Plastic and nonmetallic article shaping or treating: processes – Optical article shaping or treating – Including step of mold making
Reexamination Certificate
2002-05-29
2004-04-27
Vargot, Mathieu D. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Optical article shaping or treating
Including step of mold making
C264S219000, C425S808000
Reexamination Certificate
active
06726859
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a Fresnel lens having the same function as a convex lens almost without requiring a distance between alight incident point and alight out going point. Also, the present invention relates to a rear projection type screen, to which the Fresnel lens is applied, and an image displaying device to which the screen is applied. In addition, the present invention relates to a lens forming mold manufacturing method and a lens manufacturing method.
BACKGROUND ART
In an image displaying device represented by a rear projection type projection television, a screen is used, and image light emitted from an image light source is projected on the screen. In general, the screen of the image displaying device is formed by combining a lenticular and a Fresnel lens. The lenticular functions as a light diffusion plate in which the image light is scattered to form an image. In the Fresnel lens, the image light emitted from the image light source is refracted, and rays of refracted light go out to the lenticular almost in parallel to each other.
FIG. 1
is a view showing an external appearance of a conventional Fresnel lens.
In
FIG. 1
,
101
indicates a Fresnel lens seen on a slant.
102
indicates a sectional shape of the Fresnel lens
101
.
103
indicates an optical axis of the Fresnel lens
101
.
104
indicates a prism portion formed for each pitch area corresponding to one pitch length in the Fresnel lens
101
.
In the manufacturing of the Fresnel lens
101
, a metal mold (or a lens forming mold) is formed by rotating the mold on the optical axis
103
, synthetic resin is poured into the metal mold, the synthetic resin is hardened, the metal mold is taken off from the synthetic resin, and the manufacturing of the Fresnel lens
101
is completed. On a surface of the manufactured Fresnel lens
101
, a plurality of ring bands are formed in a concentric circular shape around the optical axis
103
. As is realized by looking at the sectional shape
102
of the Fresnel lens
101
, the ring bands formed in a concentric circular shape denote the plurality of prism portions
104
.
That is, the prism portions
104
of the sectional shape
102
formed in a saw-tooth shape are equally spaced at pitch intervals respectively corresponding to one pitch width. One pitch width of the Fresnel lens
101
actually used is almost equal to 0.1 mm, and the pitch width is very small even though the pitch width is compared with each of minimum pixels on which an image is projected through the Fresnel lens
101
. The whole Fresnel lens
101
functions as one convex lens. Because the prism portions
104
can be thinned, rays of light incident on the Fresnel lens
101
can be changed or refracted almost without requiring a distance between an incident point of the ray of incident light and an outgoing point of a ray of outgoing light.
In the image displaying device, to shorten the depth of the image displaying device, image light is often injected on the Fresnel lens
101
of the screen from a direction inclined with respect to an incident normal of the Fresnel lens
101
as much as possible. Therefore, a thinned type image displaying device can be obtained.
FIG. 2
is a view showing the configuration of an image displaying device in which a conventional Fresnel lens is applied to a screen.
A plurality of arrows indicate a plurality of rays of light.
111
indicates a light emitting source (or illumination light source means) for emitting a plurality of rays of light.
112
indicates a parabolic mirror (or illumination light source means). The light emitting source
111
is disposed on a focal point of the parabolic mirror
112
.
113
indicates a convergin glens (or converging optics means) for converging a plurality of rays of light reflected on the parabolic mirror
112
.
114
indicates a light bulb (or optical modulating means) formed of liquid crystal. An intensity of each ray of light converged by the converging lens
113
is spatially changed in the light bulb
114
to modulate the converged rays of light according to display contents written on the light bulb
114
.
115
indicates a projection optics lens (or projection optics means) for forming an image from the rays of light of which the intensities are changed by the light bulb
114
.
116
indicates a rear projection type screen for receiving the image of the rays of light formed by the projection optics lens
115
from the rear side and displaying the image. The rays of light spreading in the projection optics lens
115
are changed in the screen
116
to a plurality of rays of light parallel to each other, the image formed from the rays of light is displayed on the screen
116
, and the rays of light are diffused from the screen
116
to a wide area. Therefore, the screen
116
has a function for widening a view field.
In the screen
116
,
117
indicates a Fresnel lens described before, and
118
indicates a lenticular.
In the Fresnel lens
117
, the spreading rays of light sent from the projection optics lens
115
are received on an incident plane
117
A, and the rays of light go out at a prescribed outgoing angle through a prism portion
117
B arranged for each pitch area corresponding one pitch. In short, the Fresnel lens
117
is used to almost collimate the rays of light spreading in the projection optics lens
115
. An image is formed on the lenticular
118
from the rays of light going out from the Fresnel lens
117
, and the rays of light are diffused.
119
indicates an optical axis. The optical axis
119
exists for the parabolic mirror
112
, the converging lens
113
, the light bulb
114
, the projection optics lens
115
, the Fresnel lens
117
and the lenticular
118
, and the optical axis
119
is perpendicular to the incident plane
117
A of the Fresnel lens
117
.
Next, an operation will be described below.
The light emitting source
111
disposed on a focal point of the parabolic mirror
112
can be almost regarded as a point source. Therefore, rays of light emitted from the light emitting source
111
are reflected on the parabolic mirror
112
and goes out to the converging lens
113
as almost parallel rays of light. When the parallel rays of light are converged by the converging lens
113
onto the light bulb
114
, intensities of the converged rays of light are spatially changed by the light bulb
114
to modulate the converged rays of light according to display contents of the light bulb
114
.
The rays of light intensity-modulated are projected on the rear surface of the screen
116
at a wide angle by the projection optics lens
115
, and an image is formed from the rays of projected light. An angle between each ray of light and the optical axis
119
is called a projection angle. As shown in
FIG. 2
, the projection angle in each pitch area differs from those in the other pitch areas. However, because the pitch between each pair of prism portions
117
B is considerably shorter than the lengths of the projection optics lens
115
and the screen
116
, a plurality of rays of light incident on each prism portion
117
B can be almost regarded as a plurality of parallel rays.
An angle between a normal m
11
of the incident plane
117
A and each ray of incident light denotes an incident angle. Because the incident angle of each ray of incident light is equal to the projection angle of the ray of incident light according to the relationship of alternate-interior angles obtained from a straight line (the incident ray) intersecting two parallel lines (the optical axis
119
and the normal m
11
), the more a pitch area receiving a ray of light approaches the optical axis
119
, the smaller the incident angle of the ray of light is. Also, the more a pitch area receiving a ray of light is far away from the optical axis
119
, the larger the incident angle of the ray of light is. In particular, the ray of light going out to the prism portion
117
B placed at each end of the screen
116
is incident on the incident plane
117
A at the maximum incident angle.
A size of the screen
116
is dete
Ashizaki Yoshihiro
Kojima Kuniko
Ryuugou Tadahiko
Sekiguchi Hiroshi
Sikama Shinsuke
Birch & Stewart Kolasch & Birch, LLP
Mitsubishi Denki & Kabushiki Kaisha
Vargot Mathieu D.
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