Electric lamp or space discharge component or device manufacturi – Process – Electrode making
Reexamination Certificate
2001-04-17
2004-03-16
Ramsey, Kenneth J. (Department: 2879)
Electric lamp or space discharge component or device manufacturi
Process
Electrode making
C445S006000, C445S026000, C219S121660
Reexamination Certificate
active
06705914
ABSTRACT:
This application is based on Japanese Patent Application No. 2000-116699, No. 2000-188785, and No. 2001-94226 with domestic priority claimed from the former two applications, the content of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to an electrode for a high pressure discharge lamp, a high pressure discharge lamp, and a method of manufacturing therefor.
(2) Description of Related Art
In recent years there has been active development of projection type image display apparatuses such as liquid crystal projectors. In such a projection type image display apparatus it is necessary to have a high intensity light source close to a point light source. Generally a high pressure discharge lamp such as a high pressure mercury lamp or a metal halide lamp of the short arc type is used as this kind of light source.
One of the main technical tasks when developing high pressure discharge lamps of the short arc type is lengthening the life by improving the life characteristics. Namely, generally in high pressure discharge lamps of the short arc type, the tungsten which forms the electrode melts and disperses, the electrode tip becomes deformed and wears due to the temperature of the electrode end increasing excessively, while the dispersed tungsten is deposited on the inner surface of the light-emitting tube, causing blackening. This blackening of the inner surface of the light-emitting tube causes premature degradation of light flux. In order to solve this problem, conventionally various techniques have been investigated relating to design of electrodes for high pressure discharge lamps of the short arc type and manufacturing methods of the electrodes.
As prior art relating to the above described electrode design, an electrode which has a construction such as that shown in
FIG. 1
has been developed. The electrode
901
shown in
FIG. 1
is formed by an electrode rod
902
with a narrow shaft diameter, and a cylindrical electrode part
903
whose inside diameter is larger than the electrode rod
902
, in combination. The characteristics of the operation of the electrode are (1) the cylindrical electrode part
903
lowers the temperature of the electrode tip
904
by transferring heat generated therein rapidly to the electrode rod side, suppressing deformation and wear of the electrode tip
904
by melting and dispersion of the electrode metal, and (2) through the working of the electrode rod
902
with a narrow shaft diameter, the whole of the electrode
901
is thermally insulated, promoting the evaporation of light emitting material enclosed in the light-emitting tube.
An electrode such as the electrode
901
is ordinarily manufactured by a grinding process of a block of a high melting point metal material such as tungsten, and is used as an anode in particular in high pressure discharge lamps of the short arc type such as super high pressure mercury lamps and high pressure xenon lamps of the DC discharge type which are subject to high rises in temperature.
Meanwhile, initially electrodes of the same construction as high pressure discharge lamps used for general lighting of the long arc type were used for metal halide lamps and high pressure mercury lamps of the short arc type which are used as light sources for projection type image display apparatuses of recent years. As shown in
FIG. 2
, an electrode
911
is formed by an electrode rod
912
made from ordinary tungsten, and a coil
913
of tungsten wire which has a narrow wire diameter. However, in a high pressure discharge lamp of the short arc type which uses an electrode such as the electrode
911
, the above-described deformation and wear of the electrode tip due to melting and dispersion of the tungsten electrode material cannot be avoided, making lengthening the life of the lamp difficult.
Subsequently, as a way of solving the problem of lengthening the life of such a lamp, electrodes which have the basic structure shown in
FIG. 1
which were developed for use in conventional high pressure discharge lamps of the short arc type were re-investigated. However, as it is costly to manufacture electrodes by a grinding process, an electrode that can be manufactured cheaply while having the same basic construction as the electrode
901
in
FIG. 1
was investigated. Prior art relating to such electrodes is disclosed, for example, in Japanese Patent Number 2820864 and Japanese Patent Laid-Open No. H10-92377.
Examples of the electrodes of the above-described patents are shown in FIG.
3
A and FIG.
3
B. An electrode
921
is manufactured through two processes which are simple compared to the above-described grinding process: (a) first, a tungsten wire coil
923
is wound and set around the discharge end of the tungsten electrode rod
922
(see FIG.
3
A), and (b) the discharge side end of the electrode rod
922
and the discharge side end of the coil
923
are melted and fused by a so-called electric discharging method to form an electrode tip
924
which is substantially a semi-sphere (see FIG.
3
B).
In the electrode
921
the section formed by the coil
923
and the semi-spherical electrode tip
924
has the same effect as the cylindrical electrode part
903
and the electrode tip
904
of the electrode
901
shown in FIG.
1
. Consequently, the heat in the semi-spherical electrode tip
924
is transferred rapidly to the coil
923
, lowering the temperature of the electrode tip
924
. In this way, even electrodes manufactured using low cost manufacturing electric discharging methods, melting and dispersion of the electrode material and deformation and wear of the electrode tip can be suppressed and life can be lengthened.
Please note that another piece of prior art relating to improving life expectancy of high pressure discharge lamps is a means which uses tungsten of high purity as an electrode material, disclosed in Japanese Patent Laid-Open No. H9-165641. Here, a result is shown that using tungsten of high purity in which the sum total of the elements of the accessory constituents Al, Ca, Cr, Cu, Fe, Mg, Mn, Ni, Si, Sn, Na, K, Mo, U and Th is regulated to 10 ppm of the principal component tungsten W is used as the electrode (particularly the anode) material in large discharge lamps with high output is effective in improving lamp electrode life span.
Based on the above-described related art, the present inventors worked toward developing a high pressure mercury lamp of the short arc type which can be used as a light source in projection type image display apparatuses. In the development the inventors set two objectives which relate in particular to the performance of lamps demanded by the market. The objectives were (1) making the distance between the electrodes, in other words, the distance between the discharge ends of the two electrodes provided in opposition in the light-emitting tube, no more than 1.5 mm, which is shorter than conventional spacing, in order to improve light usage efficiency when combined with a reflective mirror, and (2) to accomplish a lamp life expectancy of at least 3000 hours. Please note that (2) lamp life expectancy, as will be explained below, is defined by the aging time when the light flux maintaining rate estimated from the average illuminance maintaining rate of nine points on a screen during light emission by the lamp unit drops to 50%.
The present inventors, when beginning development, investigated developing a high pressure discharge lamp of the short arc type which has shorter distance between electrodes than conventional lamps, using electrodes made by an electric discharging method based on the methods in the above-described patents (FIGS.
3
A and
3
B). However, when the inventors measured characteristics of mass produced lamps which use such electrodes, they discovered much variation between lamps in characteristics such as voltage and life, meaning such lamps lack commercial viability.
Subsequently, when the cause of the above-described variations in lamp characteristics was investigated, it was revealed
Kitahara Yoshiki
Shimizu Toshiyuki
Tsutatani Takashi
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