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 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, but it is also an important performance factor that the virtual image has high resolution and is highly visible.

[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 reflections that occur on the final reflective surface, the windshield or combiner.

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

[0006] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-194707 [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 using conventional technology 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 Figure 33. For convenience of explanation, Figure 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 Figure 33), and the virtual image that is generated.

[0009] In conventional technology, in order to expand the visible range of the virtual image generated by the concave mirror 1', it is possible to move the object point AB closer to the focal point F and increase the size of the concave mirror relative to the object size AB. However, achieving the desired magnification requires a smaller radius of curvature for the concave mirror, making it difficult to achieve both. As a result, the mirror size becomes smaller, resulting in a large effective magnification, but only a virtual image with a small visible range. Therefore, to simultaneously satisfy (1) the desired virtual image size and (2) the required virtual image magnification M = b / a, the dimensions of the concave mirror must be adjusted to match the viewing range, and the virtual image magnification must be determined in conjunction with the image display device.

[0010] For this reason, in the prior art, in order to obtain a large virtual image in the desired viewing range, it was necessary to increase the distance from concave mirror 1' to the virtual image, that is, 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 Figure 33. However, no consideration was given to the double image of the virtual image caused by double reflection at the windshield or combiner.

[0011] Furthermore, for example, the example of a head-up display device disclosed in the above-mentioned Patent Document 1, which is a conventional technology, includes a device for displaying an image and a projection optical system for projecting the image displayed on the display device, 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 achieving compactness. However, there is no mention of means for reducing the double images caused by reflections 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, safety issues remain, such as the possibility of injury to the driver if the HUD device becomes detached in the event of a collision.

[0013] For this reason, it is thought that the method described in Patent Document 1, in which the windshield is used as a reflective surface, will become mainstream in the future. Therefore, we have devised a technical means to reduce the reflection of the image light that generates the 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, as described in detail below, by using optical system innovations.It also aims to provide an information display device that can form a highly visible virtual image in which the distortion and aberration of the virtual image seen by the driver are reduced to a level that is practically acceptable. [Means for solving the problem]

[0015] As an example of the present invention made to achieve the above-mentioned object, 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 version 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, displays an image on the screen plate, reflects the image light from the screen plate by the concave mirror, and reflects the reflected light by the windshield to be incident on the eyes of the driver of the vehicle, and the optical element absorbs or reflects infrared light from outside.

[0016] Thus, 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. [Effects 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 distortions and aberrations in the virtual image observed by the driver while achieving a compact device and controlling the divergence angle of the light source beam entering the virtual image optical system to reduce double images that occur in the virtual image. [Brief explanation of the drawings]

[0018] [Figure 1] FIG. 2 is a schematic diagram illustrating a configuration of peripheral devices of the information display device according to the embodiment. [Figure 2] FIG. 1 is a top view of a vehicle equipped with an information display device. [Figure 3] FIG. 10 is a diagram illustrating differences in the radius of curvature of the windshield. [Figure 4] 1 is a schematic diagram showing an information display device, a windshield, and a driver's viewpoint position; [Figure 5] 1 is a schematic diagram illustrating an example of a virtual image optical system of an information display device. [Figure 6] FIG. 2 is a ray diagram of the entire virtual image optical system of the information display device according to the embodiment. [Figure 7]FIG. 2 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 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. 10 is a diagram showing resolution performance evaluation points within the eye box according to the example. [Figure 12] FIG. 10 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) showing the results of the resolution performance evaluation according to the example. [Figure 13] FIG. 10 is a diagram showing distortion performance as viewed from the center of the eye box according to the example. [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 illustrating the configuration of a light source device. [Figure 18] 1 is a schematic diagram illustrating 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 light emitted from a light source device. FIG. [Figure 20] 3A and 3B are schematic diagrams illustrating the shape of a light guide of the light source device. [Figure 21] 3 is a schematic diagram illustrating 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. [Figure 23] 10 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 brightness in the left and right directions of the screen when white is displayed on the liquid crystal panel. [Figure 25] 10 is a characteristic diagram showing the angular characteristics of backlight brightness of a liquid crystal panel in the left-right direction. [Figure 26] 10 is a characteristic diagram showing the angle characteristics of the backlight brightness of the liquid crystal panel in the vertical direction. [Figure 27] 10 is a characteristic diagram showing the angular characteristics of contrast of a liquid crystal panel in the left-right direction. FIG. [Figure 28] 10 is a characteristic diagram showing transmittance characteristics of a liquid crystal panel in the vertical direction. FIG. [Figure 29] 10 is a characteristic diagram showing the angular characteristics of brightness of a liquid crystal panel in the vertical direction. [Figure 30] 10 is a characteristic diagram showing the angle characteristics of black display luminance in the left and right direction of a liquid crystal panel. FIG. [Figure 31] 10 is a characteristic diagram showing the angle characteristics of contrast of a liquid crystal panel in the vertical direction. FIG. [Figure 32] 10 is a characteristic diagram showing the angle characteristics of the black display luminance of a liquid crystal panel in the vertical direction. [Figure 33] FIG. 1 is a schematic diagram for explaining the principle of a virtual image optical system according to the prior art. [Figure 34] FIG. 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. [Figure 35] FIG. 10 is a schematic diagram for explaining a specific method for reducing the Petzval sum of a virtual image optical system. [Figure 36] FIG. 10 is a schematic diagram for explaining a specific method for reducing the Petzval sum of a virtual image optical system. DETAILED DESCRIPTION OF THE INVENTION

[0019] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings and the like. 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. Furthermore, in all drawings used to explain the present invention, parts having the same function are designated by 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 one 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.

[0021] This information display device 100 is a device (so-called HUD (Headup Display)) that displays various information reflected by 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 as 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 may include, 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, the information display device 100 includes an image display device 4 that projects image light to display information, and a group of corrective lenses 2 that correct distortions and aberrations that occur when the image displayed on the image display device 4 is converted into a virtual image by the concave mirror 1, and these are provided between the image display device 4 and the concave mirror 1.

[0023] The information display device 100 is equipped with 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 target 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 self-luminous VFD (Vacuum Flourescent Display) in addition to a backlight-equipped LCD (Liquid Crystal Display).

[0025] On the other hand, instead of 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 rays are 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 rays are reflected above the windshield 6, which is relatively far from the driver's viewpoint). Furthermore, even better correction can be achieved by correcting the difference in virtual image magnification described above by tilting the image display device 4 with respect to the optical axis of the concave mirror to reduce the distortion itself.

[0028] On the other hand, as shown in Figures 2 and 3, the radius of curvature Rv in the vertical direction of the vehicle's windshield 6 differs from the radius of curvature Rh in the horizontal direction, with Rh > Rv generally being true. Therefore, when viewed as a reflective surface, the windshield 6 appears as a toroidal concave mirror. Therefore, in the information display device 100 of this embodiment, the shape of the concave mirror 1 is adjusted to compensate for the virtual image magnification due to the shape of the windshield 6, i.e., to compensate for the difference in the radii of curvature of the windshield 6 in the vertical and horizontal directions. In this case, if the shape of the concave mirror 1 is a spherical or aspherical shape symmetrical about the optical axis (a shape expressed by Equation 2, described later), it is a function of the distance r from the optical axis, and the horizontal and vertical cross-sectional shapes at distant locations cannot be individually controlled. Therefore, it is preferable to correct the shape as a free-form surface expressed by Equation 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 rays toward the concave mirror 1, thereby correcting distortion in accordance with the shape of the concave mirror 1, and at the same time, correcting aberrations of the virtual image, including astigmatism, which occurs due to the difference between the horizontal and vertical radii of curvature of the windshield 6 mentioned above.

[0030] To further enhance the aberration correction capability, the optical element 2 may be replaced with multiple lenses. Alternatively, a curved mirror may be used instead of a lens element to control the incident position of the light beam on the concave mirror 1 while simultaneously bending the optical path, thereby reducing distortion. As described above, it goes without saying that providing an optical element optimally designed to further improve the aberration correction capability between the concave mirror 1 and the image display device 4 does not depart from the technical spirit 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 inherent aberration correction, the optical distance between the concave mirror 1 and the image display device 4 can be changed, thereby continuously varying the display position of the virtual image from a distant 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 degrades the image quality of the information display device 100 is that the image light rays emitted from the image display device 4 toward the concave mirror 1 are reflected by the surface of the optical element 2 arranged along the way, return to the image display device 4, and are reflected again to be superimposed on the original image light, thereby degrading 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 reflected light described above is not focused on a part 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 polarizer disposed adjacent to the liquid crystal panel to absorb the reflected light from the optical element 2, a second polarizer disposed separately from the liquid crystal panel can be used to reduce degradation in image quality. Furthermore, the backlight 5 of the liquid crystal panel is controlled so that the incident direction of light entering the liquid crystal panel 4 is efficiently incident on the entrance pupil of the concave mirror 1. In this case, by reducing the divergence angle of the light beam entering the liquid crystal panel, not only can the image light be efficiently directed toward the driver's eyepoint, but also high-contrast, highly visible images can be obtained, as shown in Figures 27 and 31. The contrast performance relative to the image divergence angle is more pronounced in the horizontal direction, and excellent characteristics are obtained if the divergence angle is within ±20 degrees. To further improve 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 use an LED (Light Emitting Diode) that has little change in light output due to fluctuations in ambient temperature, and to perform polarization conversion using a PBS (Polarizing Beam Splitter) equipped with optical means for reducing the divergence angle of light.

[0035] Polarizing plates are placed 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 on the backlight 5 side (light entrance surface), a high contrast ratio can be obtained. On the other hand, if a dye-based polarizing plate is used on the optical element 2 side (light exit surface), high reliability can be achieved 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, a problem occurs in that a specific polarized wave is blocked and the image is not visible, particularly when the driver is wearing polarized sunglasses. 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 image light aligned in a specific polarization direction into circularly polarized light.

[0037] The control device 40 obtains various information from such a navigation system 61, such as the speed limit and number of lanes of the road corresponding to the current location 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 surroundings 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 surroundings monitoring device 63 is a device that monitors the situation around the vehicle, and examples include a camera that detects objects around the vehicle based on images taken of the area around the vehicle, or an exploration device that detects objects around the vehicle based on the results of sending and receiving exploration waves.

[0040] The control device 40 acquires information from the driving assistance ECU 62 as foreground information (e.g., the distance to the preceding vehicle, the direction of the preceding vehicle, the locations of obstacles and signs, etc.). Furthermore, an ignition (IG) signal and host vehicle status information are input to the control device 40. Of these pieces of information, the host vehicle status information is information acquired as vehicle information, and includes, for example, warning information indicating the occurrence of a predetermined abnormal state, such as the remaining amount of fuel in the internal combustion engine and the temperature of the coolant. The host vehicle status information also includes the operation result of the turn signal, the traveling speed of the host vehicle, and even gear position information. The control device 40 described above is activated 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 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 a vehicle equipped with the information display device 100 of this embodiment, and in front of the driver's seat of the vehicle body 101, there is a windshield as the projection target 6. Note that the inclination angle of the windshield relative to the vehicle body varies depending on the type of vehicle. Furthermore, the inventors also 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 different radii of curvature Rh in the horizontal direction parallel to the vehicle's contact surface and 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, the ratio of Rh to Rv, was in the range of 1.5 to 2.5 times in many cases.

[0044] Next, the inventors investigated the inclination angle of commercially available windshields. The results showed that, although it differed depending on the vehicle body type, it was 20 to 30 degrees for light vehicles and one-box vehicles, 30 to 40 degrees for sedan types, and 40 degrees or more for sports vehicles. Therefore, in this example, a virtual image optical system was designed taking into consideration the difference between the radius of curvature Rh of the windshield in the horizontal direction parallel to the contact surface of the vehicle and the radius of curvature Rv in the vertical direction perpendicular to the horizontal axis, as well as 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 in 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 how to miniaturize information display device 100. The study conditions were a horizontal FOV of 7 degrees and a vertical FOV of 2.6 degrees, and a virtual image distance of 2 m. At the beginning of the study, a concave mirror 1 (shown simply 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 the basic components, and a single optical path folding mirror was placed between image display device 4 and concave mirror 1. Simulations were performed using the arrangement of each component and the distance from image display device 4 to concave mirror 1 as parameters to minimize the volume of information display device 100.

[0047] As a result, when the image light from the image display device 4 was arranged so that it would not interfere with each component, the volume was found to be 3.6 liters. After that, in order to aim for further miniaturization, a direct method was investigated, in which the optical path folding mirror was eliminated.

[0048] The configuration of the virtual image optical system of this embodiment will be described with reference to Figure 4. Figure 4 is an overall configuration diagram showing the basic configuration for studying miniaturization of the virtual image optical system of this embodiment shown in Figure 1. For simplicity of explanation, optical elements for correcting aberrations and distortions are omitted, and the vertical cross-sectional shape is shown, similar to window glass 6 shown in Figure 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 image display device 4 is placed in a position where a virtual image can be obtained by converting the displayed image into a concave mirror 1.

[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 must be positioned so that they do not interfere with the image display device 4 and block the light when reflected by the concave mirror 1.

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

[0051] As described above, when the relationship between the set height and set depth of the image display device 4 is simulated using distance Z as a parameter, it is found that the set depth can be reduced by reducing distance Z, but on the other hand, the set height increases. Similarly, in the relationship between distance Z and set volume L, compared to the spatial volume from the image display device 4 to the concave mirror (labeled as the optical path volume), the change in set volume (including the LCD drive circuit, light source drive circuit, and backlight volume) changes at distance Z of 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 enlarged 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 advisable 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 the 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; this will be explained later using FIG. 8. That is, by placing 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, a virtual image can be obtained by 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 almost 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 incident on 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 also be used.

[0056] As described above, the size of the virtual image seen by the driver at this time differs between the upper and lower ends of the virtual image due to the tilt 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. As a result, a double virtual image occurs with the windshield or combiner as the reflecting surface. Therefore, in this embodiment, a technology has been developed to reduce the double virtual image that occurs in such cases by using an optical system innovation, and the details of this technology are described below.

[0057] <Mechanism of virtual and double images> As a result of various investigations, the inventors have developed a technique for reducing the occurrence of double images due to 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 caused by the inclination of the windshield and the light rays that generate the virtual image incident on the windshield at an angle. Therefore, if the thickness of the windshield is t, 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 caused by normal light and the second virtual image caused by 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 caused by back-reflected light is essential to achieving good resolution performance for virtual images.

[0060] On the other hand, the virtual image that is reflected at the bottom of the windshield and seen by the driver is similar to the reflection at the top shown in Figure 9. The light rays that generate the virtual image mentioned above enter the windshield at an angle due to the inclination of the windshield, 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 ray onto 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] Therefore, when an LCD is used as the image display device, the reflectivity of the windshield differs depending on which polarization is used for the image output light, and the brightness of the virtual image visible to the driver may 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, causing double images to appear above, below, left, and right of the screen, hindering the sense of focus of the virtual image.

[0065] For this reason, the inventors discovered that it would be 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 roughly matching the image magnification M' = b' / a' at the upper end of the virtual image with the image magnification M = b / a at the lower end of the virtual image, thereby reducing the distortion aberration that occurs.

[0066] Furthermore, by setting the average radius of curvature of the vertical cross-sectional shape of the optical element 2 to different values ​​from the average radius of curvature of the horizontal cross-sectional shape, distortion aberration and aberration that degrades the imaging performance of the virtual image, which are 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, as described above, are corrected.

[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 that occurs 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 windshield 6.

[0068] For this reason, the inventors have reduced the degradation of virtual image formation performance due to differences in the radius of curvature of the windshield by using a free-form surface shape (see equation 1 below) that allows the shape of the surface to be defined as a function of absolute coordinates (x, y) from the optical axis, as opposed to the aspherical 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 an automobile windshield is typically n=1.5, and the reflectance per surface is 5%. As described above, information display devices reflect a virtual image off the windshield to form an image in the driver's eyebox. Therefore, as shown in FIG. 9, the image light is separated into regular reflected light reflected by reflective surface 1 on the inside of the windshield and back-reflected light reflected by reflective surface 2 exposed to the outside air, which is perceived by the driver's eyes as a double image. The direction in which this double image occurs differs depending on the vertical and horizontal directions of the windshield. When information display device 100 is placed below the windshield, the double image caused by back-reflected light appears above the image caused by regular reflected light.

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

[0074] On the other hand, double images in the horizontal direction on the windshield occur to the outside (away from the driver) in the peripheral area 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 that is 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 in a projection optical system that generates a virtual image by applying the measures described below.

[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 the object point P1 and the image point P0 of a real image projection optical system. To evaluate the imaging performance, the entrance pupil is equally divided and light rays are projected from the virtual image side (the original image point) toward the panel surface (the original object point), and the imaging performance at the panel surface is evaluated.

[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 example show that, as shown in Fig. 12 and Fig. 13, the magnitude of aberration generated at the center and periphery of the screen differs, 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 chief ray, it is advisable to design the lens so that light rays passing through the upper peripheral part of the pupil are directed inward relative to the chief 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 through which the chief ray passes is relatively stronger than the refractive power in the optical path through which the chief ray passes.

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

[0080] For this reason, if the focus performance is optimal for sagittal rays, meridional rays will converge in front of the panel surface, and aberration will occur at 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 information display device 100 is placed below the windshield, the double image that occurs due to back-reflected light will occur above the image created by regular reflection light. Therefore, to alleviate this, it is advisable to make the relative refractive power of the virtual image optical system through which 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 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, double images in a direction horizontal to the windshield have a smaller radius of curvature at the periphery than at the center of the windshield, so in the periphery, double images appear to the outside (away from the driver).As a result, double images caused by back-reflected light appear outside the image caused by regular reflected light, so to reduce this, it is advisable to make the relative refractive power of the virtual image optical system through which 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 light rays passing at the center of the other entrance pupil and inside the center pass, so that aberration occurs inside the chief ray.

[0082] Alternatively, instead of the above-described lens design, the same effect can be achieved by curving the panel surface 4A, which is the image display device 4 constituting the real image projection optical system, to fit the curved surface of the windshield, as shown in FIG. 35 . More specifically, because the vertical radius of curvature of the windshield is smaller than the horizontal radius of curvature, replacing the windshield with a concave mirror results in greater optical power in the vertical direction. Therefore, by reducing the vertical radius of curvature of the panel relative to the horizontal direction, the optical Petzval sum of the entire system is reduced, thereby reducing the field curvature. This can be achieved by configuring the panel surface 4A to be convexly curved 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 to correspond to 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 and the radius of curvature of the light source 5B coincident with each other as shown in FIG.

[0084] Next, a configuration according to an embodiment of the present invention that reduces the above-mentioned double images and enables the formation of a highly visible virtual image will be described in detail with reference to Figs. 16 to 32. Fig. 16 is an enlarged view of a main portion 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 the backlight using a video signal input from a flexible substrate 10 of the liquid crystal panel, and a virtual image is generated from the displayed image using a virtual image optical system (in the embodiment, a free-form concave mirror and a free-form optical element), thereby conveying the image information to the driver.

[0085] In the above configuration, the light source element of the backlight light source 5 is a relatively inexpensive and reliable LED light source. Since a surface-emitting type LED is used to achieve high output, the light utilization efficiency is improved using the technical ingenuity described below. The luminous efficiency of an LED relative to input power varies depending on the emitted color, but is approximately 20 to 30%, with most of the remainder being converted into heat. For this reason, the frame on which the LED is mounted 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, thereby improving the luminous efficiency of the LED itself.

[0086] In particular, LEDs currently on the market that emit red light experience a significant drop in luminous efficiency as the junction temperature rises, 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 Figure 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 combine it as a backlight light source that is entirely covered by, for example, an exterior member 16 to prevent dust and other particles from adhering to it.

[0087] 17 shows an enlarged view of the main parts of the light source unit, including the LEDs serving as light sources, the light guide, and the diffuser. As is clear from Fig. 17, openings 21a, 22a, 23a, and 24a that take in divergent light rays from the LEDs in light funnels 21, 22, 23, and 24 are made flat, and a medium is inserted between them to optically connect them, or they are made convex to provide a light-collecting effect, thereby collimating the divergent light from the source as much as possible and reducing the angle of incidence of the light entering 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 from the source that is reflected by light guide 18 and heads toward the LCD panel.

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

[0089] As described above, when the polarization direction of the light source light is aligned, it is even better to use a material with low birefringence as the material for 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 slope of the light guide 18, diffused by the diffusing member 14 arranged between the opposing surface and the liquid crystal panel, and then incident on the liquid crystal panel 4 as an image display device. In this embodiment, as described above, the diffusing member 14 is arranged between the light guide 18 and the liquid crystal panel 4, but a similar effect can be obtained by providing the end face of the light guide 18 with a diffusing 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 beam, whose divergence angle has been reduced by the light funnels 21 to 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 portion of a light guide. Light from the light source, whose divergence angle has been reduced by light funnels 21-24, passes through joint 25 and enters through incident surface 18a as described above. Then, it is totally reflected by prism 18 provided on the opposing surface and directed toward opposing surface 17. Totally reflecting prism 18 is divided into stepped sections near incident surface 18a (enlarged view of part B) and at its 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 dimensions of the total reflection surface described above are used as variables to control the arrival position and energy amount of the divided light beams after reflection, so that the light beams incident on liquid crystal panel 4, which is an image display device, have a uniform light intensity distribution within the exit surface of said liquid crystal panel 4.

[0093] Figure 18 shows the results of a simulation of the state in which light emitted from the backlight passes through the liquid crystal panel in the information display device 100 of this embodiment. Figure 18(a) is a diagram showing the state of light emission as viewed from the longitudinal direction of the liquid crystal panel, and Figure 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 designed angle, the horizontal diffusion angle is made larger than the vertical angle, so that the brightness of the virtual images viewed by the left and right eyes does not change drastically even when the driver moves their eyes, for example by turning 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 also reduced, thereby suppressing the occurrence of double images. Figure 19 shows the luminance distribution on the exit surface of the 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 of the screen (short side direction), it is possible to reduce the gradient of the luminance decrease outside the effective range in the vertical direction of the screen (long side direction).

[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 exhibits a predetermined transmittance in a range of ±50° when the viewing angles in the horizontal and vertical directions are used as parameters (see FIG. 22). Even better transmittance characteristics can be obtained by limiting the viewing angle range to ±40°. As a result, as shown in FIGS. 24 and 29, the brightness of the screen varies greatly depending on the viewing direction (viewing angle) in the horizontal and vertical directions of the display screen. This is due to the angular characteristics of backlight brightness shown in FIGS. 25 and 26.

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

[0097] As mentioned above, the contrast performance that influences the image quality of a video display device is determined by how much the luminance when black is displayed (referred to as black display luminance in Figures 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 polarizer as the polarizer provided 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.

[0099] When a color display is performed on the liquid crystal panel 4, a color filter corresponding to each pixel is provided. 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 brilliance of the image. (3) By arranging red, blue, and green LEDs separately and adding a green LED, which contributes significantly to brightness, and driving the LEDs individually, the color reproduction range is expanded, the color brilliance is enhanced, and brightness is also improved. (4) By implementing (3) above, the transmittance of each color filter relative to the peak brightness of the red, blue, and green LEDs is increased, thereby improving the overall brightness. (5) Furthermore, as a second example of a 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 polarizer on the incident side of the LCD panel. It goes without saying that the polarization direction of the polarizer placed on the incident side of the LCD panel should be the same as the direction in which the polarized light that has been aligned to a specific direction passes 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 can be provided on the exit surface of the liquid crystal display panel to circularly polarize the emitted 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 reflecting 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 wave or S wave), making it possible to maintain uniform chromaticity and brightness on the screen.

[0102] Furthermore, by providing an optical element 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 polarizer can be protected from temperature rise and damage even when external light (sunlight) is incident, thereby preventing the reliability of the information display device from being impaired.

[0103] The virtual image optical system is also optimally designed, taking into account the difference between the radius of curvature of the windshield in the horizontal direction and the radius of curvature in the vertical direction of the vehicle, which was the projection target in conventional technology. A concave mirror 1 with its concave surface facing the windshield 6 is placed between the windshield and the image display device or intermediate image display unit, thereby enlarging the image from the image display device 4 and reflecting it on the windshield 6. At this time, an optical element is placed between the 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 focused corresponding to the driver's viewpoint passes through the optical element placed between the image display devices and corrects the distortion and aberration that occurs in the concave mirror 1. As a result, a virtual image with significantly reduced distortion and aberration can be obtained compared to conventional virtual image optical systems that use only a concave mirror.

[0104] Furthermore, in the configuration of this embodiment shown in FIG. 1 , the virtual image obtained by reflection on the upper part of the windshield 6 (upper part in the vertical direction of the vehicle body) needs to be formed at a greater distance. Therefore, in order to properly form the image light beam diverging from the upper part of the image display device on which the corresponding image is displayed, the focal length f1 of the optical elements arranged between the concave mirror 1 and the image display device 4 described above should be short. Conversely, the virtual image obtained by reflection on the lower part of the windshield 6 (lower part in the vertical direction of the vehicle body) needs to be formed at a closer distance. Therefore, in order to properly form the image light beam diverging from the lower part of the image display device on which the corresponding image is displayed, the composite focal length f2 of the multiple optical elements arranged between the concave mirror 1 and the image display device 4 described above should be set 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), the above-mentioned distortion correction is achieved by arranging optical elements with different axial symmetries with respect to the optical axis in the virtual image optical system.

[0106] The above describes a surface light source device suitable for use in an electronic device equipped with an image display device according to various embodiments of the present invention. However, the present invention is not limited to the above-described embodiments and includes various modifications. For example, the above-described embodiments describe the entire system in detail to clearly explain the present invention, and the present invention is not necessarily limited to a system including all of the described configurations. Furthermore, it is possible to replace part of the configuration of one embodiment with the configuration of another embodiment, or to add the configuration of another embodiment to the configuration of one embodiment. Furthermore, it is possible to add, delete, or replace part of the configuration of each embodiment with other configurations. [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 image light, R2...central image light, R3...lower image light, 10...flexible substrate, 11...image display surface, 12...frame, 13...fin, 14...diffusing member, 16...exterior member, 17...exit surface, 18...light guide, 20...light funnel unit, 21-24...light funnel, 36...light ray emitted from liquid crystal panel

Claims

1. An information display device that displays virtual image information on the windshield of a vehicle, an image generating 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 obtained by enlarging the image generated by the image generation unit; an optical member between the optical system and the windshield, the optical system includes a concave mirror; the image generating unit includes a projection device and a screen plate, displays an image on the screen plate based on the projection device, 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 eyes of the vehicle; the optical member absorbs or reflects infrared rays from external light, the light exit surface of the screen plate, which serves as the light exit surface of the image generating unit, is configured to be concavely curved with respect to the concave mirror, with the vertical radius of curvature being smaller than the horizontal radius of curvature so as to reduce the field curvature of the virtual image optical system, in correspondence with the configuration in which the vertical radius of curvature of the curved surface of the windshield is smaller than the horizontal radius of curvature of the windshield. Information display device.

2. 2. The information display device according to claim 1, The concave mirror has a shape having different average radii of curvature in the horizontal and vertical directions so as to compensate for the difference in 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 light exit surface of the screen plate of the image generation unit is inclined 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. 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.

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

Images