| 摘要 |
PROBLEM TO BE SOLVED: To enable a direct tandem type image forming apparatus to always perform excellent image formation by prolonging the life of a conveying transfer belt. SOLUTION: The image forming apparatus 10 has a transfer belt 11 which conveys a recording medium in a designated direction, a plurality of image formation units having photoreceptor drums 16a to 16d which are arranged in the moving direction of the transfer belt and carry toner images by colors, and transfer rollers 17a to 17d which face the photoreceptor drums across the transfer belt and transfer toner images on the photoreceptor drums to the recording medium. When the transfer belt is cleaned, a bias voltage having the opposite polarity from a bias voltage applied to transfer the toner images on the photoreceptor drums to the recording medium is applied as a cleaning bias to at least one of the transfer rollers. At this time, a reflection type sensor 18 detects the amount of toner sticking on the transfer belt surface as a dirt state and based upon the output of the detection sensor, it is determined whether or not the transfer belt is cleaned. COPYRIGHT: (C)2006,JPO&NCIPI
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