JP2002221759A - Projection type display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a projection type display device which can be used for displaying an image with high quality without being affected by peripheral light and which can relatively easily be produced at lower cost. SOLUTION: The projection type display device includes a lens base having arrays of bores which are arranged on a front surface and a rear surface and between the front surface and the rear surface. Each bore is made smaller in the direction from the rear surface to the front surface. A plurality of windows are formed on the front surface and the windows are aligned and communicate with bores, respectively. Light enters the bores from the rear surface of lens base and is subjected to multiple total inner-reflection when transmitted along the bores before the light goes out of the windows of the lens base.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a projection screen,
In particular, it relates to a projection screen that is used to show high quality images that are not adversely affected by ambient light and can be manufactured relatively easily and at lower cost.

[0002]

2. Description of the Related Art A display device incorporates a projection screen for displaying an image. Image quality is generally affected by the construction of the projection screen. Properties often used to determine the quality of an image displayed on a projection screen include contrast, brightness, color, and resolution. Contrast is the difference between the brightest and darkest areas in an image. The greater the contrast, the more clearly image details are visible. The projection screen plays an important role in determining the contrast characteristics of the display device.

Referring to FIG. FIG. 1 shows a Fresnel lens 1
1 shows a conventional back projection screen 1 including a lenticular lens 12 and a diffuser 13. The Fresnel lens 11 is usually placed in front of the light source and optical components of the display device, and on the back is molded a stepped setback and a rounded center to have the optical properties of a thicker lens. . The Fresnel lens 11 makes it possible to emit light rays directly to the observer. The lenticular lens 12 is positioned directly in front of the Fresnel lens 11 and has a convex projection on the back that refracts the light rays, thereby controlling the angle of divergence of the light rays in one direction, and thus the viewing angle of the light. . The diffuser 13 is located immediately in front of the lenticular lens 12 and is made of a translucent material. The diffuser 13 diverges straight light rays so as to obtain a large light viewing angle.

[0004] In this manner, the light beam striking the back surface of the screen 1 is refracted by the Fresnel lens 11 and a parallel light beam extending forward is obtained. Fresnel lens 11
After passing through the light beam, the light beam is then refracted by the lenticular lens 12 to obtain a light beam diverging forward, and this light beam is further diffused by the diffuser 13 to obtain an optimal light viewing angle.

[0005]

Some disadvantages of the above-mentioned conventional back projection screen 1 are described below.

[0006] 1. As the light passes through the three layers of the projection screen 1, it travels different paths under the influence of a plurality of refractions and reflections. In the light beam diffusion stage, the light beams interfere with each other, causing speckle effects and moiré effects that degrade the quality of the image seen on the projection screen 1. In particular, the speckle effect gives the image on the projection screen 1 a grainy appearance, while the Moiré effect gives a new set of periodic patterns at the intersection of two or more original sets of periodic patterns in the image.

[0007] 2. In the conventional projection screen 1, the light intensity is brightest at the center and gradually decreases toward the outer periphery of the projection screen 1. This phenomenon is due to the fact that the light rays reaching the outer periphery of the projection screen 1 are tilted, so that the effective intensity of the light rays at the outer circumference decreases with the inclination. This phenomenon, which is characterized by the cosine θ decay of the light intensity distribution, causes the image to have non-uniform brightness throughout the conventional projection screen 1.

[0008] 3. Ambient light incident on the front of the conventional projection screen 1 is reflected and adversely affects the contrast of an image displayed on the screen. That is, the contrast of the image seen on the conventional projection screen 1 is adversely affected by the state of the ambient light.

4. The conventional projection screen 1 includes three layers having different characteristics and different configurations. In addition, the interface between the three layers must be carefully designed to ensure a specific path of the light passing through the projection screen 1. Therefore, the conventional projection screen 1 is difficult to manufacture and more expensive.

[0010]

SUMMARY OF THE INVENTION Accordingly, the present invention is used to present high quality images that are not adversely affected by ambient light and can be manufactured relatively easily and at a lower cost. It is intended to provide a projection screen.

[0011] The projection screen of the present invention has a front surface, a rear surface,
A lens base having an array of bores extending from the back to the front, each bore being tapered in the direction from the back to the front, a plurality of windows formed in the front, each window being aligned to communicate with a respective bore; And reflective means disposed within the bore for multiple total internal reflection of light entering the bore from the back of the lens base as the light propagates along the bore before exiting the window of the lens base.

[0012] The lens base is preferably formed in such a way as to be able to absorb ambient light at the front of the lens base and thereby increase the contrast.

[0013]

BRIEF DESCRIPTION OF THE DRAWINGS Other features and advantages of the present invention will become apparent from the following description of embodiments, with reference to the accompanying drawings.

FIGS. 2 and 3 show a first embodiment of a projection screen according to the invention, including a lens base 2 and a light guiding medium 3.

The lens base 2 has a front surface, a back surface, and an array of bores 21 extending from the back surface to the front surface. Each bore 2
1 is tapered from back to front and has a rectangular cross section. A plurality of windows 22 are formed on the front surface of the lens base 2,
Each window 22 is aligned to communicate with a respective bore 21. An insertion column 23 is formed adjacent to and between the bores 21. The front surface of the lens base 2 is further provided with a black coating 24 for absorbing ambient light. In another embodiment, the lens base 2 is formed from a black light absorbing material, with the same effect.

In the present embodiment, the light guiding medium 3 is formed of a light transmitting transparent or translucent material having a predetermined refractive index and includes an array of tapered rods 31. Each tapered rod 31 is inserted into each bore 21 from the back of the lens base 2. Each tapered bar 31 has a front end 32 and a rear end 33,
It is tapered from the rear end 33 to the front end 32. Each tapered bar 31 has a rectangular cross-section to be complete in combination with the respective bore 21. Rear end 33 of tapered rod 31
Are connected to each other and are preferably arranged outside the respective bores 21. The tip 32 of the tapered rod 31
It does not enter the window 22 of the lens base 2. In this embodiment, each tapered rod 31 has an outer wall surface provided with a metal coating so as to form the light reflecting layer 34 at the interface between each tapered rod 31 and each bore 21, that is, four side walls. When light is projected from the back of the lens base 2, the light enters the light guide medium 3 at the rear end 33 of the tapered rod 31. Due to the light reflecting layer 34 on the outer wall surface of the tapered rod 31, the light is multiply totally internally reflected when the light propagates along the tapered rod 31. Light exits the tapered bar 31 at the distal end 32 of the tapered bar 31 and subsequently passes through the window 22 of the lens base 2, resulting in an image that is visible from the front of the lens base 2.

In another embodiment, instead of providing a metal coating acting as the light reflecting layer 34 on the outer wall surface of the tapered rod 31, a metal coating can be provided on the inner wall surface of the bore 21 so as to obtain the same effect. is there.

In another embodiment, instead of providing a metal coating on either the outer wall surface of the tapered bar 31 or the inner wall surface of the bore 21, a light reflecting layer as a filler layer is provided between each tapered bar 31 and each bore 21. It is also possible to form 34. The filler layer has a refractive index less than that of the light transmissive material used to form the light guiding medium 3, so that light propagating along the tapered rod 31 is multiple internally reflected. To Total internal reflection is a state in which, when Snell's law is not satisfied, light propagating in a high-speed medium is totally reflected at a boundary between a high-speed medium and a low-speed medium. That is, when light in a medium having a high refractive index reaches a medium having a low refractive index, if the incident angle is greater than the critical angle, the light is totally reflected and returns to the medium having a high refractive index. For example, in the other embodiments described above, there is air acting as a filler layer between each tapered bar 31 and each bore 21. The light-transmitting material for forming the light guide medium 3 includes a filler layer and the respective tapered rods 3.
It is selected to have an appropriate index of refraction to ensure total internal reflection at one boundary.

With respect to the cross-sectional shape of the bore 21 and the tapered bar 31, it will be apparent to those skilled in the art that the cross-sectional shape is not limited to a rectangle. Other shapes, such as circular, oval, or rectangular, can be used to achieve substantially equal results.

FIG. 4 shows a second embodiment of the projection screen of the present invention including a lens base 4 having a front, a back, and an array of bores 41 extending from the back to the front. Each bore 41 is tapered from the back to the front and has a rectangular cross section. A plurality of windows 42 are formed in the front surface of the lens base 4, and each of the windows 42 is aligned so as to communicate with the corresponding bore 41. Each bore 41 has an inner wall surface provided with a metal coating acting as a light reflection layer 43. As in the previous embodiment, a black coating 44 is provided on the front surface of the lens base 4 to absorb ambient light. Alternatively, the lens base 4 can be formed of a black light absorbing material to achieve the same effect.

When the light is projected from the back of the lens base 4, the light enters the bores 41, and due to the presence of the light reflecting layer 43 on the inner wall surface of each bore 41, the light is propagated along the bores 41. Multiple total internal reflections. The light passes through the window 42 and exits the lens base 4, resulting in an image that is visible from the front of the lens base 4.

As in the previous embodiment, the sectional shape of the bore 41 is not limited to a rectangle. Other shapes, such as circular, oval, or rectangular, can also be used to achieve substantially equal results.

FIG. 5 shows a third embodiment of the projection screen of the present invention including a lens base 5, a rear cover plate 6, a front cover plate 7, and a light guide medium 8.

The lens base 5 has a front surface, a rear surface, and an array of bores 51 extending from the rear surface to the front surface. Each bore 5
1 is tapered from the back to the front and has a rectangular cross section. A plurality of windows 52 are formed on the front surface of the lens base 5,
Each window 52 is aligned to communicate with a respective bore 51. As in the previous embodiment, a black coating 53 is provided on the front surface of the lens base 5 to absorb ambient light.

The front cover plate 7 and the rear cover plate 6 are transparent plates, respectively, and respectively seal the front and back surfaces of the lens base 5 so that the front and rear ends of the bore 51 are covered.

In this embodiment, the light guide medium 8 is provided in each of the bores 51.
And is made of a material having a refractive index greater than that of the material used to form the lens base 5 to allow multiple total internal reflection in the bore 51. In particular, as light passes through the back cover plate 6 and into the bore 51, the light undergoes multiple total internal reflection as it propagates along the bore 51. The light exits the lens base 5 through the window 52 and becomes an image visible from the front cover plate 7.

As in the previous embodiment, the sectional shape of the bore 51 is not limited to a rectangle. Other shapes, such as circular, oval, or rectangular, can also be used to achieve substantially equal results.

Some of the advantages of the projection screen of the present invention are as follows.

1. The output light intensity and the viewing angle of the light can be flexibly designed by changing the shape and size of the lens base and the density of the window.

2. As the light propagates along the bore of the lens base, it undergoes multiple total internal reflections, so that random phases and polarizations occur to minimize the presence of speckle effects. Further, since each pixel location on the screen is formed to include a plurality of bores, the occurrence of moiré effects is minimized.

3. The dimensions of the window in the lens base can be varied over the entire projection screen, for example from the center to the outer periphery of the projection screen, providing compensation for the cosine θ attenuation of the light intensity distribution and thus the overall projection screen , The brightness of the image is maintained.

4. Since the ambient light is absorbed at the front of the lens base, the contrast of the image displayed on the projection screen is increased.

5. Since the projection screen of the present invention has a relatively simple configuration, it can be manufactured at a relatively low cost.

Although the present invention has been described in terms of the most practical embodiments, the present invention is not limited to the disclosed embodiments, but is within the scope and spirit of the broad interpretation of the present invention. It is to be understood that it includes various arrangements and thus includes variations and equivalent arrangements.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a conventional back projection screen.

FIG. 2 is a perspective view showing a first embodiment of the projection screen of the present invention partially exploded.

FIG. 3 is a sectional view showing a part of the first embodiment.

FIG. 4 is a sectional view partially showing a second embodiment of the projection screen of the present invention.

FIG. 5 is a sectional view partially showing a third embodiment of the projection screen of the present invention.

[Explanation of symbols]

 Reference Signs List 1 back projection screen 11 Fresnel lens 12 lenticular lens 13 diffuser 2, 4, 5 lens base 21, 41, 51 bore 22, 42, 52 window 23 insertion column 24, 44, 53 black coating 3, 8 light guide medium 31 taper Rod 32 Front end 33 Rear end 34, 43 Light reflection layer 6 Back cover plate 7 Front cover plate

Claims (12)

[Claims] 1. A front surface, a rear surface, and an array of bores extending from the rear surface to the front surface, each bore being narrowed in a direction from the rear surface to the front surface, and a plurality of windows formed in the front surface. A lens base aligned with each of said bores, each window being disposed within said bore, and light entering said bore from said back of said lens base, said light being transmitted through said window of said lens base. Reflection means for multiple total internal reflection as it propagates along the bore before exiting. 2. The projection screen according to claim 1, wherein a black coating for absorbing ambient light is provided on the front surface of the lens base. 3. The projection screen according to claim 1, wherein the lens base is formed of a black light absorbing material such that ambient light is absorbed at the front surface of the lens base. 4. The reflecting means includes an array of tapered rods each formed from a light transmissive material and inserted into each of the bores from the back of the lens base, the tapered rods having a leading end and a trailing end. The projection screen according to claim 1, wherein the projection screen is narrowed in a direction from the rear end to the front end. 5. The projection screen according to claim 4, wherein said reflection means further includes a light reflection layer provided between each tapered bar and each of said bores. 6. The projection screen according to claim 5, wherein the light reflecting layer is a metal coating provided on an outer wall surface of each tapered bar. 7. The projection screen according to claim 5, wherein the light reflection layer is a metal coating provided on an inner wall surface of each bore. 8. The light-transmitting material has a first refractive index, and the reflecting means is provided between each tapered rod and each of the bores, and has a second refractive index smaller than the first refractive index. The projection screen according to claim 4, further comprising a filler layer having a refractive index of: 9. The projection screen according to claim 8, wherein the filler layer is air. 10. The projection screen according to claim 1, wherein said reflection means includes a metal coating acting as a light reflection layer on an inner wall surface of each bore. 11. The projection screen further includes a front cover plate and a rear cover plate that respectively cover the front and rear surfaces of the lens base so as to cover the front and rear ends of the bore. 2. The projection screen according to 1. 12. The light guide medium, wherein the lens base is formed of a material having a first refractive index, and the reflecting means fills each of the bores and has a second refractive index larger than the first refractive index. The projection screen according to claim 11, comprising: