Method and apparatus for detecting folded corner of sheet in sheet-fed printing press

An apparatus for detecting a folded corner of a sheet in a sheet-fed printing press, the sheet-fed printing press including:

• a left-hand side lay device for registering a left end position of sheets supplied from a feeder to a printing unit,
• a right-hand side lay device for registering a right end position of sheets supplied from the feeder to the printing unit, and
• a detector for detecting presence or absence of the sheet at a left end part and a right end part of a front end of the sheet whose position has been registered by one of the side lay devices,
• the apparatus comprising the detector including:
• a first left-hand end detector supported in the left-hand side lay device,
• a second left-hand end detector supported in the left-hand side lay device and provided at a position spaced from the first left-hand end detector toward a center in a lateral direction,
• a first right-hand end detector supported in the right-hand side lay device, and
• a second right-hand end detector supported in the right-hand side lay device and provided at a position spaced from the first right-hand end detector toward the center in the lateral direction,
• the apparatus further comprising:
• a control device which exercises control such that
• if the left-hand side lay device is selected among a pair of the side lay devices, the first left-hand end detector supported in the left-hand side lay device and the second right-hand end detector supported in the right-hand side lay device detect the presence or absence of the sheet at the left end part and the right end part of the front end of the sheet, or
• if the right-hand side lay device is selected, the first right-hand end detector supported in the right-hand side lay device and the second left-hand end detector supported in the left-hand side lay device detect the presence or absence of the sheet at the right end part and the left end part of the front end of the sheet.