Intermediate transfer unit comprising a control circuit for stabilizing the bias potential for transferring a toner image from a photosensitive drum to an intermediate transfer belt against current variations caused by simultaneous transfer of a toner image from the intermediate transfer belt to a copy paper

摘要

The present invention relates to an intermediate transfer unit comprising: an intermediate transfer belt (360) to which a toner image formed on a photoconductive drum (110) is primarily transferred and which secondarily transfers the toner image onto a recording medium (S), and a driving roller (310) for circulating said intermediate transfer belt (360) which has a joint. In this intermediate transfer unit a primary transfer position, where the toner image is primarily transferred, is disposed close to said driving roller (310). The intermediate transfer unit further comprises: a primary transfer member (320) for primarily transferring the toner image formed on the photoconductive drum (110), and a secondary transfer roller (380) for secondarily transferring the toner image onto the recording medium (S). When no image is formed, an electric field in the direction in which the toner is returned from the secondary transfer roller (380) to the intermediate transfer belt (360) is formed while the secondary transfer roller (380) presses on the intermediate transfer belt (360), and when the joint of the intermediate transfer belt (360) is opposite to the secondary transfer roller (380), the secondary transfer roller (380) is detached from the intermediate transfer belt (360). IMAGE