| 摘要 |
PURPOSE:To enable automatic and quick detection of an aimed mark without moving a mark detecting part, by sequentially changing and detecting, by a multiplexer, outputs obtained from each of photodetectors. CONSTITUTION:When light receiving parts 11 through 14 of a photodetectors 10 detect marks 20 through 23, a converting circuit 15 outputs signals (a) through (d) on the basis of the current outputs from these light receiving parts 11 through 14. The light receiving part 11 and 12 are arranged to detect the same position of a mark with a predetermined time difference. Moreover, the light receiving parts 13 and 14 are also arranged to detect the other same position of the mark with a predetermined time difference. Signals (a) and (b), and (c) and (d) are added to a differential circuit to obtain (b-a)=e and (d-c)=f, and the signals (e) and (f) are inputted to a peak detecting circuit to form pulses (g) and (h), respectively, showing a peak point. The differences alpha and betaare generated correspondingly to the respective inclining angles at edges 21 and 22 which are not parallel to the right-and-left direction of a web. Therefore, if a portion with less time difference is extracted, it becomes possible to extract only a parallel mark in the right-and-left direction of the web. |
