Abstract:
There is disclosed a backlit display structure with multiple LED&#39;s arranged to transmit light into a light guide plate configured to uniformly illuminate the back of a readily replaceable translucent image sheet. The display may be incorporated with a decorative frame which also may be illuminated by the same or different LED&#39;s. The display powered by a rechargeable battery pack may also be incorporated in table top boxes for condiments, straws, napkins or other conveniences for restaurant customers where it is useful for displaying replaceable advertising or current featured menu items. In another form the guide plate does not uniformly illuminate an image sheet but only illuminates temporary marks thereon from a crayon or marker, thereby providing an illuminated blackboard.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application claims priority to and is a continuation-in-part of U.S. provisional application Ser. No. 61/132,674, filed Jun. 20, 2008. 
    
    
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     Not Applicable. 
     REFERENCE TO A MICROFICHE APPENDIX 
     Not Applicable. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to the field of back lighted displays in general. In particular, the present invention relates specifically to a simple, efficient backlit display structure with multiple LED&#39;s arranged to transmit light into a light guide plate configured to uniformly illuminate the back of a readily replaceable translucent image sheet. The display may be incorporated with a decorative frame which also may be illuminated by the same or different LED&#39;s. The display may also be incorporated in table top boxes for condiments, straws, napkins or other conveniences for restaurant customers where it is useful for displaying advertising or current menu features. Another version has a light guide which does not provide uniform back lighting but only illuminates temporary marks from a marker or crayon on the front surface of the light guide, the background remaining dark. 
     2. Description of the Known Art 
     Advertising display devices and backlighting devices for general purposes have been known as shown in the following patents: U.S. Pat. No. 3,106,314, issued to Spears, on Oct. 8, 1963; U.S. Pat. No. 4,714,983, issued to Lang, on Dec. 22, 1987; U.S. Pat. No. 5,377,084, issued to Kojima et al., on Dec. 27, 1994; U.S. Pat. No. 5,730,518, issued to Kashima et al., on Mar. 24, 1998; U.S. Pat. No. 5,842,297, issued to Tung, on Dec. 1, 1998; U.S. Pat. No. 6,367,392, issued to Moore, on Apr. 9, 2002; U.S. Pat. No. 6,447,136, issued to Liu et al., on Sep. 10, 2002; U.S. Pat. No. 6,530,164, issued to Gai, on Mar. 11, 2003; U.S. Pat. No. 6,539,656, issued to Maas et al., on Apr. 1, 2003; U.S. Pat. No. 6,561,672, issued to Lessard, on May 13, 2003; U.S. Pat. No. 6,691,443, issued to Slayden, on Feb. 17, 2004; U.S. Pat. No. 6,926,420, issued to Sung, on Aug. 9, 2005; U.S. Pat. No. 6,968,959, issued to Garvin, on Nov. 29, 2005; U.S. Pat. No. 7,024,809, issued to Poma, on Apr. 11, 2006; U.S. Pat. No. 7,026,916, issued to Alexander, on Apr. 11, 2006; U.S. Pat. No. 7,048,398, issued to Bahramian, on May 23, 2006; U.S. Pat. No. 7,063,449, issued to Ward, on Jun. 20, 2006; U.S. Pat. No. 7,131,764, issued to Hsu et al., on Nov. 7, 2006; U.S. Pat. No. 7,186,015, issued to Kimmet et al., on Mar. 6, 2007; and U.S. Pat. No. 7,226,200, issued to Tsai, on Jun. 5, 2007. 
     The information deemed most relevant in these patents is as follows: 
     U.S. Pat. No. 6,447,136 issued to Liu et al. on Sep. 10, 2002 discloses a liquid crystal display having a light guide plate for a back light system. This patent discusses light guide plates with surface irregularities in the form of annular protrusions. 
     U.S. Pat. No. 7,131,764 issued to Hsu et al. on Nov. 7, 2006 discloses a backlight apparatus with and edge lit guide element with concavities for directing light. FIG. 4c discloses a hexagon configuration. 
     U.S. Pat. No. 5,377,084 issued to Kojima et al. on Dec. 27, 1994 discloses a surface illuminating apparatus including a light guide plate, irregularly reflecting plate and back reflecting plate having incandescent light sources at each lateral end. FIGS. 7, 8 and the background discuss relevant areas of this art. 
     U.S. Pat. No. 6,926,420 issued to Sung on Aug. 9, 2005 discloses a backlight unit for a liquid crystal display having reflective plate with reflection dots with varying dot size and which cooperates with a smooth light guide plate. 
     Additional patents specifically directed to napkin holders are as follows: 
     U.S. Pat. No. 6,561,672 issued to Lessard on May 13, 2003 discloses an illuminated holder for finding miscellaneous objects in the dark. The illumination is on the sides of the unit and does not teach an backlit illuminated advertisement section. 
     U.S. Pat. No. 3,106,314 issued to Spears on Oct. 8, 1963 discloses an advertising napkin holder. The advertisement is insertable and removable from flanges on the sides of the unit, but no illuminated advertisement is provided. 
     The other patents disclose additional illumination and display elements of other forms. 
     SUMMARY OF THE INVENTION 
     The present invention provides a simple, efficient backlit display structure with multiple LED&#39;s arranged to transmit light into a light guide plate configured to uniformly illuminate the back of a readily replaceable translucent image sheet. The display may be incorporated with a decorative frame which also may be illuminated by the same or different LED&#39;s. The display may also be incorporated in table top boxes for condiments, straws, napkins or other conveniences for restaurant customers where it is useful for displaying advertising or current menu features. 
     The invention provides that the use of high intensity light emitting diodes allows for a battery power or other low voltage system that reduces the risk of shock while providing sufficient light to uniformly illuminate the back of a replaceable advertising image sheet. The LED light sources can be powered for many hours from a rechargeable battery with overnight recharging as convenient. The low current drain also permits the use of disposable batteries in place of rechargeable batteries if desired. These high intensity LEDs work well with translucent image sheets that do not have high transparency. The light guide plate has light directing surface irregularities sufficiently spaced from the position of the image sheet to produce substantially uniform backlighting without interposition of a diffuser plate thereby enhancing the effectiveness and efficiency of the apparatus. 
     An important feature is the accessibility to the image sheet for replacement by separating the front window and the backlighting apparatus. This feature is also present in the tabletop units that have a rechargeable batter pack in the base thereof. Another version of the display dispenses with the backlit image sheet and the smooth surfaced light guide only illuminates marks from a marker or crayon on the front surface. 
     These and other objects and advantages of the present invention, along with features of novelty appurtenant thereto, will appear or become apparent by reviewing the following detailed description of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
       In the following drawings, which form a part of the specification and which are to be construed in conjunction therewith, and in which like reference numerals have been employed throughout wherever possible to indicate like parts in the various views: 
         FIG. 1  is a front view of a display structure according to the present invention. 
         FIG. 2  is an exploded view showing the elements of the display structure of  FIG. 1 . 
         FIG. 3  is a back view showing the back of the light guide shown in  FIG. 2 . 
         FIG. 4  is a fragmentary enlarged sectional view along line  4 - 4  in  FIG. 3 . 
         FIG. 5  is a right side view of the display structure of  FIGS. 1-4 . 
         FIG. 6  is an exploded view of another embodiment of the invention with display structures incorporated in a table top box. 
         FIG. 7  is a perspective view of a variation of the  FIG. 6  embodiment adapted for use as a napkin dispenser. 
         FIG. 8  is a perspective view of another embodiment of the invention providing a square box with front and back backlit displays. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIGS. 1 through 5  show a single-display embodiment of the invention which is enhanced by an illuminated frame and is suitable for display of advertising material or as a picture frame for personal use. As seen in  FIGS. 1-3  display structure  11  has a frame  13  to which other components are secured including fasteners  15  and extended fasteners  17 . This optional fastener arrangement provides means for holding the display structure vertically in either a portrait or landscape orientation, as shown in  FIG. 5 . The female portions of the fasteners  15  on the back of the display structure  11  may optionally be provided with internally threaded openings  16  to use for securing multiple displays on a display board for advertising purposes, for example. In this embodiment the fasteners  15  are readily manipulated from the front of the display to access and replace the image sheet  21  behind window  23  as will later be described. 
     Secured on the back of frame  13  are electrical components DC input  25  and control switch  27 . DC input  25  accepts a plug from a conventional AC-DC converter  29  (of 3 volts for example) providing power for the display. This illustrated embodiment is not provided with a battery compartment to allow cordless operation, but such could be added if desired. 
     The internal components of display structure  11  are best shown in  FIGS. 2 and 3 . In front of the frame  13  is a light guide plate  33  backed by a white reflector sheet  31 . Mounted on the edge of light guide plate  33  are a plurality of LED&#39;s  35  connected by an electrical circuit  37  to input  25  and switch  27 . The LED&#39;s  35  are typically 10 to 15 in number spaced 5 to 15 millimeters apart. Although only one edge of light guide plate is illuminated by LED&#39;s in the illustrated embodiment, the LED&#39; could be placed on two or more edges. The light guide plate uses a know expedient to direct light forward in a uniform manner in the form of a multiplicity of indentations  41 , detailed (not to scale) in  FIGS. 3 and 4  showing the back of light guide plate  33 . They are from 0.5 to 1.5 millimeters in dimension and spaced in a hexagonal array about 1 to 3 millimeters apart. Other of many known light guide configurations could be employed rather than that illustrated; some such configurations are described in the reference patents cited above. 
     Surrounding the light guide plate  33  is an outer decorative frame  43  which is of greater dimensions than the window  23  so that it forms the outer border of the display. In this embodiment decorative frame  43  is of transparent material in contact with the edges of light guide plate  33  so that it is rendered luminous by light from LED&#39;s  35 . This feature and the outer decorative frame itself is optional and not required in other embodiments. 
     The window  23  is backed by a mask  22  to conceal LED&#39;s  35  and other working parts and is secured at the front of display structure  11  by readily removable fasters  15  and  17 . Other components are fastened together in a conventional manner by screws or the like (not shown). Window  23  may have any opaque border other than mask  22  serving to conceal the LED&#39;s  35  and edges of the light guide plate  33 . 
     A selected translucent image sheet  21  is placed between light guide plate  33  and window  23  (as by taping it in place on the back of window  23 ). The conventional AC-DC converter  29  used to power (or recharge) the display is shown in  FIG. 5 . 
     The major components described above are preferably formed of plastic, especially the transparent window and light guide plate, while fasteners and other parts may be of metal or plastic or combinations thereof. Other materials such as glass, wood, fiberboard or metal could be used for some of the components, if desired. 
     An important aspect of the invention is the manner in which the light from the LED″s through the light guide plate substantially uniformly illuminates the image sheet on the back of the window without the necessity for an intervening diffuser screen. The path from the back of the light guide plate  33  to the translucent image sheet  21  is completely transparent so that there is no loss of light intensity from a diffuser screen. This is facilitated by the fact that the thickness of the light guide plate  33  is significantly greater than the dimensions of the indentations  41  and at least as great or greater than the spacing between them. The translucent image sheet being so uniformly illuminated from the back, there is no perception of the LED pattern. 
     The advantage of ready changeability for the image sheets is provided by the separate attachment of window  21  with fasteners  15  and  17 , particularly in this embodiment where they are readily accessible from the front. Other embodiments provide accessibility in different manners. 
     A variation of the back-lit display structure allows it to be used as a “blackboard” which may be written on by markers or crayons which marks represent the translucent display, rather than a separate translucent image sheet. Such a back-lit blackboard is useful for advertising menu items and has many other uses. 
     The blackboard version has significant differences, notably the absence of surface irregularities so both surfaces of the light guide are smooth and light is not directed forward from the light guide in the absence of marking material on the front of the light guide plate. Accordingly the backlit display structure  11  previously described can be changed to make a backlit blackboard by the minimal modifications of changing the reflector  31  to a black surfaced sheet and eliminating all light guide plate  33  surface irregularities such as indentations  41  and any translucent image sheet  21 . 
     Other elements such as window  23  could be retained but would be optional. Many markers or crayons will leave a mark in contact with face of the light guide that defeats the total internal reflection crucial to guiding light in the plate thereby allowing the mark to be brightly illuminated by light escaping from the guide. Alternatively a transparent sheet my be provided in place of the translucent image sheet  21  so that marks on the sheet in intimate contact with the light guide would be illuminated in a similar same manner. With the above minor changes  FIG. 2  would illustrates the back-lit blackboard display structure described above and claimed hereinafter. 
     The basic elements of the display structure described above can be usefully employed in other embodiments as exemplified by the embodiments illustrated in  FIGS. 6-8  which show restaurant tabletop customer convenience items, in the form of a napkin dispenser, for example. Such tabletop configurations could in larger versions be provided with wheels and be freestanding floor units. In  FIG. 6  the box  101  and its base  103  provide a portable container having two displays  111  each with basic elements corresponding to those of the display structure  11 , and such correspondence will be assumed herein unless otherwise indicated. Although two displays  111  are shown for box  101 , up to four displays could be provided in similar manner. 
     The interior walls  113  serve as the frame to which other components of displays  111  are secured. A case  105  slides over and surrounds box  113  and displays  111 . The portions of case in front of displays  111  have windows  123 . Case  105  when in the position shown in  FIG. 7  causes windows  123  to be positioned so that the illuminating portion of display  111  is revealed. Case  115  is held in position on box  101  by conventional releasable fasteners (not shown) A display sheet  121  similar to display sheet  21  is secured between each display  111  and the corresponding window  123 . Case  105  is lifted off the interior walls of box  113  and light guides  111  to access and replace an image sheet  121  behind window  123 . A solid top  107  may be provided for case  105  if desired. 
     Secured on the base  103  are electrical components DC input  125  and control switch  127 . DC input  125  accepts a plug from a conventional AC-DC converter (of 3 volts for example) providing power for the display and for battery compartment  109  within base  103  thereby to allow cordless operation if desired. An electrical circuit  137  includes a connection form battery compartment  109  and/or switch  127  to LED&#39;s  135  at the bottoms of displays  111 . The electrical circuit  137  and switch  127  may in conventional manner have operational modes for on, off and recharge. It will be noted that since LED&#39;s  135  are at the bottom of light guides of displays  111 , they could alternatively be mounted at top edges of base  103  simplifying the electrical connections to the LED&#39;s. 
       FIG. 7  shows the same structure as in the  FIG. 6  exploded view except that top  107  has been replaced by cover  106  having an opening  108  so that the unit of  FIG. 7  functions as a napkin dispenser. In both  FIG. 6  and  FIG. 7  the base is preferably detachably secured to the structure by releasable fasteners, not shown. This facilitates recharging the batteries and use of extra bases that can be recharged while the displays are in active use. 
       FIG. 8  shows another embodiment of the invention which is generally similar to that of  FIGS. 6 and 7  except that unit  201  has a rectangular shape rather than the square shape of unit  101 , and the manner of separating the display light guide plate from the window to replace image sheets differs from that of other units. The box may of course take any shape with three four or more sides of any proportion. Any or all sides of the box may serve as a location for a backlit display as may be desired for the particular use and environment. The unit  201  of  FIG. 8  is adapted to hold one or more boxes of straws, stirrers, table ware or he like accessible to restaurant customers or servers. 
     The unit  201  includes a box  213  having windows  223 . The backlit display structure  211  is similar to that of  FIG. 2  but it is secured against window  223  from the inside of box  213  and held in place by releasable fasters such as rotatable tabs  215 . Except for a difference in shape, base  203  is similar to base  103  of other embodiment with battery compartment connected by an electrical to switch  127  and DC input  125  and to the LED&#39;s, not shown. Preferably base  203  is likewise separable from box  213  although this is not necessary to separate display structures  211  from windows  223  to access image sheets  221 . 
     Note that due to the compatibility of the embodiments described herein, features of one can often be transferred to others within the scope of the invention. Also features of one may be substituted for a comparable feature of another. 
     A variation of the back-lit display structure allows it to be used as a “blackboard” which may be written on by markers or crayons which marks represent the translucent display, rather than a separate translucent image sheet such a back-lit blackboard is useful for advertising menu items and has many other uses. 
     The blackboard version has significant differences, notably the absence of surface irregularities so both surfaces of the light guide are smooth and light is not directed forward from the light guide in the absence of marking material on the front of the light guide plate. Accordingly the backlit display structure  11  previously described can be changed to make a backlit blackboard by the minimal modifications of changing the reflector  31  to a black surfaced sheet and eliminating all light guide plate  33  surface irregularities such as indentations  41  and any translucent image sheet  21 . Other elements such as window  23  could be retained but would be optional. Many markers or crayons will leave a mark in contact with face of the light guide that defeats the total internal reflection crucial to guiding light in the plate thereby allowing the mark to be brightly illuminated by light escaping from the guide. Alternatively a transparent sheet my be provided in place of the translucent image sheet  21  so that marks on the sheet in contact with the light guide would be illuminated in the same manner. With the above minor changes  FIG. 2  illustrates the back-lit blackboard display structure disclosed above and claimed hereinafter. 
     In addition to those described above, other modifications and variations of the disclosed apparatus will be apparent to those skilled in the art and should be considered to be within the scope of the invention.