OPTICAL DETECTING DEVICE FOR RECORDED MATERIAL, RECORDING DEVICE, AND METHOD FOR SETTING THRESHOLD OF OPTICAL DETECTING DEVICE FOR RECORDED MATERIAL

摘要

PROBLEM TO BE SOLVED: To provide an optical detecting device for a recorded material which can accurately judge whether or not the recorded material is present even if it has secular changes. SOLUTION: A controller 8 rotates a paper feed roller 4 and a paper discharge roller 5 forward to carry a printing form S downward by a distance L or a distance a little longer than the distance L. A decision unit 8a stores the value of the voltage that the output signal of an optical sensor 7 has at this time in an internal memory as a paper presence voltage V1. Then the controller 8 reverses the paper feed roller 4 and paper discharge roller 5 to return the printing form S upstream gradually. At this time, when the mentioned voltage value decreases below 85% of the value of the paper presence voltage V1, the decision unit 8a stores the value of the current voltage in the internal memory as the value of a dark voltage V2. Then the decision unit 8a stores the mean value (=(V1+V2)/2) of the values of the paper presence voltage V1 and dark voltage V2 in the internal memory as a threshold.