Abstract:
Disclosed is an arrangement for a cut type electrode, wherein the removal of a coil is prevented and the generation of gap between turns of a coil caused by repeatedly turning on and off of the lamp is suppressed. The electrode, which is for a discharge lamp, comprises: a core rod having a leading end portion for discharge formed by a cutting process; and a coil wound around the core rod in n-turns in a state exposing the leading end portion, wherein at least a first portion between a first turn and a turn adjacent to the first turn and a second portion between an n-th turn and a turn adjacent to the n-th turn are welded.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to an electrode for discharge lamp and a method for manufacturing the same. More specifically, the present invention relates to a structure of a leading-end cut-type electrode for discharge lamp around which a coil is wound. 
       BACKGROUND ART 
       [0002]    Electrodes for discharge lamp are roughly classified into leading-end melted-type electrodes and leading-end cut-type electrodes. A leading-end melted-type electrode is an electrode made by winding a coil around a leading-end portion of a core rod and melting the leading-end portion of the core rod and a portion of the coil near the leading-end portion together to form a dome-shaped leading-end portion. A leading-end cut-type electrode is an electrode made by cutting a leading end into a tapered shape, winding a coil around a core rod and fixing the coil thereon with the leading-end portion being exposed. The present invention employs the latter, the cut-type electrode, in terms of easiness of welding and the like. 
         [0003]    A coil to cover a core rod typically has a function of adjusting the temperature of an electrode. This determines ignition characteristics and heat radiation characteristics during discharge, and therefore determines discharge characteristics. It is necessary for the cut-type electrode to have a structure for preventing the coil from coming off the core rod, i.e., preventing the coming-off of the coil. Patent Documents 1 to 3 disclose examples of the cut-type electrode. 
         [0004]    Patent Document 1 discloses an arrangement in which a core rod and a rear-end portion of a coil wound around the core rod are welded together and thereby the core rod and the coil are integrated to prevent the coming-off of the coil and prevent the coil from loosening rearward, i.e., springback. 
         [0005]    Patent Document 2 discloses an arrangement in which a front-end portion and a rear-end portion of a lower-layer coil of coils wound around a core rod in layers are laser-welded to the core rod and thereby the coil is fixed on the core rod. 
         [0006]    Patent Document 3 discloses an arrangement in which protrusions are provided to a core rod to regulate the position of a coil and position the coil. 
       CITATION LIST 
     Patent Documents 
       [0007]    Patent Document 1: Japanese Patent No. 4325518 
         [0008]    Patent Document 2: Japanese Patent Application Laid-Open No. 2001-527271 
         [0009]    Patent Document 3: Japanese Patent No. 4188480 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0010]    The arrangements of Patent Documents 1 and 2 prevent the coming-off of a coil, but cannot suppress the misalignment of the coil itself. For example, with the arrangement of Patent Document 1, since repeated turn on and off (turning-on and off) of the discharge lamp causes the electrode to repeat thermal expansion/contraction and this causes forward extension of the coil, or due to other reasons, a gap is sometimes generated between turns of the coil. Meanwhile, although the positions of the two-end portions of the lower-layer coil are expected to be fixed, a gap is sometimes generated between turns of the coil even in the case of Patent Document 2 since repeated thermal expansion/contraction of the electrode due to turning-on and off loosens the arrayed upper-layer coil. 
         [0011]    The generation of such gap between turns of the coil changes the thermal conduction characteristics of the coil from that of the original design. Thus, as the number of turning-on and off cumulatively increases, intended ignition characteristics or discharging characteristics may not be obtained. Moreover, the generation of the gap between turns of the coil also changes a starting position where discharge starts. Hence, the igniting operation may be also different from that intended in the original design. 
         [0012]    Meanwhile, in order to fix the positions of the respective turns of the coil as in Patent Document 3, multiple protrusions are required according to the number of turns. This complicates the arrangement of the core rod and thus causes a problem of poor productivity. 
         [0013]    Thus, the present invention has an objective to provide a cut-type electrode having an arrangement for preventing the coming-off of a coil and generation of a gap between turns of the coil due to repeated turning-on and off. 
       Solution to Problem 
       [0014]    A first aspect of the present invention is an electrode for discharge lamp comprising: a core rod ( 10 ) having a leading-end portion ( 11 ) for discharge formed by a cutting; and a coil ( 20 ) wound around the core rod in n-turns with the leading-end portion being exposed, in which at least a first portion (Fa) between a first turn and a turn adjacent to the first turn and a second portion (Fb) between an n-th turn and a turn adjacent to the n-th turn are welded. 
         [0015]    A second aspect of the present invention is a discharge lamp including: a pair of electrodes ( 30 ) each comprising the electrode for discharge lamp according to the first aspect; and a bulb ( 40 ), in which the pair of electrodes for discharge lamp are arranged to face each other in the bulb. 
         [0016]    A third aspect of the present invention is a method for manufacturing an electrode for discharge lamp including the processes of: preparing a core rod having a leading-end portion for discharge formed by a cutting; winding a coil around the core rod in n-turns with the leading-end portion being exposed; and welding at least a first portion between a first turn and a turn adjacent to the first turn and a second portion between an n-th turn and a turn adjacent to the n-th turn. 
         [0017]    In each of the above aspects, the first portion and the second portion may be welded linearly. In this respect, a portion from the first portion to the second portion is welded continuously and substantially straight line in a longitudinal direction of the core rod. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0018]      FIG. 1  is a photograph showing an electrode for discharge lamp according to a first example of the present invention. 
           [0019]      FIG. 2A  is a view showing a modified example of the first example of the present invention. 
           [0020]      FIG. 2B  is a view showing a modified example of the first example of the present invention. 
           [0021]      FIG. 3A  is a photograph showing an electrode for discharge lamp according to a second example of the present invention. 
           [0022]      FIG. 3B  is a view showing the electrode for discharge lamp according to the second example of the present invention. 
           [0023]      FIG. 4A  is a view showing a modified example of the second example of the present invention. 
           [0024]      FIG. 4B  is a view showing a modified example of the second example of the present invention. 
           [0025]      FIG. 5  is a view showing a discharge lamp of the present invention. 
           [0026]      FIG. 6  is a flowchart showing a method for manufacturing the electrode for discharge lamp of the present invention. 
           [0027]      FIG. 7A  is a view for supplemental description of the present invention. 
           [0028]      FIG. 7B  is a view for supplemental description of the present invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
     Example 1 
       [0029]      FIG. 1  shows an electrode for discharge lamp  1  according to a first example of the present invention. The electrode for discharge lamp  1  comprises: a core rod  10  that has a leading-end portion  11  for discharge formed by a cutting; and a coil  20  that is wound around the core rod in n-turns with the leading-end portion  11  being exposed. In this example, in the coil  20 , at least a first portion Fa between a first turn Ti and a turn T 2  adjacent to the first turn Ti and a second portion Fb between an n-th turn Tn and a turn Tn- 1  adjacent to the n-th turn Tn are welded. The welding is carried out by laser beam welding, TIG welding, electric resistance welding, or the like. Note that the core rod  10  and the coil  20  are not welded. 
         [0030]    The above welding at the two portions defines diameters of the coil  20  at a leading-end-diameter portion (from the first turn Ti to the second turn T 2 ) and at a rear-end-diameter portion (from the (n- 1 )-th turn Tn- 1  to the n-th turn Tn). This prevents the coil  20  from loosening, so that the coming-off of the coil can be prevented. In addition, the above welding fixes shapes of the coil  20  at the leading-end-diameter portion and at the rear-end-diameter portion. This ensures these portions to be held on the core rod  10  and prevents the coil  20  from being shifted in an electrode axis direction, which can prevent generation of a gap between turns of the coil. 
         [0031]    Moreover, in contrast to Patent Documents 1 and 2 in both of which welding is applied between a coil and a core rod of different materials (of greatly different heat capacities even if they are of the same material), welding is applied between turns of the coil, which are of the same material, in this example, which allows for good welding workability. 
         [0032]      FIGS. 2A and 2B  further show electrodes  2  and  3  that are the modified examples of this example. In each of the electrodes  2  and  3 , intermediate welding portions Fc, Fd, Fe, and Ff are provided between the welding portions Fa and Fb and thereby the number of welding portions is increased in order to strengthen the effect of preventing the coming-off of the coil and generation of the gap between turns of the coil. In the electrode  2 , the welding portions Fa, Fb, Fc, and Fd face a single direction, while, in  FIG. 2B , the welding portions Fa, Fb, Fe, and Ff are distributed in multiple directions with respect to an electrode axis. Regarding the electrode  2 , since welding can be made on the electrode  2  in a single direction (e.g., a laser beam can be radiated in a single direction), a welding operation can be carried out efficiently. Regarding the electrode  3 , since the welding portions are distributed on the electrode  3 , the strengthening effect can be obtained with few welding portions. Note that, although the two intermediate welding portions are shown in each of  FIGS. 2A and 2B , any number of intermediate welding portions may be employed. 
       Example 2 
       [0033]    While the welding portions in the form of dots are illustrated in the first example, linear welding portions are illustrated in a second example.  FIG. 3A  shows a photograph of an electrode  4  according to the second example of the present invention, and  FIG. 3B  shows illustration thereof. In this example, welding is performed to form a welding portion Fa-b that extends continuously and substantially straight line in a longitudinal direction of a core rod  10  from a portion Fa between a first turn T 1  and a turn T 2  adjacent to the first turn T 1  to a portion Fb between an n-th turn Tn and a turn Tn- 1  adjacent to the n-th turn. While the welding portion Fa-b is preferably continuous, a partially-disconnected welding portion may also be possible. In this example as well, the welding is carried out by the laser beam welding, TIG welding, electric resistance welding, or the like, and the core rod  10  and the coil  20  are not welded. 
         [0034]    The above welding portion Fa-b defines diameters of the coil  20  at the respective turns. This prevents the coil  20  from loosening, so that the coming-off of the coil can be prevented. In addition, the above welding portion fixes shapes of the coil  20  at the respective turns. This ensures these portions to be held on the core rod  10  and prevents the coil  20  from being shifted in an axis direction, which can prevent generation of a gap between turns of the coil. 
         [0035]    Moreover, since integrating the turns, this example exhibits a stronger effect of preventing the coming-off of the coil and generation of the gap between turns of the coil than the case of  FIG. 1  of Example 1. Further, this example does not require high positioning accuracy in welding as the case of  FIG. 2A  or  FIG. 2B  and thus allows for easy welding. Furthermore, since making the welding portion in the form of a straight line, this example requires minimum welding and thus allows for good productivity. 
         [0036]      FIG. 4A  shows an electrode  5  according to a modified example of this example. While the welding portion Fa-b is made by the welding in the form of a straight line on substantially a single surface in the electrode  4 , a welding portion Fa-b is welded spirally in the electrode  5 . In this way, since the electrode  5  has a wide welding range, the effect of preventing the coming-off of the coil and generation of the gap between turns of the coil is further enhanced. Further, since the electrode  5  has welding points distributed in all directions with respect to the electrode axis, the physical profile of the electrode can be made symmetric with respect to the electrode axis. 
         [0037]      FIG. 4B  shows an electrode  6  according to a modified example of this example. While the welding portion Fa-b is formed of one line in each of the above electrodes  4  and  5 , a welding portion is formed of multiple lines in the electrode  6 . As shown in the drawing, one welding portion Fa′ includes the welding portion Fa, whereas the other welding portion Fb′ includes the welding portion Fb. Moreover, the welding portions extend in parallel with the electrode axis. This arrangement makes it possible to weld portions near end portions  21  and  22  of the coil  20  as well as to minimize a welding length. Further, this arrangement eliminates the need to perform welding while a laser and the electrode  6  are rotated relative to each other about the electrode axis (i.e., eliminates the need to radiate a laser beam while the electrode  6  is rotated about the axis, or to radiate a laser beam while the laser is rotated with respect to the electrode  6 ) at one welding operation when laser beam welding is performed for example, which facilitates manufacturing. 
         [0038]    Note that, although the lengths of the welding portions Fa′ and Fb′ are set so that these portions do not overlap in their length direction in order to minimize a welding length, the lengths of the welding portions may be larger than those illustrated. For example, the portion Fa′ may reach the n-th turn Tn, or the portion Fb′ may reach the first turn T 1 . In other words, multiple linear welding portions shown in  FIG. 3  may be provided. 
         [0039]      FIG. 5  shows a discharge lamp using a pair of electrodes  30  according to the above examples. The discharge lamp includes: a bulb  40  made of quartz glass or the like; and the pair of electrodes  30  arranged to face each other in the bulb  40 . Any of the electrodes  1  to  6  may be used for the pair of electrodes  30 . The bulb  40  includes a molybdenum foil  31  and a lead  32  that are connected to each electrode  30 . Note that at least mercury and inert gas are enclosed in the bulb  40 ; and that the electrodes according to the present invention are particularly suitable for high pressure discharge lamps. 
         [0040]    The above arrangement makes it possible to achieve a discharge lamp capable of maintaining ignition characteristics and discharge characteristics intended in the original design even when the number of turning-on and off is accumulated. 
         [0041]      FIG. 6  is a flowchart showing a method for manufacturing an electrode for discharge lamp according to the present invention. 
         [0042]    In Step S 100 , a core rod  10 , which has a leading-end portion  11  for discharge formed by a cutting, is prepared. 
         [0043]    In Step S 110 , a coil  20  is wound around the core rod  10  in n-turns with the leading-end portion  11  being exposed. 
         [0044]    In Step S 120 , at least a first portion Fa between a first turn T 1  and a turn T 2  adjacent to the first turn T 1  and a second portion Fb between an n-th turn Tn and a turn Tn- 1  adjacent to the n-th turn Tn are welded. In this respect, as described above, other welding portions may be provided between the first portion Fa and the second portion Fb; alternatively, the first portion Fa and the second portion Fb may be welded linearly. 
         [0045]    The above manufacturing method makes it possible to manufacture, with high productivity, the electrode that can prevent the coming-off of the coil and generation of a gap between turns of the coil due to repeated turning-on and off. 
         [0000]    Although the most preferred examples of the present invention have been described above, the present invention can be modified as follows without departing from the concept of the invention. 
         [0046]    (1) In each of the above examples, as shown in  FIG. 7A , the welding portions Fa and Fb may include an end portion of the first turn T 1  and an end portion of the n-th turn Tn, respectively. Thereby, undesired discharge from the end portions of the coil can be prevented. 
         [0047]    (2) Although the single-layered coil has been shown in the above examples, the effect of the present invention can also be achieved by use of a multi-layered coil by welding the coil continuously from its lower layer to its upper layer, as shown in  FIG. 7B . 
         [0048]    (3) Although, in the above examples, the winding direction of the coil  20  is in such a way that the electrode-distal-side of the coil is the first turn (the electrode-proximal-side of the coil is the n-th turn), the electrode-proximal-side of the coil may be the first turn (the electrode-distal-side of the coil may be the n-th turn). Further, the welding of the welding portions Fa, Fb, Fc, Fd, Fe, and Ff can be performed in any order, and the welding of the welding portion Fa-b, Fa′, or Pb′ can be performed in any direction. 
       REFERENCE NUMERALS 
       [0000]    
       
           1 - 6  electrode 
           10  core rod 
           11  leading-end portion 
           20  coil 
           30  electrode 
           40  bulb 
         Fa, Pb, Fc, Fd, Fe, Ff, Fa-b, Fa′, Pb′ welding portion