JPS6330837A - Transmission type screen - Google Patents

Abstract

PURPOSE:To obtain a transmission type screen in which difference in luminance by a place of the whole screen is small, and a shift of a white balance due to a place to be located when it has been seen from the front, by placing obliquely said screen against a projected luminous flux. CONSTITUTION:A light beam which has been made incident on a first face 27 of a prism element 23 from a point light source placed on a reference object point 26 is refracted and transmits through the first face 27, brought to total reflection by a second face 28 and its advance direction is changed in the forward direction, refracted by a Fresnel lens 24 and emitted from a first light-transmissible plate 21, and made incident on a second light-transmissible plate 22. This transmission type screen makes a cabinet very compact by placing it obliquely against a projected luminous flux, and also, converts the projected luminous flux which is made incident from the oblique direction, to a roughly parallel luminous flux by the prism element 23 provided on the first light-transmissible plate 21 and the Fresnel lens 24, so that the directivity direction of an emitted light beam emitted from an arbitrary position becomes roughly parallel to the center axis, therefore, a difference in luminance due to a place of the whole image is small, and a shift of a white balance due to a place in case the screen has been seen from the front can also be made small.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to a transmission type 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 transparent screens.

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 picture tubes, projection lenses, and transmissive screens, there has been remarkable progress in projection television equipment, which places the optical system and circuitry inside the cabinet and projects images from behind the transmissive screen. .

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. 57
-109481).

The schematic configuration of such a projection television system TI is described in the eighth section.
As shown in the figure, a transmission type screen 2 is arranged at the front of the upper part of the cabinet 1, a flat mirror 3 is arranged at the upper end, a picture tube 5 is arranged at the bottom with the face plate 4 facing upward, and the picture tube 5 is placed above the picture tube 5. A projection lens 6 is arranged at.

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 reflected on the screen 2.
Since the light is incident from a considerably oblique direction, the length of the plane mirror 3 in the depth direction is shortened, and the depth of the cabinet butt 1 can be made very thin.

As shown in FIG. 9, the screen 2 is made up of a transparent flat plate with prism elements 7 having triangular cross sections and elongated horizontally arranged regularly on the back surface thereof. 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. 9 is used in the projection television apparatus having the configuration shown in FIG. 8, 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. 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 overall brightness of the screen 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. 10, a black light a 12 is placed diagonally above the screen 2 shown in FIG. Consider the case where . screen 2
A group of light rays 14 emitted from the screen are also substantially in the same plane, and this plane is parallel to the central axis 15 (normal to the center of the screen 2). However, each output ray diverges within the plane containing the output ray group 14, and the rays exiting from positions near the left and right ends 16 and 17 of the screen 2 have a large horizontal inclination angle, and this tendency is similar to that of a point light source. It is most noticeable at the upper left edge 18 and the upper right edge 19 of the screen 2, which are close to 12. Even if a light diffusing material is mixed into the screen 2 or a lenticular element elongated in the vertical direction is provided, the center direction of the directivity of the light beam emitted from the positions near the left and right ends of the screen 2 at 16° and 17° remains oriented in the horizontal direction. be. Therefore, when the directivity of the screen 2 is strong, the left and right ends 16 of the screen 2
．． This means that the brightness at 17 is lower than the brightness at center 2o.

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 Because they do not overlap, there is always a direction in which the white balance becomes thicker (misaligned). Since the viewer located in front faces the direction in which the white balance is greatly deviated, the viewer sees a large deviation in the white balance at the left and right edges 16 and 17 of the screen 2, especially at the upper left edge 18 and the upper right edge 19. be.

The present invention was 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 flux, there is little difference in brightness depending on the location of the entire screen ( The purpose of the present invention is to provide a transmissive screen with less deviation in white balance depending on the location when viewed from the front.

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; A concentric Fresnel lens with positive refractive power is disposed on the exit side of the first translucent plate, and the second translucent plate converts a light beam with a sharp direction into a light beam with a gentle direction. The prism element includes a light diffusing means, and the prism element is configured such that the projected light beam is refracted and transmitted through a first surface and then totally reflected forward at a second surface, and the light beam after the total reflection is directed to a plane perpendicular to the ridgeline of the prism element. It is designed so that the light beam becomes diverging inside.

Effect According to the above configuration, when the projected light beam enters 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 at the second surface, and passes through the Fresnel lens. is refracted and transmitted, and enters the second light-transmitting plate. 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 divergence angle of the outgoing light beam becomes smaller and it becomes close to a parallel light beam, and on average, the light rays exit from the first transparent plate. The second translucent light is incident at an angle close to perpendicular. 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 screen in an embodiment of the present invention, 2) is a first transparent plate, 22 is a second transparent plate, 23 is a prism element, and 24 is a A Fresnel lens, 25 a lenticular element, and 26 a reference object point. The transmission screen of the present invention has a structure in which a first light-transmitting plate 2) and a second light-transmitting slope 22 are stacked in close contact with each other. Prism elements 23 having a triangular cross section and elongated in the horizontal direction are regularly arranged on the incident side surface of the first translucent plate 2), and the prism elements 23 have a first surface 27 as a refractive surface and a third surface as a total reflection surface. It consists of 2 pages and 2 days. 1st
A concentric Fresnel lens 24 having a positive refractive power is disposed on the exit side surface of the light-transmitting plate 2). Second translucent plate 2
A light diffusing material is mixed in 2, and elongated lenticular elements 25 are regularly arranged in the vertical direction on the incident side surface thereof.

This screen has a reference object point 26;
The digit 1 is a plane 32 that is diagonally above the center 29 of the screen and that includes the center axis 30 of the screen (normal to the center 29 of the screen) and is perpendicular to the ridgeline 31 of the prism element 23.
This plane 32 extends vertically into the image.

The projection lens is preferably arranged so that its pupil on the screen side coincides with the reference object point 26. When using three projection lenses, it is recommended that the other two projection lenses be placed at positions horizontally shifted to the left and right from the projection lens placed on the reference object point 26.The dimensions of the screen are 600 m vertically. heavy,
The horizontal direction is 800 am, the length of the straight line 33 connecting the reference object point 26 and the center 29 is 1l100t, and this straight line 33 is the central axis 3.
The angle with respect to 0 is 55''. The pinches of the prism element 23, Fresnel lens 24, and lenticular element 25 are 0.5 fl, 0.2 fl, and 0.7 fl, respectively.

Since the projected light beam enters the first transparent plate 2) from a rather 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 that enters the first surface 27 of the prism element 23 from a point light source placed on the reference object point 26 is refracted and transmitted through the first surface 27, and is totally reflected at the second surface 28. The traveling direction is changed to the front direction by the Fresnel lens 24, the light is refracted by the first light-transmitting plate 2), and the light is emitted from the second light-transmitting plate 2).
2.

The first translucent plate 2) shown in FIG. 1 includes a prism plate in which prism elements 23 are arranged on the entrance side of a transparent flat plate, and a Fresnel lens plate in which a Fresnel lens 24 is arranged on the exit side of the transparent flat plate. Since it can be thought of as a combination of two parts, the prism plate and the Fresnel lens plate will be explained separately.

The third area shows the state of the light ray that comes out from the reference object point 26 and enters one prism element of the prism plate 34, and the light ray that exits from the prism plate 34. As shown in FIG. 3, the light rays emitted through one prism element exist on almost the same plane, and this plane 35 is different from the vertical inclination angle of the plane located vertically away from the central axis 30. is large.

Further, the outgoing light rays within one plane have a larger horizontal inclination angle than the rays separated in the left-right direction.

FIG. 1+a+ and FIG. 1Cb) show the state of the emitted light ray shown in FIG. 3 divided into two parts: projection onto the horizontal reference plane 36 and projection onto the vertical reference plane 37.

The horizontal reference plane 36 and the vertical reference plane 37 each correspond to the central axis 30.
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 37 can be adjusted to the virtual object point 3.
You can make it look like it's out of the sun. The projection of the emitted light beam onto the horizontal reference plane 36 is performed at object points 39 and 40 such that the actual optical path length from the reference object point 26 to an arbitrary incident point on the first transparent plate 2) appears on the paper. If we take .41, the rays will appear to come out from the hollow object points 39, 40, and 41.

FIG. 5 shows object points arranged at the focal point 43 of the Fresnel lens plate 42 and points 44 and 45 before and after the focal point 43, and how light rays emitted from these object points are refracted by the Fresnel lens plate 42. When the object point is at the focal point 43, the emitted light beam becomes a parallel light beam as shown by the solid line. When the object point is deviated from the focal point 43, the emitted light ray is indicated by a broken line or a dashed-dotted line.

From the virtual object point 38 of the prism plate 34 to the first translucent plate 2)
Consider a case where a Fresnel lens 42 having a focal length equal to the distance to the center 29 of is bonded to the temporary prism 34. From FIG. 1(a), first opening) and FIG. 2), it can be seen that the projection onto the vertical reference plane 37 and the projection onto the horizontal reference plane 36 are nearly parallel to the central axis 30. Therefore, it can be seen that the light rays emitted from the first light-transmitting plate 2) enter the second light-transmitting plate 22 in a state close to parallel to the central axis 30, no matter where the light rays are emitted from.

The second light-transmitting plate 22 has a very gentle horizontal directionality due to the lenticular element 25, and a slightly gentle vertical directionality due to the light diffusing material.

Since the central direction of the directivity of the light beam incident on the second light-transmitting plate 22 is close to parallel to the central axis 30 regardless of the location as described above, the directionality of the light flux exiting the second light-transmissive plate 22 is The direction of the center of gravity is also close to parallel to the center axis 30 regardless of the location.In this way, the viewer located in front of the screen can be provided with an image with little difference in intensity depending on the location.
When using a wooden projection lens, although the directional characteristics of the three colors do not overlap, the direction with the least deviation in white balance faces the viewer, so the viewer located in front of the screen can adjust the white balance depending on the location. Images with less deviation can be provided.

Other embodiments of the present invention will be described.

As shown in FIG. 6, there is a light absorber 1 elongated in the perpendicular direction to the area on the exit side surface of the second light-transmitting plate 22 where the effective light beam does not pass through.
! ! 1) By arranging the elements 46 regularly, it is possible to reduce contrast deterioration due to external light.

The second light-transmitting plate in the configuration shown in FIG. 1 is constructed by arranging vertically elongated lenticular elements 47 with a flat entrance side 46 and a special cross-sectional shape on the exit side, as shown in FIG. 7. You can also replace it with something else. This lenticular element 47 has two types of cylindrical surfaces 48 and 49 with different radii of curvature alternately arranged on the output side surface, and a 7-shaped groove 50 is provided in the center of one of the cylindrical surfaces 49. Cylindrical surface 48
Similar to the conventional Lentikiera element, the directivity is made gentle only in the horizontal direction. Light v parallel to the central axis 30
When A51 enters the V-shaped groove 50, total reflection occurs and the light beam is bent in the horizontal direction, and is emitted while spreading in the horizontal direction due to the lens action of the cylindrical surface 49, so only the directivity in the horizontal direction is very wide. Become. In any case, in the configuration shown in FIG. 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 26 diagonally above the screen, and it is of course possible to arrange it diagonally below the screen. In addition, by appropriately changing the characteristics of the prism element 23 and the Fresnel lens 24, the light rays emitted from the first transparent plate 2) can be converged on an appropriate area in front of the screen regardless of the location. You can also do that.

Effects of the Invention As described above, according to the present invention, the prism provided on the first translucent plate is a transmissive screen in which the cabinet can be made very compact by being arranged diagonally with respect to the projected light beam. By using the element and Fresnel lens to convert the projected light beam incident from an oblique direction into a nearly parallel light beam, the direction of the directivity of the output light beam from any position is made to be approximately parallel to the central axis. , there is little difference in brightness depending on the location of the entire screen, and the shift in white balance depending on the location when viewed from the front can also be reduced, which is a very large effect.

[Brief explanation of the drawing]

FIG. 1 is a partially cutaway perspective view showing the structure of a transmission screen according to an embodiment of the present invention, FIG. 2 is a sectional view illustrating the operation of the transmission screen, and FIG. 3 is an operation of a prism element. A perspective view for explaining, Fig. 1(a), (
bl is a line diagram for explaining the action of the prism element in the vertical and horizontal directions, respectively, FIG. 5 is a sectional view for explaining the action of the Fresnel lens, and FIG. 6 is a transmission diagram in another embodiment of the invention. FIG. 7 is a cross-sectional view showing the configuration of a transmission screen in still another embodiment of the present invention, and FIG. 8 is a diagram showing the configuration of a conventional projection television apparatus. 9 is a sectional view showing the structure of a screen used in the structure shown in FIG. 8, and FIG. 10 is a perspective view for explaining problems with the conventional projection television apparatus. 2)...First translucent plate, 22...Second translucent plate, 23...Prism element, 24.
... Fresnel lens, 25.47 ... Lenticular element, 26 ... Base ft! object point. Name of agent: Patent attorney Toshio Nakao 1 person 2) ---
Okay, let's go, a tree, 22-11 years old, 2... 2j--"7° squirrel"/- 6- 24-Fresnel squirrel Fig. 3 Fig. 5 Fig. 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 translucent plate, linearly elongated prism elements with triangular cross sections are regularly arranged, and on the output side of the first translucent plate, concentric Fresnel lenses with positive refractive power are arranged. is disposed, the second light-transmitting plate includes a light diffusing means for converting a sharply directional light beam into a mildly directional light beam, and the prism element allows the projected light beam to refract and pass through the first surface. A transmissive screen that is then totally reflected forward at a second surface so that the luminous flux after the total reflection becomes a diverging luminous flux within a plane perpendicular to the ridgeline of the prism element. (2) 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. (3) The distance from the virtual object point to the center of the first transparent plate matches or substantially 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 (2). (4) The transmissive screen according to claim (1), wherein lenticular elements are regularly arranged on the incident side surface, the output side surface, or both surfaces of the second light-transmitting plate. (5) The transmission screen according to claim (1) or (4), wherein the second light-transmitting plate contains a light diffusing material. (6) When the projection light flux that has entered the prism element passing through the center of the first light-transmitting plate exits the first light-transmitting plate, the projection light beam entering the prism element passing through the center of the first light-transmitting plate The transmission screen according to claim 1, wherein the light beam is parallel or substantially parallel in a plane parallel to the ridgeline. (7) When the projection light beam that passes through the center of the first transparent plate and is in a plane perpendicular to the ridge line of the prism element exits the first transparent plate, The transmission screen according to claim 1, wherein the light beam is parallel or substantially parallel in a plane including the center and perpendicular to the ridgeline of the prism element. (8) 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. .