JPH05333437A - Rear projection television - Google Patents

Abstract

PURPOSE:To make the brightness of the screen uniform and reduce a color irregularity by laminating a lenticular lens, a circular Fresnel lens, and a linear Fresnel lens one over another and making the lens surface of the linear Fresnel lens aspherical. CONSTITUTION:The screen 1 has the lenticular sheet 2 and also has the circular Fresnel lens 3 laminated on its reverse side and the linear Fresnel lens 4 superposed on the reverse side of the circular Fresnel lens to have three-piece constitution. The linear Fresnel lens 4 has horizontal linear projections which horizontally run; and a flat surface 6 is formed as its one surface and a lens surface 5 is formed on the opposite surface while having saw-tooth section. Those horizontal linear projections are formed to control the up-down travel direction of light beams which are made incident on the screen 1. The light beams are directed to the optimum position of the eye of an observer through the linear Fresnel lens 4; and the brightness of the entire screen is made uniform and the color irregularity is reduced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a rear projection television for transmitting light rays from a projection source from the back side of a screen to form an image on the screen.

[0002]

2. Description of the Related Art Generally, as shown in FIG. 9, a rear projection television has a casing 50, a projection source 51 is provided obliquely below the casing 50, and a reflecting mirror is provided obliquely above the projection source 51. 52 is inclined, and the light rays reflected from the reflecting mirror 52
The projection is performed after the screen 53 provided on the entire surface of 0. As shown in FIG. 10, the screen 53 is composed of one lens 54, and a circular Fresnel lens surface 54a is formed on one side of the lens 54 and a lenticular lens surface 54b is formed on the other side thereof. Further, instead of the one-piece screen such as the lens 54, a two-piece screen may be formed as shown in FIG. That is, the two-element lens 55 may include a lenticular lens sheet 56 and a circular Fresnel lens 57.

[0003]

In such a rear projection television set, as shown in FIG.
The light beam emitted from the lens 60 of the above-mentioned lens passes through the screen 53 and is emitted in a substantially horizontal direction. From the eyes v of the viewer, as shown in FIG. There was a defect that C looked darker than the central part. In order to achieve the uniformity of the brightness of the screen as described above, the following directions have been considered, but each has disadvantages. That is, in the case of the method of converging light by increasing the lens power of the circular Fresnel lens, this method has a drawback that the difference between the lens transmittances of red and blue becomes large and color unevenness occurs. Further, as another method, there is a method in which an aperture is set in a projection lens. This method has a drawback that the brightness is uniform but the screen is dark as a whole. As another method, there is a method of brightening the peripheral part by electrical adjustment,
This method has a drawback in that the electric circuit becomes complicated and the cost is increased.

In view of the above points, an object of the present invention is to provide a projection television in which the screen brightness is uniform.

[0005]

SUMMARY OF THE INVENTION The present invention is a rear projection television for projecting light rays from a projection source onto a screen from the rear side, wherein the screen has a lenticular sheet, a circular Fresnel lens and a linear Fresnel lens superposed on each other. The linear Fresnel lens is composed of three lenses, and the lens surface of the linear Fresnel lens is an aspherical surface.

[0006]

The lens surface of the linear Fresnel lens provided with the horizontal line has an aspherical characteristic so that the light rays in the vicinity of the upper and lower ends of the screen are formed so as to be directed toward the center of the screen. The light rays emitted from the source are directed by the linear Fresnel lens in the direction of the optimum position of the observer's eyes (in the case of 40 inches, a position 3 m ahead of the screen). Therefore, a relatively large number of light rays from the four corners of the screen enter the observer's eyes, and the brightness of the screen within the frame of the screen does not decrease, resulting in uniform brightness of the entire screen and uneven color. Decrease.

[0007]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. A screen 1 according to the projection television of the present invention has a lenticular sheet 2 as shown in FIG. 1, a circular Fresnel lens 3 is superposed on the back side thereof, and a linear Fresnel lens 4 is superposed on the rear side of the circular Fresnel lens 3 pieces. It is configured. As shown in FIG. 3, the linear Fresnel lens 4 is provided with a horizontal filament that runs in a horizontal direction, one side surface of which forms a flat surface 6, and a lens surface 5 is formed on the opposite side surface thereof.
Has a saw-toothed cross section. By forming a horizontal line on the lens surface 5 in this manner, the screen 1
Controls the vertical direction of travel of light rays incident on.

The arrangement relationship between the circular Fresnel lens 3 and the linear Fresnel lens 4 may be opposite to that of the lenticular sheet 2. That is, as shown in FIG. 2, a linear Fresnel lens 4 as shown in FIG. 3 is provided next to the lenticular sheet 2, and the circular Fresnel lens 3 is superposed on the opposite side of the linear Fresnel lens 4 from the lenticular sheet 2. May be. Further, the lens surface 3a of the circular Fresnel lens 3 and the linear Fresnel lens 4a may be superposed so as to face each other. In addition, the screen having the three-sheet structure configured as described above is used for the projection source 1 as shown in FIG.
A light ray emitted from a lens 11 installed on the front surface of the cathode ray tube 12 of 0 passes through the screen and is then directed toward the center line of the screen 1. That is, the light ray 30 incident on the upper portion of the screen 1 is focused on the F ₁ point on the center line of the screen 1, and the light ray 31 dropped on the lower end portion of the screen 1 is focused on the F ₂ point on the center line of the screen 1. There is. When the observer's eye position is 40 inches, it is said that the distance L = 3 m from the entire screen position is preferable. In this way, if the light rays 30 and 31 passing through the upper and lower ends of the screen are focused in the direction of the center line of the screen, the brightness of the corner portion of the screen 1 becomes brighter when seen from the eyes v of the viewer. The brightness is uniform throughout. Further, this is preferable in order to provide the optimum image quality to a larger number of people as viewed from the viewer of the projection television. When viewed from a distance, the brighter one looks better (the light comes from the upper part)
There is no discomfort. In order to control the light rays in the vertical direction of the screen as described above, the linear Fresnel lens is formed in the shapes shown in 16 and 17 as shown in FIG. That is, the lens surface 4a of the linear Fresnel lens 4 has an aspherical characteristic as a whole. The lens surface 4a is the second lens surface 16, 17, 18
.. 19, and these unit lens surfaces 16, 17, ... 19 form an aspherical surface as a whole (FIG. 8). That is, when these unit lens surfaces 16, 17, ... 19 are continuously connected, it becomes like an aspherical surface 15. A portion 15a of this aspherical surface 15 corresponds to the unit lens surface 16, and a portion 15b is a unit lens. The portion 15c corresponds to the surface 17 and the unit lens surface 18 respectively.
Unit lens surface 1 at the lower end of the linear Fresnel lens 4
The linear tooth angle S _e of 6 is set to be larger than the tooth angle F _c of the upper end thereof, and thus the tooth angle S _e of the lower end of the linear Fresnel lens 4 is set to be larger than the tooth angle S _{c of the} upper end thereof. Then, as shown in FIG. 4, the light ray 31 having dropped on the lower end is focused on the front F ₂ point, and the light ray 30 having dropped on the upper end is focused on the rear F ₁ point. The unit lens surfaces such as the lens surfaces 17 and 18 in the intermediate portion gradually change their tooth angles. The tooth angle of the unit lens surface of the lens surface is set by the following equation in order to obtain the aspherical characteristics.

S = A1 × H + A2 × H ² + A3 × H ³ +
A ⁴ × H 4 + A 5 × C ⁵ + C Further, in this formula, A ₁ to A ₅ and C are constants, and these constants are set as shown in the following table.

[0010]

[Table 1]

Note that, in the above equation H, when the origin O is on the center line of the linear Fresnel lens 4 as shown in FIG. 7, the distance from this origin O is set to H. If the lower limit of the above-mentioned tooth angle coefficient is exceeded, the focal point becomes too distant, and a predetermined amount of light cannot be obtained at the desired position, resulting in color unevenness. Only the part looks bright, which is not desirable. In order to control the light rays 30 and 31 as shown in FIG. 4, the center O of the circular Fresnel lens 3 in FIGS. 1 and 2 may be decentered upward. By decentering the center O of the circular Fresnel lens in this way, the refractive power of the lower lens surface increases and the refractive power of the upper lens surface decreases, so that the lower light ray 31 becomes the upper light ray. It will be focused on the screen side rather than 30.

Further, such a light beam control system can also be applied to a type in which the optical axis of the lens of the projection source 10 is obliquely projected onto the screen 1 as shown in FIGS. That is, as shown in FIG. 6, the light emitted from the projection source 10 is reflected by the reflecting mirror 20 provided above the projection source 10, and the light rays 35 along the optical axis of the lens of the radiation source 10 are directed from the upper side to the lower side of the screen. It is also applied to the type that is projected with an incident angle at.

In the above-mentioned embodiment, the example in which the CRT is adopted is shown, but it goes without saying that the same effect can be obtained even if the liquid crystal is a projector.

[0014]

Since the present invention is constructed as described above,
A screen with uniform color and a uniform brightness,
The image quality is good.

[Brief description of drawings]

FIG. 1 is a diagram illustrating the configuration of a screen according to the present invention.

FIG. 2 is a structural explanatory view of another embodiment of the screen of the present invention.

FIG. 3 is a perspective view of a linear Fresnel lens according to the present invention.

FIG. 4 is an explanatory diagram of a light beam control system of the present invention.

FIG. 5 is an explanatory diagram when the present invention is applied to another embodiment.

FIG. 6 is an internal configuration diagram of the projection television corresponding to FIG. 5 to which the present invention is applied.

FIG. 7 is a side view of the linear Fresnel lens of the present invention.

FIG. 8 is an explanatory view of a state of a lens surface of a linear Fresnel lens according to the present invention.

FIG. 9 is an internal configuration diagram of a conventional rear projection television.

FIG. 10 is a side view of a conventional one-piece screen.

FIG. 11 is a side view of a conventional two-piece screen.

FIG. 12 is a ray control system diagram of a conventional projection television.

FIG. 13 is a front view of a screen of a conventional projection television.

[Explanation of symbols]

 1 ... Screen 2 ... Lenticular sheet 3 ... Circular Fresnel lens 4 ... Linear Fresnel lens 15 ... Aspherical surface 16-19 ... Unit lens surface part

Claims (2)

[Claims] 1. A rear projection television that projects a light beam from a projection source onto a screen from the rear side, wherein the screen is composed of three lenticular sheets, a circular Fresnel lens, and a linear Fresnel lens, and the linear A rear projection television characterized in that the lens surface of the Fresnel lens has an aspherical characteristic. 2. The projection television according to claim 1, wherein the projection light from the upper part of the screen is focused on the rear side of the projection light from the lower part of the screen.