Abstract:
Each element in an array of display elements has first and second limiting positions and in respective limiting positions selectively displays a bright and a dark surface in a viewing direction. A transparent sheet is intermediate the array and the viewer. Conductors on the sheet power light sources in the sheet to thereby direct light toward the array.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of Ser. No. 08/833,469, filed Apr. 7, 1997 now U.S. Pat. No. 5,943,802. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     This invention relates to means for the enhancement of the appearance of signs, particularly writable display signs. 
     2. Description of the Related Art 
     Writable display signs typically have an array of display elements which are controllable (usually electromagnetically) to display in an ON position, a bright surface for viewing by a viewer in a viewing direction and in an OFF position, a dark surface for viewing by a viewer in the viewing direction. The array may be activated so that the elements provide information or a different form of display. 
     Usually the elements are arranged as pixels in an array and usually, in such array, the pixels are arranged in rows and columns. 
     The bright surface displayed in the ON position is more or less clearly visible dependent upon the ambient light. In many applications, therefore, it is desirable to illuminate the array so the bright surfaces appear more brightly and contrast more with the dark surfaces. 
     Prior ways have been found to illuminate such elements but these have tended to increase the depth required by the array or increased the expense of making or operating such sign. In such an application as a vehicle destination sign, the increase in depth tends to increase the distance of the array from the windshield reducing the angle over which the array may be read. 
     There is herein provided a method of and means for illuminating the array of a changeable display sign comprising providing a transparent sheet in front of said array, so that the viewing direction for the sign passes through the transparent sheet. 
     The transparent sheet is typically the transparent front wall of a casing for the array. It could also be the windshield of a bus or other vehicle. 
     Using a vehicle windshield or vehicle window as the front transparent sheet would have some advantages since it would provide a wide angle for viewers located outside the vehicle. However using the vehicle windshield or window is usually inconvenient since its manufacture is primarily associated with the vehicle, rather than with the sign. 
     In accordance with the invention, the illumination for the array will be lights mounted on the transparent sheet and directed towards the array, that is away from the viewer. Thus the lights illuminate the bright surfaces of those elements which are in ON position for display in the viewing direction. This is a simple and easy way of increasing the contrast and hence the clarity of the sign without unduly increasing its depth. 
     Although the terminology used herein generally speaks of a sign viewable from the front, signs may equally be installed to be viewable from the back or sides or may be located elsewhere than on a vehicle. 
     In a preferred form of the above invention, the lights are light emitting diodes or LEDs. 
     The display elements may be of many different forms. They will quite commonly be rotatably mounted disks which are bright on one side and dark on the other, so that the bright and dark side of an element are displayed to the viewing direction in the ON and OFF positions, respectively, of the disks. 
     The transparent sheet may, if desired, be made flexible to conform to a curved space, such as inside a curved bus windshield. 
     When the illumination is by LEDs, these are preferably connected across gaps in a circuit applied to the transparent sheet to shine in a direction away from the viewer and toward the display elements. The conductor is usually a conducting ink which is usually opaque but relatively insignificant and not noticeable to the viewer. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     In drawings which illustrate a preferred embodiment of the invention: 
     FIG. 1 is a schematic view having portions broken away showing a partial array of display elements of a sign with bright and dark sides chosen to form the letter “T” in the bright surfaces of elements against a dark background; 
     FIG. 2 is a partial side view of a front of a bus with the sign casing and windshield shown in section; 
     FIG. 3 is an enlarged view of a portion of the sign as viewed from in front of the bus; 
     FIG. 4 is a view along lines  4 — 4  of FIG.  3  and showing the viewing direction V which is that of a viewer of the device some distance to the left of the array; 
     FIG. 5 is a partial perspective view showing the transparent casing front having trace conductors and LEDs; 
     FIG. 6 is a section taken along line  6 — 6  of FIG.  5  through the LED and lens system; and 
     FIG. 7 is a perspective view of a LED mounted on a transparent printed wiring board (‘PWB’) which acts as a transparent sheet and as a front of the casing. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     In the description, two definitions should be noted. 
     ‘LED’, light emitting diode, here, refers to the LED chip itself, shown at  10  in FIG.  6  and its associated wire  11  as embedded in a plastic  12  forming a lens. Other usages tend to consider the ‘LED’ as the chip and lens combined. 
     Most PWB&#39;s, printed wiring board, are opaque and hence would be useless for forming the front of a sign casing of this invention. Thus the invention is only concerned with PWB&#39;s or equivalents which are transparent or concerned with other transparent sheets for carrying the LED&#39;s and their circuits. 
     In FIG. 1 a front interior area of a bus  13  mounts a bus destination sign casing  16  containing a flip disk sign array  14 . 
     As shown in FIG. 2, the flip disk array is seen through the vehicle windshield  17  and the casing front wall  20  which is a transparent PWB usually of glass or plastic. 
     In FIG. 2 a section of the bus, illustrates the fact that the LED housings or casings  22  are mounted on the inside of the PWB,  20  with conducting adhesive  24  (FIG. 7) to shine backwardly from the PWB  20  onto the array. The LED chip  10  as shown in FIG. 6 conducts between conductors  26  which are traces printed on or attached to the inside of the PWB. Thus the conducting traces  26  (FIG. 5) carry current from a voltage V+ source through a number of LEDs  10  arranged in series circuits which series circuits are arranged in parallel. This is believed more efficient for proper energizing of the LEDs than a plurality of LEDs arranged in parallel circuits which parallel circuits are arranged in series. 
     The conducting traces are preferably formed from silver ink but may be formed of another conducting ink which is both conducting and opaque. Silver ink or silver may also be used in rendering conducting the conducting adhesive  24 . However, other conducting components in the adhesive may be used. 
     The casing forming the opaque enclosure for the LED and cell is preferably formed of white plastic apertured to allow conducting connection between a conductor  26  and the anode or cathode of LED chip  10 . The inwardly sloping walls of the casing are covered with reflecting tape  31  to assist in reflecting rays from the LED chip toward the array. The casing side walls  27  and bottom walls  29  are preferably of opaque white plastic. With its side and rear walls, the housing or casing prevents escape of LED rays in unwanted directions and prevents direct viewing of LED rays by a viewer. The inside of the casing walls is, as above described, preferably reflective of the LED rays and tends to direct them toward the display elements as desired. 
     The LEDs and lenses therefore illuminate surfaces of the disks facing in the viewing direction and cause the bright or ON areas  34  to contrast well with dark areas  36  to the viewer looking in viewing direction V. 
     The LED casing opaque side walls  27  and bottom walls  29  act as a shroud to prevent the viewer looking in direction V from seeing direct light from the LED only seeing reflected light from the disk bright faces. 
     As demonstrated by FIG. 3, the LED casings  22  are relatively small relative to a display element and with the relatively small substantially opaque traces  26  do not detract from the appearance of the display just as embedded wires for heating a rear automobile windshield are substantially invisible for most purposes. 
     In most if not all prior art light augmented flip disks there is a light (usually LED or optic fibre) for each display element, and such individual light must be shuttered or switched when the moveable disk was in OFF position. 
     However, with the invention, the LED is never directed toward the viewer. Hence shuttering and switching is not required. Thus the LEDs may be on all the time and a single LED may illuminate several elements. 
     The LEDs, therefore, must provide sufficient light to collectively illuminate all the disk bright sides visible to the viewer. 
     Although FIG. 3 shows an LED at the center of each 2×2 square of disks, there is no requirement that the center to center spacing of the LED casings in a row or column correspond to an integral multiples of the pixel spacing, so that LED casings need not align with intersections between the pixels. 
     Although rotatable disk  32  are shown, the display will be equally useful if it uses moveable but not necessarily rotatable elements which also alternate between light and dark areas in locations on the array. 
     Moreover the arrangement of pixels in the array need not be in rows and columns but may be in other arrangements. 
     The disk shown in FIGS. 3 and 4 is a preferred version for use with the invention chosen from a number of disks, and arrays which may be used with the LEDs and transparent sheets of the invention. The electromagnetic operation is well known to those skilled in the art and only briefly described here. 
     With the disk of FIGS. 3 and 4, the disk is approximately octagonal in a generally square mount and rotates just less than 180° (between the illustrated position of the top elements of FIG. 4) on its diagonal axis as defined by pivot pins  42  to display, facing the viewing direction V, either a bright side  34  or a dark side  36 . The disk contains a magnet, not shown having an axis extending between the pole pieces  44  and  46  of mutually opposite polarity and actuable by the switching of pole pieces to move between positions displaying the bright or the dark surface in the viewing direction. The coils  48  on the pole pieces  44  and  46  are joined by bridging member  50  and are actuated by conductors (not shown) on the rods  54  and  56  to switch the pole piece polarities. The pole pieces  44  and  46  also, in this version respectively act as stops for the disk which, in each limiting position, is stopped by a pole piece end, while a cut out  52  in the disk surrounds the other pole piece. The side with the cut-out rotates toward the other limiting position in a direction away from the viewer of FIG.  3  and to the right in FIG.  4 . 
     Tilt of the array and/or its casing can be arranged in any preferred manner and can be arranged to provide selected viewing directions such as a downward or leftward for the benefit of viewers on the side. 
     A disk with a vertical rather than a diagonal axis is shown in U.S. Pat. No. 4,577,427 to Brown dated Mar. 25, 1986 whose backups are incorporate herein by reference. 
     Other disks suitable for use with the backward illumination of the invention are disclosed in U.S. Pat. No. 4,156,872 Helwig, May 29, 1979, and U.S. Pat. No. 4,069,480 Helwig, Jan. 17, 1978. 
     Alternatives to a disk are movable bars of the U.S. Pat. No. 4,744,163 Browne, May 17, 1988 and U.S. Pat. No. 4,566,210 to Winrow, dated Jan. 28, 1986. These alternatives may also usefully be illuminated by rearward shining LEDs arranged on a circuit in accordance with the invention.