Abstract:
A flange portion is integrally formed with a stem which forms a sealing envelope for a gas discharge tube. Accordingly, operation for building and fixing the flange portion is not necessary, so that lamp assembly operation is simplified, and mass production is facilitated. In addition, when a gas discharge tube is to be fixed to an external stem setting portion, lamp setting is enabled at higher precision by utilizing positioning holes formed in the flange portion in advance.

Description:
RELATED APPLICATION 
     This is a continuation-in-part application of international application serial no. PCT/JP98/05818 filed on Dec. 22, 1998, now pending. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a gas discharge tube; and, more particularly, to a gas discharge tube for use as a light source for a spectroscope, chromatography, or the like. 
     2. Related Background Art 
     As a conventional technique of this field, one disclosed in Japanese Patent Laid-Open No. 7-326324 is available. As shown in FIG. 9, a gas discharge tube (deuterium lamp)  100  described in this reference has a glass sealing envelope  101 , and a light emitting part assembly  102  is held in the sealing envelope  101  in a floating state. The light emitting part assembly  102  is comprised of an anode plate  105  sandwiched by ceramic support plates  103  and  104 , a cathode section  106  located above the anode plate  105 , and a converging electrode plate  107  arranged between the anode plate  105  and cathode section  106 . To use this discharge lamp, a predetermined voltage is applied to the anode plate  105 , cathode section  106 , and converging electrode plate  107  to cause arc discharge above a converging opening  107   a  of the converging electrode plate  107 , and light generated by arc discharge is emitted outside through a light projecting window  101   a  of the sealing envelope  101 . Emitted light is guided to an optical system for focusing the light or transmitting it through a fine slit. In order to increase the light use efficiency, a portion having the highest light intensity, i.e., the emission central point, must be set on the optical path. The lamp  100  must be reliably set at a predetermined position of a lamphouse  108  and the emission central point must be accurately positioned. For this purpose, in this conventional apparatus, a flange member  109  as a separate component is fixed to the lamp  100  through an adhesive R, so that the lamp  100  can easily be set in a lamp accommodating recess  110  of the lamphouse  108 . To fix the flange member  109  by adhesion, the flange member  109  is aligned with the emission central point of the lamp  100  while observing it, and the flange member  109  is fixed to the outer surface of the sealing envelope  101 . When setting the lamp  100  in the lamphouse  108 , set screws  111  provided in the lamp accommodating recess  110  are inserted through screw insertion holes  112  in the flange member  109 , and the lamp  100  is fixed to the lamphouse  108  by using the set screws  111  and nuts  113 . Stem pins  114  of the lamp  100  are inserted in a socket  115 , thereby setting the lamp  100 . Hence, the emission central point can be arranged on a predetermined optical path. 
     SUMMARY OF THE INVENTION 
     The conventional gas discharge tube described above suffers the following problems. The flange member  109  is a component separate with respect to the lamp  100 , and is fixed to the lamp  100  through the adhesive R. As a result, the positional relationship between the flange member  109  and the emission central point of the lamp  100  may undesirably change while the adhesive R is set. It takes time to adhere the flange member  109 . Even if the emission central point and the flange member  109  of the lamp  100  are precisely aligned with each other, when setting the lamp  100  in the lamp accommodating recess  110 , the screw insertion holes  112  are not suitable for high-precision alignment as they are holes in which the set screws  111  are to be inserted. Alignment of the emission central point of the lamp  100  must accordingly be performed depending on the skill of the operator or a predetermined adjusting jig. Therefore, the lamp  100  cannot be positioned in the lamp accommodating recess  110  easily and reliably at high precision. 
     The present invention has been made to solve the above problems, and has as its object to provide a gas discharge tube in which an assembling workability and an attaching precision with respect to an optical system are improved. 
     In order to solve the above problems, according to the present invention, there is provided a gas discharge tube in which a gas is sealed in a sealing envelope at least part of which can transmit light, and discharge is caused between an anode section and a cathode section arranged in the sealing envelope, so that predetermined light is emitted through a light transmitting portion of the sealing envelope. This sealing envelope comprises a stem for securing the cathode and anode sections by way of respective stem pins independent from each other, and a side tube, at least part of which is made of a light transmitting material, surrounding the cathode and anode sections and being joined to the stem. Wherein the stem has an integrally formed flange portion extending in a direction perpendicular to an axial direction of the side tube and having a positioning reference portion when attaching the gas discharge tube to an external fixing member. 
     In this gas discharge tube, since the flange portion is integrally formed with the stem, operation for constructing and fixing the flange portion is not necessary when assembling the lamp, so that lamp assembly operation is simplified, and mass production is facilitated. In addition, since the positioning reference portion is positively formed on the flange portion integrated with the stem, lamp setting is enabled at higher precision. 
     The gas discharge tube preferably further comprises an anode support plate in contact with a surface of the stem which is inside the sealing envelope, and supporting the anode section on an opposite surface thereof, a ceramic spacer in contact with an exposed surface of the anode support plate and having an opening for exposing the anode section therethrough, and a converging electrode plate in contact with the exposed surface of the spacer to oppose the anode section and having a converging opening coaxial with the opening of the spacer, the converging electrode plate being made of a conductive member. 
     When this arrangement is employed, since the stem, the anode support plate, the spacer, and the converging electrode plate are stacked to be in contact with each other, heat generated by the anode section or converging electrode plate can be radiated outside through the stem  4 . Hence, the stem functions as a heat sink. In assembly, the positional relationship between the stem and the converging electrode plate can be regulated at high precision with the simple assembly operation of stacking the respective constituent members on the stem. This contributes to alignment of the emission central point with the flange portion integrated with the stem. 
     The positioning portion preferably has a positioning hole or notch for inserting a positioning pin inserted another end in a positioning hole formed in a stem setting portion of an external fixing member where the gas discharge tube is to be attached, or a positioning pin standing upright from the stem setting portion. In this case, positioning that keeps a relationship between the pin and hole is enabled, and setting is enabled at high precision by a simple structure in which merely a positioning pin, a positioning hole, or a notch portion is formed in the flange portion. 
     Alternatively, the positioning portion preferably has a projecting portion projecting from the flange portion laterally or a cut-off portion formed on an outer surface of the flange portion so as to conform to a shape of a stem setting portion of the external fixing member to which the gas discharge tube is to be mounted. Alternatively, the flange portion may have an outer shape of a predetermined polygon. In this case, the outer shape of the flange portion itself is a characteristic feature. As a result, the flange portion can cope with use situations in various manners with the shape of the projecting portion or the cut-off portion, or by changing its outer diameter itself, so that lamp setting is enabled at high precision with a simple arrangement. 
     The present invention can be understood more sufficiently through the detailed description and accompanying drawings which follow. Note that the detailed description and accompanying drawings are shown merely for illustrative examples and should not be construed to limit the present invention. 
     Further application of the present invention will become apparent from the following detailed invention. Although the detailed description and specific examples show preferable embodiments of the present invention, they are shown merely for illustrative examples. Various modifications and improvements in the spirit and scope of the present invention are naturally apparent to one skilled in the art from the detailed description. 
    
    
     BRIEF DESCRIPTION OF DRAWINGS 
     FIG. 1 is a sectional view showing a gas discharge tube according to the first embodiment of the present invention, and FIG. 2 is a plan view of the same; 
     FIGS. 3 to  8  are plan views respectively showing gas discharge tubes according to the second to seventh embodiments of the present invention; and 
     FIG. 9 is a sectional view showing a conventional gas discharge tube. 
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     Gas discharge tubes according to the preferable embodiments of the present invention will be described in detail with reference to the accompanying drawings. To facilitate the comprehension of the explanation, the same reference numerals denote the same parts, where possible, throughout the drawings, and a repeated explanation will be omitted. 
     FIG. 1 is a sectional view showing a deuterium lamp as a gas discharge tube according to the first embodiment of the present invention. A deuterium lamp  1  shown in FIG. 1 is a head-on-type deuterium lamp. This deuterium lamp  1  has a sealing envelope  2  in which deuterium gas is sealed at about several Torr. A light emitting part assembly  3  is housed in the sealing envelope  2 . The light emitting part assembly  3  has a ceramic anode support plate  5  arranged on a stem  4  in contact with it. An anode plate  6  is arranged on the anode support plate  5  so the anode plate  6  is separate from the stem  4 . The anode plate  6  is fixed by welding to the upper end of a stem pin  10   a  fixed to extend through the stem  4 . 
     A ceramic spacer  7  is arranged on the anode support plate  5  such that they sandwich the anode plate  6 . A converging electrode plate  8  is arranged on the spacer  7  in contact with it. An converging opening  8   a  formed in the converging electrode plate  8  opposes an opening  7   a  of the spacer  7 , and the converging electrode plate  8  and anode plate  6  are set to oppose each other. In this manner, since the stem  4 , anode support plate  5 , spacer  7 , and converging electrode plate  8  are stacked in contact with each other, heat generated by the anode plate  6  or converging electrode plate  8  can be conducted and radiated outside through the anode support plate  5 , spacer  7 , and stem  4 . Hence, the stem  4  serves as a heat sink. The positional relationship between the stem  4  and converging electrode plate  8  is defined at high precision. This contributes to positioning the converging opening  8   a  with respect to the stem  4 . 
     On a side of the converging opening  8   a , a cathode section  9  located above the spacer  7  is provided. The cathode section  9  is fixed by welding to the upper end of a stem pin  10   b  fixed to extend through the stem  4 , and generates thermions as a voltage is applied to it. A discharge straightening plate  11  is provided between the cathode section  9  and converging opening  8   a  at a position away from an optical path (immediately above the converging opening  8   a  in FIG. 1, i.e., formed in a direction of an arrow A). The discharge straightening plate  11  is formed with a rectangular open electron emission window  11   a  for allowing thermions emitted from the cathode section  9  to pass therethrough. The discharge straightening plate  11  is fixed to the upper surface of the converging electrode plate  8  by welding. The discharge straightening plate  11  is provided with a cover plate  12  having an L-shaped section so as to surround a portion above the cathode section  9  and a portion on a side opposite to the electron emission window  11   a , which is behind the cathode section  9 . The cover plate  12  prevents a sputtering substance or evaporated substance produced from the cathode section  9  from attaching to a light projection window  15  made of silica glass or ultraviolet ray transmitting glass. 
     The light emitting part assembly  3  having this arrangement is set in the sealing envelope  2 . In order to fill the sealing envelope  2  with deuterium gas of several Torr, an exhaust tube  13  is fixed to the stem  4 . By utilizing the exhaust tube  13 , air in the sealing envelope  2  can be evacuated once, and after that deuterium gas having a predetermined pressure can be filled in the sealing envelope  2 . After filling, the exhaust tube  13  is closed as shown in FIG. 1, thereby sealing the sealing envelope  2 . The sealing envelope  2  has a Koval metal side tube  14  resistance-welded to the upper surface of the stem  4 . The light projection window  15  made of UV transmitting glass is fixed to the top portion of the side tube  14 . Alternatively, the side tube  14  may be entirely made of glass, so that the top portion of the side tube  14  functions as the glass light projection window  15 . 
     The stem  4  is made of Koval metal, and formed into an almost rhombic flat plate with an overhang-molded flange portion  4 A, as shown in FIGS. 1 and 2. The flange portion  4 A extends in a direction perpendicular to the axial direction of the side tube  14 , and is integrally formed with the stem  4 . The stem  4  is utilized as the reference position with respect to the light emitting part (a-portion before the converging opening  8   a  where an arc ball S is produced) of the deuterium lamp  1 . More specifically, the stem  4  is assembled such that an emission central point P (x mark) of the arc ball S keeps a predetermined distance from a bottom surface  4   a  of the flange portion  4 A. This allows the lamp utilizing the stem  4  to be mounted as it is positioned at high precision. 
     This stem  4  is housed in a cavity-like stem setting portion  17  formed in a lamphouse  16 . In this case, the bottom surface  4   a  of the stem  4  is abutted against a support surface  17   a  of the stem setting portion  17 . A pair of right and left attaching screws  20  extend vertically upward from the support surface  17   a , and screw insertion holes  21  are formed in the flange portion  4 A of the stem  4  at positions corresponding to the respective attaching screws  20 . Hence, when setting the lamp  1  in the lamphouse  16 , the attaching screws  20  are inserted in the screw insertion holes  21  of the flange portion  4 A, the bottom surface  4   a  of the stem  4  is abutted against the support surface  17   a  of the stem setting portion  17 , and after that the lamp  1  is firmly fixed to the lamphouse  16  by using the attaching screws  20  and nuts  19 . In mounting the lamp, the position of the emission central point P is positioned correctly in an axial direction X but incorrectly in a direction Y perpendicular to the axis. This results from the magnitude of the tolerance of the screw insertion holes  21  themselves. 
     In order to achieve positioning of the lamp  1  in the Y direction, positioning holes  22  as an example of a positioning reference portion are formed in the flange portion  4 A of the stem  4 . Positioning pins  23  stand upright from the support surface  17   a  to correspond to the positioning holes  22 . Highly precise positioning not depending on the attaching screws  20  and screw insertion holes  21  is enabled by increasing the fitting precision between the positioning holes  22  and positioning pins  23 . In this case; positioning that maintains the relationship between the pins and holes is enabled. A simple structure wherein merely the positioning holes  22  are formed in the flange portion  4 A enables highly precise lamp setting. Reference numeral  25  in FIG. 1 denotes a bayonet socket for supplying a predetermined voltage to a stem pin  10 . 
     The operation of the deuterium lamp  1  described above will be briefly explained. First, a power of about 10 W is supplied from an external power supply to the cathode section  9  for about 20 sec to preheat it. After that, a DC open voltage of about 150 V is applied across the cathode section  9  and anode plate  6  to prepare for arc discharge. 
     When this preparation is completed, a trigger voltage of about 350 V to 500 V is applied across the cathode section  9  and anode plate  6 . In this case, thermions emitted from the cathode section  9  converge through the converging opening  8   a  of the converging electrode plate  8  while being straightened by the discharge straightening plate  11 , and reach the anode plate  6 . Arc discharge occurs before the converging opening  8   a . Ultraviolet rays obtained from the arc ball S because of this arc discharge are transmitted through the light projection window  15  to be emitted outside. When the emission central point P (x mark) is located on the focal point of a reflecting mirror (not shown), the light intensity of ultraviolet rays coming incident on a light-receiving object (e.g., an optical slit of about 50 μm to 100 μm in a spectrophotometer) can be increased to the maximum. 
     The present invention is not limited to the embodiment described above, but various modifications can be made. For example, the gas to be filled in the sealing envelope is not limited to deuterium gas, but various types of discharge gases such as mercury gas, helium gas, and neon gas, emission of which can be utilized upon arc discharge, can be used. Various types of embodiments are possible as the positioning reference portion. Some of these embodiments will be described. 
     For example, as shown in FIG. 3, as an example of the positioning reference portion, a pair of notches  26  are formed in a rhombic flange portion  4 B to oppose each other, and positioning pins  28  stand upright from a support surface  27   a  of a rhombic stem setting portion  27  to correspond to the respective notches  26 . A lamp  1  can be positioned at high precision by increasing the fitting precision between the notches  26  and positioning pins  28 . In this case, positioning that maintains the relationship between the pins and notches is enabled. A simple structure wherein merely the notches  26  are formed in the flange portion  4 B enables high-precision lamp setting. 
     Similarly, as shown in FIG. 4, notches  29  are formed in a circular flange portion  4 C to oppose each other so as to fit with positioning pins  31 . The bottom surface of the flange portion  4 C is set on a support surface  30   a  of a circular stem setting portion  30 . 
     As shown in FIG. 5, as an example of the positioning reference portion, a pair of positioning pins  32  extend upright from the bottom surface of a circular flange portion  4 D to oppose each other, and positioning holes  34  are formed in a support surface  33   a  of a circular stem setting portion  33  to correspond to the respective positioning pins  32 . A lamp  1  can be positioned at high precision by increasing the fitting precision between the positioning pins  32  and positioning holes  34 . In this case, positioning that maintains the relationship between the pins and notches is enabled. A simple structure wherein merely the positioning pins  32  are formed on the flange portion  4 D enables highly precise lamp setting. 
     As shown in FIG. 6, as an example of the positioning reference portion, a pair of positioning reference projections  35  are formed on a circular flange portion  4 E to extend laterally, and accommodating portions  36   b  conforming to the shapes of the positioning reference projections  35  are formed in a circular stem setting portion  36  to correspond to the respective positioning reference projections  35 . A lamp  1  can be positioned at high precision by increasing the fitting precision between the positioning reference projections  35  and accommodating portions  36   b . The contact area of the flange portion  4 E with respect to a support surface  36   a  is accordingly increased, so that the heat sink function of the stem  4  is improved. 
     As shown in FIG. 7, as an example of the positioning reference portion, a cut-off portion  37  is formed in a circular flange portion  4 F, and a circular stem setting portion  38  has a shape conforming to the outer shape of the cut-off portion  37  so as to correspond to the arcuate cut-off portion  37 . High-precision positioning is enabled by only placing the flange portion  4 F on a support surface  38   a.    
     As shown in FIG. 8, a flange portion  4 G has a square outer shape as an example of the positioning reference portion, and a stem setting portion  39  has a shape conforming to the outer shape of the flange portion  4 G. High-precision positioning is enabled by only placing the flange portion  4 G on a square support surface  39   a . The outer shape of the flange portion  4 G can be any polygonal shape and is not limited to a shape of a regular triangle or regular hexagon. 
     Since the gas discharge tube according to the present invention has the above arrangement, the assembling workability and the attaching precision with respect to the stem setting portion of the opposite part are improved. 
     From the invention thus described, it will be obvious that the invention may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended for inclusion within the scope of the following claims. 
     The present invention can be suitably applied to a gas discharge tube, particularly a deuterium lamp utilized as a light source for a spectrophotometer or chromatography. 
     From the invention thus described, it will be obvious that the invention may be varied in many ways. Such variations are not to be regarded as a departure from the spirit and scope of the invention, and all such modifications as would be obvious to one skilled in the art are intended for inclusion within the scope of the following claims.