| 摘要 |
PURPOSE:To securely discriminate a printed surface and an unprinted surface from each other and secure feeding of a sheet and controling of printing, by a method wherein reflective densities of both sides of a sheet are detected, and the maximum values of detection signals are compared with each other, in a feeder for printing on both sides of a sheet. CONSTITUTION:The sheet 1 is fed in the direction of an arrow 2, is detected by a paper presence/absence detectors 3, 4, and the surface reflective densities of the first side and the second side of the sheet 1 are detected by a pair of reflection-type sensors 5, 6. Signals 11, 12 proportional to the reflective densities outputted from the sensors 5, 6 are inputted into holding circuits 8, 9, where the maximum values of the input signals are held. The maximum values thus held are outputted as output signals 15, 16, which are compared with each other by a comparing circuit 10, and an output signal 17 is outputted when the signal 15 is higher than the signal 16. The printed surface and the unprinted surface are discriminated from each other by inspecting the waveform of the signal 17. The holding circuits 8, 9 are reset by the falling edge of a delayed signal 14 of a paper detection signal 13. |
