Abstract: Such defects as a folded back or bent portion and a notch along one or both side edges of a printing sheet is detected by a detector located on one or both sides of a front edge of a correctly fed printing sheet for detecting absence of the sheet and a timing signal generator which produces a timing signal while all length of the sheet passes by the detector. An output signal which stops printing operation is produced when the detector detects absence of the sheet while the timing signal is being produced. According to this invention it is possible to prevent formation of defective printed matter and damage of a printing press fed with defective printing sheets.

Abstract: In a printing press including an intaglio cylinder, an impression cylinder and a blanket cylinder, for the purpose of throwing on and off these cylinders there is provided a control apparatus comprising a first detection switch which produces a selection signal when a rotating radial projection passes by, and a plurality of second detection switches which generate timing signals when passing by a plurality of radially spaced projections. The selection signal is used to select either one of the second selection switches, and the timing signal generated by a selected second detection switch is used to throw on and off the cylinders.According to this invention it is not necessary to use a number of expensive multistage preset counters which are liable to misoperate due to noise.

Abstract: In an inadequately fed sheet detector of the type comprising a feed board, a transparent plate mounted on one end thereof, a swinging front guide, and a luminous element and a light receiving element respectively mounted on the feed board and the front guide on the opposite sides of the transparent plate, the luminous element is inclined with respect to the vertical.