Patent Publication Number: US-2012033307-A1

Title: Display device

Description:
CROSS REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority from the prior Japanese Patent Application No. 2010-177897, filed on Aug. 6, 2010, the entire contents of which are incorporated herein by reference. 
     FIELD 
     Embodiments basically relate to a display device. 
     BACKGROUND 
     As a display device for automobile use, there has been a single-eyed head up display (HUD) capable of visually identifying operation information such as vehicle speeds and traveling directions. 
     In such an HUD, a position of an eye of an occupant is derived from a picked-up image of a head of the occupant. An angle and a position of a plate mirror are automatically controlled on the basis of the derived result. A projected image is presented to one eye of the occupant as tracing movement of the head of the occupant. 
     However, with this HUD, it is difficult to robustly present projected image to one eye of an occupant. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Aspects of this disclosure will become apparent upon reading the following detailed description and upon reference to accompanying drawings. The description and the associated drawings are provided to illustrate embodiments of the invention and not limited to the scope of the invention. 
         FIG. 1  is a view showing a configuration of a display device according to a first embodiment. 
         FIGS. 2A and 2B  are views showing a configuration of a part of the display device. 
         FIG. 3  is a flow chart exemplifying a control method of a control unit. 
     
    
    
     DESCRIPTION 
     As will be described below, according to an embodiment, a display device includes a light flux generation unit, a reflection plate, a head detection unit, a control unit and a drive unit. The light flux generation unit generates light flux containing image information. The reflection plate reflects the light flux generated by the light flux generation unit toward one eye of an occupant. The drive unit drives the reflection plate on the basis of an output from the control unit. In addition, the head detection unit utilizes a first distance sensor pair having a distance sensor A and a distance sensor B and a second distance sensor pair having a distance sensor C and a distance sensor D to detect a position of a head of the occupant. The control unit calculates a coefficient G from output voltage difference of the first distance sensor pair and output voltage difference of the second distance sensor pair when an output voltage of the distance sensor A and an output voltage of the distance sensor D become equal to each other, or controls a direction or a position of the reflection plate on the basis of the coefficient G and either the output voltage difference of the first distance sensor pair or the output voltage difference of the second distance sensor pair. 
     In the following, embodiments will be described in detail with reference to the drawings. 
     In this specification and the drawings, the same reference numeral will be given to an element being similar to the element previously described with reference to any referred drawing and detailed explanations will not be repeated. 
     First Embodiment 
       FIG. 1  is a schematic view exemplifying a configuration of a display device according to a first embodiment. For example, with the display device, an occupant  100  driving a vehicle can visually identify operation information such as a vehicle speed and navigation information. 
     A display device  10  is provided with a light flux generation unit  115 , a reflection plate  163 , a head detection unit  612 , a control unit  620  and a drive unit  164 . 
     The light flux generation unit  115  generates light flux  112  containing image information of operation information. The reflection plate  163  reflects the light flux  112  generated by the light flux generation unit  115  toward a clear plate  310  such as a front glass and a windshield. The clear plate  310  reflects the light flux  112  toward one eye  105  of the occupant  100 . 
     The light flux generation unit  115  is provided with a light source  374 , a restriction portion  375 , a diffusion portion  376 , an image unit  377 , a first lens  371 , an opening portion  373 , and a second lens  372 . Assuming that the focal length of the first lens  371  is denoted by f 1  and the focal length of the second lens  372  is denoted by f 2 , the opening portion  373  is disposed at a position of a distance of f 1  from the first lens  371  and a distance of f 2  from the second lens  372 . 
     The light flux  112  emitted from the light source  374  enters the image unit  377  which has the diffusion portion  376  in a state that the traveling direction thereof is restricted to be directed to the reflection plate  163  by the restriction portion  375 . The light flux  112  is capable of evenly entering the image unit  377  as a result of the diffusion portion  376 . 
     The light flux  112  passes through the image unit  377  to contain image information and further passes through the first lens  371 , the opening portion  373  and the second lens  372 . The light flux  112  is incident on the reflection plate  163  in a state that a divergence angle thereof (i.e., a diffuse angle of the light flux  112 ) is controlled. 
     The image unit  377  is placed on the light source  374  side from the opening portion  373 , thereby allowing it to enhance a passing rate of the light flux  112  passing through the image unit  377  compared to a case that the opening portion  373  is placed on the light source  374  side from the image unit  377 . 
     A light-emitting diode, a high-pressure mercury lamp, a halogen lamp, a laser and the like may be employed as the light source  374 . A tapered light guide is employed as the restriction portion  375 . A diffusion filter or a diffusion plate is employed as the diffusion portion  376 . A liquid crystal display, a digital mirror device or the like is employed as the image unit  377 . 
     The display device  10  projects the light flux  112  in a projection range  113  which includes the one eye  105  of the occupant  100 . The control unit  620  controls a direction or a position of the reflection plate  163  so that the light flux  112  is projected within the projection range  113  and adjusts a projection position of the light flux  112 . The occupant  100  can visually identify the light flux  112  with the one eye  105 . The display device  10  can be used as an HUD. 
     The head detection unit  612  utilizes two pairs of distance sensors to detect relative distance between the head  101  of the occupant  100  and each distance sensor for the head  101  of the occupant  100 . 
     As will be described later, the control unit  620  controls the reflection plate  163  on the basis of output signals from the pairs of distance sensors disposed at the head detection unit  612  to adjust the projection position of the light flux  112 . 
     The head detection unit  612  will be explained in detail with reference to  FIGS. 2A and 2B . 
     As shown in  FIGS. 2A and 2B , the head detection unit  612  in the display device  10  is provided with a first distance sensor pair  615  having a distance sensor A  613   a  and a distance sensor B  613   b  and a second distance sensor pair  616  having a distance sensor C  613   c  and a distance sensor D  613   d.    
     Each distance sensor is provided with a light emitting element and a light receiving element. The light emitting element emits light and the light receiving element receives returned light to be reflected by the head  105  of the occupant  100 . 
     The distance sensors include a sensor capable of measuring a distance to an object without contacting thereto such as a laser displacement gauge and an ultrasonic distance sensor in addition to a PSD sensor. 
     Here, a first midpoint  514  denotes the midpoint of a line segment connecting the distance sensor C  613   c  and the distance sensor B  613   b . A second midpoint  515  denotes the midpoint of a line segment connecting the distance sensor C  613   c  and the distance sensor D  613   d . A third midpoint  516  denotes the midpoint of a line segment connecting the distance sensor A  613   a  and the distance sensor B  613   b . The third midpoint  516  is located at the opposite side to the second midpoint  515  as sandwiching the first midpoint  514 . 
     The line segment connecting the distance sensor C  613   c  and the distance sensor B  613   b  is defined as a line segment connecting a light receiving element of the distance sensor C  613   c  and a light receiving element of the distance sensor B  613   b.    
     The line segment connecting the distance sensor C  613   c  and the distance sensor D  613   d  is defined as a line segment connecting a light receiving element of the distance sensor C  613   c  and a light receiving element of the distance sensor D  613   d.    
     A perpendicular bisector of the line segment connecting the distance sensor C  613   c  and the distance sensor B  613   b  is denoted by a first line  514   a . A perpendicular bisector of the line segment connecting the distance sensor C  613   c  and the distance sensor D  613   d  is denoted by a second line  515   a . A perpendicular bisector of the line segment connecting the distance sensor A  613   a  and the distance sensor B  613   b  is denoted by a third line  516   a.    
     The distance sensor C  613   c  and the distance sensor D  613   d  are arranged so that the light emitted from the distance sensor C  613   c  and the light emitted from the distance sensor D  613   d  intersect with each other on the second line  515   a.    
     The distance sensor C  613   c  and the distance sensor D  613   d  are preferably arranged so that light is emitted toward a barycentric position when a geometric barycenter of the head  105  of the occupant  100  is positioned on the second line  515   a.    
     The distance sensor A  613   a  and the distance sensor B  613   b  are arranged so that the light emitted from the distance sensor A  613   a  and the light emitted from the distance sensor B  613   b  intersect with each other on the third line  516   a.    
     The distance sensor A  613   a  and the distance sensor B  613   b  are preferably arranged so that light is emitted toward a barycentric position when a geometric barycenter of the head  105  of the occupant  100  is positioned on the third line  516   a.    
     When the display device is assumed to be for, e.g., automobile use, the distance sensor pairs  615 ,  616  are located at a ceiling. 
     The first distance sensor pair  615  is arranged so that the distance between the first midpoint  514  and the third midpoint  516  is to be apart by Δx. The second distance sensor pair  616  is arranged so that the distance between the first midpoint  514  and the second midpoint  515  is to be apart by Δx. 
     It is preferable that the first distance sensor pair  615  and the second distance sensor pair  616  are placed on the same straight line. 
     The head detection unit  612  outputs an output voltage value V a  of the distance sensor A  613   a , an output voltage value V b  of the distance sensor B  613   b , an output voltage value V c  of the distance sensor C  613   c , and an output voltage value V d  of the distance sensor D  613   d  to the control unit  620 . The output voltage values V a  to V d  correspond to values of relative distance to the head  101  of the occupant  100  from the distance sensors A  613   a  to D  613   d , respectively. The output voltage values V a  to V d  correspond to d a  to d d  in  FIG. 2A , respectively. The relative distance from the light receiving element of each distance sensor to the scalp of the head  101  of the occupant  100  is denoted by d a  to d d , respectively. 
     The control unit  620  utilizes Equation 1 from the output voltage value V a  of the distance sensor A  613   a  and the output voltage value V d  of the distance sensor D 613   d  to calculate posAD. Here, posAD denotes a value corresponding to a difference between relative distance from the distance sensor A 613   a  to the head  101  of the occupant  100  and relative distance from the distance sensor D 613   d  to the head  101  of the occupant  100 . 
     
       
         
           
             
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     1 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   posAD 
                   = 
                   
                     
                       
                         V 
                         a 
                       
                       - 
                       
                         V 
                         d 
                       
                     
                     
                       
                         V 
                         a 
                       
                       + 
                       
                         V 
                         d 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     1 
                   
                   ) 
                 
               
             
           
         
       
     
     The control unit  620  utilizes Equation 2 from the output voltage value V a  of the distance sensor A  613   a  and the output voltage value V b  of the distance sensor B  613   b  to calculate posAB. Here, posAB denotes a value corresponding to difference between relative distance from the distance sensor A  613   a  to the head  101  of the occupant  100  and relative distance from the distance sensor B  613   b  to the head  101  of the occupant  100 . 
     
       
         
           
             
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     2 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   posAB 
                   = 
                   
                     
                       
                         V 
                         a 
                       
                       - 
                       
                         V 
                         b 
                       
                     
                     
                       
                         V 
                         a 
                       
                       + 
                       
                         V 
                         b 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     2 
                   
                   ) 
                 
               
             
           
         
       
     
     The control unit  620  utilizes Equation 3 from the output voltage value V c  of the distance sensor C  613   c  and the output voltage value V d  of the distance sensor D  613   d  to calculate posCD. Here, posCD denotes a value corresponding to difference between relative distance from the distance sensor C  613   c  to the head  101  of the occupant  100  and relative distance from the distance sensor D  613   d  to the head  101  of the occupant  100 . 
     
       
         
           
             
               
                 
                   [ 
                   
                     Equation 
                      
                     
                         
                     
                      
                     3 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   posCD 
                   = 
                   
                     
                       
                         V 
                         c 
                       
                       - 
                       
                         V 
                         d 
                       
                     
                     
                       
                         V 
                         c 
                       
                       + 
                       
                         V 
                         d 
                       
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
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                      
                     3 
                   
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       FIGS. 2A and 2B  are views showing states of utilizing the distance sensor A  613   a  and the distance sensor D  613   d  to calculate posAD, utilizing the distance sensor A  613   a  and the distance sensor B  613   b  to calculate posAB, and utilizing the distance sensor C  613   c  and the distance sensor D  613   d  to calculate posCD. 
       FIG. 2A  shows a position of the head  101  of the occupant  100  at a certain time.  FIG. 2B  shows a position of the head  101  of the occupant  100  at a time being different from that of  FIG. 2A . In  FIG. 2A , the head  101  of the occupant  100  is positioned to satisfy posAD=0. 
     The control unit  620  utilizes Equation 2 to calculate the value of posAB at the time when the value of posAD becomes a value being equal to zero (i.e., posAB 0 ). The control unit  620  utilizes Equation 3 to calculate the value of posCD at the time when the value of posAD becomes the value being equal to zero (i.e., posCD 0 ) by utilizing Equation 3. The control unit  620  utilizes Equation 4 to determine a coefficient G. 
     
       
         
           
             
               
                 
                   [ 
                   
                     Equation 
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                      
                     4 
                   
                   ] 
                 
               
               
                 
                     
                 
               
             
             
               
                 
                   G 
                   = 
                   
                     
                       ( 
                       
                         
                           
                             Δ 
                              
                             
                                 
                             
                              
                             x 
                           
                           
                             posAB 
                              
                             
                                 
                             
                              
                             0 
                           
                         
                         - 
                         
                           
                             Δ 
                              
                             
                                 
                             
                              
                             x 
                           
                           
                             posCD 
                              
                             
                                 
                             
                              
                             0 
                           
                         
                       
                       ) 
                     
                     2 
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                      
                     
                         
                     
                      
                     4 
                   
                   ) 
                 
               
             
           
         
       
     
     The control unit  620  utilizes the coefficient G to acquire a relative position Est 1  or Est 2  of the head  101  of the occupant  100  as will be described later. 
     The value being equal to zero is defined to include an error range due to noise involved in the output signals from the distance sensors, the shape of the head  101  of the occupant  100  and the like. That is, the value being equal to zero is defined not to be exact zero but to be a value within a certain error range. 
     The control unit  620  utilizes Equation 5 to calculate Est 1  when the head  101  of the occupant  100  is positioned on the left side of the first midpoint  514  (i.e., the side toward the third midpoint  516  from the first midpoint  514 ) as in  FIG. 2B . In this case, posAD is equal to or larger than zero. Est 1  denotes an estimated value of relative distance between the geometric barycenter of the head  101  of the occupant  100  and the first line  514   a.    
       [Equation 5] 
       Est 1   =G ×(pos AB −pos AB 0)  (Equation 5)
 
     The control unit  620  provides a command to the drive unit  164  so that the projection range  113  of the light flux  112  is moved by the distance of Est 1  from a reference position in the direction along a line segment connecting the first midpoint  514  and the third midpoint  516 . Receiving the command, the drive unit  164  drives the reflection plate  163 . 
     The control unit  620  utilizes Equation 6 to calculate Est 2  and controls the reflection plate  163  when the head  101  of the occupant  100  is positioned at the right side of the first midpoint  514  (i.e., the side toward the second midpoint  515  from the first midpoint  514 ) in  FIG. 2A . In this case, posAD is negative. Est 2  denotes an estimated value of relative distance between the geometric barycenter of the head  101  of the occupant  100  and the first line  514   a.    
       [Equation 6] 
       Est 2   =G ×(pos CD −pos CD 0)  (Equation 6)
 
     The control unit  620  provides a command to the drive unit  164  so that the projection range  113  of the light flux  112  is moved by the distance of Est 2  from the reference position in the direction along a line segment connecting the first midpoint  514  and the second midpoint  515 . Receiving the command, the drive unit  164  drives the reflection plate  163 . 
     The occupant  100  performs initialization of the display device  10  in a state that the head  101  is at the position satisfying posAD=0 (i.e., the state of  FIG. 2A ). At that time, the occupant  100  adjusts the position of the reflection plate  163  so that the projection range  113  of the light flux  112  includes the one eye  105  of the occupant  100 . The position of the one eye  105  of the occupant  100  in this state is to be the reference position. 
     Here, the position of the reflection plate  163  includes a position due to translational motion and an angle position due to rotational motion. 
     The control unit  620  calculates Est 1  or Est 2  during usage of the display device  10 . The control unit  620  provides a command (i.e., outputs a signal) to the drive unit  164  so that the projection range  113  of the light flux  112  is moved by the distance of Est 1  or Est 2  from the reference position in the direction along the line segment connecting the first midpoint  514  and the second midpoint  515 . Receiving the command, the drive unit  164  drives the reflection plate  163 . 
     For example, if the calculation result of Est 1  becomes +5 when posAD is equal to or larger than zero, the control unit  620  provides a command to the drive unit  164  so that the projection range  113  of the light flux  112  is moved by 5 cm from the reference position in the direction toward the third midpoint  516  from the first midpoint  514  to adjust the position of the reflection plate  163 . Receiving the command, the drive unit  164  drives the reflection plate  163 . 
       FIG. 3  is a flowchart showing an example of a method to control the control unit  620 . The control method shown in  FIG. 3  starts from a state that an initial coefficient G is previously provided to the control unit  620  during a manufacturing stage of the display device  10 . Alternately, the method may start from a state that the head  101  is firstly moved to a position satisfying posAD=0 and the initial coefficient G is calculated by the control unit  620  when the occupant  100  starts to use the display device  10 . 
     As shown in  FIG. 3 , the control unit  620  utilizes the output voltage value of the distance sensor A  613   a  and the output voltage value of the distance sensor D  613   d  to calculate posAD with Equation 1 (S 301 ). The control unit  620  utilizes the output voltage value of the distance sensor A  613   a  and the output voltage value of the distance sensor B  613   b  to calculate posAB with Equation 2 (S 302 ). The control unit  620  utilizes the output voltage value of the distance sensor C  613   c  and the output voltage value of the distance sensor D  613   d  to calculate posCD with Equation 3 (S 303 ). Steps S 301  to S 303  are repeatedly performed for each sampling time. Steps S 301  to S 303  are performed in random order. 
     The control unit  620  determines whether or not the value of posAD is the value being equal to zero (S 304 ). In addition to the above determination, it is also possible that the control unit  620  determines whether or not posCD is smaller than zero and the posAB is larger than zero. When the determination in step S 304  is “YES”, the control unit  620  calculates the coefficient G with Equation 4 from the value of posCD (i.e., posCD 0 ) and the value of posAB (i.e., posAB 0 ) at that time (S 305 ). 
     The control unit  620  determines whether or not posAD is equal to or larger than zero (S 306 ). When the determination result in Step S 306  is “YES”, the control unit  620  calculates Est 1  with Equation 5 (S 307 ). When the determination result in Step S 306  is “NO”, the control unit  620  calculates Est 2  with Equation 6 (S 308 ). 
     The control unit  620  controls the reflection direction of the light flux  112  on the basis of the result of Step S 307  or Step S 308  (S 309 ). 
     With this method, conversion process from output voltage values into the distance of the head  101  of the occupant  100  can be eliminated, thereby enabling it to reduce processing cost. Further, the measurement can be performed without correction due to temperatures, individual differences and the like, thereby enabling it to enhance robustness. 
     In this manner, the display device  10  according to the present embodiment enables it to provide a display device capable of tracing the position of one eye of an occupant without requiring high image processing capability. In addition, it is possible to provide a display device capable of presenting a projected image to one eye of an occupant robustly without being affected by external light and the like. 
     The present embodiment is described as an example and is not intended to limit the scope of the invention. The present embodiment can be actualized variously, so that various skipping, replacing and modifying can be performed without departing from the substance of the invention. The present embodiment and modifications thereof are included in the scope of the invention described in the claims and equivalence thereof while being included in the scope or substance of the invention. 
     While a certain embodiment of the invention has been described, the embodiment has been presented by way of examples only, and is not intended to limit the scope of the inventions. Indeed, the novel elements and apparatuses described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods described herein may be made without departing from the spirit of the invention. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the invention.