Patent ID: 8245638

Claim:
Method for aligning color separations of a printing image to each other on a printing material, the color separations being produced on the printing material by respective imaging devices, the printing material transported by a transport belt along a transport path past the respective imaging devices, the color separations being aligned in a first direction perpendicular to a transport direction of the printing material, the method comprising: applying two equal register marks to the printing material for each color separation using corresponding imaging device, the two equal register marks rotated by 180 degrees relative to each other and spaced at a distance from each other in the transport direction of the printing material, each register mark including a front and a rear edge arranged at respective angles of inclination greater than zero relative to the first direction; detecting a respective front edge and a respective rear edge of each applied register mark using a sensor; determining respective widths of the two equal register marks of a selected one of the color separations by measuring, using an encoder, an advance of the transport belt between a detection of the front edge of each register mark and a detection of the rear edge of that register mark; determining positions of the two equal register marks of the selected color separation in the first direction using the determined respective widths and the respective angles of inclination of the front and rear edges; and determining and correcting misalignments of the imaging device used for the selected color separation, the determining and correcting misalignments including determining a difference Z of the determined respective widths, and, depending on a sign and a magnitude of the difference Z, shifting a zero position or an alignment of the imaging device used for the selected color separation by a shift S.