Patent ID: 7114441

Claim:
An apparatus for controlling the amount of ink to be supplied to a printing plate mounted on a printing cylinder, which ink is reserved in an ink fountain and transferred by an ink transfer roller to said printing plate via plural ink rollers, wherein: said ink fountain includes an ink fountain roller and a blade, said blade made up of plural ink fountain keys so as to define a gap between said ink fountain roller and each of said plural ink fountain keys, through which ink flows onto said ink fountain roller, said gap being opened and closed by adjusting an opening degree of each of said plural ink fountain keys; said ink transfer roller moves back and forth between said ink fountain roller and a most upstream ink roller of said plural ink rollers with respect to an ink transfer direction so as to transfer ink adhered to said ink fountain roller to said most upstream ink roller; said apparatus comprises a means for controlling the opening degrees of said plural ink fountain keys independently of each other according to image area ratios of zones of said plate cylinder, said zones respectively defined corresponding to said plural ink fountain keys, wherein said means calculates an average value of said image area ratios so that where said average value is not less than a given value, said means selects a normal mode so as to preset, prior to starting printing operation, each of the opening degrees of the plural ink fountain keys based on a main conversion curve and the number of times at which said ink transfer roller touches said ink fountain roller per a given number of rotations of said plate cylinder to a given touching frequency, and where said average value is less than said given value, said means selects a small image mode so as to preset, prior to starting printing operation, each of the opening degrees of the plural ink fountain keys based on a modified conversion curve and the number of times at which said ink transfer roller touches said ink fountain roller to a touching frequency lower than said given touching frequency of said normal mode, said modified conversion curve allowing the increasing rate of the opening degree of each of said plural ink fountain keys relative to the increase of the image area ratio of a corresponding zone to be higher than the increasing rate of the main conversion curve of the normal mode.