| 摘要 |
A system for generating indicia of registration error between the respective printing units of a web-fed, four-color printing press. An optical line scanner is disposed over a web to generate signals indicative of the brightness level of successive nominal pixels along a line transverse to the motion of the web. The respective printing units each generate registration marks on the web, the relative positions of which are indicative of the relative cyclical (rotational) and transverse (lateral) positions of the printing units with respect to the web. As the web moves past the scanners, successive line scans generated by the scanner provide the equivalent of a two-dimensional raster scan of a strip of the web centered on the expected center line of registration marks produced by the respective printing units. The centers of the respective registration marks are determined, and the cyclical (rotational) and transverse (lateral) positions of the printing unit adjusted, in accordance with deviations from expected relative positions. The use of symmetrical marks and, in particular, right-angled diamonds, is disclosed for facilitating calculation of the center of the marks. |
