Electromagnetic induction heating fixing apparatus and image forming apparatus having the same

1. A fixing apparatus, comprising:

a magnetic flux generating source which generates a magnetic flux;

an endless belt which inductively generates heat by the magnetic flux passing through the belt while rotating in a prescribed direction;

a rotating body which rotates in a prescribed direction and, together with the belt, forms a nip section through which a recording medium carrying a toner image passes;

a core which is made of a magnetic material, and directs the magnetic flux to the belt;

a heat value adjustment member that is disposed rotatably and adjusts an amount of heat generated in the belt, the heat value adjustment member being disposed to oppose the magnetic flux generating source and the core across the belt; and

a gripping piece which is a non-rotating member, is disposed in a position corresponding to the nip section, and contacts an inner surface of the belt to rotatably grip the belt against the rotating body;

wherein the belt is wrapped between the heat value adjustment member and the gripping piece, and

the heat value adjusting member is rotated in accordance with a width dimension of a recording medium in a direction perpendicular to a conveyance direction of the recording medium passing through the nip section so that overheating is suppressed in the region outside the recording medium passage region of the belt,

the magnetic flux generating source is a winding disposed to oppose the outer circumferential surface of the belt at a position opposite to the rotating body with respect to the belt,

the core has a center core surrounded by the magnetic flux generating source and opposes the belt in a region where the magnetic flux generating source is not present, and

the belt has a prescribed rigidity and contacts an outer circumferential surface of the heat value adjustment member at a position where the heat value adjustment member opposes the center core and a position in the vicinity thereof, and the belt does not contact the outer circumferential surface of the heat value adjustment member at a position where the heat value adjustment member opposes the magnetic flux generating source.

2. The fixing apparatus according to claim 1 ,

wherein the heat value adjustment member has a coating layer which reduces friction between a surface of the heat value adjustment member and the inner surface of the belt.

3. The fixing apparatus according to claim 1 ,

wherein the heat value adjustment member includes:

a thin base member made of a magnetic material; and

a thin plate-shaped magnetic shielding plate which is made of a non-magnetic material, and is installed on an opposite surface of the base member from the belt; and

wherein the position of the magnetic shielding plate is switched between a shielding position for shielding or suppressing the magnetic flux and a restricted shielding position where shielding of the magnetic flux is restricted, in accordance with rotation of the base member; and

the amount of generated heat is adjusted by switching the position of the magnetic shielding plate between the shielding position and the restricted shielding position.

4. The fixing apparatus according to claim 3 , wherein the base member has a semi-cylindrical shape.

5. The fixing apparatus according to claim 3 , wherein the base member has a cylindrical shape.

6. The fixing apparatus according to claim 1 , wherein the gripping piece is a flat plate-shaped member extending along the nip section in parallel with the rotating body.

7. The fixing apparatus according to claim 1 ,

wherein the heat value adjustment member includes:

a thin base member made of a non-magnetic material; and

a thin plate-shaped heat generating plate which is made of a magnetic material capable of generating heat by the magnetic flux, and is installed on an opposite surface of the base member from the belt; and

wherein the position of the heat generating plate is switched between a heat generating position for generating heat by the magnetic flux and a restricted heat generating position where generation of heat is restricted, in accordance with rotation of the base member; and

the amount of generated heat is adjusted by switching the position of the heat generating plate between the heat generating position and the restricted heat generating position.

8. The fixing apparatus according to claim 7 , wherein the base member has a semi-cylindrical shape.

9. The fixing apparatus according to claim 7 , wherein the base member has a cylindrical shape.

10. An image forming apparatus, comprising:

an image forming unit which forms a toner image;

a transfer unit which transfers the toner image formed by the image forming unit onto a recording medium; and

a fixing apparatus which fixes the toner image onto the recording medium;

wherein the fixing apparatus includes:

a magnetic flux generating source which generates a magnetic flux;

an endless belt which inductively generates heat by the magnetic flux while rotating in a prescribed direction;

a rotating body which rotates in a prescribed direction and, together with the belt, forms a nip section through which the recording medium carrying the toner image passes;

a core which is made of a magnetic material, and directs the magnetic flux to the belt;

a heat value adjustment member that is disposed rotatably and adjusts an amount of heat generated in the belt, the heat value adjustment member being disposed to oppose the magnetic flux generating source and the core across the belt; and

a gripping piece which is a non-rotating member, is disposed in a position corresponding to the nip section, and contacts an inner surface of the belt to rotatably grip the belt against the rotating body; and

wherein the belt is wrapped between the heat value adjustment member and the gripping piece, and

the heat value adjusting member is rotated in accordance with a width dimension of a recording medium in a direction perpendicular to a conveyance direction of the recording medium passing through the nip section so that overheating is suppressed in the region outside the recording medium passage region of the belt,

the magnetic flux generating source is a winding disposed to oppose the outer circumferential surface of the belt at a position opposite to the rotating body with respect to the belt,

the core has a center core surrounded by the magnetic flux generating source and opposes the belt in a region where the magnetic flux generating source is not present, and

the belt has a prescribed rigidity and contacts an outer circumferential surface of the heat value adjustment member at a position where the heat value adjustment member opposes the center core and a position in the vicinity thereof, and the belt does not contact the outer circumferential surface of the heat value adjustment member at a position where the heat value adjustment member opposes the magnetic flux generating source.

11. The image forming apparatus according to claim 10 ,

wherein the heat value adjustment member has a coating layer which reduces friction between a surface of the heat value adjustment member and the inner surface of the belt.

12. The image forming apparatus according to claim 10 ,

wherein the heat value adjustment member includes:

a thin base member made of a magnetic material; and

a thin plate-shaped magnetic shielding plate which is made of a non-magnetic material, and is installed on an opposite surface of the base member from the belt; and

wherein the position of the magnetic shielding plate is switched between a shielding position for shielding or suppressing the magnetic flux and a restricted shielding position where shielding of the magnetic flux is restricted, in accordance with rotation of the base member; and

the amount of generated heat is adjusted by switching the position of the magnetic shielding plate between the shielding position and the restricted shielding position.

13. The image forming apparatus according to claim 12 , wherein the base member has a semi-cylindrical shape.

14. The image forming apparatus according to claim 12 , wherein the base member has a cylindrical shape.

15. The image forming apparatus according to claim 10 , wherein the gripping piece is a flat plate-shaped member extending along the nip section in parallel with the rotating body.

16. The image forming apparatus according to claim 10 ,

wherein the heat value adjustment member includes:

a thin base member made of a non-magnetic material; and

a thin plate-shaped heat generating plate which is made of a magnetic material capable of generating heat by the magnetic flux, and is installed on an opposite surface of the base member from the belt; and

wherein the position of the heat generating plate is switched between a heat generating position for generating heat by the magnetic flux and a restricted heat generating position where generation of heat is restricted, in accordance with rotation of the base member; and

the amount of generated heat is adjusted by switching the position of the heat generating plate between the heat generating position and the restricted heat generating position.

17. The image forming apparatus according to claim 16 , wherein the base member has a semi-cylindrical shape.

18. The image forming apparatus according to claim 16 , wherein the base member has a cylindrical shape.

19. A fixing apparatus, comprising:

a magnetic flux generating source which generates a magnetic flux;

an endless belt which inductively generates heat by the magnetic flux passing through the belt while rotating in a prescribed direction;

a rotating body which rotates in a prescribed direction and, together with the belt, forms a nip section through which a recording medium carrying a toner image passes;

a core which is made of a magnetic material, and directs the magnetic flux to the belt;

a heat value adjustment member that is disposed rotatably and adjusts an amount of heat generated in the belt; and

a gripping piece which is a non-rotating member, is disposed in a position corresponding to the nip section, and contacts an inner surface of the belt to rotatably grip the belt against the rotating body;

wherein the belt is wrapped between the heat value adjustment member and the gripping piece, and

the heat value adjusting member is rotated in accordance with a width dimension of a recording medium in a direction perpendicular to a conveyance direction of the recording medium passing through the nip section so that overheating is suppressed in the region outside the recording medium passage region of the belt, and

the heat value adjustment member includes:

a thin cylindrical base member made of a non-magnetic material; and

a thin plate-shaped heat generating plate which is made of a magnetic material capable of generating heat by the magnetic flux, and is installed on an opposite circumferential surface of the base member from the belt; and

wherein the position of the heat generating plate is switched between a heat generating position for generating heat by the magnetic flux and a restricted heat generating position where generation of heat is restricted, in accordance with rotation of the base member; and

the amount of generated heat is adjusted by switching the position of the heat generating plate between the heat generating position and the restricted heat generating position.