Image forming apparatus and fixing temperature control unit

摘要

An image forming apparatus forming toner images sequentially on recording sheets transported at intervals, and thermally fixing the toner images by passing the recording sheets through a fixing position on a heating roller. The target fixing temperature is determined according to information of an image on each page. When a first fixing temperature for a given page is higher than a second fixing temperature for the succeeding page and the difference therebetween is greater than a predefined value, part or all of a first period, during which the thermal fixing operation for the given page is performed, and a second period, which corresponds to an interval between the two pages, are reserved for raising the surface temperature by the difference, and temperature control is performed during the reserved periods such that the surface temperature reaches the second temperature before the thermal fixing operation for the succeeding page starts.

主权项

1. An image forming apparatus that forms toner images sequentially on a plurality of recording sheets transported with a sheet interval therebetween, and thermally fixes the toner images by passing the recording sheets through a fixing position on a heating roller, comprising:
an image information acquisition unit that acquires image information of an image on each of a plurality of pages to be printed; a fixing temperature determination unit that determines a target fixing temperature for each of the plurality of pages according to the image information, the target fixing temperature being a temperature at which a surface temperature of the heating roller is to be maintained during a thermal fixing operation for the corresponding page; and a temperature control unit that controls the surface temperature of the heating roller, wherein when the fixing temperature determination unit determines the target fixing temperature for a given page to be a first temperature and the target fixing temperature for a succeeding page that immediately succeeds the given page to be a second temperature that is higher than the first temperature, and when a difference between the first temperature and the second temperature is greater than a predefined nonzero value, the temperature control unit reserves part or all of a first period and a second period, the first period being a period during which the thermal fixing operation for the given page is performed, the second period being a period corresponding to a sheet interval between the given page and the succeeding page, the reserved periods serving as periods for raising the surface temperature of the heating roller by an amount that is equal to the difference, and the temperature control unit performs temperature control during the reserved periods such that the surface temperature reaches the second temperature before a start of the thermal fixing operation for the succeeding page, and when the difference between the first temperature and the second temperature is less than or equal to the predefined nonzero value, the temperature control unit reserves no part of the first period and part or all of the second period to serve as the period for raising the surface temperature.