Optics: image projectors – Composite projected image – Multicolor picture
Reexamination Certificate
2003-01-28
2004-03-02
Dowling, William (Department: 2851)
Optics: image projectors
Composite projected image
Multicolor picture
C353S034000
Reexamination Certificate
active
06698895
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a projection-type image display apparatus that displays a color image with one light valve serving as a modulating member.
BACKGROUND ART
A liquid crystal projector that now is the mainstream in the market of large-screen displays uses a light source lamp, a focusing lens and a projection lens to magnify and form an image of a liquid crystal panel (a light valve) onto a screen. Current commercial systems can be classified roughly into a three-plate system and a single-plate system.
In the former system of the three-plate liquid crystal projector, after a light beam from a white light source is separated into light beams of three primary colors of red, green and blue by a color separation optical system, these light beams are modulated by three monochrome liquid crystal panels so as to form images of the three primary colors. Thereafter, these images are combined by a color combination optical system so as to be projected onto a screen by one projection lens. Since the entire spectrum of the white light from the light source can be utilized, this system has a high efficiency of light utilization. However, because of the necessity of the three liquid crystal panels, the color separation optical system, the color combination optical system and a convergence adjusting mechanism between the liquid crystal panels, this system is relatively expensive.
On the other hand, a conventional single-plate system liquid crystal projector is compact and inexpensive because an image formed on a liquid crystal panel having a mosaic color filter simply is magnified and projected onto a screen. However, since this system obtains light with a desired color by absorbing light with an unwanted color out of white light from the light source by means of the color filter serving as a color selection member, only one-third or less of the white light that has entered the liquid crystal panel is transmitted (or reflected). Accordingly, the efficiency of light utilization is low and high-brightness images cannot be obtained easily. When the light source is brightened, the brightness of the displayed image can be improved. However, there remain problems of heat generation and light resistance owing to light absorption by the color filter, making it very difficult to increase the brightness.
A single-plate system that improves the efficiency of light utilization is suggested in JP 4(1992)-316296 A.
FIG. 8
shows a schematic configuration of this image display apparatus.
A white light beam emitted from a light source portion
100
is led to a color separation optical system
101
. As shown in
FIG. 9
, the color separation optical system
101
includes dichroic mirrors
121
a
and
121
b
and two reflection mirrors
121
c
and
121
d
. The dichroic mirror
121
a
reflects blue light and transmits green light and red light. The dichroic mirror
121
b
reflects red light and transmits green light and blue light. These dichroic mirrors
121
a
and
121
b
are crossed. A blue light beam
132
out of a white light beam
131
from the light source portion
100
is reflected by the dichroic mirror
121
a
, reflected by the reflection mirror
121
d
and passes through an aperture
102
B of a field stop
102
. A red light beam
133
is reflected by the dichroic mirror
121
b
, reflected by the reflection mirror
121
c
and passes through an aperture
102
R of the field stop
102
. A green light beam
134
is transmitted by both the dichroic mirrors
121
a
and
121
b
and passes through an aperture
102
G of the field stop
102
. The apertures
102
R,
102
G and
102
B of the field stop
102
are formed like a belt (a rectangle), and the light beams of red, green and blue are emitted adjacent to each other from these apertures.
As shown in
FIG. 8
, the belt-like light beams of respective colors emitted from the field stop
102
pass through a scanning optical system
105
, then illuminate different regions of a single transmission-type light valve (a display panel)
104
in a belt-like manner. With an effect of a rotating prism
103
constituting the scanning optical system
105
, the belt-like light beams of red, green and blue scan the light valve
104
from the bottom to the top. When a belt-like illuminated region of one of the light beams goes beyond the uppermost end of an effective region of the light valve
104
, the belt-like illuminated region of this light beam appears at the lowermost end of the effective region of the light valve
104
again. In this manner, the light beams of red, green and blue can scan over the entire effective region of the light valve
104
continuously. A light beam illuminating each row on the light valve
104
varies moment by moment, and a light valve driving device (not shown in this figure) drives each pixel by an information signal according to the color of the light beam that is illuminated. This means that each row of the light valve
104
is driven three times for every field of a video signal to be displayed. A driving signal inputted to each row is a color signal corresponding to the light beam illuminating this row among signals of the image to be displayed. The light beams of these colors that have been modulated by the light valve
104
are magnified and projected onto a screen (not shown in this figure) by a projection lens
106
.
With the above configuration, the light beam from the white light source is separated into light beams of three primary colors, so that the light from the light source can be used with substantially no loss and the efficiency of light utilization can be increased. Also, since each of the pixels on the light valve displays red, green and blue sequentially, a convergence adjusting mechanism between the liquid crystal panels as in the three-plate system is not necessary, and therefore, it is possible to provide a high quality image.
However, in the above configuration, the light beams of these colors from the field stop
102
are not converged when transmitted by the rotating prism
103
. Since the size (the radius of gyration) of the rotating prism
103
has to be in accordance with a region illuminated by the light beam emitted from the field stop
102
, the rotating prism
103
becomes large and heavy. This has made it difficult to reduce the size and weight of the apparatus. Furthermore, a powerful motor for rotating the rotating prism
103
becomes necessary, causing an increase in the size and cost of the apparatus.
Moreover, with the above-described configuration of the color separation optical system
101
, the lengths of optical paths of the light beams of individual colors from the light source portion
100
to the light valve
104
are not equal. Thus, it is impossible to focus all the light beams at a pupil position of the projection lens
106
. As a result, the light quantity of the light beam focused at the pupil position and the light quantity of the light beam focused at a position shifted from the pupil position are different on the screen, resulting in poor color uniformity in the displayed image.
DISCLOSURE OF INVENTION
It is an object of the present invention to solve the above-described problems of the conventional image display apparatus and to provide a small projection-type image display apparatus that is provided with a scanning optical system for scanning an illuminated portion (a light valve) sequentially with light beams of individual colors and has enhanced color uniformity in a displayed image.
In order to achieve the above-mentioned object, a projection-type image display apparatus of the present invention includes a light source portion for emitting a white light beam; a first optical system, which includes a white illumination optical system that the white light beam from the light source portion enters and that emits a uniform white illumination light beam having a rectangular cross-section, a color separation optical system for separating the white illumination light beam into respective light beams of red, green and blue, and a relay lens system that the resp
Hatakeyama Atsushi
Namba Shu
Yamagishi Shigekazu
Dowling William
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
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