Optical: systems and elements – Projection screen – Unitary sheet comprising plural refracting areas
Reexamination Certificate
1999-10-05
2004-04-27
Mahoney, Christopher (Department: 2851)
Optical: systems and elements
Projection screen
Unitary sheet comprising plural refracting areas
C359S460000
Reexamination Certificate
active
06728031
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
In general, the present invention relates to a projection-type picture display apparatus such as a projection television set and a screen used thereby. More particularly, the present invention relates to a projection-type picture display apparatus which has a small amount of inadvertent inclusion of external light, is capable of suppressing a reduction in contrast and capable of lowering the degree of deterioration of a picture quality by using an optical device having a structure comprising pixels laid out to form a matrix such as a liquid-crystal panel or a DMD (Digital Micromirror Device) as a picture generating source, and relates to a screen used by the projection-type picture display apparatus.
2. Description of the Related Art
With the picture source going diverse, the projection-type picture display apparatus is enjoying broad general popularity in the market by virtue of its marketability factors of a projection-type optical apparatus with a large screen such as a small weight, a low cost and a small size. On the other hand, in recent years, a projection-type picture display apparatus using a liquid-crystal panel as a picture generating source starts its participation in the market due to substantial improvement of the precision/fineness and the numerical aperture of the liquid-crystal panel. This projection-type picture display apparatus is designed into a configuration wherein a source picture displayed on the liquid-crystal panel is displayed as an enlarged picture on a screen in full colors by a projection lens unit.
In an optical system employed in this projection-type picture display apparatus, it is possible to adopt a three-panel technique employing three liquid-crystal panels as shown in FIG. 19 of Japanese Unexamined Patent Publication No. Hei9-96759, or a single-panel technique employing only one liquid-crystal panel as shown in FIG. 1 of Japanese Unexamined Patent Publication No. Hei4-60538. First of all, an optical system adopting a single-panel technique employing one liquid-crystal panel is explained by referring to FIG.
1
.
FIG. 1
is a top-view diagram showing a partial cross section of a layout of a projection-type optical system adopting a single-panel technique employing one liquid-crystal panel.
As shown in the figure, a reflective mirror
29
directs a beam emitted by a white-color light source
28
implemented by a metal halide lamp, a canon lamp, a halogen lamp or a high-pressure mercury lamp to a converging lens
27
with a high degree of efficiency whereas a collimator lens
26
converts the beam into all but parallel white-color lights. Three dichroic mirrors
23
,
24
and
25
with types different from each other are placed in front of the collimator lens
26
. The dichroic mirrors
23
,
24
and
25
exhibit characteristics to selectively reflect lights with the green, red and blue wavelengths respectively but to pass on other components. Symbols R, G and B in the figure denote respectively the red, green and blue lights split by the dichroic mirrors
24
,
23
and
25
. In this conventional configuration, the red-color light is taken as a reference while the blue-color and green-color lights are radiated to a liquid-crystal panel
22
from slanting directions relative to the red-color light.
The liquid-crystal panel
22
comprises pixels for the 3 primary colors, namely, red, green and blue. The pixels each exhibit an optical transmittivity representing the level of a luminance component of a picture signal. Thus, the red, green and blue lights are modulated in accordance with the level of the picture signal to create a desired image on the liquid-crystal panel
22
. The image displayed on the liquid-crystal panel
22
is then projected by a projection-lens unit
21
on a screen
20
as an enlarged picture.
In order to radiate an image light emitted by the liquid-crystal panel
22
to the projection-lens unit
21
with a high degree of efficiency, an optical system including a convex lens for converging a light is typically provided between the liquid-crystal panel
22
and the projection-lens unit
21
. It should be noted that such an optical system is not shown in FIG.
1
.
The white-color light source
28
itself dissipates heat which can be a cause of a damage. On the other hand, the liquid-crystal panel
22
including a polarizing plate absorbs an incident light, dissipating heat which can also be a cause of a damage. In order to reduce an increase in temperature, a cooling fan not shown in the figure is used to forcibly cool the white-color light source
28
and the liquid-crystal panel
22
so that they can be used at a temperature in a desired range.
Next, the optical system adopting the conventional three-panel technique, that is, employing three liquid-crystal panels, is explained by referring to FIG.
2
.
FIG. 2
is a top-view diagram showing a partial cross section of a layout of a projection-type optical system adopting the conventional three-panel technique employing three liquid-crystal panels. Configuration components shown in the figure identical with those of the optical system shown in
FIG. 1
are denoted by the same reference numerals as those of the latter. The optical system shown in
FIG. 2
has a configuration wherein a reflective mirror
29
collimates a beam emitted by a white-color light source
28
implemented by a metal halide lamp, a canon lamp, a halogen lamp or a high-pressure mercury lamp into all but parallel white-color lights. Two dichroic mirrors
31
and
32
with types different from each other are placed in front of the reflective lens
29
. The dichroic mirrors
31
and
32
split the beam into color components which are then radiated to their respective liquid-crystal panels
33
,
34
and
35
. Pictures displayed on the liquid-crystal panels
33
,
34
and
35
are synthesized by a color synthesizing prism
36
before being projected by a projection-lens unit
21
on a screen
20
as an enlarged picture. Since the operation of the projection-type optical system adopting the conventional three-panel technique employing the three liquid-crystal panels is the same as the conventional system shown in
FIG. 1
, it is not necessary to repeat its explanation.
In addition, a forced cooling system of the white-color light source
28
and the liquid-crystal panels each including a polarizing plate is the same as the optical system shown in FIG.
1
. Furthermore, a radiation system to increase the efficiency of light utilization has become popular in recent years. The radiation system has a polarized-light synthesizing function for synthesizing P and S polarized lights generated by a polarization beam splitter as a result of splitting of a light emitted by the light source.
A rear-projection-type picture display apparatus employing the optical systems explained above is described by referring to
FIGS. 3 and 4
.
FIGS. 3 and 4
are each a side-view diagram showing a partial cross section of main components of the rear-projection-type picture display apparatus employing the projection-type optical system. In the figures, reference numerals
11
and
12
denote a radiation system including a light source and a projection lens respectively. Reference numeral
13
denotes an optical-path reflection mirror and reference numeral
14
denotes a screen. Reference numeral
15
denotes a case. The length of an optical path from the projection lens
12
to the screen
14
in the rear-projection-type picture display apparatus shown in
FIG. 3
is equal to that of the apparatus shown in FIG.
4
. Since the rear-projection-type picture display apparatus shown in
FIG. 3
has a comparatively big depth, its height can be made relatively small. Since the rear-projection-type picture display apparatus shown in
FIG. 4
has a comparatively big height, on the other hand, its depth can be made relatively small. In either of the rear-projection-type picture display apparatuses, by shortening the projection distance of the projection lens
12
, that is, the length of the op
Hirata Koji
Inaoka Shigeru
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