Patent ID: 8494388

Claim:
An image forming apparatus, comprising: a sheet feeding section for receiving a paper sheet used for printing; an image forming section for forming a toner image; a heating section comprising a rotary member that is brought into contact with the paper sheet, for fixation of the toner image; a coil that is opposed to the heating section and is wound around the rotary member in an axis direction thereof, for heating the heating section by induction heating; a core that is opposed to the heating section, forms a magnetic path between the coil and the heating section, and has a circumferential surface covered with a magnetic shielding plate, the circumferential surface covered with the magnetic shielding plate having different lengths in the axis direction in a plurality of steps according to a position in a circumferential direction; a rotary section for causing the core to rotate; a plurality of temperature sensing elements for sensing temperatures of the heating section according to a heating width; and a control section for controlling power to be supplied to the coil based on an output from each of the plurality of temperature sensing elements, recognizing a size of the paper sheet used for the printing, controlling the heating width in the heating section by controlling the rotary section to control a rotation angle of the core, controlling the rotary section to set the heating width corresponding to the size of the paper sheet at a start of a print job, and causing the heating section to be heated by controlling the rotary section to set the heating width wider than at the start of the print job such that, irrespective of whether the paper sheet size used for a subsequent print job is known or unknown, a non-sheet passing region is heated to a fixation control temperature before the print job is completed.