JP2932609B2 - Rear projection display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial application field) The present invention relates to a rear projection display device, and more particularly to a rear projection display device for enlarging and projecting a video image, a computer image, or the like.

(Prior art) Recently, a display device using a transmission type or reflection type dot matrix liquid crystal (hereinafter referred to as a light valve) has been used.
Attention has been paid to a magnified projection system in which an image displayed on the light valve is magnified and projected on a screen to be displayed as a large screen.

This is naturally limited in the size of image display using a cathode ray tube (CRT). Larger screens are accompanied by the larger size of the cathode ray tube itself, and practically the size is limited to about 40 inches. This is in order to respond to a request to obtain an image.

On the other hand, in order to increase the area of the light valve itself, it is not easy to obtain a large-sized liquid crystal display device having no defects in manufacturing, and even if obtained, it becomes extremely expensive.

For this reason, if a transmissive (or reflective) light valve is used to magnify and project an image displayed thereon, a powerful large screen can be obtained without being limited by the size of the screen. It is possible.

However, when projecting from the front of the screen using the normal projection method, it can be used only in a dark room, not only the usage range is limited, but also because a separate screen must be prepared, There is difficulty.

Under the circumstances described above, the optical system for enlarging and projecting using the light valve is housed in the cabinet, and the rear projection is made on the screen provided on the front of the cabinet so that the enlarged image can be seen from the front of the cabinet. Display-type display devices have been provided.

A conventional rear-projection display device using a light valve of this type is, for example, as disclosed in Japanese Utility Model Laid-Open No. 1-85778, in which a transmissive liquid crystal panel is illuminated from a light source and an image displayed on the liquid crystal panel is displayed. Is magnified by a projection lens, the optical path is changed by a reflection mirror, and the light is guided to the back of the screen. In this way, the entire projection optical system is housed in the cabinet, can be moved to an arbitrary place, and the image on the screen can be viewed even in a bright room.

(Problems to be Solved by the Invention) However, in the above-mentioned conventional display-type display device using rear projection, a light beam transmitted through a light valve is converted into an optical path by a reflection mirror and guided to the rear surface of the screen. If the image is not projected with a vertical optical axis, the image will be distorted due to keystone distortion, etc., which greatly restricts the installation conditions of the reflecting mirror. (Thickness of cabinet) increases, and therefore, there is a problem that a rear projection display device using a thin cabinet cannot be provided.

In view of this, the present invention uses a light valve and projects an image of the image on the screen on the front of the cabinet to obtain an enlarged image. In this case, the depth of the cabinet can be made as thin as possible. It is intended to provide a device.

[Configuration of the invention]

(Means for Solving the Problems) To solve the problems of the conventional technology described above,
A light valve; first imaging means arranged at a predetermined angle to the surface of the light valve and configured to form an image formed by the light valve on an image forming surface; and a first image forming means formed on the image forming surface. Second to enlarge the image and form it on the screen
A projection optical system having an imaging means, and a cabinet for housing the projection optical system, wherein the screen is provided on the front surface of the cabinet, the projection optical system and the A second reflection mirror is provided at a position facing the inside of the cabinet, and a light reflected by the first reflection mirror is incident on a rear portion of the cabinet at a predetermined inclination angle with respect to a rear surface of the screen. A reflection mirror is provided, and the second reflection mirror is disposed substantially parallel to the screen. Preferably, the predetermined inclination angle is about 60 °.

(Operation) The image created on the light valve forms a real image on the reflecting means through the first lens by illumination with respect to the image, and
The optical path of this image is bent by the second lens, enlarged by the second lens, guided to the back of the screen through the two reflecting mirrors, and the image is corrected on the screen by the first lens to correct the image distortion. Thus, an image without distortion can be seen from the front side of the cabinet. At this time, since the luminous flux of the image projected on the back of the screen enters the back of the screen at an oblique angle, the depth of the cabinet is not limited by the installation position of the reflection mirror for converting the optical path to the screen. An image with a desired magnification can be created on the screen while being able to be reduced.

Hereinafter, the present invention will be described with reference to examples shown in the drawings.

The rear projection type display device according to the present invention has a box-shaped cabinet 1 having a thin depth D as shown in FIG. And a rear projection type screen 3 provided on the front surface of the cabinet 1, and first and second reflection mirrors 4 and 5 for guiding a light beam emitted from the projection optical system 2 to the rear surface of the screen 3. I have.

The projection optical system 2 includes a lighting device 6, a light valve 7, and a light-transmitting type as shown in FIG. 3 (A) and a reflection type as an example in FIG. 3 (B). First lens 8,
It comprises a reflecting means 9 and a second lens 10.

The light valve 7 uses a transmission type or reflection type dot matrix liquid crystal and is installed at a predetermined angle with respect to the optical axis 11 of the first lens 8. The reflection means 9 is installed at a position where the image is formed, and is inclined to the opposite side to the light valve 7 with respect to the optical axis 11.

In the case of the transmission type, as shown in FIG.
A second lens 10 having an optical axis 12 bent at the reflecting means 9 with respect to the optical axis 11 is disposed with the reflecting means 9 interposed therebetween, and the first lens 8 and the second lens 10 are shaped like a letter "C". It is arranged in a shape. The second lens 10 magnifies and projects the image formed on the reflecting means 9 by the first lens 8 onto the screen 3 which is arranged on the side opposite to the inclination of the reflecting means 9 with respect to the optical axis 12. It has an optical system. In the case of the reflection type, as shown in FIG. 3 (B), the reflection means 9 is a reflection mirror, and a second lens 10 is arranged on the reflection optical path and an optical system for obliquely projecting the light onto the screen 3 is provided. .

The image light flux is reflected on the first reflection mirror 4 and guided to the second reflection mirror 5, and the image light flux further reflected by the second reflection mirror 5 is provided on the back surface of the screen 3 with an inclination angle α (for example, 60
The screen 3 which is incident with the screen 3) is incident so that the light beam obliquely projected (60 °) from the back of the screen 3 does not transmit in the direction of its extension, for example, as shown partially enlarged in FIG. A prism total reflection screen that directs the light beam in a direction substantially perpendicular to the front surface of the screen 3 is used.

As the reflecting means 9 used in the transmission type, for example, as shown in part in FIG. 4, a large number of minute reflecting surfaces 13, 13... Which are long in the horizontal direction and narrow in the depth direction are arranged in the vertical direction. The light from the first lens 8 is reflected by the minute reflecting surfaces 13, 13,... And travels toward the second lens 10. The use of such a reflection means 9 is preferable because the loss of light amount due to reflection is small, but it is preferable. It can also be used.

When the above-mentioned projection optical system 2 is viewed geometrically, the light valve 7 and the reflection means 9 are located at the image forming positions A ₁ and A ₂ of the first lens 8 on the first lens 8 side as shown in FIG. The extension line 14 of the light valve 7 and the extension line 15 of the reflection means 9 intersect at a zero point on a line 16 passing through the center of the first lens 8 and perpendicular to the optical axis 11. At this time, the enlargement factor m is m = f / (x ₁ −f = x ₂ −f) / f = x ₂ / x ₁ . In other words, m = tanα ₂ / tanα ₁ (Scheimpflug's law).

By satisfying the above conditions, the image of the light valve 7 can be formed on the reflecting means 9 by the first lens 8. However, the image formed on the reflection means 9 is a trapezoidally distorted image when the original image is a square as shown in FIG.

The second lens 10 is also arranged such that the arrangement relationship between the reflection means 9 and the screen 3 is the same as that of the first lens 8 so that the image on the reflection means 9 is changed to the second lens 10.
And the image is formed on the screen 3. Since the distortion caused by the first lens 8 is corrected by the second lens 10, this image becomes a regular image as shown in FIG. 7, and the magnification of the first lens 8 is multiplied by the magnification of the second lens 10. An image of the magnification is formed.

A reflecting system for optical path conversion for guiding the image light beam reflected on the first reflecting mirror 4 to the back surface of the screen 3 has a line segment when considering a triangle ABC as shown in FIG. It can be seen that the minimum depth is to bend the optical path so as to form an isosceles triangle with AB as the base. That is, X indicates an optical path when there is no reflection mirror, Y indicates an optical path in the case of single reflection, and Z indicates an optical path in the case of double reflection.

 At this time, the angle ψ formed by the line segments AB and BC is represented by φ = π / 2−α−θ (1).

tanφ = 1 / tan (α + θ) (2) From the figure, H / 2D = tan (α + θ) (3) ∴ tanφ = 2D / H Now, H / D is 3, that is, depth D is 1 of height H. To obtain / 3, if θ = 12 °, then from equation (3), α = tan ⁻¹ 3 / 2−θ
= 56.3-12 = 44.3 ゜. If α = 60 ° as shown in FIG. 2, the depth dimension D can be further reduced, and the device can be made thin.

Therefore, as shown in FIG. 1, the projection optical system 2 is placed in the upper part of the cabinet 1, the light beam emitted from the projection optical system 2 is guided by the relay mirror 17, and the first reflection mirror 4 is placed on the bottom of the cabinet 1. The second reflecting mirror 5, which receives the reflected light from the first reflecting mirror 4, can be placed substantially parallel to the back surface of the screen 3 on the rear inner surface facing the screen 3, thereby greatly reducing the depth dimension of the cabinet 1. can do.

〔The invention's effect〕

As described above, according to the present invention, the projection optical system employs an oblique projection method in which the optical axis is bent, and has a structure in which the light is incident on the back surface of the screen from an oblique direction. The depth of the cabinet of the device can be greatly reduced as compared with the conventional device, and an ultra-thin liquid crystal projection display device can be obtained.

[Brief description of the drawings]

FIG. 1 is a perspective view showing one embodiment of the present invention, FIG. 2 is a longitudinally enlarged side view of the specific embodiment, and FIGS. 3 (A) and 3 (B) show the principle of the projection optical system in FIG. FIG. 4 is an enlarged schematic cross-sectional view of a part of the reflection means in FIG. 3, and FIG. 5 is a relation between the first lens of the projection optical system of FIG. 3, the light valve, and the reflection means. Explanatory diagram showing geometrical optics,
FIG. 6 is an explanatory diagram showing distortion of an image formed by the first lens, FIG. 7 is an explanatory diagram showing an image corrected by the second lens, and FIG. 8 is a diagram showing an arrangement relationship between the first and second reflecting mirrors. FIG. 9 is an enlarged sectional view of a part of the screen. 1 ... cabinet, 2 ... projection optical system, 3 ... screen, 4 ... first reflection mirror, 5 ... second reflection mirror,
6 lighting device, 7 light valve, 8 first lens, 9 reflecting means, 10 second lens, 11, 12 optical axis.

Claims (2)

(57) [Claims] 1. A light valve, and first imaging means arranged at a predetermined angle with respect to a surface of the light valve and configured to form an image formed by the light valve on an image forming surface;
A rear projection display device comprising: a projection optical system having a second imaging means for enlarging an image formed on the imaging surface to form an image on a screen; and a cabinet accommodating the projection optical system. Wherein the screen is provided on a front surface of the cabinet, the projection optical system and a first reflection mirror are provided at positions facing each other in the cabinet, and the first reflection mirror is provided at a rear portion in the cabinet. A second reflection mirror for causing the light reflected by the light to enter the rear surface of the screen at a predetermined inclination angle, and the second reflection mirror is disposed substantially parallel to the screen. Type display device. 2. The rear projection display device according to claim 1, wherein said predetermined inclination angle is about 60 °.