Abstract:
An apparatus and method for aligning portions of a tiled projection display which become misaligned during operation of the display, including interposing at least one two-dimensionally electro-mechanically gimballed glass plate in the projection path of one of the display sections. Sensing the misalignment of the tiles and automatically adjusting the alignment in response thereto. Further having apparatus and steps for alignment of the tiles based upon operational characteristics of an aircraft upon which the display is used.

Description:
FIELD OF THE INVENTION 
     The present invention generally relates to large area, or panoramic, cockpit displays and even more particularly relates to such displays having multiple image projectors illuminating a common viewing screen. 
     BACKGROUND OF THE INVENTION 
     In the past, designers of avionics displays have endeavored to provide larger and larger display devices to better provide for enhanced situation awareness for flight crews. The use of projection displays in cockpits is gaining many followers because of their recognized ability to provide large area, or panoramic, displays. One method for creating large, high resolution displays is to illuminate a single viewing screen with multiple image projectors, These multiple projector images may be arranged as contiguous non-overlapping, partially overlapping, or totally overlapping image segments. All such configurations may be referred to as tiled image displays. The resulting large image, being comprised of several smaller images, may be referred to as a composite image. While these displays have many advantages, they also have significant drawbacks. 
     Tiled projection displays must maintain a high degree of alignment precision to provide the superior performance necessary for avionics enhanced situation awareness displays. However, the cockpit is not a mechanically static or benign environment. In-flight turbulence, forces of impact upon landing and other forces resulting from maneuvering the aircraft can be substantial, especially for smaller aircraft and most especially, for fighter aircraft used in operation on-board aircraft carriers. These forces can cause mechanical displacement of the projectors, viewing screens, and other components. Normal variations in aircraft temperature can also cause the projectors, or their images, to move. 
     Consequently, there exists a need for dynamic alignment of tiled projection displays. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide tiled projection displays having a superior image alignment characteristic. 
     It is a feature of the present invention to utilize a multi-axis adjustable beam deflector. 
     It is an advantage of the present invention to optically align tiled projected images. 
     It is another feature of the present invention to include a static compensator. 
     It is another advantage of the present invention to reduce aberration corrections required for unequal optical path lengths. 
     It is yet another feature of the present invention to include electro-mechanical gimbal drive motors and gimbal angle sensing devices. 
     It is yet another feature of the present invention to include electro-optical sensing devices for detecting and measuring undesired image displacement. 
     It is yet another advantage of the present invention to provide a fully functional tiled projection display system which is capable of in-flight adjustment to compensate for misalignment. 
     It is yet another advantage of the present invention to provide misalignment correction in an automated manner that eliminates manual alignment operations. 
     It is still yet another feature and advantage of the present invention to provide a means for mechanically-isolated, independently mounted projectors and display screens. 
     It is still yet another advantage of the present invention to provide for easy mounting of aligned systems. 
     The present invention is an apparatus and method for aligning tiled projection images, which is designed to satisfy the aforementioned needs, provide the previously stated objects, include the above-listed features and achieve the already articulated advantages. The present invention is carried out in a “misaligned image-less” manner in a sense that the time that a misalignment condition is allowed to exist has been greatly reduced. 
     Accordingly, the present invention is a tiled projection display system which utilizes a multi-axis adjustable optical beam deflector. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention may be more fully understood by reading the foregoing description of the preferred embodiments of the invention, in conjunction with the appended drawing wherein: 
     The FIGURE is a simplified schematic diagram of a tiled projection image system of the present invention, showing light emanating from the projectors and beam deflectors as solid lines and with the dotted lines used to show a viewing angle of a camera. The projectors illuminate the viewing screen, while the camera simultaneously views the resulting composite image. 
    
    
     DETAILED DESCRIPTION 
     Now referring to the drawing wherein like numerals refer to like matter throughout, there is shown a system of the present invention, generally designated  100 , having a first projector  110  and a second projector  120 , which may be any type of projector used for projecting portions of a tiled image, such projectors being well known in the art. The description herein focuses upon a multiple projector system which is believed to be a common design choice. However, it is understood that use of a single projector is also contemplated by this invention, and the multi-projector description is merely an example of various possibilities. Projectors  110  and  120  generally emit light to form a portion of an image  160  and  170  respectively. Images  160  and  170  may be projected on to various types of viewing surfaces which are well known in the art, such as a diffuser disposed in the instrument panel of an aircraft. The diffuser or other optical device is chosen to provide a wide or tailored viewing angle to facilitate in some designs a simultaneous cross-cockpit viewing from multiple members of the flight crew and in others, a highly focused high gain display. In the present invention, we show a tiled display with separate viewing surfaces for images  160  and  170 . However, in some circumstances, it may be desirable to superimpose both images onto one screen. The images may be identical, and the superimposition may provide for redundancy and increased brightness, etc. The present invention is intended to include superimposed displays despite the references herein to tiled displays. Tiled displays are merely an example of various types, including superimposed and others. Disposed between projectors  110  and  120  and their respective viewing surfaces are beam deflectors  112  and  122  respectively. Beam deflectors  112  and  122  may be any type of optical element capable of repositioning the projected images  160  and  170  respectively, in a controllable fashion. One type of optical element that may be particularly useful for beam deflectors  112  and  122  is a relatively thick piece of transparent glass with flat, parallel faces. Because of the flat parallel faces, the glass “plate” would have zero optical power. It is well known that such glass plates will deflect an optical beam when the plate is tilted with respect to the beam direction. The amount of deflection is determined by the thickness of the plate (t), angle of incidence (θ) and index of refraction of the plate (n), according to the formula:        d   =         t      sin     [       θ   i     -       sin     -   1            (         sin      θ     i     n     )         ]     /     cos        [       sin     -   1            (         sin      θ     i     n     )       ]                                
     This equation describes the deflection in one direction only. It can be extended to two dimensions for glass plates or beam deflectors which are capable of two dimensional motion. In a preferred embodiment, beam deflectors  112  and  122  each include a two axis gimbal which are capable of horizontally deflecting the images  160  and  170 , respectively by rotation around vertical axes  114  and  124  respectively. Vertical deflections of the images  160  and  170  can be achieved by rotating the beam deflectors  112  and  122 , respectively about horizontal axes  116  and  126 . In a preferred embodiment, the beam deflectors  112  and  122  are capable of automatic self-adjusting for any misalignment that may occur during operation of the system  100 . A preferred system may include some means for electronically controlling the beam deflectors  112  and  122 , which is represented in the FIGURE as a control block  130  for controlling gimbal drives  140 , which may be a well-known electromechanical device coupled to the beam deflectors  112  and  122  by any appropriate connection means. The control block  130 , and the gimbal drives  140  and the connections with each other and the beam deflectors are well known in the art. A camera  180  is shown coupled to control block  130 . Camera  180  is also well known in the art and is used to monitor the alignment of images  160  and  170 . The camera  180  may also detect infrared registration information or fiducial marks projected along with the desired image to aid in image alignment. Control block  130  may receive a signal from the camera  180  and process it to determine the existence, extent and direction of any misalignment of images  160  and  170 . The circuitry or software for such detection is well known in the art, and it may be located in the camera  180  itself or in a central control block  130  or in any other configuration, such as in the projectors  110  and  120  or distributed among them and other control devices. 
     In an alternate embodiment, one of the beam deflectors may be omitted or may be a stationary glass plate without any gimbal and gimbal drive and which is not coupled to the camera  180 . The alignment could be completely achieved by manipulation of the other beam deflector only. This could achieve a cost and weight savings. This stationary glass plate would be optically identical to the gimballed beam deflector and, therefore, would maintain equal optical path lengths from projectors  110  and  120  to images  160  and  170 . The maintenance of equal optical path lengths should provide for less aberration correction than otherwise might occur with unequal optical path lengths. In an alternate embodiment, the beam deflectors  112  and  122  may be incorporated into their respective projectors  110  and  120  and may be located either between the projection optics of the projectors, not shown, and the images  160  and  170  (as shown in the FIGURE) or between the projection optics and an image source, not shown, in the projector. The exact implementation details may vary, depending upon the particular needs of the system and the customer and the component parts chosen by the designer and or customer. 
     In operation, the apparatus and method of the present invention could function as follows: 
     An image to be projected upon a display surface is determined, the image is projected by at least two projectors, each projecting a separate portion of the tiled image, a camera or other detector is used to monitor the alignment of the separate portions to assure that no gaps or overlapping occurs. This monitoring can be done with a servo loop feedback type arrangement where the images are moved in a predetermined manner and the motion is monitored and controlled to minimize gaps and overlapping of the separate portions. The motion of the images is achieved by manipulating, in one or more dimensions, a rotation of one or more of the beam deflectors  112  and  122 . When a misalignment occurs, the situation will be detected by the above-described monitoring function and will be corrected as part of the monitoring function. The projectors  110  and  120  and control block  130  may be coupled to flight control computers or inertial reference systems on-board the aircraft (not shown). The image to be displayed, the algorithms that control movement of gimbals, and how the image is displayed may be changed as a function of the operation of the aircraft. For example, if the aircraft is involved in landing maneuvers or is being subjected to high forces, then the image to be displayed may be altered or the system or method for monitoring the alignment of the tiled images may be adjusted. Other operational schemes can be utilized as well. 
     It is thought that the method and apparatus of the present invention will be understood from the foregoing description and that it will be apparent that various changes may be made in the form, construct steps and arrangement of the parts and steps thereof without departing from the spirit and scope of the invention or sacrificing all of their material advantages. The form herein described is merely a preferred exemplary embodiment thereof.