Short-arc discharge lamp for direct current operation with wire coil as damping guide element between the constriction section of the lamp shaft and the electrode rod

Abstract

Short-arc discharge lamp (1) for DC operation with - a lamp vessel comprising a discharge vessel (4) enclosing a discharge medium and two lamp shafts (5, 6) extending coaxially at opposite ends of the discharge vessel (4), - two external power supply sections (15, 16) extending outwards from each of the lamp shafts (5, 6), - two electrodes (2, 3), namely a cathode (2) and an anode (3), each consisting of an electrode rod (22, 32) and an electrode head (21, 31), wherein the electrode rods (22, 32) are arranged along the lamp shafts (5, 6) such that the two electrode heads (21, 31) are opposite each other inside the discharge vessel (4), - a sealing section in each of the two lamp shafts (5, 6), whereby a gas-tight current passage is formed between the two outer current supply sections (15, 16) on the one hand and the two electrodes (2, 3) on the other hand, wherein the sealing section is designed as a step melting of the electrode rods (22, 32) by means of transition glasses, - a constriction section (9, 10) in each of the two lamp shafts (5, 6), which is arranged between the respective sealing section and the electrode head of the associated electrode, wherein the constriction section (9, 10) closely surrounds the electrode rod (22, 32), characterized in that - between the constricted section (9, 10) of a lamp shaft (5, 6) and the electrode rod (22, 32) of at least one electrode (2, 3) a damping guide element is arranged, wherein the damping guide element is designed as a wire helix (11) which is arranged at least along a part of the constricted section (9, 10) on the electrode rod (22, 32), wherein the wire helix (11) has a first narrower turn for fixing the wire helix (11) on the electrode rod (22, 32) as well as further less narrow turns for damping and wherein the first narrower turn is located at the end of the wire helix (11) facing away from the electrode head (21, 31).

Description

Technical field

[0001] The invention relates to a short-arc discharge lamp for direct current operation with a wire coil as a damping and guiding element between the constricted section of the lamp shaft and the electrode rod. Such lamps are used, for example, for photo-optical purposes such as projection technology, exposure of semiconductors, curing with UV radiation, etc., but also for general lighting, stage and architectural lighting, etc. State of the art

[0002] These types of lamps feature a discharge vessel filled with a discharge medium, such as a noble gas—with or without added mercury and possibly other filling materials. Inside the discharge vessel are two opposing electrodes, each supported by a lamp shaft arranged coaxially with the respective electrode. The lamp shaft also incorporates a gas-tight feedthrough for the electrical connection between external power terminals and the electrodes. This sealing section of the lamp shaft can be achieved, for example, through a graded seal using transition glass (graded seal). However, other lamp sealing technologies, such as a foil seal using foil fusing or foil crimping, are also employed in these types of lamps.

[0003] Especially with high-power lamps, such as those in the kilowatt or multi-kilowatt range, maintaining a permanently gas-tight arrangement of the electrodes is a challenge due to their increasing mass. Even during transport of such lamps, impacts on the electrode rods supporting the massive electrode heads can cause vibrations, potentially damaging the lamp shaft and leading to premature leakage or lamp breakage. This problem is exacerbated in the case of lamps designed for direct current (DC) operation, particularly on the anode side of the lamp shaft, as the anode must be especially robust. Furthermore, the electrode rods required for the massive electrode heads are subjected to relatively high temperature fluctuations during the start-up phase and after the lamp is switched off. This complicates the centering and guidance of the electrode rods, as a mechanical force or...Voltage transfer to the lamp shafts must be avoided. Otherwise, voltage fractures can occur.

[0004] Document DE 198 12 298 A1 discloses a lamp for AC operation with a wire coil on an electrode rod, which prevents cracks in the quartz bulb in the area of ​​the molybdenum foils. However, the electrodes are identical in design; therefore, special measures to facilitate the centering and guiding of the electrode rods are not necessary, as is the case with lamps for DC operation.

[0005] Document WO 2008 / 006 759 A2 discloses a short-arc discharge lamp in which the electrode rods are centered or guided in the lamp shafts by means of a constriction section. The constriction section surrounds the electrode rod tightly but loosely. As a result, vibrations of the electrode rod can be transmitted to the constriction section during vibrations of the lamp, for example, during transport, and lead to damage (natural resonance). Furthermore, fluctuating thermal expansion of the electrode rod can cause friction between the constriction section and the inner wall of the lamp shaft, consequently leading to damage to the shaft. Similar designs in which electrode rods are arranged in a constriction section are known in the prior art, for example in DE 103 53 861 A1, US 3 219 870 A, DE 103 05 339 A1, and EP 1 047 111 A2. In some aspects, metal foils and / or retaining cylinders are used to arrange the electrode rods in the constriction section.

[0006] Alternative designs describe support elements for electrode rods arranged in lamp shafts without constrictions. Document US 5,369,329 A discloses star- or spider-shaped support elements that are slid onto the electrode rod, and document US 5,859,492 A describes a support structure that is applied to the electrode rod. Description of the invention

[0007] The object of the present invention is to provide a short-arc discharge lamp with an improved electrode arrangement. A further aspect of the invention is to improve the shock and vibration resistance in the area of ​​the lamp shafts.

[0008] This problem is solved by a short-arc discharge lamp according to claim 1.

[0009] Further details can be found in the dependent claims.

[0010] Investigations by the inventors have shown that the shock and vibration resistance of a short arc discharge lamp can be significantly increased with the help of a damping-guiding element around the electrode rod in the area of ​​the narrowing section of a lamp shaft.

[0011] The damping-guiding element serves two purposes: firstly, it dampens the electrode rod upon impact, thereby increasing the breaking strength of the lamp shaft. This damping is achieved, among other things, through the element's shape, material properties, and suitably dimensioned axial extension. The aim is to distribute the previously limited local impact of the electrode rod over a larger area when the lamp is shaken, thus preventing or at least significantly reducing damage to the lamp shaft wall. Therefore, the damping-guiding element should surround the electrode rod for a sufficient length, preferably over the entire length of the constricted section. Furthermore, the element is preferably rotationally symmetrical.This ensures good guidance of the electrode rod, even when its length changes significantly with temperature fluctuations, for example, during the lamp's warm-up cycle, relative to the lamp shaft material, typically quartz glass. The resulting relative movements between the electrode rod and the lamp shaft wall no longer cause the electrode rod to rub against the shaft wall and potentially damage its surface, leading to premature shaft breakage. Instead, the electrode rod is guided by the damping-guiding element; that is, there is no longer any direct contact between the electrode rod and the lamp shaft wall in the constricted section.

[0012] The damping guide element is first placed on the electrode rod and positioned as intended. Then, the electrode rod, together with the damping guide element, is inserted into the lamp shaft, forming the constriction section. Since this requires heating the lamp shaft material to its softening temperature, metals with a sufficiently high melting point, such as tungsten or molybdenum, are particularly suitable for the damping guide element.

[0013] Similarly, the damping guide element is designed as a wire helix, which is wound onto the electrode rod at least along part of the constriction section or applied in another way, for example pre-wound and attached.

[0014] Furthermore, in one embodiment, a gap is provided between at least two adjacent turns of the wire coil. This allows some of the lamp shaft material to penetrate between the turns when it narrows, thus axially fixing the wire coil. This prevents the wire coil from slipping on the electrode rod or from moving with the electrode rod due to thermal expansion, which would otherwise lead to undesirable friction against the lamp shaft wall and consequently damage it. Brief description of the drawings

[0015] The invention will now be explained in more detail using exemplary embodiments. The figures show: Fig. 1 a short-arc discharge lamp according to the invention for DC operation in a partially cutaway longitudinal view, Fig. 2 an enlarged section I of the constriction section of the lamp from Fig. 1 in longitudinal section, Fig. 3 A short-arc discharge lamp for AC operation in a partially cutaway longitudinal view, Fig. 4 an enlarged section II of the alternative design of the narrowing section of the lamp Fig. 3 in longitudinal section. Detailed description

[0016] The following are identical or similar features designated with the same reference symbols.

[0017] Fig. Figure 1 shows a schematic representation of a first embodiment of a short-arc discharge lamp 1 according to the invention, which is intended for projection purposes and has a power consumption of 4000 W. It is a xenon-filled noble gas short-arc discharge lamp. The lamp 1 is designed for DC operation and therefore has a cathode 2 and an anode 3. These two electrodes 2, 3 are arranged opposite each other at a distance of approximately 7 mm within a substantially ellipsoidal discharge vessel 4 made of quartz glass, thus defining a longitudinal axis A of the lamp. Cathode 2 and anode 3 each have an electrode head 21 and 31, respectively, and an electrode rod 22 and 32, respectively. Here, the head and rod are separate parts that are inserted into one another, but they can also be manufactured as a single part. The electrode rods 22, 32 extend into a substantially circular cylindrical elongated lamp shaft 5, 6.The two lamp shafts 5, 6 are coaxially attached to the two ends of the discharge vessel 4 and are each provided with a base sleeve 7, 8 at their respective ends. Beneath the base sleeves 7, 8, each of the two lamp shafts 5, 6 has a sealing section (not visible in this illustration), which here is designed as a rod seal, i.e., a graded seal using transition glasses (English: "Graded Seal"). Between the sealing section and the electrode head 21, 31, a constriction section 9, 10 is provided in each case, where the glass of the lamp shaft tightly surrounds the respective electrode rod in order to keep the two electrodes 2, 3 coaxially aligned even when the lamp 1 is in a horizontal position. Reference will also be made to the following. Fig. Figure 2 shows an enlarged view of area I of the constriction section 10. In this area, a tungsten wire helix 11 is arranged on the electrode rod 22, acting as a damping and guiding element. The turns of the wire helix 11 thus wind between the surface of the electrode rod 22 and the inner surface of the lamp shaft 6, which closely surrounds this area. The wire helix 11 has a wire diameter of 0.6 mm, a pitch of 1.6 mm, and a length L of 24 mm. The first turn of the wire helix 11 has an inner diameter of 5.35 mm, while the remaining turns have an inner diameter of 5.7 mm. During assembly, the wire helix 11 is wound onto the electrode rod 22, which has an outer diameter of 5.5 mm. The first, tighter turn ensures a secure hold on the electrode rod during this stage of lamp manufacturing.Furthermore, the wire helix 11 is oriented such that the first tighter turn is preferably located at the end furthest from the electrode head. This allows the remainder of the wire helix in the front section to better dampen any shocks. The electrode rod 22, together with the wire helix 11, is then inserted into the lamp shaft 6, and the constriction section 10 is formed by heating the lamp shaft 6 in this area and subsequently "rolling" it in, i.e., pressing a forming roller against the rotating lamp shaft. A small amount of the suitably hot and therefore viscous quartz glass is squeezed between the individual turns of the wire helix 11, thus fixing the wire helix 11 at least axially in this constriction section 10 of the lamp shaft 6. This provides axial guidance for the electrode rod 22 during thermal expansion in lamp operation. Friction of the electrode rod against the lamp shaft wall, as seen in the prior art, is thereby avoided.The damping of the electrode rod 22 under shock load is achieved by the approximately 14 turns, which distribute any shock across the entire coil and thus largely prevent local damage to the lamp shaft. The conditions are corresponding in the opposite anode-side lamp shaft 5. Due to the greater mass of the anode head, the effects and advantages of the invention described above are even more pronounced here. At the ends of both lamp shafts 5, 6, an external current supply section 15, 16 protrudes, which, in the rod melting used here, is formed by the ends of the electrode rods 22, 32.

[0018] Impact tests have shown that, with the aid of the aforementioned tungsten filament, the breaking strength of these lamps can be increased from typically up to approximately 40 g (g = acceleration due to gravity) to between approximately 50 g and 60 g. The latter corresponds to an approximate drop height of 260 cm to 320 cm for the lamp in its transport packaging, compared to the previous typical drop height of 160 cm to 200 cm. The wall thickness in the narrowing section of the lamp shafts was approximately 3.8 mm in both cases.

[0019] Fig. Figure 3 shows a schematic representation of another embodiment of a short-arc discharge lamp 40, designed for AC operation. For this reason, the two electrode heads 41, 42 are identical. Otherwise, the lamp differs in Fig. 3 of those in Fig. 1. by an alternative design of the damping guide element intended for the narrowing section. In this context, reference is also made below to the Fig. Reference is made to Figure 4, which shows an enlarged view of area II of the constriction section 10. This is a foil 44 made of molybdenum formed into a cuff. The foil 44 has embossed bumps 45 that rise towards the surrounding wall of the lamp shaft 6. The cuff 44 is first pushed over the electrode rod 22 and then the entire assembly is inserted into the lamp shaft 6. During the rolling up of the constriction section 10, the heated quartz glass of the lamp shaft 6 is soft in this area, allowing the bumps 45 to press slightly into the shaft wall. This achieves a similar axial fixation as in the previous case with the wire coil ( Fig. 1 and Fig. 2) Furthermore, the bumps 45 dampen the electrode rod 22 upon impact. The damping effect can be further enhanced if additional bumps protruding towards the electrode rod are embossed (not shown).

[0020] In a fracture test, a short-arc discharge lamp with a dimpled molybdenum foil in the constriction section exhibited a breaking strength of 70 g (impact direction perpendicular to the lamp's longitudinal axis), corresponding to an approximate drop height of 380 cm. The wall thickness in the constriction section of the lamp shaft was approximately 3.7 mm in this case.

[0021] A further improvement may be achieved by combining a springy wire helix and foil in the narrowing section.

Claims

[1] Short arc discharge lamp (1) for DC operation with - a lamp vessel comprising a discharge vessel (4) enclosing a discharge medium and two lamp shafts (5, 6) extending coaxially at opposite ends of the discharge vessel (4), - two external power supply sections (15, 16) extending outwards from each of the lamp shafts (5, 6), - two electrodes (2, 3), namely a cathode (2) and an anode (3), each consisting of an electrode rod (22, 32) and an electrode head (21, 31), wherein the electrode rods (22, 32) are arranged along the lamp shafts (5, 6) such that the two electrode heads (21, 31) are opposite each other inside the discharge vessel (4), - a sealing section in each of the two lamp shafts (5, 6), whereby a gas-tight current passage is formed between the two outer current supply sections (15, 16) on the one hand and the two electrodes (2, 3) on the other hand, wherein the sealing section is designed as a step melting of the electrode rods (22, 32) by means of transition glasses, - a constriction section (9, 10) in each of the two lamp shafts (5, 6), which is arranged between the respective sealing section and the electrode head of the associated electrode, wherein the constriction section (9, 10) closely surrounds the electrode rod (22, 32), characterized by , that - between the constricted section (9, 10) of a lamp shaft (5, 6) and the electrode rod (22, 32) of at least one electrode (2, 3) a damping guide element is arranged, wherein the damping guide element is designed as a wire helix (11) which is arranged at least along a part of the constricted section (9, 10) on the electrode rod (22, 32), wherein the wire helix (11) has a first narrower turn for fixing the wire helix (11) on the electrode rod (22, 32) as well as further less narrow turns for damping and wherein the first narrower turn is located at the end of the wire helix (11) facing away from the electrode head (21, 31). [2] Discharge lamp according to claim 1, wherein at least between two adjacent turns of the wire coil (11) a mutual distance is provided. [3] Discharge lamp (1) according to one of the preceding claims, wherein the damping guide element is made of a metal. [4] Discharge lamp (1) according to claim 3, wherein the damping guide element is made of tungsten or molybdenum. [5] Discharge lamp (1) according to one of the preceding claims, wherein the damping guide element extends over the entire length of the constriction section (9, 10). [6] Discharge lamp according to one of the preceding claims, wherein the outer current supply sections (15, 16) are formed by the ends of the electrode rods (22, 32).

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