Abstract:
A bulb comprises an airtight envelope having a filling gas therein. A conductive wire extends outwardly from the airtight envelope. A conductive pipe pin has the conductive wire passed therethrough, a predetermined welding portion, and a welded portion including a smooth surface. An outer diameter of the welded portion is no greater than the outer diameter of the pin. The welded portion may be formed in the pipe pin by the fluid of the melted conductive wire and predetermined welding portion flowing into the pipe pin and hardening.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of Invention 
     The present invention relates to a bulb having a pipe pin and a conductive wire, and a method for welding the pipe pin and the conductive wire thereof. 
     2. General Background and Related Art 
     A method for connecting a conductive wire to a pipe pin of a fluorescent lamp is disclosed in Japanese Laid Open Patent Application SHO 60-39786. Namely, the conductive wire is passed through the pipe pin. A projecting portion of the wire from a tip of the pin is cut off, leaving a predetermined length of wire projecting through the pipe pin. The predetermined portion is pushed back to the tip of the pipe pin. The pin with the conductive wire is punched at one side thereof together. 
     Using this method does not always result in a rigid joining of the wire and the pin. Accordingly, to better assure good joining by this method, it is necessary to use, in conjunction with the method a punching level detecting device measuring an extent of press. Such a device is described in Japanese Laid Open Patent Application SHO 61-51728. Occasionally, after being punched, the tip of the wire projects from the tip of the pipe pin. The projecting portion sometimes accidentally injures a user, such as, for example, when the lamp is being changed. 
     Another method for arc-welding a pipe pin and a conductive wire is described in Japanese Laid Open Patent Application SHO 60-20427. The disclosed method somewhat simplifies the processes, and prevents the tip of the wire from projecting from the tip of the pin. This method utilizes a forming process to bend the projecting tip of the wire toward one side of the pin. Though the bending portion is still welded with the pipe pin, the tip of the bending portion occasionally appears on the welding region. Accordingly, the welded pin can not be inserted in a socket. Moreover, as the bending portion is primarily welded, both the bending wire and pin can not be sufficiently connected. Furthermore, if the pin includes zinc, the zinc evaporates due to the heat of welding. Accordingly, zinc vapor sticks to an outer surface of the pin, so that the pin becomes unclean. 
     SUMMARY 
     One aspect of the claimed inventions is directed to an improved arrangement for connecting a conductive wire and a pipe pin of a bulb construction. Another aspect of the claimed inventions focuses on an improved method of welding a pipe pin and a conductive wire which provides a simpler way of welding and a more effective resulting weld. 
     Another aspect of the claimed invention is directed to the bulb construction itself. The bulb comprises an airtight envelope having a filling gas therein. A conductive wire extends outwardly from the airtight envelope. This conductive wire is passed through a conductive pipe pin. A predetermined welding portion of the wire extends from the bottom of the pipe pin. A weld at this welding portion produces a smooth surface. An outer diameter of the welded portion, which is formed from melting a portion of both the predetermined welding portion and the conductive wire, is no greater than the outer diameter of the pin. 
     Still another aspect of the claimed invention is directed to the bulb construction itself. The bulb comprises an airtight envelope having a filling gas therein. A conductive wire extends outwardly from the airtight envelope. A conductive pipe pin has the conductive wire passed therethrough, a predetermined welding portion, and a welded portion including a smooth surface. The welded portion is formed in the pipe pin by the fluid of the melted conductive wire and predetermined welding portion flowing into the pipe pin and hardening. 
     Some of the claimed inventions feature a method for welding a pipe pin and a conductive wire of a bulb. The method is generally described as follows: 
     outwardly extending the conductive wire from an airtight envelope having a bulb base; 
     arranging the pin including the predetermined welding portion, to the bulb base, the pin having an outer diameter that is less than that of a pin base; 
     passing the conductive wire through the pipe pin with a tip of the conductive wire projecting from tip of the pin; 
     cutting off the tip of the conductive wire, leaving a predetermined length; and 
     welding the pin and the conductive wire in order to form a welded portion having a smooth surface at the tip portion of the pin. 
     These and other aspects of the invention will be further described in the following drawings and detailed description of the invention. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In the following, the invention will be described in more detail by way of examples illustrated by drawings in which: 
     FIG. 1 is an enlarged longitudinal section of a part of a fluorescent lamp according to first embodiment of the present invention; 
     FIG. 2 is an enlarged longitudinal section of a conductive pin passed through a conductive wire of the lamp shown in FIG. 1; 
     FIG. 3 is a sectional view of a punching device setting up the conductive pins passed through the conductive wires of the lamp shown in FIG. 1; 
     FIG. 4 is an enlarged longitudinal section of a punched conductive pin of the lamp shown in FIG. 1; 
     FIG. 5 is a partial section of a welding device holding the punched conductive pin of the lamp shown in FIG. 1; 
     FIG. 6 is an enlarged longitudinal section of a welded conductive pin of the lamp shown in FIG. 1; 
     FIG. 7 is an enlarged longitudinal section of a welded conductive pin of a fluorescent lamp, according to another aspect of the embodiment of the present invention; 
     FIG. 8 is an enlarged longitudinal section of a welded conductive pin of a fluorescent lamp, according to another aspect of the embodiment of the present invention; 
     FIG. 9 is an enlarged longitudinal section of a conductive pin passed through a conductive wire of a fluorescent lamp, according to second embodiment of the present invention; 
     FIG. 10 is an enlarged longitudinal section of a punched conductive pin of the lamp shown in FIG. 9; 
     FIG. 11 is a partial section of a welding device holding the punched conductive pin of the lamp shown in FIG. 10; 
     FIG. 12 is an enlarged partial section of a welding device holding the punched conductive pin of the lamp shown in FIG. 1; 
     FIG. 13 is an enlarged longitudinal section of a welded conductive pin of the lamp shown in FIG. 11; 
     FIG. 14 is an enlarged longitudinal section of a conductive pin inserting a conductive wire of a fluorescent lamp, according to third embodiment of the present invention; and 
     FIG. 15 is an enlarged longitudinal section of a welded conductive pin of the lamp shown in FIG.  14 . 
    
    
     DETAILED DESCRIPTION 
     An exemplary embodiment of the invention will be described in detail with reference to FIGS. 1 to  8 . 
     FIG. 1 shows an enlarged longitudinal section of a part of a fluorescent lamp  20  according to first embodiment of the present invention. The fluorescent lamp  20  has a bulb, which in this embodiment is a circular arc tube  1 . A pair of stems  2  air-tightly seal the two ends of the arc tube. Bulb base  6  is made of plastic and has four conductive pipe pins  7 . Bulb base  6  could be constructed from other suitable materials. Each of conductive pipe pins  7  has a respective predetermined welding portion  8  and a holding portion fixed on bulb base  6  arranged between the two ends of the arc tube. The predetermined welding portion  8  of a pipe pin  7  is easily melted and is punched in order to make good contact with wire  4 . 
     Pin  7  has an outer diameter of 2.3 mm and a thickness of 0.8 mm at its holding portion side. At the predetermined welding portion side, pin  7  has a 1.7 mm in diameter and a 0.5 mm thickness. Of course these dimensions apply only to this example. Other shapes and sizes can be used. The shapes and sizes of all parts can be selected so as to be appropriate for a given size and shape of lamp. 
     The bulb including an electrode may be an incandescent lamp, a discharge lamp such as a fluorescent lamp, an electrodeless discharge lamp or a high intensity discharge lamp, or an electron tube. The arc tube may be made of a light-transmitting glass or ceramics. The arc tube may be made into any suitable shape desired, such as a linear, circular, or U-shape. 
     Each of the stems  2  has a pair of conductive wires  4 ,  4 . One end of each conductive wire is connected to a filament  5  as the electrode via inner wires. The other end of each conductive wire  4  extends from the arc tube  1 . The conductive wires  4  are respectively inserted into pipe pins  7 . The inner diameter of the pipe pin  7  is preferably 25% to 60% of its outer diameter at portion  8  of the pin. Also, the inner diameter of pipe pin  7  is preferably within 120% to 280% of the outer diameter of conductive wire  4 , in order to provide for a rigid connection. Tips of the conductive wires  4  extend from one end via the pins  7 . The tip of each conductive wires is cut off, and the tip and one end of its respective pin are welded together using a welding device. The conductive wire may comprise three parts, which are made of respective different materials, including an outer part extending from the arc tube, a part embedded in the seal, and an inner part existing in the arc tube. 
     FIG. 2 shows an enlarged longitudinal section of the conductive pin with an inserted conductive wire of the lamp. A method for manufacturing the lamp includes the following: 1) sealing the arc tube, 2) exhausting the arc tube, 3) electrode flushing, and 4) lamp base assembly. During the lamp base assembly process, a cutting device  10  cuts off a wire-projecting portion  9  extending from the conductive pin  7 . As a result, the wire-projecting portion  9  remains a predetermined length (l) as shown in FIG.  2 . 
     A welded portion  25  shown in FIG. 6 is formed by a welding device, which can melt the remaining length (l) and the predetermined welding portion  8  of the pin, together. An outer diameter of the welded portion  25  may be the outer diameter of the pin  7  or less, and larger than the inner diameter of the pipe pin. Accordingly, the welded portion can be easily inserted into a socket (not shown) and cannot go back into the pipe pin  7 . Furthermore, the volume of the remained length (l) can control the size of the welded portion  25 . 
     A surface of the welded portion can be formed smoothly, by using a plasma welding device. Of course, other types of welding devices can be used and perhaps other suitable techniques will be developed in the future. Plasma welding, which is one kind of arc welding, can be used effectively because it is possible to increase current density (A/mm 2 ) of a plasma arc by contracting the diameter of the arc. Accordingly, the plasma-welding device can melt a metal having a high melting point by 1 to 3 million degrees centigrade of a temperature of the plasma arc center. 
     A punching device shown in FIG. 3 loads the lamp having the conductive pipe pins  7  including the wire-projecting portion  9  in length (l). The punching device includes a lamp holding device (not shown), a guide block  11  having four guide holes  12  therein and punching members  17 . The holding device supports the circular arc tube  1  with the pins  7  facing downward. After the pins are located, the guide block moves in the direction of the circular arc tube  1 , so as to insert the pins  7  into the guide holes  12 . After the holes  12  accommodate pins  7 , guide block  11  stops moving, with an upper surface of the block contracting the bulb base  6 . Next, the punching members  17  respectively move to in the direction of the pins  7 , and press the predetermined welding portion of the pins  7 , in order to make a dent  7   c . Accordingly, the conductive wire  4  and the pipe pin  7  join temporary at the dent  7   c  as shown in FIG. 4, and can also conduct a current easily. 
     The welding process of the pipe pins and the conductive wires will be explained hereinafter. 
     FIG. 5 shows a partial section of the welding device holding the punched conductive pin  7  of the lamp  20 . After unloading guide block  11  from the circular arc tube  1 , another welding guide block  18  moves to in the direction of the circular arc tube  1 , so as to insert pines  7  into respective guide holes  12 . The welding block  18  has four welding torches  21  respectively arranged in opposition to the predetermined welding portion  8  of the pins  7 , and four welding electrodes  22  enabling to contact the side face of the pins  7  by moving in the direction of the pins  7 . Electrodes  22  are electrically connected to a power supply via a switching arrangement  24 . After the plasma-welding torches  21  rises adjacent to the predetermined welding portion  8  of the pins  7  except contacting, the switching arrangement  24  switches to apply power to the electrodes. Accordingly, a plasma arc generates between the welding torch  21  and the predetermined welding portion  8  of the pin  7 . The predetermined welding portions  8  and the conductive wires  4  are melted by heat of the plasma arc, so that the welded portions  25  are formed as shown in FIG.  6 . The outer diameter of the welded portions  25  are respectively less than that of the outer diameter of the pins  7 . A length of the welded portions  25  is about 2 mm from the tip of the pin  7 . Furthermore, the welded portions  25  are formed approximately spherical shape having smoothly surface. The spherical shape may be formed by means of a surface tension of the melted materials during the welding, or of a metal finishing such as a abrasive method after the welding. Accordingly, the welded portions  25  of the pins  7  prevent user from injuring, when user changes the lamp for example. 
     Furthermore, the surface of the welded portion  25  may curve continuously from an outer surface of the tip of the pin  7  as shown in FIG.  7 . In this case, the shape of the welded portion  25  is formed by means of changing a welding condition, such as increasing a welding time, or raising output current of the power supply. Furthermore, the surface of the welded portion  25  may be flattened at the tip of the pin as shown in FIG.  8 . 
     A second exemplary embodiment of the invention will be explained in detail with reference to FIGS. 9 to  13 . Similar reference characters designate identical or corresponding to the elements of above-mentioned first embodiment. Therefore, detail explanations of the structure will not be provided. 
     In this embodiment, before the inserted conductive wire  4  extending from the pipe pin  7   a  including zinc is cut off, a punching member may press the predetermined pressing portion  7   e  of the pin, in order to make a dent  7   d , as shown in FIGS. 9 and 10. In this case, the conductive pipe pin  7   a  has 2.3 mm in outer diameter and 0.8 mm in thickness at the predetermined pressing portion  7   e . Moreover, the dent  7   d  completely contacts the conductive wire  4  in order to maintain conducting a current. 
     Furthermore, the predetermined pressing portion  7   e  of 0.8 mm in thickness can be used as the predetermined welding portion. The predetermined pressing portion  7   e  can produce a large amount of melted metal, so that the melted metal of the pipe pin  7   a  can be sufficiently connected to the conductive wire  4 . 
     FIG. 11 shows a partial section of a welding device holding the punched conductive pin of the lamp according to the second embodiment. FIG. 12 shows an enlarged partial section of the welding device holding the punched conductive pipe pin of the lamp according to the second embodiment. In this embodiment, after unloaded the circular arc tube  1  from the guide block  11 , another welding guide block  18  moves in the direction of the circular arc tube  1 , so as to insert the pines  7  into the guide holes  12 . The welding block  18  has a welding torch  21 , four welding electrodes  22 , and a high heat conductive cover element  26 . The welding torch  21  is arranged in opposition to the pipe pin  7   a . The four welding electrodes  22  can contact the side faces of the pins  7   a  by means of moving in the direction of the pipe pins  7   a.    
     The high heat conductive cover element  26  made of copper defines through holes  26   a . A diameter of the holes  26   a  may be adjacent to the outer diameter of the pipe pins  7   a . Accordingly, since the pins  7   a  can pass through the through holes  26   a  of the cover element  26 , a projecting length of the pins  7   a  from the cover element  26  can change by changing the thickness of the cover element  26 . Cover element  26  can prevent a heat of the plasma arc from conducting to the bulb base  6 . Therefore, the bulb base  6  does not deform easily. Furthermore, the cover element  26  can prevent zinc included the pin vapor from sticking to the outer surface of the pins  7   a . When the projecting length of the tip portion from the cover element  26  is over 2 mm, the vapor of zinc tends to stick to the outer surface of the pins  7   a.    
     Electrodes  22  are connected to a power supply via switching means  24 . After the plasma-welding torch  21  moves adjacent to tips  8   a  of the pins  7   a  except contacting, the switching arrangement  24  is switched to apply power. Accordingly, a plasma arc generates between the welding torch  21  and the tip  8   a  the pin  7   a . Therefore, the tip  8   a  and the conductive wire  4  are melted by a heat of the plasma arc, so that the welded portion  25  are formed as shown in FIG.  13 . After one welded portion  25  was formed, the plasma-welding torch  21  moves to in the direction of another pin  7   a , one by one, in order to form the welded portion. 
     FIG. 13 shows an enlarged longitudinal section of the welded conductive pin of the lamp. The outer diameter of the welded portion  25  is larger than an inner diameter of the pipe pin  7   a , is still an outer diameter or less. Moreover, an outer surface of the welded portion  25  is formed continuously from an outer surface of the tip of the pin  7   a . Furthermore, when the conductive wire  4  is melted by the plasma arc, a fluid of the melted wire  4  and predetermined welding portion of the pipe pin  7   a  flows into the pipe  7   b  of the pin  7   a , and hardens into a part of the welded portion  25 . Namely, the fluid can also join the conductive wire  4  and pipe pin  7   a  in the pipe  7   b . Moreover, as the fluid flows into the pipe  7   b , the welded portion  25  of the pipe pin  7   a  tends to become smaller in comparison with the outer diameter of the pipe pin  7   a . In this case, an outer diameter (OD) of the conductive wire is 0.5 mm. The inner diameter (ID) of the pipe  7   b  is 0.9 mm. A length (X) of the welded portion  25  is 0.9 mm. The distance (Y) from a tip of the welded portion to a tip of the pin  7   a  is 0.3 mm. Accordingly, the welded portion  25  can increase a welded region of between the pin  7   a  and the conductive wire  4 , and volume thereof also becomes large. Therefore, the welded portion  25  can prevent the pin and the conductive wire from separating. 
     A third exemplary embodiment of the invention will be explained in detail with reference to FIGS. 14 and 15. Similar reference characters designate identical or corresponding to the elements of above-mentioned first embodiment. Therefore, detail explanations of the structure will not be provided. 
     FIG. 14 shows an enlarged longitudinal section of a conductive pin inserting a conductive wire of a fluorescent lamp. FIG. 15 shows an enlarged longitudinal section of a welded conductive pin of the lamp. 
     In this embodiment, the inserted conductive wire  4  extends from the pipe pin  71 . When the conductive wire  4  is melted by the plasma arc, a fluid of the melted wire and the predetermined welding portion of the pin  71  flows into the pipe pin  71 , and hardens into a part  25   b  of the welded portion  25 . In this case, a length (B) of the welded portion is 0.5 mm. The length of welded portion projecting from a tip of the pin  71  prefers a range of 1 mm to 2 mm, so as to join rigidly both the conductive wire  4  and pipe pin  71 . The conductive pin  71  has 2.3 mm in outer diameter and 0.3 mm in thickness at one end of the pin  71 . The conductive pin  71  also has unitary a predetermined welding portion  81 , which is 1.3 mm in outer diameter, and 0.3 mm in thickness, at the other end of the pin  71 . The welded portion  25  has an outer diameter being less than the inner diameter A of the pin  71 . An outer surface of the welded portion  25  is formed continuously from an outer surface of the tip of the pin  71 . According to this embodiment, the thickness of the pin  71  is thinner than that of above-mentioned pins  7 , 7   a , so that the output of the power supply and the welding time can be drop effectively.