JPH0998442A - Optical system for video projector - Google Patents

Abstract

PROBLEM TO BE SOLVED: To suppress ghost generation on a screen by shielding secondary reflected light by a shielding means provided between a prism and a projection lens system. SOLUTION: A shielding film 38 is vertically formed in a prescribed width at a part near an upper side wall 28c in the front end face 28a of the prism 28 and the emission of the secondary reflected light from the upper side wall 28c of the prism 28 from the front end face 28a of the prism 28 to a front part is minimized. The shielding film 38 is formed by silk-printing of black carbon coating material. A black carbon coating material is adopted so as to improve light absorptivity. Also, the forming method of the shilding film 38 is not limited to silk-printing and other printing methods or the methods of vapor deposition and sputtering, etc., can be used as well. Thus, the secondary reflected light from the upper side wall 28c is prevented or suppressed to minimum from being projected as a ghost on the front screen by the projection lens system 18.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical system for a video projector, and more specifically, it can change a reflection angle of irradiation light according to a video signal and can reflect only the signal light toward a projection lens system. The present invention relates to an optical system for a video projector using a digital micromirror device having a variable reflection angle mirror element.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal panel driven by a video signal is irradiated with light from a light source, and transmitted light carrying the video information is focused by a projection lens to project an image on a screen. Liquid crystal video projectors are known. However, in recent years, with the increasing demand for high-definition images, there is a demand in the field of video projectors for the development of a technique for dramatically increasing the number of pixels without increasing the size of the optical system.

In view of such a demand, development of a video projector using a digital micromirror device (hereinafter referred to as DMD) has been advanced. This DMD
Is a rectangular mirror with high reflectivity, which can change its inclination in the range of about 10 ° by a video signal, is formed on a silicon memory chip using CMOS semiconductor technology. is there. The video projector using this DMD controls the reflection direction of the light from the light source by changing the angle of the mirror element, and focuses only the desired reflected light on the screen to enable the photographing of a desired image. There is.

In this DMD, for example, 2.3 million mirror elements can be vertically and horizontally arranged on a substrate of 20 mm × 35 mm size, and all of these many mirror elements can be independently digitally controlled. , Each mirror element corresponds to one pixel in the image. As a result, a video projector using this DMD can obtain an image with a number of pixels several tens of times that of an average liquid crystal video projector up to now, and it is possible to dramatically improve the definition.

[0005]

By the way, as described above, the reflected light from each mirror element of the DMD is directed in the direction of the projection lens in the ON state and in the OFF state on the other hand according to the video signal. In order to prevent the light from being incident on, the light is emitted in a direction different from the ON state by about 20 °.

However, due to the design restrictions of the video projector, the reflected light from the mirror element in the OFF state is incident on the side wall of the prism which constitutes the color separation prism optical system interposed between the DMD and the projection lens. Will end up. The reflected light that has entered the side wall in this way is totally reflected by the side wall, but this secondary reflected light has such an intensity that a bright image is formed on the screen.
Since the reflected light in the F state and the reflected light in the ON state, which is the signal light, differ only by about 20 ° in the traveling direction, the secondary reflected light of the reflected light from the mirror element in the OFF state is also generated. There is a problem that an image (ghost) different from the original image is formed on the screen by being incident on the projection lens.

The present invention has been made in view of the above circumstances, and when the DMD is used, it is turned off.
An object of the present invention is to provide an optical system for a video projector capable of preventing or minimizing ghost generation on a screen due to secondary reflected light of reflected light from a mirror element in a state.

[0008]

An optical system for a video projector according to the present invention is provided so as to correspond to each pixel of an image,
Minute light reflection angle variable mirror elements are regularly arranged in one plane, and each of these mirror elements directs the irradiation light to the projection lens system direction, the mirror element and the projection lens according to an input video signal. And a digital micromirror device configured to selectively reflect in either of two directions of a side wall of a prism located between systems.

A shielding means is provided between the prism and the projection lens system for shielding the secondary reflected light from the side wall caused by the reflected light from each of the mirror elements. is there. The "shielding means" is
It is not limited to a specific structure as long as it can shield the secondary reflected light from the side wall caused by the reflected light from each mirror element. For example, the surface provided on the front end face of the prism. It is possible to adopt a configuration including a treated film. Further, it is effective to adopt a configuration in which the heat dissipation means is provided on the side wall.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a front view showing an embodiment of an optical system for a video projector according to the present invention, and FIG. 2 is a plan view thereof. As shown in FIG. 1, this video projector optical system includes a light irradiation system 12, a three-color separation prism system 14, a DMD (digital micromirror
Device) 16 and a projection lens system 18. The light irradiation system 12 includes a light source 20, a condenser lens 22, a mirror 24, and a prism 26,
The light (white light) from the light source 20 is condensed by the condenser lens 22 and reflected by the mirror 24, and the prism 26
After being reflected by, the light is incident on the three-color separation prism system 14.

As shown in FIG. 2, the three-color separating prism system 14 is composed of three prisms 28B, 28G and 28R joined together, and a B-reflecting dichroic layer is interposed at the boundary surface between the prisms 28B and 28R. R is mounted on the boundary surface between the prism 28R and the prism 28G.
A reflective dichroic layer is interposed. This allows
The white light from the prism 24 is decomposed into three colors of RGB and is incident on the DMD 16 arranged behind each of the prisms 28B, 28G and 28R.

Each of the DMDs 16 has the same structure, and includes a mirror surface 30 on which a very large number (about 2.3 million) of mirror elements (rectangular aluminum mirrors) are arranged on a substrate. Therefore, the reflection directions of the respective mirror elements constituting the mirror surface 30 can be independently switched to two directions (an included angle of about 20 °). The switching of the reflection direction is performed by the ON / OFF control of the video signal input to the DMD 16 using each of the mirror elements as a pixel.

The reflected light from the mirror surface 30 of each DMD 16 is combined through each prism 28B, 28G and 28R and then projected by the projection lens system 18 on the front screen. This projection lens system 18
Has a plurality of lenses (only the frontmost and rearmost lenses 34 and 36 are shown) arranged in the lens barrel 32.
Hereinafter, for simplicity of explanation, the above three prisms 28B,
One set of 28G, 28R and three DMDs 16 is represented, and this will be described as a prism 28 and a DMD 16 with reference to FIG. 1. As shown, the front and rear end surfaces 28a and 28b of the prism 28 and the DMD 16 are shown.
The mirror surface 30 of is orthogonal to the optical axis Ax of the projection lens system 18.

Light is incident on the mirror surface 30 of the DMD 16 from the light irradiation system 12 through the prism 28. At that time, the prism 28 is incident from a direction forming a predetermined angle with the optical axis Ax of the projection lens system 18. Light enters the mirror surface 30 through the front end surface 28a and the rear end surface 28b. The reflection direction of each mirror element forming the mirror surface 30 is the direction of the optical axis Ax of the projection lens system 18 when the pixel signal corresponding to the mirror element in the video signal input to the DMD 16 is ON, and the reflection direction when the pixel signal is OFF. Optical axis Ax
Is set to a direction opposite to the incident direction by a predetermined angle (about 20 °).

Therefore, some percentage of the reflected light from the mirror element in which the input video signal to the DMD 16 is OFF is, as shown in the figure, the upper side wall (side wall) 2 of the prism 28.
8C, the light thus incident on the upper side wall 28c becomes secondary reflected light from the upper side wall 28c, as shown by A in the figure, from the front end face 28a of the prism 28. It will be ejected forward. Therefore, with the above configuration, the secondary reflected light is projected as an inverted image (ghost) at an unexpected position on the screen in front by the projection lens system 18.

Therefore, in this embodiment, a shielding film 38 having a predetermined vertical width is formed on a portion of the front end surface 28a of the prism 28 near the upper side wall 28c, whereby the upper side wall 28c of the prism 28 is formed. The secondary reflected light from is emitted forward from the front end face 28a of the prism 28 to a minimum. The shielding film 38
Is formed by silk-printing black carbon paint. The black color is used to increase the light absorption rate. The method of forming the shielding film 38 is not limited to the silk printing described above, and another printing method or a method such as vapor deposition or sputtering can be used.

On the upper side wall 28c of the prism 28,
A heat dissipation plate 42 made of aluminum is adhered by the adhesive 40, and the lower surface of the heat dissipation plate 42 is black-anodized. As a result, the heat dissipation plate 42 allows the light incident on the upper side wall 28 c of the prism 28 to pass through the adhesive 40.
The heat energy is absorbed through the heat transfer plate 42 to be converted into heat energy, and this heat energy is further radiated from the fins formed on the upper surface of the heat dissipation plate 42.

In front of the prism 26, a correction prism 44 for correcting the optical path incident on the projection lens system 18 from the prism 26 is provided with an air gap. A shielding film 38 is formed on the front end face 28a of the prism 28.
Instead of forming the above, a shielding film may be formed on the front end face of the prism 26, or a thin shielding plate may be interposed between the prism 26 and the correction prism 44. Further, a shielding film may be formed on the front end surface of the correction prism 44, and the correction prism 44 and the projection lens system 18 may be formed.
You may make it arrange | position a shielding plate in the space between and.

As described above in detail, in this embodiment, the upper side wall 28c of the front end face 28a of the prism 28 is used.
A shielding film 38 is formed in a portion close to the top and bottom with a predetermined width, so that the secondary reflected light from the upper side wall 28c of the prism 28 is prevented from being emitted forward from the front end face 28a of the prism 28. Since the secondary reflected light from the upper side wall 28c is prevented from being projected as a ghost on the screen in front by the projection lens system 18, it can be prevented or minimized. By forming the shielding film 38, the upper side wall 2 of the prism 28 is formed.
8c as well as the secondary reflected light (A in the figure) from the upper surface of the adhesive 40 of the heat dissipation plate 42 (A in the figure).
′), And also the secondary reflected light (B in the figure) from the upper wall surface of the correction prism 44 can be cut.

If the vertical width of the shielding film 38 is made sufficiently large, the secondary reflected light from the upper side wall 28c can be completely cut off, so that it is possible to reliably prevent the generation of ghosts on the screen. In such a case, some of the original signal light is also cut, so it is desirable to set the width dimension value so that both can be balanced. 1, the three prisms 28B, 28G, and 28R shown in FIG.
In the above description, each of the prisms 28B, 28
G and 28R have the same structure as the prism 28.
That is, the shielding films 38 are formed on the front end faces of the prisms 28B, 28G, and 28R with a predetermined vertical width, so that the ghost generation on the screen due to the secondary reflected light is suppressed for each color light. There is.

The optical system for a video projector of the present invention is not limited to the above embodiment, and various other modes can be modified. For example, in the above embodiment, the video projector optical system for color image reproduction is assumed, but the present invention can be applied to a video projector optical system for monochrome image reproduction. Further, the arrangement of the prisms and the arrangement of the irradiation optical system can be appropriately changed. Further, various kinds of adhesives can be adopted as the adhesive between the prism and the heat radiating means, and instead of this adhesive, a flexible transparent buffer material such as silicone gel (resin) is used. If used, it is possible to prevent the distortion of the prism or the like due to the difference in coefficient of thermal expansion between the cushioning material and the prism.

[0022]

As described above, in the optical system for a video projector using the DMD, the input video signal of the many mirror elements arranged on the mirror surface is OF.
Although the reflected light of the mirror element in the F state is incident on the side wall of the prism, in the optical system of the present invention, the shielding element provided between the prism in front of the DMD and the projection lens system allows the light from the mirror element to be emitted from the mirror element. Since the secondary reflected light from the prism side wall generated by the reflected light is shielded, it is possible to prevent or suppress the secondary reflected light from reaching the projection lens system. It is possible to suppress the generation of ghost on the screen due to the secondary reflected light. In particular, if the shielding means is composed of a surface treatment film formed on the front end face of the prism, the shielding means can be easily provided.

[Brief description of drawings]

FIG. 1 is a front view showing an embodiment of an optical system for a video projector according to the present invention.

FIG. 2 is a plan view showing the above embodiment.

[Explanation of symbols]

 12 light irradiation system 14 three-color separation prism system 16 DMD (digital micromirror device) 18 projection lens system 20 light source 22 condenser lens 24 mirror 26 prism 28, 28B, 28G, 28R prism 28a front end face 28c upper side wall 30 mirror face 38 Shielding film 40 Adhesive 42 Heat sink Ax Optical axis of projection lens system

Claims (3)

[Claims] 1. A variable light reflection angle variable mirror element is regularly arranged in one plane so as to correspond to each pixel of an image, and each of these mirror elements is illuminated in accordance with an input video signal. A digital micro device configured to selectively reflect light in one of two directions: a projection lens system direction and a side wall direction of a prism located between the mirror element and the projection lens system. A mirror device is provided, and a shield means is provided between the prism and the projection lens system to shield secondary reflected light from the side wall caused by reflected light from each of the mirror elements. Optical system for video projector. 2. The optical system for a video projector according to claim 1, wherein the shielding means is a surface-treated film provided on the front end surface of the prism. 3. The optical system for a video projector according to claim 1, wherein the side wall is provided with heat dissipation means.