Electric lamp or space discharge component or device manufacturi – Process – With assembly or disassembly
Reexamination Certificate
2001-06-25
2004-01-20
O'Shea, Sandra (Department: 2875)
Electric lamp or space discharge component or device manufacturi
Process
With assembly or disassembly
C313S574000
Reexamination Certificate
active
06679746
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a discharge lamp and a lamp unit. In particular, the present invention relates to a discharge lamp and a lamp unit used as the light source of an image projection apparatus such as a liquid crystal projector or a digital micromirror device (DMD) projector.
In recent years, an image projection apparatus such as a liquid crystal projector or a projector using a DMD has been widely used as a system for realizing large-scale screen images. A high-pressure discharge lamp having a high intensity has been commonly and widely used in such an image projection apparatus. For the light source used in the image projection apparatus, light is required to be concentrated on an imaging device included in the optical system of the projector, so that in addition to high intensity, it is also necessary to achieve a light source close to a point light source. Therefore, a short arc ultra high pressure mercury lamp that is closer to a point light and has a high intensity has been noted widely as a promising light source.
Referring to
FIG. 4
, a conventional short arc ultra high pressure mercury lamp
1000
will be described.
FIG. 4
is a schematic view of an ultra high pressure mercury lamp
1000
. The lamp
1000
includes a substantially spherical luminous bulb
110
made of quartz glass, and a pair of sealing portions (seal portions)
120
and
120
′ also made of quartz glass and connected to the luminous bulb
110
.
A discharge space
115
is inside the luminous bulb
110
. A mercury (in an amount of, for example, 150 to 250 mg/cm
3
) as a luminous material, a rare gas (e.g., argon with several tens kPa) and a small amount of halogen are enclosed in the discharge space
115
. A pair of tungsten electrodes (W electrode)
112
and
112
′ are opposed with a certain electrode distance D (e.g., about 1.5 mm) in the discharge space
115
. Each of the W electrodes
112
and
112
′ includes an electrode axis (W rod)
116
and a coil
114
wound around the head of the electrode axis
116
. The coil
114
has a function to reduce the temperature at the head of the electrode.
The electrode axis
116
of the W electrode
112
is welded to a molybdenum foil (Mo foil)
124
in the sealing portion
120
, and the W electrode
112
and the Mo foil
124
are electrically connected by a welded portion where the electrode axis
116
and the Mo foil
124
are welded. The sealing portion
120
includes a glass portion
122
extending from the luminous bulb
110
and the Mo foil
124
. The glass portion
122
and the Mo foil
124
are attached tightly so that the airtightness in the discharge space
115
in the luminous bulb
110
is maintained. In other words, the sealing portion
120
is sealed by attaching the Mo foil
124
and the glass portion
122
tightly for foil-sealing. The sealing portions
120
have a substantially circular cross section, and the rectangular Mo foil
124
is disposed in the center of the inside of the sealing portion
120
.
The Mo foil
124
of the sealing portion
120
includes an external lead (Mo rod)
130
made of molybdenum on the side opposite to the side on which the welded portion is positioned. The Mo foil
124
and the external lead
130
are welded to each other so that the Mo foil
124
and the external lead
130
are electrically connected at a welded portion
132
. The configurations of the W electrode
112
′ and sealing portion
120
′ are the same as those of the W electrode
112
and sealing
120
, so that description thereof will be omitted.
Next, the operational principle of the lamp
1000
will be described. When a start-up voltage is applied to the W electrodes
112
and
112
′ via the external leads
130
and the Mo foils
124
, discharge of argon (Ar) occurs. Then, this discharge raises the temperature in the discharge space
115
of the luminous bulb
110
, and thus the mercury is heated and evaporated. Thereafter, mercury atoms are excited and become luminous in the arc center between the W electrodes
112
and
112
′. The higher the mercury vapor pressure of the lamp
1000
is, the higher the emission efficiency is, so that a lamp having a higher mercury vapor pressure is more suitable as a light source for an image projection apparatus. However, in view of the physical strength against pressure of the luminous bulb
110
, the lamp
1000
is used at a mercury vapor pressure of 15 to 25 MPa.
The conventional lamp
1000
is produced in the manner as shown in
FIGS. 5A
to
5
C.
FIGS. 5A
to
5
C are cross-sectional views showing a production process sequence of a method for producing the lamp
1000
.
First, a glass pipe
150
for a discharge lamp having a luminous bulb portion
110
that will be formed into the luminous bulb of the lamp
1000
and a side tube portion (sealing portion)
122
that will be formed into the sealing portion of the lamp
1000
, and an electrode assembly
140
in which the electrode
112
is joined to one end of the metal foil (Mo foil)
124
and the external lead
130
is joined to the other end are prepared. Then, as shown in
FIG. 5A
, the electrode assembly
140
is inserted in the glass pipe
150
for a discharge lamp (electrode assembly insertion process).
Next, as shown in
FIG. 5B
, when the pressure in the glass pipe
150
is reduced (e.g., less than 1 atmospheric pressure), and the glass tube
122
of the glass pipe
150
is heated and softened with, for example, a burner
54
, so that the side tube portion
122
and the Mo foil
124
are attached tightly, thereby forming the sealing portion
120
(sealing portion formation process).
The same processes as those shown in
FIGS. 5A and 5B
are performed to the other side tube portion. More specifically, another electrode assembly
140
is inserted into a side tube portion that has not been formed into a sealing portion yet. At this time, the electrode assembly
140
is inserted while being aligned with the electrode
112
of the already-sealed electrode assembly
140
in such a manner that the pair of electrodes are on the same axis as much as possible and a predetermined electrode distance D is achieved. Thereafter, the sealing portion formation process is performed.
In this manner, when the sequence of the electrode assembly insertion process and the sealing portion formation process is performed twice, the luminous bulb
110
in which the pair of electrodes
112
are arranged in the discharge space
115
sealed with the pair of sealing portions
120
can be formed, as shown in FIG.
5
C. Thus, the lamp
1000
can be produced. The luminous material enclosed in the discharge space
115
can be introduced into the luminous bulb
110
after one sealing portion
120
is formed and before the other sealing portion
120
is formed.
The electrode distance D of the lamp
1000
is a very important design matter that defines the arc length of the discharge lamp. When the electrode distance D of the lamp
1000
is short, a discharge lamp serving as a light source closer to a point light source and having higher intensity can be realized. However, the inventors of the present invention found that there are limitations of the conventional production method regarding further reduction of the electrode distance D. More specifically, the inventors of the present invention found limitations in the production process as follows. In the conventional production method, it is necessary to define the electrode distance D in the electrode assembly insertion process shown in
FIG. 5A
, so that the electrode distance D cannot be defined with a higher precision than that of the alignment in the electrode assembly insertion process.
Since the electrode assembly
140
has a configuration where the W rod
116
and the external lead
130
are joined to ends of a thin Mo foil
124
(e.g., a thickness of about 20 to 30 &mgr;m), it is difficult to improve the alignment precision because of the small thickness of the Mo foil
124
. Therefore, when the lamp
1000
is produced by the conventional production me
Horiuchi Makoto
Ichibakase Tsuyoshi
Kai Makoto
Sasaki Ken-ichi
Seki Tomoyuki
Harness & Dickey & Pierce P.L.C.
Macchiarolo Peter
Matsushita Electric - Industrial Co., Ltd.
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