Projector

Details Projector Projector

1999-08-17

2003-03-11

Dowling, William (Department: 2851)

Optics: image projectors

Housing

C349S058000

Reexamination Certificate

active

06530665

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a projector for projecting a modulated light in enlarged form on a projection screen through a projecting means as a result of modulating light from a light source by a light modulating element in accordance with image information.
2. Description of Related Art
A projector 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 projection lens for projecting in enlarged form the synthesized light onto a screen.
FIG.
14
(A) is a schematic structural view of the optical unit and the projection lens. As shown in this figure, the optical system of the optical unit
3
comprises a light source
20
included in a light source unit; a color separation optical system
40
for separating a light W, emitted from the light source
20
, into the three primary color 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 combining each of the modulated color light beams; and a projection lens
4
for projecting in enlarged form the synthesized light onto a screen
120
. The light W, emitted from the light source
20
, is separated into the respective 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 directed towards corresponding liquid crystal panels
5
R and
5
G from their corresponding light-outgoing 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.
14
(B) and
14
(C), polarizers
100
R,
100
G, and
100
B are disposed adjacent to the light-incoming surface of corresponding liquid crystal panels
5
R,
5
G, and
5
B. The polarizers
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. Polarizers
110
R,
110
G, and
110
B are disposed at the light-outgoing side of the corresponding liquid crystal panels
5
R,
5
G, and
5
B. The polarizers
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 polarizers allow an image with high contrast to be projected onto the screen
120
. Of the polarizers sandwiching their corresponding liquid crystal panels
5
R,
5
G, and
5
B, the polarizers
110
R,
110
G, and
110
B positioned at the light-outgoing surface side of the liquid crystal panels are adhered to the light-outgoing surface of their corresponding liquid crystal panels.
A generally used polarizer consists of 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 polarizer with good polarization selection characteristics to the light-outgoing surface of each of the liquid crystal panels
5
R,
5
G, and
5
B. However, polarizers with excellent selection characteristics correspondingly absorb a larger amount of light, so that a large amount of heat is generated thereat. The above-described projector is constructed so that the polarizers are cooled by air currents formed in the projector, as shown in FIG.
14
(C). However, since the polarizers are directly adhered to the light-outgoing surface of their respective liquid crystal panels, the liquid crystal panels transmit heat 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.
A possible solution to this problem is to dispose the polarizers so that they are separated from the light-outgoing surface of their respective liquid crystal panels. However, when the polarizers are merely separated from their respective light-outgoing surfaces, dust or the like sticks onto the light-outgoing surface of the liquid crystal panels by the air currents flowing in the device, causing a reduction in the quality of the projected image.
SUMMARY OF THE INVENTION
In view of the above-described problems, it is an object of the present invention to provide a projector which can project a high quality image, without deteriorating the optical characteristics of the light modulating elements and without allowing sticking of dust or the like onto the light-outgoing surface of the light modulating elements.
To overcome the above-described problems, according to the present invention, there is provided a projector comprising a light-modulating element for modulating light emitted from a light source in accordance with image information, and projecting means for projecting the light modulated by the light modulating element in enlarged form onto a projection surface;
wherein a polarizer is disposed adjacent to the light-outgoing surface side of the light-modulating element, and a dust protection member is provided so as to cut off from the outside the area between the polarizer and the light-outgoing surface of the light-modulating element.
In the projector of the present invention, a dust protection member is provided so as to cut off from the outside the area between the polarizer and the light-outgoing surface of the light-modulating element, thus forming an air layer between the polarizer and the light-outgoing surface. Therefore, the amount of heat generated at the polarizer and transmitted to the light-modulating element is reduced by the air layer. Consequently, even when a polarizer with excellent selection characteristics is used, the amount by which temperature of the light-modulating element rises by heat generated at the polarizer can be reduced, thereby obviating the problem of deterioration in the optical characteristics of the light-modulating element.
The area between the polarizer and the light-modulating element is cut off from the outside, so that even when dust or the like is scattered by air currents produced in the display interior, the dust does not enter into the area therebetween. Therefore, it is possible to eliminate the problem of dust or the like sticking onto the light-outgoing surface of the light-modulating element.
Accordingly, the projector of the present invention can project a high quality image with excellent contrast onto a projection surface, without deteriorating the optical characteristics of the light-modulating element and without allowing dirt to stick onto the light-outgoing surface of the light-modulating element.
When a polarizer is also disposed at the light-incoming surface of the light-modulating element, it is preferable to cut off from the outside the area between the polarizer and the light-incoming surface of the light-modulating element with the dust protection member. The dust protection member can prevent dirt from sticking onto the light-incoming surface of the light-modulating element, and is effective in allowing projection of a high quality image.
When a transparent plate is disposed between the light-incoming surface of the light-modulating element and the polarizer disposed adjacent to the light-incoming surface, it is desirable to cut off from the outside the area between the transparent plate

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