Printing plate registration using a camera

A method of determining an alignment of a printing plate relative to an imaging drum on which the printing plate is mounted, the method comprising:

• a) determining a location of at least one point on a reference edge of the printing plate, wherein the reference edge extends along the imaging drum in a substantially axial direction;
• the determining a location comprising:
• i) illuminating a region, the region comprising at least a part of the reference edge associated with the at least one point;
• ii) capturing at least one digital camera image of the region with a digital camera;
• and iii) locating the at least a part of the reference edge in the digital camera image;
• b) determining the alignment of the printing plate at least in part from:
• i) the location of the at least a part of the reference edge in the digital camera image of the at least one point;
• and ii) a position of the digital camera relative to the imaging drum during the capturing of the at least one digital camera image of the at least one point;
• wherein the locating at least a part of the reference edge comprises locating a mechanical edge of the printing plate;
• wherein the illuminating is performed on the side of the printing plate that is in contact with the imaging drum;
• wherein the illuminating is by diffuse reflected light reflected from at least one diffusely reflective area on the imaging drum;
• wherein the illuminating is spatially interrupted by at least one non-reflective surface on the imaging drum;
• wherein:
• a) the reference edge is positioned to extend over a slot in the imaging drum;
• b) the at least one non-reflective surface and the at least one diffusely reflective surface are on a radially recessed surface of the slot;
• and wherein the illuminating is spatially interrupted along an interrupting section of a part of the reference edge associated with the at least one point.

A method for determining the location of a reference edge of a plate relative to a substrate on which the plate is mounted, the method comprising determining a location of at least one point on the reference edge, wherein the reference edge extends along a first direction on the substrate;

• the determining a location comprising:
• a) illuminating a region, the region comprising at least a part of the reference edge associated with the at least one point;
• b) capturing at least one digital camera image of the region with a digital camera;
• c) locating the at least a part of the edge in the digital camera image;
• d) determining the location of the at least one point from:
• i) a part of the reference edge in the digital camera image of the at least one point;
• ii) a position of the digital camera relative to the substrate during the capturing of the at least one digital camera image of the at least one point;
• wherein the locating at least a part of the reference edge comprises locating a mechanical edge of the printing plate;
• wherein the illuminating is performed on the side of the plate that is in contact with the substrate;
• wherein the illuminating is by diffuse reflected light reflected from at least one diffusely reflective area on the substrate;
• wherein the illuminating is spatially interrupted by at least one non-reflective surface on the substrate;
• and wherein:
• a) the reference edge is positioned to extend over a slot in the substrate, the slot extending in substantially the first direction;
• b) the at least one non-reflective surface and the at least one diffusely reflective surface are on a recessed surface of the slot;
• and wherein the illuminating is spatially interrupted along an interrupting section of a part of the reference edge associated with the at least one point.