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Method and apparatus for improved retention copying

Image Number 5 for United States Patent #4531827.

A method of producing multiple copies of an original document with a minimum number of document imaging scannings includes impressing an electrostatic image of a reference density patch on the charge receptor together with an image of the document, detecting the potential of the patch, comparing the detected potential with a reference level, and controlling further copy production in accordance with the results of such comparison, so that additional copies are produced from the electrostatic image of the document without reimaging until the detected potential of the patch image drops below the reference level, at which time the patch and document are reimaged to form new electrostatic images of the patch and document on the charge receptor for the production of additional copies.

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