| 摘要 |
In order to detect defects such as holes and inclusions in the manufacture of a longitudinally-moving web (10), for example paper, three cameras (22a, b and c) each containing a line array (24) of photo-diodes, are imaged transversely across respective portions of the web. Each array is repetitively scanned to sample the photo-diodes in turn. The photo-diode video signals are digitised and sequentially stored in a random address memory (52) that is addressed in synchronisation with the sampling of the photo-diodes. Arithmetic circuitry (56. 58) subtracts the fresh digital value from a given diode with the value for that diode from the previous scan and signals a defect if the difference exceeds set limits. Logic circuitry (60) controlled by the sign of the difference signals whether the defect is a hole or inclusion. The fresh value is then entered in the memory to serve as a reference for that diode on the next scan. There is also described circuitry responsive to hole signals from the camera viewing the middle portion of the web to indicate when there is no web or an irregular web, and counting and indicating circuitry for the holes and inclusions.
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