JPS63316980A - Liquid crystal video projector - Google Patents

Abstract

PURPOSE:To realize the dimming of projecting light consecutively by an impression voltage impressed on TN liquid crystal, by arranging the TN liquid crystal and a polarizing plate behind a light modulating LCD. CONSTITUTION:A dimming LCD5 sandwiches the TN liquid crystal 5a between glass plates 5b and 5c, and the polarizing plate 5d is arranged only at the outside of the glass plate 5c. Incident light on the dimming LCD5 becomes a horizontal component by the light modulating LCD4. By aligning the polarizing plate 5d in a direction where light is rotated optically when no voltage is applied, transmission light L2 is dimmed consecutively corresponding to the impression voltage. Dimmed light is expanded by a projecting lens 6, and is image-formed on a screen S.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a liquid crystal video projector having a dimmer section for five projection lights.

[Prior Art 1] Conventional dimming methods for liquid crystal video projectors include directly controlling the light e from the light source, or leaving the light source as is and providing a mechanical diaphragm with an ND filter inserted. As a method for continuously changing the amount of light, a method is known in which a polarizing plate is inserted after the modulating liquid crystal and the light is adjusted by mechanically rotating the polarizing plate 411.

In this method of directly controlling the light intensity of a light source, halogen lamps and xenon lamps are used as light sources for liquid crystal video projectors that provide light wave chromaticity.

Since a metal halide lamp or the like is used, changes in color temperature and spectral distribution occur. Furthermore, since xenon lamps, metal halide lamps, etc. are discharge tubes, the variable range of light intensity is narrow, and it is practically impossible to implement them. Continuous changes are not possible with the ND filter insertion type, and continuous changes are possible with the method using an aperture, but there is a problem in that it causes uneven illuminance due to light vignetting.

In order to solve these problems, dimming is achieved by using a polarizing plate and mechanically rotating the polarizing plate, but it is essential to have a mechanism to mechanically rotate the polarizing plate. This results in a complicated system that has drawbacks such as a poor operating feel.

[Object of the invention] The object of the present invention is to create a twisted nematic liquid crystal (hereinafter referred to as T
The projected light of a video projector using an LCD (liquid crystal display device) with
Focusing on the fact that only one of the horizontal components is used, TN
Provides a liquid crystal video projector that makes use of the optical rotation effect of liquid crystal and allows continuous dimming of projected light by applying voltage to the TN liquid crystal by placing a TN liquid crystal and a polarizing plate after a light modulating LCD. It's about doing.

[Summary of the Invention] The gist of the present invention to achieve the above-mentioned object is to provide a projector that modulates and projects incident light from a light source by driving the LCD with a video signal, etc. A dimming LCD is placed behind the light modulating LCD and consists of a twisted nematic liquid crystal and a polarizing plate, and the optical rotation is controlled by the voltage applied to the liquid crystal of the dimming LCD to continuously dim the projected light. 1. A liquid crystal video projector characterized by comprising: a control means for controlling the display;

[Embodiments of the invention] The present invention will be explained in detail based on illustrated embodiments.

[Embodiments of the Invention] In FIG. 1, l is a light source, and in the projection direction of the light source 1, a condenser lens 2, a heat ray absorption filter 3, .
LCD for light modulation4. A dimming LCD 5, a projection lens 6, and a screen S are arranged.

Light emitted from a light source 1 passes through a condenser lens 2, infrared rays are cut by a heat ray absorption filter 3, and is modulated by driving a light modulating LCD 4 with an electric signal based on a video signal or the like. The light modulation LCD 4 has a TN liquid crystal 4a mounted on a glass plate 4b, as shown in the details of its structure in FIG.
, 4c, and polarizing plates 4d and 4e are arranged before and after them. Therefore, the transmitted light L1 modulated by the TN light modulation LCD 4 has only one of the horizontal component and the vertical component of the incident light LO.

The light L1 transmitted through the light modulation LCD 4 is sent to the dimming LCD 5
incident on . FIG. 3 shows the structure of the dimming LCD 5 in detail, in which a TN liquid crystal 5a is sandwiched between glass plates 5b and 5c, and a polarizing plate 5d is arranged only on the outside of the glass plate 5C.

The light incident on the light modulating LCD 5 has only one component, for example, the horizontal component in this embodiment, due to the light modulating LCD 4. The orientation of the liquid crystal molecules M of the TN liquid crystal 5a is changed by applying a voltage equal to or higher than a threshold value, thereby changing the optical rotation characteristics. If the polarizing plate 5d is aligned with the direction in which the rotated light passes when the liquid crystal molecules M are twisted by 90°, that is, when no voltage is applied, the transmitted light L2 will be transmitted continuously according to the applied voltage. It will be dimmed. In this embodiment, the amount of transmitted light is maximized when no voltage is applied, and the dimmed light is magnified by the projection lens 6 and imaged on the screen S.

In this case, the amount of projected light can be continuously varied by simply changing the voltage applied to the dimming LCD 5, and the light amount ratio is 40.
The above can be easily achieved, and there will be no deterioration in image quality or vignetting of light. 0 When the projected image is changed from 10 inches to 50 inches, the area ratio is 1:25, and the illuminance of one screen is constant. In order to achieve this, a dimming ratio of 25 or more is required, but this can be fully realized.

In the first embodiment, the light modulating LCD 4 is a normally closed type LCD, and the polarizing plate of the dimming LCD 5 is realized by orthogonal to the polarizing plates 4d and 4e of the light modulating LCD 4. .

In the second embodiment, the light modulating LCD 4 is a normally open type LCD, the polarizing plate 4d is kept in the same direction, the polarizing plate 4e is orthogonal to the polarizing plate 4d, and the light modulating LCD 4 is a normally open type LCD.
The D5 is rotated 90' as a whole with respect to the first embodiment, and the voltage applied to the iA light LCD 5 versus the amount of transmitted light is the same as that of the first embodiment.
This is realized in the same manner as in the embodiment. Note that this can also be achieved by other combinations of the rubbing direction of the liquid crystal and the direction of the polarizing plate.

In the first embodiment, the LCD was a single panel type, but R, G, B
Three-plate type L that separates each component, modulates, and combines color.
Even in a CD color video projector, by aligning the polarization directions of each color as shown in the first embodiment, dimming can be performed using a single dimming LCD after color synthesis.

In addition, there is no mechanical driving part, and the effect can be obtained by simply changing the voltage, so it can be easily applied to a complex system.For example, the projection lens 6 shown in the first embodiment can be easily applied. It is possible to use a zoom lens, generate a voltage according to the zoom magnification, and apply it to the dimming LCD 5 to automatically change the amount of projected light.

As a modification, it is also possible to link a distance measuring type autofocus or the like to automatically change the amount of projected light depending on the projection distance, that is, the screen size.

[Effects of the Invention] As explained above, in the liquid crystal video projector according to the present invention, the amount of light transmitted can be changed by changing the voltage applied to the dimming LCD.

The maximum to minimum ratio can be 40 or more.

[Brief explanation of drawings]

The drawings show an embodiment of a liquid crystal video projector according to the present invention, and FIG. 1 is a configuration diagram thereof, FIG. 2 is a configuration diagram of a light modulation LCD, and FIG. 3 is a configuration diagram of a dimming LCD. Symbol l is a light source, 2 is a condenser lens, 3 is heat absorption glass, 4 is an LCD for light modulation, 5 is an LCD for dimming, 6 is a projection L/7 lens, 4a, 5a are liquid crystals, 4b, 4c, 5b, 5C
is glass, and 4d, 4e, and 5d are polarizing plates.

Claims (1)

[Claims] 1. In a projector that modulates and projects incident light from a light source by driving an LCD with a video signal, etc., a light modulating LCD, a twisted nematic liquid crystal placed behind the light modulating LCD, and a polarizing plate are used. Light control L
A liquid crystal video projector comprising: a CD; and a control means for controlling the optical rotation of the CD by applying a voltage to the liquid crystal of the dimming LCD to continuously dim the projected light.