Unified Optical Scanning Technology

Chapter 4.3.1 - Scanner Devices and Techniques: Distinctions Between Pyramidal and Prismatic Polygons

4.3.1 Distinctions Between Pyramidal and Prismatic Polygons

Table 4.1 highlights the principal features and distinctions of typical polygon scanners. For example, because of their differing scan magnifications (item 3), a given mechanical rotation angle Φ results in an optical scan angle Θ of the prismatic polygon that is twice that of the pyramidal polygon. Thus, to scan equal optical angles of equal beam widths D (for equal resolutions N) and to realize equal duty cycle η (Section 4.3.2) at equal scan rates, the prismatic polygon requires twice the number of facets, is almost twice the diameter, and rotates at half the speed of the pyramidal polygon. The precise diameter is a function of the aperture shape factor (Section 3.2) and the changing projection of the beam cross section on the facet during its rotation (item 8 and Section 4.3.5.1). Noteworthy along with the doubling of its scan angle

by the prismatic polygon is the doubling of the along-scan angular error (item 4). Note, too, the susceptibility to shift errors due to axial and radial shifts of the polygon in noncollimated light (items 9 and 10).

 

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