Unified Optical Scanning Technology

Chapter 4.3.4 - Scanner Devices and Techniques: Facet Tracking

4.3.4 Facet Tracking

A method of avoiding much of the loss of illumination due to overfilling the facets is the technique of facet tracking. It entails the extra step of scanning the illuminating beam (of normal width D) by an auxiliary means, in synchronism with the shift of the facet during polygon rotation. Thus the illumination remains seated centrally on the full facet during scan. The facet continues to reflect this beam through its scanned angle in the conventional manner. Not only is much of the illumination conserved, but this is accomplished with a minimal facet width, allowing use of a polygon diameter that is almost as small at that of the over-filled type having the same number of facets. Forms of this general technique are represented by using acoustooptic tracking of a prismatic polygon [D&J], refractive window rotation with a prismatic polygon [Str], and an early configuration of refractive windows rotating with a pyramidal polygon [Mac].

 

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