Head-mounted display for interactive inspection of painted free-form surfaces

Defects of painted surfaces have proven to be visually disturbing even when their depth is only a few microns. Most inspection approaches neither enable a reliable classification of small defects nor provide a suitable human-machine interface to identify areas to be refinished. Consequently, in most cases the inspection still takes place manually and visually - an unsatisfactory compromise that lacks both objectivity and reproducibility. Our approach combines the reliability of automated methods with the acceptance and flexibility of human-based techniques. The measurement principle is based on deflectometry, and features a significantly higher sensitivity than triangulation methods. The developed system consists of a light source based on a digital micromirror device (DMD), a screen where defined patterns are projected on, as well as a mobile inspection device equipped with a head-mounted display (HMD) and a video camera. During operation, the camera captures images of different patterns reflected in the surface. By combining several images using one of the two techniques described to enhance surface defects, the resulting feature image is displayed in the HMD. This procedure takes place in real time and is repeated continuously. The system performance is demonstrated with the visual inspection of car doors. Promising results show that our prototype allows a reliable yet cost-efficient inspection of painted surfaces matching the needs of automotive industry.