JPH04238334A - Projection type picture display device - Google Patents

Abstract

PURPOSE:To reduce unnecessary light at the time of scattering and to attain bright image projection with high contrast in a projection type picture display device which enlarges and projects an image on a light valve which controls the transmission and the scattering of light according to an electrical signal and forms the image by using a projection lens to a screen. CONSTITUTION:This device is provided with a light source part consisting of a high-brightness light source lamp 1 and a concave reflection mirror 2, the light valve 4 consisting of an image display element which controls the transmission and the scattering of the light according to a video signal, and the projection lens 5 which enlarges and projects the image to the screen 6, and Koehler illumination that illumination is performed so that the image by the light source part may be formed at the pupil position of the lens 5 is performed. By providing a central shield near the optical axis in the vicinity of the diaphragm of the lens 5, the unnecessary light at the time of scattering in the light valve 4 is reduced and high contrast is obtained.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a projection type image display device that brightly enlarges and projects an image on a light valve that forms an image by controlling the transmission and scattering of light using electrical signals.

0002

[Background Art] There are video projectors as large-screen display devices, including a type that projects a high-brightness CRT onto a screen using a projection lens, and a type that projects an image using a liquid crystal panel as a light valve. There is. In recent years, with advances in liquid crystal technology, devices using liquid crystals have been attracting attention because they can be expected to be smaller in set size and lighter in weight. FIG. 4 shows a principle diagram of a projection type image display device using a liquid crystal panel as a light valve. In FIG. 4, 1 is a light source lamp, 2 is a concave reflector, 3 is a field lens, 4 is a liquid crystal light valve, 5 is a projection lens, and 6 is a screen. Light from a light source 1 is focused by a concave reflector 2 and enters a liquid crystal light valve 4 through a field lens 3. The liquid crystal light valve 4 controls the transmittance of the pixels according to the video signal, and the image is enlarged and projected onto the screen 6 by the projection lens 5.

The current mainstream liquid crystal light valves use twisted nematic liquid crystal or super twisted nematic liquid crystal for the liquid crystal panel, and therefore use polarizing plates to control light absorption and transmission. There is. Since the polarizing plate aligns the polarization direction of the light, it absorbs more than half of the illumination light from the light source, which has the disadvantage that the displayed image becomes dark. In addition, the polarizing plate absorbs light energy and generates heat, which may adversely affect the characteristics or reliability of the liquid crystal panel.

On the other hand, if a liquid crystal panel using, for example, polymer-dispersed liquid crystal is used as a light valve, the transmission and scattering of light can be controlled without using a polarizing plate, and the transmittance of light is high, resulting in a bright image. It will be done.

FIGS. 3(a) and 3(b) show the principle of display on a polymer dispersed liquid crystal panel. 7 is a polymer, 8 is a granular liquid crystal, and the granular liquid crystal 8 is dispersed in the polymer 7. FIG. 3(b) shows a state in which an electric field is applied to the liquid crystal. At this time, the liquid crystal molecules in the granular liquid crystal 8 are aligned in the direction of the electric field, and if the granular liquid crystal is selected so that its refractive index in the direction of the electric field is equal to that of the polymer, light is transmitted without being scattered. Figure 3(a) shows the state where no electric field is applied.
The liquid crystal molecules in the granular liquid crystal 8 are aligned along the interface between the granular liquid crystal 8 and the polymer 7. Since the refractive index of the granular liquid crystal 8 is different from that of the polymer 7, the light is repeatedly refracted through the granular liquid crystal 8 at the interface of the polymer 7 and scattered. In this way, transmission and scattering of light can be controlled according to the video signal. Here, 9 represents incident light, 10 represents scattered light, and 11 represents transmitted light.

[0006]

[Problem to be Solved by the Invention] However, when the liquid crystal is in a scattering state, if the scattered light passes through the projection lens and reaches the screen, it will reduce the contrast of the image. You need to increase the F number of the lens and stop down. That is, there is a problem in that in order to increase the contrast, the light utilization efficiency must be lowered.

In view of the above-mentioned problems, the present invention provides a projection type image display device that enlarges and projects an image on a light valve that forms an image by controlling the transmission and scattering of light using electric signals with high contrast and brightness. It is something.

[0008]

[Means for Solving the Problems] In order to achieve this object, the image display device of the present invention includes a light source section including a high-intensity light source and a concave mirror, and an image display element that controls transmission and scattering of light according to a video signal. Equipped with an image forming section using a light valve, and a projection lens that enlarges and projects the image onto a screen,
Koehler illumination is performed so that the image of the light source unit is focused on the pupil position of the projection lens, and a center shield is provided near the aperture position of the projection lens.

[0009]

[Operation] The present invention solves the above problems with this configuration. FIG. 5 shows a schematic diagram of a light source image reflected at the pupil position of the projection lens when the light valve is in the transmitting state in Kohler illumination. The refractive power of the field lens 3 was set so that the light source image was reflected in the center of the pupil of the projection lens, with vignetting of the projection lens on-axis in Figure 5(a) and off-axis in Figure 5(b). This is the case. Near the center of the light source, as shown by the hatched area in FIG. 5, there is a portion that is ineffective for illumination due to the insertion opening of the light source lamp into the concave reflector, the cap of the electrode, the light distribution characteristics of the light source, etc. Therefore, even if a shield is provided near the optical axis near the aperture of the projection lens, there is little loss of illumination light in the transmission state. On the other hand, in the scattering state, the scattered light also enters the vicinity of the center of the projection lens, which causes a reduction in the contrast of the image when projected onto the screen. Therefore, by providing a shield near the optical axis near the aperture of the projection lens, this unnecessary light can be cut, and the image on the light valve can be enlarged and projected with high contrast and brightness.

0010

[Embodiment] (Embodiment 1) An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 1, 1 is a light source lamp, 2 is a concave reflector, 3 is a field lens, 4 is a liquid crystal light valve, 5 is a projection lens, 6 is a screen, and 12 is a central shield provided near the aperture of the projection lens. It is. By cutting unnecessary scattered light, the image on the light valve can be enlarged and projected with high contrast and brightness.

(Embodiment 2) A second embodiment of the present invention will be described below with reference to FIG.

In FIG. 2, a central shield 12 is provided on the projection lens 5 near the equivalent aperture. If the central shield 12 is made circular, the effect of the shield will not change even if the lens rotates.

[0014]

As described above, the present invention includes a light source unit including a high-intensity light source and a concave mirror, an image forming unit including a light valve as an image display element that controls transmission and scattering of light according to a video signal, and an image forming unit including a light valve. The projector is equipped with a projection lens that enlarges and projects an image onto a screen, performs Koehler illumination so that the image of the light source unit is focused near the pupil position of the projection lens, and provides a center shield near the aperture position of the projection lens. By this,
It is possible to provide a projection type image display device that enlarges and projects an image with high contrast and brightness on a light valve that forms an image by controlling the transmission and scattering of light by electric signals.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram of a projection type image display device according to an embodiment of the present invention.

FIG. 2 is a schematic configuration diagram of a projection type image display device according to a second embodiment of the present invention.

[Figure 3] (a) is a diagram showing the principle of display on a polymer-dispersed liquid crystal panel, and (b) is a diagram showing the principle of display on a polymer-dispersed liquid crystal panel, showing a scattering state without an applied electric field. Diagram showing the transparent state

[Figure 4] Principle diagram of a projection type image display device using a conventional liquid crystal panel as a light valve

[Figure 5] (a) Schematic diagram when the light source image reflected on the pupil of the projection lens is on-axis (b) Schematic diagram when the light source image reflected on the pupil of the projection lens is off-axis

[Explanation of symbols] 1 Light source lamp 2　Concave reflector 3 Field lens 4.LCD light bulb 5. Projection lens 6 Screen 7. Polymer 8 Granular liquid crystal 9 Incident light 10 Scattered light 11 Transmitted light 12 Center shielding

Claims (3)

[Claims] 1. A light source unit including a high-intensity light source and a concave mirror, an image forming unit including a light valve as an image display element that controls transmission and scattering of light according to a video signal, and a projection unit that enlarges and projects the image on a screen. A projection type image comprising a lens, performing Koehler illumination so that an image of the light source unit is focused near the pupil position of the projection lens, and providing a center shield near the aperture position of the projection lens. Display device. 2. The projection type image display device according to claim 1, wherein a central shield is provided on the lens surface near the aperture position of the projection lens. 3. The projection type image display device according to claim 1, wherein the central shield near the aperture position of the projection lens is circular.