Image forming apparatus and fixing temperature control unit

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 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,
• the image forming apparatus further comprises a determination unit that performs a determination as to whether uneven gloss is likely to occur in an image on the given page by referencing the image information of the image on the given page, and
• when the determination unit determines that uneven gloss is likely to occur in the image on the given page, the temperature control unit reduces, by an adjustment amount, an increment of the surface temperature during the part or all of the first period, thereby preventing the increment of the surface temperature from exceeding a maximum value corresponding to a highest level of acceptable uneven gloss, and increases the increment of the surface temperature during the second period by the adjustment amount.

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 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,
• the image forming apparatus further comprises a determination unit that performs, for each of a plurality of areas of the given page contiguous along a sheet transport direction, a determination as to whether uneven gloss is likely to occur in an image in the area by referencing the image information of the image on the given page, and
• when the determination unit determines that uneven gloss is likely to occur in the image in the area, the temperature control unit performs the temperature control by reducing, by an adjustment amount, an increment of the surface temperature during a part of the first period corresponding to the area, thereby preventing the increment of the surface temperature from exceeding a maximum value corresponding to a highest level of acceptable uneven gloss, and increasing the increment of the surface temperature during the second period by the adjustment amount.