Fixing device for efficiently heating of heating member

摘要

A fixing device includes a pressure member, a heating member, a coil, a first magnetic core, a second magnetic core, a shielding portion, and a switching belt. The second magnetic core is disposed to extend in a width direction in a hollow portion formed by the loop of the coil, and formed in an arc shape with a protruding portion at a side facing the heating member. The shielding portion is formed of a non-magnetic material to shield a path of a magnetic flux generated by the coil between the second magnetic core and the heating member. The switching belt includes a surface where the shielding portion is disposed to face a non-paper passing region in the heating member, suspended to be rotatable between a roller and the protruding portion, and selectively arranged in one of a shielding position and a non-shielding position by rotation of the roller.

主权项

1. A fixing device, comprising:
a pressure member; a heating member configured to be brought into pressure contact with the pressure member so as to form a nipping area; a coil wound in a looped form running widthwise along the heating member orthogonal to a recording-medium conveyance direction, the coil therein configured to generate, under a current passing through the coil, magnetic flux inductively heating the heating member; a first magnetic core surrounding the coil to form a magnetic path on a side of the coil opposite from the heating member; a second magnetic core provided extending widthwise between the first magnetic core and the heating member in a hollow area formed by the loop of the coil, so as to form a magnetic path together with the first magnetic core, the second magnetic core being formed in an arcuate shape having a protruding portion along a side of the second magnetic core facing the heating member; a rotationally driving roller disposed alongside a recessed portion of the second magnetic core on a side of the second magnetic core reverse from the protruding portion; a shielding portion formed of a non-magnetic material to shield a path of the magnetic flux generated by the coil between the second magnetic core and the heating member; and an endless switching belt permeable to magnetic flux, the switching belt including a surface on which the shielding portion is provided, facing a sheet non-passing region of the heating member, the sheet non-passing region being a region outside a sheet-passing region through which recording media of width smaller than maximum-width recording media inserted through the nipping area pass, the switching belt being rotatably suspended between the rotationally driving roller and the protruding portion of the second magnetic core, and being configured to be selectively disposed, by rotation of the driving roller, in one of either a shielding position or a non-shielding position, whereby the shielding portion in the shielding position blocks magnetic flux between the second magnetic core and the heating member, and in the non-shielding position allows passing of magnetic flux between the second magnetic core and the heating member.