Patent ID: 8874013

Claim:
An image forming apparatus comprising: one or more image bearing members configured to bear different ones of a plurality primary color toner images; an endless intermediate transfer medium; a primary transfer device configured to form a primary transfer nip with the intermediate transfer member to form a combined color toner image on the intermediate transfer medium by primarily transferring each of the plurality primary color toner images from the one or more image bearing members to the intermediate transfer medium in a sequence; a nip forming member contacted with the intermediate transfer medium to form a secondary transfer nip at which the combined color toner image on the intermediate transfer medium is secondarily transferred to a recording sheet; and a transfer current output device configured to apply a transfer current to the secondary transfer nip to secondarily transfer the combined color toner image while determining the secondary transfer current based on image area ratios of the primary color toner images of the combined color toner image using a predetermined algorithm, wherein the secondary transfer current output device is configured such that, when determining the secondary transfer current, the secondary transfer current output device estimates a target value of a transfer current per unit area for each of the plurality of primary color toner images in such a manner that, for each of the plurality of primary color toner images except the last primary color toner image of the sequence, the target value of a transfer current per unit area estimated for secondarily transferring the primary color toner image is not lower than the target value of a transfer current per unit area estimated for secondarily transferring a next one of the primary color toner images in the sequence, and the target value of a transfer current per unit area estimated for secondarily transferring the primary color toner image that is primarily transferred first in the sequence, is higher than the target value of a transfer current per unit area estimated for secondarily transferring the primary color toner image that is primarily transferred last in the sequence, and wherein the secondary transfer current output device is configured to determine the secondary transfer current based on the estimated target values of the transfer currents for all the plurality of primary color toner images.