Information display device

Abstract

To provide a small information display device that displays video information as a virtual image on a windshield and reduces the occurrence of double images.SOLUTION: An information display device for displaying video information of a virtual image on a windshield of a vehicle comprises: a video generation unit for generating a video of the video information; an optical system for allowing light from the video generation unit to enter and displaying a virtual image obtained by enlarging the video generated by the video generation unit; and an optical member between the optical system and the windshield. The optical system includes a concave mirror. The video generation unit includes a screen plate, and the video is displayed on the screen plate. Video light from the screen plate is reflected by the concave mirror, and the reflected light is reflected by the windshield and is made to enter the eyes of a driver of the vehicle. The optical member absorbs or reflects infrared light of outside light.SELECTED DRAWING: Figure 8

Description

[Technical field]

[0001] The present invention relates to an information display device that projects an image onto the windshield or combiner of an automobile, train, airplane, etc. (hereinafter generally referred to as "vehicle"), and to a projection optical system that allows the image to be observed as a virtual image through the windshield, and an information display device that uses the same. [Background technology]

[0002] A so-called head-up display (HUD) device that projects image light onto the windshield or combiner of an automobile to form a virtual image and display traffic information such as route information and congestion information, and automobile information such as remaining fuel and coolant temperature is already known from Patent Document 1 listed below.

[0003] In this type of information display device, it is desirable to expand the area in which the driver can view the virtual image, while it is also an important performance factor that the virtual image has high resolution and high visibility.

[0004] A head-up display device necessarily requires a windshield or combiner as the final reflective surface that provides a virtual image to the driver, and the inventors have realized that in order to obtain high visibility and good resolution performance, it is important to improve the double image of the virtual image caused by double reflection that occurs at the final reflective surface, the windshield or combiner.

[0005] On the other hand, for example, a device in which a main body including a combiner is attached near the roof (sun visor) of an automobile has already been proposed, as disclosed in Non-Patent Document 1 below. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2015-194707 A [Non-patent literature]

[0007] [Non-Patent Document 1] PIONEER R&D (Vol.22,2013) Summary of the Invention [Problem to be solved by the invention]

[0008] The principle of virtual image generation by a concave mirror that realizes a head-up display device according to the prior art is that a virtual image can be obtained by the concave mirror 1' by placing an object point AB inside the focal point F (focal length f) with respect to point O on the optical axis of the concave mirror 1', as shown in Fig. 33. For convenience of explanation, Fig. 33 regards the concave mirror 1' as a convex lens with the same positive refractive power, and shows the relationship between the object point, the convex lens (for convenience of explanation, it is represented as a concave mirror in Fig. 33), and the virtual image that is generated.

[0009] In the conventional technology, in order to expand the range in which the virtual image generated by the concave mirror 1' can be seen, it is advisable to move the object point AB closer to the focal point F and make the concave mirror larger relative to the object size AB. However, in order to obtain the desired magnification, the radius of curvature of the concave mirror must be small, making it difficult to achieve both. As a result, the mirror size becomes small, and although the effective magnification is large, only a virtual image with a small viewable range is obtained. For this reason, in order to simultaneously satisfy (1) the desired virtual image size and (2) the required virtual image magnification M=b / a, it is necessary to match the dimensions of the concave mirror to the viewing range and determine the virtual image magnification in consideration of the image display device.

[0010] For this reason, in the prior art, in order to obtain a large virtual image in a desired viewing range, it was necessary to increase the distance from the concave mirror 1' to the virtual image, that is, to increase the distance between the final reflecting surface, that is, the windshield or combiner (not shown), and the concave mirror, and at the same time, to increase the size of the concave mirror, as shown in Fig. 33. However, no consideration was given to the double image of the virtual image caused by double reflection at the windshield or combiner.

[0011] Also, for example, in the example of a head-up display device disclosed in the above-mentioned Patent Document 1, which is a conventional technology, a device for displaying an image and a projection optical system for projecting the image displayed on the display device are provided, and the projection optical system has a first mirror and a second mirror in the optical path from the display device to the viewer, and the relationship between the angle of incidence in the image long axis direction on the first mirror and the angle of incidence in the image short axis direction on the first mirror, the distance between the image display surface of the display device and the first mirror, and the horizontal width of the virtual image viewed by the viewer satisfies predetermined conditions, thereby realizing miniaturization. However, there was no mention of any means for reducing the double image generated by reflection on both sides of the windshield (the two sides on the driver's side and the outside).

[0012] On the other hand, in a device that is installed near the roof (sun visor) of a car as disclosed in Non-Patent Document 1, the occurrence of double images is reduced by forming an anti-reflection film on the reflective surface that does not face the driver. However, there are still safety issues that remain, such as the possibility of the driver being injured if the HUD device becomes detached in the event of a collision accident.

[0013] For this reason, it is expected that the method described in Patent Document 1 above, in which the windshield is used as a reflective surface, will become mainstream in the future. Therefore, we have devised a technical means for reducing the reflection of the image light that creates a virtual image reflected on both sides of the windshield by using an ingenious technique in the projection optical system.

[0014] The present invention proposes technical means for reducing the double image of a virtual image that occurs when the windshield is used as a reflective surface, by using optical system innovations, as described in detail below.It also aims to provide an information display device that makes it possible to form a highly visible virtual image in which the distortion and aberration of the virtual image perceived by the driver are reduced to a level that is practically acceptable. [Means for solving the problem]

[0015] The present invention has been made to achieve the above-mentioned object, and as one example, an information display device that displays virtual image information on the windshield of a vehicle comprises an image generation unit that generates an image of the image information, an optical system that receives light from the image generation unit and displays a virtual image that is an enlarged image of the image generated by the image generation unit, and an optical element between the optical system and the windshield, wherein the optical system includes a concave mirror, the image generation unit includes a screen plate, an image is displayed on the screen plate, the image light from the screen plate is reflected by the concave mirror, the reflected light is reflected by the windshield and made to enter the eyes of the driver of the vehicle, and the optical element absorbs or reflects infrared light from outside.

[0016] In this way, according to the present invention, an information display device is realized that reduces the double image that occurs in the virtual image described above and provides an image with improved visibility. Effect of the Invention

[0017] According to the present invention, it is possible to provide an information display device that forms a virtual image with improved visibility by correcting distortion and aberration of the virtual image observed by the driver while achieving a compact device and controlling the divergence angle of the light source light beam entering the virtual image optical system to reduce double images that occur in the virtual image. [Brief description of the drawings]

[0018] [Figure 1] FIG. 2 is a schematic diagram showing a configuration of peripheral devices of the information display device according to the embodiment. [Diagram 2] FIG. 1 is a top view of an automobile equipped with an information display device. [Diagram 3] FIG. 2 is a diagram illustrating a difference in the radius of curvature of a windshield. [Figure 4] 1 is a schematic diagram showing an information display device, a windshield, and a driver's viewpoint position. [Diagram 5] 1 is a schematic diagram showing an example of a virtual image optical system of an information display device; [Figure 6] 3 is a ray diagram of the entire virtual image optical system of the information display device according to the embodiment. FIG. [Figure 7]4 is a ray diagram of a part of a virtual image optical system of the information display device according to the embodiment. [Figure 8] FIG. 1 is a schematic diagram illustrating the principle of a virtual image type optical system. [Figure 9] FIG. 1 is a schematic diagram illustrating the principle of double image generation. [Figure 10] FIG. 1 is a schematic diagram illustrating the principle of the present invention. [Figure 11] FIG. 13 is a diagram showing resolution performance evaluation points within an eye box according to an embodiment. [Figure 12] FIG. 11 is a spot diagram showing the results of back-tracing using a green ray (a ray is projected from a virtual image to evaluate the imaging state at the image source), illustrating the results of the resolution performance evaluation in the example. [Figure 13] FIG. 13 is a diagram showing distortion performance as viewed from the center of the eye box in the embodiment. [Figure 14] 1 shows lens data according to an example. [Figure 15] 1 shows lens data according to an example. [Figure 16] FIG. 2 is a configuration diagram showing the arrangement of a video display device and a light source device. [Figure 17] FIG. 2 is a schematic diagram showing the configuration of a light source device. [Figure 18] 1 is a schematic diagram for explaining a state in which light beams are emitted from an image display device and a light source device. [Figure 19] 4 is a characteristic diagram illustrating the distribution of emitted light of a light beam from a light source device. FIG. [Figure 20] 3 is a schematic diagram showing the shape of a light guide of the light source device. FIG. [Figure 21] 3 is a schematic diagram showing a cross-sectional shape of a light guide of the light source device. FIG. [Figure 22] FIG. 1 is a conceptual diagram showing a method for evaluating the characteristics of a liquid crystal panel. [Diagram 23] 4 is a characteristic diagram showing transmittance characteristics in the left-right direction of the screen of a liquid crystal panel. FIG. [Figure 24] 10 is a characteristic diagram showing the angular characteristics of luminance in the left-right direction of the screen when white is displayed on the liquid crystal panel. [Diagram 25] 10 is a characteristic diagram showing angular characteristics of backlight luminance of a liquid crystal panel in the left-right direction. [Figure 26] 10 is a characteristic diagram showing the angular characteristics of the backlight luminance of a liquid crystal panel in the vertical direction. [Figure 27] 10 is a characteristic diagram showing angular characteristics of contrast of a liquid crystal panel in the left-right direction. [Figure 28] 4 is a characteristic diagram showing the transmittance characteristics in the vertical direction of a liquid crystal panel. FIG. [Figure 29] 10 is a characteristic diagram showing the angular characteristics of brightness of a liquid crystal panel in the vertical direction. [Diagram 30] 10 is a characteristic diagram showing the angular characteristics of black display luminance of a liquid crystal panel in the left-right direction. [Diagram 31] 10 is a characteristic diagram showing the angular characteristics of contrast of a liquid crystal panel in the vertical direction. [Diagram 32] 10 is a characteristic diagram showing the angular characteristics of black display luminance of a liquid crystal panel in the vertical direction. [Diagram 33] FIG. 1 is a schematic diagram for explaining the principle of a virtual image optical system according to the prior art. [Diagram 34] 1 is a schematic diagram for explaining the change in reflectance of glass depending on the angle of incidence of S-polarized light and P-polarized light. FIG. [Diagram 35] FIG. 11 is a schematic diagram for explaining a specific method for reducing the Petzval sum of a virtual image optical system. [Diagram 36] FIG. 11 is a schematic diagram for explaining a specific method for reducing the Petzval sum of a virtual image optical system. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, the embodiments of the present invention will be described in detail with reference to the drawings. Note that the present invention is not limited to the following description, and various changes and modifications can be made by those skilled in the art within the scope of the technical ideas disclosed in this specification. In addition, in all the drawings for explaining the present invention, parts having the same functions are given the same reference numerals, and repeated explanations thereof may be omitted.

[0020] <Embodiment of Information Display Device> FIG. 1 is a schematic diagram showing the configuration of peripheral devices of an information display device according to an embodiment of the present invention. Here, as an example, an information display device 100 that projects an image onto the windshield of an automobile will be described in particular.

[0021] This information display device 100 is a device (so-called HUD (Headup Display)) that displays various information reflected from a projection target 6 (in this embodiment, the inner surface of the windshield) as a virtual image VI (Virtual Image) in order to form a virtual image V1 in front of the vehicle in the driver's line of sight 8. The projection target 6 may be any member onto which information is projected, and may be not only the windshield described above but also a combiner. In other words, the information display device 100 of this embodiment may be any member that forms a virtual image in front of the vehicle in the driver's line of sight 8 and allows the driver to view it, and it goes without saying that the information displayed as a virtual image includes, for example, vehicle information and foreground information captured by a camera (not shown) such as a surveillance camera or an around viewer.

[0022] In addition, in the information display device 100, an image display device 4 that projects image light to display information, and a group of corrective lenses 2 for correcting distortion and aberration that occurs when the image displayed on the image display device 4 is formed into a virtual image by the concave mirror 1 are provided between the image display device 4 and the concave mirror 1.

[0023] The information display device 100 includes a control device 40 that controls the image display device 4 and the backlight 5. The optical components including the image display device 4 and the backlight 5 are a virtual image optical system described below, and include a concave mirror 1 that reflects light. The light reflected by this optical component is reflected by a projection member 6 and directed toward the driver's line of sight 8 (EyeBox: described in detail later).

[0024] The image display device 4 may be, for example, a liquid crystal display (LCD) having a backlight, or a self-luminous vacuum flourescent display (VFD).

[0025] On the other hand, instead of using the image display device 4 described above, an image may be displayed on a screen using a projection device, and then the image may be converted into a virtual image by the concave mirror 1 described above, and reflected by the windshield 6, which is the object to be projected, toward the driver's viewpoint 8.

[0026] Such a screen may be configured, for example, by a microlens array in which microlenses are arranged two-dimensionally.

[0027] Here, in order to reduce distortion of the virtual image, the shape of the concave mirror 1 should be such that the radius of curvature is relatively small so that the magnification is large in the upper part (the region where light is reflected below the windshield 6, which is relatively close to the driver's viewpoint) shown in Fig. 1, and the radius of curvature is relatively large so that the magnification is small in the lower part (the region where light is reflected above the windshield 6, which is relatively far from the driver's viewpoint). Furthermore, even better correction can be achieved by tilting the image display device 4 with respect to the optical axis of the concave mirror to correct the difference in virtual image magnification described above and reduce the distortion itself that occurs.

[0028] On the other hand, as shown in Figs. 2 and 3, the windshield 6 of a passenger vehicle has a radius of curvature Rv in the vertical direction of the body and a radius of curvature Rh in the horizontal direction, and generally, the relationship is Rh>Rv. Therefore, when the windshield 6 is regarded as a reflecting surface, it becomes a toroidal surface of a concave mirror. For this reason, in the information display device 100 of this embodiment, the shape of the concave mirror 1 may be set to have different average radii of curvature in the horizontal and vertical directions so as to correct the virtual image magnification due to the shape of the windshield 6, that is, to correct the difference between the radii of curvature in the vertical and horizontal directions of the windshield 6. At this time, the shape of the concave mirror 1 is a function of the distance r from the optical axis in a spherical or aspherical shape symmetrical with respect to the optical axis (a shape expressed by the formula 2 described later), and since the horizontal and vertical cross-sectional shapes at distant places cannot be controlled individually, it is preferable to correct it as a free-form surface expressed by the formula 1 described later as a function of the coordinates (x, y) of the mirror surface from the optical axis.

[0029] Returning to FIG. 1 again, a transmissive optical component, for example a lens element 2, is placed between the image display device 4 and the concave mirror 1, thereby controlling the direction of light emitted to the concave mirror 1 and correcting distortion in accordance with the shape of the concave mirror 1, while at the same time achieving correction of aberrations of the virtual image including astigmatism caused by the difference between the horizontal and vertical radii of curvature of the front glass 6 mentioned above.

[0030] In addition, in order to further improve the aberration correction ability, the optical element 2 may be a plurality of lenses. Alternatively, a curved mirror may be arranged instead of the lens element to control the incident position of the light beam on the concave mirror 1 while folding back the optical path, thereby reducing the distortion aberration. As described above, it goes without saying that even if an optical element optimally designed to improve the aberration correction ability is provided between the concave mirror 1 and the image display device 4, this does not deviate from the technical idea or scope of the present invention. Furthermore, by changing the thickness of the optical element 2 in the optical axis direction, in addition to the original aberration correction, the optical distance between the concave mirror 1 and the image display device 4 can be changed, and the display position of the virtual image can be continuously changed from a distant position to a close position.

[0031] Moreover, the image display device 4 may be disposed at an angle with respect to the normal to the optical axis of the concave mirror 1, thereby correcting the difference in magnification of the virtual image in the vertical direction.

[0032] On the other hand, it is known that a factor that reduces the image quality of the information display device 100 is that the image light emitted from the image display device 4 toward the concave mirror 1 is reflected on the surface of the optical element 2 arranged along the way, returns to the image display device 4, and is reflected again and superimposed on the original image light, thereby reducing the image quality. For this reason, in this embodiment, not only is an anti-reflection film formed on the surface of the optical element 2 to suppress reflection, but further, it is preferable to design the lens surface shape of either or both of the image light entrance surface and exit surface of the optical element 2 with constraints on the surface shape so that the above-mentioned reflected light is not focused on a portion of the image display device 4 (for example, a shape with the concave surface facing the image display device 4).

[0033] Next, in the image display device 4, in addition to the first polarizing plate arranged close to the liquid crystal panel to absorb the reflected light from the optical element 2 described above, if a second polarizing plate is arranged separately from the liquid crystal panel, the deterioration of image quality can be reduced. Also, the backlight 5 of the liquid crystal panel is controlled so that the incident direction of the light entering the liquid crystal panel 4 is efficiently incident on the entrance pupil of the concave mirror 1. At this time, if the divergence angle of the light beam entering the liquid crystal panel is reduced, not only can the image light be efficiently directed to the driver's eye point, but also, as shown in Figures 27 and 31, it is possible to obtain an image with high contrast and good visibility. The contrast performance against the divergence angle of the image is more noticeable in the horizontal direction, and excellent characteristics can be obtained if it is within ±20 degrees. In order to further improve the contrast performance, it is recommended to use a light beam within ±10 degrees.

[0034] On the other hand, it is preferable to use a solid-state light source with a long product life as the light source, and furthermore, it is preferable to perform polarization conversion using a PBS (Polarizing Beam Splitter) equipped with optical means for reducing the divergence angle of light as an LED (Light Emitting Diode), which has little change in light output due to fluctuations in ambient temperature.

[0035] Polarizing plates are arranged on the backlight 5 side (light entrance surface) and the optical element 2 side (light exit surface) of the liquid crystal panel, thereby increasing the contrast ratio of the image light. If an iodine-based polarizing plate with a high degree of polarization is used for the polarizing plate provided on the backlight 5 side (light entrance surface), a high contrast ratio can be obtained. On the other hand, by using a dye-based polarizing plate on the optical element 2 side (light exit surface), high reliability can be obtained even when external light is incident or the ambient temperature is high.

[0036] When a liquid crystal panel is used as the image display device 4, particularly when the driver is wearing polarized sunglasses, a problem occurs in which a specific polarized wave is blocked and the image cannot be seen. To prevent this, it is preferable to place a λ / 4 plate on the optical element side of the polarizing plate placed on the optical element 2 side of the liquid crystal panel, thereby converting the image light aligned in a specific polarization direction into circularly polarized light.

[0037] The control device 40 obtains various information from such navigation system 61, such as the speed limit and number of lanes of the road corresponding to the current position of the vehicle, and the planned route of travel of the vehicle set in the navigation system 61, as foreground information (i.e., information to be displayed in front of the vehicle using the virtual image).

[0038] The driving assistance ECU 62 is a control device that realizes driving assistance control by controlling the drive system and control system in accordance with obstacles detected as a result of monitoring by the surrounding monitoring device 63. Examples of driving assistance control include well-known technologies such as cruise control, adaptive cruise control, pre-crash safety, and lane keeping assist.

[0039] The surrounding monitoring device 63 is a device that monitors the situation around the vehicle, and examples include a camera that detects objects present around the vehicle based on images taken of the area around the vehicle, and a detection device that detects objects present around the vehicle based on the results of transmitting and receiving detection waves.

[0040] The control device 40 acquires information from the driving assistance ECU 62 as foreground information (for example, the distance to the preceding vehicle, the direction of the preceding vehicle, the positions of obstacles and signs, etc.). Furthermore, an ignition (IG) signal and vehicle status information are input to the control device 40. Among these pieces of information, the vehicle status information is information acquired as vehicle information, and includes, for example, warning information indicating a predetermined abnormal state, such as the remaining amount of fuel in the internal combustion engine and the temperature of the cooling water. It also includes the operation result of the turn signal, the running speed of the vehicle, and even shift position information. The control device 40 described above is started when an ignition signal is input. This concludes the description of the entire information display device system of the embodiment of the present application.

[0041] <First embodiment of the virtual image optical system> Next, the virtual image optical system and the image display device according to this embodiment will be described in further detail below.

[0042] As described above, FIG. 2 is a top view of an automobile equipped with the information display device 100 of this embodiment, and in front of the driver's seat of the automobile body 101, there is a windshield as the projection target member 6. The inclination angle of the windshield with respect to the vehicle body differs depending on the type of automobile. Furthermore, the inventors investigated the radius of curvature of the windshield in order to realize an optimal virtual image optical system. As a result, as shown in FIG. 3, the windshield has a different radius of curvature Rh in the horizontal direction parallel to the ground surface of the automobile and a radius of curvature Rv in the vertical direction perpendicular to the horizontal axis, and it was found that there is generally the following relationship between Rh and Rv. Rh>Rv

[0043] It was also found that the difference in the radius of curvature, that is, Rh relative to Rv, was often in the range of 1.5 to 2.5 times.

[0044] Next, the inventors investigated the inclination angle of the windshield on the market. As a result, although it differs depending on the vehicle body type, it was 20 degrees to 30 degrees for light cars and one-box types, 30 degrees to 40 degrees for sedan types, and 40 degrees or more for sports types. Therefore, in this embodiment, the virtual image optical system was designed taking into consideration the difference between the horizontal curvature radius Rh of the windshield parallel to the ground surface of the vehicle and the vertical curvature radius Rv perpendicular to the horizontal axis, and the inclination angle of the windshield.

[0045] More specifically, since the horizontal radius of curvature Rh and the vertical radius of curvature Rv of the windshield, which is the object to be projected, are significantly different, good aberration correction is achieved by providing an optical element 2 within the virtual image optical system that is axially asymmetric with respect to the horizontal axis of the windshield and the axis perpendicular to this axis with respect to the optical axis (Z axis).

[0046] Next, the inventors studied miniaturization of the information display device 100. The conditions for the study were an FOV of 7 degrees horizontally and 2.6 degrees vertically, and a virtual image distance of 2 m. At the beginning of the study, a concave mirror 1 (simply shown as a flat mirror in FIG. 5 below) that generates a virtual image, an image display device 4, and a backlight 5 were used as basic components, and a single optical path folding mirror was placed between the image display device 4 and the concave mirror 1. Simulations were performed using the arrangement of each component and the distance from the image display device 4 to the concave mirror 1 as parameters so that the volume of the information display device 100 would be minimized.

[0047] As a result, when the image light from the image display device 4 was arranged so as not to interfere with each component, the volume was 3.6 liters. After that, aiming for further miniaturization, a direct method was studied that removes the optical path folding mirror.

[0048] The configuration of the virtual image optical system of this embodiment will be described with reference to Fig. 4. Fig. 4 is an overall configuration diagram showing a basic configuration for examining miniaturization in the virtual image optical system of this embodiment shown in Fig. 1. For simplicity of explanation, optical elements for correcting aberration and distortion are omitted, and their vertical cross-sectional shape is shown, similar to the window glass 6 shown in Fig. 1. Assuming that the image display device 4 is a liquid crystal panel, the basic configuration is one in which a backlight 5 is arranged, and the image display device 4 is arranged at a position where a virtual image can be obtained by a concave mirror 1 from the displayed image.

[0049] At this time, as shown in Figure 5, the design constraint is that the image light R2 generated from the image at the center of the screen of the image display device 4, the image light R1 from the top end, and the image light R3 from the bottom end are each positioned so that they do not interfere with the image display device 4 and cause the light to be blocked when reflected by the concave mirror 1.

[0050] Taking the above-mentioned design constraints into consideration, the inventors simultaneously set the FOV at 7 degrees horizontal and 2.6 degrees vertical, and further set the virtual image distance at 2 m, and calculated the volume of the information display device 100 using the distance Z between the concave mirror 1 and the image display device 4 (liquid crystal panel and backlight 5) as a parameter. When the distance Z is 100 mm, the vertical dimension of the concave mirror 1 can be made the smallest. When the distance Z is set at 75 mm, the angle α2 between the horizontal plane and the concave mirror 1 becomes large, and the vertical dimension of the concave mirror 1 also becomes large. When the distance Z is further reduced to 50 mm or less, the angle α3 between the horizontal plane and the concave mirror 1 becomes large, and the vertical dimension of the concave mirror 1 also becomes larger.

[0051] As described above, when simulating the relationship between the set height and set depth of the image display device 4 using the distance Z as a parameter, the set depth can be reduced by making the distance Z smaller, but on the other hand, the set height increases. Similarly, in the relationship between the distance Z and the set volume L, compared to the spatial volume from the image display device 4 to the concave mirror (referred to as the optical path volume), the change in the set volume (including the LCD drive circuit, light source drive circuit, and backlight volume) changes at the boundary of the distance Z being 60 mm.

[0052] From the above, it has been found that in order to miniaturize the information display device 100, it is necessary to realize a virtual image optical system with a short distance Z in which the image displayed on the image display device 4 is directly magnified by the concave mirror 1, and that the vertical center of the screen of the image display unit of the image display device 4 needs to be positioned below the center of the concave mirror 1.

[0053] On the other hand, with this arrangement, the distance between the image display device 4 and the upper end of the concave mirror 1 (corresponding to light ray R1) is long, and the distance between the image display device 4 and the lower end of the concave mirror 1 (corresponding to light ray R3) is short. Therefore, it is preferable to arrange the image display device 4 so that the distance between the image display device 4 and the concave mirror 1 is as uniform as possible.

[0054] In the virtual image optical system of this embodiment (see Figs. 6 and 7), distortion correction of a virtual image and aberration correction by optical elements that correct aberrations generated in the virtual image are performed between the image display device 4 and the concave mirror 1, which will be described later with reference to Fig. 8. That is, a virtual image can be obtained by the concave mirror 1 by arranging the image display device 4 (object point) inside the focal point F (focal length f) with respect to point O on the optical axis of the concave mirror 1. For convenience of explanation, Fig. 8 regards the concave mirror 1 as a convex lens with the same positive refractive power, and shows the relationship between the object point, the convex lens (for convenience of explanation, it is represented as a concave mirror in Fig. 8), and the virtual image generated.

[0055] In this embodiment, an optical element 2 is disposed to reduce distortion and aberration occurring in the concave mirror 1. This optical element may be a transmissive optical lens or a concave mirror, but it is preferable that the image light from the image display device 4 is: (1) When the light beam is incident on the reflecting surface as a telecentric beam, the refractive power of the lens or concave mirror 1 is nearly zero; (2) When the image light from the image display device 4 diverges and enters the optical element, the optical element has a positive refractive power; (3) When the image light from the image display device 4 is condensed and enters the optical element, the optical element has a negative refractive power; In this way, the direction (angle and position) of the light beam incident on the concave mirror is controlled, and distortion aberration of the virtual image that occurs is corrected. Furthermore, in the case of a transmissive optical lens, the interaction between the entrance surface on the image display device 4 side and the exit surface on the concave mirror 1 side corrects aberration related to the imaging performance that occurs in the virtual image. Although one optical element has been described in this embodiment, multiple transmissive optical elements may be used, or a combination of a reflective optical element (mirror) and a transmissive optical element may be used.

[0056] At this time, as described above, the size of the virtual image visually recognized by the driver differs between the upper end and the lower end of the virtual image due to the inclination of the windshield, that is, the distance a between the image display device 4 and the concave mirror 1 and the distance b between the concave mirror 1 and the virtual image. Therefore, a double image of the virtual image occurs with the windshield or the combiner as a reflecting surface. Therefore, in this embodiment, a technology has been developed to reduce the double image of the virtual image that occurs in such a case by devising an optical system, and the details of this technology will be described below.

[0057] <Mechanism of virtual and double images> As a result of various investigations, the inventors have developed a technique for reducing double images caused by virtual images, which will be described in detail below, based on the findings described below.

[0058] As shown in Figure 9, the virtual image that is reflected on the top of the windshield and viewed by the driver is due to the inclination of the windshield and the light rays that generate the virtual image enter the windshield at an angle. If the thickness of the windshield is t, then the reflection position a of the normal light reflected by the reflective surface closest to the driver (hereinafter referred to as reflective surface 1) and the reflection position b of the back-reflected light reflected by the reflective surface farther from the driver (hereinafter referred to as reflective surface 2) are shifted upwards by a distance L in the vertical direction, and two virtual images are formed.

[0059] The normal virtual image due to normal light and the second virtual image due to back-reflected light have almost the same brightness because the reflectance of light incident on the windshield from the air (4%) is equal to the reflectance at the interface between the windshield and the air (4%). For this reason, reducing the brightness of the virtual image due to back-reflected light is essential to obtain good resolution performance for virtual images.

[0060] On the other hand, the virtual image that is reflected at the bottom of the windshield and viewed by the driver is similar to the reflection at the top shown in Figure 9, as the windshield is tilted and the light rays that generate the virtual image enter the windshield at an angle, but the light reflected from the back side is shifted above the regular reflected light, forming two virtual images.

[0061] Furthermore, in the left-right direction of the screen, the back-reflected light is shifted in a direction away from the point where the optical axis of the concave mirror intersects with the windshield, relative to the regular reflected light, forming two virtual images.

[0062] As mentioned above, if the refractive index of the windshield is 1.5, the relationship between the angle of incidence of the image light on the windshield and the reflectance is as shown in Figure 34. In the case of perpendicular incidence, the reflectance is about 4% for both S-polarized and P-polarized light, but when the angle of incidence exceeds 25 degrees, the reflectance of S-polarized light increases.

[0063] For this reason, when an LCD is used as an image display device, the reflectivity of the windshield differs depending on which polarization is used for the image output light, and there is a possibility that the brightness of the virtual image visible to the driver will change depending on the angle of incidence on the reflective surface.

[0064] Furthermore, if the area in which the driver can see the virtual image is expanded without changing the distance between the windshield and the concave mirror, the angle at which the image light rays enter the windshield increases, resulting in double images being generated above, below, left, and right of the screen, which impairs the sense of focus of the virtual image.

[0065] For this reason, the inventors discovered that it is even better to tilt the image display device 4 with respect to the optical axis of the concave mirror 1 as shown in Figure 8, thereby making the image magnification M' = b' / a' at the upper end of the virtual image approximately equal to the image magnification M = b / a at the lower end of the virtual image, and thereby reducing the distortion aberration that occurs.

[0066] Furthermore, the average radius of curvature of the vertical cross-sectional shape of the optical element 2 and the average radius of curvature of the horizontal cross-sectional shape are set to different values, thereby correcting distortion aberration and aberration that degrades the imaging performance of a virtual image, which are generated due to the optical path difference caused by the difference between the vertical radius of curvature Rv and the horizontal radius of curvature Rh of the front glass described above.

[0067] As described above, in the information display device 100 that obtains a virtual image by directly reflecting image light onto the windshield 6, the most important thing in ensuring the imaging performance of the virtual image is to correct the aberration caused by the optical path difference resulting from the difference between the vertical radius of curvature Rv and the horizontal radius of curvature Rh of the windshield 6.

[0068] For this reason, the inventors have reduced the degradation of virtual image formation performance caused by differences in the radius of curvature of the windshield by using a free-form surface shape (see equation 1 below) that makes it possible to define the shape of the surface as a function of absolute coordinates (x, y) from the optical axis, as opposed to an aspheric surface shape (see equation 2 below) that has been used in conventional optical design and defines the shape of the lens surface or mirror surface as a function of the distance r from the optical axis.

[0069]

number

[0070] The aspheric shape that defines the shape of a lens surface or mirror surface as a function of the distance r from the optical axis is expressed by the following equation 2.

[0071]

number

[0072] The refractive index of a windshield for an automobile is usually n=1.5, and the reflectance per surface is 5%. As described above, the information display device reflects a virtual image on the windshield to form an image in the driver's eyebox. For this reason, as shown in FIG. 9, the image light is separated into regular reflected light reflected by the reflecting surface 1 on the inside of the windshield and back-reflected light reflected by the reflecting surface 2 exposed to the outside air, and is recognized as a double image by the driver's eyes. The direction in which this double image occurs differs depending on the vertical and horizontal directions of the windshield, and when the information display device 100 is placed below the windshield, the double image generated by the back-reflected light occurs above the image generated by the regular reflected light.

[0073] Similarly, even when the information display device 100 is placed above the windshield, a double image caused by back-reflected light appears above the image caused by regular reflected light.

[0074] On the other hand, double images in the horizontal direction on the windshield occur on the outside (away from the driver) in the periphery of the windshield because the radius of curvature is smaller at the periphery than at the center of the windshield. (1) An anti-reflective coating is applied to the surface of the windshield exposed to the outside air to reduce light reflected from the back side. (2) Furthermore, the inventors have devised a method for reducing the appearance of double images by applying the measures described below to a projection optical system that generates a virtual image.

[0075] Next, an embodiment for reducing the above-mentioned double images will be described in detail with reference to Fig. 10. For the sake of simplicity, a real image projection optical system will be used for the description.

[0076] Figure 10 shows the relationship between object point P1 and image point P0 in a real image projection optical system. The imaging performance is evaluated by equally dividing the entrance pupil and directing light rays from the virtual image side (the original image point) toward the panel surface (the original object point), and evaluating the imaging performance on the panel surface.

[0077] The inside of the driver's eyebox was divided as shown in Fig. 11, and ray tracing was performed at equal intervals to evaluate the imaging performance on the panel surface corresponding to each evaluation point. The results based on the lens data shown in Fig. 14 and Fig. 15 for this embodiment show that, as shown in Fig. 12 and Fig. 13, the magnitude of aberration occurring at the center and periphery of the screen is different, so the spot shape differs depending on the position on the screen, and the spot does not become concentric with respect to the chief ray passing through the center of the entrance pupil (the point where it intersects with the optical axis), resulting in blurring (aberration).

[0078] Therefore, in order to reduce aberrations occurring outside the principal ray, it is advisable to design the lens so that light rays passing through the upper peripheral part of the pupil are directed inward from the principal ray. Specifically, it is advisable to dispose an optical element having a shape such that the refractive power in the optical path through which light rays passing through the upper peripheral part above the position of the principal ray pass is relatively stronger than the refractive power in the optical path through which the principal ray passes.

[0079] This will be explained in the case of reverse tracing, in which light rays are sent from an image point to an object point, as shown in Figure 10. In this method, the object point is the virtual image side and the image point is the panel surface, the entrance pupil of the virtual image optical system is equally divided, the light rays are sent, and the imaging performance at the panel surface is evaluated. Even in the virtual image optical system, the relative refractive power of the virtual image optical system differs between the meridional ray shown by the solid line and the sagittal ray shown by the dashed line.

[0080] For this reason, if the focus performance is optimal with sagittal rays, the meridional rays will be focused in front of the panel surface, and aberration will occur on the panel surface (shown in gray (mesh portion) in the figure). For this reason, of the double images that occur on the windshield described above, when the information display device 100 is placed below the windshield, the double image that occurs due to back-surface reflected light will occur above the image due to regular reflected light. For this reason, in order to reduce this, it is advisable to make the relative refractive power of the virtual image optical system through which the light rays that pass above the center of the entrance pupil pass, smaller than the relative refractive power of the virtual image optical system through which the light rays that pass at the center and below the center of the other entrance pupil pass, so that aberration will occur below the chief ray.

[0081] On the other hand, the double image in the direction horizontal to the windshield has a smaller radius of curvature at the periphery than at the center of the windshield, so in the periphery, the double image appears on the outside (away from the driver). Therefore, since the double image caused by the back surface reflected light appears outside the image caused by the regular reflected light, in order to reduce this, it is advisable to make the relative refractive power of the virtual image optical system through which the light rays passing outside the center of the entrance pupil pass smaller than the relative refractive power of the virtual image optical system through which the light rays passing through the center of the other entrance pupil and inside the center pass, so that aberration occurs inside the principal ray.

[0082] In addition, instead of the above-mentioned lens design, as shown in FIG. 35, the panel surface 4A, which is the image display device 4 constituting the real image projection optical system, can be curved to fit the curved surface of the windshield to obtain the same effect as above. More specifically, since the vertical radius of curvature of the windshield is smaller than the horizontal radius of curvature, if the windshield is replaced with a concave mirror, the optical power in the vertical direction is large. Therefore, the vertical radius of curvature of the panel is made smaller than the horizontal radius of curvature, thereby reducing the optical Petzval sum of the entire system and reducing the curvature of the field. This can be achieved by configuring the panel surface 4A to be curved convexly toward the light source 5A. Note that, as mentioned above, the windshield has different radii of curvature in the vertical and horizontal directions, so it would be preferable to appropriately set the curvature of the panel surface 4A in accordance with the different radii of curvature of the windshield.

[0083] In order to more efficiently take in light into the above-mentioned virtual image optical system, it is advisable to make the radius of curvature of the panel surface 4B coincide with the radius of curvature of the light source 5B as shown in FIG.

[0084] Next, a configuration according to an embodiment of the present invention for reducing the above-mentioned double image and forming a highly visible virtual image will be described in detail with reference to Fig. 16 to Fig. 32. Fig. 16 is an enlarged view of a main part of a liquid crystal panel and a backlight light source 5 as an image display device 4 of a virtual image optical system according to the above-mentioned embodiment. An image is displayed on a liquid crystal panel display surface 11 by modulating light from a backlight by an image signal input from a flexible substrate 10 of the liquid crystal panel, and a virtual image is generated from the displayed image by a virtual image optical system (in the embodiment, a free-form concave mirror and a free-form optical element), and the image information is conveyed to the driver.

[0085] In the above configuration, the light source element of the backlight light source 5 uses an LED light source, which is relatively inexpensive and reliable as a solid light source. Since a surface-emitting type LED is used to achieve high output, the light utilization efficiency is improved using technical ingenuity, which will be described later. The light-emitting efficiency of an LED with respect to input power varies depending on the color of light emitted, but is about 20 to 30%, and most of the remainder is converted into heat. For this reason, the frame on which the LED is attached is provided with heat-dissipating fins 13 made of a material with high thermal conductivity (for example, a metal material such as aluminum) to dissipate heat to the outside, which has the effect of improving the light-emitting efficiency of the LED itself.

[0086] In particular, LEDs currently on the market that emit red light have a significantly reduced light emission efficiency when the junction temperature increases, and at the same time the chromaticity of the image changes, so it is preferable to give priority to reducing the LED temperature and increase the area of ​​the corresponding heat dissipation fins to improve cooling efficiency. In the example shown in Fig. 17, a light guide 18 is used to efficiently guide the diffused light from the LED to the liquid crystal panel 4, but it is preferable to use a backlight light source that is entirely covered with, for example, an exterior member 16 to prevent dust and the like from adhering to it.

[0087] 17 shows an enlarged view of the main part of the light source unit including the LEDs as the light source, the light guide, and the diffusion plate, and as is clear from Fig. 17, the openings 21a, 22a, 23a, and 24a for taking in the divergent light rays from the LEDs of the light funnels 21, 22, 23, and 24 are made flat, and a medium is inserted between them and the LEDs to optically connect them, or the openings are made convex to provide a light collecting effect, thereby making the divergent light from the light source as parallel as possible and reducing the angle of incidence of the light incident on the interface of the light funnel. As a result, the divergence angle can be further reduced after passing through the light funnel, making it easier to control the light source light that is reflected by the light guide 18 and then directed toward the liquid crystal panel.

[0088] Furthermore, in order to improve the efficiency of use of the divergent light from the LEDs, a PBS (Polarizing Beam Splitter) is used at the joint 25 between the light funnels 21-24 and the light guide 18 to perform polarization conversion and convert the light into a desired polarization direction, thereby improving the efficiency of the light incident on the LCD.

[0089] As described above, when the polarization direction of the light from the light source is aligned, it is even better to use a material with low birefringence for the material of the light guide 18, so that problems such as coloring when displaying black do not occur when the direction of polarization rotates and passes through the liquid crystal panel.

[0090] As described above, the light flux from the LED with a reduced divergence angle is controlled by the light guide, reflected by the total reflection surface provided on the inclined surface of the light guide 18, diffused by the diffusion member 14 arranged between the opposing surface and the liquid crystal panel, and then enters the liquid crystal panel 4 as an image display device. In this embodiment, as described above, the diffusion member 14 is arranged between the light guide 18 and the liquid crystal panel 4, but the same effect can be obtained by providing the end face of the light guide 18 with a diffusion effect, for example, by providing a fine uneven shape.

[0091] Next, the configuration of the light guide 18 described above and the effects obtained thereby will be described with reference to Fig. 20. Fig. 20 is an external view showing the light guide 18 of this embodiment. The light flux whose divergence angle has been reduced by the light funnels 21-24 shown in Fig. 17 is incident on the light incident surface 18a of the light guide 18. At this time, the divergence angle in the vertical direction (the up and down direction in Fig. 21) is controlled by the effect of the shape of the incident surface (the cross-sectional shape is shown in Fig. 21), and the light is efficiently propagated within the light guide 18.

[0092] 21 is an enlarged cross-sectional view of a main part of a light guide, in which the light source light, the divergence angle of which has been reduced by the light funnels 21-24, passes through the joint 25, enters from the entrance surface 18a as described above, and is totally reflected by the prism 18 provided on the opposing surface, toward the opposing surface 17. The total reflection prism 18 is formed by dividing its shape into a stepped shape in the vicinity of the entrance surface 18a (enlarged view of part B) and at the end (enlarged view of part A) according to the divergence angle of the light beam incident on each surface, thereby controlling the angle of the total reflection surface. Meanwhile, the division dimension of the total reflection surface described above is used as a variable to control the arrival position and energy amount of the divided light beam after reflection, so that the light beam incident on the liquid crystal panel 4, which is an image display device, has a uniform light amount distribution in the exit surface of the liquid crystal panel 4.

[0093] FIG. 18 shows the results of a simulation of the state in which the light emitted from the backlight passes through the liquid crystal panel in the information display device 100 of this embodiment. FIG. 18(a) is a diagram showing the state of light emission as viewed from the longitudinal direction of the liquid crystal panel, and FIG. 18(b) is a diagram showing the state of light emission as viewed from the lateral direction of the liquid crystal panel. In this embodiment, in order to widen the horizontal angle of the FOV beyond the design, the horizontal diffusion angle is made larger than the vertical direction, and the design is such that the brightness of the virtual image viewed by the left and right eyes does not change drastically even if the driver moves the position of the eyes by shaking their head.

[0094] Furthermore, by reducing the divergence angle of the backlight in the vertical direction, the divergence angle of the image displayed on the liquid crystal panel in the vertical direction of the screen is reduced, thereby suppressing the occurrence of double images. Figure 19 shows the luminance distribution on the exit surface of liquid crystal panel 4 when using a backlight in which the light exit direction and intensity are controlled using light guide 18, as in this embodiment. As is clear from Figure 19, in addition to the luminance distribution in the vertical direction (short side direction) of the screen, the gradient of the luminance decrease outside the effective range in the vertical direction (long side direction) of the screen can be reduced.

[0095] As shown in Figs. 23 and 28, the light (image light) emitted from the liquid crystal panel used as the image display device in the information display device 100 of this embodiment shows a predetermined transmittance in the range of ±50° when the viewing angles in the left-right and up-down directions are used as parameters (see Fig. 22). Better transmittance characteristics can be obtained by setting the viewing angle range within ±40°. As a result, as shown in Figs. 24 and 29, the brightness of the screen varies greatly depending on the direction (viewing angle) in the left-right and up-down directions of the display screen. This is due to the angle characteristics of the backlight brightness shown in Figs. 25 and 26.

[0096] For this reason, the inventors narrowed the viewing angle characteristic of the backlight to a small range by controlling the angle of the total reflection surface of the light guide 18 and the divergence angle of the light source light from the LEDs by the light funnels 21-24 so that the light emitted from the liquid crystal panel 4 to be taken into the virtual image optical system can be obtained as light perpendicular to the screen as much as possible, thereby obtaining high brightness. Specifically, as shown in Figures 24 and 29, in order to obtain a high-brightness image, light in the range of ±30° in the left and right viewing angles is used, and considering the contrast performance shown in Figures 27 and 31, a virtual image using a source image with good image quality can be obtained by narrowing it down to ±20° or less.

[0097] As described above, the contrast performance that influences the image quality of an image display device is determined by how much the luminance when black is displayed (referred to as black display luminance in Figs. 30 and 32), which is the basis for determining image quality, can be reduced. For this reason, it is preferable to use an iodine-based polarizing plate with a high degree of polarization between the liquid crystal panel 4 and the backlight.

[0098] On the other hand, by using a dye-based polarizing plate as the polarizing plate provided on the optical element 2 side (light exit surface), high reliability can be obtained even when external light is incident or the environmental temperature is high.

[0099] When performing color display on the liquid crystal panel 4, a color filter is provided corresponding to each pixel. Therefore, when the light source color of the backlight is white, the color filter absorbs a lot of light, resulting in a large loss. Therefore, the inventors have developed a method using multiple LEDs as shown in FIG. 17 above: (1) Adding a green LED, which contributes more to brightness than using multiple white LEDs. (2) Adding red or blue LEDs to white LEDs enhances the color gamut of the image. (3) By arranging red, blue, and green LEDs separately and adding a green LED, which contributes greatly to brightness, and driving the LEDs individually, the color reproduction range is expanded, the color gamut is improved, and brightness is also increased. (4) By implementing the above (3), the transmittance of each color filter for the peak brightness of the red, blue, and green LEDs is increased, thereby improving the overall brightness. (5) Furthermore, as a second embodiment of the backlight, a PBS is placed between the light funnel and the light guide to align the light to a specific polarization, thereby reducing damage to the polarizing plate on the entrance side of the liquid crystal panel. It goes without saying that the polarization direction of the polarizing plate placed on the entrance side of the liquid crystal panel should be the direction in which the polarized waves aligned in a specific direction pass after passing through the PBS (Polarizing Beam Splitter).

[0100] As described above, in the image display device 4 according to the embodiment of the present invention, a λ / 4 plate may be provided on the exit surface of the liquid crystal display panel to circularly polarize the exiting light. As a result, the driver can monitor a clear virtual image even when wearing polarized sunglasses.

[0101] Furthermore, by forming the reflective film of the reflective mirror used in the virtual image optical system from a metal multilayer film, the angle dependency of the reflectance is small and the reflectance does not change depending on the polarization direction (P waves or S waves), making it possible to maintain uniform chromaticity and brightness on the screen.

[0102] Furthermore, by providing an optical component having an ultraviolet reflective film or a combination of an ultraviolet reflective film and an infrared reflective film between the virtual image optical system and the windshield, the liquid crystal display panel and polarizing plate can be protected from temperature rise and damage even when external light (sunlight) is incident, thereby preventing a loss of reliability of the information display device.

[0103] In addition, the virtual image optical system is optimally designed, taking into account the difference between the radius of curvature in the horizontal direction of the vehicle and the radius of curvature in the vertical direction of the windshield, which was the projection target in the conventional technology, and a concave mirror 1 with its concave surface facing the windshield 6 side is arranged between the windshield and the image display device or intermediate image display unit, thereby enlarging the image of the image display device 4 and reflecting it on the windshield 6. At this time, an optical element is arranged between the above-mentioned concave mirror 1 and the image display device 4, and the image light beam that forms the enlarged image (virtual image) of the image that is imaged corresponding to the driver's viewpoint position passes through the optical element arranged between the image display devices, and corrects the distortion and aberration generated by the concave mirror 1. Therefore, it is possible to obtain a virtual image with significantly reduced distortion and aberration compared to a conventional virtual image optical system with only a concave mirror.

[0104] Furthermore, in the configuration of this embodiment shown in FIG. 1, the virtual image obtained by reflection at the upper part of the windshield 6 (upper part in the vertical direction of the vehicle body) needs to be imaged farther away. Therefore, in order to favorably image the image light flux diverging from the upper part of the image display device on which the corresponding image is displayed, the focal length f1 of the optical element arranged between the concave mirror 1 and the image display device 4 described above needs to be short, and conversely, the virtual image obtained by reflection at the lower part of the windshield 6 (lower part in the vertical direction of the vehicle body) needs to be imaged closer. Therefore, in order to favorably image the image light flux diverging from the lower part of the image display device on which the corresponding image is displayed, it is preferable to set the composite focal length f2 of the multiple optical elements arranged between the concave mirror 1 and the image display device 4 described above to be relatively long.

[0105] In addition, in this embodiment, in order to correct the screen distortion of the virtual image viewed by the driver due to the difference between the radius of curvature of the windshield 6 in the horizontal direction (parallel to the ground) and the vertical direction (direction perpendicular to the horizontal direction of the windshield), optical elements with different axial symmetries with respect to the optical axis are arranged in the virtual image optical system, thereby achieving the correction of the above-mentioned distortion.

[0106] Above, the planar light source device suitable for use in an electronic device having an image display device according to various embodiments of the present invention has been described. However, the present invention is not limited to only the above-mentioned embodiments, and various modified examples are included. For example, the above-mentioned embodiments are detailed descriptions of the entire system in order to easily explain the present invention, and are not necessarily limited to those having all of the configurations described. In addition, it is possible to replace a part of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add the configuration of another embodiment to the configuration of one embodiment. In addition, it is possible to add, delete, or replace a part of the configuration of each embodiment with another configuration. [Explanation of symbols]

[0107] 100...information display device, 101...automobile, 1...concave mirror, 2...optical element, 4...image display device, 4A, 4B...liquid crystal display panel, 5A, 5B...backlight light source, 6...projected member (windshield), 7...housing, V1...virtual image, 8...eye box (observer's eye), 9...light source unit, R1...upper limit image light, R2...central image light, R3...lower limit image light, 10...flexible substrate, 11...image display surface, 12...frame, 13...fin, 14...diffusion member, 16...exterior member, 17...exit surface, 18...light guide, 20...light funnel unit, 21-24...light funnel, 36...light emitted from liquid crystal panel.

Claims

1. An information display device that displays virtual image information on a windshield of a vehicle, an image generating unit that generates an image of the image information; an optical system for receiving light from the image generating unit and displaying a virtual image obtained by enlarging the image generated by the image generating unit; an optical member between the optical system and the windshield; the optical system includes a concave mirror; the image generating unit includes a screen plate, displays an image on the screen plate, reflects image light from the screen plate by the concave mirror, and reflects the reflected light by the windshield to be incident on the driver's eye of the vehicle; The optical member absorbs or reflects infrared rays of external light. Information display device.

2. 2. The information display device according to claim 1, The shape of the concave mirror is such that it has different average radii of curvature in the horizontal and vertical directions so as to compensate for the difference between the radii of curvature of the windshield in the vertical and horizontal directions. Information display device.

3. 2. The information display device according to claim 1, The image generating unit is provided at an angle with respect to the optical axis of the concave mirror so that an image magnification at an upper end of a virtual image and an image magnification at a lower end of the virtual image are equal to each other. Information display device.

4. 2. The information display device according to claim 1, The image generating unit includes a light source having a radius of curvature that matches the radius of curvature of a light exit surface of the image generating unit. Information display device.

5. The information display device according to claim 1 , The screen plate includes a microlens array in which microlenses are arranged two-dimensionally. Information display device.

6. The information display device according to claim 1 , An anti-reflection film is provided on the surface of the windshield that is exposed to the outside air. Information display device.

Images