Details:
Summary:
A computer program was written in QuickBASIC to simulate printing process of a web offset press in both 100-0-0 and 60-20-20 inker configurations. Printed ink film thickness, rates of ink flowing through each of the three ink form rollers and to the web, and quantity of ink built up in the inker all were found to follow a first order differential equation for step changes in feedrate, from which the press time constant and incubation period are derived. The simulation results indicate that based on the ink film thickness measurement both press time constant and incubation period are independent of any change in ink feedrate, whether it is a step increase or decrease and whether it is a large or small change. This finding appears to contradict results reported in the literature. However, if the optical density measurement is used as a process control means, the press needs a longer time to respond to a step decrease in ink feedrate than to a step increase, due to the non-linear relationship between ink film thickness and optical density. It was also found that the press time constant and mean ink residence time are inversely proportional to the image coverage. These findings and inker configurations effect on dynamic characteristics of press and uniformity of printed ink films are presented. Applications of press simulation to closed-loop control of the printing process are also discussed.