Importance

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Abstract

A method and apparatus for use in improving the accuracy of scanning systems is disclosed and claimed. Systems such as internal drum photoplotters include a raster scanner responsive to control signals for advancing relative to a substrate an optical beam across a substrate surface in a first direction forming a scan line of pixels and for cooperatively advancing relative to the substrate the optical beam in a second direction substantially perpendicular to the first direction. The clock signal which is provided to a spinner to advance the optical beam across the scan line is independent from the pixel clock signal which is provided to control the generation of pixels. There is a memory for storing error compensation signals indicative of compensation needed to remove deviations of the separation between adjacent pixels in said scan line from preferred values thereof. The apparatus is characterized by a controller for generating control signals in dependence on the error compensation signals such that the phase of the clock signal is adjusted, thereby removing the pixel separation error for a segment of the scan line.

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First Claim