Patent Publication Number: US-6703769-B2

Title: Short-arc type discharge lamp having ventillation apertures at the bottom of the bases

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention concerns a short-arc type discharge lamp and a light-source device that uses a short-arc type discharge lamp. 
     2. Description of Related Art 
     In recent years, liquid-crystal projectors and DMD projectors have come into extensive use as presentation tools, and short-arc type discharge lamps, such as metal halide lamps or mercury lamps, have been used since high brightness is required of such light sources for projection. In addition, short-arc type xenon lamps have been used in projector light sources that project large pictures. 
     Short-arc type discharge lamps, for example, xenon lamps, have a pair of electrodes disposed facing each other within a quartz glass emission envelope in which xenon gas is sealed, and a sealing tube is connected to each of opposite sides of the emission envelope. Electrode core rods with electrodes formed at the tips are hermetically sealed within the sealing tube in step-seamed glass sealed lamps. The electrode core rods extend out from the step-seamed glass section and double as external lead rods, and the lead lines comprising twisted wires are connected to the tail edge of the external lead rods by soldering. In addition, the cylindrical bases with bottoms are bonded by adhesive to the sealing tube, and the external lead rods and the lead lines are covered by this base. The edge of the lead wire is connected to the terminal of the base. 
     The foil sealing method, in which the edge of the electrode core rod and the edge of the external lead rods are individually connected to metal foil and the metal foil is hermetically embedded in the sealing tube, may be used instead of the step-seamed glass sealing method. 
     Incidentally, projector light-source devices reach extremely high temperatures during lighting of xenon lamps that are disposed in the casing, and external lead rods made of tungsten or molybdenum also reach high temperatures. When external lead rods reach high temperatures, the step-seamed glass section also reaches high temperatures and distortion develops. Such distortion brings about cracking of step-seamed glass. 
     Furthermore, oxidation rapidly proceeds at high temperatures since the external lead rods within the base are exposed to the atmosphere. Force that spreads open quartz glass comprising the step-seamed glass sealing sections acts when such oxidation is transmitted to the section of the external lead rods within the sealing tube, and that also can generate cracking. 
     The external lead rods and metal foil within the foil seal section oxidize when a lamp reaches extremely high temperatures even in the case of a foil sealed lamp, and the quartz glass comprising the foil seal section cracks. 
     For this reason, a pair of ventilation apertures facing each other have been formed about the periphery of the base or cooling fins have been established on the outer surface of the base in the past. However, cooling air within the light-source device often flows along the axial direction of the lamp even if ventilation apertures are formed about the periphery of the base, so that little cooling air flows to the interior of the base from the ventilation aperture orthogonally to the axis of the lamp, and the external lead rods within the base cannot be adequately cooled. The cooling air entering the base and circulating along the external lead rods results in cooling only of a narrow region of the external lead rods. Furthermore, since cooling fins established on the outer surface of the base effect cooling by using the heating attributable to thermal conduction, the external lead rods within the base cannot be adequately cooled by these either. 
     Recently, limits have been imposed on the overall lamp length in light of the demand for miniaturization of projectors, and the gap between external lead rods and electrodes, which reach high temperatures during lighting, has become narrower. Accordingly, the temperature elevation of external lead rods has become increasingly pronounced, and the problem of shorter lamp life attributable to high temperature oxidation of external lead rods has been demonstrated. 
     SUMMARY OF THE INVENTION 
     Thus, the purpose of the present invention is to provide a short-arc type discharge lamp and a light-source device that uses a short-arc type discharge lamp in which high temperature oxidation of external lead rods is restricted to prolong lamp life. 
     To attain such objectives, the invention provides a short-arc type discharge lamp in which a pair of electrodes are disposed facing each other within an emission envelope made of quartz glass, external lead rods electrically connected to said electrodes extend from sealing tubes connected to each of opposite ends of the emission envelope, and are electrically connected to cylindrical bases with bottoms that are attached to at least one of the sealing tubes, a first aperture is formed for ventilation about the periphery of the bases and a second aperture for ventilation is formed at the tail edge of at least one of the bases to facilitate the circulation of cooling air within the bases and to thereby adequately cool the external lead rods within the bases. 
     Also in accordance with the invention, a heat dissipation section is formed at the external lead rods or the lead lines within the base. Additionally, according to the invention, a ventilation-concentration hood can be provided which conducts cooling air to the first aperture for ventilation, and that permits more efficient cooling of the external lead rods within the base. 
     The invention also concerns a light-source device in which the short-arc type discharge lamp and a concave reflection mirror surrounding this short-arc type discharge lamp are disposed in a casing, wherein a threaded section is formed about the periphery of the base, an attachment hole is formed in the lamp retaining plate, and the short-arc type discharge lamp is retained by inserting said base in the attachment hole of the lamp retaining plate and screwing it. 
    
    
     The mode of implementing the present invention is explained in detail with reference to the appended diagrams. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of a step-seamed sealed xenon lamp in accordance with the present invention. 
     FIG. 2 is a sectional view of a foil-sealed xenon lamp according to the present invention. 
     FIGS.  3 ( a ) &amp;  3 ( b ) are sectional views of embodiments in which a heat dissipation section is provided. 
     FIGS.  4 ( a ) &amp;  4 ( b ) are sectional views of embodiments in which ventilation-concentration hoods are provided. 
     FIG. 5 is a perspective view of another embodiment of the bases. 
     FIG. 6 is a perspective view of the light-source device. 
     FIGS.  7 ( a ) and  7 ( b ) are cross-sectional views for explaining two different versions of the lamp support structure. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     FIG. 1 shows a short-arc type xenon lamp that is sealed by the step-seamed glass sealing method. In FIG. 1, a roughly spherical emission envelope  11  is made of quartz glass and has sealing tubes  12  integrally formed at each of opposite ends. Xenon gas is sealed within emission envelope  11  and an anode  21  and a cathode  22  pair of electrodes are disposed facing each other within the envelope  11 . Anode  21  and cathode  22  are integrally joint to the tips of electrode core rods  23  made of tungsten. 
     Step seamed glass sections  13  are disposed within sealing tubes  12  and the pair of electrode core rods  23  are hermetically sealed by sealing sections  14  of step seamed glass sections  13 . Accordingly, electrode core rods  23  protrude from sealing sections  14  so that the protrusions double as external lead rods  24 . Lead lines  25 , comprising twisted wires, are connected at the tips of external lead rods  24  by soldering. Bottomed cylindrical bases  30  are bonded by adhesive  39  to the sealing tubes  12 , and the external lead rods  24  as well as lead lines  25  are situated in a space formed within the bases  30 . The tips of lead lines  25  are then connected by solder to contact points  33  of bases  30 . 
     FIG. 2 shows a short-arc type xenon lamp sealed by the foil sealing method. In FIG. 2, the tips of electrode core rods  23  are welded to metal foil  26  made of molybdenum and a tip of each external lead rod  24  is welded to each metal foil  26 . Metal foils  26  are disposed within sealing tubes  12 , the quartz glass of sealing tubes  12  is softened by heating and contracted to form a de-pressurized state within sealing tubes  12 , thereby embedding metal foils  26  within sealing tubes  12  and sealing them. The softened sealing tubes  12  are crimped to complete embedding of metal foils  26 . Other structures are identical with those of the xenon lamp shown in FIG.  1 . 
     In both cases, at least one (two being shown) first ventilation aperture  31  is formed in the periphery of each base  30 , and at least one (two being shown) second ventilation aperture  32  is also formed in the tail end of each base  30 . Accordingly, since cooling air flows within the device in the axial direction of the xenon lamp, cooling air enters bases  30  from second ventilation apertures  32  formed when the bases  30  are situated upstream of the flow of cooling air and it flows along the lead lines  25  and the external lead rods  24 , then exhausting from the first ventilation apertures  31 . Cooling air enters bases  30  from first apertures  31 , flows along external lead rods  24  and lead lines  25 , and exhausts from second aperture  32  when the bases  30  are situated downstream of the flow of cooling air. 
     In both cases, a greater amount of cooling air can be circulated within bases  30  than when the direction of flow of cooling air within bases  30  is orthogonal to the direction of flow of cooling air within the device as occurs when ventilation apertures are established only in the periphery of the bases  30  since the direction of flow of cooling air within bases  30  coincides with the direction of flow of cooling air within the device. Furthermore, external lead rods  24  are cooled more efficiently coupled with the influx of large amounts of cooling air within bases  30  since cooling air entering bases  30  flows along external lead rods  24  and lead lines  25  that are connected to external lead rods  24 . 
     A heat dissipation section should be established in external lead rods  24  and lead lines  25  to cool external lead rods  24  more efficiently. FIG.  3 ( a ) shows an example of a heat dissipation section  27  in which the twisted wires forming lead lines  25  are disentangled to form an expansion section to increase the contact area with cooling air. FIG.  3 ( b ) shows an example in which cooling fins are attached to the lead lines  25  to form heat dissipation section  28 . Cooling fins may be attached to external lead rods  24  when external lead rods  24  within each base are long. 
     Ventilation-concentration hoods  38  may be mounted as shown in FIGS.  4 ( a ) &amp;  4 ( b ) to inject large amounts of cooling air from the first ventilation apertures  31  which are formed about the periphery of bases  30  downstream of the cooling air into each base  30 . FIG.  4 ( a ) shows the case in which ventilation-concentration hoods  38  are attached integrally with bases  30 , while FIG. ( 4   b ) shows the case in which ventilation-concentration hoods  38  are attached integrally with lamp support plate  51 . However, in both cases, the direction of flow of cooling air along the xenon lamp can be forcibly altered by ventilation-concentration hoods  38  to conduct more cooling air into each base  30 . 
     There are no specific limitations on the number, shape or aperture area of first ventilation apertures  31  and second ventilation apertures  32 , but increasing the sum of the aperture areas as much as possible is desirable. Furthermore, apertures may be cut at the corners of bases  30 , as shown in FIG. 5, so that part of the corner aperture constitutes first ventilation aperture  31  and part of the corner aperture constitutes the second ventilation aperture  32 . 
     The shapes of the lamps shown in FIGS. 1 &amp; 2 are symmetrical, and the heating conditions on both the cathode side and the anode side are roughly equal. Consequently, if the second aperture  32  is formed in the base  30  on the cathode side and in the base  30  on the anode side, and one of the sealing tubes  12  is lengthened to moderate the heating conditions of external lead rods  24 , the second aperture  32  need only be formed at base  30  on the side where sealing tube  12  is shorter and experiences more severe heating conditions. 
     FIG. 6 shows the light-source device in which the short-arc type xenon lamp  10  shown in FIG. 1 is the light-source lamp. Light output aperture  52  is formed at the front of box-shaped casing  50 . In addition, cooling air inlet aperture  53  is formed at the top of casing  50  while cooling air vent aperture  54  is formed at the back. Xenon lamp  10  with consumed power of 2000 W, for example, and concave reflection mirror  40  are disposed within casing  50 . 
     The xenon lamp  10  is held by a lamp support plate  51  that is erected on the bottom of casing  50 . Threaded section  34  is formed about the periphery of each base  30 , as shown in FIG.  7 ( a ). An attachment hole  51   a  is opened in lamp support plate  51 , and threads are formed on the inner surface of attachment hole  51   a  as well. Base  30  is fixed to lamp support plate  51  by screwing threaded section  34  of base  30  into attachment hole  51   a . FIG.  7 ( b ) shows an example in which base  30  is fixed to lamp support plate  51  by inserting base  30  into attachment hole  51   a  and screwing nut member  59  into threaded section  34  without forming any threads on the inner surface of attachment hole  51   a . In both cases, large amounts of cooling air can enter base  30  since second aperture  32  formed at the tail end of base  30  does not hinder lamp support plate  51  and is not obstructed by it. 
     The reflection surface of concave reflection mirror  40  has an aperture  41  formed at its apex. One sealing tube  12  of xenon lamp  10  is inserted in aperture  41 , and concave reflection mirror  40  surrounds xenon lamp  10  so that the optical axis matches the axis of xenon lamp  10 . 
     However, light released from the are bright point formed between the electrodes reflects off concave reflection mirror  40  and is emitted from the light output aperture  52  when the xenon lamp  10  is lit. In addition, cooling air enters casing  50  from cooling air inlet aperture  53  and cools the xenon lamp  10  as well as the concave reflection mirror  40 . As mentioned above, the external lead rod  24  is efficiently cooled since large amounts of cooling air enter base  30  from the first aperture  31  of base  30  and exit via the second aperture  32 . The cooling air is exhausted via cooling air vent aperture  54 . 
     The temperature of external lead rods  24  during lighting were actually measured in a light-source device using xenon lamp  10  with power consumption of 2000 W. The site of temperature measurement was the surface of external lead rod  24  near sealing sections  14 . The cooling air had a static pressure of 40 Pa and air volume of 2 m 3 /min. In addition, the temperature of a conventional xenon lamp without a second aperture  32  at the tail end of the base  30  was similarly measured. The results indicated the temperature of external lead rods in this embodiment to be 420° C. while the temperature in a conventional example was 500° C. In short, the temperature difference was about 80° C. 
     Incidentally, the step-seamed glass section cracked in the xenon lamp of this embodiment within 500 to 1000 hours of operation at 500° C., but cracks did not develop at 420° C. even after the elapse of over 2000 hours. As for glass cracking at the seal due to oxidation of metal foil or external lead rods, the life of the seal is concluded to be prolonged by an order of magnitude when the temperature falls below 150° C. Accordingly, if the seal life is 2000 hours when the temperature of the external lead rods is 500° C., the life of the seal of a xenon lamp pursuant to this embodiment would be expected to be 8000 hours if the temperature of the external lead rods is 420° C. 
     Effects of Invention 
     As explained above, external lead rods are efficiently cooled by the influx of large amounts of cooling air into the bases since a first aperture is formed for ventilation about the periphery of the bases and since a second aperture for ventilation is formed at the tail edge of the bases. Accordingly, high temperature oxidation of external lead rods can be inhibited and an emission envelope lamp with a long life can be provided. Furthermore, external lead rods can be cooled more efficiently by mounting a heat dissipation section for external lead rods and lead lines and by mounting ventilation-concentration hoods at the first aperture. 
     The light-source device using such a discharge lamp can serve as a highly-reliable light-source device with a lower lamp replacement frequency. The total lamp length can be shorter than in the past since the external lead rod temperature is lower and the light-source device can be miniaturized.