Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
~. 219667
D-95-1-742 -1- PATENT APPLICATION
LAMP WITH MERCURY RELEASE STRUCTURE AND METHOD FOR
DISPENSING MERCURY INTO A LAMP
FIELD OF THE INVENTION
This invention relates to electric discharge
lamps, and is directed more particularly to a
fluorescent lamp containing mercury, and to a method
for dispensing mercury into a fluorescent lamp.
HACItGROUND OF THE INVENTION
Fluorescent lamps are well-known in the art and
are used for a variety of types of lighting
installations. Such lamps are characterized as low
pressure discharge lamps and include an elongated
envelope, whose interior surface is coated with a
layer of phosphor, and an electrode at each end of
the envelope. The envelope also contains a quantity
of an ionizable medium, such as mercury, and a
starting gas at a low pressure, generally in the range
of 1 to 5 mm Hg. The starting gas may consist of
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argon, neon, helium, krypton, xenon or a combination
thereof .
One of the most commonly used methods for
introducing mercury into such lamps is by use of a
mechanical dispensing unit which forms part of an
"exhaust machine". In such a machine, mercury is
dispensed by the action of a slotted plunger passing
through a reservoir of mercury and into a closed
exhaust chamber housing an exhaust tube. The mercury
falls through the exhaust tube into the lamp. This
method of dispensing mercury has many drawbacks. The
mercury dispensing unit complicates the exhaust
machine, and the amount of mercury introduced into the
lamp envelope by this method cannot be precisely
controlled. Further, the lamp during processing is at
a high temperature and is in open communication with
the exhaust machine. As a result, it is inevitable
that a portion of the introduced mercury evaporates
and disappears from the lamp, or a portion of the
filling gas is driven out of the lamp. Still further,
the introduction of mercury through the exhaust tube
involves the risk of mercury getting stuck in the
exhaust tube so that after lamp sealing, the lamp
contains too little or no mercury at all. For these
reasons, an overdose of mercury is required to ensure
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the lamp retains a minimum amount of mercury.
Finally, working with mercury on the exhaust machine
requires additional safety precautions on medical
grounds.
An alternative method for dispensing mercury is
to place inside the lamp a mercury compound that is
inert under lamp processing conditions but can later
be activated to release mercury. Disadvantageously,
this method releases impurities, which then require
special Bettering. Moreover, this method requires a
relatively long period of time to activate the mercury
compound, typically 5 to 30 seconds. As a result,
this method of dispensing mercury does not readily
lend itself to high speed production machinery.
Another method of introducing mercury into an arc
discharge lamp is set forth in U.S. Pat. No.
4,553,067, issued on November 12, 1985 to Roche, et
al. Therein, a mercury dispensing target is located
within an exhausted lamp having a coil at each end of
the lamp. The dispensing target is affixed to a lead-
in wire adjacent to one of the coils. During
processing, the mercury target is heated by bombarding
the target with a directed stream of electrons
produced by one of the coils, which causes the
contained mercury to be released. Although this
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method reduces mercury release time to about 3
seconds, it is desirable to obtain further reductions.
U.S. Patent No, 4,870,323, which issued on
September 26, 1989, to Parks, Jr., et al, describes a
method for dispensing mercury into a fluorescent lamp
wherein portions of the mount structure are coated
with an insulating coating (e. g., zirconium dioxide).
A directed stream of electrons is focused to a portion
of the mercury dispensing capsule devoid of the
insulating coating. Although this method is effective
in reducing the mercury release time, the application
of an insulating coating to the various portions of
the mount structure may be impractical in commercial
production.
There is thus a need for a fluorescent lamp
having mercury therein and for a method for dispensing
mercury into the lamp, such that the amount of mercury
can be precisely controlled, there is no need for
introducing excess mercury into the lamp, the mercury
can be quickly released into the lamp envelope, there
are generated no medical hazards, and the process is
readily adaptable for high-speed commercial production
of lamps.
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SUN~1ARY OF THE INVENTION
Accordingly, an object of the present invention is
to provide a fluorescent lamp having therein a precise
amount of mercury, wherein all the mercury introduced into
the lamp remains in the lamp and there is no need for
providing excess mercury to the lamp to ensure completing
the lamp with a required amount of mercury therein.
A further object of the invention is to provide
such a lamp as is amenable to high-speed production.
A still further object of the invention is to
provide a method for dispensing mercury into a fluorescent
lamp envelope, such that a precise amount of contained
mercury can be introduced into the envelope and quickly
released therein.
A still further object of the invention is to
provide such a method as is substantially free from medical
hazards.
In accordance with one aspect of the invention,
there is provided a lamp comprising: a sealed transparent
elongated envelope containing a gas fill; a coil at each of
two ends of said elongated envelope, said coils extending
widthwise of said envelope; first and second lead-in wires
connected to each of said coils and connectable to an
external source of electric current; and a capsule
containing mercury and mounted within said envelope at one
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of said ends of said envelope, said capsule being connected
to one of said first and second lead-in wires of one of said
coils, said capsule being disposed adjacent to a center
portion of said one coil and having a body portion extending
axially in said envelope toward the other of said coils;
said other coil being adapted, upon energization by said
current, to emit electrons toward said capsule to heat and
burst said capsule, to release said mercury into said
envelope.
In a specific embodiment the capsule has a base
end disposed in a widthwise plane of the envelope in which
is disposed the one coil.
In accordance with a further aspect of the
invention, there is provided a method for releasing mercury
into a lamp having a sealed, transparent, elongated envelope
with two ends, a coil at each of said two ends, said coils
extending widthwise of said envelope, and first and second
lead-in wires connected to each of said coils and
connectable to an external source of electric current, said
method comprising the steps of: providing a capsule
containing mercury; mounting said capsule at one of said
ends of said envelope by connecting said capsule to one of
said lead-in wires of one of said coils; disposing said
capsule adjacent to a center portion of said one coil, with
a body portion of said capsule extending axially in said
CA 02196367 2004-05-21
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envelope toward the other of said coils; and energizing said
other coil by said connecting of said lead-in wires to said
source of electric current, to cause emission of electrons
from said other coil toward said capsule to heat and burst
said capsule, to release said mercury into said envelope.
The above and other features of the invention,
including various novel details of construction and
combinations of parts, will now be more particularly
described with reference to the accompanying drawings and
pointed out in the claims. It will be understood that the
particular device and method steps embodying the invention
are shown by way of illustration only and not as limitations
of the invention. The principles and features of this
invention may be employed in various and numerous
embodiments without departing from the scope of the
invention.
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BRIEF DESCRIPTION OF THE DRAWINGS
Reference is made to the accompanying drawings in
which is shown illustrative embodiments of the
invention, from which its novel features and
advantages will be apparent.
In the drawings:
FIG. 1 is a side elevational view, broken away
and partly in section, of one form of fluorescent lamp
illustrative of an embodiment of the invention;
FIG. 2 is an elevational view, broken away and
partly in section, of a portion of the lamp of FIG. 1;
FIG. 3 is a view taken along line III-III of FIG.
2; and
FIG. 4 is a chart illustrating a sequence of
steps in the inventive method.
DESCRIPTION OF TH$ PREFERRED EM80DIMENTS
Referring now to the drawings, there is shown in
FIGS. 1-3 an arc discharge lamp 10 (e.g., a
fluorescent lamp) having a sealed elongated envelope
12 of light-transmitting vitreous material. The
envelope 12 has opposing end portions 14, 16, and
encloses an inert starting gas, which may be argon,
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neon, helium, krypton, xenon, or a combination
thereof, at a low pressure in the range of about 1 to
mm Hg.
A first coil electrode 18 and a second coil
5 electrode 20 are located within opposing end portions
14 and 16, respectively. Coils 18, 20 may be coated
with electron-emitting materials, such as Ba0--Sr0-
Ca0 containing MZr03. A first pair of lead-in wires
22, 24, connect to first electrode 18 and a second
pair of lead-in wires 26, 28, connect to second coil
20. Suitable bases 30, 32, carrying contacts 34, 36
and 38, 40 are respectively sealed adjacent to the
end portions 14, 16. Lead-in wires 22, 24, and 26,
28 are electrically connected to contacts 34, 36, and
38, 40, respectively.
A phosphor coating 42 may be disposed on the
interior surface of the envelope 12. The phosphor
coating 42 is responsive to the ultraviolet radiation
generated by the plasma discharge to provide the
desired emission spectrum.
As further shown in FIGS. 1-3 , fluorescent lamp
10 contains a mercury dispensing target, such as a
metal capsule 46, connected to a support wire 44
connected to a lead-in wire 24 and disposed adjacent
to first coil 18.
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The mercury capsule 46 has a tubular-shaped main
body portion 48 which encloses a quantity of liquid
mercury prior to processing. The mercury is sealed
within the main body portion 48 of the capsule 46 by
means of a flattened base end portion 50. The mercury
may be sealed within the capsule, for example, by
utilizing teachings of U.S. Pat. No. 4,754,193 issued
on June 28, 1988 to James L. Holmes, et al.
The basic circuit arrangement for utilizing
electron current to release the mercury is shown in
FIG. 1 as comprising a lamp ballast 54 to regulate the
current and a DC power supply 52. Power supply 52 may
include a full-wave bridge rectifier (not shown) to
transform AC voltage from the line to DC. The end 14
of the lamp 10, containing the mount to which the
mercury capsule 46 is attached, is connected to the
positive side of the power supply 52. Contacts 38 and
40 of base 32, located at the end 16 of lamp 10, are
connected to the negative side of the power supply 52.
The current drawn through fluorescent lamp 10
during the capsule rupturing process is essentially
electron current. The primary source of electron
current within lamp 10 is the lamp cathode which, in
the d.c. circuit, is the electrode 20 connected to the
negative side of the power supply 52. The primary
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electron current generates secondary electrons through
an ionization process in the positive column of the
evacuated, filled and sealed lamp. These electrons
have a velocity established by the lamp field in the
direction from cathode-to-anode. Electrons arriving
at the positive end (i.e., anode) of the lamp are
collected by the electrode coil 18, the lead-in wires
22, 24, and the mercury capsule 46. The rate at which
the capsule temperature increases is proportional to
the amount of electrons collected. Inasmuch as
capsule rupture is caused by an increase in capsule
temperature, it is evident that the faster the capsule
heats up, the lower the rupture time will be.
Although the rupture circuit illustrated in FIG.
1 uses direct current, the lamp is generally intended
for use on an alternating current circuit.
Referring again to FIGS. 1-3, it will be seen
that in accordance with the present invention the
capsule 46 is disposed in the lamp 10 such that the
base end 50 of the capsule 46 is disposed in a
widthwise plane of the envelope in which is disposed
the first coil 18. The capsule elongated body portion
48 extends axially in the envelope 12 toward the
second coil 20. The base end 50 of the capsule 46 is
disposed adjacent to a central portion 56 of the
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first coil 18 and the body portion 48 of the capsule
extends normal to the plane of the coil 18 and along a
central axis of the envelope 12 toward the end portion
16 of the lamp 10. The base end 50 of the capsule 46
and the coil 18 define therebetween a gap (FIG 3.) of
about 1/32 - 1/4 inch in the widthwise plane of the
coil 18. The smaller the gap, the more rapid the
heating and bursting of the capsule 46 to free the
mercury, which is vaporized by the heat.
A method set forth hereinbelow facilitates the
release of mercury into the fluorescent lamp 10 having
the sealed, transparent, elongated envelope 12 with
first and second ends 14, 16, the coils 18, 20 at each
of the ends 14, 16, respectively, the coils 18, 20
extending widthwise of the envelope 12, and lead-in
wires 22, 24, and 26, 28 connected to each of the
coils 18, 20, respectively. The method includes the
steps of (FIG. 4) providing a capsule 46 containing
liquid mercury, and mounting the capsule 46 at the
first end 14 of the envelope 12 by connecting the
capsule 46, by way of support wire 44, to the lead-in
wire 24. In positioning of the capsule 46, the base
end 50 thereof is disposed in a widthwise plane of the
envelope 12 in which is disposed the first coil 18,
with the capsule body portion 48 extending axially in
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the er.~~elope 12 toward the second coil 20. The coil
20 is energized by connecting one of the lead-in wires
26, 28 to the power supply 52 to cause emission of
electrons from the coil 20 toward the capsule 46 to
heat and burst the capsule, to release vaporized
mercury into the envelope.
As noted above, the capsule base end 50 is
positioned adjacent to the center portion 56 of the
first coil 18 (FIG. 3), and preferably is spaced from
the coil 18 by about 1/32 - 1/4 inch.
It has been found that utilization of the above-
described apparatus and method in the production of 40
watt lamps results in release of mercury into the
lamps in an average time of about 1 second, whereas
using a capsule welded directly to a lead wire of a 40
watt lamp results in a longer release time, averaging
greater than 3 seconds. Thus, placing the capsule in
the position described herein substantially reduces
the release time required, from an average of about 3
seconds to an average of about 1 second. While even
further reduction may be obtained by leaving the anode
leads open, rather than in common, the lead wire to
which the capsule is molded must be known in the
manufacturing process, which is an impractical
requirement in most production lines.
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It is to be understood that the present invention
is by no means limited to the particular construction
herein disclosed and/or shown in the drawings, but
also comprises any modifications or equivalents within
the scope of the claims.
Having this described our invention, what we
claim as new and desire to secure by Letters Patent of
the United States is:
