| 摘要 |
In an electrophotographic printing device, a charging roller for a photoconductive drum is constituted by an outer, resilient and resistive layer and by a conductive core connected to earth by means of an element with adjustable resistance. The charging roller is rotated and at the same time its outer layer is charged, by an auxiliary conductive roller which is in contact with the charging roller along a generatrix, with a specific surface charge which is discharged gradually through the resistive layer and the adjustable resistor according to a law determined by the value of the adjustable resistor so that the residual charge transferred by the charging roller to the drum can be controlled simply, reliably and repetitively, so as to adopt an optimal value.
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