| 摘要 |
This invention relates to an apparatus for the detection of downlines on coated web material. The web material is transported past an inspection zone which consists of a means for projecting a narrow beam of light onto the web, means for deflecting the beam of light to scan the web repeatedly in a direction transverse to the direction of web motion, a photocell responsive to light transmitted by the web, an optical diffusing element arranged between the inspection zone and the light sensitive apparatus, and means for moving the diffusing element along a path at least partly transverse to the direction of web transport. Faults are detected by fluctuations in the photocell output. The diffuser is used so that false signals from scratches on the photocell or slight defects in the web are eliminated and it is moved so as to eliminate defects in the diffuser element surface. |
