KR20010020042A - Projective Screen of Rear Projection Display Apparatus - Google Patents

Abstract

PURPOSE: A projection screen of a rear projection display device is provided to reduce a difference of luminance between a center part and peripheral parts of a screen by increasing light amounts emitted from the peripheral parts by amending optical shafts of respective cylindrical lenses to face to views in front of the screen. CONSTITUTION: A projection screen of a rear projection display device includes a lens array, in which a plurality of cylindrical lenses(52) form a lenticular lens(50) and optical shafts(54) connecting centers of light incident surfaces and light emitting surfaces of the cylindrical lenses are facing views, and light absorbing layers(56) are formed inwardly than the light emitting surfaces for preventing reduction of optical view angles, wherein the centers of the light emitting surfaces are amended in positions toward a center of the screen by different amounts in proportion to distances from the screen center to the lenses.

Description

Projection Screen of Rear Projection Display Apparatus

The present invention relates to a projection screen of a rear projection display device, and more particularly, to a projection screen of a rear projection display device to reduce the luminance difference between the center and the peripheral portion of the screen.

Recently, in accordance with the demand for large screen and high image quality, a projection type display device that uses a projection lens to enlarge and project a small image to realize a desired size image on a large screen has been rapidly spreading. Projection-type display devices are divided into a front projection method for displaying a desired image by projecting a light beam onto the front of the screen and a rear projection method for displaying a desired image by projecting the light beam to the back of the screen according to the way the image is projected on the screen. As a representative example of a projection display device using a rear projection method, a projection television (hereinafter referred to as a “projection TV”) may be mentioned.

1A and 1B illustrate front and side internal structures of a general projection TV using a rear projection method, respectively. Referring to FIGS. 1A and 1B, a projection TV includes an image generating means 20 for realizing an image, a projection lens system 22 for enlarging and projecting the implemented image, and an image projected from the projection lens system 22. A reflector 26 for reflecting the image beam toward the projection screen 24 and a projection screen 24 for receiving and displaying the image beam reflected by the reflector 26 are provided.

The digested image implemented internally by the image generating means 20 to correspond to the image signal is enlarged through the projection lens system 22 and then transmitted to the reflector 26 in the form of a beam. The image beam reflected by the reflector 26 is projected on the rear surface of the projection screen 24 to be displayed in a large screen. In the projection TV, a cathode-ray tube (CRT) or a liquid crystal display panel (LCD) is mainly used as the image generating means 20 for realizing a fire image. The projection lens system 22 includes a plurality of lenses in order to enlarge the image to a desired magnification. The projection screen 24 serves to spread the image beam in the horizontal and vertical directions so that the enlarged image is easily seen in the viewing direction of the viewer.

In such a rear projection display device, components such as an image generating means, a projection lens system, and a projection screen are designed so that an image displayed on the projection screen is displayed with the best image quality from the viewer's point of view. For each company that manufactures projection display devices, the general design standard for viewers is 3 meters from the front of the screen. This is the point at which viewers watching TV are most commonly located. In the conventional rear projection display device designed according to this standard, one of the major problems in terms of image quality is that the luminance difference between the image displayed at the center of the projection screen and the image displayed at the peripheral edge portion is extreme. In other words, the brightness of the periphery of the screen is sharply reduced compared to the center of the projection screen from the viewer's point of view. One of the causes of this problem is the peripheral edge of the incident surface as compared to the amount of light incident on the central portion of the incident surface in the course of the incident image beam generated from the image generating means 20 incident on the incident surface of the projection lens system 22. This is because the amount of light incident to the negative is relatively small. This problem is more serious in a CRT projection TV using a cathode ray tube (CRT) as the image generating means 20 which emits a uniform amount of light in any direction. This problem arises when a liquid crystal display panel (LCD) having some directionality and emitting light beams is used as the image generating means 20, so that light beams can be incident on the incident surface of the projection lens system 22 with a more even distribution. Somewhat relaxed. However, in addition to these causes, another problem causing the difference in luminance between the center and the peripheral portion of the projection screen 24 in the conventional rear projection display device may be a problem in the lens structure of the conventional projection screen 24. 2 and 3, the problem of the lens structure of the conventional projection screen 24 will be described.

2 is a perspective view illustrating a structure of a general projection screen used in a conventional rear projection display device. The projection screen 24 includes a Fresnel lens 30 for focusing the light beam enlarged in the projection lens system 22 and a lenticular lens for evenly spreading the light beam focused by the Fresnel lens 30 in the direction of the viewer. 32 is constituted. The lenticular lens 32 is formed with a plurality of cylindrical lenses 34 side by side in the vertical direction. Between the exit surfaces of each of the cylindrical lenses 34, a light absorption layer 36 is formed to protrude. The light absorbing layer 36 absorbs external light flowing from the outside to improve the contrast of the image displayed on the projection screen.

3 is an enlarged cross-sectional view of the lenticular lens illustrated in FIG. 2 to explain a problem of luminance difference in a conventional projection screen. As shown in the drawing, in the lenticular lens 32 of the conventional projection screen 24, the optical axis 40 connecting the entrance plane center A and the exit plane center B for each cylindrical lens 34 constituting the same. ) Are all parallel to the screen center axis 42. For each cylindrical lens 34, the light beam exiting to the outside through the exit surface proceeds in a uniform distribution around the optical axis 40. Accordingly, the viewer located in front of the screen has a smaller amount of light transmitted from the periphery of the screen than the amount of light transmitted from the center of the projection screen. Thus, from the viewer's point of view, the luminance difference is felt by the difference in the amount of light transmitted from the center and the periphery of the projection screen.

Accordingly, an object of the present invention is to provide a projection screen of a rear projection display device in which the luminance difference between the center and the peripheral portion of the screen is reduced.

1A and 1B show the front and side internal structures of a typical projection television using the rear projection method, respectively.

2 is a perspective view showing the structure of a projection screen used in a conventional rear projection display device.

3 is an enlarged cross-sectional view of the lenticular lens illustrated in FIG. 2 to explain a problem of luminance difference in a conventional projection screen.

4 illustrates a cross-sectional structure of a lenticular lens used for a projection screen of a rear projection display device according to a first embodiment of the present invention.

FIG. 5 is an enlarged cross-sectional view of a cylindrical lens unit positioned at a periphery of a screen in a lenticular lens used in a projection screen of a rear projection display device according to a second embodiment of the present invention; FIG.

<Description of the code | symbol about the main part of drawing>

20: image generating means 22: projection lens system

24: projection screen 26: reflector

30: Fresnel lens 32,50: lenticular lens

34,52,60 Cylindrical lens 36,56 Light absorbing layer

40,54,62: optical axis 42: screen center axis

In order to achieve the above object, the projection screen of the rear projection display device according to the present invention includes a lens array in which optical axes connecting the center of the entrance face and the center of the exit face toward the viewer.

Other objects and features of the present invention in addition to the above object will be apparent from the description of the embodiments with reference to the accompanying drawings.

Hereinafter, exemplary embodiments of the present invention will be described with reference to FIGS. 4 to 5.

4 is a diagram illustrating a cross-sectional structure of a lenticular lens used in a projection screen of a rear projection display device according to a first embodiment of the present invention. In the present invention, in order to correct the luminance difference between the center and the peripheral portion of the projection screen, the center of the exit surface of each cylindrical lens 52 constituting the lenticular lens 50 of the projection screen by a predetermined distance toward the center of the screen Let's do it. That is, in each cylindrical lens 52 as shown in the figure, the exit face center is moved from the conventional position B toward the screen center axis 42 in a state where the position of the entrance face center A is fixed. Move by. The values of are varied depending on the distance from the screen center axis 42 of the cylindrical lens 52. The position of the new exit face center moved toward the screen center axis 42 is indicated by B '. Thus, the optical axes 54 connecting the entrance plane center A and the exit plane center B 'of each cylindrical lens 52 arranged on the projection screen are directed to the viewer's direction. In addition, in the conventional structure, the light absorbing layer is protruded, but in the present invention, the light absorbing layer 56 is formed inside the exit surface of each cylindrical lens 52 to solve the problem of narrowing the wide viewing angle. Other structural features, including Fresnel lenses, are the same as the conventional projection screen structure shown in FIG.

When the optical axes 54 of all the cylindrical lenses arranged on the screen are directed toward the viewer, a substantial amount of the light beams exiting from each exit surface is formed in a uniform distribution about the optical axis 54. Will proceed. In particular, the amount of light traveling from the periphery of the projection screen toward the viewer becomes larger than in the conventional case. Accordingly, when viewed from the viewer reference position in front of the screen, the difference between the amount of light transmitted from the center of the projection screen and the amount of light transmitted from the peripheral portion is reduced as compared with the conventional case. As a result, the luminance difference between the center and the periphery of the projection screen felt by the viewer can be reduced.

On the other hand, the angle formed by the screen center axis 42 and the line segment connecting the viewer reference position at the front of the projection screen by a reference distance ι and the incident surface center A of the specific cylindrical lens 52 located at the periphery of the screen are formed. If θ, as shown in Fig. 4, it is preferable that the optical axis 54 is directed toward the viewer position by setting the correction angle of the optical axis 54 at the same angle θ in the cylindrical lens. In this case, the luminance difference between the center and the periphery of the projection screen felt by the viewer can be minimized. The correction angle of the optical axis 54 in each cylindrical lens 52 is the position correction amount at the center of the exit plane. Depends on. In the present invention, the position correction amount by an amount proportional to the distance (x) away from the screen center axis 42 of each cylindrical lens 52 Adjust the size of the. If the distance between the center of the incident surface of the cylindrical lens located in the center of the screen and the viewer reference position in front of the screen is ι, and the distance from the screen center axis 42 of the specific cylindrical lens located near the screen is x, it can be seen in the drawing. As you can see Becomes Here, if the optical axis of the cylindrical lens is to be corrected by θ, the thickness of the lenticular lens 50 is t, so the position correction amount at the center of the exit surface of the cylindrical lens is t. Is determined by the following equation (1).

As can be seen from Equation 1, the position correction amount of the exit face center is a function proportional to the distance away from the screen center axis 42 of the cylindrical lens. As the distance between the cylindrical lens and the screen center axis 42 increases, that is, the cylindrical lens positioned at the periphery of the screen increases the position correction amount of the center of the exit plane so that all the optical axes 54 face the viewer. It is desirable to.

FIG. 5 is an enlarged cross-sectional view of a cylindrical lens unit positioned at a periphery of a screen in a lenticular lens used in a projection screen of a rear projection display device according to a second exemplary embodiment of the present invention. According to the second embodiment of the present invention, as in the case of the first embodiment of the present invention, the center of the exit face of the cylindrical lens 60 located at the periphery of the screen is toward the screen center part. As shown in the drawings, the entrance and exit surfaces of the cylindrical lens 60 are rotated by a predetermined angle. That is, the incident surface of the cylindrical lens 60 is rotated by a predetermined angle toward the viewer with the incident surface center A as the axis. Further, the exit face of the cylindrical lens 60 is rotated by a predetermined angle in a direction opposite to the direction of rotation of the entrance face with the axis of the exit face center B 'as the axis. Position correction amount in the center of exit surface Equation 1 is set to be proportional to the distance away from the screen center axis of the cylindrical lens. It is preferable to set the angle of rotation of the incident surface and the exit surface at an angle of correction of the optical axis 54 to theta or a similar angle.

As described above, when the optical axis 62 of each cylindrical lens is directed toward the viewer and the incident surface and the exit surface of the cylindrical lens 60 are rotated, the incident surface and the exit surface as shown in FIG. The light beam is refracted more toward the viewer than when not rotated. That is, the amount of light traveling toward the viewer from the periphery of the screen is further increased. Accordingly, when viewed from the viewer reference position in front of the screen, the difference between the amount of light transmitted from the center of the screen and the amount of light transmitted from the periphery of the screen is further reduced. As a result, the luminance difference between the center and the periphery of the screen felt by the viewer can be further reduced.

As described above, in the projection screen of the rear projection display device according to the present invention, the optical axes of the cylindrical lenses included in the lenticular lens constituting the projection screen are directed from the peripheral portion of the screen by directing the optical axes of the cylindrical lenses toward the viewer located in front of the screen. The amount of light traveling in the direction is increased compared to the conventional. Accordingly, the difference in the amount of light transmitted from the center and the peripheral portion of the screen to the viewer located in front of the screen, respectively, is reduced, and the luminance difference between the center and the peripheral portion felt by the viewer is reduced.

Those skilled in the art will appreciate that various changes and modifications can be made without departing from the technical spirit of the present invention. Therefore, the technical scope of the present invention should not be limited to the contents described in the detailed description of the specification but should be defined by the claims.

Claims (4)

And a lens array formed so that optical axes connecting the center of the entrance face and the center of the exit face toward the viewer. The method of claim 1, And the center of the exit face of each lens constituting the lens array is position-corrected toward the center portion of the projection screen. The method of claim 2, And a position correction amount at the center of the exit surface is differentially set to be proportional to a distance away from the center of the projection screen of each of the lenses. The method of claim 1, The incidence planes of the lenses constituting the lens array are rotated to face the viewer with respect to the incidence plane center and the emission plane is rotated in a direction opposite to the incidence plane around the emission plane center. Characterized in a projection screen of a rear projection display.