Optical: systems and elements – Projection screen – Unitary sheet comprising plural refracting areas
Reexamination Certificate
2001-06-28
2004-08-03
Adams, Russell (Department: 2851)
Optical: systems and elements
Projection screen
Unitary sheet comprising plural refracting areas
C359S453000, C359S460000
Reexamination Certificate
active
06771419
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a rear-projection image display. More specifically, the present invention relates to a rear-projection image display in which image display is conducted by superimposing projection images on a transparent screen, the projection images being projected from a plurality of image displays juxtaposed in a common horizontal plane.
BACKGROUND ART
The following description will depict a conventional rear-projection image display, while referring to the drawings.
FIG. 7
is a plan view illustrating an overall configuration of a conventional three-tube rear-projection image display
100
. The rear-projection image display (video projector)
100
presently is a main item in the market of large video-image display for home use. Images on three image display elements (CRTs)
101
,
102
, and
103
corresponding to three colors of red, green and blue colors, respectively, are enlarged and projected by projection lenses
104
,
105
, and
106
, respectively, so as to be synthesized on a transparent screen. The transparent screen includes a Fresnel lens
107
as collimating means and a lenticular lens sheet
108
as a light diffusing means. Such a transparent screen can collimate respective principal rays of color lights incident from different directions and then allows the same to leave. Hence, a phenomenon can be corrected in which shade of color varies with positions where the observer stands (color shading). In addition, on a light-outgoing surface of the lenticular lens sheet
108
, black stripes
109
are provided between adjacent lenticular lenses so as to prevent black dimming from occurring due to external light, and thus to prevent lowering of the contrast of images. Furthermore, surfaces of the lenticular lenses between the black stripes
109
are coated with a diffusing material, or a diffusing material is mixed in the lenticular lens sheet
108
, so that visibility is secured in a vertical direction.
On the foregoing transparent screen, however, light source images of three different color lights are formed at different positions within an aperture between adjacent black stripes
109
, as illustrated in FIG.
8
. Therefore, in order to avoid optical loss, it is necessary to make each space between the black stripes
109
sufficiently wide with respect to the foregoing light source images. This causes the black stripes
109
to be sparsely provided. Consequently, it has been impossible to suppress sufficiently the black dimming caused by the diffusing material reflecting external light that has entered through the aperture.
Screens that solve such a problem recently have been proposed, which are as described below. Such screens include: a first type of screen disclosed in JP 9(1997)-504882 A in which transparent beads are used; a second type of screen is disclosed in JP 10(1998)-339915 A in which black stripes are used; and a third type of screen is disclosed in the JP 10(1998)-111537 A in which a color layer is used.
A configuration of a transparent screen of the first type using transparent beads is shown in FIG.
9
. Micro beads
111
made of a transparent material are fixed to a substrate panel
110
made of a light-transmitting material with a light absorbing adhesive
112
used therebetween. Light having passed through the Fresnel lens
107
is converged by the beads
111
so as to be focused on portions (apertures) where the beads
111
and the substrate panel
110
are in contact with each other. Since the adhesive
112
is absent at these portions, the light passes through the substrate panel
110
to leave as diffused light. Each of the portions (apertures) where the beads
111
and the substrate panel
110
are in contact with each other is a very small point that occupies an area that hardly can be recognized when viewed from the observer side, and areas of the screen surface other than the apertures are covered with the light absorbing adhesive. Most of external light incident on the screen from the surroundings therefore is incident on and absorbed by the adhesive, never to be reflected toward the observer side. In this screen, such very small beads
111
allow high-definition display to be provided. Besides, the black level hardly is impaired even when strong external light is incident on the screen. Consequently, the contrast of images hardly is impaired.
A configuration of a transparent screen of the second type using black stripes is shown in
FIG. 10. A
lenticular lens sheet
113
includes lenticular lenses on a light-incident surface thereof, and a diffusing layer
116
is laminated on a light-outgoing surface of the lenticular lens sheet
113
. Black stripes
115
are formed on a light-outgoing surface of the diffusing layer
116
, and the diffusing layer
116
is laminated with a front panel
114
with a transparent adhesive layer being provided therebetween. Light having passed through a Fresnel lens
107
enters the lenticular lenses, is converged onto apertures between the black stripes
115
or the vicinities thereof, passes through the front panel
114
, and exits as diffused light. In the foregoing process, when passing through the diffusing layer
116
, image light is diffused in horizontal and vertical directions. Since the lenticular lenses that are very small are used to converge the image light, it is possible to narrow the spaces between the black stripes
115
. This allows a proportion of areas of the black stripes
115
to be increased, thereby causing most of the external light incident on the screen to be absorbed by the black stripes
115
, never to be reflected toward the observer side. This configuration of the screen therefore allows the lenticular sheet
113
to be formed thinly, thereby allowing the black stripes
115
to be provided at a fine pitch. Consequently, a high-definition display can be provided. Besides, the black level hardly is impaired even when strong external light is incident on the screen. This results in that the contrast of images hardly is impaired.
A configuration of a transparent screen of the third type using a color layer is shown in
FIG. 11. A
lenticular lens sheet
118
includes lenticular lenses
117
on a light-incident surface thereof, and a color layer
119
is provided in the vicinity of the light-incident surface of the lenticular lenses
117
. A material of the lenticular lens sheet
118
as a substrate is either non-colored, or colored to have a lighter tint than that of the color layer
119
. Light having passed through a Fresnel lens
107
enters the color layer
119
. After passing through the color layer
119
, the light enters the lenticular lenses
117
. The light is converged by the lenticular lenses
117
and is allowed to exit as diffused light to the observer side.
On the other hand, among external light from the surroundings, light incident to the color layer
119
at a small angle of incidence passes through the color layer
119
and is absorbed into a case, with substantially no light going back to the screen. Therefore, the light incident to the layer
119
at a small angle of incidence is not harmful. Moreover, light incident on the color layer
119
at a great angle of incidence is subjected to total reflection at an interface between the color layer
119
and an air layer. Normally the total reflection is repeated several times, and then some light follows an optical path going back to the observer side However, since a distance for passage through the color layer
119
increases as the total reflection is repeated, most of the light therefore is absorbed by the color layer
119
. Thus, this screen allows the lenticular lens sheet
118
to be formed thinly, thereby allowing the lenticular lenses
117
to be provided at a fine pitch. Consequently, a high definition display call be provided. Moreover, since the foregoing screen hardly allows external light incident on the screen to be reflected to the observer side without remarkable degradation of image light, incidence of strong external light onto the screen hardly causes the black
Ikeda Kenichi
Miyai Hiroshi
Yamagishi Shigekazu
Yamaguchi Hiroshi
Adams Russell
Cruz Magda
Matsushita Electric - Industrial Co., Ltd.
Merchant & Gould P.C.
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