Multi-aperture, feedback system for a laser scanner

摘要

A beam feedback synchronization system for optical sweeping apparatuses is disclosed. The system includes a multi-faceted rotating reflection mirror which acts on a collimated light beam such as a laser beam to cause it to sweep periodically in parallel straight lines across a rotating photoconducting drum. A portion of the light beam is split off and caused to sweep across an equispaced linear array of fiber optic apertures held in place by a fiber optic assembly. The light entering the fiber optic apertures is carried along fiber optic elements to one or more photodetectors which generate periodic electrical signals in response thereto. The frequency of occurrence of the electrical signals from the photodetector is a measure of the velocity of the sweeping light beam across the fiber optic array. A phase locked loop circuit connected to the photodetector(s) provides a character clock signal which is synchronized to the electrical signals received from the photodetector and compensates for variations in the speed of the light beam across the fiber optic array. The phase locked loop further comprises a fast synchronization circuit which provides immediate synchronization between the character clock signal and the first electrical signal occurring at the beginning of a new light beam sweep. In addition, hold circuitry is provided which holds the frequency of the character clock signal coming from the phase locked loop constant during the dead time occurring between laser light beam sweeps.