JP2588541B2 - Projection color display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Overview] A projection type color display device using a laminated liquid crystal panel using a nematic-cholesteric phase transition type liquid crystal as an object to be projected. The concave Fresnel lens is arranged on the light source side of the laminated liquid crystal panel, and the convex Fresnel lens is arranged on the optical system side.

[Industrial applications]

The present invention relates to a projection type color display device. The present invention
More specifically, the present invention relates to a projection type color display device using a laminated liquid crystal panel using a nematic-cholesteric phase transition type liquid crystal as a projection object, which can use a commercially available overhead projector (hereinafter, referred to as OHP). .

[Conventional technology]

In recent years, various types of projection type display devices using liquid crystal display elements have been developed. One application is to mount a super TN type (STN) liquid crystal panel on a ready-made OHP cover glass. A display device for enlarging and projecting an image displayed on a screen using an OHP optical system is commercially available.

Meanwhile, a research group including the present inventors has previously developed a bistable drive type nematic-cholesteric phase transition type liquid crystal capable of performing display by transmission and scattering of light and applied for a patent (for example, See JP-A-61-67824 and JP-A-61-174516. Since these phase-change liquid crystals do not use a polarizing plate, the display is brighter than the STN method, and a large-capacity display is possible because they utilize bistability.

In addition, the present inventors have found that unique bright color display is possible using this liquid crystal. In other words, in the cholesteric phase, the directions of the liquid crystal molecules are twisted and arranged, so that a periodic distribution of the refractive index corresponding to the birefringence effect (Δn) of the liquid crystal is formed. As light passes through such a layer, it is scattered by diffraction, and its transmittance is wavelength dependent. Therefore, the transmittance T (λ) at the Bragg angle (usually almost vertical) is expressed by the following equation (I), including the term of scattering due to refraction.

Here, κ is a coefficient indicating the effect of scattering due to refraction, d is the cell thickness, λ is the wavelength, and θ is the Bragg angle in diffractive scattering.

In the above formula (I), since Δn × d is a determining factor of the color, by stacking liquid crystal panels having different Δn × d from each other, as shown in FIGS. 3 to 5, Multicolor display by subtractive color mixture is possible. The color display device 10 of FIG. 3 comprises a light source 2 located at the bottom of the device and a frame 1
(The combination of the liquid crystal panels 4 and 14) fixed to the camera, and Fresnel lenses disposed on both sides of the object
The optical system 7 includes 11 and 12 and an optical system 7 for enlarging and projecting image light transmitted through the projection object onto a screen or the like. The illustrated optical system 7 is a combination of an imaging lens 8 and a reflecting mirror 9. In this device, since Fresnel lenses equivalent to concave lenses are arranged on both sides of the panel, light can be vertically incident on all parts of the panel.

The formation of the image light transmitted through the object is shown in FIGS.
It will be understood from the figure. In other words, when the panel 4 is used for green display and the panel 14 is used for red display among the liquid crystal panels each made of a phase change type liquid crystal, the light vertically incident from the side of the liquid crystal panel 4 for green display is And 14
During transmission, the light is scattered by diffraction, and a desired color projection display is possible. Here, the green light and the red light have Δn × d and transmission physical properties as shown in FIG. 5, respectively.

[Problems to be solved by the invention]

The projection type color display device of the type described above uses a special optical system in which Fresnel lenses are arranged on both sides of a liquid crystal panel, and therefore can perform satisfactory multicolor projection display. However, since the dedicated optical system used complicates the production of the apparatus and causes an increase in cost, it is desired to be able to use an off-the-shelf OHP. However, as shown in FIG. 6 and FIG. 7, when an off-the-shelf OHP is used, some problems currently occur. Ready-made
In the OHP, since the light incident angles of the liquid crystal panels 4 and 14 are not perpendicular, if the incident angle is {, the distance between the liquid crystal phases of the two panels is h, a pixel shift ΔI of h · tan} occurs. Normally, h2 mm and ψ are about 30 ° at the maximum, so the displacement is 1.2 mm. When a panel of 31 ine / mm is used, a displacement of 3 to 4 lin occurs, and superimposed display cannot be performed. Also, ready-made OHP
When を is used, the color becomes blurred around the panel. This is because, in the phase transition type liquid crystal, display is performed using light diffraction scattering, so that the transmittance T (λ) is affected by the light incident angle. This can be understood from the dependence of the projected display color on the light incident angle of the liquid crystal cell for providing the blue projected display color shown in FIG. Here, the birefringence effect Δ of the liquid crystal
n is 0.157, spiral pitch (grand gent state) 1.10
μm, and the cell thickness is 5.7 μm. As shown in FIG. 8, among the three elements of color, particularly, the saturation decreases as the incident angle increases (the deviation from normal incidence increases). this is,
This is because the contribution of the diffraction scattering of the above equation (1) decreases and the influence of the refraction scattering increases.

Accordingly, an object of the present invention is to provide a projection type color display device that can use an off-the-shelf OHP by utilizing the diffraction and scattering of light by a cholesteric phase.

[Means for solving the problem]

According to the present invention, the above-described problems are caused by a light source disposed at the bottom of the apparatus, a Fresnel condenser lens for collecting light from the light source, an object on the Fresnel condenser lens, A projection type color display device having an optical system for enlarging and projecting image light transmitted through an object onto a screen or the like, wherein the object is a laminated liquid crystal using a nematic-cholesteric phase transition type liquid crystal. A Fresnel lens equivalent to a concave lens on the light source side of the liquid crystal panel, and a Fresnel lens equivalent to a convex lens on the optical system side thereof.
The problem can be solved by a projection type color display device characterized by being arranged respectively.

The phase transition type liquid crystal that can be used in the display device of the present invention is, for example, a liquid crystal material described in the above-cited published patent publication. Of course, other liquid crystal materials can be advantageously used as long as they exhibit similar liquid crystal characteristics. Preferred characteristics required for the liquid crystal material include a spiral pitch of 0.5 to 2 μm and a dielectric anisotropy of 1 to 2.
0 or more, the refractive index anisotropy is 0.10 to 0.25, the viscosity is as low as possible, and it is stable against ultraviolet rays.

P-type nematic liquid crystal + chiral nematic liquid crystal can exhibit the same performance without depending on the contents of the constituent materials.

A liquid crystal panel having these liquid crystal materials can have a general configuration as an object to be projected in this technical field, and according to a desired result, a plurality of the panels can be arbitrarily combined to form a laminated liquid crystal panel. can do. For example, an object to be projected can be constituted by a laminate of two liquid crystal panels, in which case the liquid crystal panel on the light source side can be used for green display and the liquid crystal panel on the optical system side can be used for red display.

In the display device of the present invention, the main body can be preferably formed of a commercially available OPH. That is, in the present invention, the light converged by the Fresnel lens equivalent to the concave lens installed in the existing OHP is converted into parallel light once by the Fresnel lens equivalent to the concave lens, and after passing through the laminated panel, by the Fresnel lens equivalent to the convex lens. The light is collected and made incident on the imaging lens.

The distance from the Fresnel lens to the imaging lens of OHP that is generally commercially available varies depending on the model, but is approximately 340.
It is about 380mm. Therefore, if the focal length of the concave Fresnel lens is set to about 360 mm, parallel light with practically no problem can be obtained. In this way, by causing the light to be perpendicularly incident on the entire surface of the panel as parallel light, it is possible to prevent pixel shift and reduction in color purity.

(Operation)

In the projection type color display device according to the present invention, the existing OHP
Alternatively, after the light from the light source is converged by a Fresnel lens equivalent to a concave lens installed in a device having a similar structure, the converged light is once adjusted to parallel light by a Fresnel lens equivalent to a concave lens, and then projected. It is incident on a laminated liquid crystal panel as an object. Next, the image light passing through the laminated panel is condensed by a Fresnel lens equivalent to a convex lens, and is incident on an optical system for enlarged projection, for example, an imaging lens. According to the present invention, since light can enter the panel vertically, inconveniences such as pixel shift can be prevented.

〔Example〕

The projection type color display device according to the present invention includes, for example, a first type.
It can have a structure as shown in the figure. Display device 10
Is basically the same as a commercially available OHP, 1 is its frame, 2 is a light source, and 3 is a Fresnel condenser lens equivalent to a concave lens. An optical system 7 for projecting image light from a projection object onto a screen or the like in an enlarged manner includes an imaging lens 8 and a reflecting mirror 9. As is clear from the enlarged view of FIG. 2, the projection object is a laminate of liquid crystal panels 4 and 14, and a Fresnel lens 5 equivalent to a concave lens is provided on the light source side.
Fresnel lenses 6 equivalent to concave lenses are arranged on the optical system side. Manufacturing and use examples of this color display device will be described below.

Liquid crystal and panel configuration: Transparent electrodes were formed on a glass plate having a thickness of 1.1 mm, and liquid crystal was sealed therein to produce two types of liquid crystal panels for red display and green display, respectively.

In each liquid crystal panel, the number of pixels = 640 x 400,
The pixel pitch was set to 0.35 mm. The cell thickness of each panel and the physical properties of the liquid crystal were as shown in the following table.

Configuration of the red display panel green display panel cell thickness 5.7 [mu] m 5.7 [mu] m helical pitch 0.78μm 0.90μm Δn 0.146 0.216 display unit: after removal of the electrode using a thermocompression bonding type flexible cable, the two panels aligned And bonded with a transparent epoxy resin. Next, a Fresnel lens equivalent to a concave lens with a focal length of 360 mm was placed under the laminated panel with a focal length of 35 mm.
A Fresnel lens equivalent to a 5 mm convex lens was arranged on the upper side without being bonded.

Projection display: Commercially available OHP (Fujix EW- manufactured by Fuji Photo Optical Co., Ltd.)
1) The above-mentioned display unit was mounted thereon, and a panel was driven to perform display. The magnification of the projection display was set to about 7 times.

Result: The pixel shift was less than half of the pixel over the entire display surface, and the difference in color between the central part and the peripheral part was hardly observed.

〔The invention's effect〕

According to the present invention, in multicolor color display using a phase change type liquid crystal laminated panel, it is possible to prevent a pixel shift and a decrease in saturation in a peripheral portion, so that a good color projection display is performed using an existing OHP. be able to.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a preferred example of a projection type color display device according to the present invention, FIG. 2 is a layout diagram of a Fresnel lens of the device of FIG. 1, and FIG. FIG. 4 is a schematic diagram showing a mechanism of projection display in the device shown in FIG. 3, FIG. 5 is a graph showing light transmission properties, FIG. FIG. 7 is a configuration diagram showing another example of a conventional projection type color display device, FIG. 7 is an explanatory diagram showing the occurrence of a pixel shift in the device of FIG. 6, and FIGS. 8 (A) and (B). (C) and (C) are graphs showing the light incident angle dependence of the projected display color. In the figure, 1 is a frame, 2 is a light source, 3 is a Fresnel condenser lens, 4 and 14 are liquid crystal panels, 5 is a concave Fresnel lens, 6
Is a convex Fresnel lens, 7 is an optical system, 8 is an imaging lens, 9
Is a reflector, and 10 is a display device.

Continuation of front page (56) References JP-A-63-13019 (JP, A) JP-A-62-38492 (JP, A)

Claims (2)

(57) [Claims] 1. A light source disposed at the bottom of an apparatus, a Fresnel light collecting lens for collecting light from the light source, an object to be projected on the Fresnel light collecting lens, and a light transmitted through the object. A projection type color display device having an optical system for enlarging and projecting the image light onto a screen or the like, wherein the projection target is a laminated liquid crystal panel using nematic-cholesteric phase transition type liquid crystal, and the liquid crystal panel Wherein a Fresnel lens equivalent to a concave lens is arranged on the light source side and a Fresnel lens equivalent to a convex lens is arranged on the optical system side. 2. The laminated liquid crystal panel is a laminate of two panels, a lower panel for green display, and
2. The projection type color display device according to claim 1, wherein the upper panel is for red display.