Abstract:
A large scale LED display has a cable and rigid link support structure for a number of LED modules. The cable and rigid link support structure is flexible but has sufficient structural integrity to prevent misalignment of the pixel modules. The LED modules are removable from the support structure individually and as a group so as to facilitate repair of the display. The LED modules are rugged so as to withstand harsh outdoor conditions and they provide sufficient luminescence for use in sunlight.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application is related to co-pending patent applications U.S. Ser. No. 12/001,277 entitled “Data And Power Distribution System and Method For A Large Scale Display;” U.S. Ser. No. 12/001,312 entitled “Enumeration System and Method For A LED Display;” and U.S. Ser. No. 12/001,276 entitled “Large Scale LED Display System,” each filed concurrently herewith. 
     STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT 
     N/A 
     TECHNICAL FIELD 
     The present invention is directed to a large scale display and more particularly to the LED modules, segments and support structure for a large scale LED display. 
     BACKGROUND OF THE INVENTION 
     Large scale displays on the order of 10×20 ft. or 40×60 ft. are known to employ a net formed of intersecting cables to structurally support a number of pixel units as shown in Temple U.S. Patent Application Publication No. US 2006/0039142 A1. Because of its flexible nature, this net display may be supported on curved or irregular surfaces as well as flat surfaces. However, this net display is so flexible that the pixel units can twist about the cables, impairing the visibility of the pixels. Moreover, the horizontal cables of the net flex so that the pixel units become misaligned resulting in distortions in the displayed image. The pixel units of this net display include a housing for a circuit board that supports a cluster of red, green and blue LEDs wherein a potting material seals the circuit board from the environment. U.S. patent Yoksza et al. U.S. Pat. No. 5,410,328 shows similar pixel modules for a large scale LED display wherein each module is individually removable from the display by removing a few screws or twisting the module. One wall of the housing of the pixel module in Yoksza et al. extends beyond the LEDs so as to provide a sunshade for the module. Another LED module for a display, as shown in U.S. patent Simon et al. U.S. Pat. No. 4,887,074, uses a heat sinking potting compound in contact with the circuit board supporting the LEDs and heat spreader plates to dissipate heat from the module housing. 
     BRIEF SUMMARY OF THE INVENTION 
     In accordance with the present invention, the disadvantages of prior art large scale LED displays have been overcome. The LED display system of the present invention includes a novel support structure for a number of LED modules wherein the support structure is sufficiently flexible so that the display can conform to curved or irregular surfaces and yet the support structure has sufficient structural integrity to prevent twisting and sagging of the LED modules, preventing misalignment of the modules so that a distortion free image can be displayed. 
     In accordance with one feature of the present invention, the display includes a plurality of LED modules wherein each LED module includes a module housing that supports a plurality of color LEDs. The support structure for the LED modules includes a first pair of parallel cables; a first set of rigid links, extending between the cables of the first cable pair; a second pair of parallel cables, the cables of the second cable pair being parallel to the cables of the first cable pair; and a second set of rigid links extending between the cables of the second cable pair wherein each of the LED modules is mounted on one cable of the first cable pair and one cable of the second cable pair. 
     In accordance with another feature of the present invention, the rigid links are H-shaped links that are over-molded onto a pair of cables. The links are such that they locate the position of the LED modules along the cables. 
     In accordance with another feature of the present invention, the support structure includes a plurality of plates wherein the plates are mounted on one cable of the first cable pair adjacent to at least one rigid link of the first set and on one cable of the second cable pair adjacent to at least one link of the second set wherein a LED module is removably mounted on a plate. 
     In accordance with still a further feature of the present invention, a LED module for a display includes at least two red LEDs; two green LEDs; two blue LEDs; a circuit board on which the LEDs are mounted and an over-molded housing encasing the circuit board, the LEDs protruding from a front surface of the housing and the front surface of the housing including a plurality of heat sink fins. 
     In accordance with another feature of the present invention, a LED display comprises a plurality of linear segments of LED modules in each of a plurality of columns or rows of the display, each LED module having a housing supporting a plurality of multi-color LEDs and each segment including a plurality of LED modules coupled together so that the LED modules of a segment are removable from the display only as a group and each segment of LED modules is removable from the display independent of the LED modules of another segment. In this embodiment the LED display may include individual LED modules that are connected between segments of LED modules. 
     In accordance with another feature of the present invention, a segment of LED modules for use in a display comprises a first electrical connector fixedly attached to a first end of the segment; a second electrical connector fixedly attached to a second end of the segment; a plurality of spaced LED modules connected between the first electrical connector and the second electrical connector, the spaced LED modules being connected end-to-end by at least one cable capable of carrying power and/or data to each of the LED modules; and a further cable connected directly between the first connector and the second connector for carrying data directly between the first and second connectors. 
     These and other advantages and novel features of the present invention, as well as details of an illustrated embodiment thereof, will be more fully understood from the following description and drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS 
         FIG. 1  is a front view of a large scale display in accordance with one embodiment of the present invention; 
         FIG. 2  is a partial front view of the display of  FIG. 1 , illustrating a number of LED modules mounted on the support structure for the display of the present invention; 
         FIG. 3  is a partial perspective view of the support structure for the display of  FIGS. 1 and 2 ; 
         FIG. 4  is a back view of the support structure depicted in  FIG. 3 ; 
         FIG. 5  is a partial front view of a pair of master LED modules and a pair of slave LED modules mounted on the support structure depicted in  FIGS. 2-4 ; 
         FIG. 6  is a perspective view of a segment of slave LED modules in accordance with one embodiment of the present invention; 
         FIG. 7  is a side perspective view of the segment of slave LED modules depicted in  FIG. 6  with the housing of one of the modules removed; 
         FIG. 8  is a back view of a segment of slave LED modules as depicted in  FIG. 6 ; 
         FIG. 9  is a front perspective view of a master LED module in accordance with one embodiment of the present invention; 
         FIG. 10  is an illustration of the circuit boards and connectors for the master LED module depicted in  FIG. 9 ; 
         FIG. 11  is a back perspective view of the master LED module of  FIG. 9 ; and 
         FIG. 12  is a back view of a pair of slave LED module segments connected between respective master LED modules. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     A large scale LED display  10  in accordance with the present invention, as shown in  FIG. 1 , has height by width dimensions on the order of 3 m×6 m to 24 m×32 m or approximately 10 ft.×20 ft. to 80 ft.×105 ft. However, it should be appreciated, that the present invention can be used for displays that are larger or smaller as well. A display that is approximately 24 m×32 m has 480 pixels×640 pixels or a total of 307,200 pixels. These large scale LED displays are intended for both indoor use and outdoor use. The large scale display in accordance with the present invention is extremely robust and can withstand harsh outdoor environments while providing distortion free displayed images. Moreover, segments of the display can be readily replaced. 
     Each pixel of the display  10  is generated by a module  12  or  14  having two red LEDs  16 , two blue LEDs  18  and two green LEDs  20  mounted in a respective housing of the modules  12  or  14  as shown in  FIG. 2 . A circuit board contained within the housings of the modules  12  and  14  controls the intensities of the red, blue and green LEDs in order to generate pixels of a large number of different colors as is well known in the art. Although each of the modules  12  and  14  is depicted in  FIG. 2  having pairs of red, green and blue LEDs, the number of red, green and blue LEDs can vary depending upon the spacing between the individual modules and the flux density of the individual LEDs. For example, where the center-to-center spacing between adjacent LED modules is 50 mm or greater, one or more red, one or more blue and one or more green LEDs can provide a light output for the display of 5,000 nits or greater depending upon the flux density of the LEDs so that the display  10  is suitable for use outdoors in sunlight. For a display in which the center-to-center spacing between adjacent LED modules is 75 mm or greater, it is preferable to use a plurality of red LEDs, a plurality of green LEDs and a plurality of blue LEDs, such as three LEDs of each color, although the number of LEDs may be reduced depending upon the flux density of the individual LEDs. It should be appreciated that all of the LEDs of the modules as well as the entire display may be monochromatic as well. When monochromatic LEDs are used, changeable graphics and/or text can be displayed by turning on selected LEDs or modules. Moreover, to enhance the light output of the modules, it is preferred that the housing of each of the modules be black or a dark color as described in detail below. In accordance with another feature of the invention, however, the color of the housing is selected to match the color of the structure, such as a building, on which the display is mounted. Moreover, a single display can employ modules with different colored housings so that when the LEDs of the display are turned off, the different colored housings depict a fixed logo, graphic and/or text message. 
     There are two types of pixel modules employed in the display  10 , master LED modules  12  and slave LED modules  14 . Each master module is associated with a group of slave modules in a segment  24  of the display. Although  FIG. 2  illustrates a segment as including one master LED module and three slave LED modules for simplicity, in a preferred embodiment of the present invention, each segment has one master module and fifteen slave modules to generate sixteen pixels of the display. It should be apparent, however, that the number of slave modules can vary from zero to any number depending upon the aspects of the present invention that are used. In a preferred embodiment, the segments  24  of the display  10  are linear, extending in a column of the display  10 . However, segments can extend in rows of the display as well. For a 480×640 display having linear segments of sixteen pixels, there are thirty segments in each column of the display. The segments are preferably aligned so that each master module is in a row of master modules. As such, there are thirty rows of master modules with 640 master modules in each row of a 480×640 display with fifteen rows of slave modules between each of the rows of master modules. 
     The support structure for each of the LED modules  12  and  14  of the display  10 , as shown in  FIGS. 2-5 , includes a first pair of parallel cables  24  and  26  and a first set of rigid links  28  wherein each link  28  extends between the cable  24  and the cable  26 . The support structure for each of the LED modules  12  and  14  also includes a second pair of parallel cables  30  and  32  and a second set of rigid links  34  wherein each link  34  extends between the cable  30  and the cable  32 . Each of the LED modules in a first column of the display  10  is mounted on one cable  26  of the first cable pair and on one cable  30  of the second cable pair adjacent at least one link  28  from the first set and adjacent at least one link  34  from the second set. Each of the LED modules in the second column of the display  10  is mounted on the second cable  32  of the second cable pair and a cable  36  adjacent at least one link  34  of the second set of links and adjacent at least one link  38  in a third set of links that extends between cables  38  and  40  of a third cable pair. For a display having N columns, the support structure includes N+1 pairs of cables, such as cables  24  and  26 , and N+1 sets of rigid links. If the display has M LED modules in each column, each set of links would include M links. 
     In a preferred embodiment, the links  28 ,  34 ,  38  are H-shaped links that are over-molded onto the cables of each cable pair. More specifically, the two cables of a cable pair are placed in a mold into which plastic is injected around the cable to form the rigid H-shaped links connecting the two cables of a pair. A reel to reel molding process is employed in which the over-molded links are indexed through the mold and the previously molded links are used to datum and position the subsequent links. The molding process ensures that the spacing between the links along the length of the cables is constant. The H-shaped links are used to precisely and easily locate the LED modules along the lengths of the cables so that the spacing between the LED modules in a column and the spacing between the LED modules in a row of the display  10  remains constant. Moreover, the H-shaped links provide structural integrity to the cable support structure of the display  10  to prevent sagging and misalignment of the LED modules when the display is in use. It is noted that the cables are preferably steel cables that are of a gauge sufficient to bear the load of all of the LED modules in a column of the display  10 . 
     More particularly, as depicted in  FIGS. 3 and 4 , the rigid H-shaped links serve to locate steel back plates  42  of the master LED modules  12  and steel back plates  44  of the slave LED modules  14 . The back plate  42  of each of the master LED modules has four arms  45 - 48  on each side of the plate  42  wherein the arms  45 - 48  are crimped onto the cables of the support structure. The two inner arms  46  and  47  of the back plate  42  are crimped onto a respective cable on either side of a leg of the H-link  38  such that the arms  46  and  47  abut the H-link with some tolerance therebetween. Similarly, the back plate  44  of the slave LED modules has two arms  50  and  52  on each side of the plate  44  wherein the arms  50  and  52  are crimped onto the cables of the support structure on either side of the H-link such that the arms  50  and  52  abut the H-link with some tolerance therebetween. Because the arms of the back plates  42  and  44  of the LED modules are crimped onto the support cables of the display  10 , the arms and thus the back plates can rotate somewhat about the cables to provide enough flexibility for the display  10  so that the display  10  can conform to curved surfaces even though the H-links cannot rotate about the cables. The rigid H-links and LED module back plates provide structural integrity for the support structure and prevent twisting, sagging and misalignment of the LED modules of the display  10 . Moreover, the location of the links along the horizontal centerline of the back plates provides a structure that can be tensioned. This allows side tensioning of the mesh structure to cause the mesh to conform to a curved surface or to remove by tension any incidental wrinkles for a flat configuration. 
     Both the master LED modules  12  and the slave LED modules  14  are removably mounted on the respective back plates  42  and  44  so that the individual master LED modules  12  and/or a slave module segment  54  can be removed and replaced after the display  10  is installed. As seen in  FIGS. 6-8 , a slave module segment  54  includes a first electrical connector  56  that is fixedly attached to one end of the segment  54  and a second electrical connector  58  that is connected to a second end of the segment  54 . A number of spaced slave LED modules  14  are connected between the first and second electrical connectors  56  and  58  via ribbon cables  60 . The ribbon cables  60  carry power and data to each of the slave LED modules  14  of the segment  54  from a master module  12  that is connected to one of the electrical connectors  56 . 
     As seen in  FIGS. 7 and 8 , each of the electrical connectors  56  and  58  of a slave module segment  54  includes a pair of downwardly extending rubber or elastomeric prongs  62  and  64 . The prongs  62  of the electrical connector  56  snap through apertures  66  formed in the master LED module back plate  42 . After the electrical connector  56  of the slave module segment  54  is snapped into the apertures  66  of a master module back plate  42 , each of the slave modules of the segment  54  are snapped on to respective back plate  44 . As a slave LED module  14  is snapped on to its back plate  44 , a pair of module retaining members  72  are forced apart. When the slave module  14  is snapped into its back plate, the lower edge  73  of the retaining members  72  abuts the tops of a pair of protrusions  74  formed on the side walls of the slave LED module housing  100  to retain the slave module  14  securely on the back plate  44 . The electrical connector  58  on the second end of the slave module segment  54  is inserted in apertures  67  of a master LED module back plate  42  in the next row of master modules. After the slave module segment  54  is mounted on the back plates of the cable support structure, a master LED module  12  is mounted on the back plate  42 . Specifically, a master LED module  12  is mounted on the back plate  42  on top of the connector  56  with mating connector pins  68  of the module  12  extending into the apertures  70  of the electrical connector  56 . Each of the master LED modules  12  is secured to a back plate  42  by four screws  78  that extend through apertures  80  of the back plate  42 . In a preferred embodiment, the back plate  42  of the master LED modules is formed of steel or the like so that the back plate forms a heat sink that is in contact with the ground plane  82  of the printed circuit board  128  contained in the master LED module housing  124  as discussed in detail below. It is noted, that when the master LED module  12  is bolted onto the back plate  42 , the over-molded elastomeric pads  86  of the electrical connector  56  are compressed so as to provide a water tight seal between the master LED module  12  and the electrical connector  56  of the slave module segment  54  to protect the connector from environmental effects. 
     The master LED module connected to the slave LED module segment  54  via the connector  56  provides data and power to the slave LED modules  14  of the segment  54  via the ribbon connector  60 . A LVDS cable  88  that extends from the first electrical connector  56  and the second electrical connector  58  provides a direct electrical connection between a pair of master LED modules  12  and  12 ′ of adjacent segments  24  in a column of the display  10  to allow the master LED modules of adjacent segments in a column to communicate directly as discussed in detail in the copending patent application Ser. No. 12/001,277 entitled “Data And Power Distribution System And Method For A Large Scale Display,” filed concurrently herewith and incorporated herein by reference. Adjacent master LED modules  12  and  12 ″ in a row of the display  10  communicate directly via a flex cable  90 . In a preferred embodiment, the flex cable  90  overlies a H-link  34  connecting the support cables  32  and  30  as depicted in  FIG. 2 . 
     Each of the slave LED modules  14  includes a housing  100  that is over-molded about the slave module printed circuit board  102  on which the LEDs of the module are mounted and about a portion of the ribbon cables  60  connected to the printed circuit board  102  by a IDC connector  104 . Each slave LED module is connected to the ribbon cable in a common-bus manner so that a failure of any connection does not affect the other slave modules. In order to over-mold the housings of the slave LED modules  14 , a string of, for example, fifteen printed circuit boards  102  supporting the LEDs for respective slave modules are placed in a mold wherein the fifteen printed circuit boards are connected by respective ribbon connectors  60  in a string. Thereafter, a thermoset or thermoplastic resin is injected into the mold to form a casing or housing  100  about the printed circuit boards  102  and ribbon connectors  104 . The over-molded housing of the LED modules provides extremely robust modules that can withstand harsh outdoor weather. Prior to injecting the resin to form the housing  100  of the slave LED modules  14 , a flash memory contained on the circuit board  102  is programmed with the address of the slave LED module. For a slave module segment  54  having fifteen slave LED modules, the slave modules will have an address of 1 to 15 starting in sequence with the slave LED module that is closest to the electrical connector  56  to be attached to the master LED module that will control the slave modules in a segment  24  of the display. It is noted that, while the printed circuit boards are in the molding fixture, the electronics on the boards  102  can be tested prior to over-molding. It is noted, that the mold for the slave LED module housings supports the printed circuit board  102  for the LEDs at a 10° angle from the back surface  106  of the housing. As such, when the slave LED module segment  54  is mounted vertically, the LEDs are angled downward by 10° for better viewing of the pixels generated by the slave modules when the display is in use. It should be appreciated, however, that the angle of the LEDs can be 0° to 20° where the LEDs are angled up, down or to the side depending upon the use of the display. 
     Each of the housings  100  for the slave LED modules  14  has integrally formed heat sink fins on a front surface of the housing between a first column  112  of red, green and blue LEDs and a second column  114  of red, green and blue LEDs. Placing the heat sink fins  108  between the LEDs of the module, which are actuated to form a single pixel, does not interfere with the light generated by the LEDs to form the pixel. It is noted, in a preferred embodiment, the LEDs in the first column have an order of red, green and blue; whereas the LEDs in the second column have an order of green, blue and red so as to provide better color mixing to generate the various colors of a pixel. 
     Each of the housings  100  for the slave LED modules  14  also has integrally formed sunshades  110  that project outwardly above each of the LEDs  16 ,  18  and  20 . It is noted, that in an alternate embodiment that does not have the heat sink fins  108  on the front surface of the housing  100 , one sunshade  110  may be positioned above each row of LEDs. The sunshades  110  as well as the black or dark resin used to form the housing  100  of the LEDs enhances the contrast or conspicuity of the pixels generated by the modules  14  when the display  10  is used outdoors. 
     As shown in  FIG. 8 , the housing  100  of each of the slave LED modules  14  is molded so as to form a channel  116  in the back surface  106  of the housing  100 . The channel  116  is sufficiently wide so as to be able to accommodate the cable  88  therein as well as a pair of power cables  118  and  120 . The channels  116  of the housings  100  are aligned with the ribbon cables  60  so that the LVDS cable  88  and the power cables  118  and  120  are aligned in back of the ribbon cables  60 . Thus, when viewed from the front of the display  10 , the cables  88 ,  118  and  120  are not readily visible. Further, because the cables  88 ,  118  and  120  are aligned behind the ribbon cables  60 , the display still has open areas between the modules so that if the display  10  is hung in an open area outdoors, there is relief for wind. Moreover, the open areas permit viewing through the display. Such a semi-transparent display will not block the view out of windows of a building upon which the display is hung. 
     The housing  124  for each of the master LED modules is over-molded about the master module printed circuit boards  126  and  128 . The LEDs  16 ,  18  and  20  for the master module  12  are mounted on the printed circuit board  126  which is similar to the printed circuit board  102  of the slave LED modules for controlling the illumination of the LEDs of a module. The printed circuit board  128  of the master LED module includes additional circuitry for controlling the functions of the master LED module that are unique thereto, such as extracting the data intended for the master module and its associated slave LED modules in a segment  24  of the display as described in the co-pending patent application Ser. No. 12/001,277, entitled “Data and Power Distribution System And Method For A Large Scale Display,” filed concurrently herewith and incorporated herein by reference. In a preferred embodiment, the printed circuit board  126  is soldered to the circuit board  128  at a 10° angle so that when the boards  126  and  128  are placed in the mold for the master LED module housing  124 , the LEDs  16 ,  18  and  20  will be at a 10° angle to the back surface  130  of the module  12  as described above for the LEDs of the slave module  14 . 
     The front surface of the housing  124  for each of the master LED modules  12  is the same as the front surface of the housing  100  for the slave LED modules  110  so that both types of modules have the same LED order, the same heat sink fins  108  and the same sunshades  110 , providing a uniform appearance of pixels throughout the display regardless of whether they are generated by a master or a slave module. However, the sides and the back surface  130  of the master LED module housing  124  are different than those of the housing  100  for the slave modules  102 . In particular, the sides  129  and  131  of the master module housing  124  are formed with projections  132  having apertures  134  therein for the screws  78  that attach the master LED module  12  to the back plate  42  of the master LED module. The back surface  130  of the master LED module housing  124  includes a number of integrally formed heat sinks  136  so as to further aid in the heat dissipation of the master module. It is noted that the housings for the master LED modules as well as the housings for the slave LED modules are over-molded with a thermally conductive resin. The resin conducts heat away from components and the geometry of the housing spreads the heat and provides a maximized surface area for heat transfer. Moreover, the back plate  42  is thermally and electrically connected to the ground plane on the master LED module&#39;s printed circuit board to allow the back plate  42  to act as an additional and independent heat sink for the master LED module. 
     The back surface  130  of the housing  124  of the master LED module  12  is also formed with two pairs of grooves  138  and  140  through which power cable connectors  142  and  144  extend. When power cables  118  and  120  are seated in the grooves  138  and  140  of the housing  124 , the prongs of the connectors  142  and  144 , pierce the rubber insulation of the power cables so as to make electrical contact with the cables. The power cables are continuous and the insulation piercing connectors  142  and  144  are formed with sharp prongs to minimize the force required to penetrate the rubber insulation on the cables. The preferred insulation is a thermoplastic elastomer because of its resilience and toughness. This insulation tends to close around the penetrating prongs forming a seal. It is noted that when the screws  78  that attach a master LED module  12  to a back plate  42  are tightened, the prongs of the connectors  142  and  143  are driven into the power cables. A redundant set of power connections are provided for the master LED modules so that there are two positive and two neutral connections spread apart as far as possible such that the system is tolerant to a connection failure. The master LED module  12  also includes Z-axis connectors  148  and  150  surrounded by elastomeric pads  152 . These connectors are commercially available flexible connectors that are designed to conduct along a single Z-axis. The back plate  42  compresses the Z-axis connector between contacts on the printed circuit board  128  and contacts on the flex circuit  90 . The flex circuit  90  is designed as a stripline circuit with conductors and conductor spacing adjusted to achieve the desired impedance (75 ohms). The stripline configuration also provides shielding for the data conductors. The Z-axis connectors connect to the flex cables  90  so as to allow adjacent master LED modules  12  in a row of a display panel to communicate directly as discussed above. 
     In accordance with a preferred embodiment of the present invention, the display  10  is arranged in a number of panels for easy deployment. Each panel, may have, for example, sixteen columns wherein a full height panel has 480 rows, although, each of the display panels can have any height and width desired. The support cables,  24 ,  26 ,  30 ,  32 ,  36  and  40  for the LED modules of each display panel are attached to a steel bar  60  wherein each of the steel bars  160  of a display  10  are clamped together to support the multiple display panels forming the display  10 . The steel bar  160  is then attached to a support structure  162  which is used to hoist the display  10  on to a support structure such as a building or frame. Each of the display panels forming the display  10  includes a data hub  164  that provides the video data to the display panel of the display  10 . Power to the display panel  10  may also be provided to the display  10  through the data hubs  164  so that the data hubs can monitor the power supply. Details of the data hubs and power hubs for the display  10  are disclosed in the co-pending patent application Ser. No. 12/001,277, entitled “Data And Power Distribution System And Method For A Large Scale Display,” filed concurrently herewith and incorporated herein by reference. 
     The large scale LED display of the present invention is extremely robust, readily repairable and suitable for outdoor as well as indoor use. Many modifications and variations of the present invention are possible in light of the above teachings. Thus, it is to be understood that, within the scope of the appended claims, the invention may be practiced otherwise than as described hereinabove.