JP2002090888A - Rear projection display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To further reduce a device size, as compared with the conventional device, and to improve the luminance of a picture on a screen by increasing the number of lamps of a projector device consisting of plural projectors. SOLUTION: A rear projection display device is constituted of a projection type screen consisting of a Fresnel lens for converging light by total reflection or a method mixing both of total reflection and refraction and translucent diffusion plate as the minimum number of constitutional elements and a projector.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the technical field of image display, and more particularly to a rear projection display device.

[Prior art]

Most conventional rear projection display devices use a CRT (cathode ray tube) or liquid crystal (liquid crystal projector) as the projection device. Recently, there is a projector using a digital mirror device (DMD) as a projection device. A projector using a liquid crystal projector or a DMD is advantageous in terms of space because it requires only one projection system as compared with a three-projection system (three-tube type) using a CRT.

[0003] A projection type screen for projecting an image is generally composed of a Fresnel lens, a lenticular lens, and a diffusion plate.
A projection device is installed on the optical axis of the Fresnel lens due to its nature, and gives the Fresnel lens an optical shape in which light rays are incident substantially perpendicularly to the lenticular lens sheet.

[Problems to be solved by the invention]

In the current rear projection display device, a space for projecting an image is required to some extent due to the restriction of the refraction angle of the Fresnel lens. Therefore, the optical path is bent by using a reflecting mirror, or the optical axis of the Fresnel lens. In some cases, the size of the entire device can be reduced by offsetting the image from the center of the screen. There is a limit.

Further, in the case of a multi-lamp type projector comprising a plurality of projectors in order to obtain a bright display image, the number of lamps can be reduced only by disposing the lenticular lens in a laterally shifted position. However, the effect is reduced due to limitations on the arrangement of the apparatus and an obstacle to miniaturization of the apparatus.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has been made to achieve both a further reduction in the size of the device and an improvement in the brightness of a screen image by increasing the number of projectors comprising a plurality of projectors. It is intended.

[0007]

According to the present invention, there is provided a Fresnel lens for converging a light beam by total reflection or a system in which both total reflection and refraction are mixed. , A rear projection display device comprising a projection screen having a transmission type diffusion plate as a minimum component and a projector.

[0008] The invention of claim 2 is characterized in that the projection type screen is further provided with a microlens array in which the optical axes are aligned on both sides and the mutual lens positions are focused. It is a rear projection display device.

According to a third aspect of the present invention, in the rear projection type display device according to the first or second aspect, the Fresnel lens is disposed with the optical axis being offset from the center of the screen. .

According to a fourth aspect of the present invention, in the rear projection display device according to any one of the first to third aspects, the projector comprises a plurality of projectors.

<Function> A multi-lamp type projector including a plurality of projectors and a Fresnel lens which shortens the distance between the Fresnel lens and the projector, which is a factor hindering miniaturization, with a minimum loss of light. The combination of a micro-lens array capable of correcting the positional deviation of the projector position from the optical axis in a wide range and a multi-light type projector allows for downsizing of the device and the screen image by multi-lighting the projector. Improvement of luminance can be realized.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a cross-sectional view showing an example of a main configuration of a rear projection display apparatus according to the present invention. First, an image projected by the projector (1) is appropriately reflected by a plane mirror (2) toward a screen, and is arranged so as to be incident on a Fresnel lens (3) using total reflection. As shown in a Fresnel lens (6) in which a part of a Fresnel lens (3) using total reflection is enlarged, a light ray from a projector is refracted once on an incident surface and then emitted toward the observer by total reflection. . The light beam whose direction is adjusted by the Fresnel lens is a double-sided micro lens array (4).
To reach. The above-mentioned Fresnel lens (3) is configured such that a prism composed of a “refractive surface” on which a light beam enters and a “reflective surface” for guiding the refracted light to the exit surface side by reflection is arranged on a concentric circle. Alternatively, a Fresnel lens that collects light rays by a method in which both of a conventional prism composed only of a refracting surface are mixed may be used. The double-sided microlens array (4) is arranged as a set of two microlenses having the same lens pitch and having the lens positions as the focal points.

At this time, for example, when a light beam incident at an angle of 45 degrees with respect to the optical axis is bent by a conventional refraction type Fresnel lens, the angle of the Fresnel surface reaches the total reflection angle at about 68 degrees. (N = 1.53, in the case of an arrangement with a smooth surface incidence), the light beam cannot be bent at an emission angle of about 21 degrees or more at this time. On the other hand, when a Fresnel lens by total reflection is used, the refraction surface angle is 7
A similar effect can be obtained at 0 ° and the reflection surface angle is 53 °. With this method, it is possible to obtain a larger exit angle without any problem. This indicates that the visual field characteristics of the display can be freely controlled at the same time.

As shown in a double-sided micro-lens array (7) in which a part of the double-sided micro-lens array (4) is enlarged, the focal point of a lens formed on both sides is placed near the opposite lens, thereby diffusing light rays. And the optical axis shift can be corrected at the same time. This lens shape is not limited to a spherical surface,
It goes without saying that an aspherical shape may be used.

Finally, final optical characteristics are adjusted by the diffusion plate (5).

Next, FIG. 2 is a perspective view showing an example of a main configuration of a rear projection type display apparatus according to the present invention in which a plurality of projectors are installed. This is a configuration example in which a plurality of projectors (9) are installed at predetermined positions with respect to a screen (8), and an image is projected. In this arrangement, nine lights of 3 × 3 are used, but the number of lights is determined by optical and mechanical factors, and is not limited to nine lights.

A lens sheet such as a microlens array used in the present invention functions as a lens or a prism by being made of an optically transparent resin. The transparent resin for optical use is desirably a transparent synthetic resin sheet to which various molding techniques can be easily applied. As the transparent synthetic resin, an acrylic resin such as polymethyl methacrylate, a polycarbonate resin,
Acrylic-styrene copolymer resin, styrene resin, polyvinyl chloride resin and the like can be used.

[0019]

According to the first aspect of the present invention, by using a Fresnel lens using total reflection as a component of the screen, the distance between the screen and the projector can be reduced, and in particular, reflection is also used. Thus, a significant reduction is possible as compared with the case where only refraction is used.

In the second aspect, the microlens array has the effect of correcting the positional deviation of the projector at the same time as the diffusion of light, so that further miniaturization by shifting the position of the projector and the increase in the number of lights can be easily performed. It is possible to realize.

By appropriately combining the Fresnel lens and the microlens array, it is possible to reduce the size of the device and increase the brightness without adding other optical components, that is, without increasing the loss of light amount or increasing the cost. And can be realized.

According to the third aspect of the present invention, further miniaturization can be realized by adopting an arrangement in which the optical axis of the Fresnel lens is shifted from the center of the screen, that is, an offset arrangement.

According to the fourth aspect of the present invention, it is possible to increase the number of lights without adding a special optical component by the action of the above-mentioned microlens, thereby easily improving the brightness of the screen. is there. At this time, it is also important that the degree of freedom regarding the arrangement of the projectors is large.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of a main configuration of a rear projection display device of the present invention.

FIG. 2 is a perspective view showing an example of multi-lighting by a plurality of projectors in the rear projection display device of the present invention.

[Explanation of symbols]

(1) Projector (2) Reflection mirror (3) Fresnel lens using total reflection (4) Double-sided micro lens array (5) Diffusion plate (6) Magnifying lens side section of Fresnel lens using total reflection (7) Micro (8) Projection screen (9) Multi-light projector

Claims (4)

[Claims] 1. A projection screen and a projector comprising a Fresnel lens for condensing light rays in a system of total reflection or a mixture of both total reflection and refraction, and a transmission type diffusion plate as a minimum component. Rear projection display device. 2. A rear projection type display apparatus comprising a projection screen and a microlens array having optical axes aligned on both sides thereof and having a focus on each other's lens positions. . 3. The apparatus according to claim 1, wherein the Fresnel lens is disposed with its optical axis offset from the center of the screen.
Or a rear projection display device according to claim 2. 4. The rear projection type display apparatus according to claim 1, wherein said projector comprises a plurality of projectors.