| 摘要 |
PROBLEM TO BE SOLVED: To monitor the folding offset of impression paper in a relatively simple and inexpensive method. SOLUTION: The folding offset of paper Pb, formed in folding the impression paper Pa, is monitored. When the ends of the folded paper Pb being transferred via a transfer belt 54 are detected by a position sensor 3 including a photoelectric cell, an image pickup device picks up an image of preset portions of the folded paper Pb in accordance with detection signals and enlarges and displays the image as a static image on an screen of an image display 4. As a light emitter 2 is disposed opposite to the image pickup device 1, the image picked up by the image pickup device 1 is put into the condition that light from the light emitter 2 is transmitted therethrough and so the picked-up image is displayed with overlapped pages printed in superposed relation. If these portions are page number portions showing the numbers of the pages, the offset of the numbers is identified by the image and monitored therethrough.
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