US Patent 7119820 Scanning heads

A scanning head for use in a register mark detection apparatus for detecting register marks on a web during relative movement between the web and the scanning head. The scanning head comprises an optical sensor and a first optical mask spaced from the optical sensor and having an aperture therethrough to define the viewing footprint of the optical sensor. In some embodiments, the scanning head also includes a second optical mask in series with the first optical mask. The scanning head is versatile and capable of operating with high sensitivity and accuracy even with low contrast media, including with embossed or relief marks, or for fold-line registration or with translucent media.