HEAT DEVICE AND IMAGE FORMING APPARATUS INCLUDING THE SAME

Abstract

Provided is a heat device which heats and fixes a developed image onto a recording material while nipping and conveying the recording material bearing the developed image by a nip portion, in which even when a turn-on duty ratio between at least two heat generation members provided to a heat source is switched in a direction in which a maximum amount of possible heat generation is decreased, in order to suppress generation of a fixing failure of the developed image formed on the recording material due to a shortage of electric power, in a case where the turn-on duty ratio of a second heat generation member to a first heat generation member is switched, at a predetermined timing, in a direction in which the maximum amount of possible heat generation is decreased, with respect to the at least two heat generation members provided to the heat source, it is set as a condition that a turn-on ratio of the first heating member at the timing is smaller than a predetermined value.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an algorithm for a control according to a first embodiment of the present invention.

FIG. 2 illustrates an algorithm for a control according to a comparative example of the present invention.

FIG. 3 illustrates an effect of the control according to the first embodiment.

FIG. 4 schematically illustrates a structure of an example of an image forming apparatus to which a heat device according to the present invention can be mounted.

FIG. 5 schematically illustrates a cross-section of a fixing device.

FIG. 6 schematically illustrates a structure of a heater.

FIG. 7 illustrates a heat generation distribution of a small-size heat generation member and a large-size heat generation member.

FIG. 8 illustrates a relationship between a turn-on duty ratio and the heat generation distribution.

FIG. 9 illustrates an algorithm for a control according to a third embodiment of the present invention.

Claims

1. A heat device, which heats a developed image and fixes the developed image onto a recording material while nipping and conveying the recording material bearing the developed image by a nip portion, comprising: a heat source including at least two heat generation members which are separately electrified;a fixing member heated by the heat source; anda pressure member for forming the nip portion by being brought into contact with the fixing member,wherein, during continuous conveyance of the recording material, the heat device controls the at least two heat generation members to switch a turn-on duty ratio of a second heat generation member to a first heat generation member in a direction in which a maximum amount of possible heat generation is decreased, when the turn-on ratio of the first heating member at a predetermined timing is smaller than a predetermined value.

2. A heat device according to claim 1, wherein the predetermined timing corresponds to one of an interval between a time when the recording material rushes into the nip portion and a time when the recording material is discharged from the nip portion, and a vicinity of the interval.

3. A heat device according to claim 1, wherein a plurality of turn-on duty ratios of the second heat generation member to the first generating member are set, and different predetermined values are set for the plurality of turn-on duty ratios respectively.

4. A heat device according to claim 1, wherein it is set as a condition that when the turn-on duty ratio of the second heat generating element to the first heat generation member is switched in the direction in which the maximum amount of possible heat generation is decreased, an increasing amount of a turn-on ratio of the first heating member which is obtained during a time from when the recording member rushes into the nip portion until the recording member is discharged from the nip portion is smaller than a predetermined value.

5. A heat device, which heats a developed image and fixes the developed image onto a recording material while nipping and conveying the recording material bearing the developed image by a nip portion, comprising: a heat source including at least two heat generation members which are separately electrified;a fixing member heated by the heat source;a pressure member for forming the nip portion by being brought into contact with the fixing member; anda temperature detecting unit for detecting a temperature of the heat source, a first heat generation member of the at least two heat generation members having a turn-on ratio adjusted according to a variable controlled based on an integrated value for a difference between a detected value and a target value for every predetermined period of the temperature detecting unit,wherein, during continuous conveyance of the recording material, the heat device controls the at least two heat generation members to switch a turn-on duty ratio of the second heat generation member to a first heat generation member in a direction in which a maximum amount of possible heat generation is decreased, when the variable is smaller than a predetermined value, at a predetermined timing.

6. A heat device according to claim 5, wherein the predetermined timing corresponds to one of an interval between a time when the recording material rushes into the nip portion and a time when the recording material is discharged from the nip portion, and a vicinity of the interval.

7. A heat device according to claim 5, wherein a plurality of turn-on duty ratios of the second heat generation member to the first generating member are set, and different predetermined values are set for the plurality of turn-on duty ratios respectively.

8. A heat device according to claim 5, wherein it is set as a condition that when the turn-on duty ratio of the second heat generating element to the first heat generation member is switched in the direction in which the maximum amount of possible heat generation is decreased, an increasing amount of the variable which is obtained during a time from when the recording member rushes into the nip portion until the recording member is discharged from the nip portion is smaller than a predetermined value.

9. An image forming apparatus, comprising the heat device according claim 1.