Electric lamp and discharge devices – With gas or vapor – Envelope with particular structure
Reexamination Certificate
1999-11-16
2003-05-06
Patel, Ashok (Department: 2879)
Electric lamp and discharge devices
With gas or vapor
Envelope with particular structure
C313S025000, C313S573000, C313S113000, C313S332000, C362S296040, C362S310000
Reexamination Certificate
active
06559600
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a discharge lamp, a light source apparatus which prepares illumination rays using the discharge lamp, and a projection display apparatus which projects a large image onto a screen using the light source apparatus, a spatial light modulating element (for example, a liquid crystal element) for forming an optical image with video signals supplied from outside, and a projector lens.
BACKGROUND OF THE INVENTION
A small discharge lamp which is denoted by a metalhalide lamp or an ultra high pressure mercury vapor lamp is widely utilized as a light source for a projection display apparatus and the like. In such a case, it is general to combine the discharge lamp with a concave reflector to compose a light source apparatus and utilize this apparatus as a light source for the projection display apparatus.
FIG. 17
exemplifies a configuration of a conventional discharge lamp. A discharge lamp
321
is configured mainly by a light emitting bulb
301
, sealing members
302
and
303
, metal foils
304
and
305
, electrodes
306
and
307
, external conductors
308
and
309
, and discharge media
310
,
311
and
312
. Quartz glass is used as the light emitting bulb
301
and sealing members
302
,
303
, tungsten is used as the electrodes
306
and
307
, molybdenum foils are used as the metal foils
304
and
305
, and molybdenum is used as the external conductors
308
and
309
. Furthermore, mercury, a light emitting metals such as a metalhalide or the like, and a rare gas such as argon or the like, are used mainly as the discharge media
310
,
311
and
312
, respectively.
When a predetermined voltage is applied across the external conductors
308
and
309
, arc discharge takes place between the electrodes
306
and
307
, whereby the mercury
310
and the metal halide
311
emit rays characteristic thereof. The argon gas
312
is used to improve a starting characteristic.
Since a distance is extremely short between the electrodes and a high current is supplied at a start time in this kind of discharge lamp, the lamp is liable to be blackened due to deformation of the electrodes and evaporation of an electrode substance, and can hardly have a long service life. In contrast, there have been disclosed various kinds of lamps which are configured to have service lives prolonged by contriving structures of electrodes (for example by JPA 7-192688 and JPA 10-92377).
FIGS. 18 through 20
are enlarged views exemplifying configurations of the electrodes.
FIG. 18
shows an example wherein a coil
331
is disposed around a tip of an electrode
330
to enhance a heat dissipation property, thereby preventing a tip portion from being deteriorated or deformed due to excessive temperature rise.
FIG. 19
shows an example wherein a discharge portion
342
which has a diameter larger than that of an electrode shaft
341
is formed at a tip of an electrode
340
to enhance a thermal conductivity, thereby preventing a tip portion from being deteriorated or deformed due to excessive temperature rise. This kind of electrode is used as an anode of a DC type discharge lamp.
FIG. 20
shows an example wherein a discharge member
352
having a diameter larger than that of an electrode shaft
351
is formed by winding a coil thick around a tip of an electrode
350
and fusing a tip portion so as to form a lump integral with an electrode shaft
351
, and a heat dissipating member
353
is formed after the discharge member
352
by integrally fusing a coil, thereby preventing the electrode from being deteriorated or deformed. The heat dissipating member
353
is configured by a coil or a cylindrical electrode member.
However, the electrodes which have configurations shown in
FIGS. 18 through 20
pose problems which are described below.
In case of the configuration shown in
FIG. 18
, a contact area between the electrode
330
and the coil
331
is narrow, whereby the electrode has a low thermal conductivity and cannot exhibit a sufficient heat dissipating effect. Furthermore, the electrode poses a problem that the coil
331
is fused and deformed when the coil
331
is too thin. Though this problem can be solved by thickening the coil
331
, tungsten which is used as a material of the electrode
330
is hard and the coil
331
can hardly be wound when it is thick. Furthermore, the electrode poses another problem that a spot of arc discharge moves to the tip of the electrode or an end of the coil, whereby an arc is hardly be stable.
In case of the configuration shown in
FIG. 19
, the discharge member
342
which is too thick makes the electrode
340
hardly be heated to a temperature required to emit thermoelectrons, thereby posing a problem of degradation of a starting property and interception of discharge. This is remarkably problematic when a lamp is to be lit with an alternating current in particular, whereby the electrode can hardly be used for lighting a lamp with an alternating current.
In case of the configuration shown in
FIG. 20
wherein the discharge member
352
is formed integrally and continuously with the coil
353
, the discharge portion
352
and the coil
353
have high thermal conductivities and are hardly be raised to a temperature required to emit thermoelectrons, thereby degrading a starting property or allows discharge to be intercepted in the course like the structure shown in FIG.
19
. This poses a serious problem when a discharge lamp is to be ignited with an alternating current in particular. Furthermore, an electrode such as that shown in
FIG. 20
is manufactured by allowing the electrode having the coil
353
wound around the electrode shaft
351
to discharge in an atmosphere of an inert gas such as nitrogen gas or argon so as to fuse the tip portion. A doping agent such as thorium is often added to tungsten as electrode material for a discharge lamp to improve a starting property. However, the electrode manufactured by the method described above poses a problem that the doping material is evaporated at a stage to fuse the tip portion. Furthermore, the electrode poses another problem that the fusing promotes recrystallization of the tip portion, whereby the electrode is low in its strength and can hardly be worked.
When this kind of discharge lamp is to be used in a projection display apparatus, on the other hand, it is general to configure a light source by combining the discharge lamp with a concave reflector.
FIG. 21
a
exemplifies a configuration of a light source.
FIG. 21
b
is a sectional view taken along an A—A line in
FIG. 21
a
. A reflective coating
372
which is formed on an inside surface of a concave reflector
371
reflects rays emitted from a lamp
360
in a predetermined direction with a high efficiency. A lamp insertion port
373
and a conductor outlet port
374
are formed in the concave reflector
371
. The lamp
360
is fixed to the concave reflector
371
with a heat-resistant adhesive agent
375
after inserting a sealing member
362
is inserted into the lamp insertion port
373
. Furthermore, an end of an extension conductor
376
is connected to an external conductor
369
and the other end of the extension conductor
376
is led out of the concave reflector
371
through the conductor outlet port
374
. Rays can be emitted from the lamp
360
by applying a predetermined voltage across an external conductor
368
and the extension conductor
376
.
It is desired that a lamp which is to be used in the projector display apparatus is as small as possible and has a long service life. However, the conventional light source shown in
FIG. 21
a
poses problems which are described below.
First, the conventional light source poses a problem that oxidation of metal foils
364
and
365
disposed at both ends of the lamp
360
as well as the external conductors
368
and
369
results in wire breakage, thereby shortening a service life of the lamp. In case of the light source shown in
FIG. 21
a
, distortion is produced by a thermal stress at a sealing stage, whereby a gap B is formed between the external
Nakao Suguru
Ogura Toshiaki
Tsutsumi Takeharu
Wada Mitsuhiro
Parkhurst & Wendel L.L.P.
Patel Ashok
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