Electric lamp and discharge devices – With gas or vapor – Having electrode lead-in or electrode support sealed to...
Reexamination Certificate
2001-05-30
2004-05-11
Patel, Nimeshkumar D. (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Having electrode lead-in or electrode support sealed to...
C313S489000, C313S634000, C313S635000, C313S636000
Reexamination Certificate
active
06734628
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 a light source for projectors using a digital micromirror device (DMD) or a light source for a liquid crystal projector. The present invention also relates to an image display apparatus including such a discharge lamp or discharge unit.
In recent years, an image projection apparatus such as a projector using a DMD (digital light processing (DLP) projector) or a liquid crystal projector 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. In the image projection apparatus, light is required to be concentrated on an imaging device (DMD panel or liquid crystal panel or the like) 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, among high-pressure discharge lamps, a short arc ultra high pressure mercury lamp that is close to a point light and has a high intensity has been noted widely as a promising light source.
Referring to
FIG. 5
, a conventional short arc ultra high pressure mercury lamp
1000
will be described.
FIG. 5
is a schematic top 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
′ made of also quartz glass and connected to the luminous bulb
110
.
A discharge space
115
is inside the luminous bulb
110
. A mercury
118
in an amount of the enclosed mercury 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 distance (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 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
117
where the electrode axis
116
and the Mo foil
124
are welded. The sealing portion
120
includes a glass portion
122
extended 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. Both of the sealing portions
120
have a circlar 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
117
is positioned. The Mo foil
124
and the external lead
130
are welded with each other so that the Mo foil
124
and the external lead
130
are electrically connected at a welded portion
132
. The structures of the W electrode
112
′ and sealing
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 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
118
is heated and evaporated. Thereafter, mercury atoms are excited and become luminous in the arc center between the W electrodes
112
and
112
′. As the pressure of the mercury vapor of the lamp
1000
is higher, the emission efficiency is higher, so that the higher pressure of the mercury vapor is 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.
As shown in
FIG. 6
, the lamp
1000
can be formed into a lamp unit
1200
in combination with a reflecting mirror
60
.
FIG. 6
is a schematic cross-sectional view of the lamp unit
1200
. The lamp unit
1200
can be used as a light source of DLP projectors or liquid crystal projectors, for example.
The lamp unit
1200
includes the discharge lamp
1000
and the reflecting mirror
60
for reflecting light emitted from the discharge lamp
1000
, and the light emitted from the discharge lamp
1000
is reflected at the reflecting mirror
60
and emits in the emission direction
50
. The reflecting mirror
60
has a front opening
60
a
on the side of the emission direction
50
. A front glass (not shown) is to be attached at the front opening
60
a
for the purpose of preventing scattering at the time of lamp breakage. A lead wire
65
is electrically connected to the external lead
130
of the sealing portion
120
positioned on the front opening
60
a
side. The lead wire
65
is extended to the outside of the reflecting mirror
60
through an opening
62
for lead wire of the reflecting mirror
60
. The lamp base
55
is attached to the other sealing portion
120
′ of the discharge lamp
1000
, and the sealing portion
120
′ attached with the lamp base
55
is attached to the reflecting mirror
60
.
The front glass is provided at the front opening
60
a
of the reflecting mirror
60
, so that lamp unit
1200
is of an airtight structure. Therefore, when the lamp
1000
is heated, the temperature in the lamp unit
1200
becomes very high. Accordingly, the lamp
1000
is designed and produced with an estimation of the temperature of the lamp
1000
in the lamp unit
1200
to guarantee the lamp operation.
However, the inventors of the present invention found that when the conventional lamp unit
1200
is used as the light source of a DLP projector, the temperature of the welded portion
132
of the sealing portion
120
positioned on the emission direction
50
side became higher than estimated, and the welded portion
132
is oxidized and the lamp
1000
stops operating. In other words, molybdenum constituting the external lead
130
and the Mo foil
124
has the property of being oxidized at a temperature over 350° C., and in addition, the molybdenum portion is positioned in the end of the sealing portion
120
and is in contact with ambient air. Therefore, when the temperature of the welded portion
132
that is more likely to be heated than other portions because of the contact resistance is increased to about 350° C. or more, the welded portion
132
is oxidized (oxidization of molybdenum), and as a result, the conductivity of the welded portion
132
is lost, so that the lamp
1000
stops operating.
When the inventors of the present invention made research on what causes the temperature of the welded portion
132
to be higher than the temperature estimated at the time of design, they found that as shown in
FIG. 7
, reflected light
52
from an optical system
90
of a DLP projector disposed forward in the emission direction
50
of the lamp unit
1200
is incident to the reflecting mirror
60
of the lamp unit
1200
, and the welded portion
132
of the sealing portion
120
positioned on the emission direction
50
side is irradiated with the reflected light
52
. For example, in the case of a single panel DLP projector, the optical system
90
Horiuchi Makoto
Ichibakase Tsuyoshi
Kai Makoto
Sasaki Ken-ichi
Seki Tomoyuki
Harper Holly
Matsushita Electric - Industrial Co., Ltd.
Patel Nimeshkumar D.
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