| 摘要 |
In a color copier, photosensors (41Y, 41M, 41C, 41BK) detect the amount of toner deposition in a reference pattern formed on photoconductive drums (24Y, 24M, 24C, 24BK). A bias for development on sleeves (37) is changed by section (12) so as to maintain the output of the photosensor constant, so that the effective bias remains constant relative to the charge potential on the photoconductive element. Alternatively, section (12) can also change charge potential to chargers (25), the amount of exposure light from exposure units (22) or more than one of those variables. This maintains the density of a predetermined reference pattern used to sense an image density constant despite the change in, for example, the reflection characteristic of the photoconductive drum. <IMAGE>
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