Optics: image projectors – Cabinet encloses projector and one side of screen
Reexamination Certificate
1999-04-08
2001-08-21
Metjahic, Safet (Department: 2858)
Optics: image projectors
Cabinet encloses projector and one side of screen
C348S781000
Reexamination Certificate
active
06276802
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to a rear projection display for displaying an image thereon by projecting the image from the rear side of a screen.
2. Description of Related Art
Projection displays, for projecting and displaying an image in enlarged form on a screen, are known as displays with large screens. One type of such projection displays is the rear projection display.
FIG. 6
is a schematic view of the structure of a rear projection display as seen from a side thereof. The rear projection display
100
consists of, in general, an image projector
110
, two reflecting mirrors
120
and
130
, and a screen
140
. Light from the image projector
110
is reflected by the two reflecting mirrors
120
and
130
, and then projected onto the rear (back) side of the screen
140
. This causes an image to be formed at the back surface of the screen, the image being viewable from the front side of the screen.
At the front side of the rear projection display
100
, a space
150
for positioning the reflecting mirror
120
must be provided below the screen
140
. Therefore, only the upper area of the front side of the rear projection display
100
, that is, the area of the front side of the rear projection display
100
excluding the space
150
, can be used as screen
140
positioning area This does not allow effective use of the front side area of the rear projection display
100
as the screen
140
positioning area.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a technique which overcomes the above-described problem present in conventional rear projection displays in order to allow more effective use of the front side area of the rear projection display as a screen positioning area.
In order to at least partly overcome the above-described problem, according to the present invention, there is provided a rear projection display consisting of:
a screen having a front side and a back side, the screen displaying the image on the front side by light projected onto the back side;
an image projector consisting of a light source and a modulating element that modulates light emitted from the light source in accordance with image information, in which first linearly polarized light beams of the light beams modulated by the modulating element are directed towards a predetermined location on the screen;
a polarizing selection element positioned at least on an optical path extending from the image projector to a back surface on the back side of the screen, the polarizing selection element reflecting the first linearly polarized light beams emitted from the projector, and letting pass therethrough linearly polarized light beams with a polarization direction perpendicular to that of the first linearly polarized light beams; and
a polarizing conversion reflection element positioned on an optical path of the light reflected by the polarizing selection element, the polarizing conversion reflection element converting the first linearly polarized light beams, reflected by the polarizing selection element, into second linearly polarized light beams with a polarization direction substantially perpendicular to that of the linearly polarized light beams reflected by the polarizing selection element for reflection towards the screen,
at least some of the second linearly polarized light beams emitted from the polarizing conversion reflection element passing through the polarizing selection element and striking the back side of the screen.
According to the above-described construction, almost all of the first linearly polarized light beams projected from the image projector are reflected by the polarizing selection element and strike the polarizing conversion reflection element. The polarization direction of the first polarized light beams, incident upon the polarizing conversion reflection element, is changed by approximately 90 degrees in order to convert them into second polarized light beams with a polarization direction substantially perpendicular to that of the first linearly polarized light beams for reflection towards the screen. Here, the polarization direction of the second linearly polarized light beams is substantially the same as that of the linearly polarized light beams which pass through the polarizing selection element. Therefore, of the second polarized light beams which have left the polarizing conversion reflection element, those incident upon the polarizing selection element pass therethrough and strike the back side of the screen. This causes an image to be projected onto the portion of the screen located at the light-outgoing surface side of the polarizing selection element, at the front side area of the rear projection display. Therefore, the front side area of the rear projection display can be effectively used as a screen positioning area.
The polarizing selection element may be positioned on the back surface of the screen.
Here, it is preferable that the polarizing conversion reflection element consist of a reflecting mirror and a &lgr;/4 phase element positioned on an optical path of light incident upon and reflected by the reflecting mirror.
According to the above-described structure, the first linearly polarized light beams, incident upon the &lgr;/4 phase element, pass through the &lgr;/4 phase element and are then reflected by the reflecting mirror, after which the reflected light beams pass once again through the &lgr;/4 phase element in order to be converted into second linearly polarized light beams. Accordingly, the first linearly polarized light beams, incident upon the polarizing conversion reflection element, are converted into second linearly polarized light beams for reflection.
The polarizing selection element may be divided into a plurality of sections, the polarization separating characteristics of each section being adjusted in accordance with an angle of incidence of light with respect to each section.
Usually, the polarization separating characteristics of the polarizing selection element vary depending on the angle of incidence of light. According to the above-described structure, the polarizing separating characteristics of each section is adjusted in accordance with the angle of incidence of light with respect to each section, making variations in the intensity of light passing through the polarizing selection element less dependent upon the location through which the light passes, so that variations in brightness and color of the image projected onto the screen can be reduced.
REFERENCES:
patent: 5557343 (1996-09-01), Yamagishi
patent: 5611611 (1997-03-01), Ogino et al.
patent: WO98/19213 (1998-05-01), None
LeRoux E. P
Metjahic Safet
Oliff & Berridg,e PLC
Seiko Epson Corporation
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