Minimization of mixed-color image noise caused by shape error of polygonal mirror in color-laser printing system

A color-laser printing system consisting of a tandem laser scanning unit uses four laser diodes and a single polygonal mirror (PM) to expose light onto four photo-conductive drums. In this study, we developed a method to reduce periodical image noise, which is mainly generated during scanning by shape errors in a PM, during color mixing of a color-laser scanning system. Through fundamental optical and image analyses, the horizontal dot shift induced by shape errors in the PM was expected to generate visible image noise with a period of 2.8 mm. In addition, the dominant cause of the horizontal dot shift was the peak-to-valley error and the pyramidal angle of each mirror. In order to reduce the periodical image noise (moiré) in color mixing, a horizontal-synchronization detection-optics layout was proposed, and its effectiveness was verified through image-printing experiments.