JPH0510657B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Field of Application) The present invention relates to a rear projection screen for projection television. (Prior Art) A rear projection device such as a video projection television basically has the following features as shown in FIG.
Light emitted from a light source P such as a CRT is appropriately magnified by a lens system L, projected from the back side of a screen S, and observed from the opposite side of the screen S. However, increasing the distance from the light source P to the screen S in this way increases the size of the projection device, so in reality, the distance from the light source P to the screen S increases.
As shown in B and C, a method is adopted in which one to three mirrors M are combined and the light is reflected once and then projected. However, in the method shown in FIG. 1A, the height of the device increases, and in the case of methods B and C, it cannot be said that the device has been miniaturized in terms of height and depth. In addition, many of the screens used in such projection devices are equipped with a circular Fresnel lens on the incident side, which allows every corner of the screen to be seen brightly.
In this circular Fresnel lens, as shown in Figure 3, lens surface A is continuous through non-lens surface B, so that the incident light on non-lens surface B shown with diagonal lines is not condensed. Reduces Fresnel efficiency,
Additionally, there is a drawback that it has a negative effect on resolution. To prevent this problem, some methods have been used to reverse the lens surface of the Fresnel lens so that the light enters from a flat surface, and to combine it with another lenticular lens. Using a screen not only complicates assembly, but also tends to cause the screen to become blurred due to light flare between the two screens, and to reduce light utilization efficiency. In addition, as a screen device that can reduce the depth of the projection device, Japanese Patent Application Laid-Open No. 58-57120 and Japanese Patent Application Laid-Open No. 59-9649 are known, in which the projection device is projected by making the light incident on the screen from an oblique direction. It has been proposed to reduce the depth of the system, but since these utilize lens refraction, there is a limit to increasing the angle of incidence. In order to improve these points, the present inventors proposed a screen that allows light to enter at a steep angle from the back side and observe an image, and provided a large number of prism groups parallel to this plane of incidence, and We have already proposed a rear projection screen in which each prism that makes up a group is provided with a total reflection surface so that the incident light is totally reflected on the total reflection surface and exits to the viewing side (Japanese Patent Application No. 1983- No. 29964 (Unexamined Japanese Patent Publication No. 60-173533
) and Japanese Patent Application No. 1983-47936 (Japanese Patent Application No. 1983-
No. 208041)). (Problems to be Solved by the Invention) Our above proposal has made it possible to downsize the device by reducing the dimensions in the depth and height directions, and to provide a bright screen that does not reduce resolution. It was found that because the line extends horizontally, it intersects the scanning line of the projector image at a small angle, causing a moire phenomenon that adversely affects the image being viewed. One way to reduce this moiré phenomenon is to mix a large amount of diffusing agent into the screen plate, or to form many minute irregularities on the screen plate surface to reduce resolution and contrast. However, this fundamentally reduces screen performance and is not necessarily sufficient. Therefore, in the present invention, as a result of studies to reduce the moire phenomenon, it was discovered that the strength of moire is related to the pitch ratio between the scanning line and the prism, and the present invention was completed. (Means for Solving the Problems) That is, the gist of the present invention is a projection television screen that allows light to enter from the back side at a steep angle to observe an image. A large number of prism groups extending in a straight line or an arc shape are formed, and each prism constituting this prism group has a structure such that the incident light is totally reflected on a total reflection surface and exits to the observation side. A total reflection surface is formed, and when the pitch of the scanning line of the projection television to be projected is 1, the pitch of the prism group is N + 0.35 to 0.45, N + 0.55 to 0.65, or 1/N + 0.35. ~0.45
or 1/N+0.55~0.65 (however, N is 1~12
A projection television screen characterized by a range of integers). The present invention will be described below with reference to drawings of embodiments. FIG. 4 is a schematic diagram for explaining the basic configuration of the screen of the present invention, where P is a light source such as a CRT,
L is pitch type, S is rear projection screen,
The light from the light source P is designed to be incident on the back surface of the rear projection screen S at a steep angle. Here, the angle θ when the light is incident on the screen S is approximately 40 to 75 degrees. The distance l from the light source P to the screen S at this time is the same as in the conventional method, but since the light source P is located diagonally downward, the distance l' in the depth direction is l' = lcosθ, which is extremely small compared to l. can do. However, this does not necessarily mean that the height is small, so it is actually desirable to use one mirror _M1 as shown in Figure 5A to reduce the height and length in the depth direction. . In addition, in order to further reduce the height and overall size, two mirrors M ₂ and M ₃ are used as shown in FIG. 5B.
The light source P is connected to the screen S and the first mirror.
It is best to place it between M ₂ and project it after reflecting it twice. FIG. 6 shows a part of the screen of the present invention, and in this example, a large number of prism groups having the same shape are provided on the back side of the screen. In other words, this prism group is composed of a large number of prisms 1 arranged in a straight line or an arc shape, and each prism 1 has a total reflection surface so that all the incident light enters the prism 1 and exits to the observation side. It is composed of a total reflection surface 1A and a facing surface 1B corresponding to this incidence surface. The totally reflected light passes through the transparent section 1 on the observation side.
Since the light is transmitted through the portion C and then emitted, the light does not pass through the non-transmissive portion 1D, and this is repeated for each pitch of the prism. Therefore, moiré occurs due to the correlation between this phenomenon and the scanning line of the projection television. Therefore, in the present invention, when the pitch of the scanning line of the projection television to be projected is set to 1,
Adjust the pitch of the screen prism group to N+0.35~
0.45 or N+0.55~0.65 or 1/N+0.35
~0.45 or 1/N+0.55~0.65 (N is 1
~12 integers). In this case, when the scanning line pitch and the prism pitch are set to 1:1, a particularly severe moire phenomenon occurs, and even when the pitch is set to 1:1.5 or 1:1/1.5, fine moire remains. The moire does not disappear when the ratio is 1:1.5 or 1:1/1.5.
This appears to be because a 1:1 ratio is formed every other time. According to the studies of the present inventors, it has been found that the occurrence of moiré becomes extremely light when the ratio is 1:about 1.4 or 1:about 1.6, and the scope of the present invention has been defined based on this. In the screen of the present invention, the arrangement of the prism groups is not limited to the horizontal direction, but also includes a case where the prisms are arranged in an arc shape as shown in FIG. In other words, if P is a light source such as a CRT for projection, and O is the center of an arc on a plane F that includes a screen S, and if this line segment OP is perpendicular to the plane F, each arc on the same arc Since all the points are equidistant from the light source P, by making the cross sections of the prism 1 on this circular arc equal, the emission angles on the prism cross sections become equal, which not only simplifies the design, but also reduces the light in the vertical direction. A well-balanced screen S can be realized by regulating the light in the left and right directions as well. Assume that the position of the light source P is x behind the screen S and y downward from the center of the screen S as shown in FIG. Assuming that the apex angle of the prism at the point is θ ₁ and the inclination of the prism entrance surface is θ ₂ (see Figure 8), θ ₂ in the case of parallel output can be determined by the following formula (n is the refractive index of the base material). ). When the cross-sectional shape of the prism 1 is set to the shape expressed by the above formula, all light rays emitted from the screen S surface become parallel lights perpendicular to the screen S. This makes it possible to obtain a screen that is more compact and has more uniform brightness than a screen equipped with a conventional Fresnel lens. 9 to 14 show parts of embodiments of the present invention, and FIG. 9 shows the most basic rear projection screen, with a reflection surface 1A having a projection side or total reflection surface and an entrance surface. A large number of prisms 1 with 1B are formed. Fig. 10 shows the example shown in Fig. 9 above, with a lenticular lens surface 1E extending vertically on the viewing side, and this lenticular lens surface 1E imparts light diffusivity in the horizontal direction. . Also, Figures 11 and 1
In Figure 2, lenticular lens surfaces 1F and 1G equipped with total reflection surfaces 1F ₁ and 1G ₁ are similarly formed on the projection side, thereby achieving even greater horizontal light diffusivity, that is, a viewing angle. . In addition, the first
The structure and operation of the lenticular lens surfaces 1F and 1G having total reflection surfaces in FIGS. 1 and 12 are disclosed in Japanese Patent Application No. 56-51194 (Japanese Unexamined Patent Publication No. 57-165830) filed by the same applicant. No. 56-90544 (Japanese Unexamined Patent Publication No. 57-205727)
No. 57-207235), Japanese Patent Application No. 56-212584 (Japanese Patent Application No. 1983)
-114026), Japanese Patent Application No. 114026 (Japanese Patent Application No. 1983-29178)
145933), Japanese Patent Application No. 59389 (1982)
176628), so the explanation here will be omitted. 13 and 14 show an example in which a separate sheet 2 is further combined on the viewing side of the rear projection screen in FIG. 9, and FIG. 13 shows a lenticular lens extending horizontally on the projection side. The surface 2A is combined with a separate sheet 2 on which a vertical lenticular lens surface 2B having a total reflection surface _2B1 similar to that shown in FIG. A rear projection screen can also be provided with vertical light diffusion properties. Further, FIG. 14 shows a combination of a separate sheet 2 in which a lenticular lens surface 2C extending perpendicularly to the projection side is formed, and a concave lenticular lens surface 2D and an external light absorption layer 2E are formed on the observation side. This makes it possible to improve horizontal light diffusivity and contrast. In the above embodiment, the first group of prisms is arranged in series so as to extend in the horizontal direction, but this may be converted by 90 degrees and configured to extend in the vertical direction.
Of course, in this case, the projector will be installed horizontally. Since the screen of the present invention projects an image obliquely from behind, the image on the screen is distorted and blurred, but these problems can be solved by the following measures of the projection system. In other words, regarding image distortion, the amount of distortion in each part is assumed and the CRT
This can be corrected using an electric circuit. Also, the blur of the image is
This is caused by the difference in distance from the lens system to the screen, so the image incident on the lens system from the CRT is
What is necessary is to make a constant angle with respect to the optical axis so that the focal length is the same on the screen. Acrylic resin is the most suitable material for the screen of the present invention, since acrylic resin is particularly excellent in terms of optical properties and moldability. However, it is also possible to use vinyl chloride resin, polycarbonate resin, olefin resin, styrene resin, etc. instead, and when these synthetic resin materials are used, they can be molded by extrusion molding, hot pressing, or injection molding. A screen according to the invention can be manufactured. Further, it is preferable to provide a light diffusing means for further improving light diffusing properties on the base material or separate sheet constituting the screen of the present invention. As this light diffusion means, SiO ₂ , CaCO ₃ , Al ₂ O ₃ , TiO ₃ ,
One or more additives of diffusing substances that do not melt or chemically change are uniformly added to a liquid synthetic resin medium such as BaSO ₄ , ZnO, Al(OH) ₃ , glass fine powder, or an organic diffusing agent. mixed dispersion distribution or
Alternatively, a layer containing these diffusion substances may be formed. It is also effective to form a fine matte surface on the projection side surface and/or the observation side surface. If such a means for imparting light diffusivity is taken, the diffusivity of the screen in the horizontal and vertical directions is compensated for and uniformity can be improved. (Example) When manufacturing a methacrylic resin board, a resin board serving as a base material was manufactured by uniformly mixing silicon oxide as a light diffusing agent. Then, a mirror plate is applied to one side of this resin plate to the other side of the prism mold of the present invention, and after heating (approximately 150 to 200°C), pressure is applied (40 to 60 kg/
cm ² ), 7 types (4 inventive products and 3 comparative products) of one-sheet screens as shown in FIG. 12 were prepared. The appearance of moiré on the sample was observed, and the results were as shown in Table 1.

【table】

[Table] In the above embodiment, a combination in which the prism unit pitch is smaller than the scanning line pitch has been described, but it has been confirmed that the same result can be obtained with the opposite ratio. (Effects of the Invention) The present invention has the configuration as detailed above, and it is possible to efficiently and uniformly emit light incident on the rear of the screen at a steep angle to the observation surface by the shape of the prism and the action of total reflection. Therefore, when using the screen according to the present invention, the relative position of the projector serving as the light source is positioned diagonally to the rear,
This has the advantage that the entire projection device can be miniaturized, a uniform and bright rear projection screen can be easily provided, and moiré phenomena harmful to images can be minimized.

[Brief explanation of the drawing]

Figures 1 and 2 are explanatory diagrams of the optical path from a projector to a conventional screen, Figure 3 is a partial side view of a Fresnel lens used in a conventional rear projection screen, and Figures 4 and 5 are views of the present invention. FIG. 6 is a partial side view showing the progress state of light in the screen of the present invention, and FIG. 7 is an explanatory diagram of the optical path from the projector when a screen of the present invention is used. FIG. 8 is a partially enlarged view of the screen shown in FIG. 7, and FIGS. 9 to 14 are partial perspective views showing embodiments of the present invention. S...screen, P...CRT, L...lens system, _M1 , _M2 , _M3 ...mirror, 1...prism, 1A...reflection surface, 1B...incident surface.

Claims (1)

[Claims] 1. A projection television screen that allows light to enter at a steep angle from the back side to observe an image, and on this entrance surface, a large number of prism groups extending in a straight line or an arc shape are formed. At the same time, each prism that makes up this prism group is formed with a total reflection surface so that the incident light is totally reflected on the total reflection surface and exits to the observation side. Yon TV's scanning line pitch is 1
Then, the pitch of the above prism group is N+0.35
~0.45 or N+0.55~0.65 or 1/N+
0.35~0.45 or 1/N+0.55~0.65 (However, N
is an integer from 1 to 12). 2. The projection television screen according to claim 1, further comprising a lenticular lens surface extending vertically on the viewing side. 3. The projection television screen according to claim 2, characterized in that a lenticular lens surface having a total reflection surface is formed. 4. The projection television screen according to claim 1, 2, or 3, characterized in that a circular Fresnel lens is formed on the viewing side. 5. The projection television screen according to claim 1, 2, 3, or 4, characterized in that a base material constituting the screen is provided with a light diffusion means. 6. The projection television set forth in claim 1, 2, 3, 4, or 5, characterized in that it is combined with a separate sheet having a lenticular lens surface. screen. 7. The projection television screen according to claim 6, characterized in that a light diffusion means is provided on a separate sheet.