Browse Prior Art Database

Original Publication Date: 1987-Apr-30
Included in the Prior Art Database: 2004-Apr-04

Publishing Venue

Xerox Disclosure Journal


To effectively design and test xerographic copiers and printers it is essential that the percent area coverage of the copy/print be known, as this affects the type of developer, toner dispenser, cleaning mechanism, and contamination control devices that will be used in the copier. In the past this was done by inaccurate and time consuming visual and instrumental methods. Described below is the general concept of rapidly determining the percent area coverage on a document. While the unit is described as being a modified Xerox facsimile machine it will be understood that the concept is applicable to any type of input scanning device or printer. The document/copy/print to be evaluated is placed on the drum of the modified facsimile unit and the document is then scannned by the photo detector inside the facsimile unit generating a voltage proportional to the darkness of the image immediately under the photodetector. Voltages above a predefined threshold indicate black area while voltages below the threshold indicate white area on the document. A counter is gated with this voltage to produce a number corresponding to the total time that the black area is under the photodetector. Knowing the counting rate and the total time required to scan the entire document, the ercent area coverage can be calculated. This may be accomplished in the Facsimile unit merely by the addition of a separate counting circuit driven by the photodetector. In other input scanning embodiments the same principal is utilized. In a printer application the counting circuit is added to the video data signal and counts the number of black and white picture elements. This device provides a rapid means of determining the image area coverage with accuracy of better than about + or - 190 area coverage.