Lighting device with light guide and temperature monitoring

Abstract

Lighting device with a radiation source (21; 31), a light guide (22; 32; 42) coupled to this, which is arranged in the inner lumen of a metallic protective tube (23; 33; 43), and a pressure hose (27; 37; 47) that completely or at least partially encloses the protective hose (23; 33; 43), where between the pressure hose (27; 37; 47) and the protective hose (23; 33; 43) at least one wire (25; 35; 45) made of an optical plastic fiber is attached, which is separated from the protective hose (23; 33; 43) on at least part of its outer surface only by an insulating plastic (26; 36; 46), and the pressure hose (27; 37; 47) either permanently presses the wire (25; 35; 45) against the surface of the protective hose (23; 33; 43), or develops or increases this pressure force only when the temperature rises, characterized in that the pressure hose (27; 37; 47) presses the wire (25; 35; 45) made of the plastic fiber so strongly against the protective hose (23; 33; 43) when a limit temperature is reached that the light transmission in the plastic fiber drops sharply or is completely interrupted.

Description

[0001] The invention relates to a lighting device comprising a radiation source and an optical fiber connected to it. The optical fiber is flexible and mounted inside a similarly flexible metallic protective sleeve. The optical fiber incorporates a temperature monitoring mechanism that monitors the temperature along the entire length of the flexible metallic protective sleeve and, if a local temperature limit is exceeded anywhere on the outer surface of the metallic protective sleeve, switches off the radiation source within a delay of only a few minutes. Such a temperature monitoring mechanism has become necessary because increasingly powerful light sources, such as projector lamps, have recently entered the market, which are coupled to flexible optical fibers, in particular liquid optical fibers (as described, for example, in patent application DE 42 33 087 A1).

[0002] For example, it is possible to use a 200-watt projector lamp (Osram) ® -P-VIP200) or a 330-watt projector lamp (Philips) ® The TOP-UHP 330W, with an integrated elliptical reflector, is made of a liquid-filled optical fiber with a light-activated aperture of only 5 mm in diameter and a total length of several meters, capable of transmitting up to 40 watts of radiant power in the visible spectrum. Such high beam output powers from a flexible optical fiber were previously only achievable with laser radiation sources.

[0003] Lighting devices with light guides in the visible range with the highest possible beam output power are needed by industry, e.g. in optical 3D digitization and surveying, where a 200-watt projector lamp from Osram is used. ®Type P-VIP200 and a liquid light guide with a length of 10 m and a light-active diameter of 5 mm are used. The beam output power from the light guide is 20 watts in this example!

[0004] Since the core of a liquid-filled optical fiber consists of an aqueous solution with a boiling point just above 100°C, even the slightest impurities in the liquid, inadequate filtering of the infrared components from the radiation source, or mechanical deformation of the liquid-filled optical fiber due to impact can lead to bubble formation in the liquid or local overheating of the optical fiber, resulting in a rapidly escalating temperature rise of the outer sheath. This can cause the destruction of the liquid-filled optical fiber and further consequential damage within minutes. Therefore, monitoring the external temperature of the liquid-filled optical fiber and having the option to switch off the radiation source are essential.

[0005] Fig. Figure 1 shows the temperature increase of the outer tube of a liquid light guide, in this case a corrugated tube or a wound tube made of V2A stainless steel, as a function of time for a liquid light guide with a 5 mm light-active diameter and a beam output power of approximately 20 watts, in which a 3 mm diameter bubble was artificially created in the liquid. This example illustrates that the radiation source, here a Philips ® -The projector lamp with 330 watts of electrical power should be switched off after a maximum of 6 to 7 minutes because the outer covering of the liquid light guide, a flexible stainless steel corrugated tube, has already become hotter than 130°C.

[0006] Fig. Figure 1 also shows that the beam output power of the liquid light guide decreases rapidly when the temperature of the outer corrugated tube of the liquid light guide reaches values ​​above 170 to 180°C. Monitoring the liquid light guide using a beam splitter is insufficient because the transmission of the liquid light guide initially decreases only slowly, even though the outer temperature of the optical fiber's protective tube has already reached values ​​above 120°C.

[0007] A generic illumination device with a break detector for optical fibers is known from German patent application DE 38 89 876 T2. Further conventional illumination devices are described in US 2006 / 0 062 530 A1, DE 28 55 145 A1, DE 20 2005 018 553 U1, DE 10 2006 061 164 A1 and DE 10 2004 010 275 B3.

[0008] The object of the invention is to create a temperature monitoring system that is effective along the entire length of the optical fiber and that generates a warning signal and / or immediately switches off the radiation source when a critical external temperature of the outer protective sheath of the optical fiber is reached.

[0009] The problem is solved by the lighting device defined in claim 1. The dependent claims relate to preferred embodiments.

[0010] Conventional gas discharge or incandescent lamps, laser sources, or high-power LED arrays can be used as radiation sources. The optical fiber coupled to the radiation source does not necessarily have to be a liquid-filled optical fiber, although this is the primary focus here. The present invention can also be used for optical fibers made of solid materials such as SiO2, especially in conjunction with laser radiation sources.

[0011] When using a liquid light guide, the outer flexible metallic protective sleeve, generally a coiled or corrugated sleeve made of aluminum, brass or stainless steel, or a tightly wound wire spiral, preferably made of a thermally poorly conductive metal such as spring-loaded stainless steel, is preferably used as the electrical conductor. This sleeve contains the core of the liquid light guide, a Teflon. ® -FEP hose filled with a liquid, encased.

[0012] A second electrical conductor, consisting of a thin switching wire insulated along its entire length with a thin-walled polymer layer, is, for example, helically wound around the metallic protective sleeve, or it runs only linearly and parallel to it, with contact between the protective sleeve and the insulated switching wire.

[0013] A particularly preferred winding configuration is one in which the switching wire is returned at one end of the protective sleeve with a phase shift of 90° to 270°, preferably approximately 180°, in the form of a double helix. The rotationally symmetrical, double-helical winding then covers the outer surface of the metallic protective sleeve relatively densely, so that the switching mechanism can be reliably triggered as soon as local overheating occurs at any point on the metallic protective sleeve. The double helix can also be achieved using a second switching wire. Alternatively, the use of an entire wire braid as the switching wire is also possible, which is explained in more detail below.

[0014] The polymer that insulates the switching wire has a thin wall thickness of 0.1 to 0.3 mm and a melting point in the range of 60 to 200°C, depending on the critical switching temperature.

[0015] A thin-walled, expanded thermal shrink tubing is applied over the entire assembly, consisting of the insulated connecting wire and the metallic protective sleeve. After an unimpeded thermal shrinking process, the inner diameter of this tubing is less than or equal to the outer diameter of the metallic protective sleeve. The temperature at which the shrink tubing begins to reduce in diameter should be approximately 70 to 100°C.

[0016] In the presence of a bubble inside the liquid light guide, the metallic protective sleeve is initially damaged due to the light scattering caused by the bubble and the transparency of the Teflon. ®The FEP fiber optic tubing is heated. The insulating, low-melting-point, thin-walled polymer that insulates the connecting wire and contacts the metallic protective tubing on its outer surface is initially softened and eventually reaches its melting point. Simultaneously, the outer heat-shrink tubing, which is also heated by the local heat, exerts increased pressure on the insulated connecting wire against the metallic protective tubing.

[0017] Finally, after a few minutes, due to the displacement of the molten polymer, an electrical contact is made between the switching wire and the metallic protective sleeve. This electrical contact between the switching wire and the metallic protective sleeve of the liquid light guide can be used to trigger a warning signal or to switch off the radiation source immediately.

[0018] The time required to trigger the switching process in the event of local overheating of the outer tube of the liquid light guide depends on several material constants: Uncrosslinked LDPE or LLDPE, with a melting point between 60 and 120°C, can be used as insulation material for the approximately 0.5 mm thick hook-up wire.

[0019] The insulation thickness of the switch wire can, for example, be in the range of 0.1 to 0.5 mm.

[0020] The connecting wire itself can be made of copper or stainless steel. Stainless steel is preferred because of its low thermal conductivity. Stranded wires made of these materials can also be used instead of a homogeneous wire.

[0021] The metallic protective sleeve for the optical fiber can be made of a wound sleeve of aluminum or brass, but preferably of V2A stainless steel due to its desirable low thermal conductivity. Alternatively, a flexible wire spiral, tightly wound and preferably made of stainless steel or spring steel, can be used as a protective sleeve.

[0022] The thermal shrink tubing can be made of a cross-linked polyolefin or PVC.

[0023] The light-active diameter of the liquid light guide can be, for example, 5 mm, and the critical size of the bubble at which switching is to occur is typically 2 to 3 mm.

[0024] The power of the transmitted radiation is in the multiwatt range, i.e., usually over 10 watts.

[0025] The following describes a practical embodiment of a lighting device with a 120-watt projector lamp, a liquid light guide with a light-active cross-section of 5 mm, an emitted radiant power of 10 watts, and a protective sleeve consisting of a wound sleeve made of V2A stainless steel and an artificially created bubble with a diameter of 3 mm. This embodiment includes the temperature monitoring system according to the invention, which is capable of triggering the shutdown of the light source due to overheating of the light guide within a few minutes.

[0026] In this embodiment, a 0.5 mm thick hook-up wire made of annealed stainless steel is used, insulated with non-crosslinked polyethylene (PE), preferably LDPE (low-density PE) or LLPDE (linear low-density PE). Other polymers with a similarly low melting point to PE and that are not crosslinked can also be used as insulation for the hook-up wire. The wall thickness of the insulating sheath of the hook-up wire can be between 0.1 and 0.5 mm. The thickness of the hook-up wire can be between 0.3 and 1 mm. The melting point of the insulation of the hook-up wire is preferably in the range between 50 and 200°C.

[0027] The flexible metallic protective sleeve of the liquid light guide is preferably made of V2A stainless steel. The low thermal conductivity of V2A means that the heat loss from a bubble generates a higher local peak temperature on the protective sleeve, which can be used for rapid contact between the switching wire and the protective sleeve. An aluminum protective sleeve produces a lower, but more spatially distributed, local temperature increase, so the switching-off process takes longer.

[0028] In this embodiment, the insulated switching wire and the V2A winding hose are connected to an ohmmeter by means of alligator clips and stranded wires, which indicates the electrical short circuit or electrical contact by a drop in resistance from "high" to "low".

[0029] Typical switch-off or contact times under the specified conditions range from 3 to 7 minutes after the light source is switched on. The metallic protective sleeve briefly reaches a temperature of up to 150°C and cools down rapidly after the light source is switched off.

[0030] In practice, this shutdown means that the liquid light guide must be replaced because blistering with such a high local temperature increase of the stainless steel (V2A) protective sleeve is irreversible. If the goal is to keep the outer temperature of the liquid light guide below 100°C, for example, to 75°C, the liquid light guide can either be covered with an additional outer, heat-insulating, and flexible plastic sleeve, and / or a polymer with a lower melting point can be chosen as the insulating material for the connecting wire. For example, material modifications with melting temperatures in the range of 45 to 95°C can be found in the LLDPE (linear low-density polyethylene) group.

[0031] Instead of just one switching wire, for safety reasons several metal wires can also be arranged between the thermal shrink tubing and the metallic protective tubing in the manner described above.

[0032] Of course, in this embodiment, the connecting wire can also be left uninsulated, and the outer surface of the stainless steel (V2A) protective conduit can be coated with a thin insulating layer of low-melting-point polymer. This variant works just as well, but is more difficult to manufacture when using only one or more individual connecting wires. However, this variant is particularly advantageous when, instead of one or more individual wires, a tubular, metallic wire mesh is wrapped around the protective conduit sheathed with the thin-walled insulating layer. The wire mesh is simply laid over the entire insulated protective conduit, thus eliminating the complex wire winding process.The polymer insulating layer, through the pressure exerted by the heat-shrink tubing described above, which in turn encases the metallic wire mesh, establishes electrical contact between the wire mesh and the metallic protective tubing when it reaches its melting point. The wire mesh automatically lies in the desired rotationally symmetrical position around the insulated protective tubing.

[0033] Instead of heat-shrink tubing, which only exerts the increased pressure of the insulated connecting wire on the metallic protective sleeve when the temperature rises locally, a different covering, e.g., made of an elastomer such as silicone, can be chosen that constantly presses the insulated connecting wire against the metallic outer sleeve. A braid of metallic wires or plastic fibers could perform the same function, exerting constant radial pressure when stretched linearly. A metallic, electrically grounded braid would also have the advantage of shielding against electromagnetic interference that can emanate from the long metallic connecting wire. Alternatively, heat-shrinkable film can be used instead of heat-shrink tubing; this film presses the connecting wire against the metallic protective sleeve when the temperature rises.A permanent contact force on the switching wire could also be achieved by wrapping it with stretch film.

[0034] For the sake of completeness, it should also be mentioned that instead of an electrically conductive hook-up wire, a POF fiber can be used in the same configuration. This fiber is also pressed onto the metallic protective sleeve using heat-shrink tubing when heat is generated (POF = plastic optical fiber). A POF fiber has a light-guiding core, usually made of Plexiglas, a very thin optical insulation made of a fluorine-containing polymer, and an outer protective layer, usually made of PE, PVC, or PA (polyamide). Radiation from a diode (LED) is coupled into one end of the POF fiber, while the other end leads to a receiver.When the POF fiber is pressed against the structured surface (grooves) of the metallic protective sleeve by the contraction of the heat shrink tubing, such a strong deformation of the POF fiber occurs (at temperatures around 100°C and above) that the optical transmission of the POF fiber decreases drastically. This significant change in transmission can be used for a switching operation, e.g., to switch off the radiation source.

[0035] The following section explains details of the invention with reference to the drawings. These show: Fig. 1. the dependence of radiation power on temperature already discussed above; Fig. 2 a schematic and partially opened side view of the lighting device according to the invention with temperature monitoring; Fig. 3 a cross-section of the lighting device according to Fig. 2; and Fig. 4 A perspective view of the light guide and its sheathing, shown partially open.

[0036] Fig. Figure 2 shows the symbolically indicated radiation source (21), which is located in a housing and whose radiation is focused into the light guide, here a liquid light guide (22). The light guide (22) consists, for example, of Teflon. ® A flexible optical fiber (22) is enclosed in a flexible metallic protective sleeve (23), which in turn is encased in a heat-shrink sleeve (27). In this example, the protective sleeve (23) consists of a wound spiral spring, preferably made of V2A wire or spring steel wire with the lowest possible thermal conductivity.

[0037] An insulated connecting wire (24) with a metallic core (25) and an insulating plastic sheath (26) runs between the protective sleeve (23) and the heat shrink tubing (27). The connecting wire (24) is pressed against the metallic protective sleeve (23) by the tightly fitting heat shrink tubing (27) along its entire length, which can be up to 30 meters.

[0038] Electrically conductive strands (29) extend from the conductive core (25) of the connecting wire (24) and from the metallic protective sleeve (23) to the housing of the radiation source (21), where, in a manner not shown here, the change in ohmic resistance between the core (25) of the connecting wire (24) and the metallic protective sleeve (23) is recorded and evaluated. With an intact, bubble-free liquid optical fiber, this electrical resistance is defined by the resistance of the insulating sheath (practically R = ∞). It reduces to the resistance of the electrical conductor (nearly R = 0 Ω) when an air bubble forms in the liquid optical fiber due to local overheating of the metallic protective sleeve (23), and the resulting loss or scattered radiation is in the watt power range.In this case, the insulation (26) of the switching wire (24) melts and at the same time the heat shrink tubing (27) exerts an increased pressure of the switching wire (24) on the protective tubing (23) at the point where the blister is, which finally causes the electrical short circuit that can be used to switch off the radiation source (21).

[0039] The entire assembly, consisting of liquid-filled optical fiber (22), protective sleeve (23), connecting wire (24) and heat-shrink tubing (27), can be further encased in a flexible, thermally insulating plastic sleeve (28). As a result, the temperature increase on the outer surface of the entire optical fiber assembly is barely noticeable until the radiation source (21) is switched off and remains below 75°C, a requirement stipulated, for example, by the Norwegian TÜV.

[0040] It has been shown that the most sensitive and therefore the fastest switch is obtained when the flexible metallic protective sleeve (23) is made of a flexible spiral wound from V2A or spring steel wire with the lowest possible thermal conductivity, where the wire diameter is between 0.5 mm and 1 mm and there is a small air gap between the individual turns. Furthermore, the sensitivity of the switch is increased if the electrically conductive core (25) of the switching wire (24) is also made of a material with low thermal conductivity, such as annealed V2A wire or a stranded wire made of this material.

[0041] Surprisingly, it has also been shown that the grooved surface of the protective hose (23), or more generally its structured surface, accelerates the switching process, provided that the switching wire (24) runs as perpendicularly as possible to the grooves. Protective hoses in the form of wound wire spirals, as well as, to a lesser extent, metallic coiled hoses similar to those used in hand showers, have such a favorable grooved surface structure. When using a metallic coiled hose as a protective hose (23), V2A stainless steel is the preferred material. Such protective hoses (23) are also known as spirally wound metal hoses or Agraff hoses.

[0042] Fig. Figure 3 shows a longitudinal section through the liquid light guide (32) including its various sheaths, namely the metallic flexible protective sleeve (33), here in the form of a wound sleeve made of V2A, the heat shrink sleeve (37), the insulating sleeve (38) made of plastic and the connecting wire (34) running between the heat shrink sleeve (37) and the metallic protective sleeve (33), the core (35) of which preferably consists of V2A wire (annealed) or a strand of V2A wire (annealed), and the insulation (36) of which can be a low melting point plastic such as PE or LDPE or PVC or PU.

[0043] The radiation source (31) focuses the light beam (323) into the liquid light guide, which consists of a flexible tube (321) made of a carbon fluorine polymer filled with a liquid (322) and has a light-scattering bubble (39) at one point. The loss or scattering radiation caused by the bubble (39) penetrates the carbon fluorine polymer tube (321) and locally heats the metallic protective sleeve (33). This sleeve (due to its poor thermal conductivity) rapidly builds up a high peak temperature, which is transferred to the adjacent heat-shrink tubing (37).

[0044] Fig.Figure 4 shows the effect of the bubble within the liquid light guide (42), namely a distinct constriction (49) of the heat shrink tubing (47) within the insulating tubing (48), with the result that the connecting wire (44) is pressed against the hot zone of the metallic protective tubing (43), and the softened polymer insulation of the connecting wire (44) is displaced. The surface grooved structure of the metallic protective tubing (43) promotes the displacement of the softened insulation (46), and electrical contact is ultimately established between the core (45) of the connecting wire (44) and the metallic protective tubing (43). This contact can be used as a signal to switch off the radiation source.

[0045] Surprisingly, it has been shown that when using a hook-up wire (44) with a wire (45) or strand made of V2A as the core material, the electrical contact between the hook-up wire (44) and the protective sleeve (43) is unambiguous and irreversible, which is not always the case when using a copper hook-up wire. In this case, the electrical contact often oscillates repeatedly between "low" and "high" before finally reaching "low" (i.e., approximately 0 Ω).

[0046] Alternatively, a shunt resistor of a few kΩ can be used at the distal end of the optical fiber, i.e., at the light exit or entry point, to bridge both branches (43 and 45) of the circuit, so that a small control current constantly flows in the circuit. This control current indicates the integrity of the switching wire (44) as long as the switching mechanism has not yet been triggered.

Claims

[1] Lighting device with a radiation source (21; 31), a light guide (22; 32; 42) coupled to this, which is arranged in the inner lumen of a metallic protective tube (23; 33; 43), and a pressure hose (27; 37; 47) that completely or at least partially encloses the protective hose (23; 33; 43), where between the pressure hose (27; 37; 47) and the protective hose (23; 33; 43) at least one wire (25; 35; 45) made of an optical plastic fiber is attached, which is separated from the protective hose (23; 33; 43) on at least part of its outer surface only by an insulating plastic (26; 36; 46), and the pressure hose (27; 37; 47) either permanently presses the wire (25; 35; 45) against the surface of the protective hose (23; 33; 43), or develops or increases this pressure force only when the temperature rises, characterized by, that the pressure hose (27; 37; 47) presses the wire (25; 35; 45) from the plastic fiber so strongly against the protective hose (23; 33; 43) when a limit temperature is reached that the light transmission in the plastic fiber drops sharply or is completely interrupted. [2] Lighting device according to claim 1, wherein the pressure hose (27; 37; 47) is a polymer hose, preferably a thermal shrink hose. [3] Lighting device according to one of the preceding claims, wherein the radiation source (21; 31) comprises a gas discharge lamp, such as a projector lamp, a laser, an LED array or an incandescent lamp. [4] Lighting device according to one of the preceding claims, wherein the light-guiding medium of the light guide (22; 32; 42) consists of glass or of a liquid (322). [5] Lighting device according to one of the preceding claims, wherein the light guide (22; 32; 42) is flexible and is located in the inner lumen of the also flexible protective sleeve (23; 33; 43), and / or a tube (321) filled with liquid (322) made of a fluorocarbon polymer. [6] Lighting device according to one of the preceding claims, wherein the metallic protective hose (23; 33; 43) a flexible coiled hose made of aluminium, brass or stainless steel, or a spirally wound metal hose or an agraff hose made of one of these materials, or a tubular metallic mesh, or consists of a tightly wound wire spiral made of stainless steel or spring steel, whereby there may also be a small gap between the turns of the wire spiral.

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