Image forming apparatus and control method

A control method for controlling a contact switch and a semiconductor switch of an image forming apparatus to bring a demagnetizing coil of the image forming apparatus into a conductive state or a cutoff state, the image forming apparatus being for fusing toner by using a fixing roller heated by electromagnetic induction caused by a magnetizing coil, and fixing a toner image on a recording sheet,

• the image forming apparatus comprising:
• a power source applying alternating current voltage to the magnetizing coil;
• the demagnetizing coil switchable between the conductive state and the cutoff state, and when in the conductive state, cancelling out a portion of a magnetic flux produced by the magnetizing coil;
• and
• the contact switch and the semiconductor switch electrically connected in parallel and, in combination, bringing the demagnetizing coil into the conductive state or the cutoff state, and
• the control method comprising:
• when bringing the demagnetizing coil into the conductive state from the cutoff state,
• first, closing the semiconductor switch in synchronization with a zero-crossing of the alternating current voltage;
• next, closing the contact switch;
• and
• then opening the semiconductor switch.

A control method for controlling a contact switch and a semiconductor switch of an image forming apparatus to bring a demagnetizing coil of the image forming apparatus into a conductive state or a cutoff state, the image forming apparatus being for fusing toner by using a fixing roller heated by electromagnetic induction caused by a magnetizing coil, and fixing a toner image on a recording sheet,

• the image forming apparatus comprising:
• a power source applying alternating current voltage to the magnetizing coil;
• the demagnetizing coil switchable between the conductive state and the cutoff state, and when in the conductive state, cancelling out a portion of a magnetic flux produced by the magnetizing coil;
• and
• the contact switch and the semiconductor switch electrically connected in parallel and, in combination, bringing the demagnetizing coil into the conductive state or the cutoff state, and
• the control method comprising:
• when bringing the demagnetizing coil into the cutoff state from the conductive state,
• first, closing the semiconductor switch in synchronization with a zero-crossing of the alternating current voltage;
• next, opening the contact switch;
• and
• then opening the semiconductor switch in synchronization with a zero-crossing of the alternating current voltage that occurs immediately after the contact switch has been opened.