JP2985764B2 - Rear projection type liquid crystal display - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear projection display device. More specifically, the present invention relates to a non-optical axis projection display device capable of displaying moving images. A non-optical axis projection display device using a liquid crystal light valve performs addressing with laser light as described in SID'83 digest, page 36, causing a phase change of the smectic liquid crystal due to heat. To form an image. However, in the above-mentioned prior art, the address speed by the laser beam is slow, and the response of the smectic liquid crystal is slow, so that a high-speed display image rewriting corresponding to a moving image cannot be performed. . Further, since writing with a laser beam is performed from the back surface of the liquid crystal panel, the light valve itself requires a thick structure and includes a scanning system, so a large-scale device is attached. SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above problems, and an object of the present invention is to provide a compact non-optical axis projection type display device which shows a high-speed response and can display moving images. . It is still another object of the present invention to provide a non-optical axis projection display device capable of displaying a high-contrast color without the influence of unnecessary reflection. A rear projection type liquid crystal display device of the present invention is arranged on a light source and an optical axis of light emitted from the light source, and modulates the light from the light source. A liquid crystal light valve, an imaging optical system that forms an image of light emitted from the liquid crystal light valve, a screen on which the image is formed, and a light beam that is projected from the imaging optical system onto the screen. With multiple mirrors that fold the optical path,
In a rear projection type liquid crystal display device that projects light from the back side to the screen, the liquid crystal light valve is configured such that a central axis of a light beam emitted from the liquid crystal light valve is positioned on an optical axis of the imaging optical system. The screen is arranged so as to be shifted, and perpendicular to the optical axis of the imaging optical system, and the screen is arranged such that the central axis of the light beam projected on the screen is obliquely incident on the screen. The plurality of mirrors are a first mirror that folds an optical path of light emitted upward from the imaging optical system forward, and a second mirror that folds an optical path of light reflected by the first mirror backward. And a third mirror that folds the optical path of the light reflected by the second mirror so that the central axis of the light is obliquely incident on the screen.
Characterized by the following. A rear projection type liquid crystal display device according to the present invention is characterized in that a direction of a maximum display contrast of the liquid crystal light valve is aligned with an optical axis of light emitted from the light source. According to the above configuration of the present invention, the matrix type light valve enables instantaneous electrical addressing, thereby enabling high-speed display switching of moving images and the like. Since the matrix type light valve is a flat type in which addressing means is built in itself, a system such as scanning and modulation for writing an image on the light valve is not required. For this reason, the whole apparatus can be reduced in size and weight. In addition, by using a transmissive light valve, unnecessary reflected light originating from the interface between the electrode and the liquid crystal, the liquid crystal and the substrate, or the interface between the substrate and the atmosphere can be excluded from the projected light. This is a method that is more effective than the expensive antireflection film coating and can be easily performed. In this way, the contrast is improved, and the color expression characteristics in color display are also improved. Further, the means for separating incident and outgoing light is essentially unnecessary. FIG. 1 is a side view of a non-optical axis projection type display device using a simple matrix type liquid crystal light valve. The center of the liquid crystal light valve 102 is off the optical axis 103 of the imaging lens 101. The projection image 104, the illumination system lens 105, and the light source 106 are arranged on a center line passing through the center of the light valve indicated by a broken line 107. The feature of the non-optical axis optical system is that the screen 108 is perpendicular to the optical axis of the imaging lens,
The light valve is arranged, and the center of the light valve and the center of the light valve image move in parallel from the optical axis. Therefore, with an ideal imaging lens, the light valve image 104 can be obtained in a perfect light valve shape without aberration. In this embodiment, a simple matrix type liquid crystal light valve is a twisted nematic liquid crystal (hereinafter referred to as TN).
A liquid crystal panel sandwiched between XY stripe electrodes was used. In this simple matrix type liquid crystal light valve, contrast display characteristics change in the direction of transmitted light. The direction of the maximum contrast (hereinafter referred to as the clear viewing direction) depends on the orientation direction of the liquid crystal molecules, and is specified obliquely with respect to the light valve surface. In the case of the present embodiment, the clear viewing direction is aligned with the direction of the center line 107 of the light beam. For display characteristics of TN liquid crystal, see Applied Physics Vol. 44 (1).
975) 866 pages. Similar directional dependence of the display characteristics occurs because the liquid crystal has uniaxial optical anisotropy, and also appears in other display modes. Therefore, the present invention can be applied to other modes. A simple matrix type liquid crystal light valve can sufficiently cope with a moving image display as applied to a commercially available liquid crystal television. When a projection display device is constituted by this non-optical axis optical system, the arrangement shown in FIGS. 2 and 3 becomes possible. FIG. 2A shows an example of a front-type projection display device mounted on a ceiling on a wall surface, and FIG. 2B shows an arrangement example of projection from a floor surface onto a wall surface. 201 is a projection display device, and 108 is a screen attached to a wall surface. As described above, the non-optical axis projection display device of the present invention can form a matrix light valve image on a screen on a wall surface not on the optical axis without distortion. FIG. 3 is a sectional view of the rear projection display device. FIG.
FIG. 3A shows a case of a non-optical axis projection display of the present invention, and FIG. 3B shows a case of a projection display device in which a light valve and a screen are arranged on a normal optical axis. The optical path is turned back by the mirror 301 to reduce the optical path space. FIG.
Comparing (a) and (b), as can be seen, the use of the present invention can reduce the depth of the entire apparatus. [Embodiment 2] Embodiment 2 is an example of a color projection display device using an active matrix type liquid crystal light valve using a TFT as a transmission type light valve. FIG. 4 is a perspective view thereof. The frontmost mirror 405 has been removed for clarity of the internal configuration and is shown in broken lines. 101 is an imaging lens, 104
Is a projection image. The structure and operation will be described below. Reference numeral 406 denotes a light source with a reflector, from which a white light beam is incident on a dichroic mirror for color separation combined in a cross shape. The dichroic mirror comprises a blue reflecting dichroic mirror 402 and a red reflecting dichroic mirror 4.
In the case of FIG. 4, the red light beam is decomposed in the direction of the paper, the blue light beam is decomposed in the front direction, and the green light beam is decomposed in the direction of the imaging lens. Next, the red and blue rays are reflected by mirror 405 to 180
The direction is changed, and the light enters the TFT liquid crystal light valve 401 corresponding to red and blue. The green light goes straight and similarly enters the TFT liquid crystal light valve 401. Where TF
As in the first embodiment, the center of the display surface of the T liquid crystal light valve is displaced from the optical axis 103 of the image forming optical system, and moves in a plane perpendicular to the optical axis. Here, reference numeral 404 denotes a dichroic prism that recombines red, blue, and green light, and is a cube prism in which a dielectric mirror is formed in a cross shape. The function is to perform color light separation similar to that of the above-described dichroic mirror. Therefore, the central axes of the red and blue light beams are shifted by 90 ° from the green central axis by the dichroic prism.
It is located at the bent point. For this reason, the TFT liquid crystal light valves for red and blue are arranged to be inclined so as to have the same optical positional relationship as the green TFT liquid crystal light valve with respect to the central axes of the red and blue light fluxes. In the case of the present embodiment, since the TFT liquid crystal light valve uses the TN liquid crystal mode, the above-described clear viewing direction appears. Therefore, in consideration of the polarization characteristics and the clear viewing direction of the optical system such as a mirror and a prism, the transmission axis of the exit-side polarizing plate of the TFT liquid crystal light valve is arranged substantially in the direction of the crossing side of the dichroic prism. The image light beam formed by the TFT liquid crystal light valve is synthesized by the dichroic prism and is imaged on the screen by the image forming lens 101. Since the transmission type TFT liquid crystal light valve is characterized by a high-contrast image capable of displaying a moving image, in the case of this embodiment, it was possible to obtain a full-color one-projection display having excellent color reproducibility. Further, the actual device configuration can be a front type or a rear type as shown in FIGS. 2 and 3 of the first embodiment. Embodiment 3 Embodiment 3 is an example of a color projection type display device using a reflection type matrix light valve. FIG. 5A is a side view, and FIG. 5B is a front view. The reflection type light valve 501 has pixels and MOS transistors connected to the pixels arranged in a matrix on a silicon substrate.
This light valve structure for turning off is the same as that described in the Technical Report of the Institute of Television Engineers of Japan, IPD545 (January 1981), except for the liquid crystal mode used. Reference numerals 402 and 403 denote the same dichroic mirrors as in the second embodiment. These dichroic mirrors perform color separation of a light beam from the light source 106 and synthesis of blue, red, and green images with a single cross-shaped dichroic mirror. Reference numeral 101 denotes an imaging lens, and 104 denotes a projection image. The third embodiment is also a non-optical axis projection system in which the center of the light valve is moved in parallel from the optical axis 103 of the imaging system as in the above-described embodiment, and the image on the light valve is projected outside the optical axis. can do. Since the reflection type light valve of this embodiment can sufficiently respond to a moving image, it is possible to obtain a single moving image projection display by the above configuration. Also, other reflective light valves, for example, a laser drawing type, a metal reflective surface deformation type, a photoconductor light writing type, and the like can be applied to the above configuration to obtain a color projection type display. . As described above, according to the present invention, by combining a non-optical axis projection type display with a matrix type light valve, trapezoidal distortion capable of displaying moving images can be eliminated.
A rear projection display device with a small depth can be provided. The present invention realizes a color moving image projection display which cannot be realized by the conventional non-optical axis projection display apparatus in a simple configuration and a small optical path space.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side view of a non-optical axis projection display device of the present invention. FIG. 2A is a side view of a front projection type ceiling installation example of the present invention, and FIG. 2B is a side view of a floor installation example of the present invention. 3A is a cross-sectional view of a non-optical axis rear projection display device of the present invention, and FIG. 3B is a cross-sectional view of a conventional device in which a light valve is installed on an optical axis. FIG. 4 is a perspective view showing a main configuration of a color projection display device of the present invention. FIG. 5A is a side view of a color projection display device using the reflection type matrix light valve of the present invention, and FIG. 5B is a front view thereof. [Description of Signs] 101 ... an imaging lens 102 ... a liquid crystal light valve 103 ... an optical axis 104 ... a projection image 105 ... an illumination system lens 106 ... ··· Light source 107 ··· Central axis 201 of projected light beam ··· Projection display device 401 ··· Active matrix type liquid crystal light valves 402 and 403 ··· dichroic mirror 404 ··· Dichroic prism 501... Reflective light valve

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int. Cl. ⁶ , DB name) G03B 21/00 G03B 21/10 G03B 21/28 G02F 1/13

Claims (1)

(57) [Claims] A light source, a liquid crystal light valve arranged on an optical axis of light emitted from the light source and modulating light from the light source, and an imaging optical system for imaging an image of the light emitted from the liquid crystal light valve And a screen on which the image is formed, and a plurality of mirrors that fold the optical path of light projected from the imaging optical system onto the screen, and project light from the back side to the screen. In the rear projection type liquid crystal display device, the liquid crystal light valve is such that a central axis of a light beam emitted from the liquid crystal light valve is shifted from an optical axis of the imaging optical system, and The screen is arranged perpendicular to an optical axis, the screen is arranged such that a central axis of a light beam projected on the screen is obliquely incident on the screen, and the plurality of mirrors are A first mirror that folds an optical path of light emitted upward from the image optical system to the front of the device, a second mirror that folds an optical path of light reflected by the first mirror to the rear of the device, and the second mirror. And a third mirror that folds the optical path of the light reflected by the mirror so that the central axis of the light is obliquely incident on the screen. Liquid crystal display. 2. 2. The rear projection type liquid crystal display device according to claim 1, wherein a direction of a maximum display contrast of the liquid crystal light valve is aligned with an optical axis of light emitted from the liquid crystal light valve.