JPH04362623A - Rear projection type picture display device - Google Patents

Abstract

PURPOSE:To provide a compact rear projection type picture display device whose size viewed from a front side is nearly the same as a screen and whose depth is shortened. CONSTITUTION:Projected light which is projected from a projecting lens 3 is divided into two and bent in two different directions by 1st optical path bending reflection mirrors constituted of two plane reflection mirrors, and further respective images bent by the 1st optical path bending reflection mirrors 6a and 6b are bent on a transmission type screen by 2nd optical path bending reflection mirrors 7a and 7b constituted of other two plane reflection mirrors.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to a rear projection type image display device in which an image displayed on an image source is enlarged by a projection lens and projected onto a transmission screen from the rear side. The present invention relates to a compact rear projection type image display device whose viewing size is approximately the same as that of a transmission screen, and whose depth is shorter than the projection distance of a projection lens.

0002

[Prior Art] In recent years, projection television, in which an image displayed on a relatively small image source such as a cathode ray tube is enlarged using a projection lens and projected onto a screen, has developed in recent years with improvements in optical technology, circuit technology, production technology, etc. Advances have significantly improved image quality and led to widespread use.

However, since projection television uses the principle of enlarging the real image of the video source using a projection lens and forming the image on the screen, the larger the screen, the larger the device essentially becomes. There are restrictions on the installation location,
Depending on the installation conditions, there were problems such as giving viewers a feeling of pressure.

[0004] On the other hand, the device is made smaller by shortening the projection distance of the projection lens (the distance from the exit surface of the projection lens to the screen) or by using multiple reflecting mirrors for bending the optical path. For example, Japanese Patent Laid-Open No. 61-247180 and Japanese Patent Laid-open No. 59-230379
It is disclosed in the publication number etc.

[0005]

[Problem to be solved by the invention] JP-A-61-2471
The technique disclosed in Japanese Patent No. 80 reduces the depth of the device by projecting projection light from a projection lens obliquely onto a screen and bending the optical path with a reflecting mirror. However, with this method, the height of the device is
On the contrary, the depth becomes higher than when the depth is not shortened, and the oppressive feeling given to the viewer is not necessarily reduced, especially when installed indoors in a general household. In addition, since the optical configuration is for diagonal projection, the image from the video source must be trapezoidal, which lowers the resolution of the image on the screen compared to an optical system that projects perpendicularly to the screen. The top and bottom are not symmetrical, which poses an important problem in terms of image quality.

On the other hand, the technique disclosed in Japanese Patent Application Laid-Open No. 59-230379 attempts to downsize the device by using two reflecting mirrors for bending the optical path. With this configuration, if the screen size is set to about 40 to 55 inches diagonally, the height of the device will be about 80 to 100 cm, so there will be no problem in terms of height. However, in this case,
If the projection distance of the projection lens is shortened to increase the angle of view in order to shorten the device depth, the two reflecting mirrors for bending the optical path will interfere and the optical system will not be established. Therefore, since the depth dimension of the device is about 80 to 100 cm, it is hard to say that the restrictions on the installation location in the rooms of ordinary homes are improved. Also, although two reflectors are used, one has to be installed facing upwards, and the illumination light from the location where the device is installed passes through the screen and enters the upward reflector on the image source side.
The stray light inside the housing reduces the contrast of the image on the screen, causing a serious problem in terms of image quality.

An object of the present invention is to provide a rear projection type image display device that is compact and has high image quality. Therefore, the present invention provides a projection type image display device with a casing, in which a rear projection type image display device is assembled into a casing having approximately the same size as a screen, and a method for manufacturing the same.

[0008]

[Means for Solving the Problems] In order to achieve the above object, in the present invention, the projection light projected from the projection lens is doubled by a first optical path folding reflector composed of two plane reflectors. The images are divided and folded in two different directions, and the respective images folded back by the first optical path folding mirror are transmitted by a second optical path folding reflector, which is composed of two separate plane reflecting mirrors. Fold over the shaped screen. An image source and a projection lens are arranged in a space surrounded by two optical paths formed by the first and second optical path folding reflectors created by the above configuration. The image projected on the image source is switched vertically or horizontally in accordance with the division point of the projection light projected from the projection lens which is divided into two by the first optical path folding reflector.

[0009]

[Operation] By taking the above measures, even if the projection distance of the projection lens is shortened and the angle of view of the projection lens is increased in order to make the device compact, the first optical path folding reflector and the second The rear projection type image display device can be assembled into a housing having approximately the same dimensions as the screen without interference from the optical path folding reflector. Furthermore, since the projection distance of the projection lens can be shortened, the depth of the apparatus can also be shortened. As a result, the casing in which the rear projection image display device is assembled becomes compact, and the restrictions on the installation location in the rooms of ordinary homes are improved.

[0010] Furthermore, since it is possible to adopt an optical configuration that projects images substantially perpendicularly to the screen instead of projecting them diagonally,
When using a cathode ray tube as an image source, the image on the tube surface of the cathode ray tube is approximately rectangular, and by making this sufficiently large, the ratio of the bright spot size to the image size can be reduced, allowing for enlarged projection on the screen. There is no deterioration in resolution even in images that have been processed.

[0011] Furthermore, two reflectors, a first reflector for turning the optical path and a second reflecting mirror for turning the optical path, are provided between the projection lens and the screen, and some reflectors are installed facing upward. The projection light projected from the projection lens is divided into two, and the angle of view that is reflected by one set of reflectors is relatively narrow, about half of the total angle of view, so the reflector installed facing upward is small and the housing that houses the device is required. It is located deep inside the body, and the illumination light from the location where the device is installed passes through the screen and enters the upward reflecting mirror on the image source side, rarely becoming stray light inside the housing, reducing the contrast of the image on the screen. Never.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a side sectional view of a first embodiment of a rear projection image display device with a housing according to the present invention. 1 is a housing made of materials such as synthetic resin, wood, metal, etc.; 2 is a projection cathode ray tube; 3 is a projection lens; 4 is a luminous flux emitted from the projection lens 3, consisting of an upper emitted luminous flux 4a and a lower emitted luminous flux 4b. , 5 is the optical axis of the emitted light beam 4, which is composed of an upper optical axis 5a and a lower optical axis 5b, and 6 is a first optical path folding reflector, which includes an upper first optical path folding reflector 6a and a lower first optical axis. Folding reflector 6
7 is a second optical path folding reflector, consisting of an upper second optical path folding reflector 7a and a lower second optical path folding reflector 7b, and 8 is an upper output beam 4a and a lower output beam 4b. A light shielding plate of matte black or a similar color is provided in the space surrounded by , and consists of an upper light shielding plate 8a and a lower light shielding plate 8b, 9 is a transmission screen, 10 is a projection cathode ray tube 2 and a projection lens 3. 11 is an optical axis side unnecessary light removal plate that removes unnecessary light on the optical axis 5 side of the output light beam 4, and an upper optical axis side unnecessary light removal plate 11a.
and a lower optical axis side unnecessary light removal plate 11b, and 12 is an upper and lower limit side unnecessary light removal plate that removes unnecessary light on the upper and lower limit sides of the output light beam 4, and 12 is an upper limit side unnecessary light removal plate 12a and a lower limit side unnecessary light removal plate 12a. It consists of a light removal plate 12b.

In this embodiment, light emitted from a fluorescent surface (not shown) of a projection type cathode ray tube 2, which is an image source, passes through a projection lens 3 and becomes a luminous flux 4, which is then passed through an upper first optical path folding reflector. The light reflected by 6a becomes an upper emitted light beam 4a, and the light reflected by the lower first optical path folding reflector 6b becomes a lower emitted light beam 4b. The upper emitted light beam 4a is further reflected by the upper second optical path folding reflector 7a and projected onto the upper half of the transmissive screen 9, and the lower emitted light beam 4b is further reflected by the lower second optical path folding reflector 7b and transmitted. The image is projected onto the lower half of the shaped screen 9. These luminous fluxes are diffused in the horizontal and vertical directions when passing through the transmission screen 9,
In front of the transmission screen 9 (to the left in FIG. 1), the light beam becomes a diverging light beam. At this time, the image displayed on the fluorescent surface (not shown) of the projection cathode ray tube 2 is enlarged by the projection lens 3 and projected onto the transmission screen 9, thereby becoming a display image for the viewer.

The upper light-shielding plate 8a and the lower light-shielding plate 8b mainly reflect the illumination light at the installation location of the device upward through the transmissive screen 9 (in FIG. 1, the upper first optical path folding reflector 6a and the lower This prevents the light from entering the second optical path folding reflector 7b) and becoming stray light inside the housing, reducing the contrast of the image on the screen. The principle will be explained with reference to FIG. As shown in FIG. 2, the illumination light 12a at the installation location of the apparatus that enters through the transmission screen 9 does not reach the upper first optical path folding reflector 6a because it is blocked by the upper light shielding plate 8a. Illumination light 12b at the installation location of the device that enters through the transmission screen 9 passes through the lower second optical path folding reflector 7.
b, but does not return to the transmission screen 9 because it is blocked by the lower light shielding plate 8b. In this manner, the upper light shielding plate 8a and the lower light shielding plate 8b prevent illumination light from the installation location of the apparatus from entering the upward reflecting mirror and reducing the contrast of the image on the screen.

Next, the optical axis side unnecessary light removing plate 11 for removing unnecessary light on the optical axis 5 side of the emitted light beam 4 will be explained with reference to FIGS. 3 and 4. Figure 3 was created by the inventors in Japanese Unexamined Patent Publication No. 63-8507.
FIG. 2 is a cross-sectional view of the projection lens disclosed in Publication No. 0. In FIG. 3, the projection lens 3 of FIG. 1 is composed of parts 21 to 27. The lens elements are the first lens 21, the second lens 22, the third lens 23, and the fourth lens 24 from the one closest to the screen, and the first lens 21, the second lens 22, and the third lens 23 are the inner lens barrel. It is held in place by 26. Reference numeral 27 denotes an outer lens barrel, which is fixed to a coupler 10 that mechanically and optically couples the projection cathode ray tube 2, which is an image source, and the projection lens 3, and slidably holds the inner lens barrel 26. The fourth lens 24, which is the lens element closest to the projection cathode ray tube 2, is fixed to the coupler 10, and for optically coupling the projection cathode ray tube 2 and the projection lens 3, the projection cathode ray tube 2, the coupler 10, A space surrounded by the fourth lens 24 is filled with a cooling liquid 25.

Reference numeral 28 denotes a fluorescent surface formed on the inner surface of the projection type cathode ray tube 2, on which an image is projected. The image projected at the peripheral part P1 point of the fluorescent surface 28 is the upper limit light R1 and the lower limit light R2.
and is projected onto a screen (not shown). At this time, the light beam passes through the upper half of the first lens 21. On the other hand, the image projected at point P2 near the center of the fluorescent surface 28 is
The light passes between the upper limit light R3 and the lower limit light R4 and is projected onto a screen (not shown). At this time, the light beam passes above and below near the center of the first lens 21 .

FIG. 4 shows the upper limit of the image projected at point P1 on the periphery of the fluorescent surface 28 explained in FIG. light R1
, is a diagram showing the lower limit light R2 and the upper limit light R3 and lower limit light R4 of the image projected at a point P2 near the center of the fluorescent surface 28. Upper limit light R of the image projected on the peripheral part P1 point of the fluorescent surface 28
1. The lower limit light R2 is transmitted through the first lens 2 as explained in FIG.
Since it passes through the upper half of 1, it all enters the upper first optical path folding reflector 6a, and then enters the upper second optical path folding reflector 7.
It is reflected towards a. Furthermore, it is reflected by the upper second optical path folding reflector 7a, and the Q
Projected onto one point. On the other hand, the upper limit light R3 and the lower limit light R4 of the image projected at the point P2 near the center of the fluorescent surface 28 pass above and below near the center of the first lens 21, as explained in FIG. Therefore, the upper limit light R3 enters the upper first optical path folding reflector 6a, is reflected by the upper second optical path folding reflector 7a, and is reflected by the upper half of the transmissive screen 9.
The lower limit light R4 is projected onto two points, and is incident on the lower first optical path folding reflector 6b, is reflected by the lower second optical path folding reflector 7b, and is projected onto the side wall of the housing 1. This unnecessary projection light becomes stray light and reduces the contrast of the image on the screen. For the purpose of removing this unnecessary light, an unnecessary light removing plate provided on the side wall of the housing 1 is an unnecessary light removing plate 1 on the optical axis side.
1, and 11a is an unnecessary light removal plate on the upper optical axis side, and 11
b is the unnecessary light removal plate on the lower optical axis side. Good results can be obtained if the optical axis side unnecessary light removal plate 11 has a trap structure that catches incident unnecessary light 29, as shown in FIG.

In this way, the center area P2 of the fluorescent surface 28
The brightness of the image projected on the point on the transparent screen 9 is about half. Hereinafter, the brightness distribution on the transmission screen 9 will be explained using the projection lens shown in FIG. 3 as an example. FIG. 6 is a diagram in which the horizontal axis represents the image height (0 is the center of the screen and 1 represents the corner) and the vertical axis represents the brightness. The broken line shows the brightness distribution on the transmission screen 9 when the projection lens shown in FIG. 3 is used. According to the present invention, as shown by the solid line in the figure, the brightness is about 50% at the center of the screen, 70% at the middle of the screen, and 100% at the corners of the screen. Therefore, there is a substantially uniform luminance distribution over substantially the entire screen. FIG. 7 is the same as FIG. 6, but the horizontal axis represents the screen diagonal. The dashed line is the conventional technology;
The brightness pattern is obtained by folding the broken line in FIG. 6 symmetrically around the vertical axis. The solid line is a brightness pattern according to the present invention, in which the image is divided into two vertically at the center of the screen, each of which is flipped upside down with a mirror. Therefore, although there is a substantially uniform brightness distribution over almost the entire screen, the brightness slightly decreases at the center of the screen. The luminance distribution is extremely flat compared to the conventional technology, but to make it even flatter, a lens with a high peripheral illuminance ratio can be designed. At this time, as explained in FIG. 4, in the image height of the middle range, the lower limit light is removed by the unnecessary light removal plate 11 on the optical axis side, so there is no need to correct aberrations when designing the lens, increasing the degree of freedom in design. A lens with a high peripheral illuminance ratio can be designed relatively easily.

FIG. 8 is a diagram showing a method of displaying an image on the fluorescent surface of the projection cathode ray tube 2, which is an image source. A typical video image is scanned horizontally and displayed on a phosphorescent surface as shown. Therefore, when the projection light projected from the projection lens 3 is divided into two by the first optical path folding reflector 6, if the image of the image source is divided into two vertically, not only will the dividing line become difficult to see, Video replacement, which will be described later, can also be done easily. To this end, the first optical path folding reflector 6 is composed of two plane reflectors arranged in a chevron shape.
The ridgeline may be arranged so as to face the projection lens and horizontally with respect to the image displayed on the image source, and to divide the image of the image source into two vertically.

FIG. 9 shows a mirror-containing projection lens 30 in which the first optical path folding reflecting mirror 6 is integrated with the projection lens 3. When the projection lens is equipped with a mirror, the first lens 33 and the fifth lens 37 are fixed to the mirror-containing outer barrel 31, and the second to fourth lenses 34 to 36 are fixed to the sliding barrel 32, and the focus is adjusted. In this case, it is preferable to design it by moving the sliding lens barrel 32. Mirrored projection lens 30
The mirror part is large and it is not possible to use multiple mirrors in line. Therefore, it is necessary to use only one mirror-containing projection lens 30 as an image source for the mirror-containing projection lens 30, such as using a combination of a color cathode ray tube or a transmissive liquid crystal display element and a light source that illuminates it from behind. Become. In FIG. 9, transmissive liquid crystal display elements 38 to 40 (40 is located on the opposite side of 39) corresponding to red, green, and blue are shown.
An example of a method of combining images of 2 and 3 using the beam splitter 41 is shown. Note that the light source that illuminates the transmissive liquid crystal display element from behind is omitted in the figure.

The rear projection type image display device according to the present invention includes:
As shown in FIG. 1, the optical axis 5 of the emitted light beam 4 from the projection lens 3 is connected to the upper optical axis 5a and the lower optical axis by the upper first optical path folding reflector 6a and the lower first optical path folding reflector 6b. It is divided into axes 5b. Therefore, the optical axis of the projection lens is above and below the transmission screen 9. When using a Fresnel lens for a transmission screen, as shown in Figure 10,
It is necessary to configure the Fresnel lens so that two Fresnel centers are located near the upper and lower ends of the transmission screen. When the first optical path folding reflector 6 is configured to divide the image of the image source into left and right halves, it must be configured so that the Fresnel centers of the Fresnel lens are located at two points near the left and right ends of the transmissive screen. Needless to say.

The case where a projection type cathode ray tube is used as an image source has been described above, but the projection type cathode ray tube used in a rear projection type image display device usually uses three monochrome tubes of red, green, and blue. In this case, the present invention can be implemented as is by arranging red, green, and blue projection cathode ray tubes in-line. Furthermore, the present invention can be implemented as is, even if a combination of a transmissive liquid crystal display element and a light source that illuminates it from behind is used as an image source, or a plasma type image display device is used.

The rear projection type image display device according to the present invention has the following features:
When viewed from the front, it has a screen size and is thin in depth, so it can be used in a variety of applications. FIG. 11 is a front view of a multi-screen display constructed by vertically and horizontally arranging a plurality of rear projection image display devices according to the present invention on the entire wall surface of a room. Further, a cross-sectional view of the present multi-screen display is shown in FIG. In the figure, 42 is the multi-screen display according to the present invention, 43 is the wall surface of the room in which the multi-screen display according to the present invention is installed, 44 is the floor surface, and 45 is the wall surface of the room where the multi-screen display according to the present invention is installed.
is the ceiling. The feature of this multi-screen display is that it is thin, so it does not make the room in which it is installed narrow, and the entire wall surface can be used as a display. In the figure, an example has been explained in which the device is placed on a wall, but it can also be placed on the floor, ceiling, or even the entire surface of the floor, ceiling, wall, etc., to create a video space with no gaps.

[0024]

According to the present invention, even when the projection distance of the projection lens is shortened and the angle of view of the projection lens is increased in order to make the device compact, the first optical path folding reflector and the second optical path There is no interference from the folding reflector,
Since the rear projection image display device can be assembled into a housing that has approximately the same dimensions as the screen, the housing can be made compact, which is effective in reducing restrictions on the installation location in the rooms of ordinary homes.

[0025] Furthermore, since it is possible to adopt an optical configuration that projects images substantially perpendicularly to the screen instead of projecting them diagonally,
When using a cathode ray tube as an image source, the image on the tube surface of the cathode ray tube is approximately rectangular. By making this rectangular enough, the ratio of the bright spot size to the image size can be reduced, resulting in an image without resolution degradation. can be obtained.

[0026] Furthermore, two reflectors, a first reflector for turning the optical path and a second reflecting mirror for turning the optical path, are provided between the projection lens and the screen, and some reflectors are installed facing upward. The projection light projected from the projection lens is divided into two parts, and the angle of view that is reflected by one set of reflectors is relatively narrow, about half of the total angle of view, so the reflector installed facing upward is small.
In addition, it is located deep inside the housing that houses the equipment, so the illumination light from where the equipment is installed passes through the screen and enters the upward reflecting mirror on the image source side, so there is almost no stray light inside the housing, resulting in good contrast. An image is obtained.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view of a first embodiment of a rear projection image display device with a housing of the present invention;

FIG. 2 is an explanatory diagram of the principle of a light shielding plate that prevents illumination light from entering the device installation location through a transmissive screen and reducing image contrast;

[Fig. 3] Cross-sectional view of the projection lens,

FIG. 4 is an explanatory diagram of the first embodiment of the rear projection image display device with a housing of the present invention;

[Figure 5] Cross-sectional view of an unnecessary light removal plate on the optical axis side that has a trap structure to catch incident unnecessary light.

[Figure 6] An explanatory diagram with image height on the horizontal axis and brightness on the vertical axis,

[Fig. 7] An explanatory diagram in which the horizontal axis represents the screen diagonal and the vertical axis represents the brightness.

FIG. 8 is an explanatory diagram showing a method of displaying an image on the fluorescent surface of a projection cathode ray tube that is an image source;

FIG. 9 is a cross-sectional view of a mirror-containing projection lens in which a first optical path folding reflector is integrated with a projection lens;

FIG. 10 is an explanatory diagram of a Fresnel lens configured so that the Fresnel centers are located at two points near the upper and lower ends of a transmission screen;

FIG. 11 is an explanatory diagram of a multi-screen display to which the housing-equipped rear projection image display device of the present invention is applied;

FIG. 12 is a sectional view of a multi-screen display to which the housing-equipped rear projection image display device of the present invention is applied.

[Explanation of symbols]

2... Projection cathode ray tube, 3... Projection lens, 6a... Upper first optical path folding reflector, 6b... Lower first optical path folding reflector, 7a... Upper second optical path folding reflector, 7b...
Lower second optical path folding reflector, 8a... Upper light shielding plate, 8
b...Lower light shielding plate, 9...Transmissive screen, 11a...Upper optical axis side unnecessary light removal plate, 11b...Lower optical axis side unnecessary light removal plate.

Claims (12)

[Claims] 1. An image source, a transmissive screen, a lens for projecting an image displayed on the image source onto the transmissive screen from a side opposite to the viewing side, and a connection between the transmissive screen and the lens. A rear projection image display device equipped with an optical path folding reflector for folding an optical path, which is composed of a plurality of integral or separate reflecting mirrors that divides the projection light projected from the lens into a plurality of parts and returns each of them in different directions. and a second optical path folding reflector provided on the optical path of each divided image, which further folds the divided images so that they are combined again on a transmissive screen. A rear projection type image display device characterized by comprising a mirror. 2. In claim 1, the first optical path folding reflector is an integrated or two separate plane reflector that divides the projection light projected from the projection lens into two and returns it in two different directions. The second optical path folding reflector is composed of two separate planar reflectors that further reflect each image folded by the first optical path folding reflector onto the transmissive screen; A rear projection type image display device in which an image source and the projection lens are arranged in a space surrounded by two optical paths formed by first and second optical path folding reflectors. 3. According to claim 1 or 2, in a space surrounded by two optical paths formed by the first and second optical path folding reflectors, the optical path is perpendicular to the transmission screen without blocking the optical path. A rear projection type image display device provided with at least one light-shielding plate having a matte black color or a similar color and having a certain angle. 4. According to claim 1 or 2, a matte black or similar color is provided on or outside the second optical path folding reflector to absorb projection light projected outside the corresponding transmissive screen. A rear projection type image display device provided with at least one light shielding plate. 5. According to claim 1, 2, 3 or 4, the first optical path folding reflector comprises two plane reflectors arranged in a chevron shape, the ridges of which face the projection lens and serve as an image source. A rear projection type image display device arranged horizontally with respect to a displayed image and configured to divide the image of the image source into two vertically. 6. A rear projection image display device according to claim 1, wherein a cathode ray tube is used as the image source. 7. A rear projection type image display device according to claim 1, wherein the image source is a combination of a transmissive liquid crystal display element and a light source that illuminates the transmissive liquid crystal display element from behind. 8. A rear projection image display device according to claim 1, wherein the image source is a plasma type image display device. 9. In a projection lens for projecting an image displayed on an image source, the projection lens includes two planar reflecting mirrors that are integral or separate and that divide the projection light projected from the projection lens into two and reflect it in two different directions. A mirror-containing projection lens characterized by being integrated with a lens. 10. In a transmission screen having at least one Fresnel lens surface, the Fresnel center of the Fresnel lens surface is located above and below the transmission screen;
Or a transparent screen characterized by two points near both left and right ends. 11. The multi-screen display according to claim 1, 2, 3, or 4, in which a plurality of displays are arranged vertically, horizontally, or both. 12. A video source, a transmissive screen, a lens for projecting an image displayed on the video source onto the transmissive screen from a side opposite to a viewing side, and a lens comprising: the transmissive screen and the projection lens; In a rear projection image display device equipped with an optical path folding reflector that folds back a connecting optical path, the image source and the projection lens are disposed approximately at the center of the transmission screen, and the image projected by the image source is A rear projection type image display device, characterized in that the projection lens projects an image in a direction different from the transmission type screen, and the optical path folding reflector mirrors the image in the direction of the transmission type screen.