US Patent 7107903 Sheet-fed printing press

There is provided a sheet-fed printing press that is capable of rapidly performing printing preparatory work for more secured double sheet detection. A double-sheet-detector control part judges whether an ultrasonic double sheet detector outputs double sheet detected signal during test printing or during feeding a first printing sheet of successively fed printing sheets in large quantity or successive printing. Where double sheet detected signal was output, it is judged that the detection made by the ultrasonic double sheet detector is erroneous so that the double-sheet-detector control part switches to a photoelectric double sheet detector to be employed as a double sheet detector for use in large quantity or successive printing. On the other hand, where no double sheet detected signal was output, it is judged that the detection made by the ultrasonic double sheet detector is correct so that the double-sheet-detector control part keeps the ultrasonic double sheet detector in operation to employ the same as a double sheet detector for use in large quantity or successive printing.