| 摘要 |
PROBLEM TO BE SOLVED: To prevent the occurrence of an offset at a high temperature by suppressing overshooting tending to occur in the central part of a fixing roller, at the time of starting the formation of an image. SOLUTION: A main heater 3a having a heat generating part in a position corresponding to the central part in the axial direction of a transfer roller and a subheater 3b having heat generating parts in positions corresponding to both end parts are provided in the fixing roller 1 of the fixing device. The supply of power to these heaters 3a and 3b is controlled with the output of a thermistor 5 detecting the surface temp. of the fixing roller 1, to bring the detected surface temp. (Tb) close to a fixing temperature control temp. (target fixing temp.) (Ta). When the radius, angular velocity, fixing temperature control temp. and detected surface temp. of the fixing roller 1 are defined as (r),ω, Ta and Tb respectively and (n) obtained in such a manner that n0 calculated by the equation of n0 = (Tb-Ta)×(r×ω)}/350 is rounded off to the first decimal place denotes the number of passed sheets, the ratio of the power supplied to the heaters 3a and 3b is made a fixed one, up to (n) passed sheets, to prevent overshooting.
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