Abstract:
An electronic display assembly having forced-air cooling. A thermally conductive plate or a thermally conductive backlight surface is located behind an electronic display of the electronic display assembly and within a housing thereof such that a gap is formed between the plate or backlight surface and an adjacent wall of the housing. External cooling air may be caused to flow in a top-to-bottom direction through the gap in order to remove heat from the electronic display that has been conductively transferred to the gap. A plurality of ribs may be placed within the gap and in thermal communication with the electronic display to enhance the conductive transfer of heat from the electronic display.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a continuation of U.S. application Ser. No. 14/247,658 filed on Apr. 8, 2014, which is a continuation of U.S. application Ser. No. 12/952,745 filed on Nov. 23, 2010, now U.S. Pat. No. 8,693,185 issued Apr. 8, 2014. U.S. application Ser. No. 12/952,745 is a non-provisional application of U.S. Provisional Application No. 61/321,364 filed Apr. 6, 2010. U.S. application Ser. No. 12/952,745 is also continuation-in-part of U.S. application Ser. No. 12/641,468 filed Dec. 18, 2009, now U.S. Pat. No. 8,654,302 issued Feb. 18, 2014, which is a non-provisional application of U.S. Provisional Application No. 61/138,736 filed Dec. 18, 2008. U.S. application Ser. No. 12/952,745 is also a continuation-in-part of U.S. application Ser. No. 12/411,925 filed Mar. 26, 2009, now U.S. Pat. No. 8,854,595 issued Oct. 7, 2014, which is a non-provisional application of U.S. Provisional Application No. 61/039,454 filed Mar. 26, 2008. U.S. application Ser. No. 12/952,745 is also a continuation-in-part of U.S. application Ser. No. 12/556,029 filed Sep. 9, 2009, now U.S. Pat. No. 8,373,841 issued Feb. 12, 2013, which is a non-provisional application of U.S. Provisional Application No. 61/095,615 filed Sep. 9, 2008. U.S. application Ser. No. 12/952,745 is also a continuation-in-part of U.S. application Ser. No. 12/620,330 filed Nov. 17, 2009, now U.S. Pat. No. 8,274,622 issued Sep. 25, 2012, which is a non-provisional application of U.S. Provisional Application No. 61/115,333 filed Nov. 17, 2008. U.S. application Ser. No. 12/952,745 is also a continuation-in-part of U.S. application Ser. No. 12/706,652 filed Feb. 16, 2010, now U.S. Pat. No. 8,358,397 issued Jan. 22, 2013, which is a non-provisional application of U.S. Provisional Application No. 61/152,879 filed Feb. 16, 2009. U.S. application Ser. No. 12/952,745 is also a continuation-in-part of U.S. application Ser. No. 12/630,469 filed December 3, 2009, now U.S. Pat. No. 8,497,972 issued Jul. 30, 2013. U.S. application Ser. No. 12/952,745 is also a continuation-in-part of U.S. application Ser. No. 12/618,104 filed Nov. 13, 2009, now U.S. Pat. No. 8,310,824 issued Nov. 13, 2012. U.S. application Ser. No. 12/952,745 is also a continuation-in-part of U.S. application Ser. No. 12/905,704 filed Oct. 15, 2010, now U.S. Pat. No. 8,773,633 issued Jul. 8, 2014, which is a non-provisional application of U.S. Provisional Application No. 61/252,295 filed Oct. 16, 2009. U.S. application Ser. No. 12/952,745 is also a continuation-in-part of U.S. application Ser. No. 12/753,298 filed Apr. 2, 2010, now U.S. Pat. No. 8,351,014 issued Jan. 8, 2013. All aforementioned applications are hereby incorporated by reference in their entirety as if fully cited herein. 
     
    
     TECHNICAL FIELD 
       [0002]    Exemplary embodiments described herein generally relate to cooling systems, and in particular, to cooling systems for electronic displays. 
       BACKGROUND OF THE ART 
       [0003]    Improvements to electronic displays now allow them to be used in outdoor environments for informational, advertising, or entertainment purposes. While displays of the past were primarily designed for operation near room temperature, it is now desirable to have displays which are capable of withstanding large surrounding environmental temperature variations. For example, some displays are capable of operating at temperatures as low as −22 F and as high as 113 F or higher. When surrounding temperatures rise, the cooling of the internal display components can become even more difficult. 
         [0004]    Additionally, modern displays have become extremely bright, with some backlights producing 1,000-2,000 nits or more. Sometimes, these illumination levels are necessary because the display is being used outdoors, or in other relatively bright areas where the display illumination must compete with other ambient light. In order to produce this level of brightness, illumination devices (ex. LED, organic LED, light emitting polymer (LEP), organic electro luminescence (OEL), and plasma assemblies) may produce a relatively large amount of heat. 
         [0005]    Still further, in some situations radiative heat transfer from the sun through a front display surface can also become a source of heat. In some locations 800-1400 Watts/m 2  or more through such a front display surface is common. Furthermore, the market is demanding larger screen sizes for displays. With increased electronic display screen size and corresponding front display surfaces, more heat will be generated and more heat will be transmitted into the displays. 
         [0006]    Given the well-known thermodynamic property that cool air falls and hot air rises, it was previously thought that the best way to cool an electronic display was to ingest the cool air which is found near the bottom of the display. Ingesting the warm air near the top of the display as the cooling air did not seem to make thermodynamic sense. While the air near the bottom of the display is sometimes cooler than the air near the top of the display, it was found that this is not always the case. Especially in applications where the display is mounted on a sidewalk or paved environment, heat was found to emanate from the pavement and cause the air near the bottom of the display to have a higher temperature than the air found at the top. Further, the environment near the bottom of the display was found to contain various contaminants such as dirt, dust, water, leaves, and even garbage/waste materials. These contaminants can have an adverse effect on the display if ingested or clogging up the cooling air intake. 
         [0007]    Also, when cooling air was used to cool the rear portion of an electronic display (sometimes an LED backlight or LED display) it was found that the area where the cooling air was ingested was maintained at a cooler temperature than the area where the cooling air was exhausted. Temperature variations across an electronic display may be undesirable as they can alter the optical performance of the electronic display. Some components perform differently when subjected to different ambient temperatures. Thus, with temperature variations across an electronic display there can be visible variations in the image generated by the electronic display. 
       SUMMARY OF THE EXEMPLARY EMBODIMENTS 
       [0008]    An exemplary electronic display may be placed in thermal communication with a plurality of thermally conductive ribs where the ribs are placed in the path of cooling air. The heat from the electronic display is distributed throughout the ribs and removed by the cooling air. It has been discovered that forcing air through the relatively narrow channels defined by the ribs improves the ability to remove heat from the electronic display. 
         [0009]    For example, and not by way of limitation, LED arrays are commonly used as the illumination devices for LCD displays. As mentioned above, it has been found that the optical properties of LEDs (and other illumination devices) can vary depending on temperature. Thus, when an LED is exposed to room temperatures, it may output light with a certain luminance, wavelength, and/or color temperature. However, when the same LED is exposed to high temperatures, the luminance, wavelength, color temperature, and other properties can vary. Thus, when a temperature variation occurs across an LED backlight (some areas are at a higher temperature than others) there can be optical inconsistencies across the backlight which can be visible to the observer. By using the embodiments herein, heat buildup can be evenly distributed across the ribs and removed from the display. This can prevent any potential ‘hot spots’ in the backlight which may become visible to the observer because of a change in optical properties of the illumination devices (sometimes LEDs). OLED assemblies are also known to vary performance when temperatures vary. These types of displays can also be adequately cooled with the embodiments herein. 
         [0010]    The ribs may provide an isolated chamber from the rest of the display so that ambient air can be ingested and used to cool the ribs. This is beneficial for situations where the display is being used in an outdoor environment and the ingested air may contain contaminants (pollen, dirt, dust, water, smoke, etc.) that would damage the sensitive electronic components of the display. While an exemplary embodiment could accept some contaminants, it may still be desirable to limit the amount of contaminants that could be ingested into the display. Thus, some embodiments ingest cooling air from the top of the display. The air near the top of the display has been found to occasionally contain less contaminants than the air at the bottom of the display. Still further, in some applications where the display is mounted in a paved location, heat can radiate from the paved surface below and cause the air near the top of the display to actually be cooler than the air near the bottom of the display. In these situations it might make thermodynamic sense to ingest air from the top of the display. 
         [0011]    When ingesting air from the top, it has been found that as the cooling air travels across the rear portion of the electronic display and accepts heat it increases in temperature. Once the cooling air reaches the bottom of the display, it may have increased in temperature substantially and may no longer provide adequate cooling to the bottom portion of the display. Therefore, some embodiments vary the density of the thermally conductive ribs so that a consistent temperature gradient can be achieved across the electronic display. Because the bottom portion is typically warmer, the ribs may be at a higher density in the bottom portion to account for this variation. 
         [0012]    If a backlight is used with the particular display application, a backlight with front and rear sides may be used where the front side contains the illumination devices and the rear side contains a thermally conductive surface for dissipating the heat from the illumination devices. Ideally, there should be a low level of thermal resistance between the front and rear sides of the backlights. An exemplary embodiment that requires a backlight may use a metal core PCB with LEDs on the front side and a metallic surface on the rear side. 
         [0013]    The foregoing and other features and advantages will be apparent from the following more detailed description of the particular embodiments of the invention, as illustrated in the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0014]    A better understanding of the exemplary embodiments will be obtained from a reading of the following detailed description and the accompanying drawings wherein identical reference characters refer to identical parts and in which: 
           [0015]      FIG. 1  is a perspective view of an exemplary embodiment mounted in a paved environment; 
           [0016]      FIG. 2  is a rear perspective section view of an exemplary set of thermally-conductive ribs and the air inlet aperture; 
           [0017]      FIG. 3  is a front perspective section view of an embodiment for cooling a backlight with thermally-conductive ribs; 
           [0018]      FIG. 4A  is a perspective section view of an embodiment showing a path for the cooling air; and 
           [0019]      FIG. 4B  is a perspective section view of the embodiment of  FIG. 4A  where the rear plate has been removed so that the variation in rib density can be observed. 
       
    
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
       [0020]      FIG. 1  provides a perspective view of an exemplary embodiment of an electronic display  100  mounted on a paved outdoor surface  110 . Contaminants  50  may be present on the paved outdoor surface  110  and if the display  100  were to ingest air from the bottom  101 , these contaminants  50  would likely be ingested into the display  100 . Further, heat  60  is shown radiating from the paved outdoor surface  110 . If the display  100  were to ingest air from the bottom  101  it would also likely be warmer than the heat near the top  102  because of the radiating heat  60  from the paved outdoor surface  110 . 
         [0021]    Thus, the embodiment shown ingests air from the top  102  of the display  100  so that the bulk of the contaminants  50  can be avoided. An opening may be located along the top  102  of the display, preferably along the top horizontal surface of the display  100  housing. Another opening may be located along the bottom  101  horizontal surface. Further, the cooling air  20  can sometimes enter the display  100  at a lower temperature at the top  102  than air which is present near the bottom  101  of the display  100 . While this may seem counter-intuitive based on the laws of thermodynamics, acceptable results have been observed. 
         [0022]      FIG. 2  provides a sectional view of an exemplary embodiment for thermally-conductive ribs  15 , which may be sandwiched in between a front plate  55  (preferably thermally conductive) and a rear plate  10 . Preferably, the ribs  15  are in thermal communication with the front plate  55 . The front plate  55  may be in thermal communication with the electronic display or electronic image assembly (not shown) so that heat from the electronic display can flow to the front plate  55  and into the ribs  15 . Due to the thermally-conductive nature of the ribs  15  and the thermal communication between the front plate  55  and the ribs  15 , heat which is present within the electronic display may be removed by the ribs  15 . In an exemplary embodiment, a path of cooling air  20  is used to remove the heat which has accumulated on the ribs  15 . 
         [0023]    In an exemplary embodiment, the plate  10  would provide a gaseous and contaminant barrier between the side containing the ribs  15  and the opposing side (which may house various electronic assemblies). If the plate  10  provides an adequate barrier, ambient air may be ingested as cooling air  20  and the risk of contaminants entering the side of the plate  10  containing the sensitive electronic components may be reduced or eliminated. In a similar exemplary embodiment, the front plate  55  would also provide a gaseous and contaminant barrier between the side containing the ribs  15  and the opposing side which may be in thermal communication with the electronic display. This figure also provides one example of an inlet aperture  25  which accepts the cooling air  20  and directs it along the ribs  15 . The cooling air  20  may not only remove heat from the ribs  15  but may also remove it from the front plate  55  and optionally the rear plate  10 . 
         [0024]    The ribs  15  shown in this embodiment contain a ‘Z’ cross-section, but this is not required. Other embodiments may contain ribs with I-beam cross-sections, hollow square cross-sections, hollow rectangular cross-section, solid rectangular or solid square cross-sections, ‘T’ cross-sections, a honeycomb cross-section, or any combination or mixture of these. 
         [0025]      FIG. 3  shows a front perspective section view of an embodiment for cooling a backlight with thermally-conductive ribs  15 . The backlight assembly in this embodiment includes a plurality of illumination devices  32  which are mounted on a thermally conductive substrate  30 . In an exemplary embodiment, the illumination devices  32  would be LEDs and the thermally conductive substrate  30  would be a PCB and more preferably a metal core PCB. On the surface of the thermally conductive substrate  30  which faces the ribs  15  there may be a thermally conductive front plate  55 . In an exemplary embodiment, the thermally conductive front plate  55  would be metallic and more preferably aluminum. It is preferred that the ribs  15  are in thermal communication with the thermally conductive plate  55  and that the thermally conductive plate  55  is in thermal communication with the thermally conductive substrate  30 . In some embodiments however, the thermally conductive substrate  30  may comprise traditional PCB materials rather than a metal core PCB or highly thermally conductive materials. It is preferable that there is a low level of thermal resistance between the illumination devices  32  and the ribs  15 . Cooling air  20  may again be forced along the ribs  15  in order to remove heat absorbed from the backlight assembly. 
         [0026]    As noted above, many illumination devices (especially LEDs and OLEDs) may have performance properties which vary depending on temperature. When ‘hot spots’ are present within a backlight or illumination assembly, these hot spots can result in irregularities in the resulting image which might be visible to the end user. Thus, with the embodiments described herein, the heat which may be generated by the backlight assembly can be distributed (somewhat evenly) throughout the various ribs and thermally-conductive surfaces to remove hot spots and cool the backlight and/or electronic display. 
         [0027]    In a further exemplary embodiment, the ribs  15  can also be used to cool additional electronic assemblies by placing them in thermal communication with the rear plate  10 . Thus, with the ribs  15  in a central location, the ‘front’ would be towards an intended observer of the display while the ‘back’ would be on the opposite side of an intended observer. Therefore, the front side of the ribs  15  would be in thermal communication with some portion of the electronic display assembly and the rear side of the ribs may be in thermal communication with a rear plate  10  (possibly being thermally-conductive). A single path of cooling air can then be used to cool the interior of the display while the various hot spots can distribute heat throughout the ribs and other thermally conductive surfaces to provide the most efficient cooling. 
         [0028]      FIG. 4A  is a perspective section view of an embodiment showing a path for the cooling air  20  through the inlet  61  and exhaust  65  apertures. One or more fans  51  may be used to draw the air  20  into the inlet aperture  61  and through the ribs  15 . Although shown at the bottom of the display near the exhaust aperture  65 , the fans  51  may be placed anywhere within the display so that an adequate flow of cooling air  20  is supplied. Thus, although shown in the figure as ‘pulling’ the cooling air  20  through the ribs  15 , other embodiments may ‘push’ the cooling air  20  instead. Still further, some embodiments may ‘push’ and ‘pull’ the cooling air  20 . In some embodiments, the air  20  may be air conditioned before it is directed along the ribs  15 . In some embodiments, the air  20  may be filtered before it is directed along the ribs  15  in order to remove contaminants. In the embodiment shown, thermally conductive front plate  55  is in thermal communication with the front side of the ribs  15 . Preferably, the front plate  55  is also in thermal communication with the electronic display image assembly  80 , which could be but is not limited to any of the following: liquid crystal display (LCD), OLED, plasma display assembly, light emitting polymer (LEP) assembly, organic electro luminescence (OEL) assembly, or LED display assembly. 
         [0029]    The front plate  55  may be the rear surface of an OLED assembly or the rear surface of an LED backlight assembly for an LCD. A front protective glass  70  is used to protect the electronic display image assembly  80  from damage. Solar loading (radiative heat transfer from the sun through the front protective glass  70 ) may result in a heat buildup on the electronic display image assembly  80 . Thermal communication between the electronic display image assembly  80  and the front plate  55  can provide a means for transferring the solar loading (and any other heat buildup) on the electronic display image assembly  80  to the ribs  15 , cooling air  20 , and out of the display through the exhaust aperture  65 . The front plate  55  can also be the rear surface of any backlight assembly, plasma display assembly, light emitting polymer (LEP) assembly, organic electro luminescence (OEL) assembly, or LED display assembly. 
         [0030]      FIG. 4B  is a perspective section view of the embodiment of  FIG. 4A  where the rear plate  10  has been removed so that the optional variation of density in the ribs  15  can be observed. As mentioned above, as cooling air  20  enters the inlet aperture  61  the temperature of the air is relatively low and its ability to cool the upper portion  500  of the display is relatively good. However, as the cooling air  20  travels through the ribs  15 , more heat is absorbed by the cooling air  20  and thus raises the temperature of the cooling air  20 . Therefore, once cooling air  20  reaches the lower portion  600  of the display, it has risen in temperature and is no longer as effective at removing heat from the ribs  15 , electronic image assembly  80 , front plate  55 , and possibly even the rear plate  10 . If heat is not removed at the lower portion  600  in a similar amount as the top portion  500 , there may be a temperature variance between the top of the display and the bottom of the display. As discussed above, a variation in temperature across the display can sometimes cause variations in optical properties of various components and a resulting variation of the image. 
         [0031]    To counteract this phenomenon, in some embodiments the density of the ribs  15  may optionally be higher in the lower portion  600  than in the upper portion  500  to account for the reduction in heat transfer efficiency due to the higher temperature of the cooling air  20 . By providing an increased amount of surface area for the cooling air  20  to contact, heat can be removed from the lower portion  600  (where the cooling air is relatively warm) in a similar amount as the heat removed from the upper portion  500  (where the cooling air  20  is relatively cool). This optional technique can help to balance the temperature across the front plate  55  and thus the electronic image assembly  80  to ensure that the image remains consistent across the display. 
         [0032]    It should be noted that although the inlet  61  and exhaust  65  apertures are shown in a vertical orientation on the rear wall (opposite the viewable surface) of the display housing, they can also be placed on the sides of the housing. Alternatively, the inlet aperture  61  may be on the top horizontal surface of the display housing while the exhaust aperture  65  is on the bottom horizontal surface of the display housing. 
         [0033]    Although some of the figures herein may show displays which are oriented in a portrait fashion, any orientation can be used with the embodiments described herein. Thus, landscape or widescreen orientations can also be used as well as any type of square orientation. 
         [0034]    In some embodiments, the display may not be mounted on a paved surface (or some other object/surface that is radiating heat). In these embodiments, it may be desirable to ingest air from the bottom of the display because this air might be cooler than the air at the top of the display. In this type of design, the variation in rib density may still be used to account for the warming of the cooling air as it travels up the display and exhausts out the top. Here, the top of the display will likely be warmer than the bottom and providing a higher density of ribs near the top of the display can help to balance this thermal irregularity to ensure a consistent image production. 
         [0035]    The cooling system may run continuously. However, if desired, temperature sensing devices (not shown) may be incorporated within the electronic display to detect when temperatures have reached a predetermined threshold value. In such a case, the various cooling fans may be selectively engaged when the temperature in the display reaches a predetermined value. Predetermined thresholds may be selected and the system may be configured to advantageously keep the display within an acceptable temperature range. Typical thermostat assemblies can be used to accomplish this task. Thermocouples may be used as the temperature sensing devices. 
         [0036]    It is to be understood that the spirit and scope of the disclosed embodiments provides for the cooling of many types of displays. By way of example and not by way of limitation, embodiments may be used in conjunction with any of the following: LCD (all types), light emitting diode (LED), organic light emitting diode (OLED), field emitting display (FED), light emitting polymer (LEP), organic electro luminescence (OEL), and plasma displays. Furthermore, embodiments may be used with displays of other types including those not yet discovered. In particular, it is contemplated that the system may be well suited for use with full color, flat panel OLED displays. Exemplary embodiments may also utilize large (55 inches or more) LED backlit, high definition liquid crystal displays (LCD). While the embodiments described herein are well suited for outdoor environments, they may also be appropriate for indoor applications (e.g., factory/industrial environments, spas, locker rooms) where thermal stability of the display may be at risk. 
         [0037]    Having shown and described various exemplary embodiments, those skilled in the art will realize that many variations and modifications may be made to affect the described embodiments and still be within the scope of the included claims. Additionally, many of the elements indicated above may be altered or replaced by different elements which will provide the same result and fall within the spirit of the claimed invention.