| 摘要 |
PURPOSE:To make it possible to take correspondence even if the quantity of the light from a light source varies or printed matter having different blank reflectivity is supplied, by setting a threshold value on the basis of the peak value of the signal output of the blank part of printed matter and judging the presence of a register mark on the basis of said threshold value. CONSTITUTION:Reflected light is received by an image pickup element 14 and amplified to be inputted to a sample hold circuit 21 and the peak value of the output of a blank part is sampled to be allowed to correspond to the change in the luminous intensity of a light emitting lamp. Peak value hold voltage Ep is divided into a plurality of voltages by a voltage dividing circuit 22 and the threshold value for judging a mark corresponding to reflected light different by each register mark is set. This threshold value is compared with the output E of an amplifying circuit 15 by a comparing circuit 23 to be digitalized and the presence or absence of the register mark is judged by a register mark presence and absence judge circuit 24 and, if said mark is present, the length from scanning start to the blank part at the final end of the register mark is measured by a register mark measuring circuit 26 and the output LW of a printed matter end measuring circuit and the output LM of the register mark measuring circuit 25 are subtracted by a subtraction circuit 27 and the length L of an actual mark is inputted to a comparing judge circuit 28 to be compared with a tolerant range signal P to output a judged signal S. |
