| 摘要 |
An image forming apparatus is able to prevent the service life of an image bearing member thereof from expiring sooner than expected, without requiring an increase in size, complication, or increased cost of the apparatus. In an image forming apparatus adapted to form images by employing a plurality of image bearing members, when a monocolor mode wherein only a black toner is used to produce a monochrome image is selected, no toner image is formed on photosensitive drums of the colors other than the photosensitive drum on which a black toner image is formed. However, the photosensitive drums of the remaining colors continue to run while maintaining a speed difference in a four-full-color mode in relation to an intermediary transfer belt. This means that the photosensitive drums of the remaining colors wastefully slide against cleaning blades and the intermediary transfer belt, leading to wear or scratches. As a result, there have been some cases where the photosensitive drums reach their service life even if the toners contained in developing devices have not yet run out or even if images have not yet been formed on a predetermined number of transfer materials. To solve the problem, in the image forming apparatus according to the present invention, the peripheral speed of each of the photosensitive drums in the black monocolor mode for producing monochrome images is set to be faster than that in the full-color mode so as to make the peripheral speed virtually equal to the moving speed of the intermediary transfer belt.
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