JP7351818B2 - information display device - Google Patents

Description

The present invention relates to an information display device that projects an image onto the windshield or combiner of a car, train, airplane, etc. (hereinafter also generally referred to as a "vehicle"), and which allows the image to be observed as a virtual image through the windshield. The present invention relates to a projection optical system and an information display device using the same.

A so-called head-up display (HUD) projects video light onto a car's windshield or combiner to form a virtual image and displays traffic information such as route information and traffic jam information, as well as vehicle information such as remaining fuel level and coolant temperature. -Up-Display) device is already known from Patent Document 1 below.

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

A head-up display device always requires a windshield or combiner as the final reflective surface that provides a virtual image to the driver, and the inventors believe that in order to obtain high visibility and good resolution performance, the front glass or combiner is the final reflective surface. It has been realized that it is important to improve the double image of the virtual image caused by the double reflection occurring in the glass or combiner.

On the other hand, a device for mounting a main body including a combiner near the ceiling (sun visor) of an automobile has already been proposed, as disclosed in Non-Patent Document 1 below, for example.

Japanese Patent Application Publication No. 2015-194707

PIONEER R&D (Vol.22, 2013)

The principle of generating a virtual image using a concave mirror that realizes a head-up display device according to the prior art is as shown in FIG. By arranging the object point AB, it is possible to obtain a virtual image by the concave mirror 1'. In FIG. 33, for convenience of explanation, the concave mirror 1' is assumed to be a convex lens having the same positive refractive power, and the virtual image generated by the object point, the convex lens (for convenience of explanation, expressed as a concave mirror in FIG. 33), showed the relationship.

In the conventional technology, in order to widen the visible range of the virtual image generated by the concave mirror 1', it is better to bring the object point AB closer to the focal point F and make the concave mirror larger with respect to the object dimension AB, but in order to obtain the desired magnification In this case, the radius of curvature of the concave mirror becomes smaller, 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. Therefore, in order 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 should be adjusted to the viewing range and the dimensions of the concave mirror should be adjusted to suit the viewing range. It is necessary to determine the magnification of the virtual image.

Therefore, in the conventional technology, in order to obtain a large virtual image in a desired viewing range, the distance from the concave mirror 1' to the virtual image is increased, as shown in FIG. Alternatively, it was necessary to increase the distance between the combiner (not shown) and the concave mirror, and at the same time increase the size of the concave mirror. However, no consideration was given to virtual double images caused by double reflections occurring on the windshield or combiner.

Further, for example, in the example of the head-up display device disclosed in the above-mentioned Patent Document 1, which is a conventional technology, the projection optical system includes a device for displaying an image and a projection optical system for projecting the image displayed on the display device. has a first mirror and a second mirror in the optical path from the display device to the viewer, and the incident angle in the image long axis direction on the first mirror, the incident angle in the image short axis direction on the first mirror, and the angle of incidence on the first mirror in the image short axis direction, and Miniaturization is achieved by satisfying predetermined conditions for the relationship between the distance between the image display surface and the first mirror and the width of the virtual image in the horizontal direction that is visually recognized by the viewer. However, there is no description of any means for reducing the double image caused by reflection from both sides of the windshield (the driver side and the outside side).

On the other hand, in a device that is mounted near the ceiling (sun visor) of a car as disclosed in Non-Patent Document 1, double images can be prevented by forming an anti-reflection film on the reflective surface that does not face the driver. has been reduced. However, safety issues still remain, such as the possibility of injury to the driver if the HUD device comes off during a collision.

For this reason, it is thought that the method described in Patent Document 1 mentioned above, in which the windshield is a reflective surface, will become mainstream in the future. We devised a technical means to reduce this by devising the following methods.

The present invention proposes technical means for reducing the double image formation of virtual images that occurs when the windshield is used as a reflective surface, which will be described in detail below, by devising an optical system. An object of the present invention is to provide an information display device capable of forming a highly visible virtual image in which distortion and aberration of the virtual image visually recognized are reduced to a level that poses no problem in practical use.

The present invention, which has been made to achieve the above object, is an information display device that displays virtual image information on a windshield of a vehicle, which includes a display that displays the image information, and an image that is emitted from the display. a virtual image optical system that displays a plurality of virtual images in front of the vehicle by reflecting the light from the windshield, the virtual image optical system including a concave mirror and an optical element; At the top of the windshield, a virtual image such as danger information is superimposed on a distant view, and from the top to the bottom of the windshield, speed information and navigation progress are superimposed on the near view or the hood of the car. Optimizing the shape and position of the optical element in accordance with the image light flux that forms each virtual image separated between the display and the concave mirror so as to form a virtual image such as an arrow indicating a direction, etc. , is equipped with a means for reducing the double image of the virtual image that occurs when the image light flux is reflected on the front and back surfaces of the windshield, so that it can be displayed at multiple positions corresponding to the driver's viewpoint position even though it is small. forming the plurality of virtual images.

As described above, according to the present invention, the light incident on the optical system of the image light from the image display device is adjusted so that the double image generated in the virtual image described above is reduced and an image with improved visibility is obtained. An information display device with a controlled divergence angle is realized.

According to the present invention, the light source luminous flux incident on the virtual image optical system is adjusted to correct distortion and aberration of the virtual image observed by the driver and to reduce double images occurring in the virtual image while realizing miniaturization of the device. By controlling the divergence angle, it is possible to provide an information display device that forms a virtual image with improved visibility.

1 is a schematic configuration diagram showing a peripheral device configuration of an information display device according to an example. FIG. 2 is a top view of a car equipped with an information display device. It is a figure explaining the difference in the curvature radius of a windshield. FIG. 2 is a schematic configuration diagram showing an information display device, a windshield, and a driver's viewpoint position. 1 is a schematic configuration diagram showing an example of a virtual image optical system of an information display device. It is a ray diagram of the whole virtual image optical system of the information display device concerning an example. FIG. 3 is a ray diagram of a part of the virtual image optical system of the information display device according to the embodiment. FIG. 2 is a schematic explanatory diagram illustrating the principle of a virtual image optical system. FIG. 2 is a schematic diagram illustrating the principle of double image generation. FIG. 1 is a schematic explanatory diagram illustrating the principle of the present invention. FIG. 3 is a diagram showing resolution performance evaluation points in an eyebox according to an example. FIG. 3 is a spot diagram showing back tracing results using green light (light rays are skipped from the virtual image to evaluate the imaging state at the video source) showing the results of resolution performance evaluation according to the example. FIG. 3 is a diagram showing distortion performance seen from the center of the eyebox according to the example. It is lens data concerning an example. It is lens data concerning an example. FIG. 2 is a configuration diagram showing the arrangement of a video display device and a light source device. FIG. 2 is a schematic configuration diagram showing the configuration of a light source device. FIG. 2 is a schematic diagram illustrating the state of emission of light beams from an image display device and a light source device. FIG. 2 is a characteristic diagram illustrating the distribution of light emitted from a light source device. It is a schematic block diagram which shows the shape of the light guide of a light source device. FIG. 2 is a schematic configuration diagram showing a cross-sectional shape of a light guide of a light source device. FIG. 2 is a conceptual diagram showing a method for evaluating characteristics of a liquid crystal panel. FIG. 2 is a characteristic diagram showing the transmittance characteristics of a liquid crystal panel in the left-right direction of the screen. FIG. 7 is a characteristic diagram showing the angular characteristics of brightness in the horizontal direction of the screen when white is displayed on the liquid crystal panel. FIG. 3 is a characteristic diagram showing the angular characteristics of the backlight brightness of the liquid crystal panel in the left and right direction. FIG. 2 is a characteristic diagram showing vertical angle characteristics of backlight brightness of a liquid crystal panel. FIG. 3 is a characteristic diagram showing the angular characteristics of the contrast of the liquid crystal panel in the left and right direction. FIG. 3 is a characteristic diagram showing transmittance characteristics of a liquid crystal panel in the vertical direction. FIG. 3 is a characteristic diagram showing vertical angle characteristics of brightness of a liquid crystal panel. FIG. 3 is a characteristic diagram showing the angular characteristics of the black display luminance of the liquid crystal panel in the left-right direction. FIG. 3 is a characteristic diagram showing vertical angular characteristics of the contrast of a liquid crystal panel. FIG. 3 is a characteristic diagram showing vertical angle characteristics of black display luminance of a liquid crystal panel. FIG. 2 is a schematic diagram for explaining the principle of a virtual image optical system according to the prior art. FIG. 3 is a schematic diagram for explaining changes in reflectance of glass depending on the incident angle of S-polarized light and P-polarized light. FIG. 2 is a schematic configuration diagram for explaining a specific method of reducing the Petzval sum of a virtual image optical system. FIG. 2 is a schematic configuration diagram for explaining a specific method of reducing the Petzval sum of a virtual image optical system.

Embodiments of the present invention will be described in detail below with reference to the drawings and the like. Note that the present invention is not limited to the following explanation, and various changes and modifications can be made by those skilled in the art within the scope of the technical idea disclosed in this specification. Further, in all the figures for explaining the present invention, parts having the same functions are given the same reference numerals, and repeated explanation thereof may be omitted.

<Embodiment of information display device>
FIG. 1 is a schematic configuration diagram showing the peripheral equipment configuration of an information display device according to an embodiment of the present invention, and here, as an example, an information display device 100 that projects an image on the windshield of a car will be described. explain.

In order to form a virtual image V1 in front of the own vehicle in the driver's line of sight 8, this information display device 100 displays various information reflected on the projection target member 6 (in this embodiment, the inner surface of the windshield) as the virtual image VI. (Virtual Image) Display device (so-called HUD (Headup Display) In other words, in the information display device 100 of the present embodiment, it is sufficient that a virtual image is formed in front of the own vehicle in the driver's line of sight 8 so that the driver can see it, and the information displayed as a virtual image may be It goes without saying that the information includes, for example, vehicle information and foreground information captured by a camera (not shown) such as a surveillance camera or an around viewer.

The information display device 100 also includes a video display device 4 that projects video light for displaying information, and distortions and aberrations that occur when a virtual image is formed using the concave mirror 1 from the video displayed on the video display device 4. A correction lens group 2 is provided between the image display device 4 and the concave mirror 1 for correction.

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

Examples of the video display device 4 include a backlight-equipped LCD (Liquid Crystal Display) and a self-luminous VFD (Vacuum Florescent Display).

On the other hand, instead of the above-mentioned image display device 4, an image is displayed on a screen by a projection device, and the image is made into a virtual image by the above-mentioned concave mirror 1 and reflected by the windshield 6, which is a member to be projected, and directed to the driver's viewpoint 8. You can also dodge it.

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

Here, in order to reduce the distortion of the virtual image, the shape of the concave mirror 1 is such that in the upper part shown in FIG. The radius of curvature is relatively small so that the magnification becomes large, and on the other hand, the magnification becomes small in the lower part (the area above the windshield 6 where the distance from the driver's viewpoint is relatively long and where light rays are reflected). It is preferable to use a shape with a relatively large radius of curvature. Further, 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 and reduce the distortion itself.

On the other hand, as shown in FIGS. 2 and 3, the windshield 6 of a passenger car has a radius of curvature Rv in the vertical direction of the main body and a radius of curvature Rh in the horizontal direction, and generally there is a relationship of Rh>Rv. Therefore, when the windshield 6 is viewed as a reflective surface, it becomes a toroidal surface of a concave mirror. Therefore, in the information display device 100 of this embodiment, the shape of the concave mirror 1 is designed to correct the virtual image magnification due to the shape of the windshield 6, that is, to compensate for the difference in the radius of curvature of the windshield 6 in the vertical direction and the horizontal direction. The average radius of curvature may be set to be different in the horizontal direction and the vertical direction so as to correct it. At this time, the shape of the concave mirror 1 is a function of the distance r from the optical axis in the case of a spherical or aspherical shape that is symmetrical to the optical axis (a shape expressed by the equation 2 described later), and is a function of the distance r from the optical axis. Since the horizontal and vertical cross-sectional shapes cannot be controlled individually, it is preferable to correct the mirror surface as a function of the coordinates (x, y) of the surface from the optical axis as a free-form surface expressed by Equation 1 described later. .

Returning to FIG. 1 again, a lens element 2, for example, is disposed as a transmission type optical component between the image display device 4 and the concave mirror 1, thereby controlling the direction of light rays emitted to the concave mirror 1. In addition to correcting distortion aberration in conjunction with the shape of the concave mirror 1, correction of virtual image aberrations including astigmatism caused by the difference between the horizontal radius of curvature and the vertical radius of curvature of the windshield 6 is performed. Realize.

Further, in order to further improve the aberration correction ability, the optical element 2 described above may be formed of a plurality of lenses. Alternatively, distortion can also be reduced by arranging a curved mirror in place of the lens element and controlling the incident position of the light beam on the concave mirror 1 at the same time as turning the optical path. As described above, even if an optical element that is optimally designed to improve the aberration correction ability is provided between the concave mirror 1 and the image display device 4, it does not deviate from the technical spirit or scope of the present invention. Needless to say, this is not something you should do. 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 moved to a far distance. It can also be changed continuously from to a close position.

Furthermore, the difference in vertical magnification of the virtual image may be corrected by arranging the image display device 4 at an angle with respect to the normal to the optical axis of the concave mirror 1.

On the other hand, one of the factors 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 disposed in the middle and return to the image display device 4. It is known that the light is reflected again and superimposed on the original image light, degrading the image quality. Therefore, in this embodiment, not only is an antireflection film formed on the surface of the optical element 2 to suppress reflection, but also an antireflection film is formed on the surface of the optical element 2 to suppress reflection. The shape of the lens surface is constrained so that the above-mentioned reflected light does not converge on a part of the image display device 4 (for example, a shape with a concave surface facing the image display device 4). It is preferable to design.

Next, as the image display device 4, in addition to the first polarizing plate disposed close to the liquid crystal panel in order to absorb the reflected light from the optical element 2 described above, a second polarizing plate is used as the liquid crystal panel. By arranging them separately, the deterioration in image quality can be reduced. Further, the backlight 5 of the liquid crystal panel is controlled so that the incident direction of the light incident on the liquid crystal panel 4 is efficiently incident on the entrance pupil of the concave mirror 1. At this time, by reducing the divergence angle of the light flux incident on the liquid crystal panel, it is possible not only to efficiently direct the image light to the driver's eye point, but also to achieve high contrast as shown in Figures 27 and 31. It becomes possible to obtain images with good visibility. The contrast performance with respect to the divergence angle of the image is more remarkable in the horizontal direction, and excellent characteristics can be obtained within ±20 degrees. In order to further improve the contrast performance, it is preferable to use a luminous flux within ±10 degrees.

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 optical means to reduce the divergence angle of light such as an LED (Light Emitting Diode) whose light output changes little with changes in ambient temperature. It is preferable to perform polarization conversion using a PBS (Polarizing Beam Splitter).

Polarizing plates are arranged on the backlight 5 side (light incident 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 as the polarizing plate provided on the backlight 5 side (light incident 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 environmental temperature is high.

When a liquid crystal panel is used as the image display device 4, especially when the driver is wearing polarized sunglasses, a problem occurs in which certain polarized waves are 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. .

The control device 40 receives various information from the navigation system 61, such as the speed limit and number of lanes of the road corresponding to the current location on which the vehicle is traveling, and the planned travel route of the vehicle set in the navigation system 61. The information is acquired as foreground information (that is, information displayed in front of the vehicle using the virtual image).

The driving support ECU 62 is a control device that realizes driving support control by controlling the drive system and control system according to obstacles detected as a result of monitoring by the surrounding monitoring device 63. As the driving support control, for example, , including well-known technologies such as cruise control, adaptive cruise control, pre-crash safety, and lane-keeping assist.

The surroundings monitoring device 63 is a device that monitors the situation around the own vehicle, and includes, for example, a camera that detects objects existing around the own vehicle based on images taken of the surroundings of the own vehicle, and a detection wave sensor. This is an exploration device that detects objects around the vehicle based on the results of transmission and reception.

The control device 40 acquires such information from the driving support ECU 62 (for example, the distance to the preceding vehicle, the direction of the preceding vehicle, the position of an obstacle or a sign, etc.) as foreground information. Further, an ignition (IG) signal and own vehicle status information are input to the control device 40. Among these pieces of information, own vehicle status information is information acquired as vehicle information, such as information indicating that a predefined abnormal state has occurred, such as the remaining amount of fuel in the internal combustion engine or the temperature of the cooling water. Contains warning information to represent. It also includes the operation results of the direction indicators, the traveling speed of the own vehicle, and shift position information. The control device 40 described above is activated when an ignition signal is input. The above is the description of the entire system of the information display device according to the embodiment of the present application.

<First embodiment of virtual image optical system>
Next, further details of the virtual image optical system and the video display device according to this embodiment will be described below.

As already mentioned, FIG. 2 is a top view of a car equipped with the information display device 100 of this embodiment, and a windshield as the projected member 6 is present in front of the driver's seat of the car body 101. . Note that the angle of inclination of this windshield with respect to the vehicle body differs depending on the type of vehicle. Furthermore, the inventors also investigated this radius of curvature in order to realize an optimal virtual image optical system. As a result, as shown in Fig. 3, the windshield has a radius of curvature Rh in the horizontal direction parallel to the ground plane of the automobile and a radius of curvature Rv in the vertical direction perpendicular to the horizontal axis. It has been found that there is generally the following relationship between Rv.
Rh>Rv

It has also been found that the difference in the radius of curvature, that is, Rh with respect to Rv, is often in the range of 1.5 to 2.5 times.

Next, the inventors also investigated commercially available products regarding the angle of inclination of the windshield. As a result, although it varied depending on the vehicle body type, the angle was 20 degrees to 30 degrees for light cars and 1-box types, 30 degrees to 40 degrees for sedan types, and 40 degrees or more for sports types. Therefore, in this example, the difference between the radius of curvature Rh in the horizontal direction of the windshield parallel to the ground plane of the vehicle and the radius of curvature Rv in the vertical direction perpendicular to the horizontal axis and the inclination angle of the windshield are taken into consideration. , designed a virtual image optical system.

More specifically, since the horizontal radius of curvature Rh and the vertical radius of curvature Rv of the windshield, which is the projected member, are significantly different, the horizontal axis of the windshield and the vertical radius to this axis are By providing the optical element 2 which is axially asymmetric with respect to an axis in the virtual image optical system, good aberration correction is realized.

Next, the inventors investigated miniaturization of the information display device 100. As conditions for the study, the FOV was set to 7 degrees horizontally and 2.6 degrees vertically, and the virtual image distance was 2 m. At the beginning of the study, the basic configuration was a concave mirror 1 that generates a virtual image (in FIG. 5 below, it is simply displayed as a plane mirror), an image display device 4, and a backlight 5. A simulation was performed using the arrangement of each member and the distance from the video display device 4 to the concave mirror 1 as parameters so that the volume of the information display device 100 was minimized by placing one optical path folding mirror between them.

As a result, the volume was 3.6 liters when arranged so that the image light from the image display device 4 did not interfere with each component. Afterwards, with the aim of further miniaturization, we investigated a direct method that removed the optical path folding mirror.

The configuration of the virtual image optical system of this example will be explained with reference to FIG. FIG. 4 is an overall configuration diagram showing the basic configuration for considering miniaturization of the virtual image optical system of this embodiment shown in FIG. 1. To simplify the explanation, optical elements for correcting aberrations and distortion are omitted, and the vertical cross-sectional shape is shown in the same manner as the window glass 6 shown in FIG. The video display device 4 is assumed to be a liquid crystal panel, and has a basic configuration in which a backlight 5 is arranged, and the video display device 4 is arranged at a position where a virtual image of the displayed image can be obtained by the concave mirror 1.

At this time, as shown in FIG. 5, 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 upper end, and the image light R3 from the lower end are each reflected by the concave mirror 1. A design constraint is to arrange the light so that it does not interfere with the image display device 4 and block the light when reflected.

Taking into account the design constraints mentioned above, the inventors set the FOV horizontally to 7 degrees and vertically to 2.6 degrees, and also set the virtual image distance to 2 m to connect the concave mirror 1 and the image display device 4 (liquid crystal panel and back panel). The volume of the information display device 100 was determined using the distance Z from the light 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 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. If the distance Z is further shortened to 50 mm or less, the angle α3 between the horizontal plane and the concave mirror 1 becomes larger, and the vertical dimension of the concave mirror 1 also becomes larger.

As described above, when the relationship between the set height and the set depth of the video display device 4 is simulated using the distance Z as a parameter, the set depth can be reduced by decreasing the distance Z, but on the other hand, the set height is too high. Become. Similarly, the relationship between the distance Z and the set volume L is that the set volume (including the LCD drive circuit, light source drive circuit, and backlight unit volume) is smaller than the space volume from the image display device 4 to the concave mirror (displayed as the optical path volume). The change occurred when the distance Z was 60 mm.

From the above, in order to downsize the information display device 100, it is necessary to realize a virtual image optical system in which the distance Z for directly enlarging the image displayed on the image display device 4 with the concave mirror 1 is short, and the image display It has been found that the vertical center of the screen of the image display section of the device 4 needs to be placed below the center of the concave mirror 1.

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

In the virtual image optical system of this embodiment (see FIGS. 6 and 7), aberration correction is performed between the image display device 4 and the concave mirror 1 by an optical element that corrects distortion of the virtual image and corrects aberrations generated in the virtual image. , this will be explained later using FIG. That is, by arranging the image display device 4 (object point) inside the focal point F (focal length f) with respect to the point O on the optical axis of the concave mirror 1, a virtual image by the concave mirror 1 can be obtained. In FIG. 8, for convenience of explanation, the concave mirror 1 is regarded as a convex lens with the same positive refractive power, and the relationship between the object point, the convex lens (for convenience of explanation, expressed as a concave mirror in FIG. 8) and the generated virtual image is shown. Indicated.

In this embodiment, the optical element 2 is arranged to reduce distortion and aberrations generated in the concave mirror 1. This optical element may be a transmissive optical lens or a concave mirror, but the image light from the image display device 4:
(1) When the light beam enters the reflecting surface as a telecentric beam, the refractive power of the lens or concave mirror 1 becomes 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 enters the optical element, the optical element has negative refractive power;
In this way, the direction (angle and position) of the light beam incident on the concave mirror is controlled, and the distortion aberration of the virtual image that occurs is corrected. Furthermore, in the case of a transmission type optical lens, the interaction between the incident surface on the image display device 4 side and the exit surface on the concave mirror 1 side corrects aberrations related to imaging performance that occur in the virtual image. Although one optical element has been described in this embodiment, a plurality of transmissive optical elements may be used, or a combination of a reflective optical element (mirror) and a transmissive optical element may be used.

At this time, the size of the virtual image that the driver visually recognizes is determined by the distance a between the image display device 4 and the concave mirror 1 caused by the inclination of the windshield, and the distance b between the concave mirror 1 and the virtual image, as described above. and differs at the lower end. Therefore, a double virtual image is generated when the windshield or combiner is used as a reflective surface. Therefore, in this embodiment, a technique was developed to reduce the double image formation of the virtual image that occurs in such a case by devising an optical system, and the details thereof will be described below.

<Mechanism of double virtual image generation>
As a result of various studies, the inventors have developed a technique for reducing double imaging of virtual images, which will be described in detail below, based on the knowledge described below.

The virtual image that is reflected at the top of the windshield and seen by the driver depends on the thickness of the windshield, as shown in Figure 9, because the windshield is tilted and the light rays that generate the aforementioned virtual image enter the windshield obliquely. Let t be the reflection position a of the normal light reflected on the reflective surface close to the driver (hereinafter referred to as reflective surface 1), and the back reflected light reflected on the reflective surface far from the driver (hereinafter referred to as reflective surface 2). The reflection position b of is shifted upward by a distance L in the vertical direction, and two virtual images are formed.

This normal virtual image by the normal light and the second virtual image by the back reflected light are the same as the 4% reflectance of the incident light from the air to the windshield and the 4% reflectance at the interface between the windshield and the air. The brightness of the virtual image due to reflected light is almost equal. Therefore, reducing the brightness of the virtual image due to the light reflected from the back surface is essential in order to obtain good resolution performance of the virtual image image.

On the other hand, the virtual image that is reflected at the lower part of the windshield and seen by the driver is similar to the reflection at the upper part shown in Figure 9, due to the slope of the windshield and the light rays that generate the aforementioned virtual image entering the windshield obliquely. However, the other back surface reflected light is shifted above the regular reflected light, forming two virtual images.

Further, in the horizontal 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 the windshield with respect to the regular reflected light, and two virtual images are formed.

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

For this reason, when using an LCD as a video display device, the reflectance of the windshield differs depending on which side of the polarization is used for the video output light, so the brightness of the virtual image visible to the driver depends on the brightness of the virtual image that is visible to the driver. There is a possibility that it changes depending on the angle.

Furthermore, if the area where 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, creating double images on the top, bottom, left, and right sides of the screen, which makes it difficult to focus the virtual image. inhibit the sense of

Therefore, by tilting the image display device 4 with respect to the optical axis of the concave mirror 1 as shown in FIG. It has been found that it is even better to make the image magnifications M=b/a substantially equal to each other and to reduce the distortion caused by this.

Furthermore, by setting the average radius of curvature of the vertical cross-sectional shape of the optical element 2 to different values and the average radius of curvature of the horizontal cross-sectional shape, the difference between the vertical radius of curvature Rv and the horizontal radius of curvature Rh of the windshield described above Corrects distortion caused by optical path differences and aberrations that degrade virtual image formation performance.

As described above, in the information display device 100 that obtains a virtual image by directly reflecting image light on the windshield 6, 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 Correction of the aberrations that occur is most important in ensuring the imaging performance of virtual images.

For this reason, the inventors developed an aspherical shape (see equation 2 below) that defines the shape of a lens surface or mirror surface as a function of the distance r from the optical axis, which has been used in conventional optical design. In contrast, 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 the absolute coordinates (x, y) from the optical axis, the above-mentioned windshield This reduces the deterioration in virtual image imaging performance due to differences in the radius of curvature.

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

The refractive index of an automobile windshield 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 and focuses the image within the driver's eye box. Therefore, as shown in Fig. 9, the image light beam is separated into the normal reflected light reflected by the reflective surface 1 on the inside of the windshield and the back reflected light reflected by the reflective surface 2 in contact with the outside air. To the human eye, it is perceived as a double image. This double image occurs in different directions 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 back-reflected light is different from regular reflection. Occurs at the top of the image due to light.

Similarly, even when the information display device 100 is placed above the windshield, the double image generated by the back-surface reflected light is generated above the image generated by the regular reflected light.

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 it appears on the outside (in the direction away from the driver) at the periphery. To alleviate this,
(1) An anti-reflection film is provided on the surface of the windshield that is in contact with the outside air to reduce light reflected from the back surface.
(2) Furthermore, the inventors have devised a method to reduce the appearance of double images by applying the measures described below to a projection optical system that generates a virtual image.

Next, an embodiment for reducing the double image described above will be described in detail with reference to FIG. Note that here, in order to simplify the explanation, a real image projection optical system will be used.

FIG. 10 shows the relationship between the object point P1 and the imaging point P0 of the real image projection optical system. The imaging performance is evaluated by dividing the entrance pupil equally and emitting light rays from the virtual image side (original imaging point) toward the panel surface (original object point), and evaluating the imaging performance at the panel surface. Evaluate.

The interior of the driver's eyebox was divided as shown in FIG. 11, ray tracing was performed at equal intervals, and the imaging performance on the panel surface corresponding to each evaluation point was evaluated. The results based on the lens data shown in FIGS. 14 and 15 according to this example show that, as shown in FIGS. 12 and 13, the spot shape is The spot is not concentric with the principal ray that passes through the center of the entrance pupil (the point where it intersects with the optical axis), and blur (aberration) occurs.

Therefore, in designing the lens, in order to reduce aberrations occurring outside the principal ray, it is preferable to design the lens so that the rays passing through the upper peripheral portion of the pupil are directed inward from the principal ray. Specifically, it has a shape in which the refractive power in the optical path through which the light ray passes through the upper peripheral portion is relatively stronger than the refractive power in the optical path through which the principal ray passes. It is good to arrange optical elements.

This will be explained in the case of reverse tracing in which a ray is directed from an image point toward an object point, as shown in FIG. In this method, with the object point on the virtual image side and the image point on the panel surface, the entrance pupil of the virtual image optical system is equally divided to emit light rays, and the imaging performance on the panel surface is evaluated. Also in the virtual image optical system, the relative refractive power of the virtual image optical system is different between the meridional ray shown by a solid line and the sagittal ray shown by a broken line.

For this reason, if the focus performance is best with sagittal rays, the meridional rays will be focused in front of the panel surface, and aberrations will occur on the panel surface (shown in gray (mesh area) in the figure). Therefore, among the double images generated on the windshield as described above, when the information display device 100 is placed below the windshield, the double image generated by the back surface reflected light is different from the image generated by the regular reflected light. Occurs at the top. Therefore, to reduce this, the relative refractive power of the virtual image optical system, through which the rays passing above the center of the entrance pupil pass, must be adjusted to the center of the other entrance pupil and It is preferable that the relative refractive power be smaller than the relative refractive power of the virtual image optical system through which light rays passing below the center pass.

On the other hand, since the radius of curvature of a double image in the direction horizontal to the windshield is smaller at the periphery than at the center of the windshield, the double image appears on the outside (in the direction away from the driver) in the periphery. Therefore, the double image generated by the back-reflected light is generated outside the image caused by the regular reflected light, so in order to reduce this, it is necessary to It is preferable that the relative refractive power of the virtual image optical system through which the light ray passing through passes is smaller than the relative refractive power of the virtual image optical system through which the center of the other entrance pupil and the light ray passing inside the center pass.

In addition, instead of the lens design described above, as shown in FIG. 35, the panel surface 4A, which is the image display device 4 constituting the real image projection optical system, may be curved to match the curved surface of the windshield. It is also possible 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, replacing the windshield with a concave mirror increases the optical power in the vertical direction. For this reason, the radius of curvature of the panel in the vertical direction is made smaller than in the horizontal direction to reduce the optical Petzval sum in the entire system and reduce the curvature of field. This can be realized by configuring the panel surface 4A to be curved convexly relative to the light source 5A. Note that, as described above, the windshield has different radii of curvature in the vertical and horizontal directions, so the curvature of the panel surface 4A is also set appropriately in accordance with the different radii of curvature of the windshield. It would be preferable to do so.

In order to more efficiently capture light into the virtual image optical system described above, it is preferable to match the radius of curvature of the panel surface 4B and the radius of curvature of the light source 5B, as shown in FIG.

Next, a configuration according to an embodiment of the present invention for reducing the above-mentioned double image and making it possible to form a highly visible virtual image will be described in detail with reference to FIGS. 16 to 32. FIG. 16 is an enlarged view of essential parts of the liquid crystal panel and backlight source 5 as the image display device 4 of the virtual image optical system according to the above-described embodiment. An image is displayed on the liquid crystal panel display surface 11 by modulating the light from the backlight with a video signal input from the flexible substrate 10 of the liquid crystal panel, and the displayed image is transferred to a virtual image optical system (in the embodiment, a free-form concave surface mirrors and free-form optical elements) to generate a virtual image and convey video information to the driver.

In the above configuration, a relatively inexpensive and highly reliable LED light source is used as a solid-state light source for the light source element of the backlight light source 5. Since surface-emitting type LEDs are used to increase output, the light utilization efficiency is improved by using technical innovations that will be described later. The luminous efficiency of the LED relative to the input power is about 20 to 30%, although it varies depending on the color of the emitted light, and most of the remainder is converted into heat. Therefore, the frame to which the LED is attached is provided with heat dissipation 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 increasing the luminous efficiency of the LED itself. You can get the effect of improving.

In particular, the luminous efficiency of the LEDs currently on the market that emit red light significantly decreases as the junction temperature increases, and at the same time the chromaticity of the image changes, so we prioritize reducing the LED temperature. It is preferable to have a configuration in which the area of the corresponding radiation fin is increased to improve cooling efficiency. In order to efficiently guide the diffused light from the LED to the liquid crystal panel 4, a light guide 18 is used in the example shown in FIG. It is preferable to combine them as a backlight source.

FIG. 17 also shows an enlarged view of the main parts of the light source unit including the LED as the light source, the light guide, and the diffuser plate. As is clear from FIG. 17, the light funnels 21, 22, The openings 21a, 22a, 23a, and 24a that take in the diverging light rays from the LEDs 23 and 24 are made flat, and a medium is inserted between them and the LEDs for optical connection, or they are convex to have a condensing effect. By having this, the diverging light source light is made into parallel light as much as possible, and the angle of incidence of the light that enters the interface of the light funnel is reduced. 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 light source that heads toward the liquid crystal panel after being reflected by the light guide 18.

Furthermore, in order to improve the utilization efficiency of the diverging light from the LED, polarization conversion is performed using a PBS ((Polarizing Beam Splitter)) at the joint portion 25 between the light funnels 21 to 24 and the light guide 18, and the desired polarization direction is changed. By converting to , it is possible to improve the efficiency of light incident on the LCD.

As mentioned above, when the polarization direction of the light source light is aligned, a material with low birefringence is used as the material for the light guide 18, so that the direction of polarization rotates and when passing through the liquid crystal panel. For example, it is better to prevent problems such as coloring when displaying black.

As described above, the light flux from the LED with a reduced divergence angle is controlled by the light guide, is reflected by the total reflection surface provided on the slope of the light guide 18, and is reflected between the opposing surface and the liquid crystal panel. After being diffused by the disposed diffusion member 14, the light enters the liquid crystal panel 4 as a video 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 end face of the light guide 18 is provided with a fine uneven shape, for example, to have a diffusion effect. A similar effect can be obtained even if it is provided.

Next, the configuration of the light guide 18 described above and the effects obtained thereby will be explained using FIG. 20. FIG. 20 is an external view showing the light guide 18 of this example. The light flux whose divergence angle has been reduced by the light funnels 21 to 24 shown in FIG. 17 enters the light incident surface 18a of the light guide 18. At this time, the divergence angle in the vertical direction (vertical 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 propagates efficiently within the light guide 18.

FIG. 21 is an enlarged cross-sectional view of the main part of the light guide, and the light source light whose divergence angle has been reduced in the light funnels 21 to 24 enters from the entrance surface 18a via the joint 25 as described above. , the light is totally reflected by the prism 18 provided on the opposing surface and directed toward the opposing surface 17. The total reflection prism 18 has a shape divided into steps in the vicinity of the incident surface 18a (enlarged view of part B) and at the end (enlarged view of part A), depending on the divergence angle of the luminous flux incident on each surface. This controls the angle of the total reflection surface. On the other hand, in order to make the light intensity distribution of the light beam incident on the liquid crystal panel 4, which is an image display device, uniform within the exit surface of the liquid crystal panel 4, the divided light beam is Controls the position and amount of energy reached after reflection.

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 light output state seen from the longitudinal direction of the liquid crystal panel, and FIG. 18(b) is a diagram showing the light output state seen from the width direction of the liquid crystal panel. In this example, in order to widen the horizontal angle of the FOV beyond the design, the horizontal diffusion angle is increased relative to the vertical direction, so that even if the driver shakes his head or moves his eye position, the left and right It is designed so that the brightness of the virtual image seen by the human eye does not change drastically.

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

The light emitted from the liquid crystal panel (image light) used as a video display device in the information display device 100 of this embodiment is as shown in FIG. 23 and FIG. 22), exhibiting a predetermined transmittance in the range of ±50°. If the viewing angle range is within ±40°, better transmittance characteristics can be obtained. 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.

For this reason, the inventors set the angle of the total reflection surface of the light guide 18 and the light funnels 21 to 24 so that the light emitted from the liquid crystal panel 4, which is taken into the virtual image optical system, can be obtained as perpendicular to the screen as much as possible. By controlling the divergence angle of the light source light from the LED and narrowing down the viewing angle characteristics of the backlight to a small range, high brightness was achieved. Specifically, as shown in FIGS. 24 and 29, in order to obtain high-brightness images, light within a range of ±30° in left and right viewing angles is used, and the contrast shown in FIGS. 27 and 31 is Considering the performance, by narrowing down the angle to ±20° or less, it was possible to simultaneously obtain a virtual image using a source image with good image quality.

As mentioned above, the contrast performance that determines the image quality of a video display device is the basis for determining image quality.The brightness when displaying black (indicated as black display brightness in Figures 30 and 32) can be lowered to what extent. It depends. 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.

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 when the environmental temperature is high.

When performing color display on the liquid crystal panel 4, a color filter corresponding to each pixel is provided. For this reason, when the light source color of the backlight is white, light absorption by the color filter is large, resulting in large loss. Therefore, the inventors used multiple LEDs as shown in FIG. 17 above to:
(1) Add a green LED, which contributes more to brightness than when multiple white LEDs are used.
(2) Add a red or blue LED to the white LED to enhance the glossiness of the image.
(3) By arranging red, blue, and green LEDs individually, and adding a green LED that contributes significantly to brightness and driving the LEDs individually, the color reproduction range can be expanded and the color gloss improved. At the same time, brightness also improves.
(4) By implementing the above (3), the transmittance of each color filter with respect to the peak brightness of the red, blue, and green LEDs is increased, and the overall brightness is improved.
(5) Furthermore, as a second embodiment of the backlight, a PBS is placed between the light funnel and the light guide to align the polarization to a specific one, reducing damage to the polarizing plate on the incident side of the LCD panel. do. It goes without saying that the polarization direction of the polarizing plate disposed on the incident side of the liquid crystal panel may be a direction in which polarized waves aligned in a specific direction pass after passing through a PBS (Polarizing Beam Splitter).

As described above, in the image display device 4 according to the embodiment of the present invention, it is also possible to provide a λ/4 plate on the output surface of the liquid crystal display panel to make the output light circularly polarized. As a result, the driver can monitor a good virtual image even when wearing polarized sunglasses.

Furthermore, by forming the reflective film of the reflective mirror used in the virtual image optical system with a metal multilayer film, the angle dependence of the reflectance is reduced, and the reflectance does not change depending on the polarization direction (P wave or S wave). This makes it possible to maintain uniform chromaticity and brightness on the screen.

Furthermore, by providing an optical member that includes an ultraviolet reflection film or a combination of an ultraviolet reflection film and an infrared reflection film between the virtual image optical system and the windshield, even if external light (sunlight) is incident, the liquid crystal display panel In addition, since the polarizing plate can be reduced from temperature rise and damage, the reliability of the information display device is not impaired.

In addition, the virtual image optical system is optimally designed by taking into account the difference between the radius of curvature in the vehicle horizontal direction and the radius of curvature in the vertical direction of the windshield, which is the projection target member in the conventional technology. A concave mirror 1 having a concave surface facing the windshield 6 is disposed between the image display sections, thereby magnifying 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 on the other hand, an enlarged image (virtual image) of the image is formed corresponding to the driver's viewpoint position. The image light flux passes through the optical element disposed between the image display devices, and corrects distortion and aberration occurring in 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 using only a concave mirror.

Furthermore, in the configuration of this embodiment shown in FIG. 1, the virtual image obtained by being reflected on the upper part of the windshield 6 (the upper part in the vertical direction of the vehicle body) needs to be focused at a farther distance. Therefore, in order to form a good image of the image light flux diverging from the upper part of the image display device on which the corresponding image is displayed, it is necessary to use an optical element disposed between the concave mirror 1 and the image display device 4 described above. The focal length f1 is short, and on the contrary, the virtual image obtained by being reflected at the lower part of the windshield 6 (lower part in the vertical direction of the vehicle body) needs to be focused closer. Therefore, in order to form a good image of the image light flux diverging from the lower part of the image display device on which the corresponding image is displayed, a plurality of optical elements are arranged between the above-mentioned concave mirror 1 and the image display device 4. It is preferable that the composite focal length f2 is set relatively long.

In addition, in this embodiment, the screen distortion of the virtual image viewed by the driver is caused by the difference in the radius of curvature of the windshield 6 in the horizontal direction (parallel to the ground) and the radius of curvature in the vertical direction (direction perpendicular to the horizontal direction of the windshield). In order to correct the distortion, the above-mentioned distortion correction is realized by arranging optical elements having different axial symmetry with respect to the optical axis in the virtual image optical system.

Above, planar light source devices suitable for use in electronic devices equipped with image display devices according to various embodiments of the present invention have been described. However, the present invention is not limited to the above-described embodiments, and includes various modifications. For example, in the embodiments described above, the entire system is explained in detail in order to explain the present invention in an easy-to-understand manner, and the system is not necessarily limited to having all the configurations described. Furthermore, 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. Further, it is possible to add, delete, or replace a part of the configuration of each embodiment with other configurations.

DESCRIPTION OF SYMBOLS 100... Information display device, 101... Car, 1... Concave mirror, 2... Optical element, 4... Image display device, 4A, 4B... Liquid crystal display panel, 5A, 5B... Backlight light source, 6... Projection target member (windshield) ), 7... Housing, V1... Virtual image, 8... Eye box (observer's eye), 9... Light source unit, R1... Upper limit image light, R2... Center image light, R3... Lower limit image light, 10... Flexible board, DESCRIPTION OF SYMBOLS 11... Image display surface, 12... Frame, 13... Fin, 14... Diffusion member, 16... Exterior member, 17... Output surface, 18... Light guide, 20... Light funnel unit, 21-24... Light funnel, 36... Light rays emitted from the liquid crystal panel.

Claims (4)

An information display device that displays virtual image information on a windshield of a vehicle,
a display that displays the video information;
An information display device comprising: a virtual image optical system that displays a virtual image in front of the vehicle by reflecting light emitted from the display on the windshield,
The virtual image optical system includes a concave mirror and an optical element,
The optical element is disposed between the display and the concave mirror, and is configured to correct field curvature of a virtual image obtained in accordance with the driver's viewpoint position by the shape of the concave mirror and the shape of the optical element. It is composed of
The shape of the display that displays the image information in order to reduce field curvature of the virtual image optical system is configured by the display having a concavely curved light exit surface corresponding to the curved surface of the windshield. ,
The virtual image optical system includes an optical element having a weak negative refractive power, and the optical element having the weak negative refractive power is configured such that the image light from the display is incident on the optical element , and the optical element has a weak negative refractive power. An information display device configured to emit light toward a concave mirror. The information display device according to claim 1,
The shape of the concave mirror is such that the average radius of curvature is different in the horizontal direction and the vertical direction so as to correct the difference in the radius of curvature in the vertical direction and the horizontal direction of the windshield.
Information display device. The information display device according to claim 1,
The display 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 the virtual image and an image magnification at a lower end of the virtual image match.
Information display device. The information display device according to claim 1,
The display includes a light source having a radius of curvature that matches the radius of curvature of the light exit surface.
Information display device.

Images