Abstract:
A head-up display system having a diffusing image plane or diffuser. The light output of a relatively small image source is imaged on the diffuser by way of imaging optics. A mirror is used to image light from the diffuser onto a windshield and correct for distortion caused by the windshield. The diffuser is advantageously used when a large field-of-view is desired, or sun load characteristics need to be addressed. The diffuser may be flat or curved in order to optimize the system for different applications. The magnification of the mirror may be made relatively low, and the solar emergency density that is made incident on the image source is reduced, providing for a low cost, high performance, color head-up display system. A drive mechanism allows selective operator controlled repositioning of the image source and imaging optics with respect to diffuser to vary image size, position and/or intensity.

Description:
TECHNICAL FIELD 
       [0001]    The present invention generally relates to head-up display (HUD) systems, and more particularly relates to an automotive windshield projection HUD system capable of dynamically changing the projected image. 
       BACKGROUND OF THE INVENTION 
       [0002]    As the design intent image field of a head-up display projected within a vehicle operator&#39;s field-of-view (FOV) increases, the size of the image source tends to increase in order to keep a lower optical system magnification. Unfortunately, the image source size is desired to be as small as possible to reduce cost of the image source and associated packaging. 
         [0003]    As image sources become smaller, the optical system needs to increase magnification and is challenged in producing a minimally distorted image. The magnification increase can produce an unacceptable sun load condition presented to the image source as well. 
         [0004]    Sun load is a calculated energy irradiance value expressed in watts/cm 2 . The heating of the image source is due to the focusing of the sun&#39;s energy upon its surface. Should the magnification of the optical system be high enough to produce an excessive sun load condition, the image source will be damaged. 
         [0005]    Optical system performance also suffers in conventional systems when using small image sources. For a typical 10 degree horizontal field-of-view (HFOV) head-up display with an eye box of 73.5 mm in width, the relationship among vertical disparity error (the worst error within field-of-view and eye box), typical system f-number versus the horizontal dimension of the image source are shown in  FIG. 1 . As can be seen in  FIG. 1 , as the image width drops below 50 mm, the vertical disparity error increases quite rapidly. 
         [0006]    A driver has the ability to tolerate vertical disparity from 1 to 9 mrad, otherwise double vision can occur. The vertical disparity error will stay about 1 mrad when the image source is kept greater than 50 mm. The corresponding f-number of the optical system should stay above 0.8 to maintain a reasonable package size. 
         [0007]    Therefore, with the use of conventional optics, the size of the image source should be greater than 50 mm in width. A cost penalty is now realized due to the inability to use smaller than 50 mm wide image sources (for this example). 
         [0008]    U.S. Pat. No. 6,043,937 to Mark W. Hudson et al. entitled “Head-Up Display System Using A Diffusing Image Plane” provides a solution allowing the use of low cost effective image sources, which also meets heads-up display optical performance requirements, wherein a diffusing image plane or diffuser is employed. The specification of U.S. Pat. No. 6,043,937 is hereby incorporated herein by reference. 
       SUMMARY OF THE INVENTION 
       [0009]    The present invention provides a high resolution, high brightness color head-up display (HUD) for the automotive market. The present invention employs a collimated light source such as a Pico Projector to adjust the size and shape of the image field within the vehicle operator&#39;s field of view (FOV), as well as the brightness of images within the image field, thereby allowing the vehicle operator to select how much information is to be provided, where the information is to be located within the image field, and how bright the display should be. With light engines, collimated light is used to project the image into a diffusion screen creating a real image surface. The present invention overcomes a shortcoming of known HUD systems wherein the image size is fixed. With the present invention, the light engine can be moved to increase or decrease the size of the display. This has the advantage of providing a smaller, brighter image for day-time use, as well as a larger, muted image for night-time use. The present invention can accommodate night vision systems within the same package. The tolerance required to create a perfect focus image is resolved by moving the light engine in the same plane as the display diffuser base on the collimated light source. 
         [0010]    The present invention provides a HUD system in which the image size is dynamically changed to allow the driver to determine how much information or situational awareness indicators are presented and permits the creation of a larger image field within the operator&#39;s FOV in the same package. The present invention can also be employed for other display applications such as instrument clusters and infotainment displays. 
         [0011]    The present invention further provides for an improved head-up display system having a diffusing image plane or diffuser. The present diffusing image plane head-up display system comprises a windshield, an image or display source, and a mirror disposed between the windshield and image source. The diffuser comprises a diffusing image plane that is disposed between the mirror and the image source. The diffuser may be flat or curved in order to optimize the system for different applications. Imaging optics are also disposed between the diffuser and the image source that image the output of the image source into the diffuser. In addition, application optics may be disposed between the diffuser and the mirror, as required, for a particular vehicle application, to address specific imaging requirements. 
         [0012]    These and other features and advantages of this invention will become apparent upon reading the following specification, which, along with the drawings, describes preferred and alternative embodiments of the invention in detail. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The present invention will now be described, by way of example, with reference to the accompanying drawings, in which: 
           [0014]      FIG. 1 , is a graph illustrating f-number and disparity versus source width; 
           [0015]      FIG. 2 , is a schematic view of a first embodiment of an exemplary diffusing image plane head-up display system in accordance with the principles of the present invention; 
           [0016]      FIG. 3 , is a schematic view of an alternative embodiment of an exemplary diffusing image plane head-up display system in accordance with the principles of the present invention; 
           [0017]      FIG. 4 , is a broken, cross-sectional view of a vehicle equipped with a head-up windshield display in accordance with a third embodiment of the invention; 
           [0018]      FIG. 5 , is a cut-away view of the vehicle interior equipped with the head-up windshield display system of  FIG. 4 ; and 
           [0019]      FIG. 6 , is a block diagram of the system of  FIG. 4 , in accordance with one embodiment of the invention. 
       
    
    
       [0020]    Although the drawings represent embodiments of the present invention, the drawings are not necessarily to scale and certain features may be exaggerated in order to illustrate and explain the present invention. The exemplification set forth herein illustrates an embodiment of the invention, in one form, and such exemplifications are not to be construed as limiting the scope of the invention in any manner. 
       DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0021]    A conventional vehicular or automotive head-up display system includes a windshield, a mirror and an image or display source. Application optics, such as the mirror, for example, optically interfaces directly between the windshield and the image source. The optical design, sun load characteristics and performance of the conventional head-up display system are a result of the size of the image source versus the required image field of the head-up display system and performance requirements. Also, such conventional head-up display systems suffer from sun loading problems. 
         [0022]    Referring to  FIG. 2 , a schematic view of a first embodiment of a head-up display system  10  is illustrated. Head-up display system  10  has a head-up display module  12  configured for installation in a passenger vehicle and positioned to reflect an image off a surface  14  of a vehicle windshield  16  into the line-of-sight  18  of a vehicle operator or passenger  20 . 
         [0023]    When a large image field is desired, or the performance and sun load characteristics are unacceptable, a diffuser  22  or diffusing image plane may be employed in accordance with the present invention. 
         [0024]    The diffusing image plane head-up display system  10  comprises a windshield  16  which is viewed by the driver  20  and a curved or focusing mirror  24  disposed to focus an image on the windshield  16 . The diffuser  22  is disposed between the mirror  24  and an image or display source  26  substantially at a focus of the mirror  24 . Imaging optics  28  are disposed between the diffuser  22  and the image source  26  that image the output of the image source  26  onto the diffuser  22 . In addition, application optics may be disposed between the diffuser  22  and the mirror  24 , as required, for a particular vehicle application, to address specific imaging requirements and to provide a specific image field within the field-of-view (FOV) for the system  10 . 
         [0025]    The image source  26  projects an image on the diffusing plane  22 , thus creating two optical subsystems  30 ,  32  within the head-up display system  10 . The first optical subsystem  30  employs the curved mirror  24  to correct for distortion caused by the windshield  16 . 
         [0026]    The image source  26  and imaging optics  28  are fixedly carried within a unitary housing  34  disposed within the display module  12 . The housing  34  maintains the image source  26  and the imaging optics  22  in a fixed, spaced relationship in alignment with an axis  36  focused on the line-of-sight  18  of the system  10 . The assembly of the housing  34 , the image source  26  and the imaging optics  28  is defined as a light engine  38  which outputs collimated light substantially parallel to the axis  36 . The light engine  38  is arranged for limited controlled bidirectional displacement along axis  36  as suggested by double-headed arrow  40 . 
         [0027]    A drive motor  42  has an axial drive shaft  44  rotatably engaging the housing  34  as illustrated by double-headed arrow  46  rendering it infinitely axially adjustable. This results in a high resolution, high brightness color head up display. The use of a collimated light source permits adjusting the image field size, shape and brightness, allowing the driver to decide how much information is required and how bright the display should be. The light engine  38  projects a collimated light based image onto the diffusion screen  22  creating a real image surface. When the light engine  38  is repositioned, the size of the display is increased or decreased. This provides a beneficial design enabling a relatively smaller, brighter image for day time use, and then create a relatively larger, dimmer image for night time use as the night vision of the same package. The tolerance required to create a perfect focus image is resolved by incrementally moving the light engine  38  in the same plane as the display diffuser base of the collimated light source. 
         [0028]    Referring to  FIG. 3 , a schematic view of a second embodiment of a head-up display system  48  is illustrated. Head-up display system  48  has a head-up display module  50  configured for installation in a passenger vehicle and positioned to reflect an image off a surface  52  of a vehicle windshield  54  into the line-of-sight  56  of a vehicle operator or passenger  58 . 
         [0029]    The diffusing image plane head-up display system  48  comprises a windshield  54  which is viewed by the driver  58  and a curved or focusing mirror  62  disposed to focus an image on the windshield  54 . The diffuser  60  is disposed between the mirror  62  and an image or display source  64  substantially at a focus of the mirror  62 . Imaging optics  66  are disposed between the diffuser  60  and the image source  64  that image the output of the image source  64  onto the diffuser  60 . In addition, application optics  68  may be disposed between the diffuser  60  and the mirror  62 , as required, for a particular vehicle application, to address specific imaging requirements and to provide a specific image field within the field-of-view (FOV) for the system  48 . 
         [0030]    The image source  64  projects an image on the diffusing plane  60 , thus creating two optical subsystems  70 ,  72  within the head-up display system  48 . The first optical subsystem  70  employs the curved mirror  62  to correct for distortion caused by the windshield  54 . 
         [0031]    The image source  64  and imaging optics  66  are fixedly carried within a unitary housing  74  disposed within the display module  50 . The housing  74  maintains the image source  64  and the imaging optics  66  in a fixed, spaced relationship in alignment with an axis  76  focused on the line-of-sight  56  of the system  48 . The assembly of the housing  74 , the image source  64  and the imaging optics  66  is defined as a light engine  78  which outputs collimated light substantially parallel to the axis  76 . The light engine  78  is arranged for limited controlled bidirectional displacement along axis  76  as suggested by double-headed arrow  80 . 
         [0032]    A drive motor  82  has an axial drive shaft  84  rotatably engaging the housing  74  as illustrated by double-headed arrow  86  rendering it infinitely axially adjustable. This results in a high resolution, high brightness color head up display system  48  which operates in all material respects to the display system  10  described herein with respect to  FIG. 2 . 
         [0033]      FIG. 4  illustrates a non-limiting example of a vehicle  88 , equipped with a vehicle windshield display system  90 , similar in all material respects to the embodiments of the invention described herein with reference to  FIGS. 2 and 3 . In general, the system  90  is configured to project an image  92  on the inner surface  94  of a windshield  96  within the field of view  98  of an operator  100  residing in the vehicle  88 . The windshield display system  90  may be based on any technology suitable for projecting a head up display image directly on a surface of the vehicle windshield, or on a substantially transparent device that can be attached to, installed with, or otherwise integrated into a vehicle windshield. Flexible transparent displays based on organic light emitting diode (OLED) and liquid crystal device (LCD) display technologies are available from a variety of manufacturers such as Samsung, Sony, and NEC would be suitable to apply to a windshield. Suitable display types include emissive (OLED), transmissive (LCD), transparent/opaque or fluorescence (electrowetting), or projection type display projecting light onto the windshield with or without the benefit of a film or other surface treatment. The examples described herein are generally directed to the forward view windshield of a vehicle, but it is recognized that the system  90  could also be used on a side view or rear view window of a vehicle. 
         [0034]    Referring to  FIG. 4 , a head up display module  102  is mounted within a vehicle dash board assembly  104  whereby an image is projected through an opening  106  in the dash board assembly  104  to reflect off a surface  94  of the windshield  96  within the vehicle operator&#39;s field of view  98 . The opening is sufficiently dimensioned to accommodate a maximized sized image produced by a large arc of projection  108 , a minimized sized image produced by a small arc of projection  110 , and intermediate scaled images. 
         [0035]      FIG. 5  illustrates a non-limiting example of a graphic  112  being displayed on the windshield display image field  114  within the field of view  116 , i.e.—along a line of site through the windshield display image field  114 . As used herein a graphic is any character, symbol, illustration, or other feature displayed by the windshield display image field  114  such as the navigation information  118  as illustrated on the windshield display image field  114  to the left of the operator  120 , the entertainment system information  122  and vehicle speed  124  as illustrated directly in front of the operator  120 , or the tail-gate warning symbol  126  indicating that another vehicle is tail-gating the vehicle  128  as illustrated to the right of the operator  120 . The head up display system includes operator input controls  130 , operator readouts  132  and indicators  134 . 
         [0036]      FIG. 5  illustrates a maximized projected image field  136 (max) containing navigation information  118 , entertainment system information  122 , vehicle speed information  124  and tail-gate warning information  126 . Upon vehicle or operator initiated actuation, the image field can be enlarged/reduced between a maximum image field size  136 (max) and a minimum image field size  136 (min). The resealing of the image field  136  can be proportional (vertically and horizontally) as illustrated in  FIG. 5 , or alternatively, disproportionately. Additionally, the image can be transitioned from a centered position within the operator&#39;s field of view to an offset location, within the field of view, such as the bottom center of the field of view  116 , as illustrated. 
         [0037]      FIG. 6  illustrates a non-limiting example of a schematic diagram of the controller system  138  of a head up display system  140 . The system  138  may include a camera  142  configured to determine an image of the graphic displayed by a windshield display  144 . It is contemplated that the system  138  may include multiple cameras located at various locations, and that image signals from these various cameras can be combined or separately analyzed to determine what is being displayed on the windshield display  144 , and what is present in the scene surrounding the vehicle  128 . 
         [0038]    The system may also include a controller  146  that includes an input  148  configured to receive the image signal  150  from the camera  142 , where the image signal  150  may include an indication of an image of the graphic displayed by the windshield display  144 . The controller  146  may also include processor  152 . The controller  146  or the processor  152  may include a microprocessor (not shown) or other control circuitry as should be evident to those skilled in the art. The controller  146  or the processor  152  may also include memory, including non-volatile memory, such as electrically erasable programmable read-only memory (EEPROM) for storing one or more routines, thresholds and captured data. The one or more routines may be executed by the controller  146  or the processor  152  to perform steps for determining if the image signal  150  received indicates that the field of view is obstructed. The controller  146  may also include an output  154  configured to operate the windshield display by way of a graphic signal  156 . Operating the windshield display generally includes indicating what graphics are to be displayed at any given time. 
         [0039]    The system  138  may include an operator position detector  158  located, for example, in the dash so that the location of the operator&#39;s head or eyes can be determined. The system  138  may include an object detector  160  configured to detect objects in the field of view  98 , for example the approaching car. The object detector  160  may be radar or vision based, and such devices are well known in the art. 
         [0040]    The system  138  may also include an operator scale/intensity selector  162 , an ambient light detector  164 , and inputs from a navigation system  166 , an entertainment system  169 , a speed detector  170 , and a radar system  172 . 
         [0041]    It is to be understood that the invention has been described with reference to specific embodiments and variations to provide the features and advantages previously described and that the embodiments are susceptible of modification as will be apparent to those skilled in the art. 
         [0042]    Furthermore, it is contemplated that many alternative, common inexpensive materials can be employed to construct the basis constituent components. Accordingly, the forgoing is not to be construed in a limiting sense. 
         [0043]    The invention has been described in an illustrative manner, and it is to be understood that the terminology, which has been used is intended to be in the nature of words of description rather than of limitation. 
         [0044]    Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, wherein reference numerals are merely for illustrative purposes and convenience and are not in any way limiting, the invention, which is defined by the following claims as interpreted according to the principles of patent law, including the Doctrine of Equivalents, may be practiced otherwise than is specifically described.