Projector

Details Projector Projector

1999-09-23

2003-04-01

Dowling, William (Department: 2851)

Optics: image projectors

Composite projected image

Multicolor picture

C353S052000

Reexamination Certificate

active

06540360

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a projection display device for projecting in enlarged form an image through a projection optical system as a result of separating a plurality of color light beams from a light source, modulating the color light beams by light-modulating elements in accordance with image information, and synthesizing the modulated color light beams.
2. Description of Related Art
A conventional projection display device primarily comprises a light source unit, an optical unit for optically treating the light from the light source unit so as to synthesize color images in accordance with image information, and a projecting lens for projecting in enlarged form an image, formed by synthesizing the light beams, onto a screen.
FIG.
13
(A) is a schematic structural view of the conventional optical unit and projecting lens. As shown in this figure, the optical unit
3
comprises a light source
20
; a color separation optical system
40
for separating a light beam W, emitted from the light source
20
, into the three primary light beams, namely, the red light beams (R), the green light beams (G), and the blue light beams (B); three liquid crystal panels (light-modulating elements)
5
R,
5
G, and
5
B, for modulating each of the different color light beams in accordance with image information; a cross dichroic prism
60
for synthesizing each of the modulated color light beams; and a projecting lens
4
for projecting in enlarged form an image, formed by synthesizing the different color light beams, onto a screen
120
. The light beam W, emitted from the light source
20
, is separated into the color light beams, R, G, and B, by the color separation optical system
40
comprising various dichroic mirrors. Of the color light beams, the red light beams R and the green light beams G are emitted towards corresponding liquid crystal panels
5
R and
5
G from their corresponding light emitting portions in the color separation optical system
40
. The blue light beams B are guided towards the liquid crystal panel
5
B via a light-guiding optical system
50
.
In the optical unit
3
illustrated in enlarged form in FIGS.
13
(B) and
13
(C), polarizing plates
100
R,
100
G, and
100
B are disposed at the light-incoming surface side of corresponding liquid crystal panels
5
R,
5
G, and
5
B. The polarizing plates
100
R,
100
G, and
100
B are provided to align the polarization planes of the different color light beams incident upon the corresponding liquid crystal panels
5
R,
5
G, and
5
B. Polarizing plates
110
R,
110
G, and
110
B are disposed at the light emitting side of the corresponding liquid crystal panels
5
R,
5
G, and
5
B. The polarizing plates
110
R,
110
G, and
110
B are provided to align the polarization planes of the different modulated color light beams that are going to strike the cross dichroic prism
60
. The polarizing plates allows an image with high contrast to be projected onto the screen
120
. Of the polarizing plates sandwiching their corresponding liquid crystal panels
5
R,
5
G, and
5
B, the polarizing plates
110
R,
110
G, and
110
B are adhered to the light emitting surface of their corresponding liquid crystal panels.
A generally used polarizing plate comprises a polarizer and a protective layer laminated thereto, with the polarizer formed of a dichroic material such as an iodine-containing material or organic dye. For the liquid crystal panels, an active matrix type liquid crystal device is generally used, in which type of liquid crystal device the pixels disposed in a matrix arrangement are controlled by a switching element.
Here, an effective way of increasing contrast of the image projected in enlarged form onto the screen
120
is to adhere a polarizing plate with good polarization selection characteristics to the light emitting surface of each of the liquid crystal panels
5
R,
5
G, and
5
B. However, polarizing plates with excellent selection characteristics correspondingly absorb a larger amount of light, so that a large amount of heat is generated thereat. The above-described projection display device is constructed so that the polarizing plates are cooled by air currents formed in the projection display device, as shown in FIG.
13
(C). However, since the polarizing plates are directly adhered to the light emitting surface of their respective liquid crystal panels, the polarizing plates transmit heat to the liquid crystal panels easily, so that the temperature of the liquid crystal panels tends to rise. This temperature rise deteriorates optical characteristics of the liquid crystal panels, reducing contrast of the projected image.
Heat transfer to the liquid crystal panels may be kept low by disposing the polarizing plates so that they are separated from the light emitting surface of their respective liquid crystal panels. However, when the polarizing plates are merely separated from their respective light emitting surfaces, dust or the like sticks onto the light emitting surface of the liquid crystal panels by the air currents flowing in the display, causing a reduction in the quality of the projected image.
SUMMARY OF THE INVENTION
In view of the above-described problems, it is one aspect of the present invention to provide a projection display device which can prevent deterioration in the optical characteristics of the light-modulating elements caused by heat generated at the polarizing plates. In addition, it is an object of the present invention to provide a projection display device which can project a high quality image unaffected by dust or the like, even when it gets scattered by air currents in the projection display device.
To overcome the above-described problems, according to the present invention, there is provided a projection display device including a color separator for separating light emitted from a light source into a plurality of color light beams; a plurality of light-modulating elements for modulating the plurality of color light beams, formed as a result of separation by the color separator, in accordance with image information; a color synthesizer for synthesizing the color light beams modulated by the respective light-modulating elements; and a projector for projecting in enlarged form an image formed by the resulting light beam formed by the color synthesizer. In addition, at least one of the plurality of color light beams may be a blue light beam, and a light transmissive plate may be disposed at at least one of the light-incoming surface and the light emitting surface of the light-modulating elements modulating the color light beams other than the blue light.
According to the projection display device of the present invention, a light transmissive plate may be provided at the light-incoming surface, or the like, of the corresponding light-modulating elements other than that for blue light. In this case, the light transmissive plate or plates are disposed between the corresponding light-modulating elements and the corresponding polarizing plate or plates, and reduces the amount of heat transmission from polarizing plate or plates to the corresponding light-modulating elements. Therefore, rises in temperature of the polarizing plate due to the heat generated at the polarizing plate or plates, can be reduced, making it possible to obviate the problem of deterioration in the optical characteristics of the light-modulating elements. In addition, since the light-incoming surface, or the like, of the light-modulating elements are protected by the corresponding light transmissive plate or plates, it is possible to prevent direct sticking of dust, or the like, onto the light-incoming surface or surfaces even when, for example, dust is scattered by air currents in the projection display device. Consequently, dust does not appear on the projection surface.
Here, since the energy per unit quantity of light for short wavelengths of light is higher than for long wavelengths of light, the amount of heat generated at a polarizing plate disposed at the light-

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