JP3310460B2 - Rear projection screen - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear projection screen used in a transmission type projection television.

[0002]

2. Description of the Related Art A transmission type projection television (hereinafter, referred to as a rear projection type TV) enlarges and projects an optical image from a CRT or a liquid crystal panel onto a rear projection type screen by a projection lens to obtain a large-screen image. Video display device.

FIG. 7 shows a configuration example of such a rear projection type TV. As shown in the figure, in a rear projection type TV, generally, CRs of three primary colors of red R, green G, and blue B are used.
The optical image from T1 is enlarged by the projection lens 2 and formed on the rear projection screen 3. Here, the rear projection type screen 3 has a Fresnel lens 4 for condensing light projected from the projection lens 2 in the direction of the observer, and a viewing angle by dispersing the light from the Fresnel lens 4 in the horizontal and vertical directions. Diffuser 5 such as lenticular lens sheet
And a set of two sheets.

The Fresnel lens 4 is a convex lens. As shown in FIG. 8 (FIG. B), the lens surface of the convex lens (FIG. (A)) is divided into concentric circles and arranged on a flat plate. (FIG. 1B). Therefore, on the lens surface of the Fresnel lens 4, there is a surface called a rise surface 4y formed between the divided Fresnel surfaces and a Fresnel surface 4x that is a lens surface of the convex lens. Then, as shown in FIG. 9, the angle between the flat surface of the Fresnel lens 4 and the Fresnel surface 4x is called a Fresnel angle η, and the angle between the normal to the Fresnel lens 4 and the rise surface 4y is the rise angle θ. Called.

[0005] The Fresnel lens is usually produced by a 2P method, a press method, or the like. In this case, a metal plate or the like obtained by cutting with a lathe is used. Mold cutting is about 3
This is performed using a cutting tool having a blade angle of 0 ° to 90 °. At this time, as shown in FIG. 12, the portion y of the mold 7 through which the tip of the cutting tool 6 passes becomes the rise surface of the Fresnel lens, and the cutting surface x in the direction of cutting the cutting tool 6 becomes the lens surface of the Fresnel lens. In a range where the Fresnel angle η is small and the sum of the Fresnel angle η and the cutting edge angle of the cutting tool 6 is 90 ° or less, the Fresnel angle η is determined by the direction of the surface of the cutting tool 6, and the rise angle θ is a direction in which the cutting tool 6 advances. Therefore, the Fresnel angle η and the rise angle θ are independently determined. On the other hand, when the Fresnel angle η increases, the die 7 is cut by both sides of the cutting edge of the cutting tool 6, and the rise angle θ increases with the increase in the Fresnel angle η. For example, when using a cutting tool with a cutting edge angle of 50 °, if the Fresnel angle η exceeds 40 °, the rise angle θ ≧ (Fresnel angle η + the cutting edge angle 50 °) −90 °.

FIG. 1 is a diagram showing the relationship between the radius of the Fresnel lens and the rise angle. The conventional Fresnel lens has a region having a constant rise angle θ determined by the cutting angle of the cutting edge, as in case a, and a peripheral region in which the rise angle θ increases as the Fresnel angle η increases. ing. Note that the reason why the rise angle θ is approximately 1 ° in the region where the rise angle θ of the case a is constant is to enable the molded product to be easily removed from the mold.

In recent years, the rear projection TV shown in FIG. 7 has been required to be thinner, and accordingly, the distance between the projection lens 2 and the rear projection screen 5 has been shortened. In this case, to secure the brightness of the screen, C
The sizes of RT1 and the projection lens 2 are not changed. Accordingly, the angle (hereinafter, referred to as a concentration angle) ε between the optical axes of the red R and blue B projection systems with respect to the optical axis of the projection system that projects green G becomes large, and the color tone varies depending on the position of the screen to be observed. The problem of the decline of the White Uniformity has arisen. For example, in the case of a TV set with a diagonal angle of 40 inches and a large convergence angle, when an all white signal is input and the screen is observed from a distance of about 3 m in front of the rear projection type screen, as shown in FIG. There is a problem that yellow and cyan colorings are observed in an intermediate region having a radius of about 200 to 300 mm.

Further, when an all white signal is input to the rear projection type TV and the screen is observed from about 30 ° above at a position 1.5 m in front of the rear projection type screen, as shown in FIG. In the center region of about 150 mm, coloring called a color cone was observed, and there was a problem that the quality of the screen was deteriorated.

[0009]

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems of the prior art, and is intended to solve both the coloring that occurs in the intermediate area of the rear projection screen and the coloring that occurs in the central area. The purpose is to eliminate.

[0010]

According to the present invention, in order to achieve this object, in a rear projection screen comprising a Fresnel lens and a light diffusing plate, the rise angle of the central region of the Fresnel lens is increased in the middle region. A rear projection screen characterized by being smaller than a corner is provided. In particular, the present invention provides such a rear projection type screen in which the rise angle from the central region to the intermediate region of the Fresnel lens is gradually increased.

Further, in such a rear projection type screen, the center area of the Fresnel lens is in a range of 1/4 to 1/3 from the center of the diagonal of the rear projection type screen, and the intermediate area is outside the center. Provide what is an adjacent area.

The rear projection type screen of the present invention comprises a Fresnel lens and a light diffusing plate such as a lenticular lens sheet. As the Fresnel lens, in the central region, of the light incident on the Fresnel lens, total reflection occurs at the rise surface. So that the light exiting the Fresnel surface after
The rise angle is determined to be small, and in the intermediate region adjacent to the outside of the center region, the rise of the light incident on the Fresnel surface out of the Fresnel surface out of the Fresnel surface is reduced in comparison with the center region so that the light incident on the rise surface is reduced. It is characterized in that an object having a large angle is used.

The reason for making the rise angle of the Fresnel lens different in accordance with the area of the Fresnel lens is based on the following findings of the present inventors. That is, to analyze the cause of the coloring problem in each of the central region and the intermediate region of the conventional rear projection screen, the present inventors set the screen size to 40 inches, the projection distance to the screen to 730 mm, and the concentration angle ε11. 5 °, taking as an example a rear projection type TV with a distance between the exit pupils of each projection lens of 140 mm,
The optical path of the light incident on the Fresnel lens was examined in detail. In this case, as the Fresnel lens, a lens having a focal length of 660 m at the center, 730 mm at the outermost periphery, gradually increasing from the center to the outermost periphery, and a rise angle changing as in case a of FIG. 1 was used. The results are shown in FIGS.

FIG. 2 shows the angle (light ray angle in the Fresnel lens) between the rays of each color of red R, green G and blue B and the normal line of the Fresnel lens inside the Fresnel lens. It is the one expressed. In the figure, + of the angle indicates the convergence direction, and-indicates the divergence direction. Also, the broken line indicates the rise angle of case a in FIG.

FIG. 3 shows the angles (light beam angles from the Fresnel lens) formed by the light beams of each color of red R, green G, and blue B emitted from the Fresnel lens with the normal line of the Fresnel lens. It is expressed with respect to the distance from the center. Also in this figure, the broken line indicates the rise angle of case a in FIG. From the figure, it can be seen that only the blue B light is emitted in the diverging direction in the entire region of the Fresnel lens.

FIG. 4 shows a 50 mm radius of the Fresnel lens 4.
3 shows the optical paths of light rays of red R, green G, and blue B at the position shown in FIG. From the figure, the B ray is obtained after the rays in the hatched area exit from the Fresnel surface 4x.
It can be seen that it hits the rise surface 4y (hereinafter, this phenomenon is referred to as phenomenon A). Also, it can be seen that the R light beam hits the rise surface 4y before the light beam in the hatched area exits the Fresnel lens (this phenomenon is hereinafter referred to as phenomenon B).

In order to examine the phenomenon A and the phenomenon B in detail, the radius of the Fresnel lens is 25 mm and the radius is 250 mm.
The optical path was traced at the position of mm. The result is shown in FIG.
(Radius 25 mm) and FIG. 6 (radius 250 mm).

FIG. 5 shows that the radius of the Fresnel lens 4 is 25 m.
At the position of m, the R phenomenon is shown as a B phenomenon in which the R ray hits the rise surface 4y before exiting the Fresnel lens.
It can be seen that the light is emitted in the divergent direction at an angle of °. Although not shown, at the left and right target positions with a radius of 25 mm, B
Light rays also exhibit the B phenomenon and emerge in the divergent direction. It is considered that the existence of the light beam emitted in the diverging direction in the central region of the Fresnel lens is the cause of the color cone. Note that, in FIG. 5, the B ray is emitted from the Fresnel surface 4x and then strikes the rise surface y.
Although the phenomenon is shown, after the light enters the Fresnel lens from the rise surface 4y, it is totally reflected by the Fresnel surface 4x. Therefore, it is considered that this B ray does not adversely affect the image.

Further, from FIG. 6, at the position of a radius of 250 mm of the Fresnel lens 4, the R ray does not show the B phenomenon that hits the rise surface 4y before exiting the Fresnel lens, but the B ray does not come from the Fresnel surface 4x. This indicates the phenomenon A, in which the laser light hits the rise surface 4y after the injection.
After hitting y, the light enters the Fresnel lens and exits the Fresnel surface 4x in a diverging direction of 53 °. In addition, the ratio of the B light beam indicating the phenomenon A is considerably increased.
As a result, a considerable amount of the B ray is missing from the rays to be projected from the Fresnel lens onto the screen, and the screen shifts from white to yellow. The resulting color shift is considered to be the coloration that occurs in an intermediate region with a radius of about 200-300 mm from the center of the screen.

As described above, the inventors of the present invention have found that the coloring that occurs in the central area of the screen is caused by the B phenomenon of hitting the rise surface before exiting the Fresnel lens. It has been found that this phenomenon is caused by the phenomenon A, which impinges on the rise surface after being ejected from the surface. Therefore, in the present invention, in the central region of the Fresnel lens, of the light incident on the Fresnel lens, it hits the rise surface before exiting the Fresnel lens, is totally reflected by the rise surface, and exits the Fresnel surface in the divergent direction. The rise angle θ of the Fresnel lens is reduced so as to reduce the amount of light emitted. In the intermediate region of the Fresnel lens, the rise of the Fresnel lens is reduced so that, of the light incident on the Fresnel lens, the light that enters the rise surface after exiting from the Fresnel surface and exits the Fresnel surface again in the divergent direction is reduced. The angle θ is made larger than the central region.

The magnitude of the rise angle determined according to the area of the Fresnel lens depends on the projection distance, the distance between the projection lenses, the refractive index of the Fresnel lens, the focal length of the Fresnel lens, and the like. Is preferably 3 ° or less in the central region of the Fresnel lens, and is preferably larger than 3 ° in the intermediate region. For example, the Fresnel lens used in the present invention has a rise angle of 2 ° or less in a central region thereof and a rise angle of 4 ° or more in a region outside the Fresnel lens, as shown as a case c in FIG. . On the other hand, as shown in case a above,
When the rise angle is set to a constant value of about 1 ° in the central region and the intermediate region, coloring based on the phenomenon A described above easily occurs in the intermediate region of the screen. Also, as shown as case b in FIG. 1, when the rise angle is set to a constant value of about 5 ° in the central region and the intermediate region, coloring based on the phenomenon B easily occurs in the central region of the screen.

In the present invention, when the rise angle of the Fresnel lens is made different between the central region of the Fresnel lens and the intermediate region adjacent to the center region, whether the rise angle is changed discontinuously or continuously. There are no particular restrictions on the variations such as. As shown in FIG. 1 as case c, the rise angle may be changed discontinuously between the central region and the intermediate region, and as shown in case d, the rise angle may be constant in the central region and the intermediate region. The rise angle may be gradually changed at both boundaries, and case e in FIG.
As shown in (1), it may be gradually changed in the entire region from the center to the intermediate region. Generally, as shown in case d or case e, it is preferable to gradually change the rise angle. This can prevent the external light reflected light from appearing discontinuously. In particular, when the image projected on the rear projection screen is dark, it is preferable because the uniformity of the screen can be improved.

In the conventional Fresnel lens shown in the case a of FIG. 1, the rise angle is larger in the peripheral region outside the radius of 275 mm than in the center region. However, the Fresnel lens used in the present invention has It is clearly distinguished from the conventional Fresnel lens in that the rise angle of the intermediate region adjacent to the inside of the region and outside the center region is different from the rise angle of the center region.

A central region in the Fresnel lens;
The intermediate region and the peripheral region are distinguished as follows. That is, the central region refers to a radial region in which there is a light beam angle in the Fresnel lens in which the angle of convergence exists for each of R, G, and B light beams in the Fresnel lens. For example, in FIG. 2, since the R ray is converging in a region within a distance of about 140 mm from the center, a region having a radius of about 140 mm from the center is the central region. The center area defined in this way is generally from 1/4 of the diagonal of the rear projection screen.
Inside of 1/3. Therefore, in general, the diagonal 1
The rise angle of the portion inside / 4 to ３ may be 3 ° or less.

The intermediate area is an area adjacent to the outside of the center area, and when the rise angle between the center area and the area adjacent to the outside of the center area is constant as in case a of FIG.
Of the R, G, and B rays emitted from the Fresnel lens, it refers to a radius area where rays incident on the rise surface exist. For example, in FIG. 3, the distance from the center is about 380 mm.
Since the B ray intersects the broken line (rise angle) at the position, it can be seen that the B ray enters the rise surface after exiting the Fresnel lens in a region inside the B ray. Therefore, outside the radius of about 140 mm and the radius of 380 mm
The area within is the middle area. The peripheral area is outside the intermediate area defined in this way.

On the other hand, in the present invention, the light diffusing plate is not particularly limited, and various lenticular lens sheets and flat plates or flat sheets in which a light diffusing resin is dispersed can be used. For example, as a lenticular lens sheet, a single-layer lens sheet in which lenses are formed on the incident side and the output side of one resin layer, or a multi-layer lens sheet in which the incident side and the output side are formed of separate resin layers, respectively. Any of the lens sheets can be used. Light diffusing particles may be dispersed in these lens sheets, and a light absorbing layer may be provided on the emission side surface.

[0027]

EXAMPLES Next, the present invention will be described specifically with reference to examples.

Embodiment 1 A rear projection type T having a projection distance of 850 mm and a concentration angle of 10 °
As a Fresnel lens for a rear projection type screen used for V, the focal length is 780 from the center to the outermost periphery.
A 820 mm 50-inch Fresnel lens was produced. In this case, the rise angle of the Fresnel lens is as shown in FIG.
, The rise angle in the central region is 1 °, the rise angle in the middle region is 5 °, and the radius is 150
The rise angle was gradually changed at the boundary portion in the range of １７175 mm.

7. This Fresnel lens and peak gain
5 was combined with a lenticular lens sheet to form a rear projection screen, which was attached to a TV set, and an all-white signal was input. The image at that time is 3m in front of the screen
When observed from the position, no coloring as shown in FIG. 10 was observed. Also, 1.5m in front of the screen
Observing the image from 30 ° above the position of FIG.
The color corns shown in FIG.

Comparative Examples 1 and 2 In producing a Fresnel lens, the distribution of the rise angle is shown in FIG.
The rise angle of the center region and the middle region is set to 1 ° as in case a (Comparative Example 1), or the rise angle of the center region and the middle region is set to 5 ° as in Case b (Comparative Example 2).
Otherwise, a rear projection screen was configured in the same manner as in Example 1, attached to a TV set, and an all-white signal was input.
Then, the image at that time was observed from a position 3 m in front of the screen. As a result, the screen using the rear projection type screen of Comparative Example 1 had a radius of 20 mm from the center of the screen.
Yellow and cyan coloring were observed at the positions of 0 to 350 mm. Such coloring was not observed on the screen using the rear projection type screen of Comparative Example 2. Further, when an image was observed from 30 ° above a position 1.5 m in front of the screen, coloring with a color cone was hardly recognized on the screen using the rear projection type screen of Comparative Example 1, but Comparative Example 2 was used. In the screen using the rear projection type screen, strong blue and red colored cones were recognized within a radius of 150 mm from the center of the screen.

[0031]

By changing the rise angle of the Fresnel lens between the central part and the intermediate part, a screen for displaying a uniform and high-quality image can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a relationship between a radius of a Fresnel lens and a rise angle θ in the present invention and a conventional rear projection screen.

FIG. 2 is a diagram showing angles of light rays inside a Fresnel lens with respect to a distance from the center of the Fresnel lens.

FIG. 3 shows the angle of a light beam emitted from a Fresnel lens with respect to a distance from the center of the Fresnel lens.

FIG. 4 is an optical path diagram at a position of a radius of 50 mm of the Fresnel lens.

FIG. 5 is an optical path diagram at a position of a radius of 25 mm of the Fresnel lens.

FIG. 6 is an optical path diagram at a position of a radius of 250 mm of the Fresnel lens.

FIG. 7 shows a rear projection type T using a rear projection type screen.
5 is a general schematic configuration diagram of V. FIG.

FIG. 8 is a sectional view of a Fresnel lens.

FIG. 9 is a partially enlarged sectional view of a Fresnel lens.

FIG. 10 is an explanatory diagram of a colored state of an intermediate region of a conventional rear projection screen.

FIG. 11 is an explanatory diagram of a colored state of a central region of a conventional rear projection screen.

FIG. 12 is an explanatory diagram of a cutting method of a mold for producing a Fresnel lens.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Shinichi Asano 2-28 Kurashiki-cho, Nakajo-cho, Kitakanbara-gun, Niigata Kuraray Co., Ltd. (72) Inventor Takao Kibushi 2-28 Kurashiki-cho, Nakajo-cho, Kitakanbara-gun, Niigata Examiner Koichi Hoshino in Kuraray Co., Ltd. (56) References JP-A-4-296841 (JP, A) JP-A-4-281443 (JP, A) Japanese Utility Model Sho-63-188646 (JP, U) (58) Field (Int.Cl. ⁷ , DB name) G03B 21/62

Claims (5)

(57) [Claims] 1. A rear projection screen comprising a Fresnel lens and a lenticular lens sheet, wherein a rise angle defined as an angle between a rise surface of the Fresnel lens and a normal line of the Fresnel lens corresponds to the center area of the Fresnel lens. A rear projection screen, wherein a rise angle is smaller than a rise angle in an intermediate region of the Fresnel lens. 2. The rear projection screen according to claim 1, wherein the rise angle of the central region of the Fresnel lens is 3 ° or less and the rise angle of the intermediate region is larger than 3 °. 3. The rear projection screen according to claim 1, wherein the rise angle from the central region to the intermediate region of the Fresnel lens is gradually increased. 4. The center area of the Fresnel lens is in a range of 1/4 to 1/3 from the diagonal center of the rear projection screen, and the intermediate area is an area adjacent to the outside thereof.
4. The rear projection screen according to any one of items 1 to 3. 5. A light diffusing plate comprising a flat plate, a flat sheet or a lenticular lens sheet.
4. The rear projection screen according to any one of 4.