Patent Publication Number: US-6222514-B1

Title: Fault tolerant intersecting beam display panel

Description:
REFERENCE TO RELATED APPLICATIONS 
     This is a continuation-in-part of U.S. patent application Ser. No. 09/301,470 filed Apr. 28, 1999 entitled Pixel Brightness Control for and Intersecting Beam Phosphorous Display which is a continuation-in part of U.S. patent application Ser. No. 08/872,262 filed Jun. 10, 1997 now U.S. Pat. No. 6,031,511. 
    
    
     FIELD OF THE INVENTION 
     The present invention pertains to a system for producing images, and more particularly, to a display system having redundant components. 
     BACKGROUND OF THE INVENTION 
     Television receivers and other display systems use a cathode ray tube having a fluorescent coating deposited on a slightly curved screen inside the tube. In a black and white tube an electron gun directs a beam of electrons toward the screen with the electron beam being scanned over the surface of the screen by vertical and horizontal deflection systems. A control grid varies the amount of current in the beam to vary the brightness of different areas on the screen. In a color tube a trio of beams are each intensity controlled and each beam is directed toward one of three colors of phosphor on the screen. However, in both black and white and in color television the image can be viewed only from the front of the screen, which is opposite from the side of the screen containing the phosphor. Further, the electron gun requires that a cathode ray tube display system be thick. And still further, the display is constructed of a rigid glass to facilitate direction of the electron beam upon the phosphor. 
     More recent flat panel displays have significantly reduced the thickness of display systems. Liquid Crystal Display (LCD) systems require individually electrically addressable pixels on the display surface which are switched between transparent and opaque states. The pixels gate light generated typically from an electroluminescence light panel in order to generate the display. Such displays require complex circuitry to activate each pixel, and are visible typically from the side opposite to the electroluminescence panel. 
     U.S. Pat. No. 4,870,485 to Downing; Elizabeth A., et. al., Sep. 26, 1989, entitled: THREE DIMENSIONAL IMAGE GENERATING APPARATUS HAVING A PHOSPHOR CHAMBER, hereby incorporated by reference, describes a three dimensional image generating apparatus having a three dimensional image inside an image chamber. Such a system has been publicly demonstrated. An imaging phosphor distributed through the image chamber is excited by a pair of intersecting laser beams which cause the phosphor to emit visible light and form an image as the intersecting beams move through the image chamber. The imaging phosphor is a rapidly-discharging, high conversion efficiency, electron trapping type which stores energy from a charging energy beam for a very short time, such as a few microseconds. The imaging phosphor releases photons of visible light when energy from a triggering energy beam reaches phosphor containing energy from the charging beam. This triggering results in radiation of visible light from each point where the charging energy beam crosses the triggering energy beam. A first scanning system directs the charging energy beam to scan through a space in the image chamber and a second scanning system directs the triggering energy beam to scan through space in the image chamber. These two energy beams intersect at a series of points in space to produce a three dimensional image inside the image chamber. The energy beams are provided by a pair of lasers with one beam in the infrared region and the other in the blue, green, or ultraviolet portion of the spectrum. However, an electromechanical mirror based beam steering mechanism makes the display bulky, subject to vibration of the display and the glass cube is rigid. 
     Thus, what is needed is a thin flexible display panel having multi-color light generating pixels which may be viewed from either side of the panel and requires no moving parts to generate the display. Furthermore, what is need is a method and apparatus for controlling the brightness of pixels comprised within such a display. 
     Pen-link pointing devices are used in many applications to facilitate a user&#39;s interface with a computer via the computer display and are currently widely used in hand held personal computers (HPC). Other applications use CRT displays for such an interface. Most pen pointing devices require a means separate from the display to determine the location of the pen or other pointing device relative to the display. In most HPCs, the separate means takes the embodiment of a touch sensitive film placed over the display. 
     These films add cost to the product and provide an additional opportunity for failure of the device. Flexible LCDs are being produce for additional display applications and further complicates the use of a pointing device in conjunction with the display because touch sensitive film tends to falsely respond to flexing of the display. Furthermore, most current displays, including LCDs and CRTs are fragile and require a clear protective layer, such as a resilient plastic or glass be placed between the display surface and a pen-like pointing device in order to protect the display from damage by the pen-like pointing device. This additional protective layer separates the tip of the pointing device from the display increasing a parallax affect from the perspective of the user. Thus, what is needed is a display and a pen-like pointing device that can be used without additional locating means such as a touch sensitive film, and that reduces parallax when used. 
     There are many display applications where fault tolerance and high reliability are essential. Such applications include medical, military, aircraft and spacecraft applications where a failure of a display may prove critical or even fatal. The reliability of many systems is improved by adding redundancy, that is duplicating active circuitry wherein redundant circuitry continues operating in event of failure. Redundant display technology is exceedingly difficult to realize in ordinary CRT and LCD applications because of the characteristics of the display technology. Thus, what is needed is a display system having redundant active components capable of continuing operation of the display system in the event of failure of active components of the system. 
     SUMMARY OF THE INVENTION 
     A display apparatus comprises a panel having a display surface surrounded by an edge and an imaging phosphor therein. A first source for radiating a first energy beam enters through a first portion of the edge, a second source for radiating a second energy beam enters through a second portion of the edge, and a third source for radiating a third energy beam enters through a third portion of the edge. A first pixel of visible light energy is released by the imaging phosphor at an intersection of the first and third energy beams, and a second pixel of visible light energy is released by the imaging phosphor at an intersection of the second and the third energy beams, the first and second pixels of visible light having a substantially constant location on the display surface. Pixel brightness may be varied by varying the timing of the energy beams. 
     It is an object of this invention to provide a method for driving an intersecting beam display comprising the steps of sequentially enabling radiation of each of a plurality of substantially non-intersecting energy beams from a first source, and thereafter sequentially enabling radiation of each of a plurality of substantially non-intersecting energy beams from a second source wherein energy beams from the first source intersect with energy beams from the second source. 
     It is an object of this invention to provide a pointing device for indicating a location on an intersecting beam display radiated by a multiplicity of beams having first and second wavelengths to produce pixels of light having at least a third wavelength comprising a first determining means for determining reception of radiation at the first wavelength, and a second determining means for determining reception of radiation of the second wavelength. 
     It is an object of this invention to provide a method of driving an intersecting beam display comprising the steps of: radiating a first energy beam into an intersection; radiating a redundant energy beam into the intersection; and radiating a third energy beam into the intersection, wherein a first pixel of visible light occurs at an intersection of the first, redundant and third energy beams and the first pixel of visible light occurs independent of a failure of either the first or redundant energy beams. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 shows a display apparatus having a display panel excited by sources radiating energy beams. FIG. 1 also shows a display apparatus having redundant switching means, redundant row sources, and redundant column sources. 
     FIG. 2 shows a display apparatus having a panel composed of orthogonal layers of parallel wave guides having reflectors at an end and an imaging phosphor layer interposed between. 
     FIG. 3 shows an intersection of two wave guides of FIG.  2  and the imaging phosphor there between. 
     FIG. 4 shows a panel of display fabric having a plurality of parallel fiber optic threads woven orthogonal to another plurality of parallel fiber optic threads, wherein pixels of light are generated by imaging phosphor at intersections of the threads. 
     FIG. 5 shows a perspective view of the display fabric panel of FIG.  4 . 
     FIG. 6 shows a more detailed block diagram of functions included in a display generator and a switching means operating in accordance with the present invention. 
     FIG. 7 shows a timing diagram of energy beams driven by the switching means for creating a matrix of four pixels of varying brightness. 
     FIG. 8 shows an alternate timing diagram of energy beams driven by the switching means for controlling brightness of two pixels in a pixel matrix. 
     FIG. 9 shows a perspective view of the intersecting beam phosphorous display with a pen-like pointing device. 
     FIG. 10 shows a block diagram of the intersecting beam phosphorous display with the pen-like pointing device. 
     FIG. 11 shows a timing diagram of row and column energy beam radiation as well as pixel illumination in accordance with the present invention. 
     FIG. 12 shows a block diagram of the fault tolerant display system operation in accordance with the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     This is a continuation-in-part of U.S. patent application Ser. No. 09/301,470 filed Apr. 28, 1999 entitled Pixel Brightness Control for and Intersecting Beam Phosphorous Display which is a continuation-in-part of U.S. patent application Ser. No. 08/872,262 filed Jun. 10, 1997, both are hereby incorporated by reference. 
     FIG. 1 shows a display apparatus having a display panel excited by sources radiating energy beams. The display panel  10  has an edge  12  surrounding it on all sides. The display panel is preferably substantially transparent to visible light and has imaging phosphor distributed therein. A first source  20  radiates a first energy beam  22  into a first portion of edge  12 . A second source  30 , preferably having a wavelength substantially similar to that of source  20 , emits a second energy beam  32  into a second portion of edge  12 . A third source  40 , preferably having a different wavelength from sources  20  and  30 , radiates a third energy beam  42  into a third portion of edge  12 . 
     Sources  20  and  30  may represent either triggering or charging energy beams and source  40  may represent either a charging or triggering energy beam respectively, such that the imaging phosphor releases visible light energy when energy from a triggering energy beam reaches phosphor containing energy from a charging energy beam. 
     A first pixel of visible light energy  52  is released by the imaging phosphor at intersection of the first energy beam  22  and the third energy beam  42 , and a second pixel of visible light energy  53  is released by the imaging phosphor at intersection of the second energy beam  32  and the third energy beam  42 . The first and second pixels of visible light have a substantially constant location on the display surface of panel  10 . Numerous additional pixels  54  may be added by adding additional sources including sources  55  and  56 . Sources  20 ,  30 ,  40 ,  55  and  56  may be realized by lasers or solid state diodes emitting energy beams at appropriate charging and triggering wavelengths. 
     A switching means  60  is coupled to at least the first, second and third sources,  20 ,  30  and  40 . The switching means is responsive to a display generator  62  which generates a display signal for selectively activating at least the first and second pixels,  52  and  53 . Display generator  62  may be any of numerous display generators known in the art including either a television receiver or a personal computer. The switching means  60  enables the first and third energy beams  22  and  42  in response to the display signal indicating activation of the first pixel  52 , and enables the second and third energy beams  32  and  42  in response to the display signal indicating activation of the second pixel  53 . The switching means  60  enables the first, second and third energy beams,  22 ,  32  and  42  in response to the display signal indicating activation of the first and second pixels  52  and  53 . Activation of a energy beam may be either by providing energizing power to its respective source, or a switching a shutter at the output of the respective source. Numerous additional pixels  54  may be selectively activated by coupling switching means  60  to additional sources, such as sources  55  and  56  and enabling the respective energy beams in a corresponding way. 
     The display apparatus of FIG. 1 has an advantage in that the alignment of panel  10  relative to sources  20 ,  30 ,  40 ,  55  and  56  is not critical so long as the corresponding energy beams are radiated within panel  10 . The pixel location is defined by the intersection of the energy beams within the panel, not necessarily the alignment of the panel relative to the sources. This has the advantage of reducing precision manufacturing of the display apparatus. Further, panel  10  can be a relatively thin layer of glass or flexible plastic, and since no electrical wiring connection is necessary within the panel to activate pixels, the cost of the panel may be significantly reduced. Since the pixel density and display size is determined by the number and placement of the sources, and since the sources may be made from low cost high density solid state diodes, a large size, high pixel density flat panel display can be made. Since each pixel radiates light out of either surface of the panel, a display produced by the display apparatus may be viewed from either side of the panel. 
     FIG. 2 shows a display apparatus having a panel composed of orthogonal layers of parallel wave guides having reflectors at an end and an imaging phosphor layer interposed between. Panel  100  comprises a first layer having a first multiplicity of substantially parallel wave guides  70 - 79 , for channeling energy beams  22 ,  32  and  57 , and a second layer having a second multiplicity of substantially parallel wave guides for channeling energy beams  42  and  58 . The wave guides limit dispersion of the energy beams within the layer with a smooth internally reflective surface which enables internal reflection of energy beams thereby also limiting dispersion and intersection of energy beams within the layer. The layers of FIG. 2 may be comprised of numerous laminated fiber optic pipes. An imaging phosphor layer  90  interposed between the first layer  70 - 79  and second layer  80 - 88  has the imaging phosphor distributed there through. Sources  20 ,  30  and  55  are coupled to apertures at one end of the wave guides of the first layer  70 - 79  and reflector  92  is coupled to apertures at the other end of the wave guides  70 - 79 . Sources  40  and  56  are coupled to apertures at one end of the wave guides  80 - 88  of the second layer and a reflector  94  is coupled to apertures at the other end. While the sources  20 ,  30 ,  40 ,  55  and  57  and reflectors  92  and  94  are shown a distance from their respective layers for illustrative purposes, they are preferably attached to apertures at the end of the wave guides of the perspective layers. 
     In FIG. 2, source  20  radiates and energy beam  22  substantially into wave guide  78 , source  30  radiates energy beam  32  substantially into wave guide  71 , source  40  radiates energy beam  42  substantially into wave guide  82 , source  55  radiates energy beam  57  substantially into wave guide  75 , and source  56  radiates energy beam  58  substantially into wave guide  85 . The panel of FIG. 2 maintains the advantage that the alignment of the sources with the panel is not critical because a pixel of light is formed at an intersection of the energy beams. For example, energy beam  32  could be conducted not only by wave guide  71 , but by adjacent wave guides  70  or  72  without interference from adjacent energy beam  57  and while further maintaining substantially constant pixel location on the surface of panel  100 . The panel of FIG. 2 has the further advantage in that if the energy beams have a tendency to disperse or spread out as they travel further from the source, the wave guide will tend to limit the dispersion to within itself. Thus, a pixel generated farther from the source, will have substantially the same size as a pixel generated close to the source because the size is substantially determined by the dimensions of the wave guide rather than the dispersion characteristics of the charging and triggering energy beams. 
     The panel of FIG. 2 has a further advantage in that the reflector at the end of the wave guide tends to compensate for any attenuation of the energy beam by the wave guide. The sum of the power of energy beam originated from the source plus the power of the energy beam reflected by the reflector should result in a more constant distribution of power through the wave guide. This will help assure a more even brightness of pixels across the panel. 
     Another advantage of the panel of FIG. 2 is that the parallel nature of the wave guides reduces the requirement of parallel alignment of energy beams generated by the sources of one layer relative to each other, for example the parallel alignment of energy beams  22 ,  32  and  57  relative to each other, and energy beams  42  and  58  relative to each other necessary to produce evenly spaced pixels is reduced because the wave guides tend to assure the parallel nature of the energy beams even though the respective sources may not accurately generate parallel energy beams. Furthermore, the orthogonal alignment of energy beams of the two layers is reduced, for example the intersection of wave guides  70 - 79  with wave guides  80 - 88  assure an evenly space matrix of pixels without a critical orthogonal alignment of energy beams  22 ,  32  and  57  with energy beams  42  and  58 . This should significantly reduce precision manufacturing of the invention. Further, wave guides  70 - 79  and  80 - 88  may be made of an identical laminated optic material and rotated 90 degrees at the time of assembly. 
     FIG. 3 shows an intersection of two wave guides of FIG.  2  and the imaging phosphor there between. Wave guide  71 , which conducts energy beam  32  intersects with wave guide  82  which conducts energy beam  42 . Wave guides  71  and  82  may be representative of all wave guides of FIG.  2 . Wave guides  71  and  82  are shown to have hash marks or a shaded side on one surface indicating that surface is etched or made unsmooth to facilitate the energy beam of the wave guide to intersect with energy beams of wave guides of other layers. The remaining surface of the wave guide is smooth to facilitate internal reflection of an energy beam within the wave guide. As energy beam  32  it transmitted through the etched surface of wave guide  71 , it intersects with portions of energy beam  42  transmitted through the etched surface of wave guide  82 . At intersection  53  of both wave guides, the imaging phosphor layer  90  receives radiation from both charging and triggering energy beams and thus illuminates visible light. This produces a pixel having a well defined location on the surface of panel  100  of FIG. 2 due to the orthogonal relationship of the wave guides. 
     In alternate embodiments, the phosphor of the imaging phosphor layer could be incorporated into either or both the wave guides layers, thereby eliminating the need for a separate imaging phosphor layer. Furthermore color displays may be made by stacking multiple panels  100  and their associated energy beam sources, each panel capable of generating a different color of light. For example three panels, having red, green and blue pixels respectively, would produce colors commonly used in television and personal computer applications. 
     Alternately, individual wave guides could cause generation of pixels of various colors: a first compound would be distributed within one wave guide for generating a first pixel with a first color of visible light energy and a second compound distributed within another wave guide for generating the second pixel with a second color of visible light energy. For example, each wave guide could have a compound to filter light color generated by the imaging phosphor layer. For example, wave guide  78  could be tinted to allow red light to pass, while wave guide  74  could be tinted to allow green light to pass and wave guide  71  could be tinted to allow blue light to pass. In such a case, the intervening wave guides  70 ,  72 ,  73 ,  75 ,  76 ,  77  and  79  could be eliminated, combined or made redundant to an appropriate adjacent wave guide. In another example, imaging phosphor compounds could be made to generate predominantly one color of light and then dispersed through a wave guide. For example, a red imaging phosphor could be distributed in wave guide  78 , a green imaging phosphor distributed in wave guide  74  and a blue imaging phosphor distributed in wave guide  71 , this allows both the generation of color pixels and the illumination of imaging phosphor layer  90 . Finally the energy beams themselves could be modified to make a common phosphor generate various colors of light pixels. Thus, red, green and blue pixels may be generated, allowing the display panel to generate color displays. The intensity of each pixel may be varied by varying the intensity or duration of either the charging or triggering energy beam, or both. 
     FIG. 4 shows a panel of display fabric having a plurality of parallel fiber optic threads woven orthogonal to another plurality of parallel fiber optic threads, wherein pixels of light are generated by imaging phosphor at intersections of the threads. Display panel  200  is comprised of a multiplicity of substantially parallel fiber optic wave guides, including  222 ,  232  and  257 , orientated orthogonal to a second multiplicity of substantially parallel fiber optic wave guides, including  242  and  258 . Light generating pixels occur at intersections of the fiber optic threads, such as pixel  53 , resulting from a light emitting phosphor being charged and triggered by energy beam sources  20  and  40  as previously described. 
     FIG. 5 shows a perspective view of the display fabric panel of FIG.  4 . Pixel  53  is generated by and intersection of energy beams of fiber optic wave guides  242  and  222 . Wave guide fiber optic thread  242  has a surface  245  for facilitating intersection of its energy beam with energy beams of orthogonal wave guides such as fiber optic wave guide  222 . The remaining surface of fiber optic thread  242  facilitates energy beam internal reflection. Similarly, wave guide fiber optic thread  222  has a surface  225  for facilitating intersection of its energy beam with energy beams of orthogonal wave guides such as fiber optic wave guide  240 . The remaining surface of fiber optic thread  240  facilitates energy beam internal reflection Surfaces  245  and  225  may be etched or non-smooth to facilitate energy the intersection of energy beams at pixels  53  and  54 . Light emitted from pixels may be generated by illuminating phosphor deposited at the intersection of threads  222  and  242 . Alternately either or both fiber optic wave guide threads  222  and  242  may have illuminating phosphor distributed there through. The intersection forming pixels  53  and  54  may be made by a friction fit due to the weaving of flexible fiber optic threads or by fusing the fiber optic threads together at the pixel intersections. Alternately, if a fusing technique is used, a round fiber optic thread may be used, as the fuse between the threads will facilitate the intersection of energy beams of the threads to produce a pixel. 
     Referring back to FIG. 4, display panel  200  may generate color images by adding compounds to wave guide threads. For example, as previously described, a phosphor radiating a predominant red, green and blue color could be added to wave guide fiber optic threads  222 ,  257  and  232  respectively. Alternately the wave guides could be tinted, or the corresponding energy beam sources could be modified to modulate the color of a pixel. Furthermore, reflectors could be added an end of each wave guide thread to compensate for energy beam attenuation as previously described. 
     The panel of FIG. 4 has the advantage of being composed of thin flexible fiber optic threads, and thus as a panel, it is thin and flexible similar to a cloth. Since fiber optic threads are thin, the pixel density of the panel may be relatively high. And as previously described, panel  200  may produce color images. Pixels of panel  200  can radiate light from both sides of the panel. Further, as previously described, energy beam sources  20 ,  30 ,  40 ,  55  and  56  may be solid state diodes, consequently no moving parts are needed to produce an image on panel  200 . 
     Although the wave guides of FIGS. 2,  3 ,  4  and  5  show a perpendicular orientation between wave guides to form intersections defining pixels, the orthogonal relationship of the wave guides of the contemplated invention is not limited to a perpendicular configuration. The orthogonal relationship of the wave guides include any non-parallel relationship or a relationship between the wave guides which form an intersection such that illuminating phosphor may be radiated by charging and triggering energy beams. 
     FIG. 6 shows a more detailed block diagram of functions included in display generator  62  and switching means  60  of FIG.  1 . Display generator  62  includes a pixel memory  301  which contains pixel brightness signals having numerical values indicative of brightness of pixels to be displayed on a display. Switching means  60  acts as a fundamental component of a pixel brightness control means. Switching means  60  includes a row driver  302  for timing the occurrence of energy beams in rows of the display panel, such as energy beams created by aforementioned sources  20  and  30  with timing information from timing means  306  to generated pixel brightness indicated by the pixel memory. Switching means  60  includes a column driver  304  for timing the occurrence of energy beams in columns of the display panel, such as energy beams created by aforementioned sources  40  and  56  with timing information from timing means  306  to generate pixel brightness indicated by the pixel memory. The timing occurrence of an energy beam may be accomplished in a number of ways including switching the energy beam source off and on, activating a shutter associated with the source or steering an energy beam into and out of the intersection with a beam steering device. In a preferred embodiment, an energy beam radiating a row of the display panel is radiated for a predetermined time. During that predetermined time all of the column energy beams are radiated to cause pixels within the row to be illuminated. The duration of each column energy beam is modulated to set the desired brightness of each pixel of the row. Thereafter, another row energy beam is radiated for the predetermined time and the column energy beams are radiated to set the brightness of each pixel of the row. This process continues until all of the pixels of the display are illuminated, the process then repeats, creating the appearance of a continuously variable moving display on the display panel, similar to the image displayed on a CRT of a computer or television. 
     FIG. 7 shows a timing diagram of energy beams driven by the switching means for creating a matrix of four pixels of varying brightness. Line  320  indicates that the energy beam from aforementioned source  20  is radiating a first row on the display panel from events  360  to  366 . Line  330  indicates that source  30  is off from events  360  to  366 . Line  340  indicates that an energy beam from source  40  is radiating a first column on the display panel from events  360  to  362 . During this time, a pixel is formed on the display panel at the intersection of energy beams from sources  20  and  40 . Line  340  further indicates that an energy beam from source  40  is off for the duration of the energy beam from source  20 . The energy beam from source  40  is on for substantially 50% of the time that the column energy beam from source  20 . Thus the pixel occurring at the intersection of the two beams from sources  20  and  40  will be substantially half the brightness of the pixel if the beam from source  40  was on for the entire duration of the beam from source  20 . 
     Line  356  indicates the beam from aforementioned source  56  is on and radiating a second column on the display panel from events  364  to  366 . During this time, a second pixel is formed on the display panel at the intersection of energy beams from sources  20  and  56 . Line  356  further indicates that an energy beam from source  56  is off from events  360  to  364 . The energy beam from source  56  is on for substantially 25% of the time that the column energy beam from source  20 . Thus the pixel occurring at the intersection of the two beams from sources  20  and  56  will be substantially one quarter the brightness of the pixel if the beam from source  56  was on for the entire duration of the beam from source  20 . Thus, the brightness of the aforementioned pixel from source  40  is brighter than said pixel from source  56 . 
     Line  320  further indicates that the energy beam from source  20  is off after event  366 . Line  330  indicates that source  30  is radiating a second row on the display panel from events  366  to  372 . Line  340  indicates that an energy beam from source  40  is radiating the first column on the display panel from events  366  to  370 . During this time, a third pixel is formed on the display panel at the intersection of energy beams from sources  30  and  40 . Line  340  further indicates that an energy beam from source  40  is off for the duration of the energy beam from source  30 . The energy beam from source  40  is on for substantially 75% of the time that the column energy beam from source  30 . Thus the pixel occurring at the intersection of the two beams from sources  30  and  40  will be substantially three fourths the brightness of the pixel if the beam from source  40  was on for the entire duration of the beam from source  30 . 
     Line  356  indicates the beam from an energy beam from source  56  is on and radiating the second column on the display panel from events  366  to  368 . During this time, a fourth pixel is formed on the display panel at the intersection of energy beams from sources  30  and  56 . Line  356  further indicates that an energy beam from source  56  is off after event  368 . The energy beam from source  56  is on for substantially 12.5% of the time that the column energy beam from source  20 . Thus the pixel occurring at the intersection of the two beams from sources  30  and  56  will be substantially one eighth the brightness of the pixel if the beam from source  56  was on for the entire duration of the beam from source  20 . 
     FIG. 7 shows energy beam timing control for creating on the display panel four pixels of differing brightness by the intersection of constant intensity energy beams from two column sources and two row sources. In this embodiment, the energy beams from the row sources are periodically radiated at predetermined rates while the timing of the duration of energy beams from the column sources are varied in order to set the desired brightness of each pixel. The number of pixels may be substantially increased by increasing the number of row and/or column energy beams, wherein rows are sequentially, or otherwise, radiated with row energy beams of predetermined duration while variable brightness pixels of the row are created by variable duration radiation from column energy beams. By rapidly repeating timings of the row and column drives, the appearance of a moving image may be created on the display panel. 
     FIG. 8 shows an alternate timing diagram for controlling brightness of two pixels in a pixel matrix. Line  420  indicates that the energy beam from aforementioned source  20  is radiating a first row on the display panel between events  460  and  476 . Line  440  indicates that an energy beam from aforementioned source  40  is radiating a first column on the display panel between events  460 - 462 ,  464 - 466 ,  468 - 470 ,  472 - 474 . During these times, a pixel is formed on the display panel at the intersection of energy beams from sources  20  and  40 . The duty cycle of line  440  further indicates that the energy beam from source  40  is on for substantially 50% of the time that the column energy beam from source  20 . Thus the pixel occurring at the intersection of the two beams from sources  20  and  40  will be substantially half the brightness of the pixel if the beam from source  40  was on for the entire duration of the beam from source  20 . 
     The pixel generated by energy beams controlled in accord with lines  420  and  440  has a similar brightness to the pixel generated by energy beams of lines  320  and  340  of FIG. 7, except that the illumination of said pixel of FIG. 8 is distributed substantially over the entire duration of the row energy beam of line  420 , while said pixel of FIG. 7 is one for the first half of the duration of the row energy beam of line  320 . 
     Lines  456 A,  456 B and  456 C show different energy beam duty cycles for controlling an energy beam from aforementioned source  45 . A pixel is generated at the intersection of the row energy beam from source  20  and column energy beam from source  56 . The duty cycles are 50%, 75% and 25% respectively. Line  456 A is the inverse of line  440  resulting in a pixel at the intersection of energy beams from sources  20  and  56  which is on for 50% of the time and is off while the pixel of FIG. 8 from intersection of energy beams from sources  20  and  40  is on and visa versa. This has the advantages of not only spreading the illumination of the pixel for the duration of the energy beam from source  20  but also operates the pixels in a relatively complementary fashion. Lines  456 B and  456 C show variations in duty cycle from 75% on to 25% on, respectively, relative to line  456 A. The variations in duty cycle vary the duration of occurrence of the energy beam. The corresponding pixel formed at the corresponding intersection would have substantially 75% and 25% brightness. 
     Thus, FIG. 8 shows an alternate method for controlling the brightness of pixels formed on the display panel using a variable duty cycle on one of the energy beams used to form the pixel. It should be appreciated that while duty cycle variations is described in the intersection of a plurality pixels and a multiplicity of energy beam sources, the method can also be used to govern the brightness of any two energy beams for creating visible light as a result of their intersection. 
     FIG.  7  and FIG. 8 shows a first source column for radiating a first energy beam through a first portion of the edge for a first duration, a second column source for radiating a second energy beam through a second portion of the edge for a second duration less than the first duration, and a row source for radiating a third energy beam through a third portion of the edge for a third duration inclusive of the first and second durations. The methods of FIG.  7  and FIG. 8 have the advantage of providing for energy beams of constant intensity and variable duration, thereby avoiding the problem of designing energy beams sources capable of producing variable intensity energy beams to control pixel brightness. The methods of FIG.  7  and FIG. 8 describe varying pixel brightness, in the preferred embodiment the pixel brightness is varied in response to pixel brightness signals in the pixel memory. The brightness may additionally be varied in a predetermined way to compensate for bright and dark areas on the display as a result of manufacturing and other process variations. 
     Returning to FIG. 4, as previously described, a multiple color display “fabric” may be made by including a differing color phosphor in at least two wave guide fiber optic threads of the display fabric. In this way a multitude of colors may be produced by a grouping of pixels of differing colors. It is desirable to keep a common sized wave guide fiber optic thread dimension, or thread thickness. When using the aforementioned row and column drivers of FIG. 6, the resulting pixel grouping is irregularly shaped in that it length is different from its width. For example, a pixel grouping of red, green and blue pixels is formed by the intersection column save guide fiber optic threads of sources  40 ,  56  and  500 , respectively and row wave guide fiber optic threads of source  20 . In order to make the pixel grouping uniform in shape, that is the length and width the same, and in order to make the wave guide fiber optic threads of the same thickness, the grouping could be expanded to include an equal number of rows and columns. In a red, green blue (RGB) example, a red pixel is formed by the intersection of any row wave guide with a column wave guide associated with either sources  40  or  502 , a green pixel is formed by the intersection of any row wave guide with a column wave guide associated with either sources  56  or  504 , and a blue pixel is formed by the intersection of any row wave guide with a column wave guide associated with either sources  500  or  506 . A regularly shaped pixel grouping would be made by simultaneously driving sources  20 ,  55  and  30  as one row and  510 ,  512  and  514  as another row. In this way, four regularly shaped RGB pixel groupings may be formed from the sources identified in FIG.  8 . The first pixel is generated by the intersection of row sources  20 ,  55  and  30  and RGB column sources  40 ,  56  and  500 . The second pixel is generated by the intersection of row sources  20 ,  55  and  30  and RGB column sources  502 ,  504  and  506 . The third pixel is generated by the intersection of row sources  510 ,  512  and  514  and RGB column sources  40 ,  56  and  500 . The fourth pixel is generated by the intersection of row sources  510 ,  512  and  514  and RGB column sources  502 ,  504  and  506 . The brightness of pixels of the pixel group may be controlled using the aforementioned switching means of FIG.  6 . 
     Thus what is provided is a thin flexible display panel having multi-color light generating pixels which may be viewed from either side of the panel and requires no moving parts to generate the display. Furthermore, what is provided is a method and apparatus for controlling the brightness of pixels comprised within such a display, as well as a way to create regularly dimensioned pixel groupings capable of producing multiple colors with a common sized wave guide. 
     FIG. 9 shows a perspective view of the intersecting beam phosphorous display with an pen-like pointing device. The display panel  600  is operationally similar to aforementioned display panels  10 ,  100  or  200 . The display panel is driven by row and column sources  602  and  604  which include aforementioned row sources  20 ,  55 ,  30 ,  510 ,  512  and  514  and the aforementioned column sources column sources  40 ,  56 ,  500 ,  502 ,  504  and  506 . The aforementioned switching means  60  and display generator  62  may be comprised within block  606 . A pen-like pointing device  610  is coupled to block  606  with a cable  612 . In an alternate embodiment the interface to the pen may be wireless. The pen has a tip which is shown to be in substantial contact with the display  600  at a location  620  having a row and column axis of “X” and “Y” respectively. The row and column axis are also indicative of corresponding row and column energy beams having an intersection substantially at location  620  and the tip of the pen on the display panel. 
     FIG. 10 shows a block diagram of the intersecting beam phosphorous display with the pen-like pointing device and includes the corresponding items of FIG.  9 . Pen  610  has row and column receivers  632  and  634  for receiving energy beams from row and column drivers  602  and  604 . Location determining means  640  compares the timing of signals received from the row and column receivers with the timing signals generated by timing means  306  to determine the location of the pen on the display. In response to the determined location, pixel modifier  642  modifies the color and/or brightness of pixels substantially at the determined location resulting in, among other things know in the art, electronic ink. This give the user the impression that the pen  610  is enabling writing on the display  600  in much the same way that a familiar ink pen enables writing on paper. 
     FIG. 11 shows a timing diagram of row and column energy beam radiation as well as pixel illumination in accordance with the present invention. The events of the timing diagram are indicated by lines  700 - 726 . The row energy beam radiation timing is indicated by lines  750 - 756 , with the row indicated as “X” in FIG.  9  and FIG. 10 indicated by line  754 . The column energy beam timing is indicated by lines  758 - 764 , with the column indicated as “Y” in FIG.  9  and FIG. 10 indicated by line  762 . The timing of the visual illumination of the pixel at intersection  620  of FIG.  9  and FIG. 10 is shown by line  764 . 
     During events  700 - 712  the row energy beams  750 - 756  are sequentially radiated while the column energy beams  758 - 764  are simultaneously radiated. For example, between events  700  and  702 , row energy beam  750  is radiating while the other row energy beams  752 - 756  are not radiating and all column energy beams  758 - 764  are simultaneously enable and radiating for a variable duration. Then, between intervals  702  and  704  row energy beam  752  is next in sequence for radiating while the other row energy sources are not radiating and all column energy beams  758 - 764  are simultaneously enabled and radiating for a variable duration. During events  714 - 726  the column energy beams  758 - 764  are sequentially radiated while the row energy beams  750 - 756  are simultaneously radiated. During sequential radiation, the energy beams are radiated one at a time for a predetermined time. The energy beams may be radiated in a linear sequence from top to bottom or left to right, or in other non-linear sequences which may have the advantage of reducing any appearance of sweeping or flicker of the display. During simultaneous radiation, all energy beams of the row or column are enabled for radiation for a variable duration. As previously described, the duration of the radiation is varied to provide for variable pixel brightness. Variable duration is indicated by the multiple rising and falling lines. Also, during simultaneous radiation, energy beams may be kept off for the variable duration if no visible light is to be generated by the corresponding pixels, as indicated by the always “low” state during the simultaneous radiation mode. 
     The timing of the visual illumination of the pixel at intersection  620  of FIG.  9  and FIG. 10 is shown by line  764 . Line  764  indicates that the pixel is radiating visible light of variable brightness between events  706  and  708  when energy beam  754  is radiated for the predetermined duration and energy beam  762  is radiated for the variable duration. The pixel is also radiating visible light of variable brightness between events  720  and  722  when energy beam  754  is radiating for the variable duration and energy beam  762  is radiating for the predetermined duration. 
     Referring back to FIG. 10, the operation of the elements of the block diagram are explained with reference to timing diagram of FIG.  11 . The row receiver preferably includes a phototransistor optimized for receiving energy beams of the wavelength of energy beams from the row sources and column receiver preferably includes a phototransistor optimized for receiving energy beams of the wavelength from the column sources. In one embodiment the optimization includes an optical filter in front of each phototransistor for passing the desired wavelength. In another embodiment a single receiver can be electronically tuned to receive energy beams of either the row or column wavelengths while either is correspondingly operating in its sequentially driven mode. 
     Since the row sources are sequentially driven while the column sources are simultaneously driven followed by the column sources being sequentially driven and the row sources simultaneously driven, the location determining mean can determine the location of the pen by matching the generated and received occurrences of row and column sequences. In this mode the row and column receptions while either is in the simultaneous mode are ignored. For example, with the tip of the pen at intersection  620 , the row receiver receives a signal having a timing substantially equal to that of line  754  and the column receiver receives a signal having a timing substantially equal to that of line  762 . By comparing the received signal timings with the signals generated by the timing means, the location determining means can determine the location of the tip of the pen on the display to be substantially at intersection  620  of energy beams  754  and  762 . In determining the location, the location determining means could further approximate for reception of multiple adjacent energy beams by the receivers as well as a predetermined delay between the received and generated signals via system calibration. 
     Since this form of location determining relies on the reception of the substantially invisible row and column energy beams, the location of the pen may be advantageously determined independent of the pixels illuminated on the display. For example, the location of the pen may be determined when there are no pixels illuminated on the display, because the location is determined by the matching the occurrence of invisible sequential row and column energy beams. Also, since this embodiment does not rely upon visible light for determining location, interference from visible light sources can also be reduced. 
     In an alternate embodiment, row and column receivers  632  and  634  are replaced by a single visible light receiver (not shown). In this embodiment, the pen tip at location  620  receives the unique visible pixel radiation timing of line  766  of FIG.  11 . Since the pixel at line  766  has a unique visible light timing, the location determining means can compare the received signal timing with the signals generated by the timing means in order to determine the location of the tip of the pen on the display. In determining the location, the location determining means could also approximate for reception of multiple adjacent pixel by the receiver as well as a predetermined delay between the received and generated signals via system calibration. 
     This alternate embodiment has the advantage of requiring only a single visible light receiver and operates in response to illumination of pixels. In an example of this mode, the display would be illuminated as if it were a white page and the pixel modification in response to the determined location of the pen would be displayed as a colored ink. 
     The invention has the advantage of a method for driving an intersecting beam phosphorous display which facilitates locating a pen-like pointing device on the display. The location is determined by comparing received radiated signals with signals generated in order to drive the display, no additional position sensing is necessary, such as a touch sensitive pad or other means to determine the location of the pointing device. Since the display may be thin flexible glass or plastic with an imaging phosphor, and no active components on either side of the display surface, the display itself is resilient and needs very little protection from damage by the pen. Thus, the geometry of the display allows for a very close proximity between the displayed pixels and the receivers in the pen. This advantage significantly reduces parallax when using the pointing device. Furthermore, receivers of the pen may be similarly positioned very near the tip of the pen, further reducing parallax. 
     Referring back to FIG. 1, FIG. 1 shows a display apparatus having redundant switching means  780 , redundant row sources  782 ,  784  and  786 , and redundant column sources  788  and  790 . The operation of the redundant switching means  780  is substantially identical to the operation of switching means  60 . Redundant row energy beam sources  782 ,  784  and  786  operate substantially identically to corresponding row energy sources  20 ,  55  and  30 , all sources radiating invisible energy beams of substantially the same wavelength or frequency however in an opposite directions. Thus, energy beams from sources  20  and  782  radiate along path  22  but in opposite directions, energy beams from sources  55  and  784  radiate along path  57  but in opposite directions and energy beams from sources  30  and  786  radiate along path  32  but in opposite directions. Similarly, redundant column energy beam sources  788  and  790  operate substantially identically to corresponding column energy sources  56  and  40 , all sources radiating invisible energy beams of substantially the same wavelength or frequency however in an opposite directions. Thus, energy beams from sources  788  and  56  radiate along path  58  but in opposite directions, and energy beams from sources  790  and  40  radiate along path  42  but in opposite directions. 
     The redundant elements of FIG. 1 have the advantage of providing for fault tolerant pixel illumination of all pixels  52 ,  53  and  54  of the display even if one or several components fail. For example if switching means  60  were to fail, causing all energy beams controlled thereby to also fail, the energy beams from the redundant switching means and sources  780 - 790  would radiate the along paths  22 ,  32 ,  42 ,  57  and  58  to enable pixels  52 , 53  and  54  to illuminate. Similarly, should individual energy beam sources fail, the corresponding redundant source would continue to radiate an energy beam along the desired path. A similar fault tolerance occurs at an interface between the energy beam source and the display. 
     Referring back to FIG. 4, FIG. 4 further shows redundant row and column sources used in conjunction with the multiple wave guide display. The redundant row sources include sources  782 ,  784  and  786 . The redundant column sources include sources  788  and  790 . It should be appreciated row and column reflectors  92  and  94  of FIG. 2 could also be replace by redundant sources resulting in a benefit similar to the reflectors including a brighter display and more uniform pixel brightness. Also, redundant row and column sources and drivers may be incorporated into the pen pointing device of FIG. 9 without substantial modification to the operation of the pointing system. 
     FIG. 12 shows a block diagram of the fault tolerant display system operation in accordance with the present invention. The switching means  60 , pixel memory  301 , row and column drivers  303 , timing means  306 , and display  600  operate substantially identically to the corresponding elements of FIG.  10 . The row and column sources  603  include row and column sources  602  and  604  of FIG.  10 . The redundant components include switching means  780  having row and column drivers  793  and timing means  796  are coupled to redundant row and column sources  798  which includes aforementioned sources  782 - 790 . The switching means and its components are substantially identical to and operate in substantial synchronization with corresponding switching means  60  and its components in order to illuminate pixels on the display. Synchronization and fault detection means  799  operates to synchronize the two switching means  60  and  780  so that redundant energy beam radiation occurs in substantial synchronization. Means  799  further acts to monitor signals produced by the timing means  306  and  396  and row and column drivers  303  and  793  for signal indicative of a failure of circuitry therein or the energy beam sources. A signal may be generated in response to self check circuits detecting a failure in order that further corrective action may be taken. Further, if a failure causes an energy beam to remain radiating when it is supposed to be off, the source itself, all of the corresponding row or column sources, the corresponding drivers and/or timing means may be deactivated and the display continues to operate with the redundant circuitry. In alternate embodiments, additional redundant components may be added such as power supplies, pixel memories and computer systems used to generate images stored in the pixel memories. 
     The fault tolerance characteristics of the present invention have the advantage of being easily and inexpensively realized, similar redundant systems are excessively complex and/or expensive to realize in CRT or LCD displays, if at all possible. Further, the display itself is passive having no active components or liquid crystal films thereby further improving the reliability of the display system. The combination of redundant active components driving a passive display panel provides an exceeding reliable color display having in medical, military, aircraft and spacecraft applications where reliability and fault tolerance are essential. Thus what has been provided is a fault tolerant display system having redundant active components and a passive display panel.