On this sheet processing machine the sheets where transported by a frame with several vacuum suckers/ cups. Although the sheets are separated / fanned by permanent magnetic fanns , destacking must be watched for double sheets. If double sheets are detected a contact switches in the double sheet detector amplifier. This contact now repeats the sheet pick - up process again , if necessary several times to shake off the double sheets. If this is not successful the double sheets are stored in a special double sheet bin.