Patent ID: 7917048

Claim:
A fixing device comprising: a fixing member that extends along a widthwise direction of a sheet conveyed and has an outer peripheral surface to be brought in pressure contact with the sheet; an induction coil that is placed elongate in the widthwise direction of the sheet along the fixing member, for inductively heating a heat generating layer of the fixing member; a high frequency power source section that heats the heat generating layer of the fixing member via the induction coil by supplying an alternating current to the induction coil; a magnetic flux regulating section that restricts heating of a specified region of the fixing member in the widthwise direction of the sheet; a first image region detecting section that detects an image region on the sheet occupied by an image to be fixed in the widthwise direction of the sheet; and a first control section that specifies a region in which generation of heat should be restricted for the magnetic flux regulating section so that only a region of the fixing member corresponding to the image region is substantially heated in the widthwise direction of the sheet, sheet-by-sheet according to a result of detection of the first image region detecting section; wherein the magnetic flux regulating section comprises: a support member made of a nonmagnetic material placed elongate in the widthwise direction of the sheet along the fixing member and the induction coil; a magnetic flux shield portion that is formed with a prescribed pattern on a surface of the support member and interrupts a magnetic flux directed from the induction coil toward the fixing member; and a displacement mechanism that displaces the support member having the magnetic flux shield portion relatively to the fixing member and the induction coil; wherein the fixing member is a metal sleeve that extends elongate in the widthwise direction of the sheet, the support member is a cylindrical member placed so as to be brought in contact with an inner peripheral surface of the fixing member, the induction coil is placed inside the support member, the support member is divided into a first support member and a second support member in the widthwise direction of the sheet, and the magnetic flux shield portion is provided for each of the first support member and the second support member, and the displacement mechanism displaces the first support member and the second support member of the support member by independently rotating the members around a central axis of each of the members.