Skew detection system for optically read data

摘要

A skew correction system for data media, especially optical data storage media wherein a pair of identical geometric marks are spaced apart in a band or track parallel to a data track, the data tracks being transverse to the directions of relative motion of the data storage medium with respect to a detector. As the medium moves relative to the detector, a linearly scanning detector, portions of each geometric mark are observed by the detector. A ratio of picture elements is determined using the two sets of observed picture elements. If the ratio is other than 1, skew exists. A closed-loop servo system is used to restore the ratio to 1, thereby eliminating skew. The geometric marks may be disposed forward of the data tracks, astride the data tracks, behind the data tracks, interspersed with the data tracks, or if different colors of light are used, atop the data tracks.