JPH04322202A - Fresnel lens - Google Patents

Abstract

PURPOSE:To offer a screen which has no color unevenness and uniform brightness on the whole. CONSTITUTION:An incidence surface circular Fresnel lens 20 is formed in the inside area of the Fresnel lens 20 and a projection surface circular Fresnel lens 20B is formed in the outside area positioned at the outer periphery of the inside area. When the screen for projection TV is formed with using this Fresnel lens 20, the incidence surface circular Fresnel lens 20A is installed opposite a light source and then reflected light which is generated when the incidence surface at the center part is flat is precluded, so the color unevenness caused by the reflected light is prevented and the loss of light from a non-lens surface which is caused in the presence of the circular Fresnel lens on the incidence surface at the peripheral part is eliminated, so that the screen can be made uniform in brightness on the whole.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is a Fresnel lens, in particular, a Fresnel lens that, when applied to a screen for projection television, can prevent color unevenness on the screen and provide uniform brightness over the entire screen. Regarding.

0002

2. Description of the Related Art Transmissive screens are formed using various transparent or translucent plastic lens sheets (e.g., Fresnel lens sheets, lenticular lens sheets).
It has already been used as a screen for projection television.

[0003] Usually, the Fresnel lenses constituting the above-mentioned screen are of two types: a light entrance circular Fresnel lens in which the lens forming surface is placed on the light source side, and an exit surface circular Fresnel lens in which the lens forming surface is placed on the observation side. Can be divided.

As shown in FIG. 3, the incident surface of the circular Fresnel lens is such that the closer it gets from the center to the periphery of the Fresnel lens 10, the more light enters the non-lens surface N (loss light shown by diagonal lines).
increases, the amount of light at the periphery decreases, and when viewed from the viewing side, the corners of the screen are dark and
The result is a sharp image with a bright hot spot in the center. Also, when downsizing the television (TV) set,
Since the projection distance (distance between the light source and the lens) becomes short, it is necessary to increase the prism angle α, but if the prism angle α is increased in this way, total reflection is likely to occur at the lens surface L.

On the other hand, in the case of a circular Fresnel lens with an exit surface, as shown in FIG. There is no light loss at the periphery, so even for TV sets with a short projection distance, a screen with low reflection loss can be created.

[0006] From this point of view, conventionally, a circular Fresnel lens with a light exit surface has been frequently used in projection TV screens.

However, since the light-emitting surface circular Fresnel lens has a flat light-entering surface, unnecessary reflected light is generated which is reflected in a certain direction from the light-entering surface and returns to the inside of the TV set. This unnecessary reflected light does not pose a particular problem because the unnecessary reflected light can be absorbed by coating the inside of the TV set, excluding the light source such as a CRT (cathode ray tube), with a light-absorbing substance.

[0008]

[Problems to be Solved by the Invention] However, in order to make a TV set smaller and more compact, a mirror that has low reflection loss and is extremely easy to reflect light is placed inside the set to reflect light from the light source. The projection optical path is bent. Since this mirror is quite large, occupying more than half the area of the screen, the reflection of unnecessary light by the mirror may not be negligible.

That is, in a projection TV with a three-tube or one-tube light source, a CRT (light source) 1 is placed at the bottom of the TV set, as shown in FIG.
2 is placed, and the light is incident on the mirror 14 from the CRT 12,
It is designed so that the light reflected by the mirror 14 is incident on the screen 16, and the TV set uses at least one large mirror 14 as described above.

When a circular Fresnel lens on the light exit surface is adopted for the screen 16 of the projection TV having the set design described above, the reflected light from the mirror 14 is received by the flat light entrance surface of the Fresnel lens 18 as shown in FIG. Therefore, unnecessary reflected light is generated at the light incident surface. Tracing this unnecessary reflected light, we find that the light reflected at the periphery of the screen (Fresnel lens) does not go toward the mirror 14, but the light reflected at the center of the screen (indicated by the two-dot chain line) does not go toward the mirror 14.
The light is reflected again by the mirror 14, and part of this reflected light exits from the bottom of the screen, which appears as color unevenness, especially when the light source is a three-tube type.

The present invention has been made to solve the above-mentioned conventional problems, and when applied to a projection TV screen, the screen has no color unevenness and the entire screen can have uniform brightness. , our objective is to provide a Fresnel lens.

0012

[Means for Solving the Problems] The present invention provides a Fresnel lens in which circular Fresnel lenses are sequentially formed from the center of the lens toward the outer periphery. The above object has been achieved by adopting a configuration in which a circular Fresnel lens with a light exit surface disposed on the observation side is formed in an outer region located on the outer periphery of the inner region.

[0013]

[Function] In the present invention, the Fresnel lens is configured such that a circular Fresnel lens is formed on the light entrance surface in the inner region, and a circular Fresnel lens is formed on the light exit surface in the outer region located on the outer periphery of the inner region. By applying the above Fresnel lens to, for example, a projection TV screen, when the entire light exit surface is a circular Fresnel lens, it is possible to prevent unnecessary reflected light that occurs due to the light entrance surface being flat. When the incident surface is a circular Fresnel lens, it is possible to prevent the generation of lost light from the non-lens surface in the peripheral area, so it is possible to prevent the occurrence of color unevenness caused by the above-mentioned unnecessary reflected light, and also to prevent the above-mentioned lost light from occurring. It is possible to prevent brightness in the peripheral area from decreasing due to this.

As a result, by using the Fresnel lens described above, it is possible to form a screen with no color unevenness and uniform brightness as a whole.

Further, in the present invention, the formation ranges of the inner region and the outer region are arbitrarily changed depending on the TV set, since the range in which unnecessary reflected light does not enter the mirror varies depending on the design of the TV set.

[0016]

Embodiment FIG. 1 is an enlarged sectional view of a Fresnel lens according to an embodiment of the present invention, taken through its center.
FIG. 2 is a schematic explanatory diagram showing the action of the Fresnel lens of this example.

As shown in FIG. 1, the Fresnel lens 20 of this embodiment has a light entrance surface circular Fresnel lens 20A in the inner region and a light exit surface circular Fresnel lens 20B in the outer region formed on opposite surfaces. , the non-lens forming surface is flat.

The action of the Fresnel lens of this embodiment will be explained with reference to FIG. 2, which is an explanatory diagram when the Fresnel lens is applied to the screen 16 of a projection TV having the same configuration as that shown in FIG. 5. .

The light source light from the CRT 12 is reflected by the mirror 14 and then enters the Fresnel lens (screen) 20 . A part of the light incident on the central part (inner area) of the screen is reflected by the light entrance surface, but since the light entrance surface is a rough surface made of the circular Fresnel lens 20A, the reflected light is The light is scattered in such a way that it is prevented from heading toward the mirror 14.

As a result, color unevenness on the screen caused by unnecessary reflected light as shown in FIG. 6, which would occur if the light incident surface was flat, is prevented.

[0021] Furthermore, since the peripheral part is the light exit surface circular Fresnel lens 20B, the light incident on the peripheral part (outer region) of the screen is transmitted to the non-lens surface as in the case where the light entrance surface is a circular Fresnel lens. This prevents the incident light from being lost.

Furthermore, the brightness (illuminance) of the light incident from the CRT 12 is bright at the center of the screen and becomes darker as it approaches the periphery. However, in the Fresnel lens of this embodiment, the center portion is the light entrance surface of the circular Fresnel lens 20.
A, the brightness on the center side is slightly darker than when the light exit surface is a circular Fresnel lens, but since the light exit surface is a circular Fresnel lens 20B at the periphery, when the light entrance surface is a circular Fresnel lens. Since there is less light loss compared to , the entire screen can have uniform brightness as a result.

Incidentally, a Fresnel lens in which circular Fresnel lenses are formed on both surfaces is disclosed in Japanese Utility Model Application No. 64-26703. However, in this Fresnel lens, there is a loss of light that enters from the non-lens surface of the incident surface circular Fresnel lens at the periphery, so it is inevitable that the screen becomes darker toward the periphery. Furthermore, the Fresnel lens of this example has approximately the same thickness as a normal single-sided Fresnel lens, but the double-sided Fresnel lens itself has the disadvantage of being thicker and requires thickness accuracy. .

Next, the Fresnel lens of this embodiment will be explained in more detail.

Regarding the Fresnel pitch of the Fresnel lens of this embodiment, the pitch of the light entrance circular Fresnel lens portion in the inner region and the light exit surface circular Fresnel lens portion in the outer region do not necessarily have to be the same, and may be adjusted as necessary. It can be changed as desired.

Furthermore, the switching point between the light entrance circular Fresnel lens section and the light exit surface circular Fresnel lens section is such that when the light is incident almost parallel, the ends of the front and back sides coincide, as shown in FIG. It is better to have However, in cases where the luminous flux is somewhat diverging or converging, in order to prevent the emitted light from becoming discontinuous, all of the light that passes through the area outside the end of the circular Fresnel lens portion of the light entrance surface is emitted. The switching point may be shifted as appropriate so that the light enters the surface circular Fresnel lens section.

Furthermore, the focal length of the Fresnel lens is such that the outgoing light is 6 m from the observation side from the parallel light, as is generally adopted.
In addition, in order to minimize the loss of light amount at the center, from the light entrance surface of the circular Fresnel lens section at the center,
It may be designed so that parallel light is emitted and the light emitted from the outer circumference is focused on a predetermined position on the observation side.

Next, the Fresnel lens of this embodiment will be explained using a specific example.

[0029] An aluminum material was cut using a lathe to create a mold (20 mm) of a light entrance surface circular Fresnel lens designed to emit parallel light up to a distance of 200 mm from the center.
The outer periphery is flat from 0mmR) and 200mm from the center.
We created two molds for a circular Fresnel lens with a light exit surface designed to have a flat surface up to mmR and a focal length of 10 m at the outer periphery.To align these molds, we made two molds at the four corners of each mold. A through hole was drilled to allow the mold to be aligned vertically.

Next, place a vinyl chloride gasket (thickness: 3 mm) around the four sides of one of the molds, place the other mold on top of it, and then insert the gasket into the through hole for positioning. The bolts were inserted and fixed with nuts to align the top and bottom of the mold.

Next, a part of the gasket is pulled to form a gap, and from the gap, 0.5% of AIBN (azoisobutyronitrile) as an initiator and DB as a mold release agent are added.
M mixed with 5% P (di-n-butyl phthalate)
After injecting the MA (methyl methacrylate) syrup, return the gasket to its original state to seal it.

[0032] After that, the above mold was heated in an oven at 75° for 3
The MMA syrup was then cured at 130° for 30 minutes, and after cooling, the cured product was taken out of the mold to form the Fresnel lens of this example.

When the Fresnel lens of this example formed as described above is applied to the projection TV screen 16 shown in FIG. 5, a screen with no color unevenness and uniform brightness over the entire screen is formed. I was able to do that.

[0034]

As explained above, according to the present invention, it is possible to form a screen with no uneven color and uniform brightness as a whole.

[Brief explanation of the drawing]

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

FIG. 2 is a schematic explanatory diagram showing the operation of the embodiment.

FIG. 3 is a schematic explanatory diagram showing the action of a circular Fresnel lens on the light entrance surface.

FIG. 4 is a schematic explanatory diagram showing the function of a circular Fresnel lens with a light exit surface.

FIG. 5 is a schematic configuration diagram showing an example of a projection TV.

FIG. 6 is a schematic explanatory diagram showing the operation of the projection TV.

[Explanation of symbols]

N...non-lens surface, L...lens surface, 10, 18, 20...Fresnel lens, 12...CRT, 14...mirror, 16...screen, 20A...light entrance surface circular Fresnel lens, 20B...light exit surface circular Fresnel lens.

Claims (1)

[Claims] Claims: 1. A Fresnel lens in which circular Fresnel lenses are sequentially formed from the center of the lens toward the outer periphery, wherein a light entrance surface circular Fresnel lens is formed on the light entrance side of the inner region, and the light entrance surface circular Fresnel lens is formed on the outer periphery of the inner region. A Fresnel lens characterized in that a circular Fresnel lens with a light exit surface disposed on the observation side is formed in the outer region of the lens.