JPS6339294A - Video projecting device - Google Patents

Abstract

PURPOSE:To miniaturize a device and to reduce a work for maintenance by inversely using a color separation optical system such as the one which is used for tri-color color separation for a usual television camera. CONSTITUTION:A luminous flux emitted from a white light source 23 is projected in a collimation lens 22 to be a parallel luminous flux and goes towards the light division face of polarization BS 21, where S component are reflected, and becomes a straight polarizing light. The straight polarizing light is projected in the projection face 11a of a color separation prism 11 and separated from a color component light to be projected in the respective liquid crystal display elemets 12-14, where it is space-modulated according to a video signal, and then reflected by reflection mirrors 15-17 so as to pass through the liquid crystal display elements 12-14 from the opposite direction again. And since the liquid crystal display elements have the quality of birefringence, the straight polarizing light face of the luminous flux is made to rotate to emit in propotion to the video signal after a round trip in the elements. The strainght polarizing light of the respective components are composed during retrograding through an optical path and emitted from the projection face 11a of the color separation optical system 11, and meanwhile the components obtained by rotating the polarizing face by 90 deg. against a projected light passes through the polarization BS 21 to be projected on a screen 25 by a projection lens 24.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a projection device for projecting a video image onto a screen, and particularly relates to a projection device for projecting a video image onto a screen, and particularly to a projection device for projecting a video image onto a screen.
The present invention relates to a device using a dimensional liquid crystal display element.

[Conventional technology]

Projection-type television receivers have recently become popular, and can now be viewed not only in public facilities but also at home. This type of device has red (R) green (G)
The color component images projected on three high-intensity cathode ray tubes corresponding to each color component light of blue (B) are projected onto a screen using a projection lens, and are combined there to display the original color image. There is. FIG. 2 shows an overview of the video projection device. 1. 2. 3 are cathode ray tubes corresponding to R, G, and B, respectively, and R, G, and H drive circuits 4 to which R, G, and B video signals are input, respectively. 5. 6. 7. Projection lenses 8 and 9 are placed in front of the cathode ray tubes 7 and 8°9, focusing on the screen 10, respectively. Although the projection lens is shown as a single lens in this figure, in reality it is usually composed of a plurality of lenses in order to correct various aberrations.

As can be expected from FIG. 2, a major drawback of the projection device is that the device itself is large in size, and also tends to be expensive. Furthermore, when the distance between the projection lens and the screen is changed, there is a drawback that maintenance is required, such as adjusting the convergence of the optical axis of each projection lens or correcting geometric distortion of the cathode ray tube image.

[Problems to be Solved by the Invention] The present invention aims to eliminate the above-mentioned drawbacks and to provide an apparatus which is particularly compact and requires less maintenance work.

To achieve this purpose, we reversed the color separation optical system that is normally used for three-color separation in television cameras.
A two-dimensional liquid crystal display element driven by a video signal and a reflector are respectively installed on the side corresponding to the output section of the color separation optical system, and the incident light is brought into a predetermined polarization state on the side corresponding to the input section of the color separation optical system. At the same time, an optical path dividing means for dividing the optical path is arranged, and furthermore, an illumination means is arranged on one side of the optical path divided by the optical path dividing means, and a projection lens is arranged on the other side.

〔Example〕

An embodiment of the present invention will be described below with reference to FIG. First, reference numeral 11 denotes a three-color separation optical system, which includes a first prism 11A, a second prism IIB, and a third prism IIC.
corresponds to the so-called entrance surface, and llb, llc, and lid correspond to the exit surfaces of each color component light. The second of the first prism A
A dichroic interference thin film that reflects blue and transmits longer wavelengths is deposited on the surface 11e. A gap is placed between the first prism IIA and the second prism IIB, and a gap is placed between the second prism IIB and the third prism 11C.
A red-reflecting, green-transmitting dichroic interference thin film is deposited on the lf plane. Therefore, assuming that white light is incident on the incident surface 11a, the blue light is reflected on the surface 11a, and the blue light is reflected on the surface 11a.
Of the light that is totally internally reflected at a and directed to the output surface 11b and transmitted through the surface lie, the red light that is reflected at the surface 11f is internally reflected at the surface in contact with the gap and directed toward the output surface 11c, and the green light that is transmitted through the surface 11f. The light heads toward the exit surface lid. In addition to being constructed by combining prism blocks on which dichroic films are deposited, the three-color color separation optical system may be constructed by combining plate-shaped dichroic mirrors as is well known.

12, 13, and 14 are two-dimensional liquid crystal elements that display a blue component image, a red component image, and a green component image in this order.

The structure of the element itself is well known, so I will explain it here.15,-' 16. Reference numeral 17 denotes a dielectric reflecting mirror, which is provided on the back surface of the liquid crystal display element 12, 13, and 14.

18, 19. 20 is a drive circuit for a liquid crystal display element, for example, B and R are color decoded from an NTSC signal.

G video signals are respectively input, and each liquid crystal display element 12. 13. 14.

Reference numeral 21 denotes a polarizing beam splitter (hereinafter referred to as polarizing beam splitter), which is arranged on the set optical axis O of the color separation optical system 11. 2
A collimation lens 2 is placed on the optical axis branched by the polarized light BS21, and a white light source 23 such as a halogen lamp is placed approximately on the focal point of the collimation lens.

24 is a projection lens, which is arranged so that its optical axis coincides with the optical axis passing through the polarized light B521. 25 is a screen, and the screen 25 and each liquid crystal display element 12. 13. 14 is adjusted to be conjugate with respect to the projection lens 24.

With the above configuration, the light beam emitted from the white light source 23 enters the collimation lens 22 and becomes a parallel light beam, and the polarized light B52
The S component is reflected toward the light splitting plane No. 1 and becomes linearly polarized light. The linearly polarized light beams enter the incident surface 11a of the color separation prism 11, and are separated into color component lights, as described above, and sent to each liquid crystal display element 12. 13. 14, where it is spatially modulated according to the video signal, and is transmitted to a reflecting mirror 15. 16. It is reflected at 17 and passes through the liquid crystal display element 12, 13, and 14 from the opposite direction again. Here, since the liquid crystal display element has birefringence, after the light beam travels back and forth within the element, the plane of linearly polarized light rotates in proportion to the video signal and is emitted. A component whose polarization plane is rotated by 90 degrees with respect to the incident light passes through the polarized light B521 and is emitted from the incident surface 11a of the color separation optical system 11.
4, it is projected onto the screen 25.

〔effect〕

According to the present invention described above, it has the effect of being much smaller and lighter than the case where a cathode ray tube and a projection lens are respectively arranged, and also employs a configuration in which each color component light is combined and then projected. This eliminates the possibility of conversion errors (and simplifies operation by simply refocusing the projection lens even if the distance to the screen is changed.Also, an LCD is used as the image display). Therefore, it also has the effect of eliminating the geometric distortion that occurs with cathode ray tubes.

Furthermore, since the polarization BS is used to separate the illumination optical path and the floodlight optical path, and the light is sent back and forth within the color separation optical system to separate and combine colors, it has the advantage of increasing the efficiency of using the light from the light source. .

[Brief explanation of the drawing]

FIG. 1 is an optical sectional view showing an embodiment of the present invention, and FIG. 2 is a plan view showing a conventional example. In the figure, 11 is a color separation optical system, 12, 13, and 14 are liquid crystal display elements, 15, 16, and 17 are reflecting mirrors, and 21 is a polarization BS. 23 is a white light source, and 24 is a projection lens.

Claims (1)

[Claims] (1) A liquid crystal display element driven by a video signal and a reflector are installed on the side corresponding to each output part of a color separation optical system that separates light into each color component light by a dichroic film, and a reflector is installed on the side corresponding to each output part of the color separation optical system, which corresponds to the input part of the color separation optical system. An optical path splitting means for polarizing the incident light into a predetermined state and splitting the optical path is disposed on the side, and an illumination means is disposed on one side of the optical path divided by the optical path splitting means, and a projection lens is disposed on the other side. After the light from the means is polarized by the optical path splitting means, it reaches each of the liquid crystal display elements and the reflector via the color separation optical system, and each color component light that has traveled backwards along the optical path from the reflector is combined and used for the projection. A video projection device characterized by projection from a lens.