Fixing apparatus that controls power-on and power-off of an induction current generator and image forming apparatus having the same

1. A fixing apparatus comprising:

a fixing belt to fix an unfixed image on a sheet;

an induction current generator configured to generate in the fixing belt an induction current that causes heating thereof;

a first heating unit configured to generate heat through an induction current generated therein by the induction current generator, and having an opening therein;

a shutdown unit disposed near a surface of the fixing belt and in the opening and configured to cause an electrical connection between a common power source and the fixing apparatus to be cut off when a temperature of the shutdown unit reaches a first predetermined temperature;

a temperature detecting unit disposed near the surface of the fixing belt and configured to detect a temperature at a location of the temperature detecting unit; and

a control unit configured to turn off the induction current generator and stop a fixing operation to fix the unfixed image, without causing the electrical connection between the common power source and the fixing apparatus to be cut off, when the detected temperature reaches a second predetermined temperature that is smaller than the first predetermined temperature during the fixing operation.

2. The fixing apparatus according to claim 1 , wherein

the control unit is further configured to turn on the induction current generator and resume the fixing operation, when the detected temperature decreases to a third predetermined temperature that is smaller than the second predetermined temperature, after the induction current generator has been turned off and the fixing operation has been stopped.

3. The fixing apparatus according to claim 1 , wherein

both the shutdown unit and the temperature detecting unit are disposed near a region of the fixing belt in which the induction current is generated.

4. The fixing apparatus according to claim 3 , wherein

both the shutdown unit and the temperature detecting unit are disposed near a region of the fixing belt located centrally between ends of the fixing belt in a width direction thereof.

5. The fixing apparatus according to claim 1 ,

the temperature detecting unit is disposed on the first heating unit.

6. The fixing apparatus according to claim 1 , further comprising:

a second heating unit that is configured to generate heat through an induction current generated therein by the induction current generator, and disposed between the fixing belt and the first heating unit, wherein

the first heating unit is formed of a magnetic material having a Curie temperature that is higher than the second predetermined temperature, and

the second heating unit is formed of a magnetic shunt alloy having a Curie temperature that is lower than the second predetermined temperature.

7. An image forming apparatus, comprising:

an image forming section configured to form an unfixed image on a sheet;

a fixing section configured to fix the unfixed image on the sheet,

the fixing section including:

a fixing belt to fix the unfixed image on the sheet,

an induction current generator configured to generate in the fixing belt an induction current that causes heating thereof,

a first heating unit that is configured to generate heat through an induction current generated therein by the induction current generator, and formed of a magnetic material having a Curie temperature that is higher than the second predetermined temperature,

a second heating unit that is configured to generate heat through an induction current generated therein by the induction current generator, disposed between the fixing belt and the first heating unit, and formed of a magnetic shunt alloy having a Curie temperature that is lower than the second predetermined temperature,

a shutdown unit disposed near a surface of the fixing belt and configured to cause an electrical connection between a common power source and the image forming apparatus to be cut off when a temperature of the shutdown unit reaches a first predetermined temperature, and

a temperature detecting unit disposed near the surface of the fixing belt and configured to detect a temperature at a location of the temperature detecting unit;

a sheet conveying section configured to convey the sheet from the image forming section towards the fixing section; and

a control unit configured to turn off the induction current generator and stop a printing operation, without causing the electrical connection between the common power source and the image forming apparatus to be cut off, when the detected temperature reaches a second predetermined temperature that is smaller than the first predetermined temperature during the printing operation.

8. The image forming apparatus according to claim 7 , wherein

the control unit is further configured to turn on the induction current generator and resume the printing operation when the detected temperature decreases to a third predetermined temperature that is smaller than the second predetermined temperature, after the induction current generator has been turned off and the printing operation has been stopped.

9. The image forming apparatus according to claim 7 , wherein

both the shutdown unit and the temperature detecting unit are disposed near a region of the fixing belt in which the induction current is generated.

10. The image forming apparatus according to claim 7 , wherein

both the shutdown unit and the temperature detecting unit are disposed near a region of the fixing belt located centrally between ends of the fixing belt in a width direction thereof.

11. The image forming apparatus according to claim 7 , wherein

the temperature detecting unit is disposed on the first heating unit.

12. The image forming apparatus according to claim 7 , wherein

the first heating unit has an opening therein, and

the shutdown unit is disposed in the opening.

13. A method for operating an image forming apparatus comprising:

heating a fixing belt to fix an unfixed image on a sheet, through an induction current generated therein by an induction current generator;

conveying the sheet towards the fixing belt;

cutting off an electrical connection between a common power source and the image forming apparatus, by a shutdown unit disposed near surface of the fixing belt and in an opening of a heating unit that generates heat through an induction current generated therein by the induction current generator, when a temperature at a first region near a surface of the fixing belt reaches a first predetermined temperature; and

turning off the induction current generator and stopping a printing operation, without cutting off the electrical connection between the common power source and the image forming apparatus, when a temperature at a second region near a surface of the fixing belt reaches a second predetermined temperature that is smaller than the first predetermined temperature during the printing operation.

14. The method according to claim 13 , further comprising:

turning on the induction current generator and resuming the printing operation, when the temperature at the second region decreases to a third predetermined temperature that is smaller than the second predetermined temperature, after the induction current generator has been turned off and the printing operation has been stopped.

15. The method according to claim 13 , wherein

both the first and the second regions are near a region of the fixing belt in which the induction current is generated.

16. The method according to claim 15 , wherein

both the first and the second regions are near a region of the fixing belt located centrally between ends of the fixing belt in a width direction thereof.