1. Field of the Invention
The invention relates to an sheet-fed offset rotary printing machine with a plurality of print units in series configuration for multi-color printing, in which the printing units which are mutually disposed in series are offset relative to one another by a phase angle and at least one deflecting roller is respectively disposed between the printing units.
The phase angle is thereby defined as that angle between the printing units by which the identical print events are initiated mutually offset as compared to the neighboring print units; such print events are, for instance, beginning of print (position of leading edge of the plate), end of print (position of trailing edge of the plate), channel rollover or groove runby, beginning of ductor roller, transfer roller, ink feed roller, or vibrator, and caming torques, relative to the cylinder rotating at unit base speed. These and other parameters initiate oscillations in a broad spectrum in the print units and they cause undesirable oscillatory frequences of the printing machine with disadvantageous influence on the print quality. Particularly strong initiation of the machine-harmonic frequencies originate from the caming torques necessary in the paper-guiding cylinders. These oscillations lead to print errors, such as mackle and register errors in the sheet transfer.
2. Description of the Related Art
Phase angle relationships between printing units of a printing machine have been heretofore dealt with in German published, non-prosecuted application DE-OS 40 32 442. The angle in question of that publication is the defined angle between the unit-sized plate or rubber blanket cylinder and the triple-sized transfer cylinder. The proposed angle offset is 18.degree. or 54.degree., so as to enable perfector printing with a printing machine in a structurally simple manner.
From German published, non-prosecuted application DE-OS 32 03 879 there has become known a sheet-fed rotary offset printing machine of a special construction with printing units disposed in series, but without deflecting cylinders between the printing units. In that configuration the impression cylinder of the printing unit presses against the rubber blanket cylinder of the adjacent printing unit. There is provided between the connecting lines of the axes of the rubber blanket cylinder and the impression cylinder of respectively adjacent printing units an angle of between 70.degree. and 175.degree.. That angle results from a reduction in the number of components necessary for sheet transport.