Television – Video display – Projection device
Reexamination Certificate
1998-05-11
2001-05-08
Lee, Michael (Department: 2714)
Television
Video display
Projection device
C348S756000, C353S033000
Reexamination Certificate
active
06229581
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a picture display apparatus, in particular to a projection type picture display apparatus using reflective type liquid crystal display means.
FIG. 4
is an explanatory view indicating a conventional system for use as a projection type picture display apparatus. As shown in
FIG. 4
, a white light from a light source
1
is incident on a YDM (Yellow Reflecting Dichroic Mirror)
2
a
to be divided into a blue light which is a rectilinear light rectilinearly propagated through the YDM
2
a
, and a two-color light (including a green light and a red light) reflected from the YDM
2
a.
Referring again to
FIG. 4
, the blue light rectilinearly propagated through the YDM
2
a
is reflected by a reflecting mirror
3
a
and then incident on a light transmissible liquid crystal panel
4
a
(for use in processing a blue light). On the other hand, the two-color light (including a green light and a red light) is incident on a GDM (Green Reflecting Dichroic Mirror)
2
b
to be divided into a green light and a red light, respectively. Here, the green light is a reflected light from the GDM
2
b
, whilst the red light is a rectilinear light rectilinearly propagated through the GDM
2
b
. The green light reflected from the GDM
2
b
is incident on a light transmissible liquid crystal panel
4
b
(for use in processing a green light). On the other hand, the red light rectilinearly propagated through the GDM
2
b
is reflected by a reflecting mirror
3
b
and a further by a reflecting mirror
3
c
so as to be incident on a light transmissible liquid crystal panel
4
c
(for use in processing a red light).
The light transmissible liquid crystal panel
4
a
(for use in processing a blue light), the light transmissible liquid crystal panel
4
b
(for use in processing a green light), the light transmissible liquid crystal panel
4
c
(for use in processing a red light), each comprises a pair of transparent electrode substrates forming an internal space therebetween which is filled with a liquid crystal so as to form a plurality of liquid crystal cells. Further, each of the light transmissible liquid crystal panels
4
a
,
4
b
,
4
c
includes on both sides thereof a pair of polarizing plates which are provided to cause a blue, green or red light to be incident onto a light synthesizing cross-prism
5
.
The light synthesizing cross-prism
5
has a pair of dichroic mirrors
5
a
,
5
b
each consisting of a deposition film, which are arranged in a mutually crossed manner so that they are able to reflect or transmit various lights (blue, green and red lights).
In this way, a red light is allowed to pass through the dichroic mirror
5
b
and then reflected by the dichroic mirror
5
a
. A blue light is allowed to be reflected by the dichroic mirror
5
b
and then pass through the dichroic mirror
5
a
. Further, a green light is allowed to first pass through the dichroic mirror
5
b
and thens through the dichroic mirror
5
a
. Therefore, various lights (blue, green and red lights) are synthesized in the light synthesizing cross-prism
5
to form a picture which is then enlarged through a projection lens
6
so as to be projected on a screen
7
.
However, with the above-described conventional system shown in
FIG. 4
, since an optical system for dividing an incident white light into various color lights is space-apart from an optical system for synthesizing together individual color lights, the whole system for use as a projection type picture display apparatus has to be large in size, making it difficult to manufacture a picture display apparatus at a low cost.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an improved system for use as a projection type picture display apparatus which is compact in size and may be manufactured at a low cost, so as to solve the above-mentioned problems peculiar to the above-mentioned prior arts.
According to the present invention, there is provided a projection type picture display apparatus, comprising: a light source; a polarizing beam splitter capable of reflecting or transmitting an incident light; a decomposing/synthesizing prism assembly capable of receiving a reflected light from the polarizing beam splitter to decompose the incident light into red, green and blue lights, also capable of receiving reflected red, green and blue lights to synthesize these lights so as to produce a synthesized light which is then incident on the polarizing beam splitter; a plurality of reflective type liquid crystal display means capable of receiving, modulating and reflecting red, green and blue lights; a projection optical system capable of receiving a picture light passing through the polarizing beam splitter to project an enlarged picture on a screen. In particular, the decomposing/synthesizing prism assembly has a first dichroic mirror reflecting a first color light but transmitting a second and third color lights, and has a second dichroic mirror reflecting the second color light but transmitting the first and third color lights, with the first and second dichroic mirrors intersected with each other at a predetermined operable angle.
In one aspect of the present invention, the decomposing/synthesizing prism assembly comprises four right-angle prisms bonded together by means of an adhesive on their right-angle surfaces, forming the first and second dichroic mirrors intersected with each other in a crossed manner. In detail, the decomposing/synthesizing prism assembly is formed in a manner such that, an angle between the main beam of an incident light and the normal line of each dichroic mirror is 45°.
In another aspect of the present invention, the decomposing/synthesizing prism assembly may comprise four cubical trapezoidal prisms bonded together by means of an adhesive, forming the first and second dichroic mirrors intersected with each other at an angle of about 60°. In detail, the decomposing/synthesizing prism assembly may be formed in a manner such that, an angle between the main beam of an incident light and the normal line of each dichroic mirror is 30°.
In a further aspect of the present invention, the decomposing/synthesizing prism assembly may be comprised by a plate forming a first dichroic mirror and another plate forming a second dichroic mirror, both of the plates being disposed in an optical case filled with an optical liquid.
The above objects and features of the present invention will become better understood from the following description with reference to the accompanying drawings.
REFERENCES:
patent: 4464018 (1984-08-01), Gagnon
patent: 4687301 (1987-08-01), Ledebuhr
patent: 5130826 (1992-07-01), Takanashi et al.
patent: 5400180 (1995-03-01), Chung
patent: 5488436 (1996-01-01), Choi et al.
patent: 5644432 (1997-07-01), Doany
patent: 5786873 (1998-07-01), Chiu et al.
Atsuchi Naruhiko
Shirai Kazuyuki
Tomisawa Isao
Yamamoto Hideki
Yoshida Tadashi
Arent Fox Kintner & Plotkin & Kahn, PLLC
Lee Michael
Pioneer Electronic Corporation
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