Printing apparatus with positional offset detection and correction

摘要

A plurality of resist marks of K, C, M and Y color toner components are transferred at predetermined pitches onto a belt for conveying record paper, by means of a plurality of electrostatic recording units. The resist marks are optically detected by sensors. A positional offset detection unit detects positions of resist lines from phases phi obtained through Fourier transform of sensor detection signals, and employs as the reference the detected position of the resist mark of K component to thereby detect positional offsets of the detected positions of the resist marks of the other C, M and Y color toner components. A positional offset correction unit corrects the transferred positions of the other C, M and Y color toner components so as to eliminate any positional offsets relative to the K component image.