Abstract:
The present invention is compact and inexpensive, has good light efficiency, and enables a display image having a plurality of display distances to be displayed. A display emits projection light for displaying a display image at a predetermined position, and an image formation position adjusting mirror receives the projection light emitted from the display, performs conversion into a plurality of first projection light and second projection light that have different image formation distances by changing the image formation distance of the projection light that is at least part of the incident projection light, and reflects the first projection light and the second projection light to project the first projection light and the second projection light onto a first screen and a second screen.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a projection device for projecting an image onto a predetermined position and a head-up display device for throwing the image projected by the projection device onto a reflective transmissive surface to cause the image to be visually recognized with a scenery. 
       BACKGROUND ART 
       [0002]    A conventional head-up display device is disclosed in, for example, PTL 1. Such a head-up display device includes first and second displays and a half mirror and is a device for overlapping and projecting transmitted light and reflected light with the use of the half mirror, thereby causing a user to visually recognize display images (virtual images) at different display distances. 
       CITATION LIST 
     Patent Literature 
       [0003]    PTL 1: JP-A-2003-237412 
       SUMMARY OF INVENTION 
       [0004]    Technical Problem(s) 
         [0005]    However, the head-up display device disclosed in PTL 1 includes a plurality of displays, and therefore a volume of the head-up display device may be increased and a cost thereof may be increased. Further, because the half mirror is used, use efficiency of display light emitted from the displays may be reduced. 
         [0006]    The invention has been made in view of the above problems and provides a compact and inexpensive projection device and head-up display device having a high light efficiency and capable of displaying display images having a plurality of display distances. 
       Solution to Problem(s) 
       [0007]    In order to solve the above problems, a projection device according to a first viewpoint of the invention is a projection device including: a display configured to emit projection light for displaying a display image at a predetermined position; and an image formation position adjusting mirror configured to receive the projection light emitted from the display, convert the projection light into a plurality of beams of projection light having different image formation distances by changing an image formation distance of at least a part of the incident projection light, and reflect the plurality of beams of projection light. 
         [0008]    Further, a head-up display device according to a second viewpoint of the invention is a head-up display device for projecting a display image onto a projection surface to cause the display image to be visually recognized as a virtual image, the head-up display device including: a projection unit configured to emit projection light; an image formation position adjusting mirror configured to receive the projection light emitted from the projection unit, convert the projection light into a plurality of beams of projection light having different image formation distances by changing an image formation distance of at least apart of the incident projection light, and reflect the plurality of beams of projection light; a first screen configured to form a part of the projection light having a longer image formation distance; and a second screen configured to form a part of the projection light having a shorter image formation distance, the second screen being placed at a position away from the projection surface than the first screen. 
       Advantageous Effects of Invention 
       [0009]    It is possible to provide a compact and inexpensive projection device and head-up display device having a high light efficiency and capable of displaying display images having a plurality of display distances. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0010]      FIG. 1  is a schematic view showing an embodiment of the invention. 
           [0011]      FIG. 2  shows a configuration of a first screen and a second screen in the above embodiment. 
           [0012]      FIG. 3  is a schematic view showing a modification example of the invention. 
           [0013]      FIG. 4  shows a modification example of an image formation position adjusting mirror of the invention. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0014]    Hereinafter, an embodiment of a head-up display device (hereinafter, referred to as “HUD device”)  100  and a projection device  20  according to the invention will be described with reference to attached drawings. 
         [0015]    The HUD device  100  is provided in, for example, an automobile and, as shown in  FIG. 1 , includes a housing  10 , the projection device  20 , a first screen (first image formation unit)  30 , a second screen (second image formation unit)  40 , a plane mirror (relay optical system)  50 , a concave mirror (relay optical system)  60 , and a control circuit board (not shown). The HUD device  100  reflects a first display image M 1  projected by the projection device  20  onto the first screen  30  and a second display image M 2  projected by the projection device  20  as well onto the second screen  40  toward a windshield  200  of a vehicle with the use of the plane mirror  50  and the concave mirror  60 , thereby displaying a first virtual image V 1  of the first display image M 1  and a second virtual image V 2  of the second display image M 2  to a user E. 
         [0016]    The housing  10  is made of, for example, a black light-shielding synthetic resin and stores the projection device  20 , the first screen  30 , the second screen  40 , the plane mirror  50 , and the concave mirror  60  therein, and the control circuit board (not shown) is attached to the exterior thereof. 
         [0017]    The housing  10  has an opening portion  10   a  allowing display light N described below to pass therethrough toward the windshield  200 , and the opening portion  10   a  is covered with a light transmitting cover  10   b.    
         [0018]    The projection device  20  emits first projection light L 1  showing the first display image M 1  described below and second projection light L 2  showing the second display image M 2  toward the first screen  30  and the second screen  40  described below, thereby forming the first display image M 1  and the second display image M 2  on the first screen  30  and the second screen  40 . A detailed configuration of the projection device  20  will be described in detail below. 
         [0019]    The first screen (first image formation unit)  30  is a transmitting screen for receiving the first projection light L 1  emitted from the projection device  20  on a rear surface and displaying the first display image M 1  on a surface side and is made up of, for example, a holographic diffuser, a microlens array, or a diffusion plate. When the first screen  30  displays the first display image M 1 , first display light N 1  showing the first display image M 1  is projected onto the windshield  200  by the plane mirror  50  and the concave mirror  60  described below and is reflected by the windshield  200  toward a direction of the user E (eye box). With this, the user E can visually recognize the first virtual image V 1  on the other side of the windshield  200 . Note that, as shown in  FIG. 2 , the first screen  30  in this embodiment has a recessed display area having a cut-out portion  30   a  obtained by cutting out a part of an edge portion of a substantially rectangular shape so that the part thereof has a rectangular shape. Therefore, the first virtual image V 1  also has a recessed display area. Note that, as shown in  FIG. 2 , the second projection light L 2  described below passes through the cut-out portion  30   a  of the first screen  30  to reach the second screen  40  described below. 
         [0020]    The second screen (second image formation unit)  40  is formed to have a rectangular shape substantially similar to that of the cut-out portion  30   a  of the first screen  30  and is a transmitting screen for receiving the second projection light L 2  emitted from the projection device  20  on a rear surface and displaying the second display image M 2  on a surface side. The second screen  40 , as well as the first screen  30 , is made up of, for example, a holographic diffuser, a microlens array, or a diffusion plate. When the second screen  40  displays the second display image M 2 , second display light N 2  showing the second display image M 2  is projected onto the windshield  200  by the plane mirror  50  and the concave mirror  60  described below, and the second virtual image V 2  is displayed on the other side of the windshield  200 , seen from the user E. 
         [0021]    As shown in  FIG. 1 , the first screen  30  is placed to be closer to the projection device  20  than the second screen  40 . That is, an optical path length of the first display light N 1  travelling toward the user E from the first screen  30  is longer than an optical path length of the second display light N 2  travelling toward the user E from the second screen  40 . Therefore, a distance (display distance) between the user E and a position at which the first virtual image V 1  is displayed is longer than a distance (display distance) between the user E and a position at which the second virtual image V 2  is displayed, and thus the HUD device  100  in this embodiment can perform display so that the first virtual image V 1  positions farther than the second virtual image V 2 . Note that, in this embodiment, the display distance of the first virtual image V 1  is 5 meters, and the display distance of the second virtual image V 2  is 2 meters. 
         [0022]    The first screen  30  is placed to have a predetermined angle (including 0 degree) with respect to an optical axis of the first display light N 1  travelling to the user E from the first screen  30 , and, similarly, the second screen  40  is placed to have a predetermined angle (including 0 degree) with respect to an optical axis of the second display light N 2  travelling to the user E from the second screen  40 . Note that, even in the case where the first screen  30  (second screen  40 ) has the predetermined angle with respect to the optical axis of the first display light N 1 , the first virtual image V 1  and the second virtual image V 2  are formed by a free-form surface of the concave mirror  60  described below so that the first virtual image V 1  and the second virtual image V 2  face to each other while being substantially perpendicular to a line of forward sight of the user E. In the case where the user E visually recognizes the first virtual image V 1  (second virtual image V 2 ), a display distance is constant from any area in the first virtual image V 1  (second virtual image V 2 ), and therefore the user can visually recognize the whole first virtual image V 1  (second virtual image V 2 ) with ease without moving the user&#39;s focal point. 
         [0023]    The plane mirror (relay optical system)  50  is obtained by forming a reflective film on a surface of a base made of, for example, a synthetic resin or a glass material by using depositing or other means and reflects the first display light N 1  and the second display light N 2  emitted from the first screen  30  and the second screen  40  toward the concave mirror  60 . 
         [0024]    The concave mirror (relay optical system)  60  is obtained by forming a reflective film on a surface of a base made of, for example, a synthetic resin material by using depositing or other means and is a mirror having a recessed free-form surface that further reflects the first display light N 1  and the second display light N 2  reflected by the plane mirror  50  to emit the first display light N 1  and the second display light N 2  toward the windshield  200 . The first display light N 1  and the second display light N 2  reflected by the concave mirror  60  are transmitted through the light transmitting cover  10   b  provided in the opening portion  10   a  of the housing  10  and reach the windshield  200 . The first display light N 1  and the second display light N 2  reflected by the windshield  200  form the first virtual image V 1  and the second virtual image V 2  at positions in front of the windshield  200 . With this, the HUD device  100  can cause the user E to visually recognize both the virtual images V (first virtual image V 1  and second virtual image V 2 ) and outside scenery or the like actually existing in front of the windshield  200 . Note that the concave mirror  60  has a function of a magnifying glass and magnifies the display images M displayed by the projection device  20  to reflect the display images M toward the windshield  200 . That is, the first virtual image V 1  and the second virtual image V 2  visually recognized by the user E are enlarged images of the first display image M 1  and the second display image M 2  displayed by the projection device  20 . The concave mirror  60  also has a function of reducing distortion of the first virtual image V 1  and the second virtual image V 2  caused by the windshield  200  which is a curved surface. Hereinafter, a specific configuration of the projection device  20  will be described. 
         [0025]    As shown in  FIG. 1 , the projection device  20  includes a display  21  for generating and emitting the first projection light L 1  and the second projection light L 2 , a fold mirror  22  for reflecting the first projection light L 1  and the second projection light L 2  incident thereon from the display  21  to turn back the first projection light L 1  and the second projection light L 2 , and an image formation position adjusting mirror  23  for adjusting image formation distances of the light incident thereon from the fold mirror  22  and forms the first projection light L 1  and the second projection light L 2  on the first screen  30  and the second screen  40 , respectively, which are away from the projection device  20  at different distances. 
         [0026]    The display  21  has a reflective display element such as a DMD (Digital MicroMirror Device) or LCOS (registered trademark: Liquid Crystal On Silicon) or a transmissive display element such as a TFT (Thin Film transistor) liquid crystal panel and emits the first projection light L 1  and the second projection light L 2  for displaying the first display image M 1  and the second display image M 2  toward the fold mirror  22  on the basis of control signals from the control circuit board (not shown). Note that the display  21  is controlled to display the display images M (first display image M 1  and second display image M 2 ) distorted in advance in consideration of an optical characteristic, placement, and the like of each optical member so as to prevent the virtual images V (first virtual image V 1  and second virtual image V 2 ) from being distorted when the virtual images V are visually recognized by the user E via the first screen  30 , the second screen  40 , the plane mirror  50 , the concave mirror  60 , the windshield  200 , and the like. 
         [0027]    The fold mirror  22  is obtained by forming a reflective film on a surface of a base made of, for example, a synthetic resin or a glass material by using depositing or other means and is a plane mirror for reflecting the first projection light L 1  and the second projection light L 2  emitted from the display  21  toward the image formation position adjusting mirror  23  described below. Because the fold mirror  22  is provided, a package of the projection device  20  can be more compact. Note that a plurality of fold mirrors  22  may be provided between the display  21  and the image formation position adjusting mirror  23 , or no fold mirror  22  may be provided. 
         [0028]    The image formation position adjusting mirror  23  is obtained by forming a reflective film on a surface of a base made of, for example, a synthetic resin material or a glass material by using depositing or other means and has a first reflection surface  231  for receiving the first projection light L 1  and a second reflection surface  232  for receiving the second projection light L 2  on the same base. In this embodiment, the first reflection surface  231  has a reflection surface that is a flat surface and reflects the received first projection light L 1  toward the first screen  30  without changing the image formation distance, thereby forming the first display image M 1  on the surface side of the first screen  30 . Meanwhile, the second reflection surface  232  has a reflection surface that is a projected free-form surface and reflects the received second projection light L 2  toward the second screen  40  while changing the image formation distance so that the image formation distance is increased, thereby forming the second display image M 2  on the surface side of the second screen  40 . 
         [0029]    That is, in the image formation position adjusting mirror  23  in this embodiment, the first reflection surface  231  for reflecting the first projection light L 1  and the second reflection surface  232  for reflecting the second projection light L 2  have different curved surface shapes, and therefore the image formation distances of the first projection light L 1  and the second projection light L 2  can be made different only by receiving the projection light L from the single display  21 . Therefore, the first virtual image V 1  and the second virtual image V 2  visually recognized by the user E can be displayed at different display distances, and therefore it is possible to differentiate between information displayed as the first virtual image V 1  and information displayed as the second virtual image V 2 , which improves distinguishability of the information. Further, the image formation distances of at least the first projection light L 1  and the second projection light L 2  emitted from the same display  21  can be made different, and therefore it is possible to reduce a cost, as compared with the case where a plurality of displays are provided. 
         [0030]    Because the first reflection surface  231  and the second reflection surface  232  in the image formation position adjusting mirror  23  are formed on the same base, the image formation distances of the at least first projection light L 1  and second projection light L 2  can be made different only by irradiating the image formation position adjusting mirror  23  with the projection light L from the display  21 . Therefore, it is possible to save a space without complicating an optical path of the projection light L. 
         [0031]    The image formation position adjusting mirror  23  in this embodiment has, on the same base, the first reflection surface  231  and the second reflection surface  232  for making different image formation distances between the first projection light L 1  and the second projection light L 2 , and therefore relative positions between the first reflection surface  231  and the second reflection surface  232  are hardly shifted due to an assembly error or the like, and it is possible to accurately form the first projection light L 1  and the second projection light L 2  on the first screen  30  and the second screen  40 . 
         [0032]    The display  21  in this embodiment does not project the projection light L for generating an image onto the vicinity of a boundary between the first reflection surface  231  and the second reflection surface  232  of the image formation position adjusting mirror  23 . With this configuration, even in the case where a projection position of the projection light L onto the image formation position adjusting mirror  23  is shifted due to an assembly error, vibration, or the like of the HUD device  100 , it is possible to prevent the first display image M 1  to be thrown to the first screen  30  from being thrown to the second screen  40 . 
         [0033]    A part (first reflection surface  231 ) of the image formation position adjusting mirror  23  in this embodiment has a flat surface, and therefore it is possible to reflect the projection light L projected from the display  21  without distorting the projection light L. Further, it is possible to easily design and manufacture the image formation position adjusting mirror  23  and reduce design and manufacturing costs. 
         [0034]    Hereinabove, the HUD device  100  in this embodiment has been described, but the invention is not limited by the above embodiment and drawings. Needless to say, the above embodiment and drawings can be changed (including deletion of constituent elements). Hereinafter, modification examples will be described. 
         [0035]    In the above embodiment, the first reflection surface  231  has been described as a flat surface, and the second reflection surface  232  has been described as a projected free-form surface, but the first reflection surface  231  and the second reflection surface  232  are not limited thereto because the first reflection surface  231  and the second reflection surface  232  only need to have shapes that can make different image formation distances between the first projection light L 1  and the second projection light L 2 . When the reflection surface is formed to have a projected shape, the image formation distance can be increased, and, when the reflection surface is formed to have a recessed shape, the image formation distance can be reduced. Note that the first reflection surface  231  and the second reflection surface  232  do not need to have the same curved surface shape in the whole reflection areas and may have different shapes in the respective reflection areas. 
         [0036]    In the above embodiment, the first screen  30  is placed to have the predetermined angle with respect to the optical axis of the first display light N 1  travelling to the user E from the first screen  30 , and, similarly, the second screen  40  is placed to have a predetermined angle with respect to the optical axis of the second display light N 2  travelling to the user E from the second screen  40 , but the first screen  30  and the second screen  40  are not limited thereto. The first screen  30  or/and the second screen  40  may be placed to be inclined at an angle equal to or larger than the predetermined angle with respect to the optical axis of the first display light N 1  (second display light N 2 ) travelling to the user E. Specifically, as shown in  FIG. 3 , it is possible to gradually change the image formation distance of the first projection light L 1  by placing the first screen  30  so that the first screen  30  is inclined at an angle equal to or larger than the predetermined angle with respect to the optical axis of the first display light N 1  and gradually changing the curved surface shape of the first reflection surface  231  in consideration of an optical path length of the first projection light L 1  between the first screen  30  placed to be inclined and the display  21 . Therefore, even in the case where the first screen  30  is inclined at an angle equal to or larger than the predetermined angle with respect to the optical axis, it is possible to form the first display image M 1  in a wide range (including the whole area) of the first screen  30 , and it is possible to cause the user E to visually recognize the first virtual image V 1  which is not blurred and causes the user E to feel the sense of depth. 
         [0037]    Inclination of the first screen  30  to the optical axis of the first projection light L 1  may be different from inclination of the second screen  40  to the optical axis of the second projection light L 2 . With this configuration, it is possible to three-dimensionally differentiate between two virtual images (first virtual image V 1  and second virtual image V 2 ), and therefore it is possible to cause the user E to distinctively recognize pieces of information with ease. 
         [0038]    In the above embodiment, the image formation position adjusting mirror  23  for adjusting the image formation distance(s) of the first projection light L 1  or/and the second projection light L 2  emitted by the display  21  may be made up of a plurality of image formation position adjusting mirrors  23   a  and  23   b  as shown in  FIG. 4 . 
         [0039]    In the above embodiment, the first reflection surface  231  and the second reflection surface  232  are placed on the same base, but the first reflection surface  231  and the second reflection surface  232  may be placed on different bases. 
         [0040]    The first reflection surface  231  and the second reflection surface  232  may be made of a continuous reflective film, and the reflective film may not be formed in the vicinity of the boundary between the first reflection surface  231  and the second reflection surface  232 . 
         [0041]    In the above embodiment, the first screen  30  and the second screen  40  have a substantially rectangular shape, but the first screen  30  and the second screen  40  may have a polygonal shape such as a hexagonal shape or an octagonal shape. 
         [0042]    In the above description, in order to easily understand the invention, description of publicly-known unimportant technical matters has been omitted as appropriate. 
       INDUSTRIAL APPLICABILITY 
       [0043]    The invention is applicable to, for example, a head-up display device for vehicles. 
       REFERENCE SIGNS LIST 
       [0044]      100  HUD device (head-up display device),  10  housing,  20  projection device,  21  display,  22  fold mirror,  23  image formation position adjusting mirror,  30  first screen,  40  second screen,  50  plane mirror,  60  concave mirror, L projection light, L 1  first projection light, L 2  second projection light, M 1  first display image, M 2  second display image, N 1  first display light, N 2  second display light, V virtual image, V 1  first virtual image, V 2  second virtual image