Scanning beam reference and read system

摘要

The laser beam of a flying spot scanner is turned on and off to write data under control of a reference clock that generates clock signals determined by the position of the writing beam. To detect position of the writing beam a reference beam is scanned in synchronism with the writing beam along and through a coding mask to a strip of retroreflective material fixed adjacent the mask. The reference beam is retroreflected through the mask back through the scanning optics to a fixed detector that produces an output determined by the scanning coded reference beam. Unwanted reflections from the mask surface are separated by tilting the mask. Reading of a document having a pattern of opaque and transparent areas is accomplished by retroreflecting a scanning laser reading beam from a body of retroreflective material adjacent to but spaced from one surface of the document. The scanning beam passes through transparent areas of the document and is retroreflected back through the document and through the scanning optics for collection by a fixed detector.