Electric discharge lamp

Abstract: An electric arc discharge lamp (10) includes an elongated hollow tubular transparent envelope (14) having a pair of opposite ends (14A,14B), a pair of electrode mounts (16) respectively disposed in the ends of the tubular envelope, and a dosing capsule (12) defining a hermetically sealed annular cavity containing a predetermined quantity of a dosing liquid (M) therein. The dosing capsule (12) has an inner edge (36) defining an opening (38) through the capsule for receiving a portion (22A) of one the electrode mounts (16) therethrough such that the capsule is supported by the one electrode mount (16) with the sealed annular cavity substantially surrounding the one electrode mount. The electrode mount (16) includes a glass stem having inner and outer axially-displaced opposite ends, a pair of lead-in conductors extending through the glass stem (22) and from the opposite ends of the glass stem, and an electrode supported between a pair of inner ends of the lead-in conductors adjacent to and spaced from the inner end of the glass stem (22). The capsule (12) is supported about the glass stem (22) of the electrode mount spaced from the inner and outer opposite ends thereof. The capsule is rupturable by directing heat energy through the envelope and into contact with a portion of the capsule so as to raise the temperature and cause a rupture of the capsule portion, resulting in release of the dosing liquid (M) from the annular cavity of the capsule into the lamp envelope.

Description: BACKGROUND OF THE INVENTION Field of the Invention The present invention relates generally to electric arc discharge lamps. Description of the Prior Art In the manufacture of electric discharge lamps, such as fluorescent lamps, which utilize an ionizable medium containing mercury, it is necessary to introduce a quantity of the mercury into a sealed envelope of the lamp where the mercury will be employed as a vapor in the production of light. To place the desired quantity of mercury into the fluorescent lamp, one approach has been to employ a mercury dosing apparatus. One conventional dosing apparatus utilized heretofore is operable to, first, form a droplet of liquid mercury external to the lamp and, then, blow the liquid mercury droplet into the lamp with a flush or fill gas at a stage in the lamp production process prior to hermetically closing and sealing the lamp envelope. Due to inaccuracies of metering and losses of mercury during transport from the respective apparatus into the lamp, Such prior art mercury dosing apparatus has not been found capable of dispensing a precisely or accurately measured quantity of mercury, preferably in the form of a single piece or ball of mercury, into lamps on a repeatable basis. To compensate for this deficiency, in most instances a substantially larger quantity of mercury than is actually needed for operation of the lamp is intentionally introduced to ensure that, at least, the minimum quantity of mercury will be present in the lamp envelope to provide adequate lamp performance and useful life. Because of the adverse effects of mercury on the environment it would be highly desirable to be able to avoid the overuse of mercury in the manufacture of gas discharge lamps. Because a minimum quantity of mercury is needed in a lamp to meet design life requirements, reducing mercury in the lamp requires reducing the variability of the dosing technique. An alternative approach to providing accurate dosing has been to sealably encapsulate the desired quantity of mercury in a heat resistive media, usually glass or metal, and attach the mercury capsule to one of the electrode mounts so that the capsule will be located inside of the lamp envelope after sealing the lamp. U. Patent Nos. 4,494,042, 4,553,067 and 4,823,047 and EP-A-063393 disclose this alternative approach. The purpose for using the mercury capsule is to allow the mercury to stay intact and isolated from the rest of the lamp atmosphere until after the remaining operations of sealing, exhausting and tipping of the lamp are complete. Then, by the application of intense induction heating, the capsule can be ruptured, allowing the escape of mercury into the lamp atmosphere. In one current dosing method employing a mercury capsule, a shield has been used for attaching the mercury capsule to the electrode mount. The use of the shield has been required to provide the continuous current path needed for induction heating. However, the shield adds cost to the lamp and limits the range of potential lamp designs. Also, the use of the shield with induction heating requires the use of high cost and maintenance equipment both on the mount making machines and on equipment used subsequent to the exhaust process. The induction heating takes time, and in a high speed manufacturing operation, time translates into increase machine length and increased equipment and facility investment. Therefore, a need remains for another approach to mercury dosing of electric discharge lamps which eliminates the problems associated with prior art mercury dosing approaches without substituting other problems in their place. SUMMARY OF THE INVENTION According to the invention, there is provided an electric arc discharge lamp, comprising (a) an elongated hollow tubular envelope having a pair of opposite ends; (b) a pair of electrode mounts respectively disposed in said ends of said hollow tubular envelope; and (c) a mercury dosing capsule defining a hermetically sealed cavity for containing a predetermined quantity of mercury therein, characterized in that said capsule has an inner edge defining an opening through said capsule for receiving therethrough a portion of one of said electrode mounts such that said capsule is supported by said one electrode mount with said sealed cavity substantially surrounding said one electrode mount said dosing capsule being annular and mounted fittingly on said one electrode mount at a position spaced axially from an electrode disposed at one end of said electrode mount, said dosing capsule having said sealed cavity formed along at least a substantial portion of the periphery thereof. Preferably, the capsule body includes a pair of sheets of material each having inner and outer annular portions concentrically arranged and radially spaced relative to one another, the inner and outer annular portions of one of the sheets of material being attached to the corresponding inner and outer annular portions of the other of the sheets of material, the sheets of material also having middle annular portions located between the respective inner and outer annular portions and spaced apart from one another so as to define the sealed annular cavity containing the predetermined quantity of mercury. Embodiments are set out in the dependent claims. BRIEF DESCRIPTION OF THE DRAWINGS The invention will now be described, in greater detail, by way of example, with reference to the drawings in which :- Fig. 1 is a foreshortened side elevational view of an electric arc discharge lamp with one end portion broken away to illustrate an annular liquid-containing dosing capsule of the present invention installed about an electrode mount at the one end of the lamp. Fig. 2 is an enlarged view of the broken away end portion of the lamp of Fig. 1, illustrating the glass stem of the electrode mount after installation of the annular dosing capsule about the glass stem and of the electrode on inner ends of the lead-in conductors and illustrating an elongated fill tube extension of the glass stem prior to breaking off and closing the broken end of the fill tube extension to hermetically seal the envelope of the lamp. Fig. 3 is an end elevational view taken along line 3--3 of Fig. 2, illustrating a first embodiment of the annular dosing capsule of the present invention installed about the glass stem of the electrode mount. Fig. 4 is a plan view of the annular dosing capsule of Fig. 3 by itself. Fig. 5 is a cross-sectional view of the annular dosing capsule taken along line 5--5 of Fig. 4. Fig. 6 is a view similar to that of Fig. 2, illustrating the glass stem of the electrode mount prior to installation of the ahnular dosing capsule about the glass stem and installation of the electrode on ends of the lead-in conductors. Fig. 7 is a cross-sectional view of the glass stem of the electrode mount taken along line 7--7 of Fig. 6. Fig. 8 is an axial sectional view of the glass stem of the electrode mount taken along line 8--8 of Fig. 6. Fig. 9 is a view similar to that of Fig. 4, but illustrating a second embodiment of the annular dosing capsule of the present invention. Fig. 10 is a cross-sectional view of the annular dosing capsule taken along line 10--10 of Fig. 9. Fig. 11 is another cross-sectional view of the annular dosing capsule taken along line 11--11 of Fig. 9. Fig. 12 is a fragmentary front elevational view of another glass stem of the electrode mount having a shape somewhat modified from that of the glass stem of Fig. 6. Fig. 13 is a side elevational view of the modified glass stem as seen along line 13--13 of Fig. 12, illustrating the glass stem before installation thereon of the second embodiment of the annular dosing capsule of Fig. 9. Fig. 14 is a view similar to that of Fig. 13, but illustrating the glass stem after installation of the annular dosing capsule. Fig. 15 is a view similar to that of Fig. 12, but illustrating the glass stem after installation of the annular dosing capsule. Fig. 16 is a perspective view of the one end portion of the electric arc discharge lamp of Fig. 4. illustrating the fill tube extension of the glass stem broken off and closed to hermetically seal the envelope of the lamp and illustrating a laser aligned to rupture the annular dosing capsule and cause release of the liquid dose into the sealed envelope of the lamp. DETAILED DESCRIPTION OF THE INVENTION In the following description, like reference characters designate like or corresponding parts throughout the several views. Also in the following description, it is to be understood that such terms as "forward", "rearward", "left", "right", "upwardly", "downwardly", and the like, are words of convenience and are not to be construed as limiting terms. Referring now to the drawings, and particularly to Fig. 1, there is illustrated an electric arc discharge lamp, for example, a fluorescent lamp, generally designated 10, which incorporates an annular dosing capsule 12 in accordance with the present invention for reliably dispensing a quantity of liquid mercury of desired precise or accurate size in the lamp 10. The electric discharge lamp 10 includes an elongated hollow tubular transparent envelope 14 composed of a suitable material, such as glass, and having a pair of opposite ends 14A, 14B and a pair of electrode mounts 16 (only one being shown in Fig. 1) respectively disposed in and sealably connected to the opposite hollow ends 14A, 14B of the hollow tubular glass envelope 14. In addition, the lamp 10 has a pair of end caps 18 attached on the opposite ends 14A, 14B of the sealed tubular transparent envelope 14 which each support a pair of external electrical contacts 20 thereon. As shown in Figs. 1, 2 and 16, the dosing capsule 12 of the present invention is used in conjunction with only one of the electrode mounts at one end 14A of the hollow envelope 14. Referring to Figs. 1-3 and 6, each electrode mount 16 includes a glass stem 22 having inner slightly arcuate or nearly flat end portion 22A, an outer flared end portion 22B and a generally cylindrical intermediate portion 22C interconnecting and axially displacing the inner and outer end portions 22A, 22B from one another. Each electrode mount 16 also includes a pair of lead-in conductors 24 extending through the glass stem 22 and extending in opposite directions from the inner and outer end portions 22A, 22B of the glass stem 22, and an electrode 26 having a coiled configuration and being supported between a pair of inner ends 24A of the lead-in conductors 24 adjacent to and but spaced from the inner end portion 22A of the glass stem 22. The pair of outer ends 24B of the lead-in conductors 24 are electrically connected to the external contacts 20 mounted on the end caps 18. The electrode mount 16 also has an elongated hollow fill tube extension 28 connected to the intermediate portion 22C of the glass stem 22 so as to define an opening 30 in the inner end portion 22A of the glass stem 22 adjacent to the juncture between the inner end portion 22A and intermediate portion 22C thereof. At the conclusion of production of the lamp 10, the fill tube extension 28 is melted off and fused closed to hermetically seal the tubular envelope 14 of the lamp 10 leaving a short stub broken end 28A. Referring now to Figs. 1-5, there is illustrated one preferred embodiment of the dosing capsule 12 which is adapted to be supported about the glass stem 22 of the one electrode mount 16 at the juncture between the inner end portion 22A and intermediate portion 22C thereof. The dosing capsule 12 includes a body 32 defining a hermetically sealed cavity 34 having an annular configuration and a predetermined quantity of a dosing liquid, such as liquid mercury M, contained and confined therein. The capsule body 32 has an inner edge 36 defining an opening 38 through the body for receiving therethrough the inner end portion 22A of the glass stem 22 of the electrode mount 16 such that the capsule body 32 is supported by the electrode mount 16 with the sealed annular cavity 34 substantially surrounding the electrode mount 16. Spaced portions 36A of the inner edge 36 of the capsule body 32 frictionally engage the electrode mount 16 so to hold it in a stationary relation thereon. The configuration of the capsule 12 permits a form of attachment in which the capsule body 32 need not be permanently affixed to the electrode mount 16. Preferably, the capsule body 32 is formed by a pair of sheets of material 40, 42 each having inner and outer annular portions 40A, 42A and 40B, 42B being concentrically arranged and radially spaced relative to one another. The inner and outer annular portions 40A, 40B of the one sheet of material 40 is attached, such as being welded, to the corresponding inner and outer annular portions 42A, 42B of the other sheet of material 42. The sheets of material 40, 42 also have middle annular portions 40C, 42C being located between and connected to the respective inner and outer annular portions 40A, 42A and 40B, 42B and spaced apart from one another so as to define therebetween the sealed annular cavity 34 of the capsule body 32 for containing the predetermined quantity of dosing material M. Preferably, the material of the sheets 40, 42 is a metal foil, such as stainless steel foil. In one embodiment of the capsule 12 of Figs. 1-5, both the inner edge 36 of the capsule body 32 defining the opening 38 through the body 32 and the sealed annular cavity 34 have endless continuous, generally circular, configurations. In the other embodiment of the capsule 12 of Figs. 9-11, 14 and 15, the inner edge 36 of the capsule body 32 defining the opening 38 has a generally U-shaped configuration beginning and ending at spaced locations on an outer peripheral edge 44 of the capsule body 32. In this embodiment, the sealed annular cavity 34 has an interrupted, generally C-shaped configuration. The configuration of the inner end portion 22A of the glass stem 22 is slightly arcuate shaped in the embodiment of Figs. 2, 3 and 6-8, whereas it is more flat shaped in the embodiment of Figs. 12-15. The dosing capsule 12 is applied to the electrode mount 16 prior to placing the electrode mount 16 into the one hollow end 14A of the tubular envelope 14 of the lamp 10 and prior to melting off the fill tube extension 28 and sealing the one end 14A of the envelope 14. The configuration of the inner end portion 22A of the glass stem 22 is slightly arcuate shaped in the embodiment of Figs. 2, 3 and 6-8, whereas it has a more flattened shape in the embodiment of Figs. 12-15. With respect to the configuration of the one preferred embodiment of the capsule 12 of Figs. 1-5, the capsule 12 is applied about glass stem 22 of the electrode mount 16 having the configuration of Figs. 1-5 by moving the capsule 12 axially over the electrode mount 16 from the inner electrode-mounting end portion 22A of the glass stem 22 toward the middle and outer end portions 22C, 22B thereof. Since in order to mount the electrode 26 to the inner ends 24A of the lead-in conductors 24, the inner ends 24A must be spread apart, from their respective parallel relationship shown in Fig. 6 to their respective divergent relationship shown in Fig. 2, through a distance greater than the diameter size of the opening 38 in the capsule body 32, the inner ends 24 of the conductors 24 will be spread outwardly and the electrode 26 then attached thereon after the capsule 12 has been applied or placed over and about the glass stem 22 of the electrode mount 16. With respect to the configuration of the other preferred of the capsule 12 of Figs. 9-11, the capsule 12 is applied about the flattened inner end portion 22A of the glass stem 22 of the electrode mount by aligning its elongated opening 38 with the glass stem 22 and then moving the capsule 12 transversely across the electrode mount 16. The electrode 26 can be attached on the electrode mount 16 either before or after application of the capsule 12 about the electrode mount 16. As mentioned previously, preferably the material composing the dosing capsule 12 is a metal foil, such as stainless steel, which is rupturable by applying heat thereto above a predetermined temperature. Referring to Fig. 16, a suitable heat-directing source 46, preferably a laser, can be disposed at the exterior of the envelope 14 after the ends of the envelope are sealed. Heat energy is generated by a laser beam 48 being directed through the envelope 14 and into contact with a portion 12A of the capsule 12 which is sufficient to raise the temperature of the contacted capsule portion 12A above the predetermined rupture temperature of the material and thereby cause a pierce or rupture therein which releases into the sealed envelope 14 the dosing liquid mercury M contained in the annular cavity 34 of the capsule 12. In summary, the dosing capsule 12 of the present invention is a sealed rupturable annular hollow body 32 frictionally supported, but not permanently attached, about the glass stem 22 of one of the electrode mounts 16 in the lamp 10. The annular body 32 contains a desired precise quantity of a dosing material, such as liquid mercury M and like substances, for dosing the electric discharge lamp 10 after the envelope 14 has been sealed. The method of dosing the lamp 10 contemplates installing the dosing capsule 12 and utilizing an internal heat source, for instance, conventional induction heating, or an external heat source, such as a laser, to pierce or rupture the installed annular hollow body 32 so as to carry out reliable and fast dosing of the lamp 10 with the desired precise quantity of mercury M after the hermetic sealing of the lamp envelope 14. The use of the laser 46 is preferred in order to provide a very rapid method of breaking the capsule 12. The design of the capsule 12 presents a large and non-oriented target to permit easy aiming of laser 46 and to provide a high degree of certainty that the laser beam 48 will actually hit and pierce the capsule 12. This maximizes the reliability of the mercury release process. It is thought that the present invention and many of its attendant advantages will be understood from the foregoing description and it will be apparent that various changes may be made in the form, construction and arrangement of the parts thereof without departing from the scope of the invention, the detailed description hereinbefore being merely preferred or exemplary embodiments thereof.

Claims: An electric arc discharge lamp (10), comprising: (a) an elongated hollow tubular envelope (14) having a pair of opposite ends (14A, 14B); (b) a pair of electrode mounts (16) respectively disposed in said ends (14A, 14B) of said hollow tubular envelope (14); and (c) a mercury dosing capsule (12) defining a hermetically sealed cavity (34) for containing a predetermined quantity of mercury (M) therein, characterized in that said capsule (12) has an inner edge (36) defining an opening (38) through said capsule (12) for receiving therethrough a portion of one of said electrode mounts (16) such that said capsule (12) is supported by said one electrode mount (16) with said sealed cavity (34) substantially surrounding said one electrode mount (16), said dosing capsule (12) being annular and mounted fittingly on said one electrode mount (16) at a position spaced axially from an electrode (26) disposed at one end of said electrode mount (16), said dosing capsule (12) having said sealed cavity (34) formed along at least a substantial portion of the periphery thereof. A lamp as recited in claim 1, wherein said capsule (12) includes a pair of sheets of material (40, 42) each having inner (40A, 42A) and outer (40B, 42B) annular portions concentrically arranged and radially spaced relative to one another, said inner (40A) and outer (40B) annular portions of one of said sheets (40) of material being attached to said corresponding inner (42A) and outer (42B) annular portions of the other of said sheets (42) of material, said sheets of material (40, 42) also having middle annular portions (40C, 42C) located between said respective inner (40A, 42A) and outer (40B, 42B) annular portions and spaced apart from one another so as to define said sealed cavity (34) for containing the predetermined quantity of mercury (M). A lamp as recited in claim 2, wherein said material of said sheets (40, 42) is a heat rupturable metal foil. A lamp as recited in claim 3, wherein said inner (40A, 42A) and outer (408, 42B) annular portions of said sheets of material are welded together. The lamp as recited in claim 4, wherein said sealed cavity (34) is annular having a substantially circular configuration. A lamp as recited in claim 3, wherein the material composing the dosing capsule (12) is rupturable by applying heat thereto above a predetermined temperature. A lamp as recited in claim 6, wherein the capsule (12) is ruptured by: disposing a heat-directing source at the exterior of the envelope (14) after the end of the envelope (14) is sealed; and directing heat energy through the envelope (14) and into contact with a portion of the capsule (12) so as to raise the capsule portion above the predetermined temperature and cause a rupture therein which releases the mercury (M) contained in the annular cavity (34) of the capsule (12). A lamp as recited in claim 7, wherein said heat-directing source is a laser and said heat energy is a laser beam generated by the laser.

Inventors: JOHNSON WAYNE DEAN, JOHNSON, WAYNE DEAN
Applicants: GEN ELECTRIC, GENERAL ELECTRIC COMPANY
Application year: 1993
Main classification: H01J61
IPC codes: H01J61, H01J9