Light beam scanning device for correcting scanning speed

摘要

In a light beam scanning device, first and second light spots scan a scanning plane and a planar grating pattern, respectively. The grating pattern has alternating transparent and opaque parts extending parallel to one another and is rotated by a predetermined angle in its own plane. A speed of scanning the grating pattern by the second light spot is detected to correct irregularities in a speed of scanning the scanning plane with the first light spot. Further, the scanning length on the scanning plane can be finely adjusted by the rotation of the grating pattern.