JPWO1998029773A1 - Image display device - Google Patents

Abstract

(57) [Abstract] The image display device of the present invention comprises an arc (51) as a white light source, an elliptical mirror (52) that collects light rays from the arc (51), a color filter (53) that creates the three primary colors of light from the white light over time, a condenser lens (1) through which the light rays that have passed through the color filter (53) pass, a single spherical mirror (2) or aspherical mirror (3) that reflects the light rays that have passed through the condenser lens (1), a DMD (56) that receives the light rays reflected by this mirror and changes the inclination of multiple pixel micromirrors to change the output angle of the reflected light, and a projection lens (57) that magnifies and projects the light reflected from the micromirrors. In this invention, the spherical mirror (2) or aspherical mirror (3) is positioned so that the radial at the intersection of the optical axis and the optical axis is inclined by a predetermined angle with respect to the optical axis of an illumination optical system that includes the arc (51), the elliptical mirror (52), and the condenser lens (1).

Description

[Detailed Description of the Invention] Image Display Device Technical Field The present invention relates to a projection-type image display device used in projection-type high-definition television (HDTV) systems, video projectors, etc.

In particular, the present invention relates to an image display device characterized by the structure of an optical system for projecting a color image.

BACKGROUND ART Conventional projection-type image display devices include projection-type color liquid crystal display devices that use liquid crystal display panels.

Projection-type color LCDs are broadly classified into three types: three-panel color LCDs that use three LCD panels—red, green, and blue—that correspond to the three primary colors of light, and single-panel color LCDs that use a single LCD panel equipped with a mosaic or stripe-shaped three-primary color filter.

A three-panel color LCD device includes an optical system that converts white light into red, green, and blue, and a liquid crystal display panel that controls the brightness of each color to form an image.

The red, green, and blue images are then optically superimposed to form a color image for display.

A single-panel color liquid crystal display device forms and displays a color image by illuminating a single liquid crystal display panel equipped with a mosaic or stripe-shaped three-primary color filter.

Meanwhile, apart from the above-mentioned three-panel and single-panel projection-type color LCD displays, projection-type color image display devices using digital micromirror devices (DMDs: a registered trademark of Texas Instruments, Inc.) have become popular in recent years (see the magazine "Optics," Vol. 25, No. 6, pp. 313-314, 1996).

As is well known, the liquid crystal display panels used in three-panel or single-panel projection color liquid crystal displays control the orientation of liquid crystal molecules in a large number of cells arranged two-dimensionally, thereby changing the polarization state of light and thereby turning light transmission on and off.

In contrast, the DMD has a large number of pixels with tiny mirrors arranged two-dimensionally, and the tilt of each of the tiny mirrors is individually controlled by the electrostatic field generated by memory elements arranged corresponding to each pixel, thereby changing the reflection angle of the reflected light and thereby creating an ON/OFF state.

Figure 9 shows the operating state of the micromirrors provided for each pixel of the DMD. Reference numerals 101-105 denote the micromirrors of each pixel, and reference numeral 110 denotes a schematic projection lens. In Figure 9, the pixels corresponding to micromirrors 103 and 105 are in the ON state.

That is, when a pixel is in the OFF state, the light reflected by the micromirrors 101, 102, and 104 of that pixel does not enter the projection lens 110. On the other hand, when a pixel is in the ON state, the light reflected by the micromirrors 103 and 105 of that pixel enters the projection lens 110 and forms an image on the screen.

When each pixel is ON, the tilt angle of the micromirror is approximately 10 degrees relative to the horizontal state.

Compared to LCD panels that use polarizing plates, DMDs have excellent features such as better light utilization efficiency, heat resistance, and fast response speed.

A perspective view of the optical system of a conventional projection-type color image display device using a DMD is shown in Figure 10.

An arc (light emitting point) 51 of a white light source such as a xenon arc lamp is placed at one focus of a light-collecting elliptical mirror 52.

Therefore, the light emitted from the arc 51 is focused at the other focal point of the elliptical mirror 52, creating a virtual secondary light source.

A rotatable color filter 53 is disposed at the position of the secondary light source (the other focus of the elliptical mirror 52).

As shown in Figure 11, the color filter 53 has transmission filters 53R, 53G, and 53B formed by dividing its annular zone into three parts corresponding to the three colors of red, green, and blue. 531 is the axis of rotation of the color filter 53.

By rotating this color filter 53 about a rotation axis 531 parallel to the optical axis from the arc 51 in FIG. 10, the white light is converted into each of the colors red, green, and blue in a time series manner.

In Figure 10, light rays transmitted through color filter 53 pass through condenser lenses 541 and 542, are reflected by plane mirror 551, and pass through condenser lens 543. Light rays passing through condenser lens 543 are reflected by plane mirror 552, pass through condenser lens 544, and enter DMD 56. The light reflected by DMD 56 then enters projection lens 57.

Condenser lenses 541-544 serve to focus red, green, or blue light beams onto the entrance pupil of projection lens 57 via the micromirrors of the ON-state pixels of DMD 56. At the same time, these condenser lenses 541-544 also serve to reduce uneven illumination that occurs when the illumination intensity on the screen is non-uniform.

Furthermore, plane mirrors 551 and 552 play a role in complexly folding back within three-dimensional space the optical path of the illumination optical system routed by condenser lenses 541 to 544. Here, the illumination optical system refers to an optical system comprised of components present on the optical path from the light beam emitted from arc 51 to the DMD 56.

The reason for this complexity in the optical path of the illumination optical system is as follows: In order for the DMD 56 to operate properly, the angle of the light rays incident on the DMD 56 must be high (e.g., approximately 80 degrees) relative to the surface of the micromirrors. As a result, components of the illumination optical system, such as the condenser lens, are more likely to come into mechanical contact or interfere with the projection lens 57.

Therefore, in order to avoid this mechanical contact or interference, it is necessary to arrange the plane mirrors 551 and 552 three-dimensionally as shown in FIG. 10, which results in a complex optical path for the illumination optical system.

Note that the central axis of the DMD 56 does not coincide with the optical axis of the projection lens 57, and the DMD 56 is positioned offset (shifted) with respect to the optical axis of the projection lens 57. Therefore, in this prior art, only a portion of the angle of view of the projection lens 57 is used, rather than the entirety of it.

Conventional three-panel projection color LCD displays have complex optical systems, which makes the devices bulky and expensive.

Furthermore, single-panel projection-type color LCD devices have a relatively simple optical configuration and a small number of components, which allows for device miniaturization and cost reduction. However, they have the drawback of not being able to effectively utilize the light from the light source due to the use of color filters, resulting in dark images. If the brightness of the light source is increased to overcome this drawback, sufficient cooling measures must be taken for the LCD panel and other components.

On the other hand, conventional projection-type color image display devices using DMDs have the advantages of being heat resistant and capable of high resolution due to their thinner grid compared to LCD panels, but they also have the following disadvantages:

In other words, as is clear from Figure 10, the illumination optical system has a large number of components, so the high image brightness that is a characteristic of DMD cannot be fully utilized.

Furthermore, the complex three-dimensional layout of the illumination optical system requires a great deal of effort for assembly and adjustment, leading to increased size and cost of the device.

Therefore, an object of the present invention is to provide an image display device that can obtain high-brightness and high-illuminance color images by improving the efficiency of light utilization.

Another object of the present invention is to provide an image display device that can reduce the number of components in the illumination optical system, thereby making it possible to reduce the size of the device and reduce manufacturing costs.

Disclosure of the Invention The image display device of the present invention comprises a white light source, a focusing mirror that focuses light rays from the white light source to create a virtual secondary light source, a color filter positioned at the secondary light source and that generates the three primary colors of light from the white light over time, a condenser lens through which light rays passing through the color filter pass, a folding mirror that reflects light rays passing through the condenser lens, a reflective display means that receives the light rays reflected by the folding mirror and changes the tilt of the micromirrors of numerous two-dimensionally arranged pixels to change the output angle of the reflected light, thereby creating an ON/OFF state, and a projection lens that receives reflected light from the micromirrors of pixels in the ON state and magnifies and projects the incident light.

A characteristic feature of the present invention is that the folding mirror is formed from a single concave mirror, such as a spherical mirror or an aspherical mirror. Furthermore, the radial line at the intersection of the folding mirror and the optical axis is inclined by a predetermined angle with respect to the optical axis of the illumination optical system, which includes the white light source, the condenser mirror, and the condenser lens.

Furthermore, each optical component is arranged so that the optical axis of the illumination optical system, which includes the white light source, the condenser mirror, and the condenser lens, is approximately parallel to the optical axis of the projection lens, or so that the optical axis of the projection lens is contained within a plane approximately perpendicular to the optical axis of the illumination optical system.

According to the present invention configured as described above, the optical path needs to be folded only once by a folding mirror made of a spherical or aspherical mirror, simplifying the configuration of the illumination optical system and reducing the number of parts. This simplifies the assembly and adjustment of optical components, allowing for a more compact device and reduced manufacturing costs.

Furthermore, by reducing the number of condenser lenses and folding mirrors, light loss due to absorption and scattering is reduced, resulting in higher image brightness and improved color reproduction (especially red).

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagram showing the optical system configuration of a first embodiment of the present invention.

FIG. 2 is a plan view showing a mounted state of the optical component according to the first embodiment of the present invention.

FIG. 3 is a side view showing the mounted state of the optical component according to the first embodiment of the present invention.

FIG. 4 is a diagram showing the configuration of an optical system according to a second embodiment of the present invention.

FIG. 5 is a diagram showing the illuminance distribution in the image display device of the first embodiment of the present invention when one condenser lens is used.

FIG. 6 is a diagram showing the illuminance distribution when the image display device of the first embodiment of the present invention has two condenser lenses.

FIG. 7 is a diagram showing the illuminance distribution when the image display device according to the second embodiment of the present invention is used.

FIG. 8 shows the illuminance distribution when a conventional projection-type color image display device is used.

FIG. 9 is a conceptual diagram showing the operation of the micromirrors provided in each pixel of the DMD.

FIG. 10 is a perspective view of the optical system of a conventional projection-type color image display device using a DMD.

FIG. 11 is an explanatory diagram of a conventional projection-type color image display device using a DMD and a color filter used in the image display device of each embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION To more clearly illustrate the present invention, an embodiment of the present invention will now be described with reference to the accompanying drawings.

FIG. 1 is a diagram showing the configuration of an optical system according to a first embodiment of the present invention.

In Figure 1, as before, reference numeral 51 denotes the arc (light-emitting point) of a white light source, and this arc 51 is located at one focus of an elliptical mirror 52, which serves as a focusing mirror. Light rays emitted from arc 51 are focused at the other focus of elliptical mirror 52, creating a virtual secondary light source.

A rotatable color filter 53 is disposed at the position of the secondary light source (the other focal point of the elliptical mirror 52). As shown in Figure 11, this color filter 53 has transmission filters 53R, 53G, and 53B formed by dividing its annular portion into three parts corresponding to the three primary colors of red, green, and blue.

The smaller the angle of incidence at which the light reflected by the elliptical mirror 52 is incident on the color filter 53, the easier the design becomes and the better the reproducibility of red color becomes.

In this embodiment, instead of the four condenser lenses 541-544 and two plane mirrors 551, 552 shown in FIG. 10 described as the prior art, one or more (e.g., two) condenser lenses 1 having positive refractive power and one spherical mirror 2 serving as a folding mirror are provided.

The spherical mirror 2 and the DMD 56 are arranged so that the light reflected by the spherical mirror 2 is incident on the DMD 56 at a high angle.

Condenser lens 1 is a convex lens that serves to suppress the spread of light transmitted through color filter 53 and guide it to spherical mirror 2, while also reducing uneven illumination on screen 58.

It is possible to eliminate unnecessary heat rays from the light source by depositing a heat-reflecting film on the condenser lens 1 or by forming the condenser lens 1 from a heat-resistant glass material capable of absorbing heat rays.

It is also recommended to insert a rod lens or fly's eye integrator between the color filter 53 and the condenser lens 1 to reduce illumination unevenness on the screen 58.

The spherical mirror 2 has a concave reflecting surface and is disposed decentered with respect to the optical axis of the illumination optical system including the arc 51, the elliptical mirror 52, and the condenser lens 1. Here, "decentered" means that the normal at the intersection of the reflecting surface of the spherical mirror 2 and the optical axis is inclined with respect to the optical axis of the arc 51, the elliptical mirror 52, and the condenser lens 1.

The function of the spherical mirror 2 is to reflect and converge the light beams transmitted through the condenser lens 1 and guide them to the DMD 56, and also to direct the light beams to be incident on the DMD 56 at a high angle so that the DMD 56 can operate properly.

It should be noted that by forming an aluminum vapor deposition film on the reflective surface of the spherical mirror 2 or by appropriately selecting the glass material of the spherical mirror 2, it is possible to transmit and remove heat rays.

Of the light rays reflected by spherical mirror 2 and incident on DMD 56, those reflected by the micromirrors of pixels that are in the ON state travel along the optical path shown in the figure and are incident on projection lens 57, where they form an image on screen 58. Projection lens 57 is formed, for example, by combining lenses 571 to 574.

On the other hand, light rays (not shown) reflected by the micromirrors of pixels that are in the OFF state do not enter the projection lens 57 and do not contribute to image formation.

Here, the micromirrors of pixels in the ON state refer to, for example, micromirrors 103 and 105 in FIG. 9, and the micromirrors of pixels in the OFF state refer to micromirrors 101, 102, and 104 in FIG. 9.

The specific method for projecting and displaying a color image on a screen 58 using a color filter 53 and a DMD 56 is as follows.

For example, if you want to display part of an image in red, turn on the micromirror at a pixel with a specific address on the DMD 56, and light passing through the red transmission filter 53R is reflected by the micromirror and incident on the projection lens 57. The principle is similar for displaying green and blue colors; light passing through the green and blue transmission filters 53G and 53B is reflected by the micromirror at a specific address that is also in the ON state and incident on the projection lens 57. By performing these operations sequentially and at high speed, it is possible to display images of the three primary colors of light and any color combination thereof on the screen 58.

The controller for sending electrical signals to the DMD 56 and the driver for the color filter 53 are not shown in the figure.

2 and 3 are mounting diagrams of the optical component of the first embodiment, with FIG. 2 being a plan view and FIG. 3 being a side view. A front view is also shown schematically on the right side of FIG. 3.

In this embodiment, as shown in Figures 2 and 3, the optical axis L1 of the illumination optical system, which includes the arc 51, elliptical mirror 52, color filter 53, and condenser lens 1, the optical axis L2 of the projection lens 57 that constitutes the imaging optical system, and the axis L3 perpendicular to the incident surface of the DMD 56, which is the reflective display means, are all substantially parallel in three-dimensional space.

The imaging optical system refers to an optical system that is configured by components that exist on the optical path from the DMD 56 through the projection lens 57 to the screen 58.

Here, if the DMD 56 is mounted on a substrate not shown, there is a risk that the optical axis L1 passing through the condenser lens 1 may be blocked by the substrate.

Therefore, the second embodiment of the present invention is made to solve the above-mentioned problems.

4 is a diagram showing the configuration of an optical system according to a second embodiment. In this embodiment, the optical components of the illumination optical system and the imaging optical system are arranged so that the optical axis L4 of the projection lens 57 (comprising lenses 571 to 574) is included in a plane perpendicular to the optical axis L1 of the illumination optical system, which includes the arc 51, the elliptical mirror 52, the color filter 53, and the condenser lens 1.

Furthermore, in this embodiment, an aspherical mirror 3 having a concave reflecting surface is used as the folding mirror.

In FIG. 4, light rays emitted from arc 51 pass through elliptical mirror 52, color filter 53, and condenser lens 1, are reflected by aspherical mirror 3, and are incident on DMD 56 at a high angle.

The function of the aspherical mirror 3 is as follows.

If a spherical mirror is used at a certain angle, the aberration of the spherical mirror may prevent the light reflected by the spherical mirror from effectively entering the DMD 56. Furthermore, even if the light reflected by the spherical mirror does enter the DMD 56, it may not be at the required high angle. Furthermore, illumination unevenness may become more pronounced.

Therefore, in this embodiment, an aspherical mirror 3 is used to correct the aberration caused by the tilt of the mirror, so that the light beam is effectively incident on the DMD 56 at a predetermined angle.

The surface shape of the aspherical mirror 3 is preferably formed into a parabolic shape for ease of manufacturing.

Next, the illuminance distribution on the screen was calculated based on the data of the optical systems of the above-described embodiments, and the results are shown in Figures 5 to 8.

FIG. 5 shows the illuminance distribution on the screen when an image display device according to the first embodiment having one condenser lens 1 is used. FIG. 6 shows the illuminance distribution on the screen when an image display device according to the first embodiment having two condenser lenses 1 is used. FIG. 7 shows the illuminance distribution on the screen when an image display device according to the second embodiment is used. FIG. 8 shows the illuminance distribution on the screen when a conventional projection-type color image display device, as shown in FIG. 10, is used.

In Figures 5 to 8, the horizontal axis represents the position on the horizontal line H and vertical line V set on the screen (73 inches, aspect ratio 3:4). That is, as shown in the upper right diagrams of each of Figures 5 to 8, the positions on the horizontal line H and vertical line V on the screen are indicated on a scale of ±1000 with 0 as the center.

In addition, in the illuminance distribution diagrams shown on the left side of each of Figures 5 to 8, the vertical axis indicates the relative value of illuminance in the range of 0 to 1000.

As is clear from a comparison of FIGS. 5 and 7 with FIG. 8, it was confirmed that the illuminance on the screen when using the image display device of this embodiment is approximately 1.5 times brighter than that of the optical system of FIG. 10.

Furthermore, if two condenser lenses are used, as shown in Figure 6, the illuminance on the screen becomes even greater than that shown in Figure 5.

INDUSTRIAL APPLICABILITY As described above, the image display device according to the present invention can be used as an image display device for projection-type high-definition television (HDTV) systems, an image display device for video projectors, and even as an image display device for various presentations to project color images.

───────────────────────────────────────────────────── (Note) This publication is based on the publication published internationally by the International Bureau of Patents (WIPO). The effect of the international publication of the Japanese patent application (Japanese utility model registration application) related to this publication arises pursuant to Article 184-10, Paragraph 1 of the Patent Act (Article 48-13, Paragraph 2 of the Utility Model Act) and is unrelated to this publication.

Claims (20)

[Claims] 1. An image display device comprising a white light source, a focusing mirror that focuses light rays from the white light source to create a virtual secondary light source, a color filter positioned at the secondary light source to generate the three primary colors of light from the white light over time, a condenser lens through which light rays passing through the color filter pass, a folding mirror that reflects light rays passing through the condenser lens, a reflective display means that receives the light rays reflected by the folding mirror and creates an ON/OFF state by changing the tilt of numerous two-dimensionally arranged micromirrors of pixels to change the output angle of the reflected light, and a projection lens that receives reflected light from the micromirrors of pixels in the ON state and magnifies and projects the incident light, characterized in that the folding mirror is a single concave mirror and is positioned eccentrically with respect to the optical axis of an illumination optical system including the white light source, the focusing mirror, and the condenser lens. 2. The image display device according to claim 1, wherein the optical axis of the illumination optical system, which includes the white light source, the condenser mirror, and the condenser lens, is approximately parallel to the optical axis of the projection lens. 3. The image display device according to claim 1, wherein the optical axis of the projection lens is included in a plane substantially perpendicular to the optical axis of the illumination optical system including the white light source, the condenser mirror, and the condenser lens. 4. The image display device according to any one of claims 1, 2, or 3, wherein the folding mirror is a spherical mirror. 5. The image display device according to any one of claims 1, 2, or 3, wherein the folding mirror is an aspherical mirror. 6. The image display device according to claim 5, wherein the folding mirror is a parabolic mirror. 7. The image display device according to any one of claims 1, 2, or 3, wherein the folding mirror is positioned so that the normal at the intersection of the folding mirror and the optical axis of the illumination optical system is inclined at a predetermined angle with respect to the optical axis of the illumination optical system, which includes a white light source, a condenser mirror, and a condenser lens. 8. An image display device according to claim 4, wherein the spherical mirror is positioned so that the normal at the intersection of the spherical mirror and the optical axis of the illumination optical system is inclined at a predetermined angle with respect to the optical axis of the illumination optical system, which includes a white light source, a condenser mirror, and a condenser lens. 9. An image display device according to claim 5, wherein the aspherical mirror is disposed so that the normal at the intersection of the aspherical mirror and the optical axis of the illumination optical system is inclined at a predetermined angle with respect to the optical axis of the illumination optical system, which includes a white light source, a condenser mirror, and a condenser lens. 10. An image display device according to claim 6, wherein the parabolic mirror is disposed so that the normal at the intersection of the parabolic mirror and the optical axis of the illumination optical system is inclined at a predetermined angle with respect to the optical axis of the illumination optical system, which includes a white light source, a condenser mirror, and a condenser lens. 11. The image display device according to any one of claims 1, 2, or 3, characterized in that a rod lens is disposed between the color filter and the condenser lens. 12. The image display device according to claim 4, wherein a rod lens is disposed between the color filter and the condenser lens. 13. The image display device according to claim 5, wherein a rod lens is disposed between the color filter and the condenser lens. 14. The image display device according to any one of claims 6, 8, 9, or 10, characterized in that a rod lens is disposed between the color filter and the condenser lens. 15. The image display device according to claim 7, wherein a rod lens is disposed between the color filter and the condenser lens. 16. The image display device according to any one of claims 1, 2, or 3, characterized in that a fly's eye integrator is disposed between the color filter and the condenser lens. 17. The image display device according to claim 4, wherein a fly's eye integrator is disposed between the color filter and the condenser lens. 18. The image display device according to claim 5, wherein a fly's eye integrator is disposed between the color filter and the condenser lens. 19. The image display device according to any one of claims 6, 8, 9, or 10, characterized in that a fly's eye integrator is disposed between the color filter and the condenser lens. 20. The image display device according to claim 7, wherein a fly's eye integrator is disposed between the color filter and the condenser lens.