| 摘要 |
An apparatus and method of adjusting an imager in an electrophotographic printing machine to correct for registration errors when forming a composite image. Registration errors are sensed by forming one or more target lines (30) on the photoreceptor (17) surface, detecting the centre of the lines and controlling the operation of the imager in response thereto. In one embodiment, four LED print bars (10A,12A,14A,16A) form a composite color image in a single pass. A photosensor (40,42,44) is placed beneath the print bars; a narrow target line (30) is formed on the belt surface a few scan lines before the start (23) of an exposure frame. The centre of the line is detected by circuitry (Figs 4,5) connected to the photosensor output which produces a signal (Fig. 10) corresponding to detection of the centre of the target line (30). This output signal is generated for each of the three downstream print bars (12A,14A,16A) and a signal is applied to each print bar to start the image exposure sequence in registration with first image exposure (I1). In a second embodiment (Fig.6), skew registration adjustments are enabled by forming two line marks (30;30') at opposite ends of the photoreceptor (17), detecting the centre of each mark and making the adjustments of the position of the downstream print bars (12A,14A,16A) based on time differences between detection of the centre of the two marks. <IMAGE> |
