APPARATUS FOR COMPENSATING OPTICAL ERROR IN A ROTATIVE MIRROR

APPARATUS FOR COMPENSATING FOR OPTICAL ERRORS IN A ROTATING MIRROR Inherent defects in the angular relationship between facets of a rotating polygonal mirror used to sequentially scan a beam of radiation are corrected by an optical reflecting or refracting element pivotally mounted in the path of the radiation. With the use of electromechanical devices energized by timed electrical signals of appropriate value, the mirror or refracting element is pivoted to correct the scanning errors caused by angular defects in the rotating mirror. The effect of variations in the angles between facets of the polygonal mirror are also corrected by an electronic circuit which includes a delay device capable of delaying the scanning by a predetermined amount. Control means for the electromechanical devices and for the delay device are pre-programmed so as to make the proper adjustments for each facet of the rotating polygonal mirror.