Abstract:
A solid state microprocessor or digital signal processor (DSP) for dual mode illumination and dimming into modern aerospace searchlights. The system is a universal dimming platform with “smart functions” that include and are not limited to multiple light intensity linearization curves, analog and/or digital input dimming interface, built-in tests and health monitoring, synchronized dual mode light output with canopy position, light driver redundancy, lamp life reporting, and controlled switching with improved EMI. With real-time monitoring of the system parameters it monitors the lights proper operation and failures which can be a concern for flight-critical lighting.

Description:
PRIORITY CLAIM 
       [0001]    This application claims priority to provisional patent application Ser. No. 60/941,583 filed on Jun. 1, 2007 and is incorporated herein by reference. 
     
    
     GOVERNMENT RIGHTS 
       [0002]    The U.S. Government may have rights to this invention under U.S. Army contract number DAAH23-03-D-0204. 
     
    
     BACKGROUND OF THE INVENTION 
       [0003]    Aerospace searchlights that are based on mechanical switches or relays have limited or no built-in capabilities for visible (VIS) or infrared (IR) light dimming. In such searchlights the added dimming functionality in most cases will require two external dimmers; one for the VIS and the other for the IR. Because light dimming requires added electronic components within a limited space, and because of the added challenges in thermal management and electromagnetic interference (EMI), recent solid state based dual mode searchlights controllers are limited to motor actuation control and light source enabling or disabling without dimming. Older searchlight technologies do not support programmable dual mode universal light controls, interface to the canopy position, or integration to aircraft management systems. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention provides a solid state microprocessor or digital signal processor (DSP) (a system controller) for dual mode illumination and dimming into modern aerospace searchlights. The present invention provides a universal dimming platform with “smart functions” that include and are not limited to multiple light intensity linearization curves, analog and/or digital input dimming interfaces, built-in tests and health monitoring, synchronized dual mode light output with canopy position, light driver redundancy, lamp life reporting, and controlled switching with improved EMI. With real-time monitoring of the searchlight parameters, the system controller monitors the lights proper operation and failures which can be a concern for flight-critical lighting. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0005]    Preferred and alternative embodiments of the present invention are described in detail below with reference to the following drawings: 
           [0006]      FIGS. 1-3  are schematic diagrams of an example system formed in accordance with an embodiment of the present invention. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
       [0007]    As shown in  FIG. 1 , a microprocessor or digital signal processor (DSP)-based dimming control system  20  provides a universal programmable platform that can be modified to meet the needs of various lighting systems requiring variable light intensity. In one embodiment, the system  20  provides two modes of illumination. The first mode is visible light illumination, based on halogen or incandescent lighting, and the second mode of illumination is infrared (IR) illumination, based on solid state light-emitting diodes (LED). The system  20  provides dimming control during the two modes of illumination. The system  20  performs self adjustment in order to provide linear dimming from 0-100% intensity. 
         [0008]    In one embodiment, the system  20  includes a controller  24 , a visible light circuit  28 , an IR light circuit  30 , memory  34 , a canopy system  36 , user interface controls  32 , and one or more environmental sensors  40 . The controller  24  receives information from the user interface controls  32 , the canopy system  36 , stored data from memory  34  and environment sensor data in order to determine how to control operation of the circuits  28 ,  30 . The controller  24  may be an off-the-shelf microprocessor or DSP that is programmed to operate as described below. 
         [0009]    The circuits  28 ,  30  include visible and IR lights that are part of a searchlight included on a rotating hub that is housed in a canopy. The canopy system  36  provides enable and disable signals based on canopy feedback sensor(s) (not shown) to the controller  24 . When the feedback sensor(s) determines when the searchlight is clear of a aircraft mounting platform (not shown), an enable signal is produced. The controller  24  controls operation of the circuits  28 ,  30  based on the received enable and disable signals. In one embodiment, the controller  24  and canopy system  36  communicate using a serial communication interface or other comparable communication signaling method. 
         [0010]    In one embodiment, the controller  24  operates in a relatively high-voltage state thereby reducing the noise-to-signal ratio as much as possible. For example, signals outputted by the controller  24  are level shifted from 3.3 VDC to 5.0 VDC (see level shifts in the following figures). Similarly, input signals to the controller  24  are shifted down from 5.0 VDC to 3.3 VDC. Also, communication with the nonvolatile memory  34  is performed using a serial or other type of digital interface. The controller frequency is set by a built-in phase locked loop (PLL) and the base frequency is set by an external crystal oscillator. 
         [0011]    The memory  34  may include electrically erasable, programmable, read-only memory (EEPROM) or flash memory that is in communication with the controller  24 . The controller  24  may include various other types of wired or wireless communication means, such as a joint test action group (JTAG) interface or RS-232 that allow connection of an external diagnostic system (not shown), such as a hand-held computer system. 
         [0012]    In one embodiment, the environmental sensors  40  include a temperature sensor (not shown) that is mounted within or near the circuit  28 ,  30 . The temperature sensor outputs a temperature signal to the controller  24 . The controller  24  analyzes the received temperature signal to determine if the sensed temperature is above a predefined threshold temperature limit. If the sensed temperature is above the threshold temperature limit, then the controller  24  records a fault into the memory  34  and may deactivate the respective circuit  28 ,  30 . 
         [0013]      FIG. 2  illustrates a more detailed example of the visible light circuit  28 . The circuit  28  includes level shifts  70 ,  74 , a driver isolation (charge pump) component  72 , four switches  54 ,  56 ,  66 ,  68 , two halogen or incandescent lights  60 ,  62 , two current sensors  78 ,  80 , and two amplifier filters  82 ,  84 . The level shifts  70 ,  74  are configured to receive two pulse-width modulation (PWM) independent control signals from the controller  24 . In one embodiment, the switches  54 ,  56 ,  66 ,  68  are N-channel MOSFETs. The drains of switches  54 ,  56  are connected to a main bus power supply  50 . The main bus power supply  50  supplies a source voltage, an average voltage value and a current value to the controller  24  for analysis. The source of the switch  54  is connected to a first lead of the light  60 . The source of the switch  56  is connected to a second lead of the light  60  and a first lead of the light  62 . The gate of the switch  54  is connected to the driver isolation component  72  in order to receive an adjusted PWM 1  signal from the controller  24 . The gate of the switch  56  is connected to the driver isolation component  72  in order to receive an adjusted PWM 2  signal. PWM 1  and PWM 2  are increased in voltage by the level shift  70  and are controlled by the driver isolation component  72  in order to maintain the switches  54 ,  56  within an operating zone, because their sources are not connected to ground. The second level shift  74  receives a PWM 3  signal and PWM 4  signal from the controller  24 . The PWM 3  signal is increased in voltage by the level shift  74  and sent to the gate of the switch  66 . The drain of the switch  66  is connected to a second lead of the light  62 . The source of the switch  66  is connected to ground through the first current sensor  78 . The PWM 4  signal is increased in voltage by the level shift  74  and sent to the gate of the switch  68 . The drain of the switch  68  is connected to the second lead of the light  60  and the first lead of the light  62 . The source of the switch  68  is connected to ground through the second current sensor  80 . The current sensors  78 ,  80  are connected to respective amplification filters  82 ,  84 , which block high frequency noises and increase the resolution with a higher signal-to-noise ratio. The output of the amplification filters  82 ,  84  are sent to the controller  24  via analog to digital (A/D) converters  87 ,  88 . 
         [0014]    The PWM 1 - 4  signals (channels) are independent with adjustable frequency in phase in order to reduce electromagnetic interference (EMI). The PWM 1 - 4  signals control the voltage modulation across the switches  54 ,  56 ,  66 ,  68  and thus the power across the two lights  60 ,  62 . After the enable signal is received from the canopy system  36  and a visible lamp ON/OFF switch has been activated in the ON position (and possibly a master light ON signal), the PWM 1  and PWM 3  signals activate their switches  54 ,  66 , while the PWM 2  and PWM 4  signals do not. This causes power supplied by the main bus power supply  50  to pass through the switch  54  through the lights  60 ,  62  and then to ground through the switch  66  and current sensor  78 . The controller  24  performs dimming after a dimming signal has been received from the user interface controls  32 . Dimming of the halogen or incandescent lights  60 ,  62  is performed by changing the duty cycle of PWM 1  and PWM 3  signals. The controller  24  determines the duty cycle according to information stored in the memory  34 . The stored information includes a brightness linearization curve and a PWM duty cycle for a desired light output. 
         [0015]    During a running condition and after a specific halogen or incandescent start-up delay, the average halogen or incandescent current is monitored by the controller  24  to determine whether the lamp current outputted by the analog to digital (A/D) converter  87  is above the normal operating level. If the current exceeds the normal level, the halogen or incandescent lights  60 ,  62  may be deactivated for a specific predefined period of time followed by a restart attempt provided that the halogen or incandescent command is still being issued. The controller  24  identifies this condition as a fault and records the fault in the memory  34 . If the controller  24  determines that this improper lamp current still exists, the lights  60 ,  62  may be shut down. In one embodiment, the functionality provided by the A/D converter  86  can be performed by other devices, such as an external hardware interrupt request (IRQ), which forces the DSP (controller  24 ) to stop the execution and support of other functions and immediately service the fault related tasks. 
         [0016]    The control system  20  provides a “reversionary” mode where the status of both light filaments  60  and  62  is continuously monitored and the current path is switched to go through the “healthy filament” and bypass the failed or open filament. The circuit  28  includes an A/D converter  86  that samples the voltage between the two lights  60 ,  62 . The A/D converter  86  converts the voltage signal to digital form and sends it to the controller  24  for analysis. If the controller  24  determines that the sample voltage falls below a predefined set value stored in the memory  34 , an open circuit condition is identified thereby producing an indication that light  60  is in an open state. If this situation occurs, the controller  24  disables the PWM 1  signal and enables the PWM 2  and PWM 3  signals, thereby opening the switch  54  and closing the switch  56 . 
         [0017]    As an alternative “reversionary” and detection method during normal operation with the switches  54  and  66  are enabled to monitor the current from the sensor  78  and continuously provide its value to the controller  24  via the amp filter  82 . The controller  24  can change the operation of the switches  54 ,  56 ,  66 , and  68  based on the information received from the current sensor  78 . For example, if the current sensor  78  shows that the current has dropped below a predefined set value, the controller  24  disables the switches  56  and  66 , and enables the switches  54  and  68 , then checks the current sensed at the current sensor  80  as sent through the amp filter  84 . If the current received from the current sensor  80  is below an acceptable value, then the light  60  is in an open state and the light  62  is still acceptable for use. In this case, the switches  54  and  68  will be disabled and the switches  56  and  66  will be enabled. However, if the current sensed at the current sensor  80  is also below the predefined value, then both of the lights  60 ,  62  must be replaced. 
         [0018]    The controller  24  also monitors voltage and current values from the main bus power supply  50 . If the controller  24  determines that the voltage of the main bus power supply  50  exceeds an upper threshold voltage, a fault is logged into the memory  34  and may shut down the lights  60 ,  62 . If the controller  24  senses that the voltage has fallen back below the upper threshold voltage then the controller  24  reactivates the lights  60 ,  62 . 
         [0019]    The controller  24  also monitors average voltage produced by the main bus power supply  50 . The controller  24  may record average voltage at various sample rates into the memory  34  and/or may only record when the average voltage exceeds a predefined threshold value. The recorded average voltage information is used later by a health monitor component/diagnostic system to determine the life of the circuit components, specifically the halogen or incandescent lights  60 ,  62  and any LEDs. If this condition is detected as a result of the main power interruption or simply by shutting off the main power to the light system, the controller  24  will disable the power stage components ( 54 ,  56 ,  66 ,  68 ,  70 ,  72 ,  74 ,  92 ,  96 ,  100 ,  102 ,  114 ,  118 ,  120 , and  122 ), shut off the lights  60 ,  62  and save the latest system variables into the memory  34  until the monitored bus voltage returns to an acceptable voltage. The last stored variables (parameters or states like faults, temperature, average voltage, . . . etc.) will be the default starting values after power interruption recovery. 
         [0020]    The controller  24  also receives a current signal from the main bus power supply  50  for monitoring if the main bus produces an excessive current spike for a value greater than a predefined threshold stored in memory  34 . If a current spike greater than the threshold is detected, the controller  24  disables power, shuts off the lights  60 ,  62  and saves the latest system variables into the memory  34  until the monitored bus current returns to a value below the threshold. 
         [0021]      FIG. 3  illustrates a more detailed example of the IR light circuit  30  from  FIG. 1 . In one embodiment, the IR light circuit  30  includes a primary LED circuit  90  and a secondary LED circuit  110 . Each of the circuits  90 ,  110  are similar. The circuits  90 ,  110  include a first switch  92 ,  114  (N-channel MOSFET), that receives a supply voltage from a voltage regulator bus  150  that converts the main DC supply voltage into an appropriate level to operate the LEDs. It also includes a circuit to limit and regulate the current output. A gate of the switches  92 ,  114  is connected to respective power driver EMI filters  100 ,  120 . The source of the switches  92 ,  114  is connected to an input of an LED  94 ,  116 . The outputs of the LEDs  94 ,  116  are connected to a drain of a switch  96 ,  118  (N-channel MOSFET). The gates of the switches  96 ,  118  are controlled by the respective power driver EMI filter  100 ,  120 . The sources of the switches  96 ,  118  are connected to a current sensor  104 ,  124 . The circuits  90 ,  110  also include level shifts  102 ,  122  that boosts the voltage of the received PWM 5 - 8  signals. PWM 5 - 8  signals control operation of the switches  92 ,  96 ,  114 ,  118 . During normal operation, the PWM 5 ,  6  signals sent to the level shift  102  activate the switches  92  and  96 , thereby causing the LED  94  to illuminate. The PWM 7 ,  8  signals deactivate the switches  114 ,  118 . 
         [0022]    The controller  24  minimizes EMI emissions by providing a gradual increase in the duty cycle of PWM 5 ,  6  and PWM 7 ,  8  signals. The implementation of the phase shift between the signals is performed using hardware and/or software. The controller  24  may include an additional external shift register or delay circuit in order to accomplish the phase shift. 
         [0023]    Amplification filters  106 ,  126  are connected to the current sensors  104 ,  124  for amplifying a current value that is generated by the current sensors  104 ,  124 . A/D converters  108 ,  128  convert the output of the amplification filters  106 ,  126  into digital signals for use by the controller  24 . The controller  24  determines if an open or short circuit is present based on the signals sent from the current sensors  104 ,  124  via the amplification filters  106 ,  126  and the A/D converters  108 ,  128 . The controller  24  activates the secondary circuit  110  if the controller  24  determines that a short circuit condition exists in the primary circuit  90 . The controller  24  also senses if the LED circuits  90 ,  110  are operating above or below normal operating levels based on the sensed current received from the A/D converters  108 ,  128 . During a running condition, and after a specified start-up delay, the controller  24  monitors the average sensed current to determine whether the LED  94  or  116  is above or below normal operating level. If the current exceeds the normal level, the controller  24  deactivates the LEDs  94 ,  116  for a specified wait period followed by an attempt to restart provided the user interface controls  32  has IR illumination selected. The controller  24  records a fault into the memory  34 . If the controller  24  still identifies an unacceptable sensed current after the respective circuit  90 ,  110  is restarted, the LEDs  94 ,  116  are deactivated. 
         [0024]    PWM channels  5 - 8  signals also control the voltage modulation and thus power across the LEDs  94 ,  116 . The controller  24  provides dimming of the LEDs  94 ,  116  from light intensities ranging from 0-100% by changing the duty cycle of the respective PWM 5 - 8  signals. 
         [0025]    In one embodiment, the system  20  is configured to have default initial factory dimming levels for the visible light circuit  28  and the IR light circuit  30 . The factory dimming levels may be stored in the memory  34 . If the dimming levels are changed either by an operator or automatically by the controller  24 , the controller  24  stores the new dimming level in the memory  34  and uses that as the default illumination condition for the next activation of the respective circuit. 
         [0026]    The PWM 1 - 8  signals are at least partially independent of each other and include adjustable frequencies and phases that are controlled by the controller  24 . This allows the controller  24  to control noise as well as reduce EMI. 
         [0027]    The user interface controls  32  include any of a number of or combination of different types of light and dimming controllers. For example, the user interface controls  32  include push-button dimming controls or analog dimming control inputs (0.2-4.8 VDC). Also, the user interface controls  32  include a master lamp ON/OFF momentary switch that activates all lamp control operations. The activation logic for the master lamp switch is either performed on edge or level logic. A level logic is a constant voltage level applied (for example 28 VDC or 5 VDC can be defined as logic high and zero as logic low). If rising or falling edge logic is used, the edge of switch activation is detected once (logic low-to-high or high-to-low). When a second edge is detected all light controls are disabled. The enabling and disabling function continues at every other edge. If a level logic is selected, a logic high enables the light functions. 
         [0028]    The controls  32  also include two independent up/down (brighter and dimmer) momentary switches for controlling dimming of the visible light circuit  28  or the IR circuit  30 . When one of the dimming control switches is activated and held, the controller  24  increases or decreases the illumination of the lights  60 ,  62  or LEDs  94 ,  116  linearly from 0-100% within a period controlled by a variable stored in the memory  34 . This variable controls the brightness level as a function of time. 
         [0029]    The controller  24  includes a means for adjusting dimming characteristic curves for the visible light circuit  28  and the IR circuit  30 . In one embodiment, initial implementation may be non-linear. Once the proper characterization curve has been determined, scaling factors based on a correlation table/curve or function are applied to linearly dim the lights  60 ,  62  or LEDs  94 ,  116 . Light photometrics testing is initially conducted in the lab (prior to production) to establish the proper correlation between light output and the PWM duty cycles when dimming is activated. 
         [0030]    Whenever the main power bus (e.g., 28 VDC bus) is recycled (turned OFF and ON), the controller  24  assumes that the lights  60 ,  62  and LEDs  94 ,  116  are operating properly and operates according to that assumption. 
         [0031]    The controller  24  performs a soft start function. When either of the circuits  28 ,  30  are activated, the controller  24  ramps up the modulated duty cycle to a target duty cycle at a predefined rate (stored in memory  34 ). 
         [0032]    The controller  24  continuously performs health monitoring analysis. Test mode (for maintenance and diagnostics), fault isolation and life/elapsed run times for the lights  60 ,  62  and LEDs  94 ,  116  are captured and stored in the memory  34  for later diagnostic analysis and system life tracking. The controller  24  detects all faults and stores them in the memory  34 , even if the fault condition disappears. Resetting and clearing of selected fault codes may be manually or automatically performed. The following is an example of recorded faults from lowest to highest:
       1. No fault conditions;   2. Lamp invalid switch command;   3. Lamp bus under-voltage or power off;   4. Lamp power stage over temperature;   5. Lamp bus over-voltage;   6. Secondary LED open circuit;   7. Secondary LED short circuit;   8. Primary LED open circuit;   9. Primary LED short circuit;   10. Halogen or incandescent light open circuit; and   11. Halogen or incandescent short circuit.       
 
         [0044]    The controller  24  can also determine if faulty command control inputs are applied. In such a case, the controller  24  records faulty control inputs in the memory  34 . 
         [0045]    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. 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.