Browse Prior Art Database

Original Publication Date: 1988-Dec-31
Included in the Prior Art Database: 2004-Apr-04

Publishing Venue

Xerox Disclosure Journal


In electrophotographic copiers and printers, image density loss of the output may occur during lengthy copying or printing runs wherein the originals are of low image coverage in that they consist of nearly empty pages. Toner requirements are quantitatively low during such a run; for example, production of 10,000 copies of an original test pattern having about 0.2 percent image coverage requires about one teaspoonful of toner. The toner dispenser (1) shown in the following Figure, however, may sift or leak toner whether or not it is needed, as a result, for example, of a sheet of paper entering or leaving the nip between the image bearing drum (3) and the pressure roll, causing a mechanical shock to be sent through the printer, which shock affects the screen (5) at the bottom of the toner reservoir, pemitting toner to pass. Sifting or leakage of excess toner during copying periods when little toner is needed leads to addition of toner to the secondary toner roll (7), which transports toner to the metering blade (9) on the development roll (11). Since toner is constantly added at a rate greater than the removal rate, it accumulates on the secondary roll. When the secondary roll becomes saturated with toner, additional toner will not adhere to it and either falls from the development housing onto a copy, causing a coarse background deposit, or it is removed by the sump vacuum for disposal. Overloading of the secondary roll with toner contributes greatly to the output image density loss observed during long copying printing runs of originals of low image coverage, since the excess toner on the secondary roll packs tightly into the cavity formed by the two rolls (13) and the metering blade and reduces the amount of metered tuner, which causes image density loss.