectangular, as is the light guide cross-section. However, according to the invention, it can also be square, triangular, or hexagonal if this offers advantages in achieving the desired light distribution.

[0026] The entrance area 3 exhibits a tolerance-related safety distance to the LED chips R, G, whose surfaces must not be touched, thus preventing light rays from entering the entry area. 3 If light rays miss their target or are reflected superficially, they escape laterally. These unusable marginal light rays can be captured by light-guiding elements (not shown) and directed to optical sensors for monitoring the functional status.

[0027] The outer surface of the light guide rod 2 It consists of flat, highly polished surfaces for total reflection of the light and, according to the invention, widens conically towards a flat exit surface. 4 perpendicular to its longitudinal axis. The drawing shows the path of some light rays r emanating from the LED chip R. The conical expansion, as is known, leads to a focusing of the emitted light rays r within the light guide rod. 2 , which also affects the angular range of the light after it exits.

[0028] The adjacent fiber optic bundle 6However, every other rigid optical fiber also has a so-called "aperture angle," which refers to the critical angle of the incoming and outgoing light below which further transmission by total internal reflection still occurs. Light outside this angle exits through the side walls and is lost to the system. The conical shape of the optical fiber. 2 is therefore dimensioned such that the generated light emission angle A is less than or equal to the aperture angle of the adjacent optical fiber bundle. 6 This means approximately a doubling or tripling of the length and width of the light-emitting surface. 4 to the light entry surface 3 , at approximately five to ten times the length of the fiber optic rod 2 regarding the diagonal of its entrance surface 3 The length ratio of the optical fiber rod 2It also determines the number of reflections of the light rays inside it, thus the number of mirror images of each LED chip and therefore the mixing quality.

[0029] Immediately adjacent to the exit surface 4 Adjacent to this is the flat surface for light entry. 7 of the fiber optic bundle 6 , preferably they have exactly the same size and outline, so that no light is lost, but each optical fiber is fully illuminated by light.

[0030] The light in each fiber optic arm 6a , 6b ... exits at its end and enters the collecting optics 5 one which is attached to the matrix plate M and forms a light point of the symbol, and whose focus is located in the light exit of the respective light guide arm, as in Fig. 2 shown in more detail.

[0031] In Fig. 2 only the mirror images of the individual LED chip R are used Fig. 2. In cross-section, viewed from a photometric perspective. The curved arrangement of the mirror images Ra, Rb, Rc... results from the slight taper of the optical fiber. 2 For the sake of explanation, only the central light rays of the LED chip R and its reflections through the center of the emission surface are shown here. 4 Consider the following: The light rays emanating from each reflection are shown as dashed lines, since they actually originate from the single LED chip R and, after several lossless reflections at the fiber optic rod walls, result in the solid light rays r, ra, rb, rc... shown. The irregular angles of the light rays correlate with the arrangement of the reflections.

[0032] As can be seen from the aforementioned WO2012 / 068603A1, the exit area 4 of the light guide rod 2Each individual LED (R, G) is illuminated with essentially uniform brightness because every point on its surface is lit only by light rays originating directly from the LED chip and its reflections. These rays are emitted by the LED with a continuous, so-called cosine distribution. Therefore, it is unnecessary to use fiber optic bundles with mixed optical fibers, which, in incandescent lamp systems, compensates for the uneven brightness of the focused light point. However, the light emission does occur from the exit surface. 4 irregular in the form of diverging light beams in different directions, corresponding to the offset positions of the mirror images Ra, Rb, Rc .., of the LED R with respect to the emission surface 4 . This irregularity in the light emission angles is largely preserved during the division and transmission of the light, as shown in diagram D, so that each exit surface8a , 8b ... of the fiber optic bundle 6 It also has a uniform brightness, but exhibits preferred light emission angles.

[0033] If not only the central light rays but all light rays are taken into account, this phenomenon remains in principle, but the preferred light emission angles appear blurred and diffuse.

[0034] In analogy to the frequently mentioned WO2012 / 068603A1, this phenomenon is neutralized if each exit surface 8a , 8b ... in focus F of the associated subsequent collecting optics attached to the matrix plate M 5 This is achieved by aligning all light rays from any point on the exit surface. The converging optics thus create 5 According to optical laws, the light distribution takes the form of an upside-down, uniformly bright emitting surface. 8aof the fiber optic arm 6a as a projection to infinity. The converging lens 5 It captures as many outgoing light rays as possible up to the aperture angle A for maximum efficiency. Advantageously, its light-entry area extends 10 directly at the exit surface 8a of the fiber optic arm 6a approaching and is at least large enough to capture all outgoing light rays.

[0035] The geometry of the exit surfaces 8a , 8b ... the fiber optic arms 6a , 6b ...is particularly customizable when using optical fibers, but also through the targeted shaping of solid fiber optic arms. This light distribution geometry can be achieved, as is known, by superimposed optical structures S, for example on the entrance surface. 10 or the light-emitting surface 11 the converging lens 5to a certain extent, they can be modified. Subsets of light can also be refracted, for example by a converging lens. 5 Integrated reflective surfaces can be mirrored into other distribution areas. This offers a wide range of design possibilities to adapt the light distribution to the requirements.

[0036] Does the light guide bundle indicate 6 If the arms are very long, a statistical compensation of the inhomogeneous light directions occurs within the arms due to manufacturing tolerances and curvatures, so that in this case the converging lenses do not achieve a focus at the exit surfaces. 8a , 8b ... which must have fiber optic arms and can therefore be freely designed.

[0037] The cross-sectional area of ​​the optical fiber arms, as well as their number, can be freely selected within wide limits and can be easily determined by a person skilled in the art with knowledge of the invention. Naturally, within the overall optical system, the number and operating mode of the LEDs, the size of the light-emitting surface, the taper of the optical fiber, the geometry of the exit surfaces of the optical fiber arms, and the number, size, and design of the optics must be coordinated with the desired light distribution and brightness. This is usually done by means of photometric simulation. Refractive indices, absorption, surfaces, reflections, and structures, as well as nonlinear influences and distortions, are taken into account in this process.

[0038] The elements of the optical system can of course also form a modular system, which is coordinated in such a way that existing components can be accessed for every common application, accepting certain losses, especially at the entry and exit surfaces of the light.

[0039] Fig. Figure 3 shows a light-splitter element in a solid fiber optic construction. The conical fiber optic rod 2 The essentially planar split optical fiber closes immediately. 9 with towards the exit area 4 congruent entrance surface 7 on. From it, branches lead to each converging lens. 5 in the matrix plate M light-conducting arms ( 9a , 9b ...) with large radii, which are exactly at the focus F of the respective converging lens 5 The light rays r of an LED R initially distribute themselves evenly over all light-conducting arms. 9a , 9b...without changing their angles of inclination. Only the curves cause a relatively small change in these angles, so that at the exit surfaces... 8a , 8b ... a very similar directional dependence of the light rays as at the entrance surface 7 exists and the exit surfaces are therefore located in the focus F of the converging lenses 5 must be located.

[0040] This design is particularly suitable for the separately switchable straight segments of a so-called alphanumeric seven-segment display, but also, for example, for the bars of a signal position indicator, whose components are essentially located in one plane. This is because, in the arrangement shown, light guide rods 2 and split fiber optic cable 9 They can be very easily fused into a single component. For simple lighting requirements, such as concentric light focusing, even the converging lenses can be used. 5even attached in one piece to the light-conducting arms 9a , 9b ...be connected. This allows for the joint, one-piece, and therefore cost-effective production of the light guide rod, distributor, and optics from transparent plastic in a relatively simple injection mold.

[0041] Such a design is also particularly bright because both the interface losses and the gap losses between the optical fibers of a light guide bundle are reduced. 6 This can be avoided. The delicate optical fiber geometry is preferably held in position and protected by a housing (not shown), which also houses the converging lenses. 5 encompasses and is installed from the rear into the matrix plate M.

[0042] In an embodiment of the invention, star-shaped split optical fibers that are integrally connected to the optical fiber rod can also be manufactured relatively easily.

[0043] If the same LED light source is also used in signal lights, they can, in principle, be operated with the same control system. This eliminates the need to develop additional safety electronics.

[0044] The light source board is, of course, included. 1 well cooled to dissipate the waste heat from the high-power LEDs, especially by direct and full-surface mounting on housing walls, heat sinks, signs or other components, preferably made of aluminum.

[0045] Terms such as "uniform," "in focus," "flat," "high-gloss polished," "immediately before," and numerous others are to be understood and interpreted in a technical context, not in a mathematical or idealistic one. Terms such as "approximately" mean, unless otherwise specified, ranges with deviations of ±10%. QUOTES INCLUDED IN THE DESCRIPTION

[0046] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0047] WO 2012 / 068603 A1 [0001, 0014, 0032, 0034] US 2014 / 126233 A1

[0007]

Claims

[1] LED symbol display for safety-relevant use, especially in railway, maritime, aviation and traffic signaling, based on light guides, comprising a light-mixing LED light source, a light-dividing light guide element and light-exit optics in a matrix plate (M) in the arrangement of the symbol to be displayed, characterized by that immediately in front of the light source board consisting of several high-power LEDs with flat potting (R, G) arranged in a dense pack ( 1 ) a fiber optic rod ( 2 ) with a flat, preferably narrow, polygonal, in particular rectangular, triangular or hexagonal light entry surface ( 3 ) and is arranged with a cross-section of the same type, which gradually widens conically and forms a flat light-emitting surface ( 4 ) perpendicular to its axis, to which the light-entry surface ( 7) a light-dividing element preferably directly connects, which divides the incoming light into a plurality of light beams and directs each light beam separately to an exit surface ( 8a ) forwards, which is in the focus (F) of a collecting optic mounted in a matrix plate (M) in front of it ( 5 ) is located. [2] LED symbol display according to claim 1, characterized by that the light-dividing element is a light guide bundle ( 6 ) which, as is known in itself, consists of fiber optic arms ( 8a , 8b ...) consists of a multitude of light-guiding optical fibers located in the light entry surface ( 7 ) are summarized. [3] LED symbol display according to claim 1, characterized by that the light-dividing element is a light guide bundle ( 6 ) which, as is known, consists of elastic plastic light guide arms, which are located in the light entry surface ( 7 ) are summarized. [4] LED symbol display according to claim 1, characterized by that the light-dividing element is a one-piece splitting light guide ( 9 ) is, which consists of transparent material and which extends into its entry surface ( 7 ) entering light via branching light-guiding arms ( 9a , 9b ...) divides and forms converging lenses ( 5 ) leads. [5] LED symbol display according to claim 4, characterized by that split optical fiber ( 9 ) and fiber optic rod ( 2 ) are made in one piece from the same material, especially a highly transparent plastic. [6] LED symbol display according to claim 4, characterized by that split optical fiber ( 9 ) and converging lenses ( 5 ) are made in one piece from the same material, especially a highly transparent plastic. [7] LED symbol display according to claim 4, characterized by that light guide rod ( 2), Split fiber optic cable ( 9 ) and converging lenses ( 5 ) are made in one piece from the same material, especially a highly transparent plastic. [8] LED symbol display according to at least one of claims 1 to 7, characterized by that the exit surface ( 4 ) of the light guide rod ( 2 ) and the entrance area ( 7 ) of the light-dividing element have the same size and shape. [9] LED symbol display according to at least one of claims 1 to 8, characterized by that this from every exit surface ( 8a , 8b ...) of the fiber optic arm ( 6a , 6b ...) exiting light completely from the subsequent converging lens ( 5 ) is recorded and directed. [10] LED symbol display according to at least one of claims 1 to 9, characterized by that the exit surfaces ( 8a , 8b ...) the fiber optic arms ( 6a , 6b...) have such a shape which already corresponds to or at least closely approximates the intended light distribution and whose shape is determined by the focus position with respect to the converging lens ( 5 ) is projected into infinity. [11] LED symbol display according to at least one of claims 1 to 10, characterized by that the light entry surface ( 10 ) and / or light-emitting surface ( 11 ) the converging lens ( 5 ) has a superimposed scattering structure (S) or other optically effective surfaces which differ from the shape of the optical fiber exit surfaces ( 8a , 8b ...) adjusts the corresponding light distribution more precisely to the requirements. [12] LED symbol display according to at least one of claims 1 to 11, characterized by that the entrance area ( 10 ) the converging lens ( 5 ) directly at the exit surface ( 8a , 8b ...) of the respective fiber optic arm ( 6a , 6b...) borders and has at least a congruent or protruding outline. [13] LED symbol display according to at least one of claims 1 to 12, characterized by that the conicity of the light guide rod ( 2 ) generated light emission angle (A) is less than or at most equal to the aperture angle of the adjacent light-dividing element. [14] LED symbol display according to at least one of claims 1 to 13, characterized by that the symbol represents a single optical unit consisting of a light source board ( 1 ), fiber optic rod ( 2 ) and light-dividing element, is illuminated. [15] LED symbol display according to at least one of claims 1 to 13, characterized by that the symbol is displayed by means of a seven-segment display and with seven optical units, consisting of a light source board ( 1 ), fiber optic rod ( 2 ) and light-dividing element, is illuminated. [16] LED symbol display according to at least one of claims 1 to 15, characterized by that the LED chips in COB technology are mounted directly onto the light source board ( 1 ) applied and poured together. [17] LED symbol display according to at least one of claims 1 to 16, characterized by that the light source board ( 1 ) is made of electrically insulating, thermally conductive ceramic and is thermally well connected to cooling surfaces. [18] LED symbol display according to at least one of claims 1 to 17, characterized by that the fiber optic rod ( 2 ) Missing edge light rays from the high-power LEDs are preferably collected, bundled and directed onto optical sensors by means of light-guiding elements.

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