Abstract:
An image-partitioned display device for virtual image is disclosed. The display device comprises an image display unit, a refractive element, and a virtual image generation module. The refractive element is disposed between the image display unit and the virtual image generation module. Firstly, the image display unit generates at least one image, and then the refractive element refracts and partitions the image into a plurality of sub-images. Finally, the virtual image generation module receives lights of the sub-images to generate a large area virtual image or a plurality of enlarged virtual images. A volume of the virtual image generation module is reduced and all kinds of display information are provided by the image-partitioned technology.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a display device, particularly to an image-partitioned display device for virtual image. 
         [0003]    2. Description of the Related Art 
         [0004]    It is well known that the Head Up Display (HUD) is an auxiliary aviation instrument that is first utilized in an aircraft, so that a pilot is able to look at the information on the panel without lowering his head, to avoid interruption of attention and lose Situation Awareness. The Head Up Display (HUD) can not only provide convenience in usage, but it can also raise the aviation safety. Therefore, it can be used in any types of the moving vehicles, such as aircrafts, or even automobiles and ships. 
         [0005]    The prior arts or productions in existence mostly belong to a single optical path system, which displays information within a fixed range. The single optical path system has a small screen providing simple speed information, an arrowed guiding information, and vehicle information. In 2012, Audi proposes a model of a large area HUD in the Consumer Electronics Show (CES). The model uses three optical modules projecting three sets of images to provide different display information and satisfy different requirements. As the number of the optical module increases, the required space and cost will respectively enlarge and increase. Besides, the U.S. Pat. No. 7,508,356 uses reflection optical elements to partition images from a single image source. As a result, many optical devices with a large volume are required. In conclusion, in order to display multiple sets of images, the space and the cost that the HUD requires thereof cannot be effectively reduced without decreasing the number of the optical devices. 
         [0006]    Accordingly, the present invention proposes an image-partitioned display device for virtual image to overcome the abovementioned problems. 
       SUMMARY OF THE INVENTION 
       [0007]    The primary objective of the present invention is to provide an image-partitioned display device for virtual image, which uses a refractive element to partition an image to reduce the volume of a virtual image generation module and the cost, and provide different display information. 
         [0008]    To achieve the abovementioned objectives, the present invention proposes an image-partitioned display device for virtual image, which comprises an image display unit generating at least one image; a refractive element refracting and partitioning said image into a plurality of sub-images; and a virtual image generation module receiving lights of the sub-images to generate a large area virtual image or a plurality of enlarged virtual images. 
         [0009]    Below, the embodiments are described in detailed in cooperation with the attached drawings to make easily understood the technical contents, characteristics, and accomplishments of the present invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]      FIG. 1  is a block diagram schematically showing the architecture of an image-partitioned display device according to an embodiment of the present invention; 
           [0011]      FIG. 2  is a perspective view schematically showing the image-partitioned display device according to an embodiment of the present invention; 
           [0012]      FIG. 3  is a diagram schematically showing a prism reducing a volume of a virtual image generation module according to an embodiment of the present invention; 
           [0013]      FIG. 4  is a diagram schematically showing a large-curvature concave mirror at a short distance from a relay lens according to an embodiment of the present invention; 
           [0014]      FIG. 5  is a diagram schematically showing a large-curvature concave mirror at a long distance from the relay lens according to an embodiment of the present invention; 
           [0015]      FIG. 6  is a diagram schematically showing a small-curvature concave mirror at a short distance from the relay lens according to an embodiment of the present invention; 
           [0016]      FIG. 7  is a diagram schematically showing a small-curvature concave mirror at a long distance from the relay lens according to an embodiment of the present invention; 
           [0017]      FIG. 8  is a diagram schematically showing refracted optical paths of the prism according to an embodiment of the present invention; and 
           [0018]      FIG. 9  is a diagram schematically showing a distance between a position where two light beams intersect and the prism. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0019]    The present invention can partition multiple sets of images. Below is the embodiment for partitioning two images, which can not limit the scope of the present invention. Refer to  FIG. 1  and  FIG. 2 . The present invention comprises an image display unit  10  generating at least one image. The image comprises at least an external signal and at least a vehicle signal. The external signal may be an image or relate to a lane marking, a horizontal line, an obstacle contour, a distance to a front vehicle, or vehicle safety; and the vehicle signal relates to vehicle operation temperature, engine rotation speed, vehicle driving speed, guidance information, tire pressure, gear shift reminder, turning-around and back-up reminder, obstacle warning, flying attitude, flying speed, flying direction, vertical speed variations, vehicle inclination angle, wind direction, vehicle moving-forward or slow-down. The image is refracted by a refractive element  12  that can be a prism  13 . The prism  13  is composed of two symmetrical right-angle prisms, which partition the image into a plurality of sub-images by the refraction principle. The refractive element  12  is disposed between the virtual image generation module  14  and the image display unit  10 . The virtual image generation module  14  receives the lights of the sub-images to generate a large area virtual image or two enlarged virtual images, wherein the large area virtual image is combined by the two sub-images. 
         [0020]    The image display unit  10  further comprises a back light source  16  and a display panel  18 . The back light source  16  can be LEDs or a laser, and the display panel  18  can be a liquid crystal display (LCD), a liquid crystal on silicon (LCOS) display, or a cathode ray tube (CRT). The display panel  18  generates the image by the back light source  16 . The virtual image generation module  14  further comprises a relay lens  20  receiving and relaying the lights of the sub-images, and then focusing the lights on within a focus point of a virtual image element  22 . The virtual image element  22  reflects the lights of the sub-images relayed from the relay lens  20  to enlarge the sub-images. The virtual image element  22  can be a concave mirror or a convex lens. The virtual image element  22  is exemplified by a concave mirror  23  in the embodiment. In order to avoid the aberration, the relay lens  20  is a single lens or is composed of a plurality of lenses, and a mirror surface of the virtual image element  22  is an aspheric surface or a spherical surface, preferably the aspheric surface. The virtual image element  22  receives the lights of the sub-images relayed from the relay lens  20  to enlarge the sub-images and relay the enlarged sub-images to a plurality of combiners  24 . The combiner  24  respectively reflects the enlarged sub-images to eyes and combines them into the large area virtual image or the enlarged virtual images. The numbers of the combiners  24  and the sub-images are equal. Each combiner  24  is a semi-transmitted mirror with a high reflectivity optical thin film, and the thin film has a transmission rate of between 70% and 75% and a reflection rate of between 25% and 30%. The virtual image element  22  is disposed on a position-adjusting element  26 , which adjusts the displacement or angle of the virtual image element  22 . The position-adjusting element  26  can be a screw, a gear, or a mechanism able to move the virtual image element  22 . 
         [0021]      FIG. 2  and  FIG. 3  show a path of the light emitted by the image display unit  10  and refracted by the refractive element  12 , and the relay lens  20  and the concave mirror  23  are integrated in a virtual image magnifying module  28 . From the figure, compared to the unrefracted light, the virtual image magnifying module  28  with a smaller volume can use the refracted light to form an image. In other words, the present invention uses the refractive element  12  to refract the light and partition the image, so that the volume and the cost of the virtual image generation module are reduced. 
         [0022]    Refer to  FIG. 1  and  FIG. 2 . Firstly, the display panel  18  uses the back light source  16  to generate at least one image. The refractive element  12  refracts the image into a plurality of sub-images. Then, the relay lens  20  relays the light of the sub-images and focuses them on within the focus point of the concave mirror  23  and not outside the focus point, whereby the concave mirror  23  reflects the light to enlarge the sub-images. The combiners  24  respectively reflect the enlarged sub-images to eyes and combine them into the large area virtual image or the enlarged virtual images after respectively receiving the sub-images. 
         [0023]    The position-adjusting element  26  can adjust the distance between the concave mirror  23  and the relay lens  20 . A position of the projected image depends on the displacement and angle of the concave mirror  23 . And, the limit for the adjusted displacement and angle is affected by the curvature of the concave mirror  23  and the angle of the prism  13 . As a result, the abovementioned factor has to be considered. 
         [0024]    As shown in  FIG. 4 , when the concave mirror  23  is a large-curvature element and the distance between the concave mirror  23  and the relay lens  20  is shorter, the light rays L and M emit to the center of the concave mirror  23 , and the reflection angles of the light rays L and M are smaller. Thus, the light rays L and M form the images on the combiners  24 , which are split more distantly. On the contrary, as shown in  FIG. 5 , the distance between the concave mirror  23  and the relay lens  20  is longer, the light rays L and M emit to the edge of the concave mirror  23 , and the reflection angles of the light rays L and M are larger. Thus, the light rays L and M form the images on the combiners  24 , which are split more closely, and a large-area virtual image may be formed. 
         [0025]    As shown in  FIG. 6 , when the concave mirror  23  is a small-curvature or curvature-free element, the light rays L and M emit to the center and the edge of the concave mirror  23 , and the reflection angles of the light rays L and M are almost not changed. As a result, the distance between the concave mirror  23  and the relay lens  20  is shorter, the enlarged virtual images are split more closely. 
         [0026]    As shown in  FIG. 7 , the distance between the concave mirror  23  and the relay lens  20  is longer, the enlarged virtual images are split more distantly. 
         [0027]    Refer to  FIG. 8  and  FIG. 9 , an included angle and positions of the two sub-images depend on the refractive index n and an apex angle A of the prism  13 . After adjusting the angle, the volume of the virtual image generation module can be effectively reduced. After the light passes through the prism  13 , the exit angle b is described as the formula (1), wherein a is an inclined angle. 
         [0000]        b =sin −1 (sin  A √{square root over ( n   2 −sin 2    A )}−cos  A  sin  A )  (1)
 
         [0028]    The distance D between the position that the light rays intersect and the prism  13  is described as the formula (2), wherein h is the distance between the exit light ray and the center of the prism  13 , and b is the exit angle. 
         [0000]        D=h /tan( b )  (2)
 
         [0029]    Refer to  FIG. 1 ,  FIG. 2  and  FIG. 9 . Suppose that the apex angle A is 15 degrees, and that the prism  13  is made of BK7. When the light rays emit to the prism  13 , the light rays exit at ±14.868 degrees by the prism  13 . The position that the light rays focus on is 95.8 mm from the display panel  18  and is disposed at the right side of the display panel  18 . The concave mirror  23  is disposed at the position to reduce its volume. Compared with the single light path system of the traditional Head Up Display (HUD), the volume of the concave mirror  23  of the present invention is reduced by about 53.8%. 
         [0030]    In conclusion, the present invention not only provides different image information but also reduces the volume of back-end optical module. 
         [0031]    The embodiments described above are only to exemplify the present invention but not to limit the scope of the present invention. Therefore, any equivalent modification or variation according to the shapes, structures, characteristics and spirit of the present invention is to be also included within the scope of the present invention.