Method and apparatus for detection of an edge of a printing plate mounted on a drum imaging system

摘要

A method and apparatus is disclosed to precisely locate an edge (4A) of an imageable plate (4) mounted on a drum (1A) or other support surface. A light source (9A) and light sensor (10A) are used to measure the difference in reflectivity between the plate (4) and the support surface (1B). The drum (1A) or support surface (1B) contains at least one groove (3A) to increase the difference in reflectivity between the plate (4) and the support surface (1B). The groove (3A) may also contain an anti-reflecting layer to further increase the difference in reflectivity. The groove (3A) may also have a geometric shape that causes incident light (28,29) to be directed away from the light sensor (30A,30B).