PRINTING MACHINE HAVING DUCTOR ROLLER, CORRECTION DEVICE, AND PRINTING MACHINE CORRECTION METHOD

Individual graph data gr and its initial values gri, and average g of the graph data over the entire ductor roller and its initial value gi are used to change graph data gr and g during printing so as to cancel errors between measured printed densities and desired printed densities. The stable value ge of the averaged graph data g and the stable values gre of individual graph data gr are used and data including their initial values gi, gri and their stable values ge, gre are collected. In the collected data, the difference between the distributions of the stable values ge and the initial values gi makes a basic parameter B up and down. The collected data are classified according to printing speeds, and the difference between the distributions of the stable values ge and the initial values gi in each speed region makes a speed parameter V for each speed region up and down. The collected data are classified according to averaged graph data g, and the difference between the distributions of the stable values ge and the initial values gi in each region of g makes an area parameter F for each region of g up and down. The difference between the distributions of the stable values gre and the initial values gri both of the individual graph data makes a corresponding individual roller parameter R up and down. The duty ratio of the ductor roller is adjusted according to the values of the parameters.