Case Studies

LCD Screen Automated Vision Inspection System

Posted in Automotive, LabVIEW, Test & Measurement Automation, Test Stand

Summary

DMC designed, built, and programmed an automated infotainment inspection system for LCD screens for vehicle cockpit displays. The system used NI TestStand to execute a series of vision inspection algorithms to detect scratches, dead pixels, incorrect telltale symbols, and display of analog color bar patterns.

Solution

DMC delivered a custom turnkey test stand for LCD screens for dashboards for an automotive company. We used NI TestStand as a test executive to perform a series of automated vision inspections on the LCD screen and surrounding tell-tale indicators. Two cameras, one color, and one monochrome were used to perform a variety of inspections. The monochrome camera provided higher resolution to check for dead pixels and scratches on the surface of the screen. The color camera was used to verify the color of tell-tale indicators and analog color bars.

CAD model of DUT fixturing

Figure 2. CAD model of DUT fixturing.

How It Works

The automated test controlled a variety of lights to illuminate the automotive display screen from various angles and capture a series of images to be able to detect small scratches at any orientation. The software also commanded the device under test (DUT) to display a variety of test patterns to check for dead or stuck-on pixels. Every single pixel was validated in both the on and off states. The test stand communicated with the DUT via a CAN protocol. The screen had an analog video input that was validated by inputting a known pattern using an analog color bar generator. The color camera acquired an image, and the software confirmed the pattern’s presence.

Dead pixel detection.

Figure 3. Dead pixel detection

Illuminated scratches on the screen.

Figure 4. Illuminated scratches on a screen

Tell-tale indicator lights were commanded to be lit via CAN commands. Then, the color camera acquired an image to verify that the proper indicator turned on, in the expected location, with the expected symbol, and that the color matched the expected color. The automated system quickly sequenced through each tell-tale indicator individually to confirm all commands were functional.

Using NI TestStand provided the customer with the flexibility to modify the test sequence and parameters without requiring a high-level of programming expertise. DMC also leveraged TestStand’s built-in logging and reporting features to provide traceability data to the customer. DMC helped the customer commission the test station for the first model of DUT. The customer was able to subsequently expand the system to support additional DUTs with similar feature sets.

Conclusion

The fundamental designs, principle, and features of this particular custom system are directly applicable to the validation of the ever-increasing number and complexity of infotainment displays found in modern vehicles. Learn more about DMC’s LabVIEW Vision Application Development, Automated Test Stand Design, and LabVIEW Programming services.

Customer Benefits

  • Consistency – The automated system ensures that tests are performed with a consistent methodology and higher degree of sensitivity to defects.
  • Accuracy – Detection of single dead pixels or slightly inaccurate colors that cannot be reliably detected by a human.  Detection of small scratches that would require an operator to shine light at the perfect angle to make the scratch noticeable to the human eye.
  • Productivity – Inspection of far more units in less time compared to a manual inspection. The automated test sequence quickly executes inspections of each critical feature.
  • Traceability – The software used NI TestStand’s built-in report generation tools to track test results for each device under test (DUT), giving the customer a complete record of all testing activity. 
  • Flexibility – Building the system with NI TestStand allows the customer to modify test sequences to adjust parameters or to create a new sequence for a similar product.
    • The test station was designed with an interchangeable tray that captures the DUT, allowing the customer to reuse the majority of the test station with other DUT designs

Technologies

  • Software
    • NI TestStand
    • LabVIEW
    • NI Vision Development Module
  • Vision Hardware
    • Basler Ace USB3 monochrome camera
    • Basler Ace USB3 color camera
    • Machine vision lenses
    • Linear lights
    • Analog color bar generator
  • Data Acquisition Hardware
    • NI-9149 Ethernet RIO Chassis
    • NI C-series modules for voltage measurement and digital I/O
    • NI 9853 CAN module
  • Structure
    • Bed-of-nails fixture with swappable DUT nests
    • Automated Pneumatics for DUT capture