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Summary:
A prototype control system for inking in a web offset press has been developed at the Technical Research Centre of Finland. The system consists of an 8-channel on-press densitometer, a press-remote control system and a microcomputer for control algorithm realization. A process model for inking in offset printing has been completed by full-scale identification runs. The printed density has a nonlinear dependence on the ink screw position and on the duct roller speed. The number of machine revolutions is used as a time base parameter. The process response time is little more than one hundred revolutions. The inker's storaging property makes the down step response even slower. The crosswise flow of ink presupposes some cautiousness of the controller. A process model for inking in offset printing has been completed by full-scale identification runs. The printed density has a nonlinear dependence on the ink screw position and on the duct roller speed. The number of machine revolutions is used as a time base parameter. The process response time is little more than one hundred revolutions. The inker's storaging property makes the down step response even slower. The crosswise flow of ink presupposes some cautiousness of the controller. For the feedback control a recursive multilevel algorithm has been developed. The goal of the controller is to keep the density profile at the preset level during the run. The optimum density value is defined by the ink/paper combination, the contrast number being the criterion. Some preliminary test results on a full-scale web-offset unit are given in the paper.