Method of presetting plate cylinders for registering in an offset printing press

A method of presetting plate cylinders for registering before the start of a printing operation in an offset printing press in which a web runs between surfaces of opposed rotating blanket cylinders for the plate cylinders, the method comprising the steps of:

• (a) correcting rotation phase, lateral and twist errors of each plate cylinder without considering a delamination error defined by a rotational phase error caused by the web being drawn in a rotational direction of a blanket cylinder due to adherence of the web onto an inked surface of the blanket cylinder, while detecting register marks on a printing plate mounted on each plate cylinder;
• (b) calculating tension of a web on the basis of a functional expression with respect to at least one of width and weight per unit length of the web and operating tension adjusting means on the basis of a calculated value of web tension;
• (c) calculating the delamination error of each plate cylinder corresponding to each printing color on the basis of at least one functional expression with respect to at least one of the calculated tension, width, weight per unit length and rates of pattern area and operating delamination error correcting means on the basis of a calculated value of a delamination error with respect to each plate cylinder corresponding to each printing color;
• and
• (d) carrying out self-learning in which an operator manually adjusts the delamination error correcting means until delamination errors are eliminated while viewing shear of colors on printed articles to determine a suitable web tension and delamination error when shear of colors is eliminated, the suitable web tension and delamination error being used when coefficients of the functional expressions with respect to web tensions and delimination errors are calculated for subsequent printing operations.