METHOD AND APPARATUS FOR BACKGROUND CONTROL IN AN ELECTROSTATOGRAPHIC PRINTING MACHINE

摘要

A method and apparatus for determining the presence of image information in the lead edge of an input document by comparing the average difference between a plurality of instantaneous optical density measurements of a reference strip and the average optical density for the reference strip to the average difference between a plurality of instantaneous optical density measurements of a lead edge of an original input document and the average optical density for the lead edge of the original input document. Analysis of optical density measurements during scanning of the lead edge of an original input document is accomplished so that image information on the lead edge of an original input document is not misinterpreted as indicative of a dark background original input document. The method and apparatus provides novel control of bias voltages applied to subsystems in an electrostatographic printing apparatus in response to the presence or absence of image information in the lead edge of an input document so that both background development and the loss of image density for images on the lead edge of a document is minimized by setting the exposure lamp voltage, and/or the developer bias, charging potential, as well as other variable parameters to predetermined settings in response to the detection of image information in the original input document.