Aerial slow scan position control using an electronically addressable liquid crystal plate

Abstract

Printers that correct for polygon phasing errors. Such printers include a raster output scanner, a moving photoreceptor, a page sensor for sensing the position of an image area, a start-of-scan sensor for sensing the start of scan, a light valve array having a plurality of electrically controlled light valves for selectively passing light, and a system controller that controls the light valve(s). The system controller initially selects one of the light valves. When the page sensor senses the beginning of a page the system controller starts selecting sequential light valves at a controlled rate. After a start-of-scan occurs the system controller stops sequencing the light valves. The light valve that passed light when the start-of-scan occurred continues to pass light. Beneficially, the system controller monitors the photoreceptor motion. If the photoreceptor motion changes the system controller then selects a light valve that moves the scan line toward the proper position.