Patent ID: 8175509
Filing Date: 2012-05-08
Classification: G03G

Abstract:
1. An image forming apparatus comprising: an image forming section forming a toner image and transferring the toner image onto a sheet; and a fixing unit including a heating member and a pressing member, and fixing the toner image onto the sheet while nipping and conveying the sheet between the heating member and the pressing member and, wherein: the heating member has a sheet-conveyed region that the sheet passes; the fixing unit further includes, a coil arranged along an outer surface of the heating member and generating a magnetic field, a fixed core arranged opposite to the heating member with respect to the coil and forming a magnetic path, a cylindrical movable core so arranged between the fixed core and the heating member with respect to a direction in which the coil generates the magnetic field, as to form the magnetic path together with the fixed core, the cylindrical movable core having an axis extending in a width direction of the sheet being conveyed, a shielding member arranged on an outer peripheral surface of the movable core and shielding the magnetic field, and a magnetism adjusting unit rotating the movable core about the axis to switch the position of the shielding member between a shielding position where the shielding member is positioned inside the sheet-conveyed region to shield the pass of the magnetism and a retracted position where the shielding member is positioned outside the sheet-conveyed region to permit the pass of the magnetism; the shielding member is provided in a plural number in the axial direction of the movable core, the shielding members having a different length in the axial direction and a different width in a circumferential direction of the movable core, the length and the width corresponding to a plurality of sizes of the sheet in the width direction of the sheet; and the magnetism adjusting unit switches each of the shielding members between the shielding position and the retracted position in accordance with the width-direction size of the sheet.