Measuring the registration of a press and making automatic adjustments can reduce waste, maintain quality, and improve press efficiency.

The most useful registration measurements are the most accurate, frequent, and closest to the print nip. A measurement device at each printing unit measuring each impression is desirable.

Available measuring devices are point scanners, line scanners and cameras. Point scanners look at one point on the web at the registration mark, measuring the distance between marks and their darkness. Line scanners are a group of point scanners. Cameras view a small area of color dots, each colored pair printed at known angles.

Computerized control systems determine the distance between registration marks or angles between dots. Press alignments can be ordered by the controlling software and subsequent registration marks reanalyzed. A cycle of small changes followed by a web adjustment period and remeasurement can keep the press in tight registration.

Point scanning systems can automatically correct wider alignment swings, reducing setup time and makeready waste, especially on processes which are difficult to control. Camera-based systems allow for smaller registration marks and less cutoff waste and are designed primarily as fine tuning mechanisms for reasonably controlled presses.

Author: Scott Hilkert
Source: FLEXO, March, 1999, p. 64 - 75.