KR100562431B1 - Optical system and prism for an projection image display device - Google Patents

Abstract

The present invention relates to an optical system and a prism of a projection image display device for improving the contrast of an image projected on a screen. An optical system of a projection image display device according to the present invention includes a first prism having a first total reflection surface that totally reflects light incident from a light source in a direction of a micromirror in a DMD element, and a first prism disposed in contact with a lower portion of the first total reflection surface. And a second prism, an upper portion of the first total reflection surface, and a third prism disposed in contact with one surface of the second prism, wherein one surface of the second prism in contact with the third prism is formed in a micro state in a FLAT state of a DMD element. It is a 2nd total reflection surface which totally reflects the light which reflects from a mirror and injects into a projection lens direction. According to the present invention, when the DMD element is in the FLAT state, it is possible to prevent some of the light reflected from the micromirror to be emitted to the projection lens, thereby improving the contrast of the image.

Description

OPTICAL SYSTEM AND PRISM FOR AN PROJECTION IMAGE DISPLAY DEVICE}

1 is a configuration diagram schematically showing the configuration of a conventional DLP projector.

2 is a view showing in more detail the path of light in the optical system of the conventional DLP projector.

3 is a view schematically showing a structure and a light path of a prism for a projection image display device according to an exemplary embodiment of the present invention.

<Description of main parts of reference numerals>

15: micromirror

20: projection lens

30: Prism

30a: first prism

30b: second prism

30c: third prism

31a: first total slope

31b: second total slope

The present invention relates to an optical system and a prism of a projection image display device, and more particularly, to an optical system and a prism of a projection image display device for improving contrast of an image projected on a screen.

Recently, with the development of the information industry, the demand for a video display device capable of displaying a large screen image is increasing. As such, an image display device capable of displaying a large-scale image includes a projection image display device, and among these, a DLP (Digital Light Processing) projector using a DMD (Digital Micromirror Device) device has recently been in the spotlight. have.

The DMD device is exclusively developed by Texas Instruments, Inc., and has about 1.3 million micromirrors integrated therein, and the micromirror reflects light incident from the outside in response to individual digital control signals to the screen. Implement the image.

1 is a configuration diagram schematically showing the configuration of a conventional DLP projector.

Referring to FIG. 1, white light emitted from the lamp 10 is separated into R, G, and B light in time by a color wheel rotating at a predetermined rotational frequency, and is incident to the prism 14. At this time, the incident light is totally reflected in the prism 14 and is incident on the plurality of micromirrors 15 provided in the DMD element 16. In addition, the incident light is reflected by the projection lens 20 according to the inclination angle of the micrometer and displayed on the screen 22 or is projected into a light absorber (not shown) or in the air.

The angles of the plurality of micromirrors 15 are controlled according to ON, OFF, and FLAT signals input from the DMD driver 18, which determines the propagation angle of reflected light. For example, the micromirror 15 is inclined 12 ° (+ 12 °) to the left when the ON signal, and is inclined to 12 ° (-12 °) to the right when the OFF signal, and maintains a horizontal state (0 °) during the FLAT signal. Done. Here, the reason why the FLAT signal is required is that the DMD device 16 needs to be refreshed every predetermined period in order to maintain the normal operation. In this refresh operation, all the micromirrors 15 in the DMD device 16 are horizontal. State (0 °).

When the micromirror 15 is in the ON state, the reflected light is projected onto the screen through the projection lens 20, and the reflected light in the OFF state and the FLAT state is projected into the light absorber or air and is not projected onto the screen.

However, in the conventional DLP projector, some light is projected to the projection lens in the FLAT state of the DMD element, which causes the contrast of the image to drop.

2 is a view showing in more detail the path of light in the optical system of the conventional DLP projector.

Referring to FIG. 2, a conventional prism 14 applied to a DLP projector includes a first prism 14a having a total reflection surface 14c that totally reflects light incident through a color wheel in the direction of the micromirror 15. And a second prism 14b disposed in contact with the total reflection surface 14c.

Here, a gap d of a small thickness, that is, an air gap is formed between the first prism 14a and the second prism 41b. The total reflection occurs due to the difference in refractive index between the first prism and the void.

Hereinafter, the light path will be described in more detail when the DMD element is in the ON, OFF, and FLAT states.

First, FIG. 2A illustrates a light path when the DMD device is in an ON state. As shown, the micromirror 15 is tilted at + 12 °, and the totally incident light incident on the first prism 14a is reflected back from the micromirror 15 before the first prism 14a and It is emitted to the projection lens 20 via the second prism 14b.

Figure 2 (b) shows the path of light when the DMD element is in the OFF state. As shown, the micromirror 15 is tilted at −12 °, and the light that is totally reflected at the first prism 14a and incident is reflected back from the micromirror 15 and then absorbs light (not shown) or air. It is emitted to the middle. At this time, since there is no light emitted through the projection lens 20, a black image is displayed on the screen.

2 (c) shows the path of light when the DMD element is in the FLAT state. As shown, the micromirror 15 is in a horizontal (0 °) state, and a part of the light 50 totally incident on the first prism 14a and incident is reflected back from the micromirror 15 and then lighted. Although emitted into the absorber (not shown) or in the air, the other part 51 is emitted to the projection lens 20 and projected onto the screen.

When the DMD element is in the FLAT state, a black screen should be displayed on the screen, but as shown in FIG. 2 (c), some of the light reflected from the micromirror 15 is directed to the projection lens 20. It is projected onto the screen to brighten the black screen. This acts as a cause of inhibiting the contrast of the image.

As such, when the light emitted through the projection lens in the FLAT state of the DMD element can be removed, a darker black can be realized, thereby improving the contrast of the image.

SUMMARY OF THE INVENTION The present invention has been proposed to solve the above-mentioned problems of the prior art, and an object thereof is to provide an optical system and a prism of a projection image display device capable of removing light emitted to a projection lens in a FLAT state of a DMD element. .

In addition, another object of the present invention is to increase the contrast of the image displayed on the screen by realizing a darker black by removing light emitted to the projection lens in the FLAT state of the DMD element.

Other objects and advantages in addition to the above objects and advantages of the present invention will become apparent from the following detailed description and the accompanying drawings.

An optical system of a projection type image display device according to a feature of the present invention includes a first prism having a first total reflection surface for totally reflecting light incident from a light source in a direction of a micromirror in the DMD element, and in contact with a lower portion of the first total reflection surface. A second prism disposed, an upper portion of the first total reflection surface, and a third prism disposed in contact with one surface of the second prism, wherein one surface of the second prism in contact with the third prism is a FLAT of a DMD element. And a second total reflection surface that totally reflects light incident from the micromirror in the state toward the projection lens.

In a preferred embodiment according to the above feature, when the DMD element is in the ON state, the second total reflection surface transmits light reflected from the micromirror and incident in the direction of the projection lens.

In another preferred embodiment according to the above features, the light source further includes a color wheel separating the white light emitted from the light source into R, G, and B light beams between the first prism.

According to the present invention, when the DMD element is in the FLAT state, it is possible to prevent some of the light reflected from the micromirror to be emitted to the projection lens, thereby improving the contrast of the image.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

3 is a view schematically showing a structure and a light path of a prism for a projection image display device according to an exemplary embodiment of the present invention.

Referring to FIG. 3, the prism 30 includes a first prism 30a having a first total reflection surface 31a for total reflection of light incident through the color wheel, and a lower portion of the first total reflection surface 31a. A second prism 30b disposed in contact with the upper surface; an upper portion of the first total reflection surface 31a; and a third prism 30c disposed in contact with one surface of the second prism 30b. One surface 31b of the second prism 30b in contact with the third prism 30c serves as a second total reflection surface 31b that totally reflects the light reflected from the micromirror 15 in the FLAT state of the DMD element.

Here, between the first prism 30a, the second prism 30b, and the third prism 30c (d ₁ ), and between the second prism 30b and the second prism 30c (d ₂ ) An air gap is formed therein, and total reflection occurring at the first total reflection surface 31a and the second total reflection surface 31b occurs due to a difference in refractive index between the first prism and the second prism and the void.

In addition, the second total reflection surface 31b transmits all the light reflected from the micromirror 15 in the ON state of the DMD element toward the projection lens 20, and the micromirror when the DMD element is in the FLAT state. The light reflected from 15) is designed to have an angle of inclination capable of total reflection.

In addition, it is preferable that the shape where the second prism 30b and the third prism 30c are combined is a triangle, and a surface of the triangle that faces the projection lens is parallel to the bottom surface of the first prism 30a.

First, FIG. 3 (a) shows a path of light when the DMD element is in an ON state. As shown, light incident through the first prism 30a is totally reflected at the first total reflection surface 31a and is incident to the micromirror 15. Since the DMD element is in the ON state, the micromirror 15 reflects light incident in the tilted state of + 12 ° back toward the projection lens 20. The reflected light is emitted to the projection lens 20 via the first prism 30a, the second prism 30b, and the third prism 30c. At this time, the reflected light is transmitted through the second total reflection surface 31b without being totally reflected.

Next, FIG. 3B schematically shows the path of light when the DMD element is in the FLAT state. As shown, light incident through the first prism 30a is totally reflected at the first total reflection surface 31a and is incident to the micromirror 15. Since the DMD element is in the FLAT state, the micromirror 15 reflects light incident again in the horizontal (0 °) state. A part of the reflected light 60 passes through the first prism 30a and the second prism 30b to the light absorber (not shown) or in the air, and the reflected light is directed toward the projection lens. The portion 61 that proceeds is totally reflected by the second total reflection surface 31b and then proceeds into the air through the right surface of the second prism 30b.

Thus, when the DMD element is in the FLAT state, it is possible to prevent some light from being emitted toward the projection lens 20.

In addition, in the present embodiment, when the DMD element is in the OFF state (i.e., the angle of the micromirror is -12 °), all of them are emitted at an angle deviating from the projection lens 20 by a considerable amount as in the conventional case, and thus description thereof is omitted. do.

On the other hand, the present embodiment has been described taking the prism employed in the optical system of a single-plate DLP projector using one DMD element as an example, the structure of the prism proposed in the present invention is also used in the optical system of a three-plate DLP projector using three DMD elements Can be applied.

Typically, the optical system of a three-plate DLP projector employs a light incidence / emission prism and a color separation / synthesis prism and three DMD elements, and the white light incident from a lamp is separated into the color separation / synthesis in the light incidence / emission prism. After being reflected by the prism for light, the color separation / synthesis prism is separated into R, G, and B light, and then digitally processed in each of the three DMD elements, and then again via the light incident / emitting prism. It is emitted by the projection lens and projected onto the screen.

Here, when employing the structure of the prism disclosed in the present invention as the light incident / emitting prism, it is possible to prevent some light from being emitted to the projection lens in the FLAT state of the three DMD elements.

Those skilled in the art will readily appreciate that the structure of the prism disclosed in the present invention can be employed in a three-plate DLP projector.

According to the present invention, when the DMD element is in the FLAT state, some of the light reflected from the micromirror can be prevented from being emitted to the projection lens. Therefore, when the DMD element is in the FLAT state, the black projected on the screen can be displayed darker, thereby improving the contrast of the image.

While the present invention has been described with reference to the preferred embodiments, those skilled in the art will understand that changes may be made without departing from the spirit and scope of the invention. In other words, the present invention may be modified within the scope of the appended claims and should not be considered as being limited to the above-described exemplary embodiments.

Claims (4)

In the optical system of a projection type image display device comprising a light source, a prism, a DMD element, and a projection lens, A first prism having a first total reflection surface that totally reflects light incident from the light source in a direction of a micromirror in the DMD element; A second prism disposed in contact with a lower portion of the first total reflection surface; An upper portion of the first total reflection surface and a third prism disposed in contact with one surface of the second prism; One surface of the second prism in contact with the third prism is a second total reflection surface reflecting the total reflection of light incident from the micromirror in the direction of the projection lens in the FLAT state of a DMD element. . The method of claim 1, And the second total reflection surface is configured to transmit light reflected from the micromirror to the projection lens when the DMD element is in an ON state. The method of claim 1, And a color wheel that separates the white light emitted from the light source into R, G, and B light, between the light source and the first prism. A first prism having a first total reflection surface for totally reflecting light incident from a light source in a direction of a micromirror in the DMD element; A second prism disposed in contact with a lower portion of the first total reflection surface; An upper portion of the first total reflection surface and a third prism disposed in contact with one surface of the second prism; And a surface of the second prism in contact with the third prism is a second total reflection surface that reflects light incident from the micromirror in the direction of the projection lens in the FLAT state of the DMD element.

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