FIXING APPARATUS AND IMAGE FORMING APPARATUS INCLUDING THE SAME

Abstract

A fixing control section of a fixing apparatus according to the present invention includes an end section priority temperature control mode. In the end section priority temperature control mode, the fixing control section temporarily turns off a main heater heating a center section of a fixing roller among a plurarity of heaters disposed inside the fixing roller in a case where a surface temperature of the end section of the fixing roller has reached a preset upper-limit fixing temperature, even if the surface temperature of the center section of the fixing roller is lower than a preset fixing temperature. As a result, destruction of the fixing roller can be prevented by a simple arrangement in the fixing apparatus which includes a plurarity of the heaters disposed inside the fixing roller.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block diagram illustrating an embodiment of the present invention and a configuration of a control system of a fixing unit.

FIG. 2 is a longitudinal sectional view illustrating an embodiment of the present invention and a structure of an image forming apparatus including the fixing unit.

FIG. 3( a) is a sectional view illustrating a center section of the fixing unit, and FIG. 3(b) is a sectional view of an end section of the fixing unit.

FIG. 4 is a view illustrating a positional relationship between heat generating regions that give off heat in heat sources which are disposed inside a fixing roller and a pressure roller both of which are included in the fixing unit.

FIG. 5 is a flow chart illustrating an example of a flow of a surface temperature control of the fixing roller during printing and right after end of printing before the surface temperature control for the fixing roller on standby is actually subjected to the fixing roller.

FIGS. 6( a) through 6(d) each illustrates a relationship between (i) a position of the fixing roller in its axial direction and (ii) a surface temperature of the fixing roller in an image forming apparatus of the present invention, during or right after continuous printing using small-sized paper sheets.

FIG. 7 is a diagram illustrating a relationship between the position of the fixing roller in its axial direction and a heat supply rate of each of a main heater and a sub-heater.

FIGS. 8( a) and 8(b) each is a diagram illustrating a relationship between the position of the fixing roller in its axial direction and a surface temperature of the fixing roller in a conventional image forming apparatus, during or right after continuous printing using small-sized paper sheets.

Claims

1. A fixing apparatus which causes a recording material to pass through a space between a rotatable fixing member and a pressure member that press-contacts the fixing member, so as to fix a toner image formed on the recording material, the fixing apparatus comprising:a heating section, provided inside the fixing member, which includes a plurality of heat sources having mutually different heating regions;a temperature detecting section which detects surface temperatures of areas on the fixing member corresponding to the heating regions of the respective heat sources; anda fixing control section which controls (i) rotation of the fixing member and (ii) power supply to each of the heat sources so that the surface temperatures of the fixing member become a preset fixing temperature, in accordance with temperatures detected by the temperature detecting section, wherein:the fixing control section (i) controls power supply to a center section heat source which heats as the heating region a center section of the fixing member, in accordance with (a) a detected surface temperature of an area on the fixing member corresponding to the heating region of the center section heat source and (b) a detected surface temperature of an area on the fixing member corresponding to the heating region of an end section heat source which heats as the heating region end sections of the fixing member, the heating region of the end section heat source being provided on an end section side of the fixing member with respect to the center section heat source, and (ii) includes an end section priority temperature control mode in which a high priority in the control of power supply to the center section heat source is put on the detected surface temperature of the area corresponding to the heating region of the end section heat source.

2. The fixing apparatus as set forth in claim 1, wherein: the fixing control section temporarily stops or suppresses the power supply to the center section heat source in the end section priority temperature control mode when the fixing control section judges that the surface temperature of the area corresponding to the heating region of the end section heat source has reached a preset upper-limit fixing temperature, even when the surface temperature of the area corresponding to the heating region of the center section heat source is lower than the preset fixing temperature.

3. The fixing apparatus as set forth in claim 2, wherein: the upper-limit fixing temperature is set in a range between the preset fixing temperature and a destructive temperature at which the fixing member is destroyed.

4. The fixing apparatus as set forth in claim 2, wherein: in the end section priority temperature control mode, the fixing control section restarts or restores the power supply to the center section heat source, when the fixing control section judges that the surface temperature of the area corresponding to the heating region of the end section heat source has decreased to a preset allowable temperature which is in a range between the upper-limit fixing temperature and the preset fixing temperature.

5. The fixing apparatus as set force in claim 1, wherein: the heating section includes two heat sources, (i) a main heat source which heats the center section of the fixing member as the heating region, and (ii) a sub-heat source which heats the end sections of the fixing member as the heating region.

6. The fixing apparatus as set forth in claim 1, wherein: the fixing control section carries out the end section priority temperature control mode (i) during printing or (ii) during a temperature restoration process of the fixing member right after end of printing.

7. An image forming apparatus including a fixing apparatus which causes a recording material to pass through a space between a rotatable fixing member and a pressure member that press-contacts the fixing member, so as to fix a toner image formed on the recording material, wherein: the fixing apparatus includes:a heating section, provided inside the fixing member, which includes a plurality of heat sources having mutually different heating regions;a temperature detecting section which detects surface temperatures of areas on the fixing member corresponding to the heating regions of the respective heat sources; anda fixing control section which controls (i) rotation of the fixing member and (ii) power supply to each of the heat sources so that the surface temperatures of the fixing member become a preset fixing temperature, in accordance with temperatures detected by the temperature detecting section, wherein:the fixing control section (i) controls power supply to a center section heat source which heats as the heating region a center section of the fixing member, in accordance with (a) a detected surface temperature of an area on the fixing member corresponding to the heating region of the center section heat source and (b) a detected surface temperature of an area on the fixing member corresponding to the heating region of an end section heat source which heats as the heating region end sections of the fixing member, the heating region of the end section heat source being provided on an end section side of the fixing member with respect to the center section heat source, and (ii) includes an end section priority temperature control mode in which a high priority in the control of power supply to the center section heat source is put on the detected surface temperature of the area corresponding to the heating region of the end section heat source.