Electric lamp and discharge devices – With gas or vapor – Having particular electrode structure
Reexamination Certificate
2000-07-05
2002-10-01
Day, Michael H. (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Having particular electrode structure
C313S491000, C313S632000
Reexamination Certificate
active
06459202
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention concerns discharge lamps, and in particular, the manner in which each of the electrodes is connected to the tip of an electrode support bar within a bulb of the lamp.
2. Description of Related Art
Conventionally, a discharge lamp has a bulb that comprises a light-emitting tube, which forms the light emitting space, and seal tubes connected to it on opposite sides. Sealed within the light-emitting tube of the bulb is a pair of facing electrodes (anode and cathode) made of tungsten, xenon gas, for example, and mercury. Each of the electrodes is fixed to the tip of a supporting electrode support bar that is made of tungsten and extends along the tube axis from the seal tube of the bulb into the light-emitting tube.
A well-known means of fixing the electrode to the tip of the electrode support bar, is to form a concavity in the base surface of the electrode, and fit the tip of the electrode support rod into the cavity with a buffer material between them. To explain more concretely, FIG.
7
(
a
) shows a tapered concavity
50
a
formed in the base surface
50
b
of the electrode
50
, such that the diameter of the concavity grows smaller from the base toward the tip of the electrode
50
. The tip
51
a
of the support bar
51
is also tapered, such that its diameter grows smaller moving toward the tip of the bar, to match the shape of the concavity
50
a
of the electrode
50
. The buffer material
52
is formed around the tip
51
a
of the electrode support bar
51
. Next, as shown in FIG.
7
(
b
), the tip
51
a
of the electrode support bar
51
is inserted into the concavity
50
a
of the electrode
50
and, as shown in FIG.
7
(
c
), by pressing the tip
51
a
of the electrode support bar
51
so that the entire tip is accommodated within the concavity
50
a
of the electrode
50
, the tip
51
a
of the electrode support bar
51
is fitted into the concavity
50
a
of the electrode
50
, and is fixed to it.
Nevertheless, there are the following problems with such a technique.
(1) The buffer material
52
is formed by wrapping molybdenum foil or a tantalum sheet around the tip
51
a
of the electrode support bar
51
, but adjustment of the thickness of the buffer material
52
, i.e., adjustment of the thickness of the molybdenum foil or tantalum sheet used or of the number of turns wrapped, is determined by the fabricator through repeated trial and error, and so this operation is quite complex and requires relatively advanced technology. Moreover, after the tip
51
a
of the electrode support bar
51
is fitted into the concavity
50
a
of the electrode
50
, a procedure is required to trim away any excess buffer material
52
that is exposed outside the concavity
50
a
of the electrode
50
. In addition, both the concavity
50
a
of the electrode
50
and the tip
51
a
of the electrode support bar
51
are tapered to facilitate the insertion of the tip
51
a
of the electrode support bar
51
into the concavity
50
a
of the electrode
50
, and the machining process to form the tapered concavity
50
a
in the electrode
50
and that to form the tapered tip
51
a
of the electrode support bar
51
require a high degree of machining precision. For those reasons, this means of fitting and fixing the tip
51
a
of the electrode support bar
51
into the concavity
50
a
of the electrode
50
takes time and effort, and so a high level of productivity is not possible.
(2) The holding power of the electrode support bar
51
on the electrode
50
(the force necessary to remove the tip
51
a
of the electrode support bar
51
from the concavity
50
a
of the electrode
50
) depends on the thickness of the buffer material
52
. Moreover, adjustment of the thickness of the buffer material
52
is done by repeated trial and error by the fabricator, as stated above, and so it is difficult to fix the electrode
50
to the tip
51
a
of the electrode support bar
51
with a holding power that is consistent from one product to the next. As a result, there is great fluctuation in the holding power of the electrode support bar
51
on the electrode
50
from one product to the next, and if the electrode support bar
51
has too little holding power on the electrode
50
, the electrode
50
could fall off the electrode support bar
51
during shipping of the discharge lamp, or when the lamp is lighted.
SUMMARY OF THE INVENTION
In view the situation described above, it is a primary object of this invention to provide a discharge lamp in which, by a simple procedure, the tip of the electrode support bar can be fitted easily into a concavity formed in the base of the electrode, and can be stably fixed to the electrode with high holding power.
The discharge lamp of this invention is a discharge lamp having an electrode supported by an electrode support bar, preferably one made of molybdenum, by means of the tip of the electrode support bar engaging in a concavity formed in the electrode, in which the tip of the electrode support bar is made with a slit into which a spreader piece is pressed to spread the slit.
More specifically, in accordance with the invention, a spreader piece is mounted in a slit formed in the tip of the electrode support bar, and when the tip of the electrode support bar is pushed into the concavity in the electrode in that state, the spreader piece is pushed, by the bottom of the concavity in the electrode, into the slit in the electrode support bar. As a result, the slit is spread and the outer surface of the electrode support bar puts pressure on the inner surface of the concavity in the electrode, by which means the electrode is fixed to the tip of the electrode support bar. Thus, there is no need to use buffer material, and there is no need to taper the concavity in the electrode or the tip of the electrode support bar, and so the tip of the electrode support bar can be fitted easily to the concavity in the electrode by a simple process. Moreover, because a slit in the tip of the electrode support bar is spread and the outer surface of the electrode support bar is pressed against the inner surface of the electrode, the electrode is fixed to the tip of the electrode support bar stably and with great holding power. In addition, by forming the electrode support bar of molybdenum, which has high plasticity and toughness, it is possible to prevent damage to the tip of the electrode support bar when the slit is spread.
REFERENCES:
patent: 3902090 (1975-08-01), Ekkelboom et al.
patent: 5451837 (1995-09-01), Stevens et al.
Hagi Shigehisa
Kira Takehiro
Day Michael H.
Nixon & Peabody LLP
Safran David S.
Ushiodenki Kabushiki Kaisha
Zimmerman Glenn
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