| Developers' Corner

Inspection of specular surfaces with deflectometry in HALCON

Finding defects on reflective surfaces with deflectometry.
MVTec's deflectometry demo at the machine vision fair VISION 2018.

With the help of deflectometry you can easily inspect flat but also curved specular surfaces. Defects like scratches, bumps, cracks, and dents can be detected robustly and fast. Deflectometry is used in various industries like microelectronics, automotive, production of household goods, glass, plastic, ceramics, as well as polished, reflecting surfaces. This article demonstrates the functionality and advantages of deflectometry in HALCON, using a demo setup that was also shown at the VISION fair 2018.

This demo includes two independent deflectometry setups to inspect smartphone displays and chromed car components. For the pattern projection we used a DLP® LightCrafter™ device by Texas Instruments, which is controlled directly via HALCON. For image acquisition, any USB3Vision or GenICam-compliant industrial camera can be used. To achieve the necessary synchronization between projectors and cameras, a hardware trigger was also needed. The samples were transported by a Beckhoff eXtended Transport System (XTS). The data exchange between HALCON and the Beckhoff PLC was realized via a Hilscher CIFX-50RE EtherCAT fieldbus interface card and the Hilscher cifX interface included in HALCON 18.11. For the graphical user interface, C# WPF was used.

With this setup we generated a fully synchronized image acquisition at a rate of 80 images within 1.6 seconds. In addition, by using HDevEngine, the image processing can be improved or adapted to new samples without the need to recompile the whole application, reducing changeover times.

Key features of this deflectometry setup

  • Inline inspection of flat and curved specular surfaces
  • Robust and sensitive inspection
  • Fast image sequence acquisition and fast processing (less than 3 seconds per sample)
  • Usage of industrial off-the-shelf components together with HALCON
  • Full flexibility of the HALCON standard image processing library including more than 2,000 operators in all fields of industrial vision
  • Short upgrade/changeover time for the image processing thanks to HDevEngine