Image forming apparatus that adjusts the start timings of transfer bias voltage applications to prevent nonuniformity in printed image density

摘要

An image forming apparatus includes a plurality of photosensitive drums, and a controller for executing, when an absolute value of a set point of a charged potential is not higher than a predetermined threshold, an operation in a first mode in which charging bias voltages and transfer bias voltages are applied to image regions of the drums, at a preset length of time before image exposures are carried out by the exposure members and thereafter, the image exposures are carried out by the exposure members, respectively, and for executing, when the absolute value of the set point of the charged potential is higher than the predetermined threshold, an operation in a second mode in which timings of starting applications of the transfer bias voltages to the transfer members are delayed as compared with those in the first mode, respectively.

主权项

1. An image forming apparatus comprising:
a plurality of photosensitive members; charging members configured to be supplied with charging bias voltages to charge surfaces of said photosensitive members at charge portions, respectively; exposure members configured to effect image exposure of said photosensitive members charged by said charging members on the basis of image signals at image regions, respectively; developing devices configured to deposit toners onto the surfaces of said photosensitive members exposed by said exposure members to form toner images thereon, respectively; transfer members configured to be supplied with transfer bias voltages to transfer the toner images deposited on the surfaces of said photosensitive members by said developing devices, respectively, onto an intermediary transfer member or a recording material carried on a recording material feeding member at transfer portions, respectively; a common charging bias voltage source configured to apply the charging bias voltages to said charging members in accordance with set points of charged potentials, respectively; transfer bias voltage sources configured to carry out applications of the transfer bias voltages to said transfer members at predetermined timings, respectively; and a controller configured to execute, when an absolute value of a set point of a charged potential is not higher than a predetermined threshold, an operation in a first mode, in which application of the charging bias voltage is started at a timing not less than a preset length of time, which is a time equivalent to two or more full rotations of said photosensitive members, before starting of formation of a latent image on the image region, in each of said photosensitive members, and application of the transfer bias voltage is started at a timing after a preset length of time from the start of the application of the charging bias voltage, which is a time required for a predetermined peripheral position of each of said photosensitive members to move from the charge portion to the transfer portion, and said controller being further configured to execute, when the absolute value of the set point of the charged potential is higher than the predetermined threshold, an operation in a second mode in which timings of a start of applications of the transfer bias voltages to said transfer members are delayed as compared with those in the first mode, respectively.