US3529209A - Self-starting compact arc lamp - Google Patents

Description

s p 5, 1970 (5. E. LIENHARD ETAL 3,529,209

SELF-STARTING COMPACT ARC LAMP Filed June 12, 1967 FIG. 2

INVEN TOR.

OTTO E. LIENHARD BY MICHAEL SKAL AGENT United States Patent 3,529,209 SELF-STARTING COMPACT ARC LAMP Otto E. Lienhard, Upper Montclair, and Michael Skal, Passaic, N.J., assignors to Engelhard Hanovia, Inc., Newark, N.J., a corporation of New Jersey Filed June 12, 1967, Ser. No. 645,187 Int. Cl. H01j 7/36; Hb 31/22 US. Cl. 315--327 1 Claim ABSTRACT OF THE DISCLOSURE BACKGROUND OF THE INVENTION Compact arc lamps of the type containing electrodes spaced apart less than about 1 cm. in an ionizable atmosphere comprising rare gas, e.g. xenon, at a pressure above about 2 atmospheres, e.g. 3-12 atmospheres, at temperatures of about 25 C. have been used as light sources of high intensity, e.g. in searchlights. Starting the arc of such lamps normally requires much higher voltages than the voltages necessary to operate the lamps. The high voltage necessary to start such lamps is conveniently supplied by well known pulse-type ignition circuits. To ignite a DC. xenon lamp, e.g. having an operating voltage of 22 volts, requires high voltage pulse of the order of 20 to 30 kv. and in addition, for the first second of operation, a DC voltage of at least 70 volts. After ignition the lamp may be operated from a 24 volt battery. The high voltage starter and the means to provide the initial elevated DC. voltage together weigh approximately 40 lbs. Another disadvantage of interest in the use of a high voltage pulse-type starter is the radio interference produced by it.

The present invention contemplates to eliminate to a large degree the above-mentioned disadvantages by eliminating the necessity for high-voltage starting and the heretofore necessary high-voltage starting circuitry.

SUMMARY OF THE INVENTION The invention deals with a low voltage starting compact arc lamp herein regarded as a self-starting compact arc lamp since it does not require separate pulse-type high voltage nor booster high voltage starting circuitry, the arc ignition being accomplished by DC. supply voltages of the order of about 16 volts to 36 volts appropriately ballasted to provide lamp-operating voltages of from about 15 volts to about 30 volts. The lamp comprises a tubular quartz envelope containing a pair of electrodes spaced apart from each other less than about 1 cm. and electrical input means hermetically passed through both ends of the envelope. One of the electrodes, preferably the cathode electrode, is movable relative to the anode electrode and is provided preferably at one end portion thereof with a magnetic body, e.g., a magnetic body of ferromagnetic material at the end portion remote from the anode and operating as a solenoid core movable within a magnetic field provided by a pair of solenoid coils longitudinally adjacent one another and mounted coaxially of the lamp envelope on the outer surface of the lamp envelope. One of the coils provides a magnetic field to move the cathode towards the anode and the other coil provides a magnetic field to move the cathode away from the anode. The core is provided at one end thereof with a conductor longitudinally flexible within the lamp envelope and connected to input leads appropriately hermetically sealed through the end of the lamp. Thus, when the lamp input terminals are connected to a battery of approximately 24 volts in series with a proper resistor to limit the operating current to the desired value, the lamp is started without need of any high voltage RF starter or booster voltage simply by moving the cathode through magnetic interaction with the magnetic core towards the anode until the cathode and anode touch each other and then magnetically retracting the cathode to its spaced operating position immediately thereafter.

DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a partly cross-sectional and partly elevational view of a lamp according to the invention, and

FIG. 2 illustrates an enlarged elevational side view of lamp components along lines 2-2 of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings, the self-starting compact arc lamp of the invention comprises a tubular fused quartz envelope 1 having initially open opposite end portions 2 and 3. An anode assembly is hermetically sealed into end portion 2. The anode assembly comprises a molybdenum seal foil 4 having input leads 5 welded to one end thereof and a tungsten anode electrode 6 mounted on one end of a stem 7 with the other end of the stem being welded to the opposite end of the seal foil 4. A short quartz collar 8 is mounted on stem 7 intermediate the seal foil 4 and anode. The anode assembly is positioned into lamp end tube with the input leads 5 extending outwardly thereof, and the envelope is heat sealed onto the seal foil 4 and the collar 8 whereby the anode assembly is hermetically sealed by means of the foil 4 and the quartz collar 8 contacts the inner tube walls maintaining the anode rigidly centered in the lamp envelope. An elongated quartzbushing 9 having a precision bore 10 formed longitudinally therethrough is mounted inside the envelope 1 and secured against the inner walls of the envelope substantially midway intermediate the ends 2 and 3 of the envelope. A cathode assembly is hermetically sealed into end portion 3. The cathode assembly comprises an elongated cathode electrode 11 having a length exceeding that of the bushing 9 and a diameter slidably fittable in precision bore 10 of bushing 9. One end of the cathode is mounted on an end 12 of cylindrical core 13 composed of ferromagnetic material. The other end 14 of the core 13 is provided with a short stud 15 extending axially thereof and to which is welded one end 16 of a flexible corrugated molybdenum conductor strip 17. The other end 18 of the conductor strip is welded to one end of a molybdenum seal foil 19 with input leads 20 welded to the opposite end of seal foil 19. The cathode assembly is positioned into the lamp envelope with the cathode 11 passing into close fitting slidable engagement with precision bore 10 of sleeve 9 and the input leads extending outwardly of the end portion 3. A quartz sleeve 21 is passed into the end portion 3 over the input leads 20, seal foil 19, and corrugated conductor 17 with its outer surface engaging the inner walls of the envelope and until its end 22 is spaced from the end 23 of bushing 9 a greater distance than the length of cylindrical core 13, and whereby the end 22 acts as a calculated motion-limiting abutment for the core 13. Having so positioned the cathode assembly, both the lamp envelope and the quartz sleeve are partially fused at the area 24 over the seal foil 19 to hermetically seal the lamp. With the lamp so assembled, it is apparent that the core 13 is movable longitudinally of the envelope -1 between the motion-limiting abutment 22 and the anode '6, which determine the arc gap, and consequently moves the tip 25 of cathode 11 into and out of touching contact with anode 6 to provide an arc gap of about 0.080". In order to accomplish such movement while the lamp is energized without any deterrent physical resistance to motion, the molybdenum conductor 17 is rendered longitudinally flexible, i.e. expansible and contractable, by virtue not only of its corrugated nature, but because the conductor 17 is a composite conductor of a plurality of foil strips 26, 27 and 28 each about 0.003" thick bonded to each other only at end portions 29 and 30 to provide both sufficient current carrying mass while having a flexibility greater than if the layers were completely bonded to each other. This construction enables the cathode movement with minimum force.

Having mounted the electrodes and hermetically sealed the lamp as hereinbefore described, the lamp is provided with an ionizable atmosphere of xenon at a pressure between about 3-12 atmospheres when cold, i.e. at a temperature of about 25 C., and a pair of solenoid coils 31 and 32 are mounted on the lamp envelope. The pair of coils 31 and 32 are mounted on the envelope adjacent one another longitudinally of and co-axially of the envelope with the core 13 positioned co-axially and substantially centrally intermediate the outer ends of the combined pair of coils. The coils are encased in an iron shell 31a and 32a and separated from each other by a partition 31b. The coils 31 and 32 are each independently energized as illustrated by FIG. 1 by a source of voltage, e.g. a 12-volt battery. Conductor leads 33 and 34 are connected to coil 31 and conductor leads 35 and 36 are connected to coil 32. When the lamp leads 5 and 20 are connected with a source of DC. voltage (not shown) the switch 37 is closed and switch 38 is opened whereby the coil 31 is energized to magnetically move the core 13 which moves the cathode tip 25 into contact with anode 6. As

soon as the contact is made, the switch 37 is opened, and switch 38 is closed whereby the coil 32 is energized to magnetically move the core 13 to the position shown in FIG. 1 and cathode 11 is retracted to assume a spaced position of the cathode tip 25 relative to anode 6 establishing the arc gap therebetween.

Consequently, by the structure hereinbefore described, the lamp is easily self-ignited without the employment of high voltages.

Various modifications of the invention are herein contemplated within the scope of the appended claim.

We claim:

1. A high pressure arc lamp comprising a substantially tubular light-transmissive envelope containing an anode electrode and a cathode electrode positioned to provide an arc therebetween and an ionizable atmosphere at a pressure above about two atmospheres at a temperature of about 25 0, one of the electrodes being movable relative to the other axially of the lamp envelope, said one electrode having a magnetic body mounted thereon,

a bushing means having a bore formed therethrough coaxially of the envelope and mounted in the lamp envelope, said one electrode being slidably movable in the bore of said bushing,

said magnetic body is mounted on one end of said one .electrode remote from the other electrode, a sleeve coaxially mounted in the envelope in spaced relationship with said bushing and the magnetic body being positioned in the space between the bushing and the sleeve, said magnetic body being movable in said space axially of the envelope and abuttable withthe ends of said bushing and said sleeve, the degree of movement of said magnetic body in said space being a calculated motion-limiting movement determining the length of the arc gap between the anode electrode and cathode electrode,

seal means at an end portion of said envelope, a flexible longitudinally expansible and contractable conductor strip secured to and between said magnetic body and said seal means,

said flexible conductor is composed of a plurality of corrugated foil strips bonded to each other only at their end portions,

a pair of solenoid coils mounted on the lamp envelope adjacent one another longitudinally of andcoaxially of the envelope, electrical circuit means for independently energizing each of the solenoid coils, the magnetic body being positioned coaxially centrally inter mediate the outer ends of the combined pair of the coils for response to the magnetic field of either solenoid coil when electrically energized, and means for selectively electrically energizing each coil to magnetically move the magnetic body and consequently the said one electrode axially of the lamp envelope.

References Cited UNITED STATES PATENTS 287,067 10/1883 Tibbits 335-256 X 2,446,855 8/1948 Seibel 335-256 745,427 12/1903 Edmonds 313-152 X 758,842 5/1904 King 315-327 X 769,637 9/1904 Rice 315-327 X 902,427 10/ 1908 Mildebrath 315-327 X 1,344,757 6/1920 Darran 315-327 X 2,016,131 10/1935 Beese 313-152 X 2,492,669 12/1949 Taylor 313-152 X 2,545,345 3/1951 Deri 313-152 X 3,278,778 10/1966 Retzer 313-217 X JAMES W. LAWRENCE, Primary Examiner D. OREILLY, Assistant Examiner US. Cl. X.R.

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