Abstract:
A projector system has an image display with at least two image display portions each displaying a respective image. At least two projection assemblies are provided, each associated with a respective image display portion. These projection assemblies each receive a respective image from the respective image display portion and project this image onto the projection screen. The projection assemblies each include a system for independently and selectively locating the projected image on the screen. The projection assembly includes a stationary mirror supported adjacent the image display portion receiving the image therefrom and reflecting said image outwardly from the image display to the movable mirror. Preferably, the stationary mirror has an upper end portion and a lower edge portion. The lower edge portion is adjacent the image display portion and the mirror extends obliquely upwardly therefrom. Most preferably, the stationary mirror flares outwardly from the lower edge portion, and the stationary mirrors are grouped together over the image display, with the lower edge portions of adjacent stationary mirrors being supported generally perpendicular to each other.

Description:
FIELD OF THE INVENTION  
         [0001]    This invention relates to the field of projection systems, and more particularly to the field of projection systems for vehicle simulators.  
         BACKGROUND OF THE INVENTION  
         [0002]    Simulation systems are often used to simulate systems and vehicles, especially aircraft, for training users or pilots. In these simulation systems, an out-the-window scene is generated and displayed to the user. The image is generated as pixels and projected on one or more projection screens to constitute a field of view covering a substantial area. The projected out-the-window (OTW) image is consequently so much enlarged that it has a rather coarse, low resolution.  
           [0003]    It is desirable to display at least certain objects, such as other aircraft, in small enough resolution to train a user to see and recognize targets at great distances such as those in the real world, i.e., at or near eye-limiting resolution. As an example of the target resolution now desired, it has been expressed that a desirable standard would be that a trainee in an aircraft simulator would be able to discern the attitude of a target aircraft at a simulated distance of two to three miles.  
           [0004]    This level of resolution cannot be achieved with the coarse projected pixels of the larger OTW imagery. To try to improve target resolution, projector systems have been developed that include a separate higher-resolution target projector that projects a single higher-resolution target image on the screen superimposed with a lower resolution background image.  
           [0005]    The prior art projectors, however, have the very substantial drawback that they can project only one target on the screen at a time. If a simulation is desired in which multiple targets are present on the screen, a second projector must be provided at substantial additional cost, especially where the simulator has a large number of screens are used. For example, in a Raytheon SimuSphere simulator system, there are nine faceted screens. To provide enough single-target projectors to afford four active targets in the overall field of view would require four single-target projectors for each screen, totaling 36 target projectors needed. With the cost of each current-technology target projector at about 100,000 U.S. year 2000 dollars, such a system would be too expensive to be practical.  
           [0006]    In addition to being very expensive and having only single target functionality, prior art target projectors are generally too large, making them difficult to package, and also difficult to place in a structural environment inside or around the simulator that is already crowded with other projectors and support equipment. Furthermore, the prior art projectors often are monochrome, reducing the realism of the projected display.  
         SUMMARY OF THE INVENTION  
         [0007]    Accordingly it is an object of the invention to provide a projection system that allows for the projection of multiple high-resolution images with a single projector.  
           [0008]    This object is achieved by providing a projector system having an image display with at least two image display portions each displaying a respective image. At least two projection assemblies are provided, each associated with a respective image display portion. These projection assemblies each receive a respective image from the associated image display portion and project this image onto the projection screen. The projection assemblies each include a system for independently and selectively locating the projected image on the screen.  
           [0009]    In a preferred embodiment, the projection assembly includes a stationary mirror supported adjacent the image display portion receiving the image therefrom and reflecting said image outwardly from the image display to the movable mirror.  
           [0010]    Preferably, the stationary mirror has an upper end portion and a lower edge portion. The lower edge portion is adjacent the image display portion and the mirror extends obliquely upwardly therefrom. Most preferably, the stationary mirror flares outwardly from the lower edge portion, and the stationary mirrors are grouped together over the image display, with the lower edge portions of adjacent stationary mirrors being supported generally perpendicular to each other.  
           [0011]    In another aspect of the invention, the system for locating the projected image includes a movable mirror supported on a controlled support system selectively positioning the movable mirror in varying angular positions.  
           [0012]    It is further an object of the invention to provide a method of projection that overcomes the disadvantages of the prior art. According to the inventive method, a background projector and a target projector are provided, both positioned so as to project images on a screen. The target projector includes a target image display having at least two image display portions each configured to display a respective image. Each image display portion has associated therewith a respective target projection assembly for receiving and projecting the image on the projection screen. Each projection assembly includes a system for independently and selectively locating the projected target image on the screen. The method further includes causing the background projector to project a background image on the screen, forming target images on said display portions of the target projector, and causing the target projector to locate said target images on said projector screen. The target images are at a higher resolution than the background image.  
           [0013]    According to a preferred embodiment, the target images are formed with a distortion to compensate for any angular alignment of the screen with the target projector.  
           [0014]    Other objects and advantages of the invention will become apparent from the specification herein. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0015]    [0015]FIG. 1 is a side view diagram of a simulation system having a projection system according to the invention;  
         [0016]    [0016]FIG. 2 is an exemplary view of a simulated OTW scene displayed according to the invention;  
         [0017]    [0017]FIG. 3 is a perspective view of a target projector according to the invention;  
         [0018]    [0018]FIG. 4 is a perspective view of a target projector according to the invention with the cover thereof removed.  
         [0019]    [0019]FIG. 5 is a perspective view of the target projector of FIG. 4 with the automatic alignment system removed.  
         [0020]    [0020]FIG. 6 is a sectional view taken along line A-A of FIG. 5.  
         [0021]    [0021]FIG. 7 is a view of an exemplary display on the imaging screen of the target projector.  
         [0022]    [0022]FIG. 8 is detailed side view of the image display, lens assembly and stationary mirrors of a target projector;  
         [0023]    [0023]FIG. 9 is a perspective view of the detail view shown in FIG. 8;  
         [0024]    [0024]FIG. 10 is a plan view of the detail view shown in FIG. 8;  
         [0025]    [0025]FIG. 11 is a view as in FIG. 10, showing in phantom the image sectors of the display below the mirrors. 
     
    
     DETAILED DESCRIPTION  
       [0026]    According to the preferred embodiment, as best seen in FIG. 1, a simulator system is provided, in this example one for simulating an aircraft. The exemplary system includes a projection screen system sold by L-3 Communications Corp., Link Simulation and Training Division, Arlington, Tex., under the name SimuSphere. It will be understood, however, that the present invention may be applied to any of a variety of simulator projection systems other than the one of the present illustration.  
         [0027]    In the illustrated system, the user or trainee is enclosed in a projection screen system in the form of simulation chamber  3 , which is comprised of a number of planar rear-projection screens  5  supported by an external support structure (not shown). A number of projectors  7  surround the projection screen system  3 , each projector  7  being supported so as to be directed at a respective screen  5 . Some of these projectors are mounted on posts extending up from the floor of the location, while the projectors  9  above the screen system  3  are usually supported on an elevated platform (not shown).  
         [0028]    The host computer system that runs the simulator includes an image generating system connected with the simulator controls and other sensors of the simulator system to generate real-time background images for projection to be viewed by the user. The image generator transmits the images to the individual projector  7  responsible for the given region of the projection screen system.  
         [0029]    Each screen  5  also has associated therewith a respective target projector  9  that is also connected with the image generator. The image generator also sends imagery data and commands to these target projectors, and responsive to this data and commands, the target projectors  9  each project, when appropriate, targets or other objects on the associated screen  5  at a resolution higher than the resolution of the images projected by projectors  7 . The use of the higher resolution target projector allows the background image to be of even lower resolution, reducing computational load in preparing those images.  
         [0030]    [0030]FIG. 2 shows an example of an OTW scene projected on the screens  5 . The projectors  7  project the background scene visible therein, i.e., the hills, the sky, etc., which is prepared by the image generator as a set of images each defined as a matrix of pixels, as is well known in the art. Each individual projector  7  projects one of the background images on its associated pentagonal screen  5 .  
         [0031]    Also, where the simulation requires, targets, such as enemy or friendly aircraft  11 ,  13 ,  15 , and  17 , ground vehicles, or other stationary or mobile installations are also projected on the screens  5 . These targets are projected so as to simulate real-world resolution, i.e., at or near eye-limiting resolution, to increase the realism of the simulation and the effectiveness of the training. This level of projected resolution of the background projectors  7  is too low to approximate this eye-limiting resolution because each projector  7  must provide an image to the entire area of the pentagonal screen  5  with which it is associated. Each screen  5  is about five feet across, and even a fairly high number of pixels applied over this area would not be near the resolution of human visual acuity.  
         [0032]    Therefore the targets are projected on screens  5  by the separate target projectors  9 , which are able to project at least four independently positioned and movable targets with much higher resolution. Each target projector  9  projects targets for only the screen  5  associated therewith, so, in the example of FIG. 2, targets  11 ,  13 , and  15  are all projected by one of the target projectors, and target  17  is projected by another target projector associated with the adjacent screen  5 . As a target crosses from one screen to the next, the image generator transfers the image of the target from the first target projector to the one associated with the next screen  5 . According to the preferred embodiment each target projector is capable of projecting at least four independent target images on the associated screen.  
         [0033]    The external structure of the target projectors  9  is best seen in FIG. 3. The target projector  9  has an external cover  19  with a plurality of apertures  21  therein. A target image is projected through each of these apertures  21  along an independently controllable projection path A, B, C, and D by a projection assemblies which each include a controlled gimbaled mirror structure, generally indicated at  23 .  
         [0034]    Referring to FIG. 4, as may be seen when the cover  19  is removed, the target projector  9  includes a base plate  25  on which the mirror structures  23  are supported, and a raised center portion  27 . The center portion  27  supports a central assembly indicated at  29  mounted thereon.  
         [0035]    Each mirror structure  23  includes a silvered mirror  31  secured in a tray  33  pivotally supported on a mounting structure  35  to provide a gimbal assembly. Tray  33  pivots about an axis parallel to the surface of the base plate  25  and is positioned so that the rotational axis lies on the reflective surface of the mirror  31 . The position of the tray  33  is controlled by servomotor system  37 , which selectively rotates tray  33  responsive to commands from the image generator and connecting intermediate circuitry.  
         [0036]    Each mirror structure  23  is mounted so that the mounting structure  35  is rotatable about a vertical axis perpendicular to base plate  25 . The rotation about this axis is controlled by an azimuth drive assembly  39  under base plate  25  connected with a pivot extending downward from mounting structure  35  through the base plate. Each azimuth drive assembly includes a servomotor and is controlled by the image generator and the connecting circuitry, or, during maintenance, manually by an operator using a joystick or a keyboard.  
         [0037]    Central assembly  29  includes first and second support plates  41  and  43  fixedly supported over four partially silvered beamsplitters  45 . Four optical sensors or photocells  47  are supported in second support plate  43 . These components coact with the mirror structures  23  to automatically align the target projector  9  during installation, based on principles analogous to those disclosed in U.S. Pat. No. 5,707,128 to Jonathan L. Dugdale, which is herein incorporated by reference. At installation, the mirror structures  23  are rotated to a 45-degree angle relative to base plate and at 90 degrees to the centerline of base plate  25  passing through the mirror structure  23 . Preselected points of light are then illuminated on the associated screen  5 . The light from these points enters the target projector  9  through apertures  21  and is reflected by mirrors  31  to center assembly  29 . Solenoids are activated which slide the beamsplitter mirror  45  into the path of incoming light. If the target projector is properly aligned, the light is reflected by each mirror  31  to a respective beamsplitter  45 , and then to a respective photocell  47 , which produces a signal indicating optical alignment. The target projector  9  is repositioned during installation until this alignment is achieved. Once the adjustment is completed, the solenoids are switched off and the beamsplitter mirrors  45  are retracted by springs to prevent these mirrors  45  from obstructing operation of the target projector  9 .  
         [0038]    In FIG. 5, the target projector  9  is shown with the central alignment assembly  29  and beamsplitters  45  removed. Center portion  27  of base plate  25  has a square aperture  49  therein, and image display screen  50  is supported in this aperture  49 . A mirror assembly  51  is supported on the underside of first support plate  41  (FIG. 4) directly above the image display screen  50 .  
         [0039]    As best seen in FIGS. 5, 6 and  8 , the mirror assembly  50  includes a supporting plate  53  and four mirrors  55  extending obliquely downwardly from the supporting plate  53  so that the lower edges of the mirrors  55  thereof are adjacent to the image display screen  50 . A lens assembly  57  overlies the image display screen  50  and transmits the light therefrom upward as conically expanding beams to the mirrors  55  which direct the beams thereof radially outwardly of the central portion  27  along centerline paths A 1 , B 1 , C 1  and D 1  to the gimbaled mirror structures  23 , to be directed against the screen in selected positions as required by the image generator system. It will be understood that in the assembled target projector, during the installation alignment discussed previously, the beamsplitters  45  are pushed by solenoids to lie in these paths, but, after installation, the solenoids are released and the beamsplitters  45  retract out of the way.  
         [0040]    The target projector of the present invention may be used with a variety of image sources. The image display screen may be the output of a commercial projector using digital micromirror devices (“DMD”), liquid crystal diodes (“LCD”), integrated light amplification (“ILA”) technology as developed by Hughes and JVC, digital light processing (“DLP”), or variants or analogues thereof, or any of a variety of other projection or display technologies. One such projector is the DMD projector sold by Davis A/S of Drammen, Norway, and another is sold by Christie Digital Systems, Inc. Ktchener, Ontario, Canada. However, in the preferred embodiment the image display screen  55  is a microdisplay unit based on active matrix liquid crystal diode (“AMLCD”) or DMD, or other suitable technology, and most preferably a DMD microdisplay such as those developed by Texas Instruments. These DMD microdisplays are approximately one inch in diagonal measurement, but have a display of at least 720          720 pixels.  
         [0041]    The target image projected or created in the microdisplay is exemplified in FIG. 7. The image display field  59  is divided into four equal-sized quadrants or sectors each containing a respective image portion  61 A,  61 B,  61 C, and  61 D each having therein a target image  63  defined by the set of pixels therein. In the preferred embodiment the image portions are circular, to pass properly through the circular lenses of lens assembly  57 , and the diameter of the circular field represents 360 pixels, i.e., half of the pixel dimension of the entire microdisplay.  
         [0042]    The target imagery received by the display screen  55  from the simulator image generating system is a standard RGB signal produced by video cards, such as VGA, XGA, or SXGA boards, HDTV, or other similar video formats. These boards are either supported in the target projector  9  in the concave underside of center portion  27  of base plate  25 , or as part of the image generating system.  
         [0043]    Projection of the target images  63  is best understood by reference to FIGS. 6, 9,  10  and  11 , which define the optical assembly that brings each target image on image screen  59  to be projected on screen  5 . This optical assembly comprises, for each image portion  63 , a respective lens assembly  57 , a respective stationary trapezoidal mirror  55 , and a respective gimbaled mirror structure  23 .  
         [0044]    The image portions  61 A, B, C and D face upward to lens assemblies  57 . The light from the image portions  63  passes through the lens assemblies  57 , which are preferably lens groupings that cause the light passing therethrough to diverge in a widening conical path. As best shown in FIG. 9, the four trapezoidal mirrors  55  are supported each above a respective lens assembly  57 , and these align with the image display portions  63 . The mirrors  55  each has a shorter lower end  65  adjacent and above the image display  59  and the lens assemblies, and this lower end  65  has a length that is approximately the same as the lateral dimension of the target image portion  61 A, B, C, or D. The mirrors  55  extend obliquely upward from this lower end  65  at a 45-degree slope to a relatively wider upper end  67 , flaring wider upwardly. This flaring allows the mirrors  55  to be packed together with the lower ends  65  generally perpendicular to each other, and to accommodate at the same time the widening projection cones of the target images  65  without occulting any of the other mirrors  55  or the mirrors  31  of the gimbaled mirror structures  23 .  
         [0045]    As can be seen in FIGS. 6, 8, and  9 , the stationary mirrors  55  fold the conical image projection beams 90 degrees, to project laterally outwardly of the raised center portion  27  of the base plate  25 . These beams are each conical around beam center ray lines A 1 , B 1 , C 1 , and D 1 , and the beams continue to expand as they proceed outwardly to the mirror structures  23 .  
         [0046]    The projector beams are reflected by gimbaled mirrors  31  and then proceed through openings  21  in cover  19  to reach the screen  5  and display the target image  65  thereon. Mirror structures  23 , as discussed above, have servomotors or step motors that drive the rotation thereof to adjust the angular positions of the mirror  31 , and thereby adjust the reflected angles of the beams, and thus the azimuth and elevation of the projected target on screen  5 . The angular orientations of the mirror  31  are each individually selectable, and are in a range of about 15 degrees about each axis. The servomotor or step motors are driven by position signals from the image generation system, which uses the simulator data defining the position and nature of the target relative to the observer ownship, i.e., the simulated vehicle itself, and the observer ownship attitude to derive the appropriate values for azimuth and elevation of the target.  
         [0047]    The target imagery is supplied from a set of PC graphics cards or from a more sophisticated image generation system that computes and furnishes the multiple target images  63 . Each target image  63  is computed independently based on data from the host computer and this preferably includes target attitude, range, visibility, time of day and sun angle.  
         [0048]    The target images  63  may be views of the target at various orientations, e.g., a head-on view or a tail end view, or an oblique top or bottom view, not just simple top views as seen in FIG. 7. The orientation and scale of the displayed target is controlled by rotating the target image and enlarging or shrinking it within the associated image portion  63 , that is, by displaying the image at the desired orientation and size. The largest target size that can be displayed by the target projector of the preferred embodiment is therefore a target image that fills the entire quadrant, as does the upper left image  63  in FIG. 7.  
         [0049]    This dimension is referred to as the nominal size, which is preferably about 5 to 10 inches in the SimuSphere system shown. This size target allows for an acceptable range of target sizes while at the same time keeping the size of projected image pixels small enough to provide eye-limiting or near eye-limiting resolution on the target. If a larger target, i.e., a target that subtends a greater angle than nominal size the target projector can produce, is required, such as when a target aircraft is at very close range, the image generator hands off the particular target image to the coarser imagery of the associated background projector  7 , and the target image is blanked off in the target projector  9 .  
         [0050]    However, because some projector imaging devices produce distracting visual artifacts, it may be desirable, alternatively, to insert a dynamic image rotation optical assembly, such as a pechan prism or a k-mirror assembly in the projection path of the images to control the orientation and/or size of the projected image.  
         [0051]    Also, because the target projector is most likely off-axis relative to the screen  5  to provide clearance for the background projector  7  to project the background image over the entire screen  5 , the image generation system incorporates necessary keystone corrections in the target images  63  produced on display  50  to compensate for the position of the target projector  7  and to produce proper target images without distortion when projected.  
         [0052]    The nominal focus of the projected image is generally preset by lens assemblies  57 . Additional lenses are preferably provided in the projection pathway between the beamsplitter assembly  45  and mirror structures  23  that can be controlled by the image generator to change the depth of focus of the images to maintain proper focus as the target image moves across screen  5 . The preferred location for these controlled lenses is best indicated in phantom as reference number  69  in FIG. 6.  
         [0053]    The terms herein should be read as terms of description rather than limitation, as those of skill in the art with this specification before them will be able to make variations and modifications therein without departing from the spirit of the invention. In particular, it will be understood that the present invention may be applied to any of a variety of simulated vehicles or systems, and to any of a variety of simulator projection systems other than the one of the present illustration. For example, a spherical projection screen instead of a planar one can also be used with the invention herein. Similarly, the target projectors of the present system can be used on new or retrofitted to existing L-3 SimuSphere visual displays, Raytheon F16 UTD visual displays, Raytheon C130 or F18 Reserve VIVID visual displays, and partial dome displays, such as the Taiwan F16, Navy T45, or Air Traffic Control visual displays. Simulated vehicles may include any aircraft, such as, e.g., F-15, F-16, A-10, or various non-U.S. aircraft, non-aircraft such as tanks, or simulations of systems like air traffic control systems.  
         [0054]    Similarly, either front- or rear-projection screens may be used with target projection systems incorporating the invention herein.  
         [0055]    It will also be understood that more than four images may be projected by a given target projector by dividing the image display screen into a larger number of sectors and providing independent projection assemblies for each of these sectors.