JPH04329533A - LCD color projection device - Google Patents

Abstract

PURPOSE:To prevent picture elements from shifting owing to a difference in the frequency of transmission of a dichroic mirror for multiplexing by correcting a difference in refraction quantity due to the difference in the frequency of transmission of the dichroic mirror and completely matching the optical axes of R, G, and B light beams transmitted through a liquid crystal plate. CONSTITUTION:The dichroic mirror 31 for multiplexing which reflects magenta color video light 14 and transmits green video light 11a is arranged in the optical paths between a projection optical system 19, and a mirror 16 and the dichroic mirror 13 for multplexing. Then a parallax correction plate 32 is arranged in the optical path between a liquid crystal panel 12 and the dichroic mirror 13 for multiplexing. This constitution reduces the frequency of transmission of the respective R, G, and B light beams through the dichroic mirrors 13 and 31 for multiplexing to >=1. Red video light 10a whose transmission frequency becomes 0 increases in transmission frequency to one as well as the G and B light beams by arranging the parallax correction plate 32 in the optical path and the refraction quantity of the R light due to the difference in transmission frequency can be corrected so as to be equal the refraction quantity of the G and B light beams.

Description

[Detailed description of the invention]

0001

FIELD OF INDUSTRIAL APPLICATION The present invention relates to a liquid crystal color projection device using a liquid crystal plate, and more particularly to a liquid crystal color projection device that adds and mixes and projects images displayed on black and white liquid crystal plates provided separately for R, G, and B. It is related to.

0002

[Background Art] In recent years, the progress of liquid crystal display technology has been remarkable, and with the advent of liquid crystal plates with excellent contrast and color reproducibility, liquid crystal color projection devices that use color liquid crystal plates as image display carriers and enlarge and project images onto large screens have been developed. It has been put into practical use. This type of device converges light from a light source into approximately parallel light beams using a converging optical system, irradiates the transmissive color liquid crystal panel, and then enlarges and projects the transmitted light onto a screen via a projection optical system. The number of pixels of color liquid crystal panels currently in practical use is 70,000 to 90,000 pixels, and if one picture element is a set of red (R), green (G), and blue (B) pixels, , the number of pixels is one third of this, and when projected onto a large screen, the roughness of the pixels becomes noticeable, which is not practical.

[0003] Therefore, in order to overcome the roughness of the number of picture elements when using a liquid crystal panel, three black and white liquid crystal plates were used, and a light source of all wavelengths was installed on these liquid crystal plates to produce three color lights of R, G, and B. Separation (
R through a color separation (dichroic) mirror
, G, and B light are incident, R, G, and B images are generated on each liquid crystal plate, mixed by a dichroic mirror (mirror method), and a color image is displayed on a large screen via a projection optical system. A regeneration method has been proposed and put into practical use.

FIG. 5 is a schematic diagram showing a conventional example of a liquid crystal color projection device called a mirror type, which uses dichroic mirrors for color separation and mixing of light. In the same figure,
1 is a light source such as a xenon lamp, and the light emitted from this light source 1 is reflected by a total reflection mirror 2, and then passed through a converging optical system 3.
The light is converged into a substantially parallel light beam and enters a blue dichroic mirror 4 that separates and reflects only the blue light. The blue light 5 separated by the blue dichroic mirror 4 is reflected by the mirror 6 in parallel to the optical axis of the converging optical system 3, and enters the transmissive liquid crystal panel 7. A voltage is selectively supplied to the liquid crystal panel 7 according to the constituent pixels of an arbitrary image to be projected, and the blue light 5 transmitted through the liquid crystal panel 7 becomes blue image light 5a having a video signal.

The blue component 5 is lost in the blue dichroic mirror 4, and the light transmitted through the mirror 4 becomes yellow. The yellow light 8 enters the red dichroic mirror 9, and the red light 10
is separated, and the remaining green light 11 is transmitted through the mirror 9. The separated red light 10 enters a transmissive liquid crystal panel 12 having the same configuration as the liquid crystal panel 7, and is converted into red image light 10.
It becomes a. The blue image light 5a and the red image light 10a are mixed by a mixing dichroic mirror 13 to become magenta image light 14.

On the other hand, the green light 11 also enters a transmissive liquid crystal panel 15 having the same structure as the liquid crystal panel 7, becomes green image light 11a, is reflected by a mirror 16, and enters a mixing dichroic mirror 17. The green image light 11a and the magenta color image light 14 are mixed by a dichroic mirror 1.
7 to form RGB additive color mixed image light 18, which is enlarged and projected onto a large screen 20 via a projection optical system 19 to reproduce a color image.

[0007]

By the way, in the liquid crystal color projection device having the above-described structure, the light from the light source is split into R, G, and B light and the liquid crystal panels 7, 12, and 1 are divided into R, G, and B lights.
After passing through the liquid crystal panels 7, 12, and 15, each pixel of the liquid crystal panels 7, 12, and 15 must be completely overlapped on the screen 20 because the colors are mixed and enlarged and projected onto the screen 20. For this reason, dichroic mirrors 4, 9, 13,
17, liquid crystal panels 7, 12, 15 and total reflection mirror 6
, 16 mounting positions, especially the mounting angles, are required to be accurate. Therefore, these optical components are usually mounted on an optical base 21 made of die-cast aluminum or the like, which is rigid and precisely machined so that the mounting position is on an accurate horizontal plane, and the liquid crystal panel 7, 12, 15 as X,
Although each pixel of each liquid crystal panel is adjusted to completely overlap on the screen 20 by an adjustment mechanism that can be moved in the Y direction and rotated within the X and Y planes, it is necessary to accurately adjust the mounting position and angle. However, there is a problem in that a pixel shift occurs near the top or bottom end of the projection screen. Therefore, as a result of considering the relationship between the separated three-color light beams and the synthesis dichroic mirrors 13 and 17, the present inventor found that each channel of the separated three-color light beams is reflected or transmitted by the synthesis dichroic mirrors 13 and 17. Focusing on the fact that the number of times the channel passes through the combining dichroic mirrors 13 and 17 is different, it is refracted, albeit slightly, and this refraction is reflected in the screen 20 due to the difference in the number of times the combining dichroic mirror passes through each channel. We discovered that this appears as pixel shift when enlarged and projected. That is, in the conventional device shown in FIG. 5, the number of reflections and transmissions is different for each of the R, G, and B lights, and the B light has a reflection number of 0 and a transmission of two times (
dichroic mirrors 13, 17), the R light is reflected once (dichroic mirror 13) and transmitted once (dichroic mirror 17), and the G light is reflected once (dichroic mirror 17), and the number of transmissions is 0. FIG. 6 shows the number of reflections and transmissions of these lights. Based on the relationship of the incident angles of the R, G, and B lights with respect to the combining dichroic mirrors 13 and 17, the B light transmitted through the combining dichroic mirrors 13 and 17 is
, the optical axes of the R lights are shifted parallel to the plane of the paper in FIG. 5 due to refraction. This will be further explained with reference to FIGS. 7 and 8.

FIG. 7 is a diagram showing the refraction state when the parallel light ray 22 passes through the liquid crystal panel 23 and enters the dichroic mirror 24. Since they are incident at an incident angle θ, they are both refracted at the same angle, and the transmitted light becomes parallel light that is translated by the amount of refraction with respect to the incident light. Therefore, the position of the liquid crystal panel 23 as seen from the projection lens 25 side is offset to the position 23a as shown by the broken line, but since the offset amounts d1 and d2 are equal, the offset from the dimension v of the liquid crystal panel 23 is It becomes equal to the dimension v2 of the liquid crystal panel 23a. Therefore, in this case, the pixel shift can be corrected by adjusting the position of the liquid crystal panel 23 by an amount corresponding to the parallel movement distance. However, as shown in FIG. 8, liquid crystal color projection devices generally have a condenser lens 26 disposed in front of a liquid crystal panel 23 to converge parallel incident light 22 toward a projection lens 25. Therefore, the focused light 27 transmitted through the liquid crystal panel 23
The upper edge 27a and the lower edge 27b are incident on the dichroic mirror 24 at different incident angles θ1 and θ2, and are therefore refracted at different angles. Therefore, the position of the liquid crystal panel 23 viewed from the projection lens 25 side is offset to the position 23b shown by the broken line, but since the incident angles θ1 and θ2 are different, the upper edge of the transmitted light,
The lower edge has a different amount of offset with respect to the incident focused light,
It appears as if the liquid crystal panel 23 had been extended in the vertical direction. That is, since the incident angle θ1>θ2, the incident focused light 27
The offset amount of the transmitted light becomes d1>d2, and the size V1 of the liquid crystal panel 23 becomes extended as shown as V2. In the figure, since there is no inclination of the dichroic mirror 24 in the direction perpendicular to the paper surface, the refraction thereof is negligible compared to the vertical direction. As a result, if the number of transmissions differs, the amount of refraction will differ slightly for each R, G, and B light.
In other words, when the optical axis is shifted and this is magnified by the lens 19, a shift of 0.5 to 1 pixel occurs on the screen 20. Note that the number of reflections is not accompanied by a shift of the optical axis and can be ignored.

Therefore, the present invention has been made in view of the above-mentioned conventional problems, and its purpose is to correct the difference in the amount of refraction due to the difference in the number of times of transmission of the synthesis dichroic mirror, and to improve the quality of the liquid crystal plate. R, G, B transmitted through
It is an object of the present invention to provide a liquid crystal color projection device that can prevent pixel misalignment due to a difference in the number of times of transmission by completely aligning the optical axes of light.

0010

[Means for Solving the Problems] The present invention has been made to achieve the above object, and a first aspect of the invention is to use a dichroic mirror for spectroscopy to separate light from a light source into R, G, and B.
In a liquid crystal color projection device that separates color light and transmits it through three liquid crystal plates, and then combines it with a dichroic mirror for synthesis and projects it, the separated three-color light is transmitted according to the difference in the number of times the separated three-color light passes through the dichroic mirror for synthesis. A predetermined number of parallax correction plates are placed in the combined optical path of the three color lights,
The sum of the number of times of transmission through the synthesis dichroic mirror and the parallax correction plate is made equal for each optical path. Second
The invention provides that, in the first invention, the separated three
The color light synthesis projection optical system is configured so that the number of times of transmission through the synthesis dichroic mirror is 1 or less, and a parallax correction plate is arranged in the optical path where the number of times of transmission is 0. A third invention is based on the first or second invention, wherein the parallax correction plate is made of a transparent plate made of the same material and has the same thickness as the dichroic mirror for synthesis, in the same direction and at the same inclination angle as the dichroic mirror for synthesis. It is located in According to a fourth invention, in the first or second invention, the parallax correction plate is arranged at an angle smaller than the angle of the synthesis dichroic mirror. According to a fifth aspect of the present invention, in the fourth aspect, the parallax correction plate has a thickness greater than that of the synthesis dichroic mirror. A sixth invention is based on the fourth invention, wherein the parallax correction plate has a larger refractive index than the synthesis dichroic mirror.

[0011]

[Function] In the present invention, the parallax correction plate disposed in the combined optical path of the three color lights is used for R, G, and B
The number of times that light passes through the combining dichroic mirror is made equal, thereby preventing the optical axis from shifting due to a difference in the number of times of light passing through.

0012

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be explained in detail below based on embodiments shown in the drawings. FIG. 1 is a schematic diagram showing an embodiment of a liquid crystal color projection device according to the present invention. Components in the figure that are the same as those in FIG. 5 are designated by the same reference numerals, and their explanations will be omitted. In the figure, in this embodiment, a combining dichroic mirror 31 that reflects the magenta image light 14 and transmits the green image light 11a is arranged in the optical path between the projection optical system 19, the mirror 16, and the combining dichroic mirror 13. 5, a parallax correction plate 32 is arranged in the optical path between the liquid crystal panel 12 and the dichroic mirror for composition 13, and the projection optical system 19 and the screen 20 are arranged above the dichroic mirror for composition 31 in FIG. This is different from the conventional device shown in . The parallax correction plate 32 is composed of dichroic mirrors 13 and 3 for synthesis.
It is made of a transparent glass plate that is made of the same material and has the same thickness as those of 1, and is arranged at the same angle as the combining dichroic mirrors 13 and 31, so that it is inclined at 45 degrees with respect to the red image light 10a. Reference numeral 33 is a reflecting mirror whose reflecting surface is a paraboloid and converts the light source light into parallel light parallel to the optical axis. It will be converged towards 19th. Note that the other configurations are substantially the same as the conventional device shown in FIG.

[0013] Thus, in a liquid crystal color projection device equipped with such a composite projection optical system, the R
The number of times that the , G, and B lights pass through the combining dichroic mirrors 13 and 31 can be reduced to 1 or less, and for the red image light 10a whose number of passes is 0, the parallax correction plate 32 is installed in the optical path. As shown in Figure 3, by placing it inside, the number of transmissions is one, similar to the G and B lights, and the amount of refraction of the R light due to the difference in the number of transmissions is corrected so that it is equal to the amount of refraction of the G and B lights. can do. As a result, the optical axes of all the separated three color lights can be perfectly aligned,
Each pixel of the liquid crystal panels 7, 12, and 15 can be completely overlapped on the screen 20, and pixel misalignment can be prevented from occurring.

FIG. 4 is a schematic diagram showing another embodiment of the present invention. In this embodiment, in order to downsize the device, the parallax correction plate 32 is replaced with the dichroic mirrors 13 and 31 for synthesis.
It is arranged at an angle smaller than the angle of .

[0015] In general, such a liquid crystal color projection device is constructed as compactly as possible, and the composition dichroic mirrors 13 and 31 are usually arranged at an angle of 45°.
The parallax correction plate 32 is placed at the same angle as the liquid crystal panel 10.
It is difficult to arrange the optical base 21 between the composing dichroic mirror 13 and the combining dichroic mirror 13 without interfering with other optical paths, and if this is done, the optical base 21 will become larger as shown in FIG. 1, leading to an increase in the size of the apparatus itself. Therefore, as in this embodiment, the parallax correction plate 32 is arranged so that it does not interfere with the optical path of the magenta color image light 14.
, 31, and the thickness of the parallax correction plate 32 is selected so as to obtain the same amount of refraction as both mirrors, the same effect as in the above embodiment can be obtained. Enables downsizing of equipment. in this case,
The thickness of the parallax correction plate 32 is such that the amount of refraction decreases as the angle of intersection with the red image light 10a increases.
A dichroic mirror for synthesis that is thicker than the plate thickness of the dichroic mirrors 13 and 31 is used. The same effect can also be obtained by making the plate thickness the same as that of the synthesis dichroic mirrors 13 and 31 and selecting a material with a large refractive index.

Although the above embodiments have been described with respect to the case of convergent light rays, the present invention is not limited to this, and can also be applied to the case of parallel light rays.

[0017]

As explained above, the liquid crystal color projection device according to the present invention arranges a parallax correction plate in the optical path to equalize the total number of transmissions of R, G, and B lights that pass through the compositing dichroic mirror. However, since it is configured to correct the difference in the amount of refraction due to the difference in the number of times of transmission, the three
The optical axes of all colored lights can be perfectly aligned, and pixel misalignment on the screen can be prevented.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram showing an embodiment of a liquid crystal color projection device according to the present invention.

FIG. 2 is a diagram showing the number of reflections and transmissions of R, G, and B lights.

[Figure 3] R, G, B after correction by parallax correction plate
FIG. 3 is a diagram showing the number of times of light reflection and transmission.

FIG. 4 is a schematic diagram showing another embodiment of the present invention.

FIG. 5 is a schematic diagram showing a conventional example of a liquid crystal color projection device.

FIG. 6 is a diagram showing the number of reflections and transmissions of R, G, and B light in a conventional device.

FIG. 7 is a diagram showing a refraction state when parallel light rays are incident on a dichroic mirror.

FIG. 8 is a diagram showing a refraction state when a convergent light beam is incident on a dichroic mirror.

[Explanation of symbols]

1 Light source 4, 11 Dichroic mirror for spectroscopy 7, 12, 1
5 Liquid crystal panels 13, 17, 31 Dichroic mirror for synthesis 32
parallax correction plate

Claims (6)

[Claims] Claim 1: A liquid crystal color display in which light source light is separated into three color lights of R, G, and B using a spectroscopic dichroic mirror, transmitted through three liquid crystal plates, and then combined by a composition dichroic mirror and projected. In the projection device, a predetermined number of parallax correction plates are arranged in the optical path for synthesizing the three-color light according to the number of times the separated three-color light is transmitted through the dichroic mirror for synthesis, and the dichroic mirror for synthesis and the parallax correction plate A liquid crystal color projection device characterized in that the sum of the number of times of transmission is equal for each optical path. 2. The liquid crystal color projection device according to claim 1, wherein the optical system for synthesizing and projecting the separated three-color light is configured such that the number of times of transmission through a combining dichroic mirror is one or less, and the number of times of transmission is one or less. A liquid crystal color projection device characterized in that a parallax correction plate is arranged in the zero-time optical path. 3. The liquid crystal color projection device according to claim 1, wherein the parallax correction plate is a transparent plate made of the same material and having the same thickness as the dichroic mirror for composition, and is arranged in the same direction and in the same direction as the dichroic mirror for composition. A liquid crystal color projection device characterized by being arranged at an inclined angle. 4. The liquid crystal color projection apparatus according to claim 1, wherein the parallax correction plate is arranged at an angle smaller than the angle of the compositing dichroic mirror. 5. The liquid crystal color projection apparatus according to claim 4, wherein the parallax correction plate is thicker than the compositing dichroic mirror. 6. The liquid crystal color projection device according to claim 4, wherein the parallax correction plate has a larger refractive index than the compositing dichroic mirror.