JPH05203903A - Projection type display device - Google Patents

Abstract

PURPOSE:To obtain a high-contrast image while preventing a device which uses liquid crystal of such a type that a diffusion state is changed from increasing in size, power consumption, etc., by making light incident from the direction wherein the maximum contrast ratio is obtained according to the characteristics of a light valve. CONSTITUTION:A light source 1 and an aperture stop position, and macromolecular high dispersion type liquid crystal and a screen 7 are in conjugate relation respectively, and light diffused by the macromolecular high dispersion type liquid crystal is cut by an aperture stop 5 to improve the contrast ratio. Further, those optical elements are arranged obliquely, bit by bit, in parallel. The normal of the liquid crystal 3 is slanted to, specially, the optical axes of lighting optical systems 1 and 2. Thus, a panel is slanted and then the optical path length of a light beam passing through the panel is made long. Consequently, the high-contrast image is obtained without boosting the driving voltage of the panel. The inclination at this time is only set corresponding to the characteristics of the light valve so that the maximum 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 display device for projecting an image formed by a light valve, and more particularly as a light valve, a polymer dispersed liquid crystal; PDLC (Pol).
ymer Dispersed Liquid Cry
The present invention relates to a projection type display device using a digital camera.

[0002]

2. Description of the Related Art As a light valve for a projection type display device, a TN (Twisted Nematic) liquid crystal is sandwiched by a polarizing plate to control ON / OFF of an electric field, thereby transmitting or blocking light to the light valve. It is common to form such an image. Proposals relating to such a projector are proposed in JP-A-62-30215 and JP-A-62-186225.

On the other hand, in recent years, although the light transmittance of a TN type liquid crystal device using the above polarizing plate as a liquid crystal element is reduced by 50%, the diffusion state of light is changed without a polarizing plate depending on the presence or absence of a signal. Polymer-dispersed liquid crystal (PDLC) has been attracting attention as a type of liquid crystal that can reduce the basic loss of light quantity by doing so. This PDLC has a structure in which a TN liquid crystal is enclosed in a polymer, and when the electric field is turned off, the light is diffused by the TN liquid crystal to block the light, while the light is transmitted without being diffused when the electric field is turned on. To do. Therefore, by controlling the ON-OFF of this electric field, a desired image is formed.

[0004]

By the way, the contrast ratio of such a type of liquid crystal itself is not sufficient for forming an image, and is shown in, for example, FIG. 2 in order to prevent the diffused light from the diffused type liquid crystal from being projected on the screen. It requires a special system such as Schlieren optics. In particular, 1 and 2 are illumination optical systems, 3 is a polymer dispersed liquid crystal for image display, and 5 is an optical diaphragm for cutting diffused light.

However, in such an optical system, it is necessary to narrow the optical diaphragm in order to improve the contrast ratio, and there is a problem that the brightness on the screen is reduced. On the other hand, in order to improve the contrast ratio of the polymer high-dispersion liquid crystal itself, it is conceivable to increase the thickness of this panel, but this time, the desired contrast can be obtained unless the drive voltage applied to the light valve is increased. As a result, the size of the device is increased, the power consumption is increased, and the driving circuit is complicated.

In view of the above problems, the present invention provides a projection type display device capable of obtaining a high-contrast image while preventing an increase in the size of a device using a liquid crystal of a type that changes a diffusion state and an increase in power consumption. To provide.

[0007]

A feature of the present invention is that a light valve that forms an image by changing the diffusion state of light depending on the presence or absence of a signal, an illumination optical system that illuminates the light valve, and the light. In a projection type display device having a projection lens for projecting an image on the bulb, the light valve is arranged so as to incline the normal line of the light valve with respect to the optical axis of the illumination optical system.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A projection type display device according to the present invention will be described below with reference to the drawings.

FIG. 1 is a diagram showing a projection type display device according to the present invention, in which 1 is an illumination light source, 2 is a lens for collimating the light from the illumination light source 1, and 3 is the diffusion state of the light depending on the presence or absence of a signal. High-dispersion polymer liquid crystal (PDLC) that forms an image by 4 is a condenser lens, 5 is an aperture stop,
6 is a projection lens, and 7 is a screen.

In this embodiment, the light source 1 and the aperture stop position, and the high-polymer high-dispersion liquid crystal and the screen 7 are in a conjugate relationship, and the aperture stop 5 is a light diffused by the high-polymer high-dispersion liquid crystal. Is cut to improve the contrast ratio of the image. Further, these optical elements are arranged so as to be sequentially shifted in parallel little by little. In particular, the normal line of the liquid crystal 3 is inclined with respect to the optical axis of the illumination optical system (1, 2).

As described above, in the present invention, the normal line direction of the light valve in the figure is tilted from the optical axis direction of the illumination optical system. It has been reported that, in a normal PDLC light valve, the thicker the panel, the higher the scattering power and the higher the contrast, but tilting the panel as in this example does not increase the actual panel thickness. The optical path length of the light beam passing through can be made longer than that when not tilted. As a result, a high-contrast image can be obtained without increasing the driving voltage of the panel. Further, the tilt angle at this time may be set to an angle at which the maximum contrast ratio is obtained according to the characteristics of the light valve.

In particular, when a liquid crystal panel having a thickness d is tilted by θi degrees with respect to the optical axis as shown in FIG. 2, assuming that the inclination of a light beam that actually passes through the liquid crystal from the panel normal direction is θ1 degree, the panel The optical path length of light passing through is represented by d / cos θ1. θ
In the small range of 1 (that is, small θi), it is not possible to expect a large increase in the optical path length, but it is predicted that it is difficult to realize an extremely large incident angle θi. Therefore, a realistic range of about 5 ° ≦ θi ≦ 45 ° is appropriate.

[0013]

According to the present invention, light is incident from the direction in which the maximum contrast ratio is obtained according to the characteristics of the light valve.-Even when the panel is thin, sufficient diffusion can be secured.

Therefore, the contrast ratio can be increased with a low driving voltage.

Since the contrast ratio of the panel is high, it is not necessary to narrow down the luminous flux as in the conventional example, so that the light utilization efficiency is improved and the brightness on the screen can be increased. The effect is obtained.

[Brief description of drawings]

FIG. 1 is an optical cross-sectional view of a projection display device according to the present invention.

FIG. 2 is a diagram showing an optical path of a light valve.

FIG. 3 is an optical sectional view of a conventional projection display device.

Claims (1)

[Claims] 1. A projection type display having a light valve for forming an image by changing a diffusion state of light depending on the presence or absence of a signal, an illumination optical system for illuminating the light valve, and a projection lens for projecting an image on the light valve. In the device, the projection display device is characterized in that a normal line of the light valve is inclined with respect to an optical axis of the illumination optical system.