JPS6378140A - Transmission type screen - Google Patents

Abstract

PURPOSE:To reduce difference in luminance due to the position of the whole of a picture plane, by setting a prism element so that a projecting beam of light is total-reflected on a second surface in a forward direction after transmitting refractably a first surface, and changing the beam of light immediately after total reflection, so that it becomes a divergent beam of light within a plane perpendicular to the ridge of a prism element. CONSTITUTION:When the projecting beam of light is made incident on a first translucent plate 19 from an oblique direction, the projecting beam of light transmits refractably the first surface of the prism element 21, and is total-reflected on the second surface, and transmits refractably the first translucent plate 19, and transmits refractably the Fresnel lens 22 of a second translucent plate 20. As for the beam of light total-reflected on the second surface of the prism element 21, projection on the inside of a plane perpendicular to the ridge of the prism element 21 becomes a divergent beam of light, and the projection on the inside of the plane in parallel with the ridge of the prism element 21 including the center of a screen, also becomes the divergent beam of light. Since the Fresnel lens 22 has a positive refracting power, when the divergent beam of light is made incident on the Fresnel lens 22, the divergent angle of the refracting beam of light of the lens is reduced, then it becomes nearly a parallel beam of light, and on an average, the beam of light advancing the inside of the second translucent plate 20 becomes the beam of light almost in parallel with a center axis.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a transmission screen that is effective for use in a projection type image display device, and is particularly effective when projecting a projection light beam onto the screen from an oblique direction. This relates to a transmissive screen.

2. Description of the Related Art In order to obtain a large-screen television image, it has been well known that the television image is projected onto a relatively small picture tube and enlarged and projected onto the screen using a projection lens. Nowadays, due to improvements in the performance of two picture tube projection lenses and transmissive screens, progress has been made in projection-type television equipment that places one optical circuit in the cabinet and projects images from behind the transmissive screen. It's amazing.

Furthermore, recently, with the aim of making the depth of this type of projection television device extremely thin, a method has been proposed in which the light flux emitted from the projection lens enters the transmissive screen from a considerably oblique direction (for example, , Japanese Patent Publication No. 5
7-109481).

The schematic configuration of such a projection television set is shown in FIG. 7. A transmission screen 2 is arranged at the front of the upper part of a cabinet 1, a flat mirror 3 is arranged at the upper end, and a face plate 4 is arranged at the bottom. A picture tube 5 is arranged facing the camera, and a projection lens 6 is arranged above the picture tube 5. The image projected on the picture tube 5 is enlarged and projected onto the screen 2 by the imaging action of the projection lens 6 and the reflection action of the plane mirror 3, but the light flux coming out of the projection lens 6 is from a direction quite oblique to the screen 2. Since it is incident, the plane mirror 3
The length in the depth direction is shortened, and the depth of the cabinet 1 can be made very thin.

As shown in FIG. 8, the screen 2 has prism elements 7 having a triangular cross section and elongated in the horizontal direction regularly arranged on the back surface of a transparent flat plate. The light beam 9 incident on the first surface 8 of the prism element 7 is refracted and transmitted through the first surface 8, and then totally reflected on the second surface 10 and bent forward. A light diffusing material is mixed inside the screen 2, and light is diffused within a suitable viewing angle range. In this way, even if the light rays are incident on the screen 2 from a considerably oblique direction,
Due to the light beam bending effect of the prism element 7 and the light diffusing effect of the light diffusing material, a bright projected image can be provided to an observer located in front of the screen 2.

Problems to be Solved by the Invention When the screen 2 shown in FIG. 8 is used in the projection television apparatus having the configuration shown in FIG. 7, the brightness at the left and right edges of the projected image is lower than the brightness at the center. The problem arises.

Furthermore, conventionally the mainstream method has been to use red, green, and blue video tubes and three projection lenses and arrange them horizontally, but this method and the screen 2 shown in Fig. 8 are different from each other. When combined, a problem arises in that when viewed from the front, the white balance appears to be significantly shifted near the upper left end and near the upper right end of the screen. These problems are not noticeable when the directivity of the screen is very weak, but when using a screen with strong directivity to increase the brightness on both sides, or when the distance from the projection lens to screen 2 is short. becomes a big problem.

This problem can be explained as follows.

As shown in FIG. 9, a point light source 1) is placed diagonally above the screen 2 shown in FIG. Consider the case where the group of light rays 12 is incident. The light source group 13 emitted from the screen 2 is also approximately in the same plane, and this plane is centered on the central axis 14 (modulus vA at the center of the screen 2).
is parallel to However, each output ray diverges within the plane containing the output ray group 13, and the left and right 41 of the screen 2
5.16, the horizontal inclination angle becomes large, and this tendency is most noticeable at the upper left end 17 and the upper right end 18 of the screen 2, which are close to the point light source 1). Even if a light diffusing material is mixed into the screen 2 or a vertically elongated lenticular element is provided, the center direction of the directivity of the light flux emitted from positions near the left and right ends 15 and 16 of the screen 2 remains oriented in the horizontal direction. There is even. For this reason, when the directivity of the screen 2 is strong, the left and right ends 15.
This means that the brightness at 16 is lower than the brightness at the center.

In addition, in a system in which red, green, and blue video tubes and three projection lenses are arranged horizontally, if the horizontal directionality of screen 2 is sharp, the characteristics of the horizontal directionality of the three colors will change. Because there is no overlap, there is always a direction in which the white balance shifts significantly. If the central direction of the directivity of the light beams emitted from positions close to the left and right ends 15 and 16 of the screen 2 is oriented in the horizontal direction, the direction in which the white balance is largely deviated will be directed to the observer located in front of the screen 2. To the observer, the white balance appears to be greatly shifted at the left and right edges 15 and 16 of the screen 2, especially at the upper left edge 17 and the upper right edge 18.

The present invention has been made in view of these points, and although it is a transmissive screen that allows the cabinet to be made very compact by arranging it diagonally with respect to the projection light beam, there is little difference in brightness depending on the location of the screen as a whole, and it It is an object of the present invention to provide a transmissive screen with less deviation in white balance depending on the location when viewed from above.

Means for Solving the Problems In order to solve the above problems, the transmission screen of the present invention includes a first light-transmitting plate disposed obliquely with respect to the projection light beam, and a first light-transmitting plate arranged diagonally with respect to the projection light beam. a second light-transmitting plate superimposed on the light-emitting side surface of the plate; on the light-incidence side surface of the first light-transmitting plate, linearly elongated prism elements each having a triangular cross section are regularly arranged; The second light-transmitting plate includes a concentric Fresnel lens with a positive refractive power disposed on the incident side, and a light diffusing means for converting a light beam with a sharp direction into a light beam with a gentle direction, The element is such that the projected light beam is the first
After being refracted and transmitted through the prism element, the light beam is totally reflected forward at the second surface, and the light beam immediately after the total reflection becomes a diverging light beam within a plane perpendicular to the ridgeline of the prism element.

Effects According to the above configuration, when the projected light beam is incident on the first light-transmitting plate from an oblique direction, the projected light beam is refracted and transmitted through the first surface of the prism element, is totally reflected on the second surface, and is reflected on the first surface of the prism element. The light is refracted and transmitted through a second light-transmitting Fresnel lens. The luminous flux that is totally reflected on the second surface of the prism element becomes a diverging luminous flux when it is projected onto a plane perpendicular to the ridgeline of the prism element, and also when it is projected onto a plane that includes the center of the screen and is parallel to the ridgeline of the prism element. becomes. Since the Fresnel lens has positive refractive power, when a diverging light beam enters the Fresnel lens, the refracted light beam has a small divergence angle and becomes close to a parallel light beam, and on average it travels inside the second transparent plate. The rays of light become nearly parallel to the central axis. Therefore, even if the directivity of the second transparent plate is quite sharp, the central direction of the directivity of the light flux emitted from the second transparent plate will be close to parallel to the central axis regardless of the location, and the direction of the directivity of the light beam exiting the second transparent plate will be close to parallel to the central axis, regardless of the location of the image. In addition, it is possible to provide an image with less deviation in white balance to an observer located in front of the screen.

Embodiment An embodiment of a transmission screen according to the present invention will be described with reference to the accompanying drawings.

FIG. 1 shows the configuration of a transmission chamber screen in an embodiment of the present invention, in which 19 is a first light-transmitting plate, 20 is a second light-transmitting plate, 21 is a prism element, and 22 is a Fresnel element. A lens, 23 is a lenticular element, and 24 is a reference object point.The transmission screen of the present invention has a structure in which a first light-transmitting plate 19 and a second light-transmitting plate 20 are closely stacked. ing. Prism elements 21 having a triangular cross section and elongated in the horizontal direction are regularly arranged on the incident side surface of the first translucent plate 19, and the prism elements 21 have a first surface 25 as a refractive surface and a second surface as a total reflection surface. It is composed of a surface 26. Second
A light-diffusing material is mixed in the translucent plate 20, a concentric Fresnel lens 22 with positive refractive power is arranged on the incident side, and elongated lenticular elements 23 are regularly arranged in the vertical direction on the output side. .

This screen has a reference object point 24;
is located diagonally above the center 27 of the screen, on a plane 30 that includes the center axis 28 of the screen (normal to the center 27 of the screen) and is perpendicular to the ridgeline 29 of the prism element 21.
This plane 30 coincides with the vertical direction of the image.

The projection lens should be arranged so that the pupil on the screen side coincides with the reference object point 24. If three projection lenses are used, the other two projection lenses should be arranged so that the pupil on the screen side coincides with the reference object point 24. It is best to place it at a position shifted from the lens on both sides in the horizontal direction. The dimensions of the screen are 600 f1. The width is 800 m, and the length of the straight line 31 connecting the reference object point 24 and the center 27 is 1)00 m, and the angle that this straight line &1) 31 makes with the central axis 28 is 55°.

The pitches of the prism element 21, Fresnel lens 22, and lenticular element 23 are each 0. 5m, 0.2
0.7 fl.

Since the projected light beam enters the first transparent plate 19 from a considerably oblique direction, the width of the projected light beam becomes narrow. Therefore, the length in the depth direction of the plane mirror disposed in the optical path in the middle of the projection light beam is shortened, and the depth of the cabinet can be made extremely thin.

The operation of the present invention will be explained below.

As shown in FIG. 2, a light beam incident on the first surface 25 of the prism element 21 from a point light source placed on the reference object point 24 is refracted and transmitted through the first surface 25, and is totally reflected on the second surface 26. The direction of travel is changed to the front direction, the light exits the first light-transmitting plate 19, and enters the Fresnel lens 22 of the second light-transmitting plate 20.

FIG. 3 shows a light ray that comes out from the reference object point 24 and enters one prism element of the first light-transmitting plate 19, and a light ray that enters one prism element of the first light-transmitting plate
9 shows the state of the light rays emitted from 9. As shown in FIG. 3, the light rays exiting through one prism element exist on almost the same plane, and this plane 32 is the central axis 2.
The planes located vertically away from the plane 32 have a large vertical inclination angle, and the outgoing light rays within one plane 32 have a horizontal horizontal inclination angle large.

FIG. 4 fat and FIG. 4 (bl) show the state of the emitted light ray shown in FIG. 3 divided into two parts: projection onto the horizontal reference plane 33 and projection onto the vertical reference plane 34.

The horizontal reference plane 33 and the vertical reference plane 34 are each centered on the central axis 28.
It is a plane that extends horizontally and vertically. By appropriately selecting the inclination angles of the first and second surfaces of each prism element, the projection of the emitted ray onto the vertical reference plane 34 can be adjusted to the virtual object point 3.
You can make it look like it came out of 5. The projection of the emitted light beam onto the horizontal reference plane 33 is performed at object points 36, 37, . If we take 38, the rays will appear to come out from the hollow object points 36, 37, and 38.

In FIG. 5, object points are placed at the focal point 40 and points 41 and 42 before and after the focal point 40 of the Fresnel lens plate 39, which has the same structure as the Fresnel lens 22 of the second translucent plate 20, and This figure shows how a ray of light is refracted by the Fresnel lens plate 39. When the object point is at the focal point 40, the emitted light ray becomes a parallel ray as shown by a solid line, and when the object point is deviated from the focal point 40, the emitted light ray becomes a broken line or a dashed-dotted line.

Consider a case where a Fresnel lens plate 39 having a focal length equal to the distance from the center 27 of the first transparent plate 19 to the virtual object point 35 is superimposed on the first transparent plate 19 . Fourth
From Figure (a), Figure 4 (bl) and Figure 5, the reference object point 2
It can be seen that no matter which position of the first transparent plate 19 the light rays emitted from the second transparent plate 20 are incident on, the light rays traveling inside the second transparent plate 20 are nearly parallel to the central axis 2.

The second light-transmitting plate 20 has a very gentle horizontal directivity due to the lenticular element 23, and a slightly gentle vertical directivity due to the light diffusing material.

As described above, since the central direction of the directivity of the light beam traveling inside the second light-transmitting plate 20 is close to parallel to the central axis 28 regardless of the location, the light flux exiting the second light-transmitting plate 20 The center and direction of the directivity become almost parallel to the central axis 28 regardless of the location.

In this way, an image with little difference in brightness depending on location can be provided to the viewer located in front of the screen. Also, when using three projection lenses, although the directional characteristics of the three colors do not overlap, the direction with the least deviation in white balance is directed toward the viewer (so the direction toward the viewer located in front of the screen It is possible to provide an image with less deviation in white balance depending on location.

Other embodiments of the present invention will be described.

The exit side surface of the second light-transmitting plate 20 in the configuration shown in FIG. can. This lenticilla element 44 has two types of Nissin W45 and 46 with different radii of curvature arranged alternately on the emission side, and a V-shaped groove 4 in the center of one cylindrical surface 46.
The 0 cylindrical surface 45 provided with 7 has a gentle directivity only in the horizontal direction, similar to the conventional lenticular element. A ray 48 parallel to the central axis 28 forms a figure 7 groove 4.
When the light beam is incident on the light beam 7, total reflection occurs and the light beam is bent in the horizontal direction, and is emitted while being diffused in the horizontal direction due to the lens action of the cylindrical surface 46, so that only the directivity in the horizontal direction becomes very wide. In any case, 1) In the configuration shown in 1, it is desirable that the second light-transmitting plate 20 is a light diffusing means that has a wide horizontal directivity. Even with a light diffusing means, it is possible to obtain the same functions and effects as the configuration shown in FIG. 1, and the problems with the conventional configuration can be improved.

It is not necessary to arrange the reference object point 24 diagonally above the screen, and it is of course possible to arrange it diagonally below the screen.Also, by appropriately changing the characteristics of the prism element 21 and the Fresnel lens 22, First translucent property 1) It is also possible to make the light rays emitted from the screen 9 converge on a suitable area in the front direction of the screen regardless of the location.

Effects of the Invention As described above, according to the present invention, although it is a transmissive screen in which the cabinet can be made very compact by arranging it diagonally with respect to the projected light beam, the prism element and the Fresnel lens allow light to enter from an oblique direction. The projected light flux is converted into a nearly parallel light flux, and the direction of the directivity of the emitted light ray from any position is made to be approximately parallel to the central axis, so there is little difference in brightness depending on the location of the entire screen. It is also possible to reduce the deviation in white balance depending on the location when viewed from the front, which has a very large effect.

[Brief explanation of the drawing]

Fig. 1 is a partially cutaway perspective view showing the configuration of a pass-through screen in an embodiment of the present invention, Fig. 2 is a cross-sectional view for explaining the operation of the i3 pass-through screen, and Fig. 3 is a view of a prism element. A perspective view for explaining the action, FIG. 4 fat,
(bl is a diagram for explaining the action of the prism element in the vertical direction and horizontal direction, respectively, FIG. 5 is a cross-sectional view for explaining the action of the Fresnel lens, and FIG. 6 is a diagram for explaining the action of the prism element in the vertical direction and the horizontal direction, respectively. FIG. 7 is a sectional view showing the configuration of a conventional projection type television set; FIG. 8 is a sectional view showing the configuration of the screen used in the configuration shown in FIG. 7; The figure is a perspective view for explaining the problems of the conventional projection television device. 19...First translucent plate, 20...Twentieth translucent plate , 21...prism element, 22.
... Fresnel lens, 23.44 ... Lenticular element, 24 ... Reference object point, - Name of agent Patent attorney Toshio Nakao and one other person 9-4'
r Lottery 1 + II 3 [Jun-・-su 2 ship 2f--Alice゛≦1) 3-? 2--~) and half-luresis. δ3 1 figure
23--L nodeffiushu) 24-11 Tosho ↑ Tsukasa,! . Figure 5 3q Figure 6 Figure 7

Claims (8)

[Claims] (1) A first light-transmitting plate disposed obliquely with respect to the projection light beam, and a second light-transmitting plate overlaid on the exit side surface of the first light-transmitting plate; On the entrance side of the first light-transmitting plate, linearly elongated prism elements having a triangular cross section are regularly arranged, and the second light-transmitting plate has concentric circular prism elements arranged on the entrance side and has a positive refractive power. The prism element includes a Fresnel lens and a light diffusing means for converting a light beam with a sharp direction into a light beam with a gentle direction, and the prism element is arranged so that the projected light beam is refracted and transmitted through a first surface and then directed forward at a second surface. A transmissive screen that undergoes total reflection so that the luminous flux immediately after total reflection becomes a diverging luminous flux within a plane perpendicular to the ridge line of the prism element. (2) When the projection light beam incident on the prism element passing through the center of the first transparent plate is refracted by the Fresnel lens of the second transparent plate, it passes through the center of the first transparent plate. The transmission screen according to claim 1, wherein the light beam is parallel or substantially parallel in a plane parallel to the ridgeline of the prism element. (3) When the projected light flux passing through the center of the first translucent plate and in a plane perpendicular to the ridgeline of the prism element is refracted by the Fresnel lens of the second translucent plate, the first translucent The transmission screen according to claim 1, wherein a parallel or substantially parallel light beam is generated in a plane that includes the center of the plate and is perpendicular to the ridgeline of the prism element. (4) When the projected light beam that comes out from the reference object point and lies in a plane that includes the center of the first transparent plate and is perpendicular to the ridgeline of the prism element is totally reflected by the prism element, the first transparent plate The transmission screen according to claim 1, wherein the light beam is diverging as if it were emitted from a virtual object point on the central axis of the plate. (5) The distance from the virtual object point to the center of the first transparent plate matches or approximately matches the distance from the position of the reference object point to the center of the first transparent plate. A transmission screen according to claim (4). (6) The transmission screen according to claim (1), wherein the focal length of the Fresnel lens matches or substantially matches the distance from the position of the reference object point to the center of the first transparent plate. . (7) The transmission screen according to claim (1), wherein lenticular elements are regularly arranged on the light exit side of the second light-transmitting plate. (8) The transmission screen according to claim 1 or 7, wherein the second light-transmitting plate contains a light diffusing material.