Fixing apparatus

A fixing apparatus comprising:

• a fixing device which includes a fixing roller and a pressing roller pressed against the fixing roller, the fixing roller and the pressing roller defining a region through which sheets of various sizes pass while being heated;
• an induction-heating device which heats the fixing roller by induction heating and which includes first and second excitation coil units provided inside the fixing roller and spaced from each other by a predetermined distance in an axial direction of the fixing roller;
• and
• a control device which varies an output applied to the first and second excitation coils in accordance with a surface temperature as measured in the axial direction of the fixing roller,
• said first excitation coil unit including a center coil unit located in an axially central portion of the fixing roller, and said second excitation coil units including a pair of end coil units located at axially end portions of the fixing roller, and
• each of the center and end coil units including a bobbin and a coil provided around the bobbin, the bobbin of the center coil unit and the bobbins of the end coil units differ from each other in sizes as measured in a direction perpendicular to an axial direction of the heating roller.

A fixing apparatus comprising:

• a fixing device which includes a fixing roller and a pressing roller pressed against the fixing roller, the fixing roller and the pressing roller defining a region through which sheets of various sizes pass while being heated;
• an induction-heating device which heats the fixing roller by induction heating and which includes first and second excitation coil units provided inside the fixing roller and spaced from each other by a predetermined distance in an axial direction of the fixing roller;
• and
• a control device which varies an output applied to the first and second excitation coils in accordance with a surface temperature as measured in the axial direction of the fixing roller,
• said first excitation coil unit including a center coil unit located in an axially central portion of the fixing roller, and said second excitation coil units including a pair of end coil units located at axially end portions of the fixing roller, and
• said center coil unit including a lead wire extending along one of said pair of end coil units, and the end coil unit along which the lead wire passes has coil turns smaller in number than that of a coil section of the other end coil unit.

A fixing apparatus comprising:

• a fixing device which includes a fixing roller and a pressing roller pressed against the fixing roller, the fixing roller and the pressing roller defining a region through which sheets of various sizes pass while being heated;
• an induction-heating device which heats the fixing roller by induction heating and which includes first and second excitation coil units provided inside the fixing roller and spaced from each other by a predetermined distance in an axial direction of the fixing roller;
• and
• a control device which varies an output applied to the first and second excitation coils in accordance with a surface temperature as measured in the axial direction of the fixing roller,
• said first excitation coil unit including a center coil unit located in an axially central portion of the fixing roller, and said second excitation coil units including a pair of end coil units located at axially end portions of the fixing roller, and
• said fixing apparatus further comprising:
• a first temperature sensing unit and an abnormal temperature sensing unit which oppose a fixing roller portion heated by the center coil unit;
• a second temperature sensing unit which opposes a fixing roller portion heated by one of the end coil units;
• and a second abnormal temperature sensing unit which opposes a fixing roller portion heated by the other one of the end coil units, the first and second temperature sensing units sensing setting temperatures of the center and end coil units, thereby controlling a heating operation performed by the fixing roller.

A fixing apparatus comprising:

• a fixing device which includes a fixing roller and a pressing roller pressed against the fixing roller, the fixing roller and the pressing roller defining a region through which sheets of various sizes pass while being heated;
• an induction-heating device which heats the fixing roller by induction heating and which includes first and second excitation coil units provided inside the fixing roller and spaced from each other by a predetermined distance in an axial direction of the fixing roller;
• and
• a control device which varies an output applied to the first and second excitation coils in accordance with a surface temperature as measured in the axial direction of the fixing roller, said first excitation coil unit including a center coil unit located in an axially central portion of the fixing roller, and said second excitation coil units including a pair of end coil units located at axially end portions of the fixing roller,
• each of the center and end coil units including a bobbin and a coil provided around the bobbin, and
• that portion of the bobbin around which the coil is provided facing an inner circumferential surface of the fixing roller and being located in the neighborhood of the inner circumferential surface.

A fixing apparatus comprising:

• a fixing device which includes a fixing roller and a pressing roller pressed against the fixing roller, the fixing roller and the pressing roller defining a region through which sheets of various sizes pass while being heated;
• an induction-heating device which heats the fixing roller by induction heating and which includes first and second excitation coil units provided inside the fixing roller and spaced from each other by a predetermined distance in an axial direction of the fixing roller;
• and
• a control device which varies an output applied to the first and second excitation coils in accordance with a surface temperature as measured in the axial direction of the fixing roller,
• said first excitation coil unit including a center coil unit located in an axially central portion of the fixing roller, and said second excitation coil units including a pair of end coil units located at axially end portions of the fixing roller, and
• each of said center coil unit and said pair of end coil units including a lead wire, the lead wire of the center coil unit extending through a region in the neighborhood of the end coil units, the lead wire of the end coil units extending through a region in the neighborhood of the center coil unit, and the lead wires of the center and end coil units being guided by an insulating guide member in the regions in the neighborhood of the center and end coil units.