Patent Publication Number: US-2009218946-A1

Title: Lamp and method for manufacturing same

Description:
The invention relates to a lamp as well as a manufacturing method therefor. Particularly, it relates to flash lamps. 
     A flash lamp according to the preamble of the independent claims is known from DE 102 57 477.4.  FIG. 11  shows the seal known from DE 102 57 477.4. Reference numeral  6  denotes a glass tube which is sealed at one end by a melted-on aluminum seal  7 . Towards the inner side of the tube, the seal  7  has a concave surface  8 , i.e., an outwardly arching surface. 
     Here, the opening of a glass tube is sealed by melted-on aluminum. This may be carried out on both sides in the same way. In order to obtain favorable ignition characteristics of the flashtube, specifically formed auxiliary bodies made of specific materials are melted inside the flash lamp into the sealing aluminum. The auxiliary bodies are made of, or provided with, materials which easily emit electrons so as to be able to readily provide the electrons necessary for sparking. 
     In order to obtain favorable ignition characteristics substantial attention was put on the material selection for the auxiliary bodies because this may improve the ignition quality of the above-described flash lamps. In fact, good ignition of the flash lamps can be achieved by means of this technology. The separate auxiliary body was provided because it was not possible to directly provide the aluminum melted on for sealing the tube opening at the inner surface thereof with the desired material properties. Accordingly, it was necessary to insert a correspondingly made auxiliary body into the tube interior and to melt it onto the sealing aluminum to also bring it into electrical contact. 
     The known structure has the drawback that its manufacture is cumbersome and therefore expensive. First, the auxiliary body has to be produced, next it has to be inserted into the tube interior and then brought into contact in a suitable manner. Moreover, as an auxiliary body is provided in addition to the seal, the dimensions of the flash lamp are comparatively long as the flash length (gap between the electrodes) in the axial direction is lengthened by the axial extension of the two seals and that of the auxiliary body. 
     Both drawbacks—laborious and thus expensive manufacturing method and comparatively large design—comply less and less with modern requirements. On the one hand, more and more disposable cameras (i.e., which serve for exposing a single film) are also equipped with flash lamps. These must be especially cheap. Moreover, an increasing number of mobile electronic devices, such as palms, mobile phones, PDAs, are equipped with cameras which themselves require a flashlight. In this case, in particular the dimension is a critical value. 
     It is the object of the invention to provide a flash lamp and a manufacturing method therefor which permit the assembly of a compact and easily ignitable lamp of long durability in a simple manufacturing process. 
     This object is achieved by means of the features of the independent claims. The dependent claims are directed to preferred embodiments of the invention. 
     A lamp comprises a preferably tubular container consisting of at least partly transparent material, such as glass, in particular quartz glass or hard glass, with at least a first opening sealed by a metallic, preferably aluminum-containing first seal. The surface of the first seal facing the interior of the container includes a convex portion, in particular a dome arching towards the interior of the container. The angle between the inner wall of the container and the surface of the seal may be acute, particularly &lt;90°, preferably &lt;45°. 
     The connection of the first seal to the container and the container wall, respectively, can be achieved by melting the first seal onto the container surface. 
     A lamp, particularly a flash lamp, may include a preferably tubular container consisting of an at least partly transparent material, preferably glass, quartz glass or hard glass, which has a first opening sealed with a first seal that may be metallic and preferably contains aluminum. Inside the container there may be a material which easily emits electrons. The material may include barium and/or caesium. It may be caesium iodide. 
     Cameras and in particular portable telecommunications devices equipped with cameras may include the above-described flash lamps. 
     According to the invention the metal sealing the container opening has an electrical function as a cathode and a mechanical function as a seal. It has surprisingly been found that the comparatively low-melting aluminum is yet suitable as an electrode material. Due to its low vapor pressure, its low tendency to sputter and its good thermal conductivity it does not lead to any blackening of the inner wall of the lamp when it is used as an electrode material. 
    
    
     
       In the following, separate embodiments are described with reference to the drawings, wherein: 
         FIG. 1  shows the general view of a flash lamp, 
         FIG. 2  shows an embodiment of the first seal, 
         FIG. 3  shows another embodiment of the first seal, 
         FIG. 4  shows a cross-section through the lamp and the first seal, 
         FIG. 5  shows another embodiment of the first seal, 
         FIG. 6  shows another embodiment of the first seal, 
         FIG. 7  shows a detail to illustrate geometrical proportions, 
         FIGS. 8A and 8B  show the view of a further embodiment, 
         FIGS. 9A and 9B  show the view of a further embodiment, 
         FIG. 10  schematically shows a process in an embodiment of a manufacturing method, and 
         FIG. 11  shows the illustration of a known seal. 
     
    
    
       FIG. 1  shows the general view of a lamp. It may be a flash lamp. Reference numeral  10  denotes a glass tube,  11  denotes the first seal,  12  stands for a second seal,  13  indicates a first end of the container,  14  signifies a second end of the container,  15  refers to a face surface of the container,  16  denotes the inner wall of the container. Reference numeral  17  stands for the interior of the container,  18  indicates the farthermost inner spot of the first seal,  19  refers to a convex portion, and  20  signifies a material in the interior of the container. 
     The lamp comprises an container which in the embodiment of  FIG. 1  includes a glass tube  10  having a first end  13  and a second end  14 , both of which are to be sealed. The glass tube  10  may completely or partly consist of quartz glass or hard glass. The first end  13  of the tube is sealed by the first seal  11 . The second end  14  may be sealed by the second seal  12 . Generally, a second seal  12 , which is to be provided if needed, may be formed like the first seal  11  (as to shape and/or material). At least one of the seals and preferably both form the electric connections of the lamp. It is not necessary to differ between cathode and anode of the flash lamp in every case. 
     The first seal includes aluminum or an aluminum alloy. Due to their material characteristics with respect to durability, connectibility with the surrounding glass and electric values, aluminum and aluminum alloys are very suitable materials. The seal does not include auxiliary bodies, at least not of the kind which would have an electrical function as an interior anode or cathode. The surface of the first seal  11  facing the interior  17  of the container may directly be the material of which the first seal  11  is made. Its material composition may be comparatively homogeneous across the whole volume, which, however, does not exclude the provision of coating layers. It is preferred for the first seal not to include any auxiliary body. It will then have a comparatively homogeneous structure. However, a contact may for example be cast onto or into the outside. 
     When the first seal is produced (attachment to the tube), it is ensured that in the end the interior surface of the first seal  11  is not oxidized. This may comprise removing any previously generated oxide layers and/or subsequent working in an inert or evacuated environment. 
     The first seal  11  may be formed inside without an auxiliary body. The surface of the first seal  11  facing the interior  17  of the container is convex in at least some parts and may be dome-shaped, as shown in  FIG. 1 . Here, “convex” should be understood as parallel to the longitudinal direction of the lamp (transverse direction of  FIG. 1 ) in a sectional plane. 
     The connection of the first seal  11  to the glass tube is vacuum-tight and gastight, respectively. Neither does ambient air from outside enter into inside the glass tube nor does the gas filling of the tube in turn pass from inside to the outside during the life-time of the flash lamp. The gastight connection between the first seal  11  and the glass tube  10  can be made at the inner wall  16  of the glass tube  10 . However, the connection between the first seal  11  and the face  15  of the glass tube may also be gastight if and as far as this face  15  is covered by the first seal  11 . 
     The outside surface of the first seal  11  may level with the face  15  of the tube  10 . It may also arch convexly to the outside or concavely to the inside. The first seal  11  may completely or partly cover the face  15 . On the left,  FIG. 1  shows a seal  12  that does not cover the face of the tube  10  and the outside surface of which convexly arches to the outside. The first seal  11  on the right-hand side of  FIG. 1  is also convex on the outside and partly covers the face  15 . 
     Reference numeral  18  denotes the spot of the first seal  11  extending farthermost into the tube, i.e. which is closest to the other, opposite electrode. In any way, it is preferred that this portion  18  be convex. The first seal  11  is electrically conductive and forms a first electrode of the lamp. The second seal  12  may be conductive and form the second electrode of the lamp. The foremost portion  18  does not abut the inner wall  16  of the glass tube  10 . Rather, it is spaced apart therefrom, preferably by at least 10% of the inner diameter d i  of the tube. 
     The invention as described by means of the embodiment of  FIG. 1  is an obvious improvement of the known flash lamp. It has been shown that good ignition characteristics can already be achieved if the inner surface of the seal is convex. A specific electrode material which easily emits electrons is not necessary. Therefore, the auxiliary body and the production labor related thereto are no longer required. The dimension is reduced according to the omitted auxiliary body. 
       FIG. 2  shows another embodiment of the first seal. In the Figures, the same reference numerals generally refer to the same features. The first seal  11  has a convex portion  19  which is formed in a comparatively pointed shape. In an extreme case, it might be a conical construction of which the point, which also forms the farthermost inner portion  18 , is hardly rounded or not rounded at all. The outside surface of the first seal  11  is level and located in the same plane as the face  15  of the tube  10 . 
       FIG. 3  shows an asymmetrical embodiment. Reference numeral  31  shows a symmetry axis which in the case of a glass tube is its longitudinal axis in the center. The first seal  11  is asymmetrically shaped with respect to the symmetry axis  31 . Though it includes a convex portion  19 , the farthermost inner portion  18 , however, is not positioned on the symmetry axis  31  but is offset against it to the side (vertical direction in the drawing plane). But it does not abut the inner wall  16  of the tube either. The offset against the symmetry axis  31  is preferably smaller than 30% of the inner diameter d i , more preferably smaller than 15% or smaller than 5%. 
     The outside surface of the first seal  11  can be shaped in such a way that it is solderable. For example, the shaping may comprise a coating  32  which completely or partly covers the outside surface of the first seal  11 . The coating consists of a different material or alloy than the material of the first seal  11 . 
       FIG. 4  shows a section through the flash lamp perpendicular to its longitudinal axis near the face  15 . The section runs through the material of the tube  10  as well as the material of the first seal  11 . The interface between the two materials at the inner surface  16  of the tube  10  is the gastight connection sealing the outer space against the interior. The shape of the cross-section may be circular, but does not have to be. It may be oval. The shape of the cross-section may be constant or variable along the length of the lamp (transverse direction in  FIG. 1 ). The dimensions, such as the inner diameter d i  or the outer diameter d a , may also be constant or variable along the length. 
     In the case of a constant circular cross-section, the outer diameter d a  is preferably &lt;20 mm, more preferably &lt;10 mm, more preferably &lt;5 mm and more preferably &lt;3 mm. The inner diameter d i  is preferably &lt;18 mm, preferably &lt;8 mm, more preferably &lt;3 mm, more preferably &lt;2 mm. The flash length  1   a  (gap between the electrodes of the lamp, more concretely between the foremost portions  18  of the seals) is preferably &lt;15 mm, more preferably &lt;6 mm, more preferably &lt;3 mm, more preferably &lt;2 mm. 
       FIG. 5  shows an embodiment of the first seal  11  which also includes concave portions  51   a ,  51   b  in the section plane parallel to the longitudinal direction. It is not necessary that the complete inner surface of the first seal  11  be convex. Apart from the convex portion  19  a concave portion  51  may be provided as well. In the embodiment of  FIG. 5 , a concave portion  51 , which in the present embodiment reaches up to the inner wall  16  of the glass tube  10 , is concentrically located around the convex portion  19 . The farthermost inner portion  18  of the first seal  11  is located in the convex portion  19 . 
       FIG. 6  shows another embodiment of the first seal  11 . The convex portion  19  is shaped like a head. A concave portion  51  forms a constriction  62  which forms the head  61  as a convex portion  19 . The diameter d 1  of the head  61  is larger than the diameter d 2  of the constriction  62 . 
       FIG. 7  shows a detail as to dimensioning instructions. The angle α between the inner wall  16  of the tube  10  and the surface of the first seal  11  is shown. It is taken to the surface of the first seal  11  between the inner wall  16  and the tangent. The angle α is preferably &lt;90°, more preferably &lt;60°, more preferably &lt;30°. As far as the proportions are not constant, average values across the circumference will have to be applied. In this case it is not necessary to apply microscopic proportions but is possible to consider the geometry prevailing in a portion the size of which is 10% of the inner diameter d i  away from the inner wall  16  towards the center. 
     The material of the first seal contains aluminum. It may be a specific aluminum alloy. The aluminum or its alloy does not include elements which vaporize easily. Pure aluminum (weight proportion in particular &gt;98%, preferably &gt;99.9%) may also be used. 
     The interior  17  of the lamp contains an inert gas, preferably xenon, at a predetermined filling pressure. It is preferred for the interior  17  of the lamp to also contain a material which easily emits electrons. The material may include pure caesium and/or barium or compounds of these elements. It may include caesium iodide. At room temperature, the material is present as gas or vapor. Liquid droplets may also be present. 
     As far as it is stated that the first seal does not include an auxiliary body this may be understood implicitly or to the effect that it does not include an auxiliary body with an electrical function, in particular as an inside cathode and anode, respectively, of the flash lamp. However, auxiliary bodies with a different function, for example, for forming a volume at the seal, may be provided, such as a molded-in body consisting, for example, of glass, which seals at least a part of the volume of the opening and is at least partly surrounded by the aluminum-containing material. 
     Preferably at least 20%, more preferably at least 40%, of the surface of the first seal located inside the container are convexly shaped. 
     Starting from the face  15  of the tube, the depth of penetration t of the first seal  11  into the interior of the tube is preferably smaller than twice the inner diameter d i  of the tube. 
     The first seal can be melted on the container wall—as schematically shown in FIG.  10 —as a method for manufacturing the seal and the lamp, respectively, in a way that the liquid or doughy material  112  of the seal is pressed against the capillary resistance and possibly against the material resistance from a supplied external device  110  into the opening of the container  10  to be sealed where it cools and solidifies. When it is pressed inside, the material at first only passes to the face of the tube  10  (dashed surface  114 ) while lying inside the device  110  (dashed surface  113 ), then begins to extend into the tube  10  (dashed surface  113 ) and finally assumes the ultimate position (surface  113 ) in which it solidifies. The symbol  111  denotes heating means. Controlled pressing means which effect that the material is pressed inside are not shown. An optical sensor may be provided for the control feedback. 
     Comparatively pure aluminum can be processed in a temperature range of above 660° C. and preferably below 700° C. It may also be processed in a temperature range below 660° C. and preferably above 640° C. When it is still in a warm state exchange processes (diffusion) after the pressing-in take place between the seal material and the material of the container wall which result in an intimate and durable vacuum-tight connection. 
     Depending on the temperature of the pressed-in material the process may include features of impact extrusion, i.e. wherein more or less doughy material is pressed into the opening with the required pressure. 
     As an alternative, the method may provide the formation of a preshaped solid formed body which is positioned in the opening to be sealed and, if needed, is subsequently heated together with the material of the container until is softens (doughiness) or melts to a degree that it melts onto the wall. 
     In all above-mentioned method options the container material may be preheated at least in the area of the opening to be sealed, particularly up to a temperature of over 100° C., preferably over 200° C. Method processes may take place in an inert atmosphere or in a vacuum. After the material has been melted on, it is possible to control the course of the cooling, for example via adjusting the ambient temperature, heat supply, cooling or the like. These parameters may also change with time. 
     In all previous embodiments, the metal seal assumed an electrical function (in particular contacting from the inside of the lamp to the outside of the lamp, formation of electrodes, arranging the ignition and burning characteristics) as well as a mechanical function (gastight, preferably vacuum-tight seal of an opening). In the embodiments described below with reference to  FIGS. 8 and 9 , however, a division of labor can be made such that the mechanical function (sealing) is effected by a glass/glass connection and a glass/metal connection, respectively, with the metal being a contact pin in the latter that penetrates the glass seal and preferably is comparatively refractory, for example includes molybdenum or tungsten or Kovar (Fe—Ni—Co alloy). It is not necessary to produce a gastight or vacuum-tight glass/aluminum connection such that insofar operations under protective gas or in an evacuated state may be avoided. The electrical function in the interior on the other hand is fulfilled by a body located inside and including or consisting of aluminum. This body may have shape features towards the interior, in particular a convex portion  19 , as described in relation to the previous embodiments. 
       FIG. 8   a  shows the preparative step during the manufacture of the lamp and in particular the sealing of one end of the lamp. Reference numeral  81  denotes a metal pin which contributes to the electric contacting from the outside to the inside of the lamp. It is preferred that it includes a refractory material (melting point &gt;1000° C.), such as molybdenum and/or tungsten and/or Kovar. This pin  81  is provided in advance with a collar  82  made of glass by melting it for example vacuum-tightly onto the pin  81 , the outer diameter of which is slightly smaller than the inner diameter of the tube  10 . Moreover, a body  83  consisting of a metal material, in particular including or consisting of aluminum, is loosely placed into the interior of the lamp. The body  83  may be an annular body which is pulled over the inner end of the pin  81 . The outer dimensions of the body  83  are also smaller than the inner dimensions of the tube  10 . 
     As shown in  FIG. 8   a , this structure is pushed inside the tube  10 . This may be effected in an ambient atmosphere and at room temperature. Then the general structure is heated. This results in the glass collar  82  melting onto the inner wall of the tube  10 , thus causing the sealing of the tube. The body  83  will also melt, attach to the inner wall of the tube and also melt onto the pin  81 . The connection between the melted-on body  83  (see body  85  in  FIG. 8   b ) and the inner wall of the tube  10  need not be gastight but may be a simple physical, electrically conductive adjacency. 
       FIG. 8   b  shows the final state: The body  85 , the shape of which has been changed (due to melting and resolidification) adjoins the pin  81  on the one hand and the inner wall of the tube  10  on the other hand. The pin  81  penetrates the body  85  and its inner end forms the innermost portion  18 . The symbol  84  denotes the material which corresponds to the preglassification  82  and is intimately amalgamated with the inner wall of the tube  10 . The pin  81  has an end protruding outside which is used for the outer contacting of the lamp. 
     Thus, with its electric properties the inner aluminum body  85  may contribute to the improvement of the discharge characteristics and ignition characteristics of the tube. In particular, it has surprisingly been found that aluminum is generally well suited as an electrode material. It has a low tendency to sputter and a low vapor pressure and, contrary to the usual expectations, will thus not contribute to blackening the inner wall of the tube even after repeated discharges despite its comparatively low melting point. This especially applies if comparatively pure aluminum is used (also in the embodiments described before), that is, aluminum of a purity of &gt;99 wt. %, preferably &gt;99.9 wt. %, more preferably &gt;99.97 wt. %. 
       FIGS. 9   a  and  9   b  qualitatively show the same Figures as  FIGS. 8   a  and  8   b  such that in the following only the differences are described. In  FIG. 9   a , the preformed body  86  is no longer shaped as a cylinder in such a way that it could be pushed over a free end of the pin  81 . It is rather a block that tends to be massive and simply lies on the free end of the pin  81  before it is melted on. The material of the block  86  may be aluminum or include aluminum and may particularly be of a purity as described above. The inner end of the pin  81  is comparatively short but it penetrates the preglassification  82  towards the inside such that the pin  81  may be metallic resulting from the metal of the body  86  and thus be electrically contacted therewith. 
     In the final state ( FIG. 9   b ) the melted-on and resolidified body  87  covers the pin  81  completely such that the body  87  exclusively effects the electrical contacting towards the inside. The farthermost inner portion  18  then corresponds to those as shown in  FIG. 1 to 7 . 
     In the embodiment of  FIGS. 9   a  and  9   b  an annular body  83  as shown in  FIG. 8   a  may initially be used, as a massive body  86  as shown in  FIG. 9   a  may in turn initially be used in the embodiment of  FIGS. 8   a  and  8   b.    
     The features of the various embodiments described in the specification may be combined as far as they are no technical alternatives which exclude each other.