Multichannel telecentric flying spot scanner for real-time surface inspection

摘要

Abstract: A telecentric flying spot scanner consisting of a rotating multifaceted mirror and a 500 mm diameter parabolic mirror for the inspection of large flat and embossed surfaces up to 400 mm wide is described. Real time high resolution 2-D images at three different angles are obtained providing various types of intensity profiles of the surface. These channels are linearly combined to form pseudo-color images. The image size per channel is limited to about 4 Mbytes by the maximum direct memory access buffer area used by the image grabber card. Images with variable resolutions (for example, 2048 $MUL 2048 pixel or 10000 $MUL 400 pixel) are therefore feasible. Photomultiplier tubes are used for light detection to offer good signal-to-noise ratio and to cover a wide dynamic signal detection range varying from scattered to specular light. Composite images for ceramic tiles with different textures, colors and surface features are presented. These images show some interesting features of the surface profile and texture which otherwise could not be observed using a CCD camera or a single channel scanner. Subtle flaws such as fine scratches and finger marks on the surface and the surface texture variations can be easily identified. !6