JPH0769567B2 - Projection display device - Google Patents

Description

The present invention relates to a projection display device using a plurality of transmissive light valves for image formation.

[Conventional technology]

A conventional light valve type projection type color display device, as disclosed in JP-A-58-150937 (US Pat. No. 334680,334682), combines and projects a single color image by a reflection type light valve and a dichroic mirror. What to do, SID '
75 Digest P.24, SID'72 Digest P.62, Optronics (1985) No.4 There is an oil film light valve system described in P.73.

[Problems to be solved by the invention]

The former reflection type light valve system is, firstly, a reflection type light valve, so that the contrast is lowered due to the light reflected on the surface. Second, the light valve is a cathode ray tube (CR
Since it is addressed by the light of T), it becomes a large-scale device. Thirdly, the dichroic mirror is required to have not only color separation characteristics but also excellent polarization separation characteristics for separating incident light and emitted light.

The latter oil film light valve system requires a large device, is expensive, and is not sufficient in terms of life and light utilization efficiency.

Therefore, the present invention solves such a problem,
It is an object of the invention to provide a compact projection display device which has excellent contrast and high utilization efficiency of light from a light source.

[Means for solving problems]

The projection type display device of the present invention includes a light source, a color separation unit that separates light from the light source into color lights of three primary colors, and three transmissive liquid crystals that modulate each color light separated by the color separation unit. In a projection type display device having a light valve, a color synthesizing unit for synthesizing the color lights modulated by the transmissive liquid crystal light valves, and a projection optical unit for projecting the color-synthesized light by the color synthesizing unit Each of the transmissive liquid crystal light valves is composed of a twisted nematic (hereinafter referred to as TN) type liquid crystal panel, and the main wavelength of each color light of the three primary colors modulated by each and the peak of the wavelength-transmittance characteristic of each liquid crystal are shown. It is characterized in that it is set so as to match.

〔Example〕

FIG. 1 shows an illumination structure of a full-color projection display device according to the present invention. A dichroic mirror (B mirror) 1 that reflects blue light and a dichroic mirror (R mirror) 2 that reflects red light are combined in a cross shape to separate and combine incident light beams. Reference numeral 3 is a mirror for bending the direction of the light beam. Reference numeral 4 is a transmissive light valve that forms an image corresponding to red, green, and blue. Here, a liquid crystal panel driven by an active matrix (thin film transistor matrix or the like) is used.

FIG. 2 is an overall configuration diagram including the projection type optical system. Only green is drawn for simplicity. As the illumination system, Koehler illumination, critical illumination, telecentric illumination, or the like can be adopted. 5 is a condenser lens, 6
Is a projection lens, 7 is a light source, and 9 is a screen.

Next, the operation will be described. As shown in FIG. 2, the light source 7 emits white light (for example, a halogen lamp) and is condensed by the condenser lens 5. The white light 8 incident on the dichroic mirrors 1 and 2 is separated into red (R), green (G), and blue (B) light. The separated color light is bent by the mirror 3 and enters the transmissive light valve 4. The light valve surface is coated with an antireflection coating to effectively transmit incident light. The light valve is placed at a position where an image is formed on the screen 9 by the projection lens 6. The light valve forms an image corresponding to each color light. In this case, red, green, and blue video signals 18 were supplied to each liquid crystal panel to form a monochromatic moving image.

The transmissive light valve matches the wavelength dependence of the extinction ratio with the dominant wavelength of the color light with respect to the transmitted color light, and improves the contrast of an image obtained by combining and projecting them. For example,
The peak of the wavelength-transmittance curve due to the retardance of the twisted nematic liquid crystal mode (hereinafter referred to as TN liquid crystal mode) is made to coincide with the dominant wavelength of each color light. The dichroic ratio peak of the guest-host liquid crystal mode dichroic dye is matched with the dominant wavelength of each color light.

In the light valve of the present invention, the parameters are changed so that the dominant wavelength of each color light matches the wavelength dependence. In the present embodiment, the liquid crystal panel uses the TN liquid crystal mode. The liquid crystal panel is separated from the light source light by changing the parameters on the light valve configuration so that the dominant wavelength of each color light matches the wavelength dependence characteristic of the following formula. It is set so that the main wavelength of each color light that is incident on and modulated by and the peak of the wavelength-transmittance characteristic of each liquid crystal match.

Δn = birefringence of liquid crystal, T = transmittance, λ = wavelength, d = thickness From the wavelength dependence shown in the above formula, using a nematic liquid crystal with Δn = 1.5, the second peak is adjusted to give a red light. The liquid crystal layer thickness of the bulb was set to 8.4 μm, the liquid crystal layer thickness of the green light valve was set to 7.1 μm, and the liquid crystal layer thickness of the blue light valve was set to 5.8 μm. The thickness of each liquid crystal layer is determined in consideration of the steady temperature after the irradiation of the projection light.

Further, since the TN liquid crystal mode has an incident light angle dependence of the extinction ratio, it is more effective to arrange the incident light at an angle with respect to the normal to the light valve surface as shown in FIG. However, in this case, since the projection lens deviates from the optical axis, the imaging position deviates from the optical axis or a trapezoidal image is formed. The tilt angle of the light valve is determined in consideration of the characteristics of the projection lens and the image formation range, but in the case of the TN liquid crystal mode that we used here, it is 0
A range of ~ 30 ° was practical.

Here, the driving of the TFT liquid crystal panel will be briefly described with reference to FIG.

Since the liquid crystal panel requires AC drive, the video signal 18 is 1
The polarity inversion circuit 10 inverts every field (1F). Synchronous control circuit is VCO 11, loop filter 12,
It is composed of a phase comparator 13 and a frequency divider 14, and generates an X, Y clock, data, and a 1F signal. The liquid crystal panel 4 is connected with an X side shift register 15, a transmission gate 17 for distributing a video signal to each pixel thereby, and a Y side shift register 16.

The X-side shift register performs address in the column direction of the TFT, and the Y-side shift register performs address in the row direction.

As a result, the pixel voltage corresponding to the video signal is applied to the TFT liquid crystal pixel, and pixel display can be performed. Details of drive and liquid crystal panel are Nikkei Electronics No.351
(1984) P.211 and SID'83 DIGEST P.156.

Further, the liquid crystal panels of the respective colors are aligned so that the displayed images match on the screen.

When the three primary colors of R, G, and B are combined and full-color display is performed, if misconvergence occurs, a color shift or a color ghost is displayed. In particular, when a matrix panel is used, it is desired to perform alignment at a pixel pitch or less. Further, when the pixel pitches of the respective colors are the same, by regularly displacing about half a pixel, it is possible to achieve a higher resolution change than a monochrome panel.

As is clear from FIG. 1, the R panel image and the B panel image have a left-right mirror image relationship with the G panel image.

The dichroic mirror of the present invention only needs to have a separating and combining function for each color, but the dielectric thin film always reflects a polarizing action. That is, in FIG. 1, red light and blue light have many vertical polarization components, and green light has many horizontal polarization components. Therefore, in the electro-optical effect mode using a polarizing plate, it may be necessary to appropriately adjust the direction of the polarizing plate. For example, TN (90
When using the twisted nematic liquid crystal) liquid crystal display mode, in order to use the luminous flux most effectively, the transmission axis of the incident side polarization plate of the R panel and the B panel is perpendicular to the transmission of the G panel in FIG. The axis should be horizontal. In addition, white balance adjustment, that is, intensity adjustment of each color can be performed by setting the orientation of the polarizing plate.

Thus, the color light image-modulated by the transmissive light valve enters the dichroic mirror group again. First
As shown in the figure, the red, green, and blue lights are reversibly combined and projected and imaged on the screen 9 by the projection lens 6.

The dichroic mirror may use considerations other than that shown in FIG. 4 and 5 are examples of the configuration. Fourth
In the case of FIGS. 5 and 5, the dichroic mirror, the light valve, and the projection optical system are arranged on the same plane. Therefore, a thinner system can be constructed as compared with the example shown in FIG.

The dichroic mirrors 1 and 2 in FIG. 4 are a simple system that does not need to be formed in a cross shape. The mirror 3 for bending the colored light is also arranged on the same plane as the dichroic mirror. As in the case of FIG. 1, 5 is a condenser lens, 4 is a light valve, and 6 is a projection lens.

FIG. 5 shows a cross-shaped dichroic mirror used in the case of FIG. 1 arranged in a plane.

The feature of the system shown in FIG. 5 is that the optical path length between the light valve 4, the light source 7, and the condenser lens 5 is different between red light and green light, and blue light and green light. Further, since red light and blue light reflected by the dichroic mirrors 1 and 2 have many polarization components perpendicular to the paper surface, the reflection efficiency of the mirror 3 for changing the light ray direction can be increased.

The position of the light valve 4 for each color light is
In the case of FIG. 5 and FIG. 5, as in FIG. 1, each color must be at an image forming position that is optically equidistant to the projection lens 6.

Further, as shown in FIGS. 2, 3, 4, and 5, the present system requires only one projection lens, and when the projection magnification or the projection distance is changed, it is not necessary to adjust the convergence between the color images. There is also an advantage.

The operation and effect of this embodiment will be described below.

In this embodiment, the light source light is separated into a plurality of color lights by the first dichroic mirror group. Next, an image is formed by a transmissive light valve corresponding to color light, and the color light undergoes image modulation. As a result of using the transmissive light valve, the influence of the reflected light on the surface of the light valve, which cannot be avoided by the reflective light valve, can be removed from the projected light, and the contrast of the projected image is improved. In addition, a moving image can be displayed by adopting an image display panel using the electro-optical effect. An electro-optical material such as liquid crystal or PLZT can be used as the light valve. In any case, compared with the CRT optical writing type reflection type light valve and the oil film type light valve, it has a thin plate-like compact shape, which increases the degree of freedom in the configuration of the entire device and allows a compact system configuration.

Next, the image-modulated color light is combined by the second dichroic mirror group. At this time, the second dichroic mirror group has substantially the same wavelength separation performance as the first dichroic mirror group, and reversibly combines the separated color lights. For example, in contrast to the first dichroic mirror group that separates white light into red, green, and blue, the second dichroic mirror group has substantially the same red, green, and blue color light separation characteristics as the first dichroic mirror group. And reversibly synthesizes red, green, and blue image color lights. If all light valves are transparent, the combined light will be the source color. As for the function of the dichroic mirror of the present invention, only the separation of the color light is sufficient, and the performance of separating the polarization component, which was necessary in the conventional technique, is not necessary.

In this way, since the light source light is separated into color light, modulated, and combined, a plurality of light sources corresponding to each color light is unnecessary, and a single light source is sufficient.

Since a plurality of color lights are combined, the images corresponding to the respective colors are accurately arranged. For example, when full-color display is performed using light of three primary colors of red, green, and blue, the respective primary color images are converged and combined.

In addition, the first dichroic mirror and the second dichroic mirror are formed by combining two sheets having different color light separation characteristics in a cross shape to shorten the optical path length from the light source to the light valve and from the light valve to the projection optical system. It has become possible to take. Furthermore, by arranging these dichroic mirrors on a plane, a thin and compact system can be constructed.

In the transmissive light valve, the light transmission direction of the transmitted color light may be inclined at 0 to 45 ° with respect to the normal line of the light valve surface. That is, it means that the light valve surface is inclined to obtain a larger extinction ratio with respect to the incident angle dependence of the extinction ratio of the transmissive light valve. Examples of the light valve mode having an incident light angle dependency include a TN type liquid crystal mode, a guest-host mode, and a birefringence mode.

Although the TN liquid crystal panel is used as the transmissive light valve in the above, the light valve modes of the birefringence mode and the guest-host mode can of course be used. In addition, light valve modes other than the above, for example, switching phenomenon between scattering state and transparent state (dynamic scattering mode of liquid crystal, etc.) and memory type display mode of liquid crystal can be used. Further, the present invention is not limited to liquid crystals, and any transmission type light valve can be applied without any problem. For example, the electro-optic effect of translucent ceramics such as PLZT, electrochromic, or electrophoretic can be used. Further, although an example of separating and synthesizing three colors of red, green, and blue has been described here, two colors or more colors are also effective.

〔The invention's effect〕

As described above, according to the present invention, the light source, the color separation means for separating the light from the light source into the respective color lights of the three primary colors, and the three transmissions for respectively modulating the respective color lights separated by the color separation means. Type liquid crystal light valve, a color synthesizing means for color synthesizing the respective color lights modulated by the respective transmissive liquid crystal light valves, and a projection optical means for projecting the light color-synthesized by the color synthesizing means In the device, each of the transmissive liquid crystal light valves is composed of a TN type liquid crystal panel, and is set so that the main wavelength of each color light of each of the three primary colors modulated by each liquid crystal coincides with the peak of the wavelength-transmittance characteristic of each liquid crystal. As a result, the following remarkable effects can be achieved.

(A) By adopting the transmissive liquid crystal light valve, it is possible to reduce the influence of the reflected light on the surface of the light valve, which has been a problem in the reflective light valve, and improve the contrast of the projected image.

(B) Since the transmissive liquid crystal light valve has a thin plate-like compact shape and can be projected by a single light source, and a single projection optical means is sufficient, compared with a conventional projection display device, The entire device can be significantly downsized.

(C) The main wavelength of the red light separated by the color separation means and the peak of the curve of the wavelength-transmittance characteristic of the transmission liquid crystal light valve for red light are made to coincide with each other, and the main wavelength of the green light and the transmission liquid crystal for green light are matched. By matching the peak of the curve of the wavelength-transmittance characteristic of the light valve and the peak of the wavelength of the blue-light transmissive liquid crystal light valve for blue light and the peak of the curve of the transmittance characteristic of the light valve, By sufficiently taking out the extinction ratio characteristic, it is possible to further improve the contrast and color reproducibility of the image which is synthetically projected.

[Brief description of drawings]

FIG. 1 is an illumination structure diagram showing an example of a full-color projection type display device according to the present invention. FIG. 2 is a configuration diagram of a projection type display device using the illumination structure of FIG. FIG. 3 is a configuration diagram of a projection type display device using a tilted light valve. FIG. 4 is a plane layout type configuration diagram according to the present invention. FIG. 5 is a plane layout type configuration diagram using a cross type dichroic mirror according to the present invention. FIG. 6 is a circuit diagram for explaining the driving of the light valve used in the embodiment. 1 …… Blue reflection dichroic mirror 2 …… Red reflection dichroic mirror 3 …… Mirror 4 …… Transmissive light valve 5 …… Condenser lens 6 …… Projection lens 7 …… Light source 8 …… Screen

 ─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-58-193520 (JP, A) JP-A-60-2916 (JP, A) JP-A-58-150937 (JP, A)

Claims (1)

[Claims] 1. A light source, color separation means for separating light from the light source into color lights of three primary colors, three transmissive liquid crystal light valves for modulating each color light separated by the color separation means, and In a projection type display device having color synthesizing means for synthesizing the color lights modulated by the transmissive liquid crystal light valves, and projection optical means for projecting the light color-synthesized by the color synthesizing means, The liquid crystal light valve is composed of a TN type liquid crystal panel, and is set so that the main wavelengths of the lights of the three primary colors modulated by each and the peak of the wavelength-transmittance characteristic of each liquid crystal are matched. Projection type display device.