Heating device and fuser utilizing electromagnetic induction

A fuser utilizing electromagnetic induction for fusing unfused toner on a recording medium by melting and pressurizing the unfused toner on the recording sheet while nipping and transporting the recording medium by a fusing nip portion, comprising:

• a heating member that is a magnetic metal member as a rotary body;
• induction heating means opposed to the heating member, for causing the heating member to heat through electromagnetic induction, the induction heating means including an exciting coil for generating a magnetic field and a coil guide member on which the exciting coil is wound;
• and
• a pressing member that is brought into pressure contact with the heating member or a belt member that is heated by the heating member and is rotated in a forward direction to form the fusing nip portion,
• wherein the exciting coil is formed in at least two layers in such a manner that a first layer is formed on a circumferential surface of the coil guide member by winding a plurality of turns and a second layer is formed around and outside the first layer on a side opposite to the coil guide member, and
• winding of each of the second layer and following layers is started from a position close to a winding start position of the first layer.

A heating device for an image forming apparatus comprising:

• an exciting coil;
• a heating roller that is induction-heated through a magnetic field of the exciting coil;
• a fusing roller for thermally fusing an unfused image on a recording medium;
• a heat conduction belt stretched between the heating roller and the fusing roller, for transmitting heat from the heating roller to the fusing roller;
• and
• a core member that is shaped like a pyramid so as to cover part of the heating roller and on which the exciting coil is wound,
• wherein the exciting coil is wound in more layers on a top portion of the pyramid-shaped core member than on a foot portion thereof.