JPH0334742Y2 - - Google Patents

Description

[Detailed description of the invention] This invention is a projection television display,
The present invention relates to a transmission screen configured to allow images projected by a projector or slide projector to be observed in a bright environment rather than in a dark room.

As conventionally known transmission screens, the following several types of configurations are known.

A scattering screen containing or coating a light diffusing material.

This screen has the disadvantage that when the screen gain is increased, a hot spot phenomenon or color shading appears.

A screen constructed by superimposing a Fresnel lens on the screen mentioned above.

Although this can overcome the drawbacks seen in the above-mentioned scattering type screen, it has the disadvantage that when television images are projected, Moiré fringes are produced due to the scanning line structure and Fresnel lens structure.

A screen constructed by stacking two plano-convex lenticular sheets so that they are perpendicular to each other in the generatrix direction. For example, NHK Giken Monthly Report (Showa 49
A transmission-type lenticular screen for use in bright rooms is known, as described in the February 2015 issue, page 54).

Since this screen does not provide a Fresnel lens effect, the divergence characteristics of the light rays at the edges of the screen are unsatisfactory. As a result, there is a drawback that the favorable region that can be observed without causing any shading becomes narrower.

A screen consisting of a biconvex lens array.
For example, a bright room projection screen disclosed in Japanese Patent No. 130893 and a transmission type projection screen described in Japanese Patent Application Laid-Open No. 57-81255 are known.

This screen has the disadvantage that it is difficult to construct a large biconvex lens array screen with an accurate and uniform convex surface. That is, although the transmission type screens using biconvex lens groups in these earlier applications can be ideal screens in principle, they have great difficulties in manufacturing technology. In other words, the screens according to these prior applications have the disadvantage that it is extremely difficult to make a large-sized, highly accurate and uniform mold, and that they are extremely expensive.

In view of the above-mentioned points, the purpose of the present invention is to solve the problems with the divergence characteristics of conventionally known transmission screens and the manufacturing problems that occur when the screen is enlarged. An object of the present invention is to provide a transmissive projection screen having the following structure.

In order to achieve this objective, in the present invention, a plurality of biconvex columnar lenses of the same shape are arranged in parallel at equal pitches, and the position of the convergence point of the light beam by the incident surface is set so that the incident light is perpendicular to the screen surface. In this case, the position of the entrance surface is adjusted so that the position is within the allowable range of +0.3t to -0.3t (t is the thickness of the biconvex columnar lens) front and back, with the position of the convex surface of the exit surface as a reference. The shape and the thickness t of the biconvex columnar lens are set, and a light absorption band is provided in each trough on the exit surface parallel to the screen surface, at the same width, and at the same position. Two types of lenticular sheets with large exit surface curvature were used, one set of two sheets, so that the generatrix direction of the biconvex columnar lens was horizontal to the ground on the light source side sheet and perpendicular to the observer side sheet. It is characterized by the fact that they are superimposed, and that the output surface on the viewer side is made matte.

Here, the "convergence point of the luminous flux" corresponds to the point where the light sources A ₀ to K ₀ converge on the exit surface 12 in FIG. 4.

Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 shows an example of a combination of a projector 2 and a transmissive projection screen 4 according to the present invention. Here, the screen 4 is made up of double-convex lenticular sheets 6 and 8 that are opposed to each other and brought into close contact with each other so that their generatrix directions are orthogonal to each other, as shown in the figure.

FIG. 2 is an enlarged view showing details of the transmissive projection screen shown in FIG. Here, the first lenticular sheet 6 on the projector side (left hand side in this figure) has columnar convex surfaces 10 and 12.

Further, a plurality of light absorption bands 14 are provided in each valley of the convex surface 12 on the exit surface side (right hand side in this figure) of the lenticular sheet 6. The second lenticular sheet 8 on the observation side (right hand side in this figure) is
Although it basically has the same structure as the sheet 6 described above, the difference is that the surface of the convex surface 18 on the exit surface side is a matte surface.

FIG. 3 shows a portion of the lenticular sheet shown in FIG. 2 extracted and the light beam path of that portion. In this figure, 30 indicates a portion of the first lenticular sheet 6, and 32 indicates a portion of the second lenticular sheet 8. this part 3
The light beams a, b, c, and d incident on 0 can all be regarded as parallel rays.

Now, as shown in FIG. 3, in the first lenticular sheet 30, the position of the convergence point of the light beam by the incident surface is selected so as to almost coincide with the convex surface on the exit side. In other words, the incident light fluxes a, b, c, d
is configured to converge on a horizontal line segment 34 on the output surface of the first lenticular sheet 30. Similarly, in the second lenticular sheet 32, the position of the convergence point of the light beam on the incident surface is selected so as to substantially coincide with the convex surface on the exit side.

In this way, the light beams a, b, c, and d converged on the horizontal line segment 34 are finally converged in the horizontal direction by the second lenticular sheet 32, while diverged in the vertical direction. As a result, the luminous flux a,
b, c, and d converge on a vertical line segment 36 on the exit surface. Thereafter, the light beams a, b, c, and d diverge in each direction and head in the directions indicated by a', b', c', and d'.

The above description describes the trajectory of the light ray when the light ray is perpendicularly incident on the screen surface of the screen according to the present invention.

Next, a description will be given of the trajectory of the light rays in the periphery of the screen in the case where the light rays are incident on the screen surface at a certain angle.

4 and 5 are cross-sectional views of the transmission type projection screen according to the present invention taken along a plane perpendicular to the generatrix direction of the first lenticular sheet 6. As shown in FIG. In this paper, if incident rays A ₀ to K ₀ are perpendicularly incident on the screen as shown in FIG. 4, the trajectories of these rays are
Due to the lens effect shown in the figure, the emitted light rays diverge as shown by the solid line at the exit surface 12 as A ₀ ' to K ₀ '.

Next, the trajectory of the light rays A ₁ to K ₁ incident on the screen surface at an angle of θ = 20 degrees is shown as follows:
It looks like the solid line in FIG. That is, the output surface 12
On the plane of , the central ray F ₁ does not go straight, but is bent toward the optical axis of this lens system,
It becomes almost parallel to F ₀ ' (see Figure 4). Along with this, other light rays are also bent in the same direction and exit as shown. Thus, in order to widen the favorable area, the radii of curvature r ₁ and r ₂ of the lens at the incident surface and the exit surface are set to r ₁ > as shown in FIGS. 4 and 5.
It is preferable to set it to r ₂ .

Next, a preferred relationship between the shape of the entrance surface and the thickness t (thickness from apex to apex) in the lenticular sheet of the present transmission type projection screen will be described.

To begin with, one of the structural features of the present invention is that a biconvex columnar thick lens is used, and the position of the convergence point of the light beam on the incident surface is made to almost coincide with the convex surface on the exit side. According to this, the exit surface for the luminous flux is almost a flat surface, and when the incident angle of the luminous flux with respect to the screen surface changes, the inclination angle of this plane changes in a favorable direction accordingly.
The effect is as if Fresnel lenses were placed in close contact with each other.

In the present invention, if the position of the convergence point deviates significantly from the above, the exit surface cannot be regarded as a plane, and the divergence characteristics change. This change is in an unfavorable direction. This phenomenon will be explained below.

FIG. 4 described above shows the case where the thickness t is designed so that the position of the convergence point of the light flux incident perpendicularly to the screen surface coincides with the exit surface. In this lenticular sheet, the trajectory of convergence and divergence of light rays when the angle of incidence with respect to the screen surface is 20 degrees on the paper surface is as shown in FIG.

FIG. 6 shows the divergence characteristics of the luminous flux when the thickness t of the lenticular sheet in FIG. 5 is reduced by 0.3t. When compared with the divergence characteristics shown in FIG. 5, the following two problems arise.

(1) The ratio between the minimum and maximum angles between adjacent rays is large.

Since the brightness directional characteristic is proportional to the reciprocal of the angle between adjacent light rays, a large ratio between the minimum value and the maximum value indicates that the brightness unevenness of the screen is large.

Specifically, in FIG. 5 the ratio is approximately 4, while in FIG. 6 it is greater than 10. That is, E
The brightness when the screen is observed from a direction halfway between I and J decreases to 1/10 or less of the brightness when the screen is viewed from a direction halfway between I and J.

(2) A part of the surrounding light beam (K in Figure 6) is totally reflected and cannot be emitted.

This narrows the effective field of view of the screen and reduces image quality due to flare.

From the comparison between FIG. 5 and FIG. 6, it is understood that the light flux passing portion of the exit surface needs to be converged sufficiently small with respect to the pitch of the lenticular sheet so that it can be regarded as a flat surface.

When the incident light beam is perpendicular to the screen surface, the spot size (diameter of the cross section of the light beam) of the light beam in the plane perpendicular to the generatrix direction of the lenticular sheet at the exit surface of the lenticular sheet. is approximately 3/7 of the pitch P of the lenticular sheet when the convergence point is located at +0.3t in front of the exit surface. this is,
It is clear that the spot size is proportional to the distance from the focal point.

Next, FIG. 7 will be explained. Figure 7 is the 5th
The thickness of the lenticular sheet is 0.3t compared to the diagram.
This shows the divergence characteristics of the luminous flux when the thickness is increased by . As is clear from this figure, most of the light rays are blocked by the light absorption band 14 and cannot be emitted.
Since it cannot be used in this state, the incident angle to the screen must be narrowed to 20°. That is,
The projection angle of the projector must be narrow, resulting in a screen that is difficult to use.

For the above reasons, for practical screens, the allowable limit for the thickness of the lenticular sheet is -0.3t to +0.3t centered on the thickness t shown in Figure 4.
It is necessary to keep it within the range of .

As mentioned above, the way in which light rays that enter the screen surface at a certain angle (occurring at the periphery of the screen) are bent at the exit surface is as if a Fresnel lens was attached to a normal transmission screen. . This effect is as disclosed in the above-mentioned Japanese Patent No. 130893 and Japanese Patent Application Laid-Open No. 57-81255. However, the difference between these two prior applications and the present invention is that
The screen according to the present invention uses two biconvex lenticular sheets without using a spherical lens group, and both sheets have divergence characteristics in the horizontal and vertical directions independently. At the point.

Although only the first lenticular sheet 6 is shown in FIGS. 4 and 5, the divergence properties of the second lenticular sheet 8 are also the same.

The first and second lenticular sheets 6 and 8 described above may have the same shape as each other, but in response to the general demand that the horizontal divergence angle be wider than the vertical divergence angle, they are made to have independent shapes. is appropriate. In the screens using biconvex lens arrays described in the aforementioned Patent No. 130893 and Japanese Patent Application Laid-open No. 57-81255, the lens elements are spherical, so when you want to change the horizontal or vertical divergence angle, The aperture of the lens element must be rectangular. As a result, a problem arises in that the horizontal and vertical resolutions are different, but such a problem does not occur with the screen according to the present invention.

The lens surface of the screen according to the present invention is
The surface is not limited to a cylindrical surface, and a non-cylindrical surface such as a parabolic cross section can be used.

As explained above, according to the present invention, a double-convex lenticular sheet, which is easy to manufacture, is used without using a double-convex lens, so a screen with high precision and uniform characteristics can be manufactured at low cost. I can do it. In addition, by manufacturing lenticular sheets using a rolling method, the length of the generatrix can be easily extended to about 10 m, so a large transparent screen of about 10 m x 10 m can be made by arranging them in the width direction and gluing them together. It becomes possible to manufacture.

Furthermore, according to the present invention, it is easy to apply black paint or the like to the portions through which the light beam does not pass (troughs on the exit surface) to provide linear light absorption bands, thereby reducing the average reflectance of the screen. I can do it. As a result, a screen with excellent contrast can be manufactured even in a bright room.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an example of a combination of a transmission screen and a projector according to an embodiment of the present invention, FIG. 2 is an enlarged view showing details of the transmission projection screen shown in FIG. 1, and FIG. FIG. 2 is a perspective view showing a part of the lenticular sheet, FIGS. 4 and 5 are views showing the optical path in a cross-sectional view of the lenticular sheet shown in FIG. 2, and FIGS. The figure is a diagram showing the divergence characteristics of the luminous flux in this example. 2... Projector, 4... Transmissive projection screen according to the present invention, 6, 8, 30, 32... Lenticular sheet, 12... Output surface, 10, 1
2, 16, 18... Columnar convex surface, 14, 20...
Light absorption band, 34, 36...line segment on the exit surface.

Claims (1)

[Claims for Utility Model Registration] 1. A plurality of biconvex columnar lenses of the same shape are arranged in parallel at equal pitches, and the position of the convergence point of the light beam by the incident surface is determined when the incident light is perpendicular to the screen surface. Based on the position of the convex surface of the exit surface, adjust the shape of the entrance surface so that the position is within the allowable range of +0.3t to -0.3t (t is the thickness of the biconvex columnar lens) in the front and rear directions. The thickness t of the biconvex columnar lens is set, and a light absorption band is provided in each valley on the exit surface parallel to the screen surface, at the same width, and at the same position, so that the exit surface is smaller than the entrance surface. Lenticular sheet 2 with increased curvature
A set of two lenses are stacked so that the generatrix direction of the biconvex columnar lens is horizontal to the ground on the light source side sheet and perpendicular to the observer side sheet, and the output surface on the observer side is A transparent projection screen characterized by its matte structure. 2. The transmission type projection screen according to claim 1, wherein the convex surface of the biconvex columnar lens is a non-cylindrical surface.