Abstract:
The objective of the present invention is to provide a heads-up display device able to efficiently orient image light towards a viewer by means of a simple configuration. The heads-up display device is provided with: a projection unit that emits projection light depicting a display image; a first reflection unit and second reflection unit that reflect the projection light exiting the projection unit towards a transmissive screen; and the transmissive screen that outputs image light towards an observer by transmitting/scattering the projection light. By adjusting the angle of the light axis of the projection light entering the transmissive screen by rotating the first reflection unit and second reflection unit, the angle of the image light exiting the transmissive screen is adjusted.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a heads-up display device for causing an image superposed on a real view to be visually recognized. 
       BACKGROUND ART 
       [0002]    A heads-up display device displays a virtual image while superposing the virtual image on a real view in front of own vehicle, thereby generating augmented reality (AR) in which information and the like are added to a real view, and accurately provides desired information to a viewer who drives the vehicle while reducing a move of the viewer&#39;s line of sight as much as possible, which contributes to safe and comfortable driving of a vehicle. 
         [0003]    As a device for causing a viewer to visually recognize a virtual image, for example, PTL 1 discloses an image display device that includes a projection unit for projecting a luminous flux onto a predetermined projected position to cause a viewer to visually recognize a virtual image and detects the viewer&#39;s point-of-sight position to rotate a movable mirror on the basis of the detected point-of-sight position, thereby orienting the luminous flux emitted by the projection unit toward the viewer&#39;s point-of-sight position. 
         [0004]    For example, PTL 2 discloses a display device that adjusts an angle by moving a display and a reflection unit along a circular arc, thereby orienting image light emitted from the display toward a viewer&#39;s point-of-sight position, which causes the viewer to visually recognize the image light from the display efficiently. 
       CITATION LIST 
     Patent Literatures 
       [0005]    PTL 1: JP-A-2009-246505 
         [0006]    PTL 2: JP-A-7-329603 
       SUMMARY OF INVENTION 
     Technical Problem(s) 
       [0007]    In the case where the movable mirror is rotated in accordance with a viewer&#39;s point-of-sight position to adjust a projected position of a luminous flux as in PTL 1, as illustrated in, for example,  FIG. 10 , a display  101  for emitting image light N, a reflection unit  102  for reflecting the image light N from the display  101 , and a concave reflection unit (movable mirror)  103  for reflecting the image light N reflected by the reflection unit  102  toward a transmissive reflective surface  200  are included, and a position onto which the image light N is projected is adjusted by rotating the concave reflection unit  103 . 
         [0008]    When referring to  FIG. 10 , beams of the image light N oriented toward respective viewers who are different in height of a point of sight are beams of light emitted from a display surface  101   a  of the display  101  in different directions. In order to prevent a change in brightness of a virtual image to be visually recognized even in the case where viewers are different in height of a point of sight, a light distribution characteristic of the image light N emitted by the display  101  needs to be constant in a wide range. Therefore, it is necessary to increase a light distribution angle (diffusion angle) (reduce directivity) of the image light N emitted from the display  101 , and thus efficiency of the display  101  is reduced. 
         [0009]    Further, as disclosed in PTL 2, in order to move the display which is an electronic device along a circular arc to orient image light toward a viewer&#39;s point-of-sight position, it is necessary to provide a complicated and large-scaled moving mechanism and the like. 
         [0010]    The invention has been made in view of the above circumstances, and an object of the invention is to provide a heads-up display device capable of efficiently orienting image light toward a viewer with a simple configuration. 
       Solution to Problem(s) 
       [0011]    In order to achieve the above object, a heads-up display device according to the invention, which is for projecting image light onto a transmissive reflective surface to cause a virtual image based on the image light to be visually recognized together with a real view through the transmissive reflective surface, includes: a projection unit for emitting projection light forming a display image; a transmissive screen for orienting the image light obtained by transmitting and diffusing the projection light toward the transmissive reflective surface; and an optical axis adjustment unit for adjusting an angle of an optical axis of the projection light incident on the transmissive screen, the optical axis adjustment unit being arranged between the projection unit and the transmissive screen and including a first reflection unit for reflecting the projection light emitted by the projection unit, a second reflection unit for reflecting the projection light reflected by the first reflection unit, and actuators for rotating the first reflection unit and the second reflection unit. 
       Advantageous Effects of Invention 
       [0012]    According to a heads-up display device of the invention, it is possible to efficiently orient image light toward a viewer with a simple configuration. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0013]      FIG. 1  is a schematic diagram in which a heads-up display device in an embodiment of the invention is mounted on a vehicle. 
           [0014]      FIG. 2  is a schematic cross-sectional view of the HUD device in the same embodiment. 
           [0015]      FIG. 3  is an explanatory view of a configuration of a projection unit and an optical axis adjustment unit in the same embodiment. 
           [0016]      FIG. 4  is an explanatory view of a projected image distance of a projector lens in the same embodiment. 
           [0017]      FIG. 5  is a block diagram showing an electric configuration of the HUD device in the same embodiment. 
           [0018]      FIG. 6  is a flowchart showing optical axis adjustment processing in the same embodiment. 
           [0019]      FIG. 7A  illustrates a state of the optical axis adjustment unit occurring when the HUD device in the same embodiment orients image light toward a comparatively high point-of-sight position. 
           [0020]      FIG. 7B  illustrates a state of the whole HUD device occurring when the image light is oriented toward the comparatively high point-of-sight position shown in  FIG. 7A . 
           [0021]      FIG. 8A  illustrates a state of the optical axis adjustment unit occurring when the HUD device in the same embodiment orients image light toward a comparatively low point-of-sight position. 
           [0022]      FIG. 8B  illustrates a state of the whole HUD device occurring when the image light is oriented toward the comparatively low point-of-sight position shown in  FIG. 8A . 
           [0023]      FIG. 9  illustrates a state of an optical axis adjustment unit occurring when an HUD device in a modification example orients image light toward a comparatively low point-of-sight position. 
           [0024]      FIG. 10  is an explanatory view of a conventional heads-up display device. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0025]    An embodiment of the invention will be described below with reference to the drawings. Note that, although luminous fluxes of image light  100 , projection light  200 , illumination light  300 , and the like described below innumerably exist in various directions, only an optical axis that is the center of each luminous flux is shown in order to easily understand the drawings. 
         [0026]      FIG. 1  illustrates an overview of a heads-up display device (hereinafter, referred to as an HUD device)  1  according to this embodiment. As illustrated in  FIG. 1 , the HUD device  1  is typically provided in a dashboard of own vehicle  2 , but a part or all of the HUD device  1  may be provided on the dashboard. 
         [0027]      FIG. 2  is a schematic cross-sectional view illustrating a configuration of the HUD device  1 . 
         [0028]    As illustrated in  FIG. 2 , the HUD device  1  includes a projection unit  10 , an optical axis adjustment unit  20 , a transmissive screen  30 , a folding mirror  40 , a concave mirror  50 , a housing  60  receiving the above members, and a control unit  70  for electrically control the HUD device  1 . When image light  100  emitted by the HUD device  1  is projected onto a projected point P of a windshield (an example of a transmissive reflective surface)  2   a  and is reflected by the windshield  2   a , a virtual image V is visually recognized at an arbitrary position in front of the windshield  2   a  (for example, 10 to 20 m in front thereof). 
       (Projection Unit  10 ) 
       [0029]      FIG. 3  is an explanatory view of a specific configuration of the projection unit  10  and the optical axis adjustment unit  20  and an optical path of projection light  200 . 
         [0030]    The projection unit  10  in  FIG. 3  includes a light source  11  for emitting illumination light  300 , a light source mirror  12 , a prism  13 , a reflective display  14 , and a projector lens  15  and emits the projection light  200  for forming a display image (not illustrated) on the transmissive screen  30  toward the optical axis adjustment unit  20 . Note that the display image formed on the transmissive screen  30  may also be generally called a real image. 
         [0031]    The light source  11  in  FIG. 3  includes, for example, a plurality of LEDs capable of outputting light of red, blue, and green, respectively, and emits the illumination light  300  of a desired color with desired light intensity at a desired timing under the control of the control unit  70  described later. The projection unit  10  in this embodiment employs a field sequential color driving method, and the light source  11  of each color emits the illumination light  300  in time division. 
         [0032]    The light source mirror  12  in  FIG. 3  is obtained by, for example, forming a reflective film on a surface of a base made of a synthetic resin material by using depositing or other means and reflects the illumination light  300  from the light source  11  to cause the illumination light to be incident on the reflective display  14  at a proper angle. 
         [0033]    The prism  13  in  FIG. 3  is arranged between the light source mirror  12  and the reflective display  14  and has an inclined surface  13   a  that is inclined at a predetermined angle with respect to an optical axis of the illumination light  300  incident from the light source mirror  12 . The illumination light  300  from the light source mirror  12 , which has been incident on the inclined surface  13   a , is transmitted through the inclined surface  13   a  and is incident on the reflective display  14 , and then the projection light  200  emitted from the reflective display  14  is incident on the prism  13  again and is reflected by the inclined surface  13   a  in a direction toward the projector lens  15 . 
         [0034]    The reflective display  14  in  FIG. 3  is, for example, a reflective display device such as a DMD (Digital Micromirror Device) or an LCoS (registered trademark: Liquid Crystal On Silicon) and converts the illumination light  300  incident from the prism  13  into the projection light  200  for displaying a virtual image V and reflects the projection light toward the prism  13  under the control of the control unit  70  described later. 
         [0035]    The projector lens  15  in  FIG. 3  is made up of, for example, a convex lens and enlarges the projection light  200  incident from the prism  13  to emit the projection light in a direction toward the optical axis adjustment unit  20 . The projector lens  15  images the projection light  200  on the transmissive screen  30 . 
         [0036]    A projected image distance  151  of the projector lens  15  in  FIG. 3  will be described with reference to  FIG. 4 . The projector lens  15  can generate the display image obtained by imaging the projection light  200  emitted from the reflective display  14  at a position apart from the projector lens  15  by a predetermined projected image distance  151  and can generate the display image that is substantially in focus by using the projection light  200  within a projected image plane depth  152  which is a predetermined range around the projected image distance  151 . The optical axis adjustment unit  20  described later is arranged between the projector lens  15  and the transmissive screen  30  and changes an optical path length of the projection light  200  between the projector lens  15  and the optical axis adjustment unit  20  in the case where an angle of an optical axis of the projection light  200  incident on the transmissive screen  30  is adjusted. Hereinafter, the optical path length of the projection light  200  between the projector lens  15  and the optical axis adjustment unit  20  is also called a projection distance. When the optical axis adjustment unit  20  adjusts the angle of the optical axis of the projection light  200  within a range in which the projection distance of the projection light  200  falls within the projected image plane depth  152  of the projector lens  15 , it is possible to generate the display image that is substantially in focus on the transmissive screen  30 . Note that the projected image plane depth  152  has a front projected image plane depth  152   a  from the projected image distance  151  to the projector lens  15  side and a rear projected image plane depth  152   b  from the projected image distance  151  to the side opposite to the projector lens  15  side. Specifically, the projected image plane depth  152  has, for example, a range of about 3.319 mm in which the front projected image plane depth  152   a  has 1.641 mm and the rear projected image plane depth has 1.678 mm. Note that the projected image distance  151  and the projected image plane depth  152  may also be called a focal distance and a focal depth, respectively. 
       (Optical Axis Adjustment Unit  20 ) 
       [0037]    The optical axis adjustment unit  20  in  FIG. 3  receives the projection light  200  emitted by the projection unit  10  and adjusts the optical axis of the projection light  200  to project the projection light onto the transmissive screen  30 . The optical axis adjustment unit  20  includes a first reflection unit  21  for allowing the projection light  200  from the projection unit  10  to be incident thereon and reflecting the projection light, a first actuator  22  for rotating the first reflection unit  21  around a first rotation axis  23 , a second reflection unit  24  for allowing the projection light  200  reflected by the first reflection unit  21  to be incident thereon and reflecting the projection light toward the transmissive screen  30 , and a second actuator  25  for rotating the second reflection unit  24  around a second rotation axis  26 . 
         [0038]    The first reflection unit  21  in  FIG. 3  is, for example, a plane mirror and reflects the projection light  200  emitted by the projection unit  10  toward the second reflection unit  24 . The first actuator  22  in  FIG. 3  is made up of, for example, a stepping motor, and a gear is provided to a rotating shaft thereof. The first actuator  22  is placed in the housing  60 , and the gear is engaged with a gear of the first reflection unit  21 . Thus, an angle of inclination of the first reflection unit  21  is adjusted around the first rotation axis  23  in accordance with rotational drive of the first actuator  22 , and therefore a reflection direction of the projection light  200  can be adjusted. Note that the first reflection unit  21  may have a concave, convex, or free-form surface shape. 
         [0039]    The second reflection unit  24  in  FIG. 3  is, for example, a plane mirror and reflects the projection light  200  reflected by the first reflection unit  21  toward the transmissive screen  30 . The second actuator  25  in  FIG. 3  is made up of, for example, a stepping motor, and a gear is provided to a rotating shaft thereof. The second actuator  25  is placed in the housing  60 , and the gear is engaged with a gear of the second reflection unit  24 . Thus, an angle of inclination of the second reflection unit  24  is adjusted around the second rotation axis  26  in accordance with rotational drive of the second actuator  25 , and therefore the reflection direction of the projection light  200  can be adjusted. Note that the first rotation axis  23  serving as the center of rotation of the first reflection unit  21  and the second rotation axis  26  serving as the center of rotation of the second reflection unit  24  are positioned in parallel in the same direction. The optical axis adjustment unit  20  is placed so that the projection light  200  from the projection unit  10  is vertically incident on the first rotation axis  23  (second rotation axis  26 ). With this, even in the case where the first reflection unit  21  and the second reflection unit  24  are rotated by “optical axis adjustment processing” described later, an optical path of the projection light  200  reflected by the first reflection unit  21  between the projection unit  10  and the second reflection unit  24  and an optical path of the projection light  200  reflected by the second reflection unit  24  between the first reflection unit  21  and the transmissive screen  30  always pass on the same plane. That is, a change in the optical path of the projection light  200 , which is caused by rotation of the first reflection unit  21  and the second reflection unit  24 , can be simplified, and therefore it is possible to simplify arrangement and a mechanism of the optical axis adjustment unit  20 . Note that the second reflection unit  24  may have a concave, convex, or free-form surface shape. 
         [0040]    That is, the optical axis adjustment unit  20  in  FIG. 3  can adjust an angle of incidence of the optical axis of the projection light  200  to be incident on the transmissive screen  30  by adjusting the angles of both the first reflection unit  21  and the second reflection unit  24  in conjunction with each other. The “optical axis adjustment processing” for adjusting the angle of the optical axis of the projection light  200 , which is performed by the optical axis adjustment unit  20 , will be described in detail below. 
         [0041]    The transmissive screen  30  in  FIG. 3  is made up of, for example, a holographic diffuser, a microlens array, or a diffusion plate and receives the projection light  200  from the optical axis adjustment unit  20  (second reflection unit  24 ) on a rear surface thereof and emits the transmitted and diffused image light  100  toward a light distribution area E in  FIG. 1 . The transmissive screen  30  orients light obtained by causing the projection light  200  to be incident thereon and diffusing the projection light toward the folding mirror  40 . When a viewer&#39;s point-of-sight position is in the light distribution area E, the transmissive screen  30  orients the image light  100  so that the virtual image V to be visually recognized has a substantially uniform brightness. The HUD device  1  of the invention can adjust a direction of an optical axis of the image light  100  emitted from the transmissive screen  30  by using the optical axis adjustment unit  20 . That is, the HUD device  1  of the invention can adjust a position of the light distribution area E to which the image light  100  is distributed, and therefore it is possible to efficiently orient the image light  100  (light distribution area E) toward a viewer&#39;s point-of-sight position. 
         [0042]    The folding mirror (relay optical system)  40  in  FIG. 2  is obtained by, for example, forming a reflective film on a surface of a base made of a synthetic resin material by using depositing or other means and reflects the projection light  200  diffused by transmitted through the transmissive screen  30  toward the concave mirror  50  described later. 
         [0043]    The concave mirror (relay optical system)  50  in  FIG. 2  is obtained by, for example, forming a reflective film on a surface of a base made of a synthetic resin material by using depositing or other means, and a curvature of the concave mirror  50  has a concave free-form surface. A detailed shape of the surface thereof is calculated by optical design software on the basis of a positional relationship with the transmissive screen  30 , the folding mirror  40 , the windshield  2   a , and a moving range of a viewer&#39;s point of sight (eye box), a curvature of the windshield  2   a , a required imaging distance of the virtual image V, and an angle of view of the HUD device  1  visually recognized by the viewer. The concave mirror  50  can be designed by the optical design software so that distortion of the virtual image V is minimized in a constraint condition in which a position of the virtual image V is not changed even in the case where the viewer&#39;s point-of-sight position is moved. The concave mirror  50  enlarges the projection light  200  reflected by the folding mirror  40  and reflects the enlarged projection light toward the windshield  2   a . Note that a relay optical system that orients the image light  100  from the transmissive screen  30  toward the light distribution area E is not limited to a reflective relay optical system such as the folding mirror  40  and the concave mirror  50  and may be a refractive relay optical system such as a lens. 
         [0044]    The housing  60  in  FIG. 2  is a substantially box-shaped member made of a metal material such as aluminum, has various attaching shapes (not illustrated) thereinside, and holds the projection unit  10 , the optical axis adjustment unit  20 , the transmissive screen  30 , and the folding mirror  40  in a predetermined positional relationship in this embodiment. An internal surface of the housing  60  is painted with, for example, black to make it difficult to generate stray light caused by the outside of the HUD device  1  and the projection unit  10 . A light transmitting portion  61  made of, for example, a transparent resin material through which the image light  100  reflected by the concave mirror  50  is transmitted is provided on an upper surface of the housing  60 . 
         [0045]    An electric configuration of the HUD device  1  will be described with reference to  FIG. 4 . As illustrated in  FIG. 4 , the control unit  70  includes a processing unit  71  including one or a plurality of microprocessors, microcontrollers, ASICs, FPGAs, arbitrary other ICs, and the like, a storage unit  72  including one or a plurality of memories capable of storing programs and data, such as a ROM, an EEPROM, and a flash memory that is a nonvolatile memory, and an input/output unit  73  connected to a network unit  80  described later. Note that the control unit  70  is mounted on, for example, a printed circuit board (not illustrated) which is provided inside the housing  60  or is partially or completely provided outside the housing  60 . 
         [0046]    The network unit  80  is, for example, a CAN (Controller Area Network) and connects the control unit  70  (input/output unit  73 ) to a sight position detection unit  91 , an operation input unit  92 , and the like described later on a vehicle side so that signals can be transmitted/received therebetween. 
         [0047]    The sight position detection unit  91  in  FIG. 5  detects a viewer&#39;s point-of-sight position (at least upper and lower positions in a vertical direction of the point of sight) and, in this embodiment, includes an infrared camera (not illustrated) for capturing an image of a viewer and a point-of-sight image analysis unit (not illustrated) for analyzing data of the captured image acquired by this infrared camera. 
         [0048]    The infrared camera captures an image of eyes of a viewer, and the point-of-sight image analysis unit performs image analysis on the data of the captured image acquired by the infrared camera with publicly-known image processing, a pattern matching method, or the like, thereby analyzing the viewer&#39;s point-of-sight position and outputting information on the viewer&#39;s point-of-sight position (point-of-sight position information B) to the control unit  70 . Based on the point-of-sight position information B from the sight position detection unit  91 , the control unit  70  drives the first actuator  22  and the second actuator  25  as described later, thereby rotating the first reflection unit  21  and the second reflection unit  24 . Note that the viewer may operate the operation input unit  92  to adjust a direction of the image light  100  so that the direction is matched with the viewer&#39;s point-of-sight position. In such a case, the control unit  70  inputs operation information via the input/output unit  73  from the operation input unit  92  and drives the first actuator  22  and the second actuator  25  as described later on the basis of this operation information, thereby rotating the first reflection unit  21  and the second reflection unit  24 . 
         [0049]    The input/output unit  73  in  FIG. 5  inputs the point-of-sight position information B from the sight position detection unit  91  and the operation information from the operation input unit  92  via the network unit  80 . The processing unit  71  reads a program of the optical axis adjustment processing from the storage unit  72  and executes the program on the basis of the point-of-sight position information B or the operation information input via the input/output unit  73 . 
         [0050]    For example, the storage unit  72  stores in advance table data in which the point-of-sight position information B or the operation information and control data of the first actuator  22  and the second actuator  25  are associated with each other. The processing unit  71  reads the control data associated with the point-of-sight position information B or the operation information input via the input/output unit  73  by using the table data stored in the storage unit  72  and drives the first actuator  22  and the second actuator  25 . Note that the first reflection unit  21  and the second reflection unit  24  rotate at a constant ratio of rotation, and therefore it is unnecessary to individually store the control data. This makes it possible to reduce a capacity of the storage unit  72 . Note that the input/output unit  73  in this embodiment also has functions of point-of-sight position information acquiring means and operation information acquiring means recited in Claims. 
         [0051]    When the processing unit  71  distorts an image generated by the reflective display  14  in advance and emits the image in the form of the projection light  200 , it is possible to offset or reduce distortion of the image generated due to the angles of the first reflection unit  21  and the second reflection unit  24 , the curvature of the concave mirror  50 , the curvature of the windshield  2   a  (reflective transmissive surface), a viewer&#39;s point-of-sight position, and the like. The “optical axis adjustment processing” in this embodiment will be described with reference to  FIGS. 6 to 8 . 
         [0052]      FIG. 6  is a flowchart of the optical axis adjustment processing in this embodiment. 
         [0053]    In Step S 1 , the processing unit  71  inputs current point-of-sight position information B on a viewer&#39;s point-of-sight position (including at least a height) from the sight position detection unit  91  via the input/output unit  73 . When the current point-of-sight position information B is input, the processing unit  71  proceeds to Step S 2 . 
         [0054]    In Step S 2 , the processing unit  71  reads past (previous) point-of-sight position information A stored in the storage unit  72 . In Step S 3 , the processing unit  71  calculates a difference C between the past point-of-sight position information A and the current point-of-sight position information B. 
         [0055]    In Step S 4 , the processing unit  71  determines whether or not an absolute value of the difference C is larger than a threshold x determined in advance (|C|&gt;x). In the case where the absolute value of the difference C is larger than the threshold x (|C|&gt;x) in Step S 4  (YES in Step S 4 ), i.e., in the case where a change in the viewer&#39;s point-of-sight position (a change in a vertical direction) is larger than a predetermined value, the processing unit  71  proceeds to Step S 5 . On the contrary, in the case where the absolute value of the difference C is equal to or smaller than the threshold x (|C|≦x) in Step S 4  (NO in Step S 4 ), the processing unit  71  proceeds to Step S 1  again. 
         [0056]    In Step S 5 , the processing unit  71  reads, from the storage unit  72 , control data (correction values) of the first actuator  22  and the second actuator  25  corresponding to the current point-of-sight position information B. Then, in Step S 6 , the control data is output to the first actuator  22  and the second actuator  25 . Note that, for example, the control data of the first actuator  22  and the second actuator  25  is stored in the storage unit  72  as table data associated with the point-of-sight position information. The first actuator  22  is rotationally driven on the basis of the input control data to adjust the angle of inclination of the first reflection unit  21 , and the second actuator  25  is rotationally driven on the basis of the input control data to adjust the angle of inclination of the second reflection unit  24 . 
         [0057]    In Step S 7 , the processing unit  71  stores the current point-of-sight position information B in a general-purpose memory as the past point-of-sight position information A and updates the past point-of-sight position information A. 
         [0058]    The processing unit  71  repeatedly executes the above control until a power supply is turned off, and therefore the processing unit  71  can operate the first actuator  22  and the second actuator  25  in accordance with the viewer&#39;s newest point-of-sight position information B to adjust the angle of inclination of the first reflection unit  21  and the angle of inclination of the second reflection unit  24 , thereby adjusting a projected position of the image light  100  in accordance with the height of the viewer&#39;s point-of-sight position. 
         [0059]      FIG. 7A  illustrates a state of the optical axis adjustment unit  20  occurring when image light  100   a  is oriented toward a point-of-sight position  3   a  that is comparatively higher than a point-of-sight position  3  serving as a reference position. 
         [0060]    The processing unit  71  executes the above control method to control the first actuator  22  and the second actuator  25  in accordance with input of the newest point-of-sight position information B. The first actuator  22  is rotationally driven to rotate the first reflection unit  21  in a clockwise direction in  FIG. 7A , thereby adjusting the angle of inclination of the first reflection unit  21  in a steeper direction. Therefore, a reflection direction of the projection light  200  received from the projection unit  10  is adjusted in a direction denoted by a reference sign  200   a  shown in  FIG. 7A . Simultaneously, the second actuator  25  is rotationally driven to rotate the second reflection unit  24  in the clockwise direction in  FIG. 7A , thereby adjusting the angle of inclination of the second reflection unit  24  in a steeper direction. Therefore, the projection light  200   a  received from the first reflection unit  21  is reflected to pass through a predetermined point D on the transmissive screen  30 . The transmissive screen  30  receives the projection light  200   a  reflected by the second reflection unit  24  on the rear surface and emits the image light  100   a  corresponding to the projection light  200   a.    
         [0061]      FIG. 7B  illustrates a state of the whole HUD device  1  occurring when the image light  100   a  is oriented toward the point-of-sight position  3   a  that is comparatively higher than the point-of-sight position  3  serving as the reference position as described above with reference to  FIG. 7A . The image light  100   a  whose angle has been adjusted by the optical axis adjustment unit  20  in  FIG. 7A  is reflected toward the point-of-sight position  3   a  at a projected point Pa positioning above the projected point P of the image light  100  oriented toward the point-of-sight position  3  serving as the reference position as illustrated in  FIG. 7B . The image light  100   a  oriented toward the viewer&#39;s point-of-sight position  3   a  passes through the predetermined point D on the transmissive screen  30  in the same way as the image light  100  and  100   b  oriented toward the point-of-sight positions  3  and  3   b  in  FIG. 7B . Therefore, an imaging position of the virtual image V to be visually recognized at the comparatively higher point-of-sight position  3   a  is substantially matched with imaging positions of the virtual image V to be visually recognized at the standard point-of-sight position  3  and the comparatively lower point-of-sight position  3   b . Further, the image light  100  emitted from the transmissive screen  30  can be efficiently oriented toward the comparatively higher point-of-sight position  3   a  by the optical axis adjustment processing of the optical axis adjustment unit  20 . 
         [0062]      FIG. 8A  illustrates a state of the optical axis adjustment unit  20  occurring when image light  100   b  is oriented toward the point-of-sight position  3   b  that is lower than the point-of-sight position  3  serving as a reference position. 
         [0063]    The processing unit  71  executes the above control method to control the first actuator  22  and the second actuator  25  in accordance with input of the newest point-of-sight position information B. The first actuator  22  is rotationally driven to rotate the first reflection unit  21  in a counterclockwise direction in  FIG. 8A , thereby adjusting the angle of inclination of the first reflection unit  21  in a gentler direction. Therefore, the reflection direction of the projection light  200  received from the projection unit  10  is adjusted in a direction denoted by a reference sign  200   b  illustrated in  FIG. 8A . Simultaneously, the second actuator  25  is rotationally driven to rotate the second reflection unit  24  in the counterclockwise direction in  FIG. 8A , thereby adjusting the angle of inclination of the second reflection unit  24  in a gentler direction. Therefore, the projection light  200   b  received from the first reflection unit  21  is reflected to pass through the predetermined point D on the transmissive screen  30 . The transmissive screen  30  receives the projection light  200   b  reflected by the second reflection unit  24  on the rear surface and emits the image light  100   b  corresponding to the projection light  200   b.    
         [0064]      FIG. 8B  illustrates a state of the whole HUD device  1  occurring when the image light  100   b  is oriented toward the point-of-sight position  3   b  that is comparatively lower than the point-of-sight position  3  serving as the reference position as described above with reference to  FIG. 8A . The image light  100   b  whose angle has been adjusted by the optical axis adjustment unit  20  in  FIG. 8A  is reflected toward the point-of-sight position  3   b  at a projected point Pb positioning below the projected point P of the image light  100  oriented toward the point-of-sight position  3  serving as the reference position as illustrated in  FIG. 8B . The image light  100   b  oriented toward the viewer&#39;s point-of-sight position  3   b  passes through the predetermined point D on the transmissive screen  30  in the same way as the image light  100  and  100   a  oriented toward the point-of-sight positions  3  and  3   a  in  FIG. 8B . Therefore, the imaging position of the virtual image V to be visually recognized at the comparatively lower point-of-sight position  3   b  is substantially matched with the imaging positions of the virtual image V to be visually recognized at the standard point-of-sight position  3  and the comparatively higher point-of-sight position  3   a . Further, the image light  100  emitted from the transmissive screen  30  can be efficiently oriented toward the comparatively lower point-of-sight position  3   b  by the optical axis adjustment processing of the optical axis adjustment unit  20 . 
         [0065]    For example, as illustrated in  FIG. 7A  and  FIG. 8A , the first reflection unit  21  and the transmissive screen  30  are arranged at or near positions of focal points Fa and Fb, respectively, in a predetermined ellipse Q. Specifically, for example, a center point  21   r  of a reflection surface of the first reflection unit  21  is positioned at one focal point Fa in the ellipse Q, and a center point of the transmissive screen  30  is positioned at the other focal point Fb. The second reflection unit  24  reflects the projection light  200  reflected by the first reflection unit  21  toward the predetermined point D on the transmissive screen  30  at a reflection position  24   r  ( 24   ra ,  24   rb ) near a locus of the ellipse Q indicated by a dotted line in  FIG. 7A  and  FIG. 8A . 
         [0066]    Because of a property of the ellipse, a sum total of a distance between the one focal point Fa and the reflection position  24   r  and a distance between the reflection position  24   r  and the other focal point Fb is the same as long as the reflection position  24   r  is on the locus of the ellipse Q, irrespective of a position of the reflection position  24   r . In other words, when the light (projection light  200 ) from the one focal point Fa (first reflection unit  21 ) is reflected on the locus of the ellipse Q toward the other focal point Fb (transmissive screen  30 ), an optical path length of the light (projection light  200 ) between the one focal point Fa (first reflection unit  21 ) and the other focal point Fb (transmissive screen  30 ) can always be the same. However, the second reflection unit  24  rotates around the second rotation axis  26  in this embodiment, and therefore, in the case where the reflection point  24   r  is positioned on the locus of the ellipse Q, the projection light  200  reflected by the second reflection unit  24  does not pass through the predetermined point D on the transmissive screen  30 . That is, in the case where the angle of the second reflection unit  24  is adjusted so that the reflection point  24   r  of the second reflection unit  24  is positioned on the locus of the predetermined ellipse Q, a position of the display image to be formed on the transmissive screen  30  is shifted. In the case where the display image to be formed on the transmissive screen  30  is shifted due to optical axis adjustment of the optical axis adjustment unit  20 , it is necessary to increase a size of the transmissive screen  30  in advance so that the display image to be formed is not outside the transmissive screen  30 . 
         [0067]    In the second reflection unit  24  in this embodiment, a position that is not on the locus of the ellipse Q is set to be the reflection position  24   r  ( 24   ra ,  24   rb ) so that the projection light  200  reflected by the first reflection unit  21  is reflected toward the predetermined point D on the transmissive screen  30 . Thus, a shift of the display image to be formed on the transmissive screen  30 , which is caused by adjustment of the angle of the second reflection unit  24 , is suppressed, and therefore the size of the transmissive screen  30  can be reduced. Note that, because the reflection point  24   r  of the second reflection unit  24  is not positioned on the locus of the ellipse Q in this embodiment, the optical path length of the projection light  200  between the first reflection unit  21  and the transmissive screen  30  is not always the same due to the optical axis adjustment processing. However, the projection distance that changes due to the optical axis adjustment processing falls within a range of the projected image plane depth of the projector lens  15 , and therefore it is possible to generate the display image that can be considered to be in focus on the transmissive screen  30 . 
         [0068]    The HUD device  1  described above causes a viewer to visually recognize the virtual image V and includes the projection unit  10  for emitting the projection light  200 , the first reflection unit  21  for reflecting the projection light  200  emitted by the projection unit  10 , the first actuator  22  for rotating the first reflection unit  21 , the second reflection unit  24  for reflecting the projection light  200  reflected by the first reflection unit  21 , the second actuator  25  for rotating the second reflection unit  24 , the control unit  70  for controlling the first actuator  22  and the second actuator  25 , the transmissive screen  30  for allowing the projection light  200  reflected by the second reflection unit  24  to be transmitted therethrough and diffusing the projection light  200 , and the concave mirror  50  for reflecting the image light  100  emitted from the transmissive screen  30  toward the windshield  2   a  (transmissive reflective surface), the concave mirror  50  having a concave curved surface for suppressing a shift of a position at which the virtual image V is visually recognized with respect to a real view even in the case where a height of the viewer&#39;s point of sight is changed within a predetermined range, and the control unit  70  drives the first actuator  22  and the second actuator  25  to adjust the angle of the optical axis of the projection light  200  incident on the transmissive screen  30 . Therefore, it is possible to orient the direction of the image light  100  emitted from the transmissive screen  30  toward the viewer&#39;s point-of-sight position with a simple method of rotating the first reflection unit  21  and the second reflection unit  24 . 
         [0069]    The optical axis adjustment unit  20  adjusts the angle of the projection light  200  to be incident on the transmissive screen  30  within a predetermined angle range in order to orient the image light  100  toward a range of the height of the point of sight (point-of-sight positions  3   a  to  3   b ) which is normally used and causes the projection distance of the projection light  200  adjusted within this angle range between the projection unit  10  and the transmissive screen  30  to fall within the projected image plane depth of the projector lens  15 . Therefore, even in the case where the optical axis adjustment processing is performed, it is possible to form the display image that can be considered to be in focus on the transmissive screen  30 . 
         [0070]    The optical axis adjustment unit  20  can adjust the projection light  200  to at least the first projection light  200  along a first optical axis, the second projection light  200   a  along a second optical axis, and the third projection light  200   b  along a third optical axis, whose angles incident on the transmissive screen  30  are different from one another, and orients the first, second, and third image light  200 ,  200   a , and  200   b  toward the predetermined point D on the transmissive screen  30 . Thus, even in the case where the optical axis adjustment processing is performed, the display image is formed in substantially the same region on the transmissive screen  30 , and therefore it is possible to reduce the size of the transmissive screen  30 . Further, the image light  200  ( 200   a ,  200   b ) which has been subjected to the optical axis adjustment processing passes through the predetermined point D, and therefore a viewer having a different point-of-sight position can also visually recognize the virtual image V at the same position with respect to a real view. Note that the predetermined point D is positioned on the transmissive screen  30  in the above embodiment but may not be positioned on the transmissive screen  30 . Specifically, the position of the transmissive screen  30  may be shifted to the folding mirror  40  side or the projection unit  10  side from the position shown in  FIG. 7B . 
         [0071]    The concave mirror  50  has the concave curved surface for suppressing a shift of a position at which the virtual image V is visually recognized with respect to a real view even in the case where a height of a viewer&#39;s point of sight is changed within a predetermined range, and therefore the virtual image V having a fixed brightness, whose relative position visually recognized with respect to the real view is not changed even in the case where the viewer&#39;s point-of-sight position (height) is changed, can be visually recognized with a simple configuration in which the first reflection unit  21  and the second reflection unit  24  are rotated in the housing  60 . 
         [0072]    Although the second reflection unit  24  only rotates around the second rotation axis  26  in the above embodiment, the second reflection unit  24  may rotate while moving as illustrated in  FIG. 9 . With this configuration, it is possible to orient the projection light  200  incident from the first reflection unit  21  toward the predetermined point D while keeping the same optical path length between the projection unit  10  and the transmissive screen  30 . 
         [0073]    Although the first reflection unit  21  and the second reflection unit  24  are individually rotated by the respective actuators in the above embodiment, the first reflection unit  21  and the second reflection unit  24  may be rotated by a common actuator (not illustrated). Note that, by changing a gear ratio of gears that transmit power from the common actuator to the first reflection unit  21  and the second reflection unit  24 , the first reflection unit  21  and the second reflection unit  24  are rotated at a predetermined ratio of rotation in accordance with drive of the common actuator. 
         [0074]    In the case where the projected position of the projection light  200  is changed on the windshield  2   a  that is a curved surface, distortion of the virtual image V is changed depending on the projected position in some cases. In response to this, the control unit  70  may change a correction parameter for correcting the distortion of the virtual image V in accordance with an operation state of the first actuator  22  and/or the second actuator  25 , i.e., an angle of incidence of the projection light  200  on the transmissive screen  30 . This correction parameter is a parameter for distorting the display image in advance in a direction opposite to a direction of distortion on the windshield  2   a  and displaying the display image in order to suppress the distortion of the virtual image V projected onto the windshield  2   a . For example, a plurality of correction parameters are stored in the form of a data table in the storage unit  72  so as to be associated with control data of the first actuator  22  and/or the second actuator  25 , and the processing unit  71  determines the correction parameter in accordance with the control data of the first actuator  22  and/or the second actuator  25  determined with the above control method and outputs the correction parameter to the projection unit  10 . Thus, it is possible to suppress the distortion of the virtual image V even in the case where the projected position of the projection light  200  on the windshield  2   a  is adjusted. 
         [0075]    The reflective transmissive surface onto which the projection light  200  is projected is not limited to the windshield  2   a  of the own vehicle  2 . The reflective transmissive surface onto which the projection light  200  is projected may be, for example, a combiner member provided dedicatedly. 
         [0076]    Note that the projection unit  10  may have, for example, a function of adjusting a position of the projector lens  15  to adjust the projected image distance  151 . 
         [0077]    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 
       [0078]    The invention is applicable as a heads-up display device to be mounted on a mobile body such as a vehicle. 
       REFERENCE SIGNS LIST 
       [0000]    
       
         
           
               1  HUD device (heads-up display device) 
               2  own vehicle 
               2   a  windshield (transmissive reflective surface) 
               3  viewer 
               10  projection unit 
               11  light source 
               12  light source mirror 
               13  prism 
               14  reflective display 
               15  projector lens 
               20  optical axis adjustment unit 
               21  first reflection unit 
               22  first actuator 
               24  second reflection unit 
               25  second actuator 
               30  transmissive screen 
               40  folding mirror 
               50  concave mirror 
               60  housing 
               70  control unit 
               71  processing unit 
               72  storage unit 
               73  input/output unit (point-of-sight position information acquiring means, operation information acquiring means) 
               80  network unit 
               91  sight position detection unit 
               92  operation input unit 
               100  image light 
               200  projection light 
               300  illumination light