Abstract:
A system and method for determining when a LED-based position light is nearing its end of life by providing to maintenance personnel visible indication that end of life is approaching. An example system includes a controller, a main LED light, an indicator LED light, a first elapsed time counter, a second elapsed time counter, and an oscillator. The first elapsed time counter recognizes when a first time threshold is exceeded, causing the indicator LED light to flash and triggering the second elapsed time counter to start counting. The second elapsed time counter recognizes when a second time threshold is exceeded, disabling both the indicator LED light and the main LED lights, thereby notifying maintenance personnel that the main LED lights have reached their end of life.

Description:
BACKGROUND OF THE INVENTION 
     In vehicle applications, such as aviation and boating, vehicle-to-vehicle collisions are prevented by mounting navigation lights on the exterior of the vehicle. The lights function by alerting approaching vehicles of the presence and orientation of the first vehicle. The success navigation lights have in preventing collisions is partly due to an industry standard that dictates the color of light a navigation light must emit depending on the light&#39;s position on the body of the vehicle. Based on the color pattern of navigation lights visible to an approaching vehicle, the approaching vehicle can quickly deduce the direction, and therefore heading, of the vehicle it is approaching. For example green, red or white are often used to indicate the starboard, port or rear positions of a vehicle, respectively. 
     Several types of lighting are used in navigation light applications. One lighting type is the light emitting diode (LED). One problem with LED lighting in navigation lighting applications is that LED lights degrade gradually over time, compared with the catastrophic failure of incandescent lights. As a consequence of their gradual failure, LED lights carry the risk of being left in use after their level of intensity has degraded below that required for industry compliance. The airline industry imposes minimum standards for intensity level, as shown in the following table. According to industry guidelines, an aircraft should not be allowed to dispatch without navigation lights that are compliant with the following minimum standards: 
     
       
         
               
               
               
               
               
             
           
               
                   
               
             
             
               
                 Degrees from longitudinal axis 
                 0-10 
                 10-20. 
                 20-110 
                 110-180 
               
               
                 Minimum intensity (cd) 
                 40 
                 30 
                 5 
                 20 
               
               
                   
               
             
          
         
       
     
     To prevent LED lights from being inadvertently left in operation after their intensity has fallen below an accepted intensity threshold, a number of systems have been developed. One system is a timer system that disables LED light operation after a certain period of time. Another is a manual maintenance log system. The timer system does provide a level of assurance that the lights will comply with requirements, however disablement can occur unexpectedly, leading to the need for unexpected delays in vehicle operation for maintenance. The manual maintenance log system suffers from the requirement for human diligence. An ideal maintenance system would provide an indication a certain period of time in advance that an LED lighting system is approaching the time when it needs to be replaced. 
     SUMMARY OF THE INVENTION 
     The present invention provides systems and methods for determining when an LED-based navigation light is nearing its end of life, and for providing visible indication to maintenance personnel that the light&#39;s end of life is approaching. 
     An example system includes a controller, a main LED light, an indicator LED light, a first elapsed time counter, a second elapsed time counter, and an oscillator. According to the method, the first elapsed time counter monitors the time that the main LED lights are illuminated. When the elapsed time counter recognizes that a first threshold is exceeded, the first elapsed time counter outputs a signal to the oscillator and to the second elapsed time counter. The oscillator enables the indicator LED light to illuminate and/or flash, providing an indication to maintenance personnel that the main LED lights have entered a near end of life period. 
     The second elapsed time counter starts counting, measuring the duration of time the main LED lights are illuminated during the near end of life period. When the second elapsed time counter recognizes that a second threshold is exceeded, the second elapsed time counter outputs a signal that disables both the indicator LED lights and the main LED lights. Disablement of both the main and indicator LED lights notifies maintenance personnel that the main LED lights have reached their end of life. In an alternative approach, the indicator LED light continues to illuminate and/or flash after the main LEDs are disabled due to exceeding the second time threshold. In a third approach, the indicator LED light continues to illuminate and/or flash after the main LEDs are disabled from exceeding the second time threshold, but flashes at a different frequency or according to a different pattern than during the period before the second time threshold. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings: 
         FIG. 1  illustrates a top view of an aircraft having an example light emitting diode (LED) navigation light module formed in accordance with an embodiment of the present invention; 
         FIG. 2  illustrates a block diagram of the LED navigation light module shown in  FIG. 1 ; 
         FIG. 3  illustrates a flow diagram of an example method performed by the LED navigation light module of  FIG. 2 ; 
         FIG. 4  illustrates an example embodiment of an LED navigation light module; 
         FIG. 5  illustrates a bottom view of an example embodiment of the LED navigation lights used in an LED navigation light module; and 
         FIG. 6  illustrates a perspective view of an LED light unit from an LED navigation light module. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       FIG. 1  illustrates an aircraft  10  having a light emitting diode (LED) navigation light module  14  mounted to a wing  16 . The LED navigation light module  14  prevents collisions with other aircraft by alerting approaching aircraft of the presence and navigation direction of the aircraft  10 .  FIG. 1  also illustrates an example of the illumination requirements by color for various illumination zones  17 ,  18 ,  19  around the aircraft  10  according to one industry standard. 
       FIG. 2  illustrates a block diagram of the LED navigation light module  14  and a control interface  20 . The LED navigation light module  14  includes a controller  22 , main LED lights  24 , an indicator LED light  26  and a memory  28 . 
     The control interface  20  is in signal communication with the controller  22 . The controller  22  is in signal communication with both the main LED lights  24  and the indicator LED light  26 , and memory  28 . In this embodiment, the control interface  20  is located remotely from the LED navigation light module  14  however in other embodiments the control interface  20  can be located within the LED navigation light module  14 . The main LED lights  24  alert approaching aircraft to the position and direction of the aircraft  10 . The indicator LED light  26  visibly alerts maintenance personnel when the main LED lights  24  are nearing their end of life. The memory  28  stores current and historical information about the operation of the LED navigation light module  14  that maintenance personnel are able to access and view. 
     The control interface  20  allows personnel to change control parameters that affect the operation of the LED navigation light module  14 . In one embodiment, the control interface  20  is located within the LED navigation module  14 , so that the control interface  20  is accessible to personnel. In another embodiment, the control interface  20  is located in a cockpit of the aircraft  10 , so that the control interface  20  is accessible to a pilot or flight crew. In another embodiment, the control interface  20  is within the LED navigation module  14 , but an indication signal is also passed to the aircraft cockpit to alert the pilot or flight crew. 
       FIG. 3  illustrates a flow diagram of an example process  30  as performed by the LED navigation light module  14  of  FIG. 2 . Starting at a block  32 , the example process  30  starts an elapsed time counter  1 . Next at a first decision block  34 , the example process  30  determines if the main LED lights  24  are on. If the main LED lights  24  are not on, then the example process  30  proceeds to a first delay block  36  and a delay occurs. After the delay at the first delay block  36 , the example process  30  proceeds back to the first decision block  34  again. If at the first decision block  34  the main LED lights  24  are on, then the example process  30  proceeds to a block  38  that adds a length of time to elapsed time counter  1  equal to the length of the delay in the first delay block  36 . 
     Next at a second decision block  40 , the example process  30  determines if the accrued time in elapsed time counter  1  exceeds alarm threshold  1 . If the value in elapsed time counter  1  is less than alarm threshold  1 , then the example process  30  proceeds back to the first delay block  36 . If at the second decision block  40  the elapsed time counter  1  exceeds the alarm threshold  1 , then the example process  30  intermittently illuminates the indicator LED light  26 , indicating that the main LED lights  24  are nearing end-of-life, see block  42 . 
     Next at a block  44 , an elapsed time counter  2  starts. Next at a third decision block  46 , the example process  30  determines if the main LED lights  24  are on. If the main LED lights  24  are not on, then the example process  30  proceeds to a second delay block  48  and a delay occurs. After the delay at the second delay block  48 , the example process  30  proceeds back to the third decision block  46 . If at the third decision block  46  the main LED lights  24  are on, then the example process  30  adds a length of time to the elapsed time counter  2  equal to the length of the delay in the second delay block  48 , see block  50 . 
     Next at a fourth decision block  52 , the example process  30  determines if the accrued time in elapsed time counter  2  exceeds alarm threshold  2 . If the value in elapsed time counter  2  is less than alarm threshold  2 , then the example process  30  proceeds back to the second delay block  48 . If at the fourth decision block  52  the elapsed time counter  2  exceeds alarm threshold  2 , then the example process  30  disables the main LED lights  24 , see block  54 , then proceeds to disable the indicator LED light  26 , see block  56 . 
       FIG. 3  also includes an alternative outcome, whereby after the fourth decision block  52  the example process  30  disables the main LED lights  24  at block  54  and then proceeds to change the intermittent illumination frequency or the intermittent illumination pattern of the indicator LED light  26 , see block  58 . 
       FIG. 4  illustrates an example embodiment LED navigation light module  14 - 1 . The LED navigation light module  14 - 1  includes main LED lights  24 - 1 , an indicator LED light  26 - 1 , a first elapsed time counter  60 , a second elapsed time counter  62 , an oscillator  64 , an inverter  66 , an AND gate  68 , a power supply  70 , a driver  72  and a switch  74 . 
     An example control interface  20 - 1  is communicatively coupled with the main LED lights  24 - 1 , the first elapsed time counter  60 , and the switch  74  of the example LED navigation light module  14 - 1 . An output of the first elapsed time counter  60  is communicatively coupled with an input of the second elapsed time counter  62 . An output of the second elapsed time counter  62  is fed to the inverter  66  which proceeds to one of a plurality of inputs of the AND gate  68 . One of the inputs from the AND gate  68  is communicatively coupled to the oscillator  64 , which is communicatively coupled to the output of the first elapsed time counter  60 . An output of the AND gate  68  is communicatively coupled to the driver  72 . The driver  72  receives power from the power supply  70 . An output of the driver  72  is coupled to indicator LED light  26 - 1 . 
     A positive output at the first elapsed time counter  60  triggers an oscillating positive output signal from the oscillator  64 . Intermittent and/or continuous illumination of the indicator LED light  26 - 1  occurs by the oscillating positive output signal from the oscillator  64  in combination with a negative signal at the output of the second elapsed time counter  62 . The intermittent positive signal at the output of the AND gate  68  directs the driver  72  to intermittently deliver power from the power supply  70  to the indicator LED light  26 - 1 , causing the indicator LED light  26 - 1  to flash. 
     Disabling of the indicator LED light  26 - 1  occurs whenever a positive signal exists at the output of the second elapsed time counter  62 . A positive signal at the output of the second elapsed time counter  62  permanently causes at least one input of the AND gate  68  to receive a negative signal because the output of inverter  66  goes low/negative. The permanently negative input prevents the AND gate  68  from enabling the driver  72  from delivering any power to the indicator LED light  26 - 1 , thereby disabling the indicator LED light  26 - 1 . A positive signal at the output of the second elapsed time counter  62  also causes the switch  74  to interrupt power to the main LED lights  24 - 1 , disabling the main LED lights  24 - 1 . 
     For the optional outcome of the example process  30  of  FIG. 3 , it should be apparent to someone skilled in the art that the circuit of  FIG. 4  could be modified to allow the indicator LED light  26 - 1  to continue to be illuminated after the main LED lights  24  are disabled. In one embodiment, the oscillator  64  is communicatively coupled to the driver  72 , bypassing the AND gate  68 . Once the elapsed time counter  160  exceeds its threshold, the oscillator  64  enables the driver  72  to illuminate the indicator LED light  26 - 1  independent of the elapsed time counter  262 . 
       FIG. 5  illustrates a bottom (maintenance worker) view of an example LED navigation light module  14 - 2  formed according to another embodiment. Example navigation LED light module  14 - 2  includes main LED lights  24 - 2 , an indicator LED light  26 - 2 , a transparent lens  80 , a lens frame  82  and a lens space  84 . The lens frame  82  holds the lens  80  fast to the body of the vehicle  10 . Within the lens space  84  defined by the lens  80  are the LED main lights  24 - 2  and the indicator LED light  26 - 2 , both of which are visible from the exterior due to the transparency of the lens  80 . In one embodiment, the LED navigation light module  14 - 2  operates consistent with the example process  30  of  FIG. 3 . 
       FIG. 6  illustrates an embodiment of how the main LED lights  24 - 2  and the indicator LED light  26 - 2  of  FIG. 5  are fastened to the body of the vehicle  10 . The LED navigation light module  14 - 2  includes an LED light unit  90 . The LED light unit  90  includes a mount  92 , at least one circuit board  94 , the main LED lights  24 - 2  and the indicator LED light  26 - 2 . In this embodiment of the LED light unit  90 , a pair of main LED lights  24 - 2  is mounted to each of at least one circuit board  94 . At least one of the circuit boards  94  includes the indicator LED light  26 - 2 . The at least one circuit board  94 , carrying at least one indicator LED light pair  24 - 2 , is affixed to the mount  92 . In this embodiment of the LED navigation light module  14 - 2 , two LED light units  90  are included, but in alternative embodiments any number of the light units  90  can be included. 
     In another embodiment the indicator LED light  26 - 2  is 2 mm×3 mm in size and powered by 10 mA of current at 1.2 volts. The main LED light  24 - 2  can be Honeywell Part No. 72324693 and the entire LED anti-collision light module  14 - 2  can be Honeywell Part No. 72303144. However embodiments using components from other sources are still within the scope of this invention. 
     In yet another embodiment, the indicator LED light  26  is fitted on the aircraft so that the indicator LED light  26  is conspicuous to maintenance personnel, but does not interfere with the function of the main LED lights  24 . Once the indicator LED light  26  becomes illuminated, maintenance personnel have a predetermined number of hours to replace the associated main LED light  24  prior to the main LED light  24  ceasing operation. 
     In a further embodiment, the LED navigation light module  14  is located on the wing  16  according to aviation regulatory requirements. 
     An advantage of an additional LED indicator  26  that energizes prior to the end-of-life of the main LED light  24  is that the aircraft operator can schedule for replacement during normal maintenance downtime. Scheduling for replacement can be especially important in embodiments of an LED navigation light module  14  that require the removal of a lens  80  to replace the main LED lights  24 . In instances where accessing and re-assembly of the LED navigation light module can take a day, if one light is replaced but a short time later another main LED light  24  fails, a significant opportunity for cost savings can be lost. Therefore there is a practical advantage to having an indicator LED light  26  to notify maintenance personnel about other main LED lights  24  in the LED navigation light module  14  approaching their end of life. 
     While the preferred embodiment of the invention has been illustrated and described, as noted above, many changes can be made without departing from the spirit and scope of the invention. For example, the number of main LED lights  24  and indicator LED lights  26  in each LED light unit  90  or in each LED navigation light module  14  can vary. Alternatively, the frequency of illumination of the indicator LED light  26  can vary, or the pattern of illumination can vary from other than simply intermittent. Furthermore, a plurality of alarm stages, rather than just one, is considered within the invention&#39;s scope. Finally, it should be recognized that a number of alternative circuit embodiments to that disclosed in the LED navigation light module  14 - 1  of  FIG. 4  are also considered included within the invention&#39;s scope. Accordingly, the scope of the invention is not limited by the disclosure of the preferred embodiment. Instead, the invention should be determined entirely by reference to the claims that follow.