Optics: image projectors – Miscellaneous
Reexamination Certificate
2002-01-07
2004-07-13
Adams, Russell (Department: 2851)
Optics: image projectors
Miscellaneous
C353S094000, C353S007000, C353S010000, C353S099000, C353S030000, C359S443000, C359S453000, C359S459000, C359S462000, C359S471000
Reexamination Certificate
active
06761459
ABSTRACT:
FIELD OF THE INVENTION
The invention relates to projection systems to project mono- and stereoscopic images on a large viewing screen by the optical projection technique.
The proposed projection systems are intended for the consumer-oriented and professional applications in cine-, tele-, video- and computer-projection, projection of theatrical scenery, advertisements, as well as for other purposes. For generating the projected images, the presently-used and proposed updated episcopes, diascopes, cine-projectors, and video, tele- and computer projectors can be used. The proposed reflecting or translucent viewing screens are capable of providing high optical parameters of the screen images and considerable operation capabilities of projection not known in the prior art.
PRIOR ART
The extensively-used and available projection systems comprise a projector and a projection screen. The front-projection systems serve to project images onto a reflecting (front-projection) screen or a white wall, and the rear-projection ones—to project images onto a translucent (rear-projection type) screen. U.S. Pat. No. 6,600,600 to Chen, Shane; U.S. Pat. No. 6, 609,799 to Myers, Kenneth J.; U.S. Pat. No. 6,543,999 to Covannon et al.; U.S. Pat. No. 6,601,961 to Masaki, Tadahiro; U.S. Pat. No. 6,600,528 to Colgan et al. and U.S. Pat. No. 6,469,830 to Dubin et al disclose variations on projection screen that performs the diffusive scattering.
For example U.S. Pat. No. 6,469,830 teaches that a rear-projection screen has, at the side of projection onto the screen (at the reverse, or rear side of the screen), a lens raster, surface area of all the raster lenses covering the entire surface area of an image (that is projected onto the screen); the screen, at its front side (from the viewers' side), is provided with a plate having a surface that scatters the light diffusively; on which surface each one of the raster lenses focuses the projection rays; for the purpose to smooth over the viewed brightness uniformity, when viewing an on-screen image, a number of projectors is positioned behind the screen(each of them being positioned at a predetermined projection point to provide a greater density of the image dots (that are focused by the raster lenses), as well as for the purpose to arrange an optimal directional pattern of the viewed on-screen image so that to enhance the on-screen image brightness uniformity (when said image is seen by viewers from different viewing sectors).
The known projectors are described in: Makartsev V. V., Khesin A. Ya., Steierberg A. L., Large-screen video systems, Moscow, <<Panas>> publishers, 1993, pp. 15-22, 57-83, 96-99, 147-155, FIGS. 1, 2 and 22, 23.
The major disadvantage of the above-discussed projection systems is their large dimensions and considerable weight. This disadvantage is connected with the necessity to carry out projection in a large projection space between a projector and viewing screen at a projection distance that must be not less than the length of the screen image diagonal. Further, there is a possibility that the projection and images on the screen can be shadowed by viewers and objects that are present in this space. The technical paradox is that a reflecting or translucent viewing screen in case of projection of a bright and sharp image must reflect or, respectively, transmit the projected light flux to the maximal extent. Thereupon in viewing the screen images when a viewing screen has an external parasitic illumination, the image contrast deteriorates significantly, brightness is lowered at the edges of the screen image field, and the colour-rendering accuracy is lost. These parameters can be optimal only on a black screen (similar to a black screen of the direct vision kinescopes). In this case, a lower quality of the screen images restrains possibilities to use projection systems in illuminated premises and outdoors. This difficulty is connected with design problems of the modern projection systems that permit the projection within the projection angles (angle of the axis inclination with respect to the viewing screen perpendicular) of not over 30°.
A rear projection system comprising a lenticular-raster rear projection (translucent) viewing screen is the most proximate one to the claimed invention in terms of the set of the characteristic features and attained technical result. The screen consists of two parts: on the projection side disposed is a Fresnel lens, whereto, on the viewer side, attached are vertically positioned are lenticular elements divided by black vertical strips. The presence of these black strips ensure an image of an high contract even in brightly-illuminated premises. Axial magnification factor (of brightness) of a screen is 5.7 units. A Fresnel lens having a very great axial directivity factor (up to 100) concentrates the projector light flux within a very narrow angle of diffusing. Lenticular lenses direct the concentrated light flux in slots between the black vertical strips, diffusing the same in the viewer direction within a relatively broad observation angle. Thereby an optimum tradeoff of the light concentration (luminous efficacy) and viewing zone width against the screen reflectance is achieved. A dark screen is not sensitive to external illuminations, and an high concentration of light in narrow slots is perceived as an high brightness of an image.
A disadvantage of the rear- and front projection systems is the necessity of a large volume of the projection space, without shadowing by external objects. Further, the lenticular-raster screens are known to reduce significantly the brightness and colour-rendering accuracy from the centre to edges of the screen image, particularly when in viewing at the aspects near to the edge of the viewers' location sector. Besides, an excessive growth of dimensions and weight of the prior-art rear projection systems is caused by the necessity to place a projection system in a light-protected premises or a housing containing projection mirrors, and the need to have means for rigid suspension of a projector. These problems, and also the need for a longer projection distance between a projector and screen (comparable with the image diagonal length) complicate design of the prior-art rear- and front projection systems and make them more expensive.
DISCLOSURE TO THE INVENTION
The object of the invention is to provide inexpensive small-dimension and lower-weight projection systems having reflecting or translucent viewing screens to project mono- and stereoscopic quality images in any scales of magnification of an image in a bright external parasitic illumination of the screen image.
The common technical result achieved through embodying of the claimed invention is a flat design of a projection system that provides a reduction of the projection space, improvement of the basic parameters and also provides novel parameters of a projection system, with a maximal luminous efficacy by virtue of effecting the projection from the screen end-face.
An additional technical result according to claim
2
is the possibility of the separate or simultaneous frontal and/or translucent projections and viewing of images from two sides of a screen.
Another additional technical result according to claims 3 and 4 is the use of the end-face projection to project the rays into the interior of a screen in the form of a light guide to form a screen image by way of multiple reflection of the rays in a light guide. This approach will exclude shadowing of the projection and that of the pre-screen and post-screen projection space volume.
Still another additional technical result according to claim 5 is formation of a screen image in projection of the rays that correspond to certain image elements (pixels) and characterised with different angles of entrance—incidence on the reflecting surfaces inside a screen so that to output said rays by screen light-diffusers in the appropriate coordinates of a screen image formation.
Still another additional technical result according to claim 5 is broadening of
Adams Russell
Baker & Botts LLP
Koval Melissa J
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