JPS59107337A - Transmission screen - Google Patents

Abstract

PURPOSE:To obtain a transmission screen having a large horizontal view angle, which is suitable for a slide projector, etc. by forming repeatedly a slender projecting part on which the contour of a cross section is formed by a parabola along the plane of a transparent plate, on one surface of a thin transparent plate. CONSTITUTION:A Fresnel lens 3 for changing a diverging luminous flux from a light source to a parallel luminous flux or a converging luminous flux is formed on the surface of a light source 2 side of one thin transparent plate 1 in which an optical diffusing material is mixed, and a lot of slender projecting parts 13 on which the cross section is formed by a parabola or a rough parabola along the plane formed by the transparent plate 1 are formed in parallel at prescribed intervals on the other surface, bywhich a transmission screen is obtained. In this way, parallel beams going toward the surface of the projecting part 13 from the inside of the transparent plate 1 are curved in the lateral direction and are made incident to the surface near the top of the projecting part 13, and a beam diverging to the outside from the surface near the top is emitted, by which a horizontal view angle can be widened.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a screen that is effective for use in slide projectors and projection television devices, and more specifically,
This relates to a transmissive screen in which images are projected from the front of the screen and images are viewed from the front.

Conventional Structure and Problems There is a conventional screen of this type as shown in FIG. To explain this, a Fresnel lens 3 for converting the emitted light beam from the light source 2 into a parallel light beam or a convergent light beam is formed on one surface of the thin transparent plate 1a, and a convex lens 41 is formed on the other surface. 4 is repeated in the horizontal direction with respect to the viewer to form a lenticular lens, and a light diffusing material for projecting a projected image is mixed inside this transparent plate. A lenticular lens in which semicylindrical convex lenses 4 are repeatedly formed can efficiently diffuse light only in the horizontal direction, so it reduces the vertical viewing angle.
The horizontal viewing angle can be increased.

By the way, in order to widen the horizontal viewing angle of a fast-pass type screen IJ as shown in FIG. 1, the viewing angle 2θ as viewed from the center of curvature 5 of the semicylindrical convex lens 4 may be increased. However, if the viewing angle 2θ is increased by a certain amount, the light rays 7 parallel to the optical axis 6 of the transmission screen may be totally reflected on the surface of the semicylindrical convex lens 4. thin transparent plate 1
Acrylic resin (refractive index: 1.491) as a
When using , the critical angle for total reflection is 42.10, so the maximum value of the angle of view 2θ is 84.2°. At this time, the maximum value of the output 9J inclination angle β (the angle formed by the output light?fM8 and the optical axis 6) is 47.9°. 1. When a ray of light is refracted, if the angle of incidence exceeds the Brewster angle, the reflectance at the refracting surface gradually increases, so if the viewing angle 2θ is increased to increase the horizontal viewing angle, the efficiency will decrease. I end up. For example, when the refractive index is 1.491, the Brewster angle is 33.80, and the exit angle is 1.491.
The angle will be β-22,30.

For this reason, there was a problem that the horizontal viewing angle of the transmissive screen shown in FIG. 1 could not be made very large.

In addition, as shown in Figure 2, two thin transparent plates 9.10
A Fresnel lens 3 is formed on one surface of the transparent plate 9, a hook-shaped convex lens 4 is repeatedly formed on the surface 11 of the transparent plate 10 on the light source 2 side, and 12 is a transmissive screen provided with a light diffusion screen. In this transmission screen, the light ray 7 incident parallel to the optical axis 6 is bent by the semicylindrical convex lens 4, and further bent by the lens 12 on the observer's side, so that the maximum value of the exit angle β is set to the first
It can be made larger than shown in the figure, thus allowing for a larger horizontal viewing angle.

However, since the transmission screen shown in FIG. 2 has a two-layer structure, a gap is likely to occur between the two transparent plates 9 and 10, and if the gap becomes large, double images or blurring will occur. Furthermore, a process of bonding the two transparent plates 9 and 10 together without any gaps is required, resulting in high costs.

OBJECTS OF THE INVENTION The present invention seeks to provide a single-panel transmissive screen that has a larger horizontal viewing angle than conventional screens.

Composition of the Invention The transmission screen of the present invention has a thin, thin transparent plate on one side of which a long and narrow convex part whose cross-sectional profile is partially or entirely formed as a parabola or a substantially parabola along the plane formed by the transparent plate. When a parallel ray of light enters the surface of the convex part from the inside of the transparent plate, the light ray is first bent in the horizontal direction by total reflection and then enters the beam near the apex of the convex part. The horizontal viewing angle is made extremely wide by emitting light rays that diverge to the outside from the surface near the apex.

DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the drawings.

FIG. 3 shows a cross-section of an embodiment of a transmission screen according to the present invention. is light source 2
A Fresnel lens 3 is formed on the other surface to convert a diverging light beam from the rays into a parallel light beam or a convergent light beam, and the cross section is several'l/li! A large number of side-long protrusions 13 are formed parallel to each other at predetermined intervals along the plane formed by the transparent plate 1 in the direction of S or approximately radial aJ. This transmission type screen has a convex portion 13
It is used by arranging it so that the longitudinal direction of the mW is perpendicular to the mW operator.

FIG. 4 shows an enlarged cross-sectional view of the convex portion 13. The outline of the +j4vfjT surface of the convex portion 13 is the same as the outside, and has a convex shape of 9,000 mm, among which l1yln 14r
J, perpendicular to the plane formed by the transparent plate 1.

First, the effect when a light ray 15 parallel to the center line 14 is incident on the surface of the convex portion 13 shown in FIG. 4 will be explained.

When the distance between the incident light ray 15 and the center line 14 is small, the light is divided into a component 16 that exits to the outside by refraction and a component 17 that returns to the inside by reflection. Since the convex portion 13 is convex in the same way as the outside, the larger the distance between the incident light ray 15 and the center line 140, the larger the incident angle a on the surface of the convex portion 130. As the incident angle α increases, the reflected component The ratio of the light intensity of 17 increases. When the distance between the incident ray 15 and the center line 140 becomes wider than a certain value, the transmitted component 16
is eliminated, and only the reflected component 17, that is, total reflection occurs.

From this, when the incident light ray 16 is incident on the surface of the convex portion 13, it can be classified into two cases: a case in which total reflection occurs, and a case in which total reflection does not occur. Therefore, the surface of the convex portion 13 can be divided into a soil surface 19 above the boundary 18 and a side surface 20 below the boundary 18 by the boundary 18 where total reflection begins, and the incident light parallel to the center line 14 16 can also be divided into two types, a double-incident ray 21 and a side-incident ray 22, depending on the incident location. Top incident light? The llI21 is refracted by the upper surface 19 and emitted to the outside, but since the upper surface 19 is a curved surface, the output inclination β (the angle 9 between the center line 14 and the output beam 16) differs depending on the incident position.

Output # for top incident light #21: around 11 Angle β is the convex portion 13
It becomes the minimum when it is incident on the vertex 23 of , and becomes the maximum when it is separated into the boundary 18 . Side-incident ray 22 is incident on side 20
After total reflection, the light enters the upper surface 19. In this case, as described later, if the outline of the cross section of the convex portion 13 is a parabola, then the light incident on the soil surface 19? fM24 is emitted to the outside without causing total internal reflection. In this case as well, since the upper part 19 is a curved surface, the output IJv +FA angle differs depending on the incident position. The output angle for the side incident light ray 22 is minimum when it is incident on the lower end 25 of the convex portion 13, and maximum when it is incident on the boundary 18. Based on the principle described above, it is possible to make a light beam parallel to the central axis 14 enter the surface of the convex portion 13 and diffuse the light.

With the configuration shown in Figures 3 and 4, the center line 1
Since there are also light rays emitted in a direction perpendicular to 4, the horizontal viewing angle can be made larger compared to the transmission-type Sufu IJ'-7 with the configuration shown in Figure 1, and the horizontal viewing angle can be increased compared to the configuration shown in Figure 2. horizontal viewing angle equivalent to that of a transmissive screen.

Next, the reason why the cross-sectional profile of the convex portion 13 is shaped like a parabola will be explained as it has three significances.

The first meaning is the position at which the light beam exits from the convex portion 13 to the outside. In the field of physics, it is known that when a ray of light is incident on a parabolic mirror parallel to its central axis, the reflected ray will pass through the focal point of the parabolic mirror. Also in the case of the configuration shown in FIG. 4, the focal point 26 exists near the vertex 23 on the center line 14. And side 2
All of Shun's light rays 24 that are totally reflected at zero pass through the focal point 26 and are emitted to the outside from the upper surface 19. By the way, the light beam with a large emission angle is transmitted to one end 2 of the convex portion 13
When emitted from a place close to 5, the adjacent convex part 1
3, and it is not possible to increase the actual horizontal viewing angle. Therefore, in order to increase the horizontal viewing angle, the light beam with a large output angle should be directed to the tip of the protrusion 13.
It is necessary to emit the light from a location close to 3. Therefore, if the outline of the cross section of the convex part 13 is made into a parabola convex toward the outside as shown in FIG. A light beam with a large inclination angle can be emitted from a location close to the tip 23 of the convex portion 13.

The second meaning m concerns whether the light ray 24 incident on the 1]2 surface 19 after the side-incident light ray 22 is totally reflected on the side surface 20 is emitted to the outside. From the aforementioned reflection properties of a parabolic mirror, it can be seen that a ray of light passing through the focal point of a parabolic mirror always travels parallel to the central axis after being reflected by the parabolic mirror. Also in the case of the configuration shown in FIG.
After being totally reflected on the side surface 20, it passes through the focal point 26, so
Thereafter, when the light ray 27 enters the upper surface 19, the traveling direction of the reflected component light ray 27 is always parallel to the center line 14. In other words, the reflected component ray 27 is parallel to the dihedron incident ray 21. Considering that the angle of incidence when the top surface incident ray 21 is incident on the first surface 19 is an incident angle that does not cause total reflection, when the side surface incident ray 21 reaches the top surface 19 after being totally reflected, it is totally reflected. It can be seen that the light is not always emitted to the outside.

The third significance is that although the convex portion 13 having the shape shown in FIG. 4 has a relatively long and narrow shape, it does not include any sharply bent portions except for the lower end 25. Therefore, machining the convex portion 13 is not particularly difficult, and it is possible to process the convex portion 13 using conventional techniques for machining semicylindrical convex lenses.

Note that the outline of the cross section of the convex portion 13 does not need to be an exact parabola, and the light rays can be concentrated near the tip 23 of the convex portion 13, and when the side incident light ray 22 reaches the second surface 19. A shape slightly deviated from a parabola may be used as long as it does not cause total internal reflection.

Other embodiments of the present invention will be described below.

In FIG. 5, the shape of the convex portion 13 is slightly modified from the shape shown in FIG. 4, and the shape is formed in the center when the same parabola is overlapped with a slight shift in the direction of lateral force. in this case,
There are two focal points, a focal point 29 regarding the left surface 28 and a focal point 31 regarding the right surface 30. In this way, the fourth
Since the proportion of the light amount of the upper surface incident light ray 21 is reduced compared to the case of the convex portion 13 shown in the figure, it is possible to control the portion of the light distribution characteristic where the output angle is small.

In FIG. 6, the shape of the convex portion 13 is further widened from the configuration shown in FIG.
．． 31 is arranged to protrude outside the convex portion 13. When the focal point 29.31 is outside the convex portion 13, the side-incident light beam 32 is totally reflected on the side surface 28 and then reflected on the opposite side surface 3.
0 as a convergent light beam. Since this light beam is further converged at the side surface 30, it becomes a light beam with a large divergence angle after passing through the convergence point 33. On the other hand, when the focal point 29.31 is inside the convex portion 13, the side-incident light beam 32 is totally reflected on the side surface 28 and then enters the opposite side surface 30 as a divergent light beam. Even if it is affected by the direction, it does not become a luminous flux with a large divergence angle. In this way, the outgoing inclination angle for the side incident light beam can be controlled depending on whether the two focal points 29, 31 are located inside or outside the convex portion.

By changing the distance between the two focal points 29.31 while the focal point 29.31 is outside the convex portion 13, it is possible to control a large part of the light distribution characteristic with an exit angle.

In FIG. 7, the outline of the cross section of the convex portion 13 is such that the side surface 35 is formed by a parabola and the upper surface 36 is formed by a circular arc with the boundary 34 as the boundary. In the present invention, the outline of the cross section of the convex portion 13 is a parabola because the light rays totally reflected on the side surface of the convex portion 13 are
This is because the purpose is to concentrate near the vertex 23 of vertex 2.
The shape of the upper surface 36 does not need to be limited to a parabola as long as the light rays concentrated around 3 can be emitted to the outside and the double-incident light rays 21 can be emitted at various exit inclinations.

Although FIG. 7 shows an example in which the shape of the second surface 36 is an outwardly convex arc, it is also possible to change the shape of the second surface 36 to be an outwardly concave arc. The light distribution characteristics change depending on the shape of the upper surface 36. Utilizing this fact, it is also possible to control the light distribution characteristics.

FIG. 8 shows a modification of the configuration in which convex portions 13 are repeatedly formed as shown in FIG. 3, and semicylindrical convex lenses 4 as shown in FIG. It is something. In this way, it is possible to strengthen the light distribution characteristics in the portion where the exit angle is small. By appropriately selecting the ratio of the amount of light incident on the convex portion 13 and the semicylindrical convex lens 4, the light distribution characteristics can be controlled.

Effects of the Invention As is clear from the above description, according to the present invention, it is possible to obtain a single-panel transmissive screen having a larger horizontal viewing angle than conventional screens. Further, horizontal light diffusion can be performed efficiently. Furthermore, since the configuration of the convex portion depends on many parameters, it has many excellent effects such as being able to control light distribution characteristics.

[Brief explanation of drawings]

1 and 2 are sectional views of main parts showing a conventional example of a transmission screen, FIG. 3 is a sectional view of main parts showing an embodiment of a transmission screen according to the present invention, and FIG. FIG. 6 is an enlarged plan view of the convex portion shown in FIG. 6. FIGS. 6 and 7 are enlarged sectional views showing other examples of the convex portion,
FIG. 8 is a sectional view of a main part showing another embodiment of a transmission type screen according to the present invention. 1...A cutting plate, 3...Fresnel lens, 4...Kamaboko-shaped convex lens, 13...
・Protrusion, 19.36...Soil surface, 20.28,3
0.35...Side, 26.29.31...
·focus. Name of agent: Patent attorney Toshio Nakao and 1 other person No. 4
Figure 5 Figure 6

Claims (1)

[Scope of Claims] (]) An elongated protrusion on one surface of a thin transparent plate, whose cross-sectional profile is partially or entirely formed as a parabola or a substantially parabola along a substantially plane formed by the transparent plate. A transparent screen characterized by repeatedly forming the following. (2) The transmissive screen according to claim (1), wherein a part or all of the outline of the cross section of the convex portion is a parabola or a substantially parabola convex toward the outside. (3) Claim (2) characterized in that the central axis of the parabola defining the profile of the cross section of the convex portion is perpendicular to the substantially plane formed by the transparent plate. Transparent screen. (4) A transmissive screen according to claim (2), characterized in that a part or all of the contour of the cross section of the convex portion is formed into two parabolas or approximately radial PDn whose central axes are shifted from each other. . (5) The transmissive screen according to claim 4, wherein the transmissive screen is formed so that the focus of the parabola is not included within the contour of the cross section of the convex portion. (6) The transmissive screen according to claim (2), wherein the shape of the cross-sectional profile of the convex portion near the corner point A is a curve different from a parabola. (7) The transmissive screen according to claim (6), characterized in that the shape near the apex of the cross-sectional profile of the convex portion is an arc convex or concave toward the outside. (8) The transmission screen according to claim (1), wherein a convex portion or a concave portion having a different configuration from the convex portion is formed between adjacent convex portions. (9) The transmission screen according to claim (8), characterized in that substantially the same cylindrical surface that is convex toward the outside is formed between adjacent convex portions. (10) 7 on the side of the transparent plate where the convex portion is not formed.
A transmission type screen according to claim (1), characterized in that a flannel lens is formed. (11) A transmission screen according to claim (1), characterized in that a light diffusing material is distributed inside the transparent plate.