JPS62186225A - Projector - Google Patents

Abstract

PURPOSE:To obtain a video sharply improved at its contrast with a simple constitution by including a liquid crystal plate around an optical axis from its vertical plane in the direction of a visual angle with maximum contrast. CONSTITUTION:Light beams radiated from a light source 2 are turned to parallel beams LC through a condenser lens 3 and made incident upon the liquid crystal plate 1. When voltages applied to respective liquid crystal cells of the liquid crystal plate 1 are changed by a video signal, the transmitted light forms video light LD, condensed by a condenser lens 11, and then projected on a screen 4 through a field lens 5, so that the video formed by the liquid crystal plate 1 is expansively displayed on the screen 4. Since the optimum contrast direction of the liquid crystal plate 1 coincides with the direction of the optical axis (a), the contrast of the video obtained on the screen 4 is remarkably improved.

Description

DETAILED DESCRIPTION OF THE INVENTION A. Industrial Field of Application The present invention relates to a projector, and in particular to a projector that forms image light using a transmissive liquid crystal plate and projects this image light onto a screen to display an image on the screen. It was designed so that

B Summary of the Invention The present invention forms image light by using a liquid crystal plate,
In a projector that projects this image light onto a screen, by tilting the liquid crystal plate at a predetermined angle from a plane perpendicular to the optical axis in the direction of the maximum contrast angle, the direction of the best contrast of the liquid crystal plate and the optical axis can be adjusted. By matching, the contrast of the image on the screen is improved.

C. Prior art Conventionally, this type of projector has the configuration shown in Fig. 3 (Japanese Patent Laid-Open No. 55-553
(See Publication No. 14).

That is, a liquid crystal plate 1 consisting of liquid crystal cells arranged in a matrix whose transmittance changes depending on the applied voltage is disposed between a light source 2 and a screen 4, and the vertical axis passing through the center of the liquid crystal plate l is an optical axis a. The light LA emitted from the light source 2 is condensed and transmitted to the liquid crystal plate 1 by the condenser lens 3, and thus an image light LB with each liquid crystal cell as one pixel is formed on the liquid crystal plate 1, and this image light LB is used as a field. The image is projected onto the screen 4 via the lens 5.

In the configuration shown in FIG. 3, if the voltage applied to the liquid crystal cells of the liquid crystal plate l is changed by, for example, a television video signal, then
A corresponding image can be formed on the screen 4.

By the way, when trying to form a moving image on the screen 4, it is necessary to use a liquid crystal whose transmittance can quickly follow changes in the voltage applied to each liquid crystal cell (that is, have a fast response speed). It is necessary to use a cell.

Also, when trying to form images with good clarity,
In addition to displaying the black level of the video signal as dark as possible,
It is desirable to use a liquid crystal cell that displays a white level as brightly as possible and has a wide range of change in transmittance (and thus has a large contrast).

As a liquid crystal cell that can practically satisfy these conditions,
Generally, the so-called TN mode (twisted nemasti
A liquid crystal plate 1 using a liquid crystal cell of C mode) is used.

D Problems to be Solved by the Invention However, the contrast of a TN mode liquid crystal changes depending on the viewing direction, as shown in FIG.

That is, as shown in FIG. 5, the vertical axis passing through the center of the liquid crystal plate 1 is taken as the Z axis, and the direction in which the liquid crystal cells of the liquid crystal plate 1 are arranged are taken as the X axis and the Y axis, respectively.

Furthermore, the direction in which the liquid crystal plate 1 is viewed is expressed as the direction of the viewing angle θ with respect to the liquid crystal plate l with the plane of the liquid crystal plate 1 as a reference.

When defined in this way, when the viewing direction changes on a virtual plane including the Y-axis direction and the The contrast is at its maximum in this direction, and thereafter, as the viewing angle θ changes, the contrast gradually decreases.

On the other hand, if the viewing direction changes on a virtual plane including the X-axis direction and the X-axis direction, the song! As shown by aL2, the viewing angle θ
The contrast reaches its maximum in the direction W of 90° - α (hereinafter, this angle α is referred to as the maximum contrast viewing angle), which is tilted several tens of degrees from the 90° direction, and after that, the contrast sharply decreases as the viewing angle θ changes. begins to decline.

Therefore, there is a problem in that the image projected onto the screen 4 also has a contrast lower than the best contrast by a value corresponding to the viewing angle α.

Furthermore, 1. In addition to this, there is a problem in that the contrast changes rapidly when the viewing direction of the image on the screen 4 moves in the X-axis direction and on a virtual plane including the X-axis direction.

However, in -a, when a person views an image on the screen 4, there are far fewer changes in the viewing direction in the vertical direction (i.e., changes in the viewpoint) than in the horizontal direction (i.e., changes in the viewpoint). By configuring the liquid crystal panel 1 so that the direction of the X-axis is the vertical direction of the projected image, the contrast in the vertical direction has been improved by preventing changes in contrast due to changes in viewpoint.

That is, by improving the liquid crystal material and cell structure, the direction of the best contrast point is brought closer to the optical axis direction.

The present invention has been made in consideration of the above points, and it is an object of the present invention to propose a projector with a simple configuration that can produce images with significantly improved contrast compared to conventional projectors.

E Means for solving the problem In order to solve the problem, in the present invention, the light source 2
In a projector in which image light LD is formed by transmitting light LC from a transmission type liquid crystal plate 1, and this image light LD is projected onto a screen 4, the liquid crystal plate 1
is tilted at or near a predetermined angle α in the direction of the maximum contrast viewing angle from the perpendicular plane 10 with respect to the optical axis a.

By tilting the liquid crystal plate 1 by a predetermined angle α from a plane 10 perpendicular to the optical axis a, and aligning the direction W of the best contrast of the liquid crystal plate 1 with the direction of the optical axis a, the image is projected onto the screen 4. It is possible to significantly improve the contrast of images.

G example Hereinafter, one embodiment of the present invention will be described in detail with reference to the drawings.

In FIGS. 1 and 2, in which parts corresponding to those in FIG. 3 are denoted by the same reference numerals, the optical axis
A perpendicular plane lO is taken, a direction corresponding to the vertical direction of the screen 4 on the perpendicular plane 10 is taken as a C-axis, and a direction orthogonal to this is taken as a b-axis. The liquid crystal plate 1 has a direction corresponding to the horizontal direction of the screen 4, that is, the b-axis direction, which is the Y-axis direction, and a direction W (fourth direction) where the contrast is maximum.
The lens is tilted from the vertical plane IQ by an angle α (FIG. 4) in the direction of the maximum contrast visual angle with the b-axis as the rotation axis so that the optical axis (FIG. 4) coincides with the optical axis a.

In addition, by setting the distance between the light source 1 and the condenser lens 3 short, the light LC emitted from the condenser lens 3 is made to be a substantially parallel light beam.

Furthermore, a condenser lens 11 is inserted between the liquid crystal plate l and the field lens 4, and the liquid crystal plate 1 consists of parallel light beams.
The image light LD is focused on a field lens 5.

In the configuration shown in FIG. 1, the light emitted from the light source 2 becomes parallel light LC through the condenser lens 3, and the liquid crystal plate 1
incident on . When the voltage applied to each liquid crystal cell of the liquid crystal plate 1 changes depending on the video signal, the transmitted light forms video light LD, which is focused by the condenser lens 11 and then projected onto the screen 4 via the field lens 5. Ru. The image thus formed by the liquid crystal plate 1 is enlarged and displayed on the screen 4.

According to the configuration shown in FIG. 1, since the direction W of the best contrast of the liquid crystal plate 1 coincides with the direction of the optical axis a, the image obtained on the screen 4 has a higher contrast than before. can be obtained.

Furthermore, by using parallel light rays as the incident light LC of the liquid crystal plate 1, the imaging points of the pixels at the upper and lower parts of the liquid crystal plate 1 can be formed on the same screen 4 perpendicular to the optical axis a. As a result, local defocus caused by tilting the liquid crystal plate l can be prevented.

In the above embodiment, by setting the distance between the light source 2 and the condenser lens 3 short, the parallel light ray L
Although C is obtained, the same effect can be obtained by using condenser lenses with different focal lengths instead.

FIG. 2 shows a second embodiment of the present invention, in which shrinkage of the image in the vertical direction caused by tilting the liquid crystal plate 1 in the embodiment of FIG. 1 is corrected.

That is, in addition to tilting the liquid crystal plate 1 at an angle α with the b-axis as the rotation axis, it is also tilted by an angle β with the C-axis as the rotation axis, so that the angle β is equal to the angle α.

In the configuration shown in FIG. 2, the image on the screen 4 becomes an image that is smaller in the vertical direction by cos α than when the liquid crystal plate 1 is mounted perpendicularly to the optical axis a.

Similarly, in the horizontal direction of the screen 4, the image becomes smaller by Cog β.

Here, since the angles α and β are equal, the image on the screen 4 becomes an image shrunk at the same ratio in the vertical and horizontal directions, and as a result, the image formed on the liquid crystal panel 1 has the same aspect ratio. An image is formed on the screen.

According to the configuration shown in FIG. 2, in addition to the same effects as in the first embodiment, it is possible to obtain an image having the same aspect ratio as the image formed on the liquid crystal panel 1.

Therefore, in the case of the first embodiment, in order to obtain an image with a predetermined aspect ratio, it was necessary to use the liquid crystal plate 1 that forms an image extending in the vertical direction, but in this embodiment, the conventional projector A liquid crystal plate 1 having the same shape as the liquid crystal plate 1 that has been used can be used.

In the above-mentioned embodiment, local defocusing of the image on the screen was prevented by making parallel light rays incident on the liquid crystal plate 1, but instead of this, it is possible to prevent local defocusing of the image on the screen. A similar effect can be obtained by using an optical system with a deep depth of focus.

Furthermore, in the above-mentioned embodiment, a case was described in which the present invention is applied to a projector using one liquid crystal plate, but the present invention is not limited to this, but can be applied to a color projector using a plurality of liquid crystal plates, etc. can also be widely applied. In this case, three liquid crystal plates for red, green, and blue may be used to form color image light.

In the above embodiment, the tilt angle of the liquid crystal plate 1 was set to be equal to the maximum contrast viewing angle α, but instead of this, if the liquid crystal plate 1 is tilted to approach the viewing angle α, Focusing on the fact that the above-mentioned effects can be gradually obtained, this may be determined within a practically acceptable contrast range.

H Effects of the Invention As described above, according to the present invention, by matching the direction of the best contrast of the liquid crystal plate with the direction of the optical axis a, the contrast of the image obtained on the screen is further improved compared to the conventional method. be able to.

[Brief explanation of drawings]

FIG. 1 is a cross-sectional view showing the first embodiment of the projector of the present invention, FIG. 2 is a perspective view showing the arrangement of the liquid crystal plate of the second embodiment of the present invention, and FIG. 3 is a conventional projector. A sectional view, FIG. 4 is a viewing angle characteristic diagram of the liquid crystal plate for explanation, and FIG.
The figure is a perspective view for explaining the same. l...Liquid crystal plate, 2...Light source, 3.11
...Condenser lens, 4...Screen, 5...Field lens.

Claims (3)

[Claims] (1) In a projector that forms image light by transmitting light from a light source through a transmissive liquid crystal plate, and projects this image light onto a screen, the liquid crystal plate is placed in a plane perpendicular to the optical axis. A projector characterized in that it is tilted at a predetermined angle or in the vicinity thereof in the direction of the maximum contrast viewing angle. (2) The projector according to claim 1, wherein the light transmitted through the liquid crystal plate is parallel light. (3) The projector according to claim 1, wherein the liquid crystal plate is tilted at or near a predetermined angle in the vertical and/or horizontal directions of the liquid crystal plate from a plane perpendicular to the optical axis.