Patent ID: 9471013
Filing Date: 2016-10-18
CPC Classification: G03G

Claim Text:
1. An image forming apparatus comprising: an image forming unit that forms an unfixed toner image on a recording material; a fixing unit that heats the unfixed toner image formed on the recording material and fixes the unfixed toner image to the recording material, the fixing unit having a heat generating member that generates heat with power supplied from a commercial AC power supply; a control unit that controls the supply of the power to the heat generating member from the commercial AC power supply according to the temperature of the fixing unit, the control unit performing control so that an alternating-current waveform corresponding to the supplied power flows into the heat generating member; a power supply unit that generates a DC voltage from an AC voltage; a voltage detecting unit that detects a voltage accumulated in a primary smoothing capacitor provided in the power supply unit, and an acquiring unit that acquires an output impedance of the commercial AC power supply, the acquiring unit acquires the output impedance based on the difference between the output voltage of the voltage detecting unit when no power is supplied to the heat generating member and the output voltage of the voltage detecting unit when power is supplied to the heat generating member, wherein the control unit uses a predetermined number of successive half-waves of an alternating current as one control cycle, sets the supplied power corresponding to the temperature of the fixing unit every one control cycle, and performs control so that an alternating-current waveform including both a phase control waveform and a wave-number control waveform flows into the heat generating member during one control cycle, the control unit is configured to select a first waveform table in which the alternating-current waveforms corresponding to the supplied powers are set and a second waveform table in which alternating-current waveforms different from the alternating-current waveforms set in the first waveform table are set, the alternating-current waveforms set in the second waveform table are alternating-current waveforms in which the proportion of phase control waveforms in one control cycle is larger than that in the first waveform table, the control unit selects the first waveform table or the second waveform table according to the output impedance acquired by the acquiring unit, and the control unit selects the first waveform table when the output impedance is smaller than a reference value and selects the second waveform table when the output impedance is larger than the reference value.