Optical: systems and elements – Single channel simultaneously to or from plural channels – By surface composed of lenticular elements
Utility Patent
1999-04-26
2001-01-02
Mack, Ricky (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By surface composed of lenticular elements
C359S619000, C359S457000
Utility Patent
active
06169633
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a lenticular lens sheet suitable for projecting thereon an image from an imaging light source having a cellular structure such as an LCD (Liquid Crystal Display) or DMD (Digital Micromirror Device), and to a rear projection screen using the same.
BACKGROUND ART
There have conventionally bee known rear projection type televisions comprising an imaging light source consisting of three CRTs (Cathode Ray Tubes) of red, green and blue, and a rear projection screen.
In such projection televisions, for example, a combination of a Fresnel lens sheet for making rays projected from the CRTs almost parallel with each other, and a light-diffusing sheet for diffusing light over a wide range is used as the rear projection screen. Used herein as the light-diffusing sheet is a lenticular lens sheet in which lens elements light-entering lenses) for condensing light such as lenticular lenses are formed on the light-entering side, and a light-emerging face is formed in the vicinity of the focal points of these light-entering lenses. Further, a light-absorbing layer (black stripe) is provided on the light-emerging face of the lenticular lens sheet, between the focal points of the light-entering lenses, so that light can be diffused and that the effects of extraneous light can be reduced.
By the way, in such projection televisions, those ones using as the imaging light source an LCD, DMD or the like have been developed. Since the LCD, DMD or the like has a cellular structure, a grating pattern originated from such cellular structure is to be projected on the rear projection screen. For the rear projection screen, a lenticular lens sheet or the like having a cyclic structure with a constant pitch is used. Therefore, when an image is projected on such a rear projection screen and observed, a moire pattern may appear due to the sampling effect of the lenticular lenses (light-entering lenses).
In order to prevent the production of such a moire pattern, it is preferable to make the pitch of the lenticular lens as small as 1/3.5 or less of the grating constant of the grating pattern projected. Further, in those projection televisions using an LCD, DMD or the like, the glaring of an image called scintillation occurs. To make the pitch of the lenticular lens small is also effective for attenuating this scintillation. In the above-described rear projection screen using a lenticular lens sheet provided with light-absorbing layers (black stripes), it has generally been known that it is necessary to make the distance between the lenticular lenses (light-entering lenses) and the light-emerging face not greater than approximately 1.3 times the pitch of the lenticular lens if light is diffused over such a wide range that the angle of deviation (angle of diffusion) is 40° or more, and black stripes are to be formed on the light-emerging face.
For this reason, in the conventional rear projection screens, in order to make a moire pattern which appears due to both the grating pattern projected on the rear projection screen and the cyclic structure of the lenticular lenses obscure, the pitch of the lenticular lens is made 0.4 mm or less, and the thickness of the lenticular lens sheet, which corresponds to the distance between the lenticular lenses and the light-emerging face, is made 0.52 mm or less.
SUMMARY OF THE INVENTION
However, in the conventional rear projection screens, when the thickness of the lenticular lens sheet is made small, the rigidity is decreased, so that it becomes difficult to maintain the lenticular lens sheet flat. Further, it is quite difficult to form a thin lenticular lens sheet by means of extrusion molding or the like with high accuracy. Furthermore, under the present conditions, the power of a light source using an LCD, DMD or the like is not so high as that of a light source using three CRTs of red, green and blue, and the contrast is also poor. Therefore, those rear projection screens which are used in combination with an LCD, DMD or the like are demanded to have high contrast as compared with the conventional rear projection screens which are used along with CRTs The most effective method for improving the contrast of a rear projection screen using a lenticular lens sheet is to increase the ratio of a total area of light-absorbing layers (black stripes) to area of light-emerging face of the screen (black stripe ratio).
The present invention was accomplished in the light of the foregoing. An object of the present invention is to provide a lenticular lens sheet and a rear projection screen using the lenticular lens sheet, in which the thickness of a lenticular lens can be increased while keeping its pitch fine, and the black stripe ratio can also be increased.
A first aspect of the present invention is a lenticular lens sheet comprising a light-entering lens part formed on the light-entering surface, in which a plurality o light-entering lenses, each having a substantially elliptical cross section are arranged, and a light-emerging lens part formed on the light-emerging surface, in which a plurality of light-emerging lenses, each having a concave-lens-like cross section are arranged so at they correspond to the condensing positions of the respective light-entering lenses in the light-entering lens part.
A second aspect of the present invention is a lenticular lens sheet comprising a light-entering lens part formed on the light-entering surface, in which a plurality of light-entering lenses, each having a substantially elliptical cross section are arranged, a light-emerging lens part formed on the light-emerging surface, in which a plurality of light-emerging lenses, each having a concave-lens-like cross section are arranged so that they correspond to the condensing positions of the respective light-entering lenses in the light-entering lens part, and a plurality of light-absorbing layers formed on the light-emerging surface, arranged so that they correspond to the non-condensing positions of the respective light-entering lenses in the light-entering lens part.
A third aspect of the present invention is a rear projection screen for use in a rear projection type television, comprising a Fresnel lens sheet for making projected rays almost parallel with each other, and a lenticular lens sheet arranged on the light-emerging of the Fresnel lens sheet, wherein the lenticular lens sheet comprises a light-entering lens part formed on the light-entering surface, in which a plurality of light-entering lenses, each having a substantially elliptical cross section are arranged, and a light-emerging lens part formed on the light-emerging surface, in which a plurality of light-emerging lenses, each having a concave-lens-like cross section are arranged so that they correspond to the condensing positions of the respective light-entering lenses in the light-entering lens part.
A fourth aspect of the present invention is a rear projection screen for use in a rear projection type television, comprising a Fresnel lens sheet for making projected rays almost parallel with each other, and a lenticular lens sheet arranged on the light-emerging of the Fresnel lens sheet, wherein the lenticular lens sheet comprises a light-entering lens part formed on the light-entering surface, in which a plurality of light-entering lenses, each having a substantially elliptical cross section are arranged, a light-emerging lens part formed on the light-emerging surface, in which a plurality of light-emerging lenses, each having a concave-lens-like cross section are arranged so that they correspond to the condensing positions of the respective light-entering lenses in the light-entering lens part, and a plurality of light-absorbing layers formed on the light emerging surface, arranged so that they correspond to the non-condensing positions of the respective light-entering lenses in the light-entering lens part
In the above-described second and fourth aspects of the present invention, it is preferable that a protruded portion having a substantially trapezoidal cross section be formed
Dai Nippon Printing Co. Ltd.
Mack Ricky
Parkhurst & Wendel L.L.P.
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