Optics: image projectors – Reflector
Patent
1998-11-12
2000-10-10
Dowling, William
Optics: image projectors
Reflector
353 37, 348743, G03B 2128
Patent
active
061294373
DESCRIPTION:
BRIEF SUMMARY
This application is the national phase under 35 U.S.C. .sctn.371 of prior PCT International Application No. PCT/JP97/04822 which has an International filing date of Dec. 25, 1997 which designated the United States of America, the entire contents of which are hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projection-type image display apparatus for use in a projection-type high-definition television system or video projector. More particularly, the present invention relates to an image display apparatus having a unique feature in the structure of the optical system for projecting a color image.
2. Description of the Related Art
One of known conventional projection-type image display apparatus is a projection-type color liquid-crystal display apparatus using a liquid-crystal display panel.
The projection-type color liquid-crystal display apparatuses are roughly divided into a three-panel color liquid-crystal display apparatus having three liquid-crystal display panels for red, green and blue primaries and a single-panel color liquid-crystal display apparatus having a single liquid-crystal display panel with a mosaic- or stripe-patterned tricolor filter.
The three-panel color liquid-crystal display apparatus comprises an optical system for converting a white light into red, green and blue primaries, and a liquid-crystal display panel for controlling luminance of each color to form an image.
The final color image is produced and presented by optically superimposing red, green, and blue color images.
The single-panel color liquid-crystal display apparatus introduces a white light into a single liquid-crystal display panel with a mosaic- or stripe-patterned tricolor filter to form and present a color image.
Besides the three-panel and single-panel projection-type liquid-crystal display apparatuses, another projection-type color image display apparatus using a digital micromirror device (DMD: trade name of Texas Instruments) is recently available (reference is made to magazine "Optics", vol. 25, No. 6, p.313-314, 1996).
The liquid-crystal panel used in the three-panel or single-panel projection-type liquid-crystal display apparatus, as already known, controls a number of two-dimensionally arrayed cells of liquid-crystal molecules in orientation to vary polarization of light, thereby switching on and off the transmission of light.
The above-cited DMD, having a two-dimensional array of a number of pixels each having a micromirror, controls the tilt of each mirror individually through the effect of electrostatic field caused by a memory element arranged respectively for each pixel and varies the angle of reflection of reflected light ray thereby causing on/off state.
FIG. 9 shows the operation of the micromirror arranged for each pixel in DMD. Diagrammatically shown in FIG. 9 are micromirrors 101 through 105 and a projection lens 110. As shown, the pixels corresponding to micromirrors 103 and 105 are in the on state.
Light rays reflected off the micromirrors 101, 102, and 104 of pixels in the off state are not directed to the projection lens 110. Light rays reflected off the micromirrors 103 and 105 of the pixels in the on state are directed to the projection lens 110 and forms an image on a screen.
The tilt angle of the micromirror of a pixel in the on state is 10 degrees or so with respect to a horizontally aligned micromirror.
The advantages of DMD over the liquid-crystal display panel employing a polarizer include a better utilization of light, heat resistance property, high-speed response characteristics, and the like.
FIG. 10 is a perspective view of an optical system for a conventional projection-type color image display apparatus using a DMD.
A white light arc lamp (light emission point) 51 such as a xenon arc lamp is arranged at one focus of a collector ellipsoidal mirror 52.
The light beam emitted from the arc lamp 51 is focused at the other focus of the ellipsoidal mirror 52, thereby forming a virtual secondary light source.
A
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patent: 5905545 (1999-05-01), Poradish et al.
"Optics" vol. 25, No. 6, pp. 313-314 (1996).
Koga Ritsuo
Kubouchi Hideto
Dowling William
Plus Corporation
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