Patent ID: 6866432

Claim:
A method for replenishing a developer of an automatic developing apparatus for photosensitive lithographic printing plates, the method comprising: developing a plurality of photosensitive lithographic printing plates subjected to an image exposure with a developer containing an electrolyte, while measuring an electric conductivity value of the developer; and keeping the developer activity constant in accordance with the measured electric conductivity value of the developer, wherein the method comprises: preliminarily storing: an electric conductivity value of the developer having a developer activity falling within a proper range as a target electric conductivity value; a plurality of target electric conductivity arithmetic expressions set according to different aging exhaustion conditions; and threshold values of replenishment time interval for determining the target electric conductivity arithmetic expressions; measuring the electric conductivity value of the developer in a predetermined cycle; replenishing the developer with a predetermined amount of a developer replenisher when the measured electric conductivity value of the developer is lower than the target electric conductivity value; and measuring the replenishment time interval between the previous replenishment of the developer replenisher and the present replenishment of the developer replenisher; selecting one of the target electric conductivity arithmetic expressions based on the measured replenishment time interval and the threshold value of replenishment time interval; and updating the target electric conductivity value based on the selected target electric conductivity arithmetic expression and the measured replenishment time interval.