| 摘要 |
PURPOSE:To correct a form slide drift in a vertical scanning direction by detecting the number of scanning lines which scan the sense marks of the form slide in a light beam recording device and by taking the difference between the number of scanning lines detected and a reference value. CONSTITUTION:Sense marks 27A and 27B are formed in the vertical scanning direction A long one side out of form image zone 29. The first sense mark 27A is considered the slender portion formed to have a length of L4 from the position of vertical scanning starting point in the form image zone 29 to the straight line D crossing over the geometrical center O of form image zone 29 in the horizontal scanning direction. The number of pulses corresponding to the number of rasters which crossed the first sense mark 27A is obtained at every period of vertical scanning. Moreover, let the number of pulses in case of no drift be the number of scanning lines, and this number of pulses is compared with the number of pulses obtained in case drift exists, and the difference signal is obtained. This difference signal is used to correct the drift in the vertical direction.
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