DEFECT CHECKING DEVICE FOR LONG-SIZED SHEET

摘要

PURPOSE:To improve the defect check precision of a long-sized sheet by providing calculating means of the centroid position in the scanning direction of a repeat pattern, a meandering extent calculating means, and a meandering correcting means. CONSTITUTION:An image sensor camera 1 continuously picks up an image in the direction orthogonal to the movement direction of the sheet and sends the video signal of the repeat pattern image on the sheet to an amplifier 2. An amplified signal (a) is compared with a preliminarily set threshold voltage Vth to obtain a binary signal (b). A meadering correcting circuit 4 corrects the binary signal (b) with the extent of meandering fed back from a centroid detecting circuit 5 and sends the result as a video signal (c) to a memory 6 and a defect discriminating circuit 7. The inputted corrected signal (c) is successively stored in the memory 6 and is periodically sent to the centroid detecting circuit 5. This circuit calculates the centroid of a specific pattern of the repeat pattern and sends the deviation from a learnt reference position to the meandering correcting circuit 4. The discriminating circuit 7 uses a reference mask pattern to mask the corrected signal (c) at the pattern repeat period, and it is discriminated whether a remining picture is defective or not, and the result is outputted.