JPH0462532A - Projection type image display device - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention is a method for projecting an image formed on a transmissive display panel having a large number of picture elements arranged in a matrix onto a screen. The present invention relates to a projection type image display device, and is particularly used in a large screen projection television system and an information system.

(Prior Art) Conventionally, in projection type image display devices, parabolic reflecting mirrors, elliptical reflecting mirrors, spherical mirrors, etc. have been used to convert light from a light source into parallel rays.

When using a parabolic reflector, the light source is placed at its focal point. When using an elliptical reflector, the light source is
The reflected light from the elliptical mirror converges on the second focal point. The converged light is made into parallel light by a condenser lens having a focal point at the second focal point. When using a spherical mirror, the light source is placed at the center of the sphere, and the light reflected by the spherical mirror converges on the light source again. The light thus converged, together with the direct light from the light source, is converted into parallel light by a condenser lens having its focal point at the center of the sphere.

The parallel light rays are incident on a transmissive display panel, and their intensity is adjusted by each picture element of the panel to display images and characters. Examples of display panels include liquid crystal display panels, electrochromic displays, and displays using ceramics such as PLZT (lead lanthanum titanate zirconate). Among these,
Liquid crystal display panels are widely used in portable televisions, word processor displays, etc., and because of their high degree of perfection, they are also frequently used in projection type image display devices.

Therefore, below, a case will be described in which a liquid crystal display panel is used as a transmissive display panel.

In a matrix-type liquid crystal display panel, the smallest display units called picture elements are regularly arranged, and independent drive voltages are applied to picture element electrodes that constitute these picture elements.

This voltage adjusts the transmittance of the liquid crystal layer that makes up each picture element, and images and characters are displayed on the screen. As methods for applying independent driving voltages to each picture element electrode, there are simple matrix method, M I M (Metal-Insul
There is an active matrix method in which a non-linear two-terminal element such as a 2-terminal element (Ator-Metal) or a 3-terminal switching element such as a thin film transistor is provided for each pixel electrode.

In order to provide high-definition display using an active matrix type liquid crystal display panel, the pitch between each picture element must be small. As the pitch between picture elements becomes smaller, the aperture ratio, that is, the ratio of the area of the picture elements that contributes to display to the area of the entire display screen decreases. The reduction in the aperture ratio is due to the fact that even if the pitch between picture elements is reduced, all of the constituent elements of the liquid crystal display panel cannot be made similarly small. Since there are limits to etching accuracy and mask positioning accuracy in photolithography, it is necessary to reduce the width of metal wiring connected to picture element electrodes, the size of nonlinear elements, thin film transistors, etc. to below a certain level. This is because it is not possible. Therefore, if an attempt is made to obtain a high-definition screen by reducing the pitch between picture elements, the brightness of the screen will decrease.

(Problem to be Solved by the Invention) In order to prevent the brightness from decreasing due to the increase in screen definition, a microlens array having microlenses corresponding to each picture element is installed on the light source side or both sides of the liquid crystal display panel. Allotted. A structure including such a microlens is disclosed in, for example, Japanese Patent Application Laid-Open No. 60-262131 and Japanese Patent Application Laid-open No. 61-117.
No. 88. FIG. 4 shows how parallel light rays converge when a microlens is used. The parallel light beams are converged onto the liquid crystal display panel 1 by the microlens 15. However, the light incident at an angle of ±θ with respect to the parallel rays converges at a position different from the position at which the parallel rays converge, resulting in a spot having a diameter of 2XfXtanθ. In this way, the microlens 15 cannot converge all of the light that is incident in the form of a spot onto the picture element. Therefore, the light incident on the microlens is required to be highly parallel.

However, there is a limit to the degree of parallelism of parallel light rays that can be obtained using a parabolic reflector or an elliptical reflector.

FIGS. 5(a) and 5(b) show how light from a light source travels when an elliptical reflector and a parabolic reflector are used, respectively. When an elliptical reflector is used as shown in Figure 5(a), the light emitted from the light source located at the first focus of the elliptical reflector will be completely reflected by the ellipse if the light source is a complete point light source. It converges on the second focal point of the mirror. However, since the light emitting portion of the actual light source has a certain length, and due to the precision of the reflecting mirror, the light emitted from the light source does not completely converge on the second focal point. Moreover, as shown in FIG. 5(b),
Even when a parabolic reflecting mirror is used, the longer the length of the light emitting portion of the light source, the larger the angle α of the deviation between the parallel rays. In this way, when parallel light beams obtained by an elliptical reflector or a parabolic reflector are used, it becomes difficult to fully exhibit the effect of the microlens, as shown in FIG. 4 described above. Also, if the length direction of the light emitting part of the light source is aligned with the optical axis, the shadow of the light source electrode will cause
The cross section perpendicular to the traveling direction becomes a ring-shaped parallel ray. When an image is projected onto a screen using such light, uneven illuminance occurs, making it impossible to obtain a uniform image.

In a configuration in which the light source is arranged at the spherical center of a spherical mirror and the focus of the condenser lens is made to coincide with the spherical center, better parallel light rays can be obtained than when using the aforementioned elliptical or parabolic reflecting mirror. In this configuration, the light traveling toward the spherical mirror is reflected by the spherical mirror and then converged on the light source again. The light then passes through the light source and is converted into parallel light by a condenser lens.

However, since the light source is generally a spherical body made of a transparent material such as glass or quartz, the light reflected from the spherical mirror is reflected and refracted by the light source itself.

Therefore, the light reflected by the spherical mirror has an intensity of 50 to 60% of the light that reaches the condenser lens directly from the light source.

The present invention has been made to solve these problems, and an object of the present invention is to provide a projection type image display device that effectively utilizes light from a light source. Another object of the present invention is to provide a projection type image display device that has a bright screen by fully utilizing the effects of microlenses.

(Means for Solving the Problems) A projection type image display device of the present invention includes a spherical mirror, a condenser lens having a focal point at the spherical center of the spherical mirror, and a light source located between the spherical mirror and the condenser lens. a matrix type transmission panel provided on the opposite side of the condenser lens from the light source and having a large number of picture elements; and a micro lens provided on the light source side of the matrix type transmission panel and having microlenses corresponding to each of the picture elements. A projection type image display device comprising a lens array, wherein the light source is disposed at a position different from the spherical center on a straight line passing through the spherical center of the spherical mirror and perpendicular to the optical axis. The above objective is achieved.

Further, the light source may be arranged such that direct light from the light source and reflected light from the spherical mirror are respectively converged onto the adjacent picture elements by one of the microlenses. This achieves the above objective.

(Function) In the projection type image display device of the present invention, the focus of the condenser lens is placed on the spherical center of the spherical mirror. The light source is arranged at a position different from the spherical center of the spherical mirror on a straight line passing through the spherical center and perpendicular to the optical axis. With this configuration, the light emitted from the light source to the spherical mirror at the same time is reflected by the spherical mirror and then converges at a different position from the light source. Therefore, the converged light is not reflected, refracted, etc. by the light source, and the light from the light source can be used effectively.

Further, in the projection type image display device of the present invention, the light source is arranged such that the direct light from the light source and the reflected light from the spherical mirror are converged onto adjacent picture elements by one of the microlenses. By doing so, the effect of the microlens can be fully exhibited.

(Example) Examples of the present invention will be described below. FIG. 1 shows a schematic diagram of an embodiment of a projection type image display device of the present invention. The projection type image display device of this embodiment includes a spherical mirror 3 and a spherical mirror 3.
a condenser lens 4 having a focal point at the spherical center of the spherical mirror 3;
a light source 2 located between the light source 2 and the condenser lens 4; a matrix-type transmissive panel 1 provided on the opposite side of the condenser lens 4 from the light source 2 and having a large number of picture elements; A microlens array 5 having microlenses provided therein and corresponding to each of the picture elements is provided. A field lens 6 and a projection lens 7 are arranged in this order on the opposite side of the matrix type transmission panel 1 from the condenser lens 4. An image produced by this projection type image display device is projected onto the screen 8.

In this example, a metal halide lamp with an arc length of 5- was used as the light source 2. Here, the arc length refers to the distance between electrodes that perform arc discharge. As the light source 2, other than metal halide lamps, halogen lamps, xenon lamps, etc. can be used. In addition, in this embodiment, as the matrix type transmission panel 1,
An active matrix drive type liquid crystal display panel was used. The pitch of the picture elements in the vertical direction is 190 μm1, and the pitch in the horizontal direction is 161 μm. The opening of the picture element is 88 μm in height.
x width: 104 μm1 The aperture ratio of the matrix type transmission panel 1 is 30%.

The condenser lens 4 has an aspherical surface, has a diameter of 80mm, and a focal length of 60+mn. One focal point of the condenser lens 4 is set to coincide with the spherical center of the spherical mirror 3, as described above.

The microlens array 5 is a matrix type transmission panel 1
It has a large number of microlenses 15 corresponding to each picture element. The focal length of each microlens 15 is 720 μm. The microlens array 5 was formed by imparting a refractive index distribution to glass using an ion exchange method.

The field lens 6 has a focal length of 200 mm.

A plano-convex lens with a diameter of 100 was used. As the projection lens 7, a convex lens with a focal length of 200 mm and a diameter of 40 mm was used.

2nd ffi (a) shows a view of the spherical mirror 3 and the light source 2 viewed from the condenser lens 4 side along the optical axis a. Second
As shown in Figure (a), in this embodiment, the light source 2 has an optical axis a
It is not located at the upper spherical center, but is placed at a different position from the spherical center on a straight line passing through the spherical center and perpendicular to the optical axis a. According to this arrangement, the imaging point B of the light emitted from the light source 2 and reflected by the spherical mirror 3 and the light source 2 are in a symmetrical positional relationship with respect to the optical axis a (FIG. 2(a)). When a lenticular lens is used as the microlens 15,
It is preferable that the long side of the lenticular lens corresponds to the longitudinal direction of the light emitting portion of the light source 2.

The distance between the light source 2 and the imaging point B is the sum of the pitch between picture elements multiplied by the ratio of the focal length of the microlens 15 and the focal length of the condenser lens 4, that is, L = 190 μm x (60 wm /720μm)=15
．． It was set to 8mm.

The optical system shown in FIG. 1 was constructed by setting the value of L to 15.8 mm as described above. Assuming that the light utilization rate when condensing light using only the condenser lens 4 without using the spherical mirror 3 is 1, when the light source 2 is aligned with the spherical center of the spherical mirror 3 as in the conventional case, the light utilization rate is 1. The ratio was 1°5-1.6. On the other hand, in this example, the light utilization rate improved to 1.7 to 1.8. This improvement in light utilization can be explained as follows. That is, in this embodiment, the light source 2 and the imaging point B
Since the position of the image forming point B is different from that of the light source 2
This is because all the reflected light converged on the imaging point B can be made to enter the condenser lens 4 without being subjected to reflection, refraction, etc. Furthermore, as shown in FIG. 2(b), the light source 2
The direct light 10 from the spherical mirror 3 and the reflected light 20 that has passed through the imaging point B from the spherical mirror 3 are converged onto adjacent picture elements by one microlens 15. Therefore, the direct light 10 and the reflected light 20 can be used effectively, and the effect of the microlens 15 can be fully exhibited.

As shown in FIG. 3, when using a matrix-type transmission panel having a delta arrangement in which the rows of picture elements are shifted by 1/2 pitch from each other, for example, direct light 10 from light source 2 hits picture element X. If the position of the light source 2 is set so that the reflected light 20 from the spherical mirror 3 converges on the picture element Y, the light from the light source can be used effectively in the same way as described above. .

(Effects of the Invention) In the projection type image display device of the present invention, since the light from the light source is effectively used, a bright and uniform image can be obtained. In addition, in response to the demand for high-definition images,
By applying the present invention, it becomes possible to deal with this without reducing the brightness of the screen.

4. Figure 1 is a schematic diagram of one embodiment of the projection type image display device of the present invention, and Figure 2 (a) is a diagram showing the optical axis from the condenser lens side in the display device of Figure 1. 2(b) is a diagram showing how direct light and reflected light are converged onto a pixel by a microlens, and FIG. 3 is a diagram showing another matrix constituting the present invention. A diagram showing a mold transmission panel, Figure 4 is a diagram showing how light is converged by a microlens,
FIGS. 5(a) and 5(1)) are diagrams showing the condensing state when using an elliptical reflecting mirror and a parabolic reflecting mirror, respectively.

1... Matrix type transmission panel, 2... Light source, 3...
... Spherical mirror, 4... Condenser lens, 5... Micro lens array, 6... Field lens, 7...
- Projection lens, 8... Screen, 10... Direct light, 15... Micro lens, 20... Reflected light.

that's all

Claims (1)

[Claims] 1. A spherical mirror, a condenser lens having a focal point at the spherical center of the spherical mirror, a light source located between the spherical mirror and the condenser lens, and a light source located on the opposite side of the condenser lens from the light source. A projection type image display comprising: a matrix type transmission panel provided with a large number of picture elements; and a microlens array provided on the light source side of the matrix type transmission panel and having microlenses corresponding to each of the picture elements. 1. A projection type image display device, wherein the light source is disposed at a position different from the spherical center on a straight line passing through the spherical center of the spherical mirror and perpendicular to the optical axis. 2. The light source is arranged such that the direct light from the light source and the reflected light from the spherical mirror are respectively converged onto the adjacent picture elements by one of the microlenses. projection type image display device.