Automated Backlit Character Evaluation for Aircraft Panels

Backlit panels in aircraft cockpits and vehicle dashboards provide critical information for operators. Illuminated controls and instrumentation, gauges, characters, symbols, and shapes must be clearly visible in all ambient conditions day and night. Today LED illumination is being used most often as the backlight source. To ensure correct operation, panels must be rigorously inspected. 

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Coutries and standards organizations around the globe have strict requirements for visual quality, for example compliance with CNS/ATM and NVIS-visual standards, EASA (European Aviation Safety Agency) specifications, U.S. MIL-DT-7788 (formerly SAE-AS7788) specifications, standards by SAE-AS25050, JS G-2010-5, and others are used to determine acceptable luminance for backlit characters in aviation. The most common test method for backlit characters employs three analysis points per character, where luminance is measured and reported.

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Using three character measurement points is a common test method, with luminance measured at each point to determine character quality for pass/fail.

Quality Testing Challenges

For aircraft panel manufacturers, adherence to these standards can require extensive time and resources. The complexity of panel design for different aircraft leads to a wide range of shapes, layouts, character sets, and customized shapes that have to be inspected to ensure proper luminance and color. The result is a low volume / high mix inspection need. But there haven't been efficient and cost-effective inspection solutions for backlit panels that can easily enable manufacturers to ensure quality and to meet regulatory requirements. 

There can also be multiple parameters that need to be measured and tested, such as luminance (brightness), minimum brightness, light leakage from nearby LEDs, chromaticity (color), contrast, sunlight readability contrast defects, character position/orientation, and character verification (OCR/OCV). Quality testing typically require manufacturers to collect multiple measurements, which can require multiple metrology systems—spectrometers (spot meters), photometers and colorimeters, machine vision cameras—plus optical character recognition (OCR) capability. Each system must be set up separately to take panel measurements, and ‘trained’ on any variations in panel shape, dimensions, fonts, symbols, etc. These systems typically have extremely low tolerance for misalignment between measurement instrument and device under test (DUT), adding to QA time and complexity. If the three points aren’t aligned, pass/fail measurements aren’t accurate. 

New Solution Automates Three-Point Character Inspection 

Now Radiant has developed a new solution called Aerospce Character Evaluation (ACE) that combines our expertise in photometric imaging with OCR/OCV capabilites to perform automated three-point character recognition and measurement.  Comprising a ProMetric Imaging Photometer or Colorimeter ad TrueTest Software with ACE tools, this new approach offers multiple benefits to aircraft panel manufacturers:

Easy connectivity and integration with calibrated light sources, production systems, etc.

• High tolerance for panel placement and alignment
• High resolution sensors capture large panels in a single image or multiple small panels simultaneously
• High-quality camera hardware ensures speed, precision, and repeatability of luminance and color measurements
• Automatic alignment and dynamic registration means no repositioning
• Software provides automated sequencing and image processing in seconds
• Automated report generation 
• Ultimately, Radiant's ACE method dramatically reduces inspection time. Traditional solutions can take 30 minutes to an hour or even significantly more to inspect a single panel; ACE can complete thorough measurement of an entire panel in approximately 1 minute.

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The software has identifed this character as the letter "E" and applied the three measurment points to that character, measuring the luminance of each point against set pass/fail thresholds. 

To learn more, watch the recent webinar hosted by GlobalSpec: Automated Inspection and Verification of Backlit Character Luminance and Color (on demand with free registration). It it, Radiant's Chris Williamson reviews the methods of backlit character inspection and shows the ACE solution that integrates OCR for precise, dynamic alignment providing rapid, accurate backlit panel inspection with a single metrology system.

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