JP2006317979A - Image forming apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an inexpensive image forming apparatus which can prevent degradation in the image contrast produced, when a DMD (digital micromirror device) is utilized as an image forming element. <P>SOLUTION: A glass substrate is provided between a 1st reflecting mirror 9a and a 2nd reflecting mirror 9b and a light source 5, a reflection-type image forming element 2 and the 1st reflection mirror 9a are closely sealed by the glass substrate and a cabinet 21 for a light source, while being separated from the 2nd reflecting mirror 9b. Thereby the deterioration of image, due to sticking of dirt and dust to the reflection type image forming element 2, is prevented and fogging of light which is produced, when the DMD is used as the image forming element is prevented and image of high contrast can be obtained. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an improvement of an image forming apparatus, and more particularly to an improvement of an image forming apparatus using a DMD (Digital Micromirror Device) as an image forming element.

  In the projector market in recent years, instead of a CRT projector, an apparatus for enlarging and projecting with a DMD projector has started to appear. The demand for thin and lightweight rear projectors is increasing due to their structure, and there is a need for front projectors that can be enlarged and projected even in small rooms for home use. That is the reason.

  As countermeasures for short-distance projection and wide angle of view, methods using a reflective imaging optical system are disclosed in Patent Document 1 and Patent Document 2. The reflective imaging optical system has many advantages such as no chromatic aberration, foldable optical path and miniaturization, low internal reflection and high contrast, and high resolution with a simple configuration. Various proposals have been made using this fact.

  The present applicants also disclosed a reflective imaging optical system as shown in FIG. 6 as Japanese Patent Application No. 2000-228798. As shown in FIG. 6, the imaging optical system 1 includes a first reflecting mirror 3a having a free-form surface with a concave surface facing the image forming element 2, and a convex surface for the light flux from the first reflecting mirror 3a. A second reflecting mirror 3b having a free curved surface shape directed to, a third reflecting mirror 3c having a free curved surface shape having a convex surface directed to a light beam from the second reflecting mirror 3b, and a third reflecting mirror 3c A fourth reflecting mirror 3 d having a rotationally symmetric aspherical shape with a concave surface facing the light beam is formed, and an illumination optical system 4 that illuminates the image forming element 2 is formed by a lamp 5.

  However, when such a configuration is applied, it is necessary to use the third reflecting mirror 3c having a free-form surface on the reflecting surface constituting the imaging optical system 1, so that the manufacturing accuracy and incorporation into the apparatus are possible. The accuracy was relatively severe.

  In the case of an image forming apparatus using DMD as the image forming element 2, the postures of a large number of micromirrors on the image forming element 2 are digitally controlled, and a part of the light beam emitted from the lamp 5 is image forming optical system. When the light beam is guided to one optical path and the other part of the light beam is removed from the optical path of the imaging optical system 1, an image is generated by forming light and darkness in the light beam guided to the imaging optical system 1. A part of the light flux that should be removed from the optical path of the imaging optical system 1 may enter the imaging optical system 1 as stray light, and there is a problem that the image contrast tends to be lowered due to the fogging of the light. There is a problem to do.

PCT / JP96 / 01767 JP-A-10-111458

  Accordingly, an object of the present invention is to eliminate the disadvantages of the prior art described above, reduce the image contrast that occurs when the DMD is used as an image forming element, and is compact and has a wide angle of view and high uniformity in the vertical direction of the screen. It is an object of the present invention to provide an inexpensive image forming apparatus that can be prevented.

The present invention controls the attitude of a light source, a light source housing, and a micromirror disposed on a substrate, guides a part of a light beam emitted from the light source to the substrate, to an imaging optical system, and An image forming apparatus comprising: a reflective image forming element that generates an image by forming light and darkness in the light beam guided to the imaging optical system by removing the other part of the light beam from the optical path of the imaging optical system In order to achieve the above object, in particular,
The imaging optical system includes at least a first reflecting mirror having a rotationally symmetric aspherical shape that serves as an incident portion of the imaging optical system, and a rotationally symmetric aspherical surface that receives a light beam emitted from the first reflecting mirror. A second reflecting mirror having a shape and a glass substrate;
The glass substrate is provided between the first reflecting mirror and the second reflecting mirror so that the surface of the glass substrate and the main optical path are orthogonal to each other,
The light source, the reflective image forming element, and the first reflecting mirror are separated and sealed from the second reflecting mirror by the glass substrate and the light source casing. .

The light beam from the light source is irradiated on the micro mirror whose posture is controlled on the substrate, and the reflected light from the micro mirror whose posture is controlled in a state corresponding to the bright part, that is, the state where the emitted light is directed to the imaging optical system. Contrary to this, the reflected light from the micro mirror whose posture is controlled in a state corresponding to the dark part, that is, in a state where the emitted light does not enter the imaging optical system, is conversely guided. Removed from the optical path of the image optical system.
As a result, bright and dark images are formed in the cross section of the light beam traveling toward the imaging optical system, and this light beam is applied to the first reflecting mirror that is the incident portion of the imaging optical system. And is transmitted through a glass substrate provided between the second reflecting mirror and the second reflecting mirror.
At this time, the glass substrate functions as a part of a substantial optical system between the first reflecting mirror and the second reflecting mirror. The glass substrate is changed from the first reflecting mirror to the second reflecting mirror. Therefore, adverse effects such as astigmatism and internal reflection caused by the glass substrate can be suppressed (see paragraph 0033).
Thereafter, the light beam applied to the second reflecting mirror is enlarged through this imaging optical system and finally projected onto a screen or the like.
As described above, by sealing the reflective image forming element using the glass substrate and the light source casing, it is possible to prevent image deterioration due to adhesion of dust and dust to the reflective image forming element (paragraph). 0032, 0033).

  The image forming optical system of the image forming apparatus may include at least four reflecting mirrors including the first reflecting mirror and the second reflecting mirror.

The glass substrate is preferably composed of a flat glass plate.
By forming a glass substrate that is placed perpendicular to the main optical path from the first reflecting mirror to the second reflecting mirror with a highly accurate flat glass, adverse effects such as astigmatism and internal reflection are minimized. (See paragraph 0033).

In the image forming apparatus of the present invention, a glass substrate is disposed between the first reflecting mirror and the second reflecting mirror, and the light source, the reflective image forming element, and the first reflecting mirror are used for the glass substrate and the light source. Since the casing is separated and sealed from the second reflecting mirror, image deterioration due to adhesion of dust and dirt to the reflective image forming element is prevented (see paragraphs 0032 and 0033), and reflective image formation is performed. In an image forming apparatus using an element, in particular, an image forming apparatus using a DMD (Digital Micromirror Device), a high-contrast image without fogging can be obtained.
In addition, the glass substrate is provided between the first reflecting mirror and the second reflecting mirror so as to be orthogonal to the main optical path, which may cause adverse effects such as astigmatism and internal reflection. (See paragraph 0033).

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. 1 is a side view showing an internal structure of an image forming apparatus according to an embodiment to which the present invention is applied, FIG. 2 is a front view showing the image forming apparatus of FIG. 1 from the right side, and FIG. 3 is an image forming apparatus of FIG. FIG. 2 is a top view showing the position of the components constituting the optical system conceptually.

  As shown in FIG. 1, the image forming apparatus of this embodiment includes a reflective image forming element 6 constituted by DMD (Digital Micromirror Device (trademark of Texas Instruments)). An illumination optical system 7 for irradiating the forming element 6 and an imaging optical system 8 that receives and expands the light beam reflected by the reflective image forming element 6 are provided.

  2 and 3, the illumination optical system 7 includes a lamp 11 composed of an arc 11a and an elliptical mirror 11b as a light source, a rod lens 12, lenses 13, 14, 15, and 16 and a plane reflecting mirror 17. The light beam emitted from the arc 11a of the lamp 11 is condensed on the incident side opening 12a of the rod lens 12 by the elliptical mirror 11b, and the rod lens is passed through the lenses 13, 14, 15, 16 and the plane reflecting mirror 17. The reflection image forming element 6 is enlarged and irradiated with the illuminance distribution of the 12 emission ends 12b together with the shape thereof.

  The DMD constituting the reflective image forming element 6 digitally controls the postures of a large number of micromirrors arranged on the substrate, and forms a part of the light beam irradiated onto the substrate from the illumination optical system 7 as image forming optics. While guiding the optical path of the system 8, the other part of the light beam irradiated from the illumination optical system 7 is removed from the optical path of the imaging optical system 8 to form an image by forming a light and dark in the light beam guided to the imaging optical system 8. The reflective image forming element.

  Specifically, about 500,000 to 1.3 million micromirrors are mounted on the DMD substrate constituting the reflective image forming element 6, and each of them is, for example, ±± by a microprocessor that drives and controls the DMD. The light beam reflected by the micro mirror whose posture is controlled to be tilted within a range of 10 ° and whose posture is controlled to + 10 ° enters the optical path of the imaging optical system 8 having the first reflecting mirror 9a as the incident portion. Most of the light beam that forms the bright part of the image and is reflected by the micro mirror whose attitude is controlled to −10 ° is shifted in the direction in which it does not enter the first reflecting mirror 9a of the imaging optical system 8. .

  That is, the part of the micro mirror whose attitude is controlled to + 10 ° is a white part in the final image, and the part of the micro mirror whose attitude is controlled to −10 ° is a black part in the final image. When an image is formed by controlling the postures of a large number of mirrors in this way, a part of the light beam reflected by the micro mirrors whose postures are controlled at −10 ° strays and the first reflecting mirror 9a and the like are connected. In some cases, the optical path of the image optical system 8 enters the optical path. In the conventional imaging optical system 1 as shown in FIG. 6, the stray light is fogged and the contrast of the image is lowered.

  In the case of the present embodiment, the imaging optical system 8 that receives the reflected light from the micromirror whose attitude is controlled to + 10 ° on the reflective image forming element 6 is connected to the reflective image forming element 6 as shown in FIG. A first reflecting mirror 9a having a rotationally symmetric aspherical shape facing the concave surface, a second reflecting mirror 9b having a rotationally symmetric aspherical shape facing the convex surface toward the first reflecting mirror 9a, and a second reflecting mirror A third reflecting mirror 9c having a rotationally symmetric aspherical shape with a concave surface facing 9b, and a fourth reflecting mirror 9d having a rotationally symmetric aspherical shape with a convex surface facing the third reflecting mirror 9c. .

  That is, as compared with the imaging optical system 1 of the conventional example shown in FIG. 6, the third reflecting mirror 9c having a concave rotationally symmetric aspherical shape instead of the third reflecting mirror 3c having a convex free-form surface. And a fourth reflecting mirror 9d having a convex rotationally symmetric aspheric shape is used instead of the fourth reflecting mirror 3d having a concave rotationally symmetric aspherical shape.

  Compared to the third reflecting mirror 3c having a convex free-form surface shape, the third reflecting mirror 9c having a concave rotationally symmetric aspherical shape has a reduced manufacturing accuracy and accuracy of incorporation into the apparatus. Thus, by applying the third reflecting mirror 9c having a concave rotationally symmetric aspherical shape, there is an advantage that the manufacturing cost of the apparatus is reduced.

  On the other hand, since the concave third reflecting mirror 9c is used instead of the convex third reflecting mirror 3c, the enlargement ratio of the image by the third reflecting mirror 9c is the enlargement of the image by the third reflecting mirror 3c. Although the ratio is inferior to the ratio, since the convex fourth reflecting mirror 9d is used instead of the concave fourth reflecting mirror 3d, the final image enlargement ratio is compared with the conventional example of FIG. As a result, the wide angle of view and the downsizing of the device have been achieved.

  That is, the imaging optical system 8 in the image forming apparatus of this embodiment includes a first reflecting mirror 9a having a rotationally symmetric aspherical shape with a concave surface facing the reflective image forming element 6, and a first reflecting mirror 9a. A second reflecting mirror 9b having a rotationally symmetric aspherical shape with a convex surface facing, a third reflecting mirror 9c having a rotationally symmetric aspherical shape with a concave surface facing the second reflecting mirror 9b, and a third reflecting mirror A fourth reflecting mirror 9d having a rotationally symmetric aspherical shape with a convex surface facing 9c, and is reflected from the optical path by the reflective image forming element 6 between the first reflecting mirror 9a and the second reflecting mirror 9b. An imaging optical system for forming an image of the reflective image forming element 6 on the screen, including the third reflecting mirror 9c, is provided with a stop 10 that prevents the removed light beam from entering the optical path. All the reflecting mirrors 9a, 9b, 9c, and 9d are rotationally symmetric aspherical shapes Consists of a concave mirror or a convex mirror, and this configuration reduces the manufacturing accuracy of the device and reduces the manufacturing cost of the device compared to the case of using a reflecting mirror having a free-form surface. Yes.

The free-form surface shape of each reflector is, for example, the depth of the surface is Z, the cone constant is k, the curvature at the optical axis vertex is c, the height from the optical axis is ρ, and the correction coefficient is α _i (i = 1, 2,..., 7, 8), where the radius of curvature at the apex of the optical axis is r, and the values of coordinates in the direction orthogonal to the depth Z are x and y, Can be applied.

  Further, in the present embodiment, the position where the principal ray intersects between the first reflecting mirror 9a and the second reflecting mirror 9b (the focal position of the first reflecting mirror 9a) is orthogonal to the main optical path. A diaphragm 10 is provided. FIG. 4 shows an enlarged view of the peripheral structure of the diaphragm 10.

  The diaphragm 10 reflects the reflected light of the light beam reflected by the micro mirror whose posture is controlled at a position of + 10 ° which is a bright portion on the reflective image forming element 6 and applied to the first reflecting mirror 9a. The light beam straying to the first reflecting mirror 9a from the minute mirror whose posture is controlled at a position of −10 °, which is a dark portion on the reflective image forming element 6, is not disturbed, but is directed to the first reflecting mirror 9b. The light beam generated by being reflected by the mirror 9a deviates from the inner diameter of the diaphragm 10 to the outside in the radial direction, so that the stray light is blocked (shielded) from entering the second reflecting mirror 9b.

  As a result of the stray light being removed in this way, the light beam incident on the second reflecting mirror 9b is reflected by a micro mirror whose posture is controlled at a position of + 10 ° which is a bright portion on the reflective image forming element 6. (The other part is a complete dark part), the influence of fog due to the invasion of stray light, which has been a problem until now, is removed, and the final output light from the fourth reflecting mirror 9d A clear contrast can be obtained in an image projected on a screen (not shown).

In addition, since the diaphragm 10 is provided at the crossing position of the principal ray located substantially at the center between the first reflecting mirror 9a and the second reflecting mirror 9b, the first reflecting mirror 6 is reflected from the reflecting image forming element 6. The outer peripheral portion of the diaphragm 10 does not protrude in the optical path leading to the mirror 9a, and the outer peripheral portion of the diaphragm 10 does not protrude in the optical path leading from the second reflecting mirror 9b to the third reflecting mirror 9c. The occurrence of vignetting can be prevented in advance.
Thus, by providing the stop 10 at a position where the chief rays intersect between the first reflecting mirror 9a and the second reflecting mirror 9b, the position of the stop 10 is changed from the reflective image forming element 6 to the first. Both the optical path to the reflecting mirror 9a and the optical path from the second reflecting mirror 9b to the third reflecting mirror 9c are separated from each other, and the occurrence of vignetting due to the installation of the diaphragm 10 is prevented.

  FIG. 5 is a diagram schematically showing an embodiment in which the image forming apparatus of the present invention is applied to a rear projector. An arrangement of an illumination optical system 7 including a lamp 11 and the like, a configuration of a reflective image forming element 6 made of DMD, a first reflecting mirror 9a, a second reflecting mirror 9b, a third reflecting mirror 9c, and a fourth The arrangement of the imaging optical system 8 including the reflecting mirror 9d is substantially the same as that of the above-described embodiment described with reference to FIGS. 1 to 3, but the first reflecting mirror 9a and the second reflecting mirror 9d are the same. A diaphragm 10 ′ between the mirror 9 b is constituted by a light-shielding part on a transparent flat glass substrate, and the flat glass substrate and the light source housing 21 make the illumination optical system 7, the reflective image forming element 6, and the first one. The above-described embodiment is that the reflecting mirror 9a is separated from the second reflecting mirror 9b, the third reflecting mirror 9c, and the fourth reflecting mirror 9d and is hermetically disposed in the light source casing 21. Is different.

  That is, in the embodiment of FIG. 5, the illumination optical system 7, the reflective image forming element 6, and the first reflecting mirror 9 a form the light source casing 21 and a part of the light source casing 21 as described above. The structure is completely sealed from the outside by the glass substrate, and image deterioration due to adhesion of dust and dirt to the reflective image forming element 6 can be prevented.

At this time, the inner portion of the stop 10 ′, which is a through portion of the flat glass substrate, functions as a part of a substantial optical system between the first reflecting mirror 9a and the second reflecting mirror 9b. Since the glass substrate is formed of high-precision flat glass and is disposed perpendicular to the main optical path from the first reflecting mirror 9a to the second reflecting mirror 9b, astigmatism, internal reflection, etc. The adverse effects of can be minimized.
In this way, by sealing the reflective image forming element 6 using the flat glass substrate on which the diaphragm is formed and the light source casing 21, it is possible to prevent image deterioration due to intrusion of dust and dirt, In addition, a glass substrate that functions as a substantial part of the optical system is formed between the first reflecting mirror 9a and the second reflecting mirror 9b with a high-precision flat glass, and the first reflecting mirror 9a. By installing perpendicularly to the main optical path from to the second reflecting mirror 9b, adverse effects such as astigmatism and internal reflection can be minimized.

  The plane reflecting mirrors 18 and 19 are for reflecting the light beam output from the fourth reflecting mirror 9d of the imaging optical system 8 and projecting it onto the scoon 20. By folding the entire optical path, the rear projector can be made compact. Are arranged to configure.

1 is a side view showing an arrangement of main parts of an internal structure of an image forming apparatus according to an embodiment to which the present invention is applied. FIG. 3 is a front view showing an arrangement of main components for the internal structure of the image forming apparatus according to the embodiment. FIG. 3 is a top view showing an arrangement of main components for the internal structure of the image forming apparatus of the embodiment. It is the figure which expanded and showed the periphery structure of the aperture_diaphragm | restriction. It is the figure which simplified and showed one Embodiment of the rear projector to which this invention is applied. It is the conceptual diagram which showed an example of the conventional reflection type imaging optical system.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Imaging optical system 2 Image forming element 3a 1st reflective mirror 3b 2nd reflective mirror 3c 3rd reflective mirror 3d 4th reflective mirror 4 Illumination optical system 5 Lamp 6 Reflective image forming element (DMD)
DESCRIPTION OF SYMBOLS 7 Illumination optical system 8 Imaging optical system 9a 1st reflective mirror 9b 2nd reflective mirror 9c 3rd reflective mirror 9d 4th reflective mirror 10,10 'Aperture | stop 11 Lamp 11a Arc (light source)
11b Elliptical mirror 12 Rod lens 12a Incident side opening 12b Outgoing end 13, 14, 15, 16 Lens 17, 18, 19 Planar reflector 20 Screen 21 Light source casing

Claims (3)

Controls the attitude of the light source, the housing for the light source, and the micromirrors disposed on the substrate, guides a part of the light beam emitted from the light source to the substrate to the imaging optical system, and the other part of the light beam An image forming apparatus comprising: a reflective image forming element that forms an image by forming light and dark in a light beam guided to the image forming optical system by removing from the optical path of the image forming optical system;
The imaging optical system includes at least a first reflecting mirror having a rotationally symmetric aspherical shape that serves as an incident portion of the imaging optical system, and a rotationally symmetric aspherical surface that receives a light beam emitted from the first reflecting mirror. A second reflecting mirror having a shape and a glass substrate;
The glass substrate is provided between the first reflecting mirror and the second reflecting mirror so that the surface of the glass substrate and the main optical path are orthogonal to each other,
The light source, the reflective image forming element, and the first reflecting mirror are hermetically sealed separately from the second reflecting mirror by the glass substrate and the light source casing. apparatus. The image forming apparatus according to claim 1,
The image forming apparatus, wherein the imaging optical system includes at least four or more reflecting mirrors including the first reflecting mirror and the second reflecting mirror. The image forming apparatus according to claim 1,
The image forming apparatus, wherein the glass substrate is a flat glass plate.

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