| 摘要 |
Four image forming units corresponding to yellow, magenta, cyan and black color toners are disposed in row along a rotatable intermediate transfer belt. Primary transfer rollers for primarily transferring images formed by respective image forming units to the intermediate transfer belt and a secondary transfer roller for secondarily transferring the images on the intermediate transfer belt to a paper sheet are also disposed. During the warm-up time, simultaneous controls for determining transfer voltages to be applied to those primary transfer rollers for yellow and cyan and the secondary transfer roller are performed first. Thereafter, simultaneous controls for determining transfer voltages to be applied to those primary transfer rollers for magenta and black are performed. The controls performed in such a manner make it possible to complete the determination of the primary transfer voltages in a shorter time, thereby shortening the warm-up time.
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