Optical: systems and elements – Projection screen – Unitary sheet comprising plural refracting areas
Reexamination Certificate
1998-07-27
2001-10-30
Metjahic, Safet (Department: 2858)
Optical: systems and elements
Projection screen
Unitary sheet comprising plural refracting areas
Reexamination Certificate
active
06310722
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a lenticular lens sheet for enlarging a view angle. Also, this invention is directed to a projection screen that is adapted to assure a great view angle as well as to minimize a color shift and a white non-uniformity using the lenticular lens sheet.
2. Description of the Prior Art
Recently, there has been spread a projection system enlarging a small picture in order to satisfy a user's desire for a large picture. The projection system uses a projection screen to enlarge and image a small picture revived by means of a cathode ray tube(CRT) or a liquid crystal display(LCD). Such a projection screen for imaging a large picture must assure as great view angle as possible so as to enlarge a visual area. To this end, the projection screen uses a lenticular lens sheet.
For example, in a projection system as shown in
FIG. 1
, each picture on red(R), green(G), and blue(B) CRTs
11
,
12
and
13
are enlargedly cast on a projection screen
19
by means of corresponding projective lens
14
,
15
and
16
, thereby imaging a large color picture on the projection screen
19
. At this time, because lights progressing from each projective lens
14
,
15
and
16
to the projection screen
19
are diffused, lights received to the incident face (i.e., front surface) of the projection screen
19
have different incidence angles in accordance with their positions on the projection screen
19
. Due to this, a distribution of lights output from the output face (i.e., rear surface) of the projection screen
19
becomes non-uniform, and a light quantity in the incident face of the projection screen
19
becomes different from that in the output face thereof. In order to overcome such a light quantity difference and such a non-uniform light distribution, a Fresnel lens sheet
17
having prism type lenses are provided in the incident face of the projective lens
19
. This Fresnel lens sheet
17
may overcome the light quantity difference and the non-uniform light distribution, but has a disadvantage in that it causes a small view angle of the projection screen
19
.
Further, projective center axes extending from the center of each projective lens
14
,
15
and
16
to the center of the projection screen
19
usually make an angle more than 8°. Accordingly, light rays incident to a point on the projection screen
19
from each projective lens
14
,
15
and
16
have different angles each other with respect to the surface of the projection screen
19
. Due to this, there occur a phenomenon called “color shift”, in which a color of a picture displayed on the projection screen
19
becomes different depending upon a viewing position, and a phenomenon called “white uniformity deterioration”, in which same color is displayed differently depending upon a position on the projection screen
19
.
In order to solve such problems, the projection screen
19
includes a lenticular lens sheet
18
provided in the output face (i.e., rear surface) thereof. The lenticular lens sheet
18
converges lights passing through the projection screen
19
and then diverges the converged lights, thereby enlarging a view angle of the projection screen
19
as well as preventing the color shift and the white uniformity deterioration. To this end, as shown in
FIG. 2
, the lenticular lens sheet
18
includes half-cylinder shape lenses
21
arranged in parallel in a direction perpendicular to the incident face of a wave guide film
20
, hereinafter referred to as “incident side lenses”, and half-cylinder shape lenses
22
arranged in a direction perpendicular to the output face of the wave guide film
20
, hereinafter referred to as “output side lenses”. Each incident side lens
21
converges a light on the surface of a corresponding output lens
22
, and each output side lens
22
diverges a light in the horizontal direction at the surface thereof. An angle at which a light is diverged on the surface of the output side lens
22
defines a view angle. In order that the lenticular lens sheet
18
having such incident side lenses
21
and such output side lenses
22
may assure a horizontal view angle and prevent the color shift and the white uniformity deterioration, the surfaces of the incident side lenses
21
and the surfaces of the output side lens
22
must be defined to satisfy the following formula (1):
Z
(
x
)
=
C
x
2
1
+
(
1
-
(
k
+
1
)
C
2
x
2
)
1
/
2
(
1
)
wherein C is a curvature of lens; k is a conic constant; and x and Z represent positions in the x axis and the z axis, respectively. Further, curved surfaces of the incident and output side lenses
21
and
22
according to the above formula (1) are shown in FIG.
3
. In the lenticular lens sheet
18
in which the output lenses
22
are formed in such a half-cylindrical element, a horizontal view angle fails to be enlarged beyond a certain limit value. When the lenticular lens sheet having such a structure is used for the projection screen, it is difficult to reduce the color shift and the white non-uniformity to less than a certain limit value.
Light diffusive particles
24
are distributed at the interior of the wave guide film
20
in the lenticular lens sheet
18
. These particles
24
diffracts a light passing through the wave guide film
20
to enlarge a vertical view angle. When the particles
24
are injected too much to the wave guide film
20
, however, an amount of light transmitting the output side lens
22
via the wave guide film
20
becomes small. Accordingly, an image displayed on the output side lens
20
is blurred. In order to solve this problem, there has been used various schemes, i.e., a method that adds a lens sheet having half-cylinder shape lenses arranged in parallel in the horizontal direction to the surfaces of the output side lenses
22
, a method that presses a thermal plastic resin film having light diffusive particles distributed and defined by thin bands with prominence and depression onto the surfaces of the output side lenses
22
, or a method that grounds the surfaces of the output side lenses
22
using a sandpaper so as to smooth them. However, such methods complicate the structure and the manufacturing process of the lenticular lens sheet.
As described above, in the conventional lenticular lens sheet, it was impossible to enlarge the vertical and horizontal view angles beyond a certain limit value and it was difficult to raise a light utility factor above a certain limit value, due to its structural affect. Also, the conventional lenticular lens sheet failed to reduce the color shift and the white non-uniformity when it was used for the projection screen. Moreover, the conventional lenticular lens sheet may act as a cause of forbidding the projection screen to provide a bright picture.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide a lenticular lens sheet that is adapted to enlarge vertical and horizontal view angles.
Further object of the present invention is to provide a lenticular lens sheet that is adapted to raise a light utility factor.
Another object of the present invention is to provide a projection screen that is adapted to enlarge view angles in the vertical and horizontal directions thereof as well as to minimize the color shift.
Still another object of the present invention is to provide a projection screen that is adapted to supply a bright picture.
In order to achieve these and other objects of the invention, a lenticular lens sheet according to one aspect of the present invention includes incident side lenses arranged in parallel to converge an incident light, the incident side lens having a half-cylinder shape; and output side lenses formed in a prism shape to diffuse a light converged by each of the incident side lenses in the vertical and horizontal directions.
A lenticular lens sheet according to another aspect of the present invention includes incident side lenses arranged in parallel to converge an incident light, the incident side lens having a h
Fleshner & Kim LLP
LeRoux E. P.
LG Electronics Inc.
Metjahic Safet
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