Abstract:
The present invention relates to a head-up display device that allows a viewer to view an actual scene overlapped with a virtual image, and that is capable of creating a display image with suppressed luminance variation. A MEMS scanner scans synthesized laser light two-dimensionally in the main scanning direction H and the sub-scanning direction V substantially orthogonal to the main scanning direction H. A controller unit causes a first scan for generating a display image M on a transmissive screen by scanning in the main scanning direction H at high speed while scanning in the sub-scanning direction V, and a second scan for scanning a position displaced more toward the sub-scanning direction V than the first scan on the transmissive screen.

Description:
TECHNICAL FIELD 
       [0001]    The present invention relates to a head-up display device that causes a viewer to visually recognize a virtual image with scenery. 
       BACKGROUND ART 
       [0002]    A head-up display device (hereinafter, HUD device) in which a semiconductor laser is provided as a light source is disclosed in, for example, PTL 1. This HUD device includes a semiconductor laser for outputting laser light, a scanning unit for two-dimensionally deflecting the laser light emitted from this semiconductor laser to thereby generate an image, a screen for emitting the laser light scanned by the scanning unit as diffused image light, and a relay optical system for directing the image light emitted from the screen to a transmissive reflective surface. 
         [0003]    Generally, a spot pattern referred to as “speckles” is generated in an image generated by a HUD device using laser light. The speckles are caused by high coherence of laser light and is generated when laser beams diffused on a screen interfere with each other and strength and weakness of the beams occur. For example, speckles are remarkably generated in a diffusion plate having a diffusion material on the inside thereof and a frosted diffusion plate for diffusing light by using unevenness of a surface thereof. When speckles are generated, resolution of an image is reduced due to a spot pattern, thereby reducing visibility. 
         [0004]    As a technique for solving such a problem, PTL 2 discloses a technique in which a double micro lens array (DMLA) formed by doubly arranging micro lens arrays (MLAs) is used for a screen of a HUD device. When the DMLA is used as described above, laser light is diffused by a refraction effect of a micro lens group, and therefore it is possible to reduce generation of speckles. 
         [0005]    However, in order to reduce speckles by using MLAs with a screen, it is also necessary to devise laser light. Laser light emitted from a semiconductor laser normally has an oval shape, and an intensity distribution thereof is substantially Gaussian. Therefore, in the HUD device disclosed in PTL 2, laser light is shaped to have the same shape as a single lens of an MLA and, in addition, an intensity distribution of the laser light is converted into a top-hat intensity distribution by using a lens or the like. 
         [0006]    With this combination of shaping of laser light, conversion of an intensity distribution, and MLAs, interference patterns of the top hat are arranged in the whole eye box with no gap, and a light distribution having no difference in light intensity between interference patterns is achieved. Thus, in a case where pupils of a viewer are in the eye box, an amount of light incident on the inside of the pupils is not changed even when positions of the pupils are moved, and therefore it is possible to cause a viewer to visually recognize a display image with a satisfactory quality. 
       CITATION LIST 
     Patent Literature (s) 
       [0007]    PTL 1: JP-A-7-270711 
         [0008]    PTL 2: JP-T-2007-523369 (The term “JP-T” as used herein means a published Japanese translation of a PCT patent application.) 
       SUMMARY OF INVENTION 
     Technical Problem(s) 
       [0009]    However, in a case where shaping of beams and conversion of an intensity distribution described above are not appropriately performed, interference patterns caused by the MLAs and laser light are not arranged at a high density on the eye box, and therefore unevenness of luminance and unevenness of color occur in a display image. Further, in fact, even in a case where shaping of beams and conversion of an intensity distribution described above are appropriately performed, it is difficult to completely eliminate gaps between interference patterns in the whole eye box, and, when positions of pupils are moved, an amount of light incident on the pupils is changed, and therefore unevenness of luminance and unevenness of color occur in a display image. 
         [0010]    In view of this, the invention has been made in view of the above problems, and an object thereof is to provide a head-up display device capable of generating a display image in which unevenness of luminance is reduced. 
       Solution to Problem(s) 
       [0011]    The invention employs the following means in order to solve the above problems. 
         [0012]    That is, a head-up display device in the first invention includes: a light source configured to emit laser light; a scanning unit configured to two-dimensionally scan the laser light in a main scanning direction and a sub-scanning direction different from the main scanning direction; a lens array screen having a plurality of micro lenses that are periodically arranged, the lens array screen being configured to diffuse the laser light scanned by the scanning unit and direct the laser light to a visual recognition region; and a control unit configured to control the light source and the scanning unit to generate a display image on the lens array screen, wherein the control unit causes first scanning to be performed and causes second scanning to be performed, the first scanning being scanning in which scanning is performed in the sub-scanning direction while scanning is being performed in the main scanning direction at a high speed, the second scanning being scanning in which a position shifted in the sub-scanning direction from the first scanning on the lens array screen is scanned. 
       Advantageous Effects of Invention 
       [0013]    The invention can generate a display image in which unevenness of luminance is reduced. 
       DESCRIPTION OF EMBODIMENTS 
       [0014]    Hereinafter, a first embodiment of a head-up display device (hereinafter, referred to as “HUD device”) of the invention will be described with reference to the attached drawings. 
         [0015]    As shown in  FIG. 1 , a HUD device  1  according to this embodiment is a device that is provided in a dashboard of a vehicle  2  and causes a windshield  3  to reflect image light  600  showing a display image M (see  FIG. 2 ) generated on a transmissive screen  40  described below so that a driver visually recognizes a virtual image W (display image) of the display image M indicating vehicle information. The driver visually recognizes the display image M as the virtual image W in an eye box  4  serving as a visual field. Note that the virtual image W in  FIG. 1  is schematically shown in order to facilitate sensuous understanding. The same applies to the display image M in  FIG. 2 . 
         [0016]    As shown in  FIG. 2 , the HUD device  1  shown in  FIG. 1  includes a synthesized laser light generation device  10 , a MEMS (Micro Electro Mechanical System) scanner  20 , a field lens  30 , the transmissive screen  40 , a relay optical unit  50 , and a housing  60 . 
         [0017]    The synthesized laser light generation device  10  is a device for adjusting optical axes of laser beams B, R, and G emitted by respective light sources  11   b,    11   r,  and  11   g  described below and emitting a single beam of synthesized laser light  500 , and includes alight source  11 , a condensing optical unit  12 , and an optical axis adjustment unit  13  as shown in  FIG. 3 . 
         [0018]    As shown in  FIG. 3 , the light source  11  is made up of the blue light source  11   b  for emitting blue laser light B, the red light source  11   r  for emitting red laser light R, and the green light source  11   g  for emitting green laser light G. The light sources  11   b,    11   r,  and  11   g  are arranged so that polarization directions (electric field oscillation directions) of the respective laser beams B, R, and G are matched when the laser beams B, R, and G are emitted as the synthesized laser light  500 . 
         [0019]    The condensing optical unit  12  is a lens whose aberration is corrected so that the laser beams B, R, and G serving as divergent light emitted from the light source  11  are converted into convergent light and are condensed into a lower surface of the transmissive screen  40  described below and is made up of a blue condenser lens  12   b,  a red condenser lens  12 R, and a green condenser lens  12 G arranged on optical paths of the laser beams B, R, and G emitted from the respective light sources  11   b,    11   r,  and  11   g.  Each of the laser beams B, R, and G emitted from the light source  11  has a substantially Gaussian light intensity distribution (not shown), and therefore the synthesized laser light  500  (laser beams B, R, and G), which is condensed by the condensing optical unit  12  and reaches the transmissive screen  40 , can be similarly considered to have a substantially Gaussian light intensity distribution  710 . 
         [0020]    The optical axis adjustment unit  13  roughly aligns the optical axes of the laser beams B, R, and G and directs the laser beams as the synthesized laser light  500  toward the MEMS scanner  20  and is made up of a first dichroic mirror  13 R for reflecting only a wavelength range of red laser light R and a second dichroic mirror  13 G for reflecting only a wavelength range of green laser light G. 
         [0021]    Referring back to  FIG. 2 , the MEMS scanner  20  scans the synthesized laser light  500  emitted by the synthesized laser light generation device  10  and generates the display image M on a surface side of the transmissive screen  40 . As shown in  FIG. 4 , the MEMS scanner  20  performs main scanning in a main scanning direction H a plurality of times while performing sub-scanning in a sub-scanning direction V substantially orthogonal to the main scanning direction H, thereby generating the display image M on the transmissive screen  40  described below. 
         [0022]    The field lens  30  causes the synthesized laser light  500  scanned by the MEMS scanner  20  to be incident on the transmissive screen  40  at an angle of incidence based on a scanning position. The field lens  30  is formed and arranged to optimize the angle of incidence of the synthesized laser light  500  on the transmissive screen  40  in accordance with characteristics of optical systems (relay optical unit  50 , windshield  3 ) subsequent to the transmissive screen  40 . 
         [0023]    As shown in  FIG. 6 , the transmissive screen  40  is made up of a micro lens array (hereinafter, MLA)  41  and an aperture array  42  arranged on a front surface side of the MLA  41  and displays the display image M on the surface side. The transmissive screen  40  enlarges an exit pupil of the synthesized laser light  500  entering from the MEMS scanner  20  and emits the synthesized laser light  500  as the image light  600  toward the relay optical unit  50 . 
         [0024]    Herein, the transmissive screen  40  will be described with reference to  FIGS. 5 and 6 . 
         [0025]      FIG. 5( a )  is a plan view of the MLA  41 , and  FIG. 5( b )  is a plan view of the aperture array  42 . Further,  FIG. 6  is a cross-sectional view of the transmissive screen  40  and is a cross-sectional view taken along A-A in  FIG. 4 . 
         [0026]    As shown in  FIG. 5( a ) , the MLA  41  includes a plurality of micro lenses (hereinafter, referred to as “MLs”)  41   a  on a surface thereof and is formed so that the MLs  41   a  are periodically arrayed with a pitch of dH 1  in the main scanning direction H and with a pitch of dV 1  in the sub-scanning direction V. In this embodiment, dH 1 &gt;dV 1  is satisfied, and the MLs  41   a  are periodically arrayed in a rectangular grid pattern and are formed so that a gap and a level difference generated in adjacent MLs  41   a  are minimized. The pitch herein means a distance between centers of lenses of the MLs  41   a  adjacent to each other. With this rectangular lens array, it is possible to efficiently illuminate the eye box  4  with laser light emitted through the transmissive screen  40  with a rectangular shape. In this embodiment, the pitch dV 1  in the sub-scanning direction V is set to a size corresponding to substantially one pixel. 
         [0027]    Although rectangular micro lenses are arrayed in a grid pattern in this embodiment, the lenses may have a square shape. Further, hexagonal micro lenses may be arrayed in a honeycomb pattern. 
         [0028]    As shown in  FIG. 5( b ) , the aperture array  42  includes in a surface thereof, a plurality of opening portions  42   a  that are periodically arrayed with a pitch of dHA in the main scanning direction H and with a pitch of dVA in the sub-scanning direction V. The pitch herein means a distance between centers of the opening portions  42   a  adjacent to each other. 
         [0029]    In this embodiment, dHA&gt;dVA is satisfied in the same way as the MLA  41 . Further, the pitch in the aperture array  42  is slightly larger than the pitch in the MLA  41 , i.e., dHA&gt;dH 1  is satisfied. 
         [0030]    The opening portion  42   a  of the aperture array  42  is formed so that the size thereof is adjusted to be about ⅕ to 1/10 the size of the lens of the ML  41   a.  A region other than the opening portions  42   a  in the aperture array  42  is a light shielding portion  42   b  as shown in  FIG. 5( b ) . The light shielding portion  42   b  is made of, for example, a material that absorbs visible light such as black resist for use in a liquid crystal panel. In other words, regions other than the opening portions  42   a  on both surfaces of the aperture array  42  are surfaces of the light shielding portion  42   b.  Therefore, among beams of laser light reaching the aperture array  42 , beams other than beams passing through the opening portions  42   a  are mostly absorbed into the light shielding portion  42   b.    
         [0031]    As shown in  FIG. 6 , the MLA  41  and the aperture array  42  are arranged so that surfaces of the MLA  41  and the aperture array  42  are parallel to each other and the center of the opening portion  42   a  positioned at the center of the aperture array  42  is positioned on an optical axis AX of the ML  41   a  positioned at the center of the MLA  41 . Further, both the MLA and the aperture array are arranged at an interval of a focal length f of the ML  41   a.  Note that the ML  41   a  positioned at the center of the MLA  41  means an ML  41   a  provided at a position irradiated with light existing at the center of laser light scanned by the MEMS scanner  20 . Further, the MLA  41  and the aperture array  42  are formed and arranged so that each of the plurality of opening portions  42   a  of the aperture array  42  and each of the plurality of micro lenses  41   a  of the MLA  41  are paired and the center of the opening portion  42   a  is positioned at a condensing point P of laser beams R, G, and B by using the MLA  41 . 
         [0032]    The transmissive screen  40  is configured as described above, and therefore laser light condensed by the MLA  41  exactly passes through the opening portion  42   a  of the aperture array  42 . Thus, it is possible to efficiently use laser light emitted by the light source  11  as light showing the display image M. Meanwhile, external light that is inversely transmitted through the optical path of the laser light in the HUD device  1  shown in  FIG. 2  and reaches the transmissive screen  40  is mostly absorbed into the light shielding portion  42   b  of the aperture array  42 . Therefore, reflection of external light is remarkably reduced. In a case where the light shielding portion  42   b  is not provided, external light diffused and reflected by the transmissive screen  40  reaches eyes of a viewer through the optical path of the HUD device  1 . In this case, the transmissive screen  40  is superimposed on a display image and appears as a white frame, and therefore visibility is deteriorated. 
         [0033]    Further, among beams of laser light reaching the transmissive screen  40 , beams other than the image light  600  (i.e., beams showing display image M) passing through the opening portions  42   a  of the aperture array  42  are mostly absorbed into the light shielding portion  42   b  of the aperture array  42 . Therefore, it is also possible to reduce internal reflection of laser light in the transmissive screen  40 . 
         [0034]    Although the aperture array  42  is formed on the transmissive screen  40  in this embodiment, the MLA  41  may be provided alone. 
         [0035]    The relay optical unit  50  is provided in an optical path between the transmissive screen  40  and the windshield  3  and is an optical system for correcting light so that the display image M displayed on a front surface of the transmissive screen  40  is formed as the virtual image W having a desired size at a desired position. The relay optical unit  50  is made up of two mirrors, i.e., a plane mirror  51  and a concave mirror  52 . 
         [0036]    The plane mirror  51  is a planar total reflection mirror or the like and reflects the image light  600  showing the display image M displayed on the transmissive screen  40  toward the concave mirror  52 . 
         [0037]    The concave mirror  52  is a concave mirror or the like and causes a concave surface to reflect the image light  600  reflected by the plane mirror  51 , thereby emitting the reflected light toward the windshield  3 . With this, the size of the virtual image W to be formed is a size obtained by enlarging the display image M. 
         [0038]    The housing  60  has an opening portion having a predetermined size in an upper portion thereof and is made of hard resin or the like to have a box shape. The housing  60  houses the synthesized laser light generation device  10 , the MEMS scanner  20 , the field lens  30 , the transmissive screen  40 , the relay optical unit  50 , and the like at predetermined positions thereinside. Further, a window portion  61  is attached to the opening portion of the housing  60 . 
         [0039]    A control system of the HUD device  1  will be described with reference to  FIG. 7 . 
         [0040]    As shown in  FIG. 7 , the HUD device  1  includes, in addition to the members described above, an LD control unit  100 , a MEMS control unit  200 , and a controller unit  300  for controlling the LD control unit  100  and the MEMS control unit  200 . Those control units are mounted on, for example, a printed circuit board (not shown) provided in the housing  60 . Further, those control units may be provided outside the HUD device  1  and be electrically connected to the HUD device  1  (light sources  11   r ,  11   g,  and  11   b,  MEMS scanner  20 , and the like) via wiring. 
         [0041]    The LD control unit  100  is made up of, for example, a driver IC for driving the light sources  11   b,    11   r,  and  11   g  and drives the light sources  11   b,    11   r,  and  11   g  with a PWM method or a pulse amplitude modulation (PAM) method under the control of the controller unit  300  (on the basis of an LD drive signal from a display control unit  340 ). 
         [0042]    The MEMS control unit  200  is made up of, for example, a driver IC for driving the MEMS scanner  20  and drives the MEMS scanner  20  under the control of the controller unit  300  (on the basis of a scanning control signal from the display control unit  340 ). The MEMS control unit  200  causes the MEMS scanner  20  to resonate in the main scanning direction H by using a sinusoidal main scanning drive signal (main scanning driving voltage). Further, the MEMS control unit  200  vibrates the MEMS scanner  20  in the sub-scanning direction V by using a sub-scanning drive signal (sub-scanning driving voltage). 
         [0043]    The MEMS control unit  200  acquires an oscillation position of a piezoelectric element that moves a mirror of the MEMS scanner  20  at each time point, calculates feedback data on the basis of this oscillation position, and outputs this feedback data to the display control unit  340  described below. 
         [0044]    The feedback data output from the MEMS control unit  200  is data containing scanning position detection data related to scanning positions by the MEMS scanner  20 , such as the number of main scanning lines n, a scanning start position Ya, a display start position (not shown), a display end position (not shown), and a scanning end position Yb shown in  FIG. 4 , actually measured main resonance frequency data showing a resonance frequency obtained when the MEMS scanner  20  actually resonates in the main scanning direction H, and actually measured sub-resonance frequency data showing a resonance frequency obtained when the MEMS scanner  20  actually resonates in the sub-scanning direction V. 
         [0045]    The controller unit  300  is made up of a microcontroller, an FPGA (Field Programmable Gate Array), an ASIC (Application Specific Integrated Circuit), and the like and includes an input processing unit  310 , a memory control unit  320 , a frame buffer  330 , and the display control unit  340 . The controller unit  300  controls LDs (light source  11   r,  light source  11   g,  light source  11   b ) and the MEMS scanner  20  via the LD control unit  100  and the MEMS control unit  200  on the basis of an image signal input from a vehicle ECU 5 , thereby generating an image M based on the image signal on the transmissive screen  40 . Note that the control unit of the invention is made up of the LD control unit  100 , the MEMS control unit  200 , and the controller unit  300 . 
         [0046]    The input processing unit  310  inputs an image signal from the vehicle ECU 5  and processes data thereof to provide a format suitable for processing in the controller unit  300 . 
         [0047]    The memory control unit  320  stores frame data converted in the input processing unit  310  on the frame buffer  330 . The frame buffer  330  is made up of, for example, a volatile memory such as a DRAM and an SRAM or a rewritable nonvolatile memory such as a flash memory. 
         [0048]    Upon receipt of a command from the display control unit  340 , the memory control unit  320  further extracts the frame data from the frame buffer  330  and outputs the frame data to the display control unit  340 , and the display control unit  340  stores the frame data on a buffer memory  341  in the display control unit  340 . 
         [0049]    The display control unit  340  executes program data stored in advance and therefore outputs an LD drive signal to the LD control unit  100  and further outputs a scanning control signal to the MEMS control unit  200  to control the light sources  11   r ,  11   g,  and  11   b  and the MEMS scanner  20 , thereby generating the display image M on the transmissive screen  40 . 
         [0050]    The configuration of the HUD device  1  according to this embodiment has been described above. 
         [0051]    A shape and the light intensity distribution  710  ( 720 ) of the synthesized laser light  500  reaching the transmissive screen  40  in this embodiment and a distributed light intensity distribution  810  ( 820 ) of the image light  600  obtained by causing the synthesized laser light  500  to pass through the transmissive screen  40  will be described with reference to  FIG. 8  and  FIG. 9 .  FIG. 8  is a diagram for explaining a relationship between the transmissive screen  40  and the synthesized laser light  500  and the light intensity distribution  710  ( 720 ) of the synthesized laser light  500 , and  FIG. 9  is a diagram for explaining the distributed light intensity distribution  810  ( 820 ) of the image light  600  emitted from the transmissive screen  40 . 
         [0052]    The synthesized laser light  500  converted into convergent light by the condensing optical unit  12  is condensed to have a substantially minimum beam diameter at a position at which the synthesized laser light is incident on the MLA  41 . This beam diameter is a diffraction limit determined on the basis of a beam diameter in the condensing optical unit  12  and a distance between the condensing optical unit  12  and the MLA  41 . Note that the following description will be made on the premise that the beam diameter of the synthesized laser light  500  incident on the transmissive screen  40  in the main scanning direction H is referred to as “DH” and the beam diameter thereof in the sub-scanning direction V is referred to as “DV”. The beam diameter DH(DV) in the description of this embodiment is prescribed as a diameter from a peak intensity of the synthesized laser light  500  in the main scanning direction H (sub-scanning direction V) to positions at which the intensity is 1/e 2  (13.5%) of the peak intensity. 
         [0053]    (Main Scanning) 
         [0054]    As shown in  FIG. 8 , the beam diameter DH in the main scanning direction H is smaller than the pitch dH 1  of the MLA  41  in the main scanning direction H, and the light intensity distribution  710  in the main scanning direction H can be considered to be substantially Gaussian. The image light  600  refracted by the ML  41   a  of the MLA  41  passes through the opening portion  42   a  of the aperture array  42  and is diverged and is then directed to the eye box  4 . As shown in  FIG. 9 , the distributed light intensity distribution  810  of the image light  600  in the main scanning direction H, the image light  600  being image light with which the eye box  4  is irradiated, behaves like a substantially Gaussian distribution. When the beam diameter DH in the main scanning direction H is set to be smaller than the pitch dH 1  of the MLA  41 , the synthesized laser light  500  is hardly incident on the plurality of MLs  41   a,  and therefore the image light  600  emitted from the MLA  41  hardly generates an interference fringe in the eye box  4 . 
         [0055]    In main scanning of this embodiment, the light source  11  is driven for about 10 nsec in order to form a single pixel of the display image M (scan a single ML  41   a ). During that time, the MEMS scanner  20  continuously performs scanning in the main scanning direction H, and therefore the synthesized laser light  500  is moved in the main scanning direction H by an amount of a substantially single ML  41   a  within a driving period of the light source  11 . Then, a peak of the distributed light intensity distribution  810  of the image light  600  emitted from the transmissive screen  40  in the main scanning direction H is shifted in the eye box  4 . 
         [0056]      FIG. 10  shows a relationship between a position of the synthesized laser light  500  incident on the ML  41   a  in the main scanning direction H and the distributed light intensity distribution  810  in the main scanning direction H in the eye box  4 , and (a) and (f), (b) and (g), (c) and (h), (d) and (i), and (e) and (j) correspond to each other. When a single MLA  41  is scanned by the synthesized laser light  500  in the main scanning direction H as shown in  FIGS. 10( a ) to ( e ) , different distributed light intensity distributions  810  ( 811 ,  812 ,  813 ,  814 ,  815 ) shown in  FIGS. 10( f ) to ( j )  are obtained. When those different distributed light intensity distributions  810  are integrated by a time taken to scan a single ML  41   a,  as shown in  FIG. 11 , it is possible to form a substantially uniform distributed light intensity distribution  810  that can be considered to be substantially top-hat in the main scanning direction H in the whole eye box  4 . 
         [0057]    (Sub-Scanning) 
         [0058]    As shown in  FIG. 8 , the beam diameter DV in the sub-scanning direction V is smaller than the pitch dV 1  of the MLA  41  in the sub-scanning direction V, and the light intensity distribution  720  in the sub-scanning direction V can be considered to be substantially Gaussian. The image light  600  refracted by the ML  41   a  of the MLA  41  passes through the opening portion  42   a  of the aperture array  42  and is diverged and is then directed to the eye box  4 . As shown in  FIG. 9 , the distributed light intensity distribution  820  of the image light  600  in the sub-scanning direction V, the image light  600  being image light with which the eye box  4  is irradiated, behaves like a substantially Gaussian distribution. When the beam diameter DV in the sub-scanning direction V is set to be smaller than the pitch dV 1  of the MLA  41 , the synthesized laser light  500  is hardly incident on the plurality of MLs  41   a,  and therefore the image light  600  emitted from the MLA  41  hardly generates an interference fringe in the eye box  4 . 
         [0059]    The MEMS scanner  20  performs main scanning while performing sub-scanning, and therefore a scanning line on the transmissive screen  40  is not parallel to the main scanning direction H and is formed on the transmissive screen  40  as an oblique scanning line (see  FIG. 4 ). Specifically, the scanning line is moved in the sub-scanning direction V by an amount of a substantially single ML  41   a  while a single line is being scanned in the main scanning direction H. Therefore, a position of the synthesized laser light  500  scanned in the ML  41   a  in the sub-scanning direction V is changed as shown in  FIGS. 12( a ), ( b ), and ( c )  while a single line is being scanned in the main scanning direction H, and a peak position of the distributed light intensity distribution  820  in the sub-scanning direction V is shifted as shown in  FIGS. 12( f ), ( g ), and ( h ) . Then, when the virtual image W is visually recognized from a predetermined position in the eye box  4 , a pixel that can be visually recognized clearly and a pixel that cannot be visually recognized are mixed among pixels arranged in the main scanning direction H. This reduces visibility of the virtual image W. According to the HUD device  1  of the invention, variation of the distributed light intensity distribution  820  in the sub-scanning direction V in the eye box  4 , the variation occurring due to sub-scanning, can be reduced by using a scanning method described below. 
         [0060]    With this, a scanning method using the MEMS scanner  20  of the invention will be described with reference to  FIG. 13  to  FIG. 15 .  FIG. 13  shows time transition of the sub-scanning position Y.  FIG. 14  is a plan view of the transmissive screen  40 , which shows a state in which the synthesized laser light  500  is scanned on the transmissive screen  40 .  FIG. 15  shows the distributed light intensity distribution  820  in the sub-scanning direction V in the eye box  4  by applying the invention. 
         [0061]    In this embodiment, as shown in  FIG. 13 , a frame F for drawing the display image M includes three sub-frames SF, i.e., a first sub-frame SF 1 , a second sub-frame SF 2 , and a third sub-frame SF 3 . Further, each sub-frame SF includes an actual scanning period (first actual scanning period SF 1   a,  first actual scanning period SF 2   a,  or third actual scanning period SF 3   a ) in which a display area  40   a  is scanned to generate the display image M and a blanking period (first blanking scanning period SF 1   b , second blanking scanning period SF 2   b,  or third blanking scanning period SF 3   b ) in which the display image M is not generated. 
         [0062]    Note that the frame F is set to be smaller than 1/60 second (temporal resolution of human eye) of a critical fusion frequency (60 Hz) or more with which a human can visually recognize flickering. That is, the first sub-frame SF 1 , the second sub-frame SF 2 , and the third sub-frame SF 3  forming the frame F is set to be smaller than 1/180 second (180 Hz or more). 
         [0063]    First, in the first sub-frame SF 1 , the display control unit  340  starts main scanning and sub-scanning of the MEMS scanner  20  from a first scanning start position Y 1   a  and controls lighting of the light sources  11   r,    11   g,  and  11   b  on the basis of drawing data of the first sub-frame SF 1  stored on the buffer memory  341  at a timing at which a scanning position approaches the display area  40   a , thereby drawing the display image M. Then, in a case where the scanning position of the MEMS scanner  20  is moved to a non-display area  40   b , the display control unit  340  moves the scanning position of the MEMS scanner  20  from a first scanning end position Y 1   b  to a second scanning start position Y 2   a  in the first blanking scanning period SF 1   b  (example of first scanning). 
         [0064]    Then, in the second sub-frame SF 2 , the display control unit  340  starts main scanning and sub-scanning of the MEMS scanner  20  from the second scanning start position Y 2   a  and controls lighting of the light sources  11   r,    11   g,  and  11   b  on the basis of drawing data of the second sub-frame SF 2  stored on the buffer memory  341  at a timing at which the scanning position approaches the display area  40   a , thereby drawing the display image M. Then, in a case where the scanning position of the MEMS scanner  20  is moved to the non-display area  40   b , the display control unit  340  moves the scanning position of the MEMS scanner  20  from a second scanning end position Y 2   b  to a third scanning start position Y 3   a  in the second blanking scanning period SF 2   b  (example of second scanning). 
         [0065]    Then, in the third sub-frame SF 3 , the display control unit  340  starts main scanning and sub-scanning of the MEMS scanner  20  from the third scanning start position Y 3   a  and controls lighting of the light sources  11   r,    11   g,  and  11   b  on the basis of drawing data of the third sub-frame SF 3  stored on the buffer memory  341  at a timing at which the scanning position approaches the display area  40   a , thereby drawing the display image M. Then, in a case where the scanning position of the MEMS scanner  20  is moved to the non-display area  40   b , the display control unit  340  moves the scanning position of the MEMS scanner  20  from a third scanning end position Y 3   b  to the first scanning start position Y 1   a  in the third blanking scanning period SF 3   b  (example of third scanning). 
         [0066]    Note that the second scanning start position Y 2   a  is a position shifted from the first scanning start position Y 1   a  in the sub-scanning direction V direction by a predetermined value, and the third scanning start position Y 3   a  is a position shifted from the second scanning start position Y 2   a  in the sub-scanning direction V direction by a predetermined value. A shift width P from the first scanning start position Y 1   a  to the third scanning start position Y 3   a  in the sub-scanning direction V direction is desirably set to be smaller than the pitch dVA of the MLA  41  in the sub-scanning direction V. 
         [0067]    Further, the drawing data of the first sub-frame SF 1 , the drawing data of the second sub-frame SF 2 , and the drawing data of the third sub-frame SF 3  are the same drawing data, and the same display image M is generated on the transmissive screen  40  in the first sub-frame SF 1 , the second sub-frame SF 2 , and the third sub-frame SF 3 . 
         [0068]    With this scanning method, beams of the synthesized laser light  500  whose positions are different in the sub-scanning direction V because of the plurality of sub-frames (first sub-frame SF 1 , second sub-frame SF 2 , and third sub-frame SF 3 ) can be incident on the ML  41   a  in a single frame. Therefore, the distributed light intensity distribution  820  in the sub-scanning direction V in the eye box  4  can be a distributed light intensity distribution  820   a  that is substantially uniform in the sub-scanning direction V direction as shown in  FIG. 15 , the distributed light intensity distribution  820   a  being obtained by hourly averaging the distributed light intensity distribution  820  having peaks at different positions as shown in  FIGS. 12( a ), ( b ), and ( c ) . In this scanning method, when the beam diameter DH in the main scanning direction H is set to be smaller than the pitch dH 1  of the MLA  41 , the synthesized laser light  500  is hardly incident on the plurality of MLs  41   a.  This makes it possible to reduce speckles and interference fringes and reduce unevenness of luminance in each pixel of the virtual image W visually recognized by a viewer. 
         [0069]    Note that the invention is not limited to the above embodiment and drawings. It is possible to make modification (including deletion of constituent elements) as appropriate within the scope of the invention. 
         [0070]    In the above embodiment, the distributed light intensity distribution  820  in the sub-scanning direction V in the eye box  4  is made substantially uniform by using three sub-frames SF in a single frame. However, the number of sub-frames for use in uniformity is arbitrary. The distributed light intensity distribution  820  may be made uniform in the sub-scanning direction V in two sub-frames SF or four or more sub-frames SF. 
         [0071]    Further, in the above embodiment, the frame F is divided into sub-frames SF, and a scanning position is shifted in the sub-scanning direction V between the sub-frames SF. However, an operation position may be shifted in the sub-scanning direction V between continuous frames F. 
         [0072]    Further, in the above embodiment, pieces of drawing data in a plurality of kinds of scanning (first scanning, second scanning, and third scanning) in which a scanning position is shifted in the sub-scanning direction V are the same drawing data. However, the drawing data is not limited thereto, and different kinds of drawing data may be used. 
         [0073]    Further, in the above embodiment, main scanning is performed while sub-scanning is being performed. However, a sub-scanning drive signal may be adjusted so that a scanning line on the transmissive screen  40  is substantially parallel to the main scanning direction H. For example, a sub-scanning drive signal may be a signal that is gradually changed with respect to time. 
         [0074]    Further, a single scanning line in the main scanning direction H does not necessarily need to scan a single lens row of the MLA  41  and may scan two lens rows adjacent to each other in the main scanning direction H. Furthermore, lens rows adjacent to each other in the main scanning direction H between the sub-frames SF may be scanned. 
         [0075]    Further, in the above embodiment, a member for diffusing a display image M is a transmissive screen (transmissive screen  40 ). However, a reflective screen may be applied. 
         [0076]    Further, in the above embodiment, the transmissive screen  40  made up of a combination of a single MLA  41  and a single aperture array  42  has been described. However, the transmissive screen  40  may be made up of a dual micro lens array including two micro lens arrays. With this configuration, the distributed light intensity distribution  810  in the main scanning direction H and the distributed light intensity distribution  820  in the sub-scanning direction V in the eye box  4  can be made more uniform. Note that, as a configuration of the dual micro lens array, a dual micro lens array in which both convex surfaces of two micro lens arrays are directed outside, a dual micro lens array in which convex surfaces of two micro lens arrays face each other, and the like can be considered, and it is possible to apply various publicly-known dual micro lens arrays. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0077]      FIG. 1  is a conceptual diagram showing a mode in which a HUD device according to an embodiment of the invention is mounted on a vehicle. 
           [0078]      FIG. 2  is a schematic configuration diagram of the HUD device according to the above embodiment. 
           [0079]      FIG. 3  is a schematic configuration diagram showing a synthesized laser light generation device in the above embodiment. 
           [0080]      FIG. 4  shows a scanning mode on a transmissive screen in the above embodiment. 
           [0081]      FIG. 5( a )  is an enlarged plan view of an MLA.  FIG. 5( b )  is an enlarged plan view of an aperture array. 
           [0082]      FIG. 6  is a schematic cross-sectional view of the transmissive screen in  FIG. 4  in a side view. 
           [0083]      FIG. 7  is a block diagram for explaining a control system of the HUD device according to the above embodiment. 
           [0084]      FIG. 8  is a conceptual diagram showing a relationship between a beam diameter on the transmissive screen and a pitch of the MLA in the above embodiment. 
           [0085]      FIG. 9  shows a distributed light intensity distribution in a main scanning direction in an eye box by using the HUD device of the above embodiment. 
           [0086]      FIG. 10  shows scanning in the main scanning direction in the above embodiment and distributed light intensity distributions in the main scanning direction in the eye box, the distributed light intensity distributions being generated by this scanning in the main scanning direction. 
           [0087]      FIG. 11  shows an hourly averaged distributed light intensity distribution in the main scanning direction in the eye box in the above embodiment. 
           [0088]      FIG. 12  shows scanning in a sub-scanning direction in the above embodiment and distributed light intensity distributions in the sub-scanning direction in the eye box, the distributed light intensity distributions being generated by this scanning in the sub-scanning direction. 
           [0089]      FIG. 13  shows time transition of a sub-scanning position in the HUD device of the above embodiment. 
           [0090]      FIG. 14  is a diagram for explaining a mode of a scanning line scanned in each sub-frame in the above embodiment. 
           [0091]      FIG. 15  shows an hourly averaged distributed light intensity distribution in the sub-scanning direction in the eye box in the above embodiment. 
       
    
    
     INDUSTRIAL APPLICABILITY 
       [0092]    The invention relates to a head-up display device for superimposing a virtual image on a real view to cause the virtual image to be visually recognized. The head-up display device is placed in, for example, a dashboard of a vehicle and is suitable as a display device for emitting image light toward a windshield of a vehicle. 
       REFERENCE SIGNS LIST 
       [0000]    
       
         
           
               1  HUD device (head-up display device) 
               2  vehicle 
               3  windshield 
               4  eye box 
               10  synthesized laser light generation device 
               11  LD ( 11   r,    11   g,    11   b ) 
               12  condensing optical system ( 12   r ,  12   g ,  12   b ) 
               13  optical axis adjustment unit ( 13   r ,  13   g ) 
               20  MEMS scanner 
               30  field lens 
               40  transmissive screen (lens array screen) 
               41  MLA (micro lens array) 
               41   a  micro lens 
               42  aperture array 
               42   a  opening portion 
               42   b  light shielding portion 
               50  relay optical unit 
               51  plane mirror 
               52  magnifying mirror 
               100  LD control unit (control unit) 
               200  MEMS control unit (control unit) 
               300  controller unit (control unit) 
               310  input processing unit 
               320  memory control unit 
               330  frame buffer 
               340  display control unit 
               500  synthesized laser light 
               600  image light 
               710  light intensity distribution in main scanning direction 
               720  light intensity distribution in sub-scanning direction 
               810  distributed light intensity distribution in main scanning direction 
               820  distributed light intensity distribution in sub-scanning direction 
             R red laser light 
             G green laser light 
             B blue laser light 
             M display image 
             W virtual image