Patent ID: 7412187

Claim:
An apparatus for applying a cleaning electric power to a transfer roller of an image forming apparatus to clean the transfer roller, wherein the transfer roller faces a transfer backup roller to transfer an image formed on an intermediate transfer medium to a printing paper, and wherein the intermediate transfer medium is installed between the transfer roller and the transfer backup roller, the apparatus comprising: an electric power source to apply a cleaning electric power among the transfer backup roller, the intermediate transfer medium, and the transfer roller; a carrier supplying unit installed near one of the transfer roller and the intermediate transfer medium to supply carrier to a developer on the transfer roller; and a controller to measure a resistance among the transfer backup roller, the intermediate transfer medium, and the transfer roller, calculate a density of a toner of the developer on the transfer roller based on the resistance, and control the carrier supplying unit to supply carrier to at least one of the transfer roller and the intermediate transfer medium if the density of the toner is greater than or equal to a predetermined reference value.