JPWO2019171449A1 - Image display device - Google Patents

Abstract

In the projection optical system (11), the image light generated by the light source unit (110) and the display element (111) is magnified by the projection optical system (112) and projected onto the screen (12). As a result, an image of a predetermined size is formed on the screen (12). The image light transmitted through the screen (12) is collimated by the collimated optical system (13) and introduced into the light guide (10). The image light is reflected by the incident side reflecting surface (101) inside the substrate (100) of the light guide (10), and is reflected between the first surface and the second surface (100a, 100b) to be a beam splitter. It reaches the ejection side reflecting surface (102a to 102e). A part of the image light is reflected by each of the plurality of emission side reflecting surfaces (102a to 102e) and reaches the observer's eye E. Since the size of the image on the screen (12) can be adjusted arbitrarily, the optical design of the collimator optical system (13) can be facilitated, the equipment cost can be reduced, and the design with a high degree of freedom in optical performance and layout is realized. it can.

Description

The present invention relates to an image display device that displays image information as a virtual image in front of the user's eyes, and more particularly to an image display device that uses a light guide that enlarges a luminous flux (emission pupil). The image display device according to the present invention is suitable for image display devices such as helmet mount displays, head-up displays, and eyeglass-type displays (so-called smart glasses).

In automobiles and trains, a head that forms a virtual image display image in front of the driver by projecting an image displayed on a display element such as a liquid crystal display (LCD) onto a windshield or combiner and reflecting it toward the driver. Up display is used. Further, in an aircraft, a helmet mount display is used in which an image is projected onto a combiner provided on a helmet worn by the pilot on the head by a similar mechanism to form a virtual image display image in front of the pilot's eyes. .. Recently, eyeglass-type or head-mounted head-mounted displays called smart glasses have also begun to spread.

Various types of such image display devices are known as optical systems for displaying a virtual image in front of the observer's eyes, and one of them is a method using a light guide (light guide plate). As described in Patent Documents 1 to 3, a light flux having a small cross-sectional area including image information formed by the image forming portion and the collimating optical system is introduced into a light guide having a substantially rectangular flat plate shape. The light beam is magnified and displayed by the light guide. In the following description, an image display device using such a light guide is simply referred to as an image display device.

FIG. 2 is a schematic view showing an optical path configuration in an example of a conventional image display device. This schematic diagram assumes a state in which an observer observing the displayed image is viewed from the side, and for convenience of explanation, the x, y, and z axes orthogonal to each other are defined as shown in the figure. There is.

The image display device 2 includes a light source unit 21, a display element 22, a collimating optical system 23, and a light guide 20. The display element 22 is a transmissive liquid crystal display element, and the light source unit 21 is a backlight light source for a so-called transmissive liquid crystal display element. The light emitted from the light source unit 21 illuminates the display element 22 from the back surface side, and the light including the image formed on the display surface of the display element 22 as information is emitted from the display element 22. The collimating optical system 23 introduces the image light emitted from each point (pixel) on the display surface of the display element 22 into the light guide 20 as a substantially parallel luminous flux. Therefore, the light introduced from the collimating optical system 23 into the light guide 20 includes information on different parts of the image formed on the display surface of the display element 22, and parallel light flux incident on the light guide 20 at different angles. Is a set of.

The light guide 20 is a transparent substrate 200 having a flat cubic shape having a first surface 200a and a second surface 200b parallel to the yz plane, and a third surface and a fourth surface not shown parallel to the xy plane. Be prepared. One incident-side reflecting surface 201 and a plurality of (five in this example) injection-side reflecting surfaces 202a to 202e are formed inside the substrate 200. The incident side reflecting surface 201 is perpendicular to the third and fourth surfaces and is inclined with respect to the first surface 200a and the second surface 200b. The plurality of ejection side reflecting surfaces 202a to 202e are also perpendicular to the third and fourth surfaces, inclined with respect to the first surface 200a and the second surface 200b, and they are parallel to each other. Further, the incident side reflecting surface 201 is a reflecting surface by a mirror or the like, and the emitting side reflecting surfaces 202a to 202e are partial reflecting surfaces having a predetermined reflectance, that is, a peep splitter.

As described above, the luminous flux including the image information introduced from the collimating optical system 23 into the light guide 20 is reflected by the incident side reflecting surface 201 and then reflected once or more times by the first surface 200a and the second surface 200b. While passing through the inside of the substrate 200, it reaches the reflection surface 202a on the injection side. The emission side reflecting surface 202a reflects a part of the reached light flux and transmits the rest. The transmitted light reaches the next emission side reflecting surface 202b, a part of the light flux is reflected, and the rest is transmitted. The same applies to the injection side reflecting surfaces 202c to 202e. Therefore, the light flux transmitted through the inside of the substrate 200 of the light guide 20 is reflected by the plurality of ejection side reflecting surfaces 202a to 202e, and is transmitted to the outside through the first surface 200a of the substrate 200. The light reflected by the reflecting surfaces 202a to 202e on the emitting side is incident on the observer's eye E at a predetermined angle.

In this way, the image display device 2 parallelizes the light including the image formed on the display surface of the display element 22 as information, magnifies the parallel luminous flux, and provides the light to the observer. Further, since the substrate 200 of the light guide 20 is transparent and the emission side reflecting surfaces 202a to 202e are partially reflecting surfaces, the observer can also visually recognize the scenery in front through the light guide 20.

A see-through type image display device using such a light guide has a feature of being compact and lightweight. However, this image display device has a problem that optical design is more difficult than an image display device that does not use a light guide, for example, a reflection mirror, a lens system, or the like to project an image onto a combiner.

That is, in such an image display device, the viewing angle (angle of view) when viewed from the observer is determined as the specifications of the device, and therefore, first, the optical design of the light guide is performed so as to satisfy the specifications. This determines the size of the luminous flux introduced into the light guide, and the collimating optics are designed to accommodate this. When a light guide that expands the luminous flux only in the uniaxial direction as shown in FIG. 2 is used, the size of the luminous flux introduced into the light guide becomes smaller in the direction of expanding the luminous flux (y-axis direction). In the direction in which the luminous flux is not expanded (z-axis direction), the luminous flux becomes larger than that in the optical system that does not use the light guide, which causes difficulty in designing the optical system. The collimated optical system is designed according to the size of the emitted parallel light and the spreading angle of the incident light from the display element and its size, but it has been decided that it is easily available as a display element in order to reduce the cost of the device. You need to use a size one, and there are not always many options. Further, since the number of pixels of the display element is also limited in order to obtain the required resolution, the range of selection of the display element is further narrowed. Therefore, the range of selection of display elements is quite narrow, and even if an attempt is made to design a collimating optical system under such limited conditions, it becomes difficult to obtain sufficient performance.

Japanese Patent No. 5447714 Japanese Patent No. 5299391 Japanese Patent No. 5698297

"3. Video equipment for presentations", [online], Ushio, Inc., [Search on December 25, 2017], Internet <URL: https://www.ushio.co.jp/jp/technology/lightedge /200007/100221.html ＞

The present invention has been made to solve the above problems, and in a see-through type image display device using a light guide, the device cost is reduced while maintaining high performance by reducing the difficulty of designing an optical system. The main purpose is to obtain an image display device that can be suppressed.

The image display device according to the present invention made to solve the above problems is
a) A projection optical system that has an image display unit and a projection optical system and emits light containing an image by the image display unit.
b) A screen on which an image is formed by irradiation of light from the projection optical system, and
c) A collimating optical system that converts the transmitted light from the screen into a parallel luminous flux,
d) The parallel light flux by the collimating optical system is totally reflected inside the transparent substrate, and a part of the light is reflected by one or more partial reflection surfaces provided inside or on the surface of the substrate to obtain the parallel light flux. A light guide that expands and emits to the outside,
It is characterized by having.

In the image display device according to the present invention, a small projection optical system and a screen are used as an image forming unit. The projection optical system that projects an image on the screen has various configurations or various methods, but in any case, for example, by adjusting the distance between the projection optical system and the screen, any size can be used. The image of (angle of view) can be projected on the screen. Since it can be considered that the light including the display image is emitted from this screen, the size of the image on the screen may be adjusted according to the design requirements of the collimating optical system.

According to the image display device according to the present invention, the degree of freedom in the size of the substantially image display surface that emits light introduced into the collimating optical system is increased, so that the design of the collimating optical system suitable for the light guide becomes easy. .. As a result, the cost of the device can be suppressed, and a design with a high degree of freedom in optical performance and layout can be realized. For example, an image display device capable of displaying a good image without distortion is mounted on the helmet. Can be placed.

FIG. 6 is a schematic configuration diagram of an optical system in an image display device according to an embodiment of the present invention. The schematic block diagram of an optical system in an example of a conventional image display device.

An image display device according to an embodiment of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic configuration diagram of an optical system in the image display device of this embodiment. FIG. 1 is a diagram assuming a state in which an observer of an image is viewed from the side, similar to FIG. 2 already described.
The image display device 1 of this embodiment includes a projection optical system 11, a screen 12, a collimating optical system 13, and a light guide 10.

The light guide 10 is basically the same as the light guide 20 in FIG. 2 (however, parameters such as size do not have to be the same), and the first surface 100a and the second surface 100b parallel to the yz plane are used. A transparent substrate 100 having a flat cubic shape having a third surface and a fourth surface (not shown) parallel to the xy plane. The substrate 100 is made of, for example, a polycarbonate resin or quartz glass. One incident side reflecting surface 101 and a plurality of emitting side reflecting surfaces 102a to 102e are formed inside the substrate 100. The incident side reflecting surface 101 is perpendicular to the third surface and the fourth surface, and is inclined with respect to the first surface 100a and the second surface 100b. The plurality of injection side reflecting surfaces 102a to 102e are also perpendicular to the third and fourth surfaces, inclined with respect to the first surface 100a and the second surface 100b, and they are parallel to each other. The incident side reflecting surface 101 is a reflecting surface formed by a mirror or the like, and the emitting side reflecting surfaces 102a to 102e are partial reflecting surfaces having a predetermined reflectance.

The projection optical system 11 is a small rear liquid crystal projector, which is a light source unit 110 using an LED, a laser, or the like, a liquid crystal display element, a fluorescent display tube, or a display element 111 such as a MEMS (Micro Electro-Mechanical Systems) mirror element, and projection. Includes optical system 112. When a liquid crystal display element is used as the display element 111, the light including an image formed on the display screen of the display element 111 by a signal supplied from an external electric circuit (not shown) (hereinafter referred to as image light) is a projection optical system. It is magnified to an appropriate magnification by 112 and is ejected from the projection optical system 11.

The screen 12 is a rear transmission type screen, and the image light emitted from the projection optical system 11 is projected onto the screen 12. Then, the image light transmitted through the screen 12 is introduced into the collimating optical system 13 as it is. The image light, which is the diffused light, is converted into parallel light by the collimating optical system 13 and introduced into the light guide 10. The size of the image on the screen 12 does not depend on the size of the display screen of the display element 111, and can be adjusted by the optical path configuration of the projection optical system 11 and the distance between the projection optical system 11 and the screen 12. Therefore, the size of the image on the screen 12 may be appropriately determined according to the characteristics of the collimating optical system 13.

The image light parallelized by the collimated optical system 13 and introduced into the light guide 10 is reflected by the incident side reflecting surface 101 and then reflected by the first surface 100a and the second surface 100b one or more times while being reflected on the substrate. It passes through the inside of 100 and reaches the reflection surface 102a on the injection side. The emission side reflecting surface 102a reflects a part of the reached light flux and transmits the rest. The transmitted light reaches the next emission side reflecting surface 102b, a part of the light flux is reflected, and the rest is transmitted. The same applies to the injection side reflecting surfaces 102c to 102e. Therefore, the light flux transmitted through the inside of the substrate 100 of the light guide 10 is reflected by the plurality of ejection side reflecting surfaces 102a to 102e, and is transmitted to the outside through the first surface 100a of the substrate 100. Then, the light reflected by the light emitting side reflecting surfaces 102a to 102e is incident on the observer's eye E at a predetermined angle. Due to the parallel light containing the enlarged image information, the image is displayed as a virtual image in front of the observer's eyes with the exit pupil wide.

The light guide 10 is not limited to the above configuration, and is a light guide using a hologram surface or a single axis used in an image display device using a conventional ride guide such as Patent Documents 1 to 3. Various light guides such as a light guide that expands the luminous flux not only in the direction but also in the biaxial direction can be used instead.
Further, as for the projection optical system 11, projectors having various conventionally known configurations or methods, such as those described in Non-Patent Document 1, can be used instead.

In general, for a head-up display in which compactness is important, a single-panel transmissive liquid crystal projection configuration as in the above embodiment or a reflective liquid crystal projection configuration using only one display element is suitable. .. Further, in a head-up display that requires higher brightness, a three-panel transmissive liquid crystal projection configuration or a reflective liquid crystal projection configuration using three display elements is suitable. Of course, the image may be monochrome or color.

Furthermore, the above-described embodiment is merely an example of the present invention, and is not limited to the above-described modification, and is included in the claims of the present application even if appropriate changes, modifications, and additions are made within the scope of the present invention. It is natural that.

1 ... Image display device 10 ... Light guide 100 ... Substrate 100a ... First surface 100b ... Second surface 101 ... Incident side reflecting surface 102a, 102b, 102c, 102d, 102e ... Ejecting side reflecting surface 11 ... Projection optical system 110 ... Light source Unit 111 ... Display element 112 ... Projection optical system 12 ... Screen 13 ... Collimating optical system E ... Observer's eye

Claims (1)

a) A projection optical system that has an image display unit and a projection optical system and emits light containing an image by the image display unit.
b) A screen on which an image is formed by irradiation of light from the projection optical system, and
c) A collimating optical system that converts the transmitted light from the screen into a parallel luminous flux,
d) The parallel light flux by the collimating optical system is totally reflected inside the transparent substrate, and a part of the light is reflected by one or more partial reflection surfaces provided inside or on the surface of the substrate to obtain the parallel light flux. A light guide that expands and emits to the outside,
An image display device comprising.

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