JPH0580421A - Projection screen - Google Patents

Abstract

PURPOSE:To decrease moires without enhancing the fineness of the pitch of lenticular lenses and Fresnel lenses to the threshold and without degrading the resolution of an image. CONSTITUTION:The projection screen 10 is constituted by disposing the Fresnel lenses 12, a plastic substrate 16 provided with a diffraction grating 14 and the lenticular lenses 18 in this order. The diffraction grating 14 constitutes a diffusion plate which can blur the shades of the Fresnel lenses 12 on the lenticular lenses 18 sufficiently on the lenticular lenses 18. The diffraction grating as the diffusion plate allows the free selection of characteristics, does not diverge light to directions exclusive of the necessary direction and decreases the losses of the light.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transmissive screen used in a projection television, and more particularly to an L for projecting an image formed by a liquid crystal display (LCD).
The present invention relates to a transmissive projection screen used for a CD projector.

[0002]

2. Description of the Related Art In an LCD projector, after separating light source light into three primary colors by a dichroic mirror, each projection light is transmitted through a liquid crystal cell displaying an image corresponding to each color, and the projection light of these three colors is again transmitted. It is configured to be combined and projected on the screen.

Here, the liquid crystal cell has a lattice pattern for forming pixels, and moire occurs due to the lattice pattern and the lens pattern of the lenticular lens sheet and / or Fresnel lens sheet constituting the screen, There is a problem that the image quality is deteriorated.

In order to reduce the occurrence of moire, conventionally, means for optimizing the combination of the pitches of the lenticular lens and the Fresnel lens, and defocusing to intentionally blur the image are used. It was

[0005]

However, the means for optimizing the combination of the pitches of the lenticular lens and the Fresnel lens as described above is, as the LCD pitch becomes finer, the lens sheet becomes finer. There is a problem that the pitch is changed and the combination of pitches is limited due to the limitation of the processing technique.

In particular, a composite moire caused by a lenticular lens, a Fresnel lens and an LCD grating is
Since it is considered that the grating is modulated by the Fresnel lens pattern, and further lenticular lenses and moire are generated, it was not possible to solve it by only making the pitch fine.

Further, in the case of defocusing, there is a problem that the resolution of an image is lowered.

The present invention has been made in view of the above-mentioned conventional problems, and the pitch can be made as fine as possible,
An object of the present invention is to provide a projection screen capable of reducing moire without reducing the resolution of an image.

[0009]

The present invention was made based on the following idea.

First, since the above-mentioned moire is caused by the LCD grating being modulated by the Fresnel lens pattern, it is necessary to prevent the modulation by the Fresnel lens from reaching the lenticular lens.

That is, the shadow of the Fresnel lens must be sufficiently blurred on the lenticular lens.

For this purpose, the light emitted from the Fresnel lens may be diffused, and a diffusion plate may be placed on the light emitting surface of the Fresnel lens.

When the diffusion angle is θ, the shadow of the Fresnel lens on the lenticular lens when the diffuser plate is placed is the gap S when the Fresnel lens is displaced by one pitch,
Assuming that the pitch of the Fresnel lens is P, it is possible to sufficiently blur on the lenticular lens with a value S given by S = P / tan θ (1).

However, since it is not possible to freely select the characteristics with an ordinary diffuser plate, it is difficult to determine θ in the equation (1), and light is diffused in directions other than necessary. Moreover, since a large amount of passing light collides with the internal diffusing agent in the diffusion plate, the light loss is large.

Here, the inventor has paid attention to a diffraction grating which can freely select the characteristics, does not diffuse light in an unnecessary direction, and has a small light loss as the diffusion plate.

The present invention achieves the above object by constructing a projection screen by arranging and combining a lenticular lens, a diffraction grating and a Fresnel lens in this order.

The diffraction grating may be formed on a transparent plastic substrate.

The diffraction grating may have a grating pattern.

Further, the thickness T of the plastic substrate is
The relationship of T ≧ P / tan θ may be satisfied, where P is the pitch of the Fresnel lens with respect to the first-order diffraction angle θ of the diffraction grating.

Furthermore, the diffraction grating is multi-faced with a plurality of small patterns, and each small pattern is shared by adjacent small patterns in accordance with a normal distribution so that the boundaries thereof are inconspicuous. May be included.

[0021]

[Operation and effect] When a diffraction grating is used as a diffusion plate arranged between a lenticular lens and a Fresnel lens, its characteristics can be freely selected, and light is not diffused in an unnecessary direction. Also, the light loss is small.

According to the second aspect, since the diffraction grating is formed on the transparent plastic substrate, there is an advantage that it is convenient for mounting due to the compatibility of the physical properties with the lenticular lens and the Fresnel lens.

According to the third aspect, since the pattern on the grating is used as the diffraction grating, the diffusion direction is limited to one point on the vertical and horizontal gratings, which is convenient for diffusing the LCD dot pattern. ..

According to the fourth aspect, when the thickness of the plastic substrate on which the diffraction grating is formed is designed so as to satisfy the above equation, the distance between the lenticular lens, the diffraction grating and the Fresnel lens is constant and necessary. Can be kept at a value.

With the current technology, it is impossible to expose a pattern at once to a large area such as a projection screen, and it is necessary to divide the pattern into several small patterns, but at this time, If there is a slight positional error at the boundary of each small pattern, the image quality will deteriorate.

According to a fifth aspect of the present invention, each small pattern has a lattice pattern which is shared with an adjacent small pattern according to a normal distribution so that the boundary thereof is inconspicuous, and adjacent patterns are exchanged and connected to each other. You can make your eyes less noticeable. Further, since the number of dots to be exchanged is set according to the normal distribution, the obtained pattern can have a reliable reproducibility.

[0027]

Embodiments of the present invention will be described below with reference to the drawings.

In this embodiment, as shown in FIG. 1, a projection screen 10 is provided with a Fresnel lens 12, a transparent plastic substrate 16 on which a diffraction grating 14 is formed, and a lenticular lens 18 from the light incident side. It is configured by combining the arrangements in order.

The projection screen 10 is
As shown in FIG. 2, the image formed by the LCD panel 20 is used so as to be projected from the Fresnel lens 12 side via the projection lens 22.

The diffraction grating 14 is formed on the plastic substrate 16 as follows.

First, chrome is patterned by photolithography on a glass substrate having a flat surface as a diffraction grating in which rectangles having a pitch of 70 μm are arranged, and the chrome surface is flattened by mirror-polishing.
The diffraction grating 14 is obtained with a uniform thickness of 0 nm.

Next, a UV (ultraviolet curing) resin 24 containing urethane acrylate as a main component is applied on the diffraction grating 14, and the plastic substrate 16 made of an acrylic plate having a thickness of 3 mm is loaded and nipped from above. While UV resin 24
To cure. As a result, the diffraction grating 14 integrated with the plastic substrate 16 is obtained.

The diffraction grating 14 integrated with the obtained plastic substrate 16 is arranged between the Fresnel lens 12 and the lenticular lens 18 with the diffraction grating surface facing the Fresnel lens 12 side, as shown in FIG.

Here, the thickness T of the plastic substrate 16 satisfies the following equation, where P is the pitch of the Fresnel lens 12 with respect to the first-order diffraction angle θ of the diffraction grating 14.

T ≧ S = P / tan θ (2)

That is, as described above, in order to diffuse the light emitted from the Fresnel lens 12, the Fresnel lens 1
This is possible when the gap S between the 2 and the lenticular lens 18 is larger than the numerical value given by the above-mentioned equation (1), and the thickness T may be S or more.

As a result, the moire generated between the pixels of the LCD, the lenticular lens 18 and the Fresnel lens 12 is greatly reduced.

Next, the patterning of the diffraction grating on the glass substrate will be described.

According to the current technology, it is practically impossible to expose a pattern to a large area such as a projection screen at once, and it is necessary to divide the pattern into several small patterns for exposure.

In this case, the boundaries of the small patterns are conspicuous even with a slight positional error. Therefore, in this embodiment, the patterns are exchanged with each other between adjacent small patterns so that the joints are conspicuous. I'm losing.

That is, first, in the first step of creating a grid pattern, as shown in FIG. 3, the number of dots to be exchanged first is set according to a normal distribution or a target distribution function.

Next, as a second step, replacement is performed in the vertical direction as shown in FIG.

For this, the smallest numerical value congruent with the numerical value obtained by selecting one numerical value that is prime to the number of dots in the vertical direction and adding that numerical value to the initial value. It can be realized by adopting an object as the vertical mapping position.

As a third step, as shown in FIG. 5, the phase in the vertical direction with respect to the horizontal direction is obtained by the same method as the shift amount, and by shifting the phase, a pattern in which the seam is not conspicuous can be obtained. it can.

In the pattern thus obtained, the exchange amount of the boundary can be made to follow a predetermined statistic, and since random numbers are not used, reliable reproducibility can be obtained.

In this embodiment, the diffraction grating as the diffusing plate has its characteristics freely selected, there is no diffusion in an unnecessary direction, and there is no light loss due to collision of the passing light and the diffusing agent. Since there is no moiré, it is possible to reduce moire without increasing the pitch of the lenticular lens or Fresnel lens with high definition and without lowering the image resolution.

In general, the diffraction image produced by the aperture plane on the virtual screen when the diffraction grating is illuminated with plane waves is such that the light amplitude distribution of the aperture plane (Z = 0) is G (X, Y) on the virtual screen ( If the optical amplitude distribution of the diffraction image of Z) is U (ξ, η),

[0048]

[Equation 1] Given in.

Therefore, if a grating pattern is used as the diffraction grating, the diffusion direction is limited to one point on the vertical and horizontal gratings, which is convenient for diffusing the LCD dot pattern.

Further, in the above-described embodiment, since the diffraction grating 14 having a fine grating pattern is formed on the plastic substrate 16 by using the UV resin 24, the production is easy and the productivity is improved. There is.

In the above embodiment, the diffraction grating 14
Is formed on the plastic substrate 16 via the UV resin 24, but the present invention is not limited to this and may be formed on, for example, an EB curable resin. The pattern of the diffraction grating may be directly formed on the substrate 16.

Further, the diffraction grating 14 may be formed by promixy exposure (projection exposure) using a stepper or the like. In this case, it is possible to blur the boundary portion when the mask image is attached to multiple surfaces, and thus the pattern replacement work as in the embodiment is not necessary.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a projection screen according to the present invention.

FIG. 2 is a schematic cross-sectional view showing an example of use of the projection screen according to the embodiment in a projection television.

FIG. 3 is a plan view showing a first step of patterning the diffraction grating of the above embodiment.

FIG. 4 is a plan view showing the second step.

FIG. 5 is a plan view showing the third step.

[Explanation of symbols]

 10 ... Projection screen, 12 ... Fresnel lens, 14 ... Diffraction grating, 16 ... Plastic substrate, 18 ... Lenticular lens, 20 ... LCD panel, 22 ... Projection lens, 24 ... UV resin.

Claims (5)

[Claims] 1. A projection screen in which a lenticular lens, a diffraction grating and a Fresnel lens are arranged and combined in this order. 2. The projection screen according to claim 1, wherein the diffraction grating is formed on a transparent plastic substrate. 3. The projection screen according to claim 1, wherein the diffraction grating has a grid pattern. 4. The thickness T of the plastic substrate according to claim 2, which satisfies the relationship of the following equation when the pitch of the Fresnel lens is P with respect to the first-order diffraction angle θ of the diffraction grating. A projection screen featuring. T ≧ P / tan θ 5. The diffraction grating according to claim 1, wherein the diffraction grating is multi-faced with a plurality of small patterns, and each small pattern is shared by adjacent small patterns according to a normal distribution. A projection screen characterized by having a pattern.