Abstract:
The present invention is related to a curved surface, real image, laser-based rear projection display system. A plurality of translucent panel members are assembled into a spherical dome assembly. The panels have concave inner surfaces treated with an optical medium to create a diffusion surface onto which the projected visual image is displayed to a design eye point located within the dome. The laser-based projectors have a greatly expanded focal range as compared to conventional sources of illumination. This allows the curved panel members to remain in focus when the dome is moved as much as two (2) relative to the location of the laser projector.

Description:
RIGHTS OF THE GOVERNMENT 
     This invention was made with Government support under contract No. F41624-97-D-5000 awarded by the Department of the Air Force. The Government has certain rights in this invention. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to real time, curved surface imaging systems. More particularly, the present invention is directed to a laser-based, rear projector imaging system. 
     2. Description of the Related Art 
     Spherical dome imaging systems have long been used in a variety of applications ranging from planetariums and commercial entertainment systems to military flight simulators. Domed imaging visual systems are capable of generating scenes with a high degree of realism because the scene is presented to the view in many directions at once, not just from a single flat plane as in most conventional imaging systems. The capacity for producing a wide field of view is highly desirable in both commercial and military imaging systems applications. 
     Most conventional dome display systems in use are front projection systems. Like conventional movie theaters, front projection systems employ one or more projectors positioned on the same side of the screen as the viewer and serve to project still and/or moving images onto the screen. On conventional front projection spherical dome displays, it is often necessary to use elaborate mounting mechanisms and costly optical lens arrangements to insure a collect viewing perspective, without interfering with the projected light path. Subtle protrusions of the “rib” structure located on the exterior of the dome are frequently apparent on the interior screen surface. Because the projector and projected light rays are on the same side of the screen as the viewer, physical limitations are imposed which restrict placement and movement of the viewer. When employed in simulation and training systems, the necessity for avoiding occluding projected light rays places severe limitations on training device location and configuration. In domed imaging systems which employ multiple front projectors, the physical limitations may also undesirably restrict the number of projectors and, as a result, the number of images that the system can employ. 
     Conventional front-projected dome surfaces are often painted with a display screen medium to enhance visibility. This can result in irregularities being visible on the display surface, such as mottling. The viewing dome surface also must have very critical optical characteristics necessary to produce sufficient off-axis luminance. Producing dome screens with these desired optical characteristics is an expensive process requiring specialized talent to produce the required finish. 
     Another factor which contributes to the complexity and cost of front projection domed imaging systems is the distortions caused by off-axis projection of images onto the curved dome surfaces. Correcting such distortions requires special video projectors capable of performing such corrections. This can increase the cost of the system and require a significant amount of time. 
     In an effort to overcome the problems associated with front projection systems, some display systems use rear-projection techniques, often referred to as “dome displays”. In actuality, such systems are not true spherical dome displays. Rather, they usually employ multi-faceted, flat panel displays, configured with multiple flat panel display screens, specifically designed to encapsulate the viewer. While such systems may provide certain advantages achieved by a true dome display, they lack a key feature of a true spherical dome display. Namely, they do not have true spherical geometry. This can result in undesirable visual irregularities or artifacts when the imaging system is employed within the exacting requirements of military flight simulation or other visually demanding applications. One such artifact is variable eye relief distance. In a true spherical dome display wherein the design eye point is at the center of the sphere, the ideal eye relief distance is equal to all points on the display surface. This is not true when using a flat panel, multi-faceted, dome display. In such flat panel displays, as the viewer&#39;s gaze moves away from the line of sight between the design eye point and the screen normal, the eye relief will increase at a rate inversely proportional to the cosine of the angle traversed. In comparison, in a true spherical dome display, the design eye relief remains constant regardless of gaze direction. As can be easily understood, an advantage of a true spherical dome over a multi-faceted, flat panel is the fixed eye relief to all points on the display surface. 
     When employing conventionally illuminated projectors, i.e. light valve, CRT, LCD and DMD projectors with standard lenses, the projected image size is a function of the projection lens and the throw distance. After the image size has been established, a mechanical focus adjustment procedure is employed to correct for center and off-axis corner focus of the displayed image. The available range of adjustment for off-axis focus depth is very limited. With conventional non-laser light sources, any change of screen position in relation to the position of the projector lens requires re-focusing of the display image. The focus adjustment is within the acceptable range at only a very specific distance between the projector and the display screen. If there is even a slight change in projector throw distance, it is necessary to again perform the focus adjustment procedure. Thus, when employing non-laser projectors, it is usually not possible to focus a display image on a curved dome surface without employing costly special optics to compensate for the curvature of the dome surface. 
     It is clear that there exists a need in the art for a full field-of-view (FOV), spherical dome display system employing a rear-projection imaging source capable of displaying images in real time on a curved surface of the dome. Such a display system should overcome the problems associated with conventional illumination light sources while being cost efficient. As will become apparent, the present invention meets all of these requirements in a unique dome display system. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the need in the art for a true spherical dome imaging system having a FOV limited only by normal cockpit obstructions. The dome imaging system of the present invention employs a rear-projected laser light source with its expanded focal range. The dome structure is fabricated from a plurality of separate, translucent panels including both curved side panels and curved cap panels. The panels are specially molded to serve as display screens with appropriate optical characteristics. The panels are curved and have an optical medium affixed to the concave side to create a diffusion surface onto which the projected visual image is displayed. The optical characteristics of the system direct the displayed image toward the system design eye point. 
     Each of the curved panels has an outer edge formed as an upturned flange. When assembled, the flange portions of adjacent panels make surface contact with one another and are clamped together to create a substantially spherical dome structure. Because the curved panels form a translucent dome, the concave inner surface of each panel serves as a screen for displaying to a viewer positioned in the dome a real time display image projected through the dome by a rear-projector. The assembled dome imaging system achieves a full 360° horizontal FOV and a total vertical FOV of approximately 130°, of which, approximately 70° is provided by the side panels. 
     The rear-projection system of the present invention employs at least one laser-based projector to illuminate each dome panel. By using a laser-based rear projection system, the resulting display images on the dome panels will have significantly improved resolution, brightness and contrast compared to conventional flat panel, multi-faceted displays. Finally, by employing a true spherical dome, the benefits associated with a spherical dome are assured. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a front cut-out view of a curved surface, rear-projection dome display system formed in accordance with the present invention. 
     FIG. 2 is a left rear view of the dome formed in accordance with the present invention, wherein one of the side panels is removed to allow viewing of the dome interior. 
     FIG. 3 is a perspective view of the dome formed in accordance with the present invention, illustrating the arrangement of side and cap panels. 
     FIGS.  4   a ,  4   b  and  4   c  depict top, front and side views, respectively, of a side panel formed in accordance with the present invention. 
     FIGS.  5   a ,  5   b  and  5   c  depict top, front and side views, respectively, of a cap panel formed in accordance with the present invention. 
     FIG. 6 is a perspective view of the display system formed in accordance with the present invention wherein the panels are removed for viewing inside the dome. 
     FIG. 7 is a perspective view of the dome display system including supporting structure formed in accordance with the present invention. 
    
    
     DESCRIPTION OF THE INVENTION 
     Illustrative embodiments and exemplary applications are described below with reference to the accompanying drawings in order to disclose the advantageous teachings of the present invention. Referring now to the drawings wherein like reference numerals designate like elements throughout. 
     One aspect of the present invention comprises utilization of a laser-based projector in place of conventionally illuminated CRT, LCD, DMD or light valve projectors. Laser-based projectors have greatly expanded focal ranges as compared to such conventional light projectors. For a prototype laser projection system, the laser has a focal depth range of approximately two (2) feet. This means, for example, when using an initial ten (10) foot throw distance, it is possible to move a display panel anywhere between nine (9) and eleven (11) feet from the laser-based projector and still maintain a focused image at all points on the display panel. This advantage is achieved with no cost penalties for specialized optics that would otherwise be necessary when employing a conventional, non-laser projection system. 
     A spherical display dome formed in accordance with the present invention is shown at  10  in FIG.  1 . Display dome  10  can be used in a number of applications such as military and civilian simulation systems and commercial entertainment applications. The diameter of dome  10  may vary depending on the application, for example, the type and size of aircraft cockpit to be simulated. As best shown in FIG. 6, display dome  10  includes a plurality of separate panels forming a curved surface, real image display assembly  12  including at least one rear-projector for each curved panel. 
     Turning to FIGS. 1 and 2, display dome  10  is formed from a plurality of separate panel members. Preferably, five (5) side panels  14  and three (3) cap panel members 16 are employed. Each of the side panels  14  is of similar curved shape and size. When positioned side-by-side, side panels  14  form a substantially cylindrically-shaped, hollow member open at either end. Curved side panels  14  are preferably supported on a cockpit simulator  18  having a forward panel  14   a  of similar contour to an aircraft cockpit. The specific details of simulator  18  make up no part of the present invention. The three cap panel members  16  are of similar size and curved shape. When positioned end-to-end on top of panels  14 , cap panels  16  form a hemispherically-shaped member that, when combined with panels  14 , form display dome  10 . 
     The three similar cap panels  16  are wedge-shaped and intersect one another at the upper pole  20  of display dome  10 . As viewed from the system design eye point  22  located with dome  10 , each side panel provides substantially 72° horizontal FOV and a vertical FOV of substantially 30° in an upwardly direction and substantially 40° in a downwardly direction, comprising a total vertical FOV of substantially 70°. From the design eye point  22 , each of the cap panels  16  provides substantially 120° horizontal FOV and substantially 60° vertical FOV. The combined vertical FOV for the side and cap panels is substantially 130°. 
     The side panel  14  located directly in front of the simulator seat  24  serves as a front display screen for dome assembly  10  and is preferably cut to the match the cockpit shape of front surface  19  of simulator  18 . The interior surfaces of the remaining side panels  14  as well as the interior surfaces of the cap panels  16  each serve as a display screen for displaying an image provided by one of the rear projectors as will be explained. As shown in FIGS. 4 and 5, respectively, each of the side panels  14  includes a molded flange portion  26  forming an outer edge extending completely around the panel. Likewise, each of the cap panels  16  includes a molded flange portion  28  forming an outer edge extending completely around the panel. When the side panels  14  are assembled to form the cylindrically-shaped hollow member, the flanges  26  of adjacently disposed panels make surface contact with one another. In a similar manner, when cap panels  16  are positioned adjacent one another and adjacent the side panels  14  to form dome  10 , flanges  28  of adjacent cap panels  16  make surface contact with one another. In addition, the flanges  28  of cap panels  16  disposed adjacent the side panels  14  make surface contact with flanges  26 . 
     Once the side and cap panels  14  and  16 , respectively, are assembled, the abutting flanges  26  and  28  of adjacent panels may be secured by any conventional fastening assembly. For example, bolts may be extended through aligned openings formed in the flanges  26  and  28 . Alternatively, clamps may straddle each flange and serve to press the flanges into contact with one another. Regardless of how flanges  26  and  28  are secured, the geometry of flanges  26  and  28  is such that they do not interfere with the light path of the rear-projection image display system as will become clear. 
     For the dome shown in FIG. 1, the design eye point  22  of the curved surface, real image, rear-projection display system is located at the center of spherical dome  10 . The interior diameter of dome  10  is considered a design choice. In a preferred embodiment shown in FIG. 1, the diameter is chosen to be 97 inches. It provides an eye relief of 48 ½ inches from eye point  22  to all points on the interior display surfaces of panels  14  and  16 . The three cap panels  16 , when assembled on side panels  14  will have an outer radius of about 45 ¾ inches, including the mounting flanges  26  and  28 . At its highest point, the intersection  20  of cap panels  16  is located substantially 28 ¾ inches above the top of side panels  14 . Each cap panel  16  provides a substantially 120° azimuth viewing angle, as referenced from the design eye point  22 . 
     Only one mold is necessary to fabricate the three (3) similarly-shaped cap panel members  16 . Likewise, only one mold is necessary to fabricate the five (5) similarly-shaped side panel members  14 . All of the panels are formed of a translucent substrate, with appropriate optical characteristics that allow the panels to function as concave shaped display screens capable of receiving and displaying images projected from a plurality of rear-projection assemblies. As shown in FIGS. 4 and 5, the flanges  26  and  28  extending in a direction substantially perpendicular to their attached panel. All of the flanges are substantially four (4) inches wide and are integrally molded along with their attached panel  14  or  16 , respectively. 
     When dome  10  is employed as an aircraft simulator, the simulator  18  is positioned within dome  10  such that the eye of the person seated in simulator  18  coincides with design eye point  22  of dome  10 . This is achieved by adjusting the elevation of simulator  18  until the design eye point  22  coincides with the cockpit eye point. Within limits of the display system  12 , the only change to simulate different cockpits is the display system elevation and the specific cut-out of the panels to achieve a match with the contour of the cockpit to be simulated. 
     As shown in FIGS. 2,  3  and  4 , panels  14  and  16  are shaped so that the intersection between adjacent panels do not interfere with significant training requirements of high-speed fighter aircraft. In particular, the front panel display screen  14   a , has a relatively wide horizontal FOV of 72°. There are no abutments obscuring the view from the design eye point  22  created by adjacent panel flanges within the primary forward area of interest or at the three (3) o&#39;clock and nine (9) o&#39;clock wing locations. The specific placement of the boundaries for the upper, forward cap display screens is such that there is minimal interference with air refueling training operations. The intersection pole  20  of the three cap panels  16  is designed to be directly above the design eye point  22 , an area normally not in the pilot&#39;s line of sight. 
     As shown in FIG. 2, the dome  10  has a left rear side panel removed. In normal operation, the missing panel along with the right real side panel will be hinged to allow sufficient pivoting movement of the panels to allow a subject to enter or exit simulator  18 . A conventional hinge mechanism is mounted on each of two fixed position side panels  14   b  and  14   e , allowing the other two panels, including panel  14   c  shown in FIG. 6, to pivot out of contact with one another. 
     The display system  12  in FIG. 7 includes a plurality of three support towers  30 ,  32  and  34 , respectively. Tower  32  is located adjacent the right rear portion of dome  10 , while tower  32  is located adjacent the left rear portion of dome  10  and tower  34  is positioned adjacent the front of dome  10 . The flanges  26  and  28  located between the side and cap panels as well as the flanges  26  located between side panels  14  and simulator  18  may be used as attachment points for mounting dome  10  to the rear towers  30  and  32 . It is noted that the flanges also serve to provide an attachment point of affixing light baffles used to prevent projected stray light from spilling into adjacent screens. 
     The rear towers  30  and  32  may each contain two (2) laser-based projector assemblies  36  and  38  and a fold mirror as shown in FIG.  7 . The front tower  34  contains the remaining four (4) laser-based projector assembly  42 . The towers  30 ,  32  and  34  preferably have wheels, allowing them to be rolled into place during initial assembly of imaging system  12 . After the towers  30   32  and  34  have been properly positioned, adjustable leveling pads, not shown, are employed to assure that all the towers are level relative to one another and are set at the correct height. To reduce the overall size of display imaging system  12 , the projected images are reflected to the display surface by fold mirrors  44  mounted on the towers. The front tower  34  optionally may house a heads-up-display (HUD) projector. The structure of dome  10  is supported above simulator  18  by means of steel sheets  46  which are extend between and are attached to the rear towers  30  and  32  and the bottom flanges  26  of side panels  14 . Support columns, not shown, are preferably positioned between the bottom flanges  26  of the two side panels  14   a  and  14   b  located at the forward portion of dome  10  and the floor, for providing support for the front portion of dome  10 . 
     At least one laser-based projector is employed for each of the eight side and cap panels  14  and  16 , respectively. A separate HUD projector may be employed, or the HUD graphics may be embedded in the video of the forward panel  14   a  laser projector. It will be necessary for the system imaging generator to have image distortion correction capability to compensate for the curvature of the side and cap panel display screens. 
     Thus, the present invention has been described herein with reference to a particular embodiment for a particular application. Those having ordinary skill in the art and access to the present teachings will recognize additional modifications, applications and embodiments within the scope thereof. While the preferred embodiment employs five ( 5 ) side panels, it is considered within the scope of the present invention to have a greater or lesser number of side panels depending on the particular FOV and the location of the flange abutments therein. In a similar manner, the preferred use of three (3) cap sections may be increased or decreased depending on the ultimate use of the dome assembly  10 . The number of support towers may be altered and their location changed as required. While at least one laser-based projector for each display panel is considered to provide the best obtainable image, the number of projectors may be altered for specific applications. 
     It is therefore intended by the appended claims to cover any and all such applications, modifications and embodiments within the scope of the present invention. 
     Accordingly,