JPH03211540A - Transmission type screen - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a transmissive screen suitable for a thin projection TV system that projects image light from the back at a steep angle.

[Conventional technology]

Regarding the Projection TV system, various developments and research are being carried out to make the TV set thinner.

FIG. 3 is a schematic diagram showing a projection system of a conventional projection TV system.

Conventionally, in this type of projection TV system, by arranging the light source 3 diagonally below the transmissive screen 4, the distance between the light source 3 and the transmissive screen 4 is shortened, and the TV set is made thinner. ing.

The transmissive screen 4 used in this TV system has a triangular cross section and a horizontally long screen on the incident side of the light source 31.
A prism group 41 is provided in which a plurality of prism elements each having a total reflection surface are arranged.

The light source light 31 enters the prism group 41 at a steep angle, is reflected by the total reflection surface, refracted toward the observation side, and then exits as parallel reflected light 32 within a vertical plane.

Problem to be solved by the invention C] However, in the conventional transmissive screen 4, the prism group 4
1, when refracting the light source light 31, only the reflected light 32 in the vertical plane is regulated to be parallel, so an imbalance occurs between the reflected light 33 in the horizontal plane whose emission direction is not regulated. was.

For this reason, when a lenticular lens sheet is combined on the output side of the transmissive screen 4 shown in FIG. There was a problem in that the brightness of the image decreased and color unevenness occurred.

In order to solve this problem, Japanese Patent Application Laid-Open No. 63-30837 proposes that ``the luminous flux after total reflection is made to become a diverging luminous flux within a plane perpendicular to the ridgeline of the prism element.'' However, no specific means were disclosed as to how and what kind of diverging light flux the luminous flux after total reflection should be made into.

An object of the present invention is to solve the above-mentioned problems, and even if the light source light incident at a steep angle is totally reflected, the output state of the reflected light in the vertical plane and in the horizontal plane can be balanced, and the output state of the reflected light in the vertical plane and in the horizontal plane can be balanced. It is an object of the present invention to provide a transmissive screen that can prevent a decrease in brightness and the occurrence of color unevenness.

[Means for Solving the Problems] In order to solve the above problems, the transmission screen according to the present invention includes a prism group in which a large number of prism elements each having a total reflection surface are arranged in parallel on one side of the screen substrate. and make light from a light source enter the prism group at a steep angle,
In the transmission type screen that is reflected by the total reflection surface and emitted to the observation side, an extension line of the light emitted to the observation side toward the light source passes through the light source and intersects on a plane parallel to the screen substrate. It's Toshide.

In this case, a circular Fresnel lens is provided on the other side of the screen substrate, the normal line of the screen substrate passing through its center intersects with the extension line of the emitted light on a plane that passes through the light source and is parallel to the screen substrate. It can be a formed configuration.

〔Example〕

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described in detail below with reference to the drawings and the like.

1 and 2 are diagrams for explaining an embodiment of a transmission type screen according to the present invention, in which FIG. 1 is a schematic diagram showing the optical path of light source light, and FIG. 2 is a screen of the same embodiment. FIG. 2 is a schematic diagram showing a projection system of a projection TV system using the following.

In this embodiment, the light tA1 is arranged obliquely below the transmissive screen 2, and after the light source light 11 at an angle θ1 enters the transmissive screen 2 and is totally reflected, the reflected light tA1 at an angle θ2
The case where the light is emitted as 2 will be explained.

On the incident side of the screen substrate 20, there is provided a prism group 2A in which a plurality of prism elements 21 long in the left-right direction are formed in parallel. This prism group 2A includes an entrance surface 21a for the light source light 11 and a total reflection surface 21b for totally reflecting the light source light 11.
The incident surface 21a and the total reflection surface 21b are arranged to intersect at an apex angle τ.

Also, due to the prism group 2A, the extension lines 12A and 12A of the reflected light 12 toward the light source intersect at a virtual focal point on a plane parallel to the rescreen substrate 20 through which the light 'a1 passes. Therefore, the light emitted from that virtual focus is
The output light (reflected light 12) is optically equivalent to being transmitted through the transmissive screen 2 and diverged (see FIG. 2). Therefore, the emitted light (reflected light 12) diverges in a well-balanced manner in the vertical and horizontal directions.

At this time, the angle β (touch angle β) between the entrance surface 21b of the prism element 21 and the normal line of the screen substrate 20 is given by the following equation.

However, ^-cos (θ,) / n-cos(2r-θ2
) ・, −... (2) B = sin (θ+)/n
+5in(2r-θ2)・----・(3)n: refractive index θ1: human incidence angle θ2: exit angle 5qrt (X): square root of X, and incident angle θ0. The output angle θ2 is cos (θl)−・・・・・・(4)sqrt((H
+R)”+F”) cos (θ2)−・・・・・・(5) sqrt(R”
+F") F Distance between the screen substrate and a plane that passes through the light source and is parallel to the screen substrate R: Distance from the normal line of the screen substrate passing through the virtual focal point to the position of the prism element H: Distance between the light source and the virtual focal point be.

The prism group 2A as described above can be easily formed by sequentially cutting the prism elements 21 according to the contact angle β of equation (1) using a double-sided cutting tool corresponding to the tip angle τ.

A circular Fresnel lens 2B is formed on the exit side of the transmission screen 2, and is manufactured so that the normal N passing through the center of the circular Fresnel lens 2B passes through the virtual focal point IA.

Next, the transmission type screen according to the present invention will be specifically explained using manufacturing examples.

Screen substrate 20 made of acrylic resin with a refractive index of 1.57
On one side, the pitch is 0.625 mm and the tip angle τ is 60
A prism element was cut using a double-sided cutting tool while setting the contact angle β corresponding to the angle θ1 of the incident light according to the above formula (1) to form a prism group. However, in formula (4) and formula (5), F = 771 mm, H = 1337
mm and R is a variable.

Further, on the output side of the screen substrate 20, the pitch is 0.
A 112 mm circular Fresnel lens was formed at a position such that the normal passing through its center passed through the virtual focal point.

The transmission screen produced in this way was
．． When combined with a 625 mm lenticular lens with a black stripe and projecting image light from the light source, as shown in Figure 2, the reflected light that was totally reflected on the prism surface diverged in a well-balanced manner in the vertical and horizontal planes. It was as if there was a light source on the central axis of the Fresnel lens.

Furthermore, since the emission angle of the reflected light is changed to increase the angle of total reflection, the screen can be made wider than before.

[Effects of the Invention] As explained in detail above, according to the present invention, the extension line of the light emitted to the observation side toward the light source passes through the light source and intersects on a plane parallel to the screen substrate. The output light is emitted from that point and is equivalent to being diffused, and even if the light source light incident at a steep angle is totally reflected, it is possible to balance the output state of the reflected light in the vertical and horizontal planes. This has the effect of preventing a decrease in brightness and color unevenness on the screen.

[Brief explanation of drawings]

FIG. 1 FIG. 2 is a diagram for explaining an embodiment of a transmission type screen according to the present invention, FIG. 1 is a schematic diagram showing the optical path of light source light, and FIG. 2 is a screen of the same embodiment. FIG. 2 is a schematic diagram showing a projection system of a projection TV system using the following. FIG. 3 is a schematic diagram showing a projection system of a conventional transmission type projection TV system. 1... Light source IA... Virtual focus 11... Light source light 12... Reflected light 2... Transmissive screen 2A... Prism surface 2B... Circular Fresnel lens 3... Light source 31 ...Light source light 4...Transmissive screen 41...Prism surface 42.43...Reflected light

Claims (2)

[Claims] (1) On one side of the screen substrate, a prism group is formed in which a large number of prism elements with total reflection surfaces are arranged in parallel,
In a transmission type screen in which light from a light source enters the prism group at a steep angle, is reflected by the total reflection surface, and is emitted to the observation side, an extension line of the light emitted to the observation side toward the light source side is the light source. , and intersects on a plane parallel to the screen substrate. (2) On the other side of the screen substrate, a normal line of the screen substrate passing through the center thereof is an extension line of the emitted light;
2. The transmission screen according to claim 1, further comprising a circular Fresnel lens that passes through the light source and intersects with the screen substrate on a plane parallel to the screen substrate.