Abstract:
A discharge lamp of the short arc type having a trigger wire which can be installed in a state which is suitable for a directional capacity of the electrode regardless of what type of base the lamp has is achieved by the trigger wire on the outside surface of an arc tube having the following characteristic:  
     an annular area that is formed by a portion of the trigger wire which is looped around the arc tube and elastically held against the outside surface of the arc tube;  
     a first holding part which adjoins a first end of the portion of the trigger wire that forms the annular area and which extends in an axial direction along the arc tube;  
     a second holding part which adjoins a second end of end of the portion of the trigger wire that forms the annular area and which extends in the axial direction along the arc tube.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    1. Field of the Invention  
           [0002]    The invention relates to a discharge lamp of the short arc type which is used, for example, as a light source for a projection apparatus and is filled with xenon, or discharge lamp of the short arc type which is used as a light source in semiconductor exposure and is filled with mercury.  
           [0003]    2. Description of the Related Art  
           [0004]    In a discharge lamp of the short arc type which is filled, for example, with xenon, there are cases in which the breakdown voltage is greater than or equal to 30 kV, by which the voltage charge of the operating device is significantly raised. Here, there is the disadvantage that the starting voltage of the operating device punctures and the disadvantages of increasing the size of the operating device and increasing costs. Proceeding from such a circumstance, there is a trigger wire located on the outside surface of the arc tube and thus the breakdown voltage of the lamp is reduced.  
           [0005]    [0005]FIG. 4 is a schematic of a conventional discharge lamp of the short arc type in which the outside surface of the arc tube is provided with a trigger wire. In the figure, an arc tube  11  contains a pair of electrodes, specifically an anode  21  and a cathode  22 . The outside surface of the arc tube  11  is provided with a trigger wire  5 . The trigger wire  5  is formed with an annular area  51  which is in contact with the outside surface of the arc tube  11 . Furthermore, there is a holding part  52  which is connected to this annular area  51  and which extends in the lengthwise direction of the lamp. Part of this holding part  52  is wound around a side tube part  12  which adjoins the arc tube and is attached and is connected to the base  42  on one end of the holding part  52 .  
           [0006]    [0006]FIG. 5 shows a perspective view of only the trigger wire  5 . Here, the holding part  52  is connected by welding or the like to a part of the annular area  51  which is formed in the shape of an uninterrupted ring. The annular area  51  has elasticity to the extent to which it is deformed by application of a force. The length of the wire-like component comprising the annular area  51  is however always constant and never changes. The diameter d of the annular area  51 , in the state before its installation on the arc tube  11 , is smaller than the maximum diameter D of the arc tube shown in FIG. 4. By inserting the annular area  51  from the direction of the base  41  into the lamp the annular area  51  comes into contact with the outside surface of the arc tube  11 , is slipped on and attached.  
           [0007]    [0007]FIG. 6 is a schematic of a conventional discharge lamp of the short arc type in which the trigger wire is wound differently. The arc tube  11  is provided with the remainder of the filler tip  1   a . The trigger wire  5  is provided with an attachment part  50  which is attached by one end being wound around the remainder of the filler tip  1   a . A holding part  52  which extends in the lengthwise direction of the lamp is connected to this attachment part  50 . Part of this holding part  52  is wound around the side tube part  12  which is connected to the arc tube  11 , and attached. One end of the holding part  52  is connected to the base  42 .  
           [0008]    The lamp shown in FIG. 7 has a base  41  that is provided with an installation part  41   a  of a diameter D′ that is greater than the maximum diameter D of the arc tube  11  and which is used for mounting the lamp is mounted in a device. In such a case in which the diameter D′ of this installation part  41   a  is greater than the maximum diameter D of the arc tube  11 , there is the disadvantage that the trigger wire  5  which is shown in FIG. 4, having the uninterrupted annular area  51 , cannot be inserted onto the lamp from the direction of the base  41 , because the diameter of the annular area  51  of the trigger wire  5  is smaller than the maximum outside diameter of the arc tube  11 , and thus, smaller than the diameter of the installation part  41   a.    
           [0009]    In this case, as is shown in FIG. 8, the annular area  51  is inserted onto the lamp from the base  42  on the opposite side, the annular area  51  is located on the outside surface of the arc tube  11  and one end of the holding part  52  is connected to the base  41 .  
           [0010]    In the operating process, in which a high voltage is applied to the cathode  22  which is located on the side opposite the anode  21  and which is not electrically connected to the trigger wire  5 , the trigger wire  5  being electrically connected to the anode  21  via the base  41 , the high voltage is not applied to the trigger wire  5 . The trigger function therefore does not take effect here. In a lamp in which such an operating process is undertaken, therefore, there is inevitably the disadvantage that the trigger wire cannot be in the optimum state.  
           [0011]    The lamp shown in FIG. 6 has the remainder of a filler tip  1   a  for attachment of the trigger wire  5 . However, in a lamp which does not have a remainder of a filler tip  1   a , there is the disadvantage that the winding process shown in FIG. 6 cannot be used to wind the trigger onto the arc tube.  
           [0012]    Furthermore, in an arrangement of the trigger wire as is shown in FIG. 5, there is also a process in which the shape of the trigger wire does not have a given shape beforehand, but in which the wire-like component which is to become the trigger wire is bent on the outside surface of the arc tube and installed. This case is described below using FIG. 4. By bending this wire-like component into a ring shape, an annular area  51  is formed. Afterwards, using a tool, such as pliers or the like, one end of the annular area  51  is bent around. The wire-like component is turned such that the annular area  51  is formed uninterruptedly in alignment and that the length of the wire-like component comprising the annular area  51  thereafter never changes. A holding part  52  can also be made in alignment on this turned area.  
           [0013]    When such a process is used in which a wire-like component which is to become the trigger wire is bent and installed on the surface of the arc tube, it becomes possible to arrange the trigger wire on the arc tube with optimum directional capacity, regardless of what kind of electrode, whether anode or cathode, to which the high voltage is applied. However, it is necessary to carry out the work of bending or twisting the wire-like component on the surface of the arc tube into an annular shape. This poses the disadvantage that the tool can come into contact with the surface of the arc tube and the surface of the arc tube is scratched as a result.  
           [0014]    In the case of the trigger wire  5  which is shown in FIG. 6, there is also the disadvantage that, when the trigger wire  5  is attached in the remainder of the filler tip  1   a , the tool comes into contact with the surface of the arc tube  11  and the surface  11  of the arc tube is scratched.  
         SUMMARY OF THE INVENTION  
         [0015]    The invention was devised to eliminate the above described defects in the prior art. Thus, a primary object of the present invention is to devise a discharge lamp of the short arc type in which the following is enabled:  
           [0016]    There can be a trigger wire even in a lamp which has a base with a diameter which is larger than the maximum outside diameter of the arc tube;  
           [0017]    The trigger wire can be arranged in the state which is appropriate to the alignment of the electrode to which a high voltage is applied during operation;  
           [0018]    The trigger wire is located on the arc tube at an optimum site, even if the arc tube does not have any remainder of the filler tip; and  
           [0019]    The arc tube is not scratched when the trigger wire is installed on it.  
           [0020]    The object is achieved in the invention described, according to the invention, in a discharge lamp of the short arc type in which a pair of electrodes are located within an arc tube and in which the outside surface of this arc tube is provided with a trigger wire, in that the above described trigger wire has:  
           [0021]    an annular area which is elastically deformed when the trigger wire is installed on the outside surface of the arc tube and which is looped around the arc tube and attached;  
           [0022]    a first holding part adjoins one end of the annular area and extends in the axial direction of the arc tube;  
           [0023]    a second holding part adjoins the other end of the annular area and extends in the axial direction of the arc tube.  
           [0024]    The invention is described below using drawings. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0025]    [0025]FIG. 1 shows a schematic of a discharge lamp of the short arc type according to the invention;  
         [0026]    FIGS.  2 ( a ) &amp;  2 ( b ) each show a schematic of the trigger wire which is located on a discharge lamp of the short arc type in accordance with the invention;  
         [0027]    FIGS.  3 ( a ) to  3 ( d ) each show a schematic of the process by which the trigger wire is installed on a discharge lamp of the short arc type in accordance with the invention;  
         [0028]    [0028]FIG. 4 shows a schematic of a conventional discharge lamp of the short arc type;  
         [0029]    [0029]FIG. 5 shows a schematic of the trigger wire which is located on a conventional discharge lamp of the short arc type;  
         [0030]    [0030]FIG. 6 shows a schematic of another conventional discharge lamp of the short arc type;  
         [0031]    [0031]FIG. 7 shows a schematic of a conventional discharge lamp of the short arc type in which the base is provided with an installation part; and  
         [0032]    [0032]FIG. 8 shows a schematic of a conventional discharge lamp of the short arc type in the case in which the arrangement of the trigger wire is inappropriate. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0033]    A discharge lamp of the short arc type according to the invention is described below with reference to FIG. 1. Here, there is a pair of electrodes, i.e., an anode  21  and a cathode  22  within the arc tube  11 . A respective side tube part  12  adjoins each of opposite sides of the arc tube  11 . A base  41  is formed on the outer end of the side tube part  12  at one side of the arc tube  11 , and is electrically connected to the anode  21 . On the opposite side of the arc tube  11 , a base  42  is formed on the outer end of the side tube part  12  and is electrically connected to the cathode  22 . A trigger wire  3  located on the outside surface of the arc tube  11 .  
         [0034]    Part of the trigger wire  3  is turned one time. Thus, an annular area  31  is formed which has a smaller diameter than the maximum outside diameter D of the arc tube  11  and which comes into contact with the outside surface of the arc tube  11  when it is slipped on, and attached.  
         [0035]    This annular area  31  adjoins a holding part  32   a  and another holding part  32   b  which extend in the lengthwise direction of the lamp. These holding parts  32   a ,  32   b  adjoin an attachment part  33  which is wound around the side tube part  12  and by which the trigger wire  3  is attached. This attachment part  33  adjoins a connection part  34  which is connected to the base  42  and attached. A high voltage is applied to the cathode  22  in this lamp. An insulation breakdown occurs within the arc tube  11  between the annular area  31  formed on the outside surface of the arc tube  11  and the anode  21 , and thus the lamp is operated.  
         [0036]    The trigger wire  3  is explained in detail below.  
         [0037]    FIGS.  2 ( a ) &amp;  2 ( b ) show only the trigger wire  3 . The trigger wire  3  was produced such that a wire-like component of stainless steel with a diameter of 0.5 mm was bent such that it is matched to the shape of the arc tube  11  and the shape of the side tube part  12 . In the state prior to installation in the arc tube, it is already bent into a given shape.  
         [0038]    As shown in FIG. 2( a ), in the annular area  31  of the trigger wire  3  part of the wire-like component which is to become the trigger wire  3 , the wire has been turned at least one time and is formed such that, prior to installation in the arc tube, it has a diameter d which is smaller than the maximum diameter D of the arc tube  11  shown in FIG. 1.  
         [0039]    One end of this annular area  31  is adjoined by the holding part  32   a  which extends in the axial direction of the arc tube  11 . The other end of the annular area  31  is adjoined by the other holding part  32   b  which extends in the axial direction of the arc tube  11 . The annular area  32  differs from the uninterrupted annular area of the conventional trigger wire and has an arrangement in which the two ends of the annular area  31  are not connected to one another.  
         [0040]    In the case of installation of the trigger wire  3  on the outside surface of the arc tube  11 , the annular area  31  deforms elastically, as is shown in FIG. 2( b ), and widens in such a way that an increased diameter d′ of the annular area  31  is obtained because the two ends of the annular area  31  are not connected to one another and because holding part  32   a  and the other holding part  32   b  are connected individually and independently of one another to the two sides of the area.  
         [0041]    FIGS.  3 ( a ),  3 ( b ),  3 ( c ), &amp;  3 ( d ) each show, in a schematic, the installation of the trigger wire on a short arc lamp in which a base with a larger diameter than the maximum diameter of the arc tube is located. In this lamp, a high voltage is applied to the cathode  22  during operation, and it is necessary to position the annular area  31  of the trigger wire on the outside surface of the arc tube  11  in the vicinity of the anode  21 .  
         [0042]    As is shown in FIG. 3( a ), in this lamp there is a base  41  which has an installation part  41   a  which has a larger diameter D′ than the maximum diameter D of the arc tube  11 . The trigger wire  3 , as shown in FIG. 3( b ), before installation in the arc tube  11 , is widened beforehand with bare hands or with a tool such that the diameter of the annular area  31  of the trigger wire  3  increases and the diameter d′ is made larger than the diameter D′ of the installation part  41   a.    
         [0043]    Next, as shown in FIG. 3( c ), proceeding from the FIG. 3( b ) state, the annular area  31  is inserted over the base  41 . Afterwards, the force with which the diameter of the annular area  31  has been increased in the stage in which the annular area  31  has passed through the installation part  41   a  is released. By means of the inherent spring force of the annular area  31  the diameter of the annular area  31  can be made smaller than the maximum outside diameter D of the arc tube  11  by itself. As a result, as shown in FIG. 3( d ), the annular area  31  of the trigger wire  3  comes into contact with the outside surface of the arc tube  11 . Next, the holding part  32  is extended along the lengthwise direction of the arc tube  11 . The attachment part  33  is wound around the side tube part  12  and the connection part  34  is connected to the base  42  and attached.  
         [0044]    In a modification of the process shown in FIGS.  3 ( a ),  3 ( b ),  3 ( c ), &amp;  3 ( d ), the trigger wire can also be installed by inserting the annular area  31  over the base  42  which is shown in FIG. 3( a ),  3 ( b ), &amp;  3 ( d ). In this case, as was described above, the diameter of the annular area  31  of the adjusted trigger wire  3  is widened beforehand such that it passes over the area with the maximum diameter D of the arc tube  11 . After passage of the annular area  31  over the area with the maximum diameter D of the arc tube  11 , the force with which the annular area  31  is being widened is released. In this way the diameter of the annular area  31  is reduced such that it agrees with the outside diameter of the arc tube  11 . Thus, the annular area  31  is located on the outside surface of the arc tube  11 .  
         [0045]    The above described installation process involves a lamp in which a high voltage is applied to the cathode  22  during operation. Here, it has been described that the annular area  31  of the trigger wire  3  is positioned on the outside surface of the arc tube  11  in the vicinity of the anode  21 . However, in the lamp in which, conversely, the high voltage is applied to the anode  21  during operation, it is necessary to position the annular area  31  of the trigger wire on the outside surface of the arc tube  11  in the vicinity of the cathode  22 . This case differs from the above described installation process only in that the arrangement position of the annular area  31  is located on the outside surface of the arc tube  11  in the vicinity of the cathode  22  and is otherwise identical to the above described installation process. This means that there can be a trigger wire even in a lamp which has a base with a larger diameter than the maximum outside diameter of the arc tube  11 . Furthermore, the trigger wire can be in the state which is appropriate to the alignment of the electrode to which the high voltage is applied during operation. Furthermore, for the trigger wire  3 , since the annular area  31  comes into contact with the outside surface of the arc tube  11 , is slipped on and attached, even in a lamp without a filler tip remainder on the arc tube  11 , the trigger wire  3  can be safely located on the surface of the arc tube  11 .  
         [0046]    Moreover, instead of the process in which a wire-like component which is to become the trigger wire  3  is bent and installed on the outside surface of the arc tube  11  using a tool, a process is undertaken in which the trigger wire  3  is adjusted in the stage prior to installation in the arc tube  11  beforehand into a given shape and afterwards can be installed in the lamp, and the formation of scratches on the outside surface of the arc tube  11  by the tool is prevented.  
         [0047]    Action of the Invention  
         [0048]    As was described above, in the discharge lamp of the short arc type in accordance with the invention the effects are achieved:  
         [0049]    there can be a trigger wire even in a lamp which has a base with a diameter which is larger than the maximum outside diameter of the arc tube,  
         [0050]    the trigger wire can be in the state which is appropriate to the alignment of the electrode to which a high voltage is applied during operation;  
         [0051]    the trigger wire can be located in the arc tube at an optimum site, even if the arc tube does not have any remainder of the filler tip; and  
         [0052]    the arc tube is not scratched when the trigger wire is installed in it.