| 摘要 |
PROBLEM TO BE SOLVED: To properly suppress the excessive temperature rising of an area outside the widths of narrow sheets of various sizes caused by a consecutive paper passage without making an apparatus large in size and high in cost. SOLUTION: The induction heating unit includes: an excitation coil 31 that extends over the entire maximum heating area of a heating roller 21 and generates a magnetic flux interlinking with the heating roller; a plurality of demagnetization coils 35 to 37 that are arranged along the excitation coil, have demagnetization areas individually corresponding to areas outside sheet widths corresponding to the sizes of the passed sheets, and nullify the magnetic fluxes of the excitation coil, thereby reducing the magnetic fluxes interlinking with the heating roller; and switches 41 to 43, each of which opens and closes a power supply path connecting both ends of each of the demagnetization coils, thereby switching between the operating state and non-operating state of the demagnetization coil. The plurality of demagnetization coils are arranged in the circumferential direction of the heating roller so that the wider demagnetization coils surround narrower demagnetization coils. COPYRIGHT: (C)2010,JPO&INPIT
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