Electric lamp and discharge devices – With gas or vapor – Having electrode lead-in or electrode support sealed to...
Reexamination Certificate
2000-04-19
2002-08-13
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Having electrode lead-in or electrode support sealed to...
C313S625000
Reexamination Certificate
active
06433479
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention concerns a short-arc type discharge lamp used for a light source in such applications as projectors, exposure or semiconductors, ultraviolet hardening and so on.
2. Description of Related Art
Short-arc discharge lamps have been used, for example, as light sources in light source equipment, such as projectors or other light projection equipment. In such short-arc discharge lamps, a cathode and anode have faced each other within a bulb made of quartz glass, in which xenon gas, for example, was sealed.
FIG. 5
is a cross-sectional explanatory drawing that shows one example of a conventional short-arc discharge lamp. The bulb
30
of this short-arc discharge lamp comprises a light-emitting tube
31
to which an outwardly extending sealing tube
32
is connected at each side. A constricted portion
32
a
, which is a part of the sealing tube
32
, is formed where the sealing tube
32
joins the light-emitting tube
31
.
Within the light-emitting tube
31
, a cathode
33
and anode
34
are located facing each other. The cathode
33
and the anode
34
are each mounted on the end of an electrode rod which passes through a sleeve material
35
of quartz glass, for example, and projects outward through the sealing tube
32
. An air seal
37
is formed by fusing the end of the sealing tube
32
to the electrode rod
35
. The sleeve material
36
is fastened in place by fusing it into a single piece with the constricted portion
32
a
. In this way, the electrode rod
35
is held in place by the sleeve material
36
and the end of the sealing tube
32
.
FIG. 6
is a cross-sectional explanatory drawing of a key part of the short-arc discharge lamp shown in
FIG. 5. A
pendant ridge
38
formed when the constricted portion
32
a
of the sealing tube
32
is formed extends around the full inner circumference of the sealing tube
32
near to the end of the sleeve material
36
which is closest to the light-emitting tube
31
. A wedge-shaped space
39
is thus formed between the pendant ridge
38
and the end of the sleeve material
36
that is closest to the light-emitting tube
31
. The constricted portion
32
a
of the sealing tube
32
is formed by reducing the diameter of the sealing tube
32
, by means of heating a portion of the outer periphery of the sealing tube
32
while the pressure within the bulb is reduced, for example, to between 1×10
-3
and 1×10
-4
Torr.
However, in recent years, there have been demands for greater lighting power in these short-arc discharge lamps. To satisfy these demands, it has become necessary to increase the amount of gas sealed into the light-emitting tube
31
, leading to the problem that, when the amount of gas sealed into the light-emitting tube
31
of this kind of short-arc discharge lamp is increased, the pressure of the gas sealed within the light-emitting bulb
31
increases to perhaps 7500 Torr or more when the lamp is lit. The sleeve material
36
and the constricted portion
32
a
are fused into a single piece, so that the stress is concentrated on the wedge-shaped space
39
and cracks appear in the constricted portion
32
a
. When the lamp is turned on and off repeatedly, the cracking progresses until finally the sealing tube
32
is broken.
In order to prevent cracks from appearing in the sealing tube
32
in this way, it has been proposed that the sleeve material
36
be fixed in place while preventing the constricted portion
32
a
of the sealing tube
32
and the sleeve material
36
from fusing into a single piece, by means of placing molybdenum foil between the sleeve material
36
and the constricted portion
32
a
. It has been found, however, that even with such a construction, it is not possible to completely resolve the problem described above, and cracks sometimes appear in the constricted portion when the lamp is turned on and off repeatedly.
SUMMARY OF THE INVENTION
This invention was perfected as a result of long research to understand the causes of the problem stated above. Its purpose is to reliably prevent the appearance of cracks in the sealing tube, and thus to provide a short-arc discharge lamp with a long service life.
The short-arc discharge lamp of this invention is one having a bulb comprising a light-emitting tube and sealing tubes connected to both sides of the light-emitting tube, with an anode and a cathode positioned facing each other within the light-emitting tube, the anode and cathode being on the ends of electrode rods that pass through sleeve material that is supported by the sealing tubes, in which short-arc discharge lamp, molybdenum foil is located between the sleeve material and the sealing tube, the outer surface of the molybdenum foil which faces the sealing tube having undergone surface treatment with a high-melting-point metal that is resistant to oxidation. The high-melting-point metal is preferably chosen from among tungsten, rhenium, tantalum, rhodium and platinum.
In the arrangement described above, molybdenum foil is located between the sleeve material and the sealing tube, and the outer surface of the molybdenum foil which faces the sealing tube has undergone surface treatment with a high-melting-point metal with resistance to oxidation. Because of this, the molybdenum foil does not fuse with the sealing tube, and it is possible to prevent the appearance of cracks in the sealing tube, and as a result, it is possible to obtain a short-arc discharge lamp with long service life.
These and further objects, features and advantages of the present invention will become apparent from the following description when taken in connection with the accompanying drawings which, for purposes of illustration only, show a single embodiment in accordance with the present invention.
REFERENCES:
patent: RE31519 (1984-02-01), Sobieski
patent: 5200669 (1993-04-01), Dixon et al.
patent: 5576598 (1996-11-01), Zaslavsky et al.
Higashimoto Youichirou
Yamane Takumi
Clove Thelma Sheree
Nixon & Peabody LLP
Patel Nimeshkumar D.
Safran David S.
Ushiodenki Kabushiki Kaisha
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