Image forming apparatus using power control to select power levels based on temperature

摘要

One disclosed aspect of the embodiments relates to power control of a heater in a fixing unit. A plurality of control tables having different ratios of phase control waveforms and wave number control waveforms in one control cycle have been set, and a control table is selected depending on a set target temperature.

主权项

1. An image forming apparatus comprising:
a fixing unit configured to perform heat fixing an unfixed toner image formed on a recording sheet onto the recording sheet, the fixing unit includes a heater that generates heat by electric power supplied from an alternating-current power supply; and a power control unit configured to control the electric power to be supplied to the heater such that the fixing unit is kept to a target temperature, wherein the power control unit is configured to select a power level per one control cycle from a control table in which a plurality of power levels have been set in accordance with a temperature of the fixing unit, the duration of the one control cycle being defined by a predetermined number of consecutive half-cycles in an alternating-current waveform, wherein the alternating-current waveform flowing in the heater in the one control cycle including a phase control waveform in which a current flows only in a part of a half-cycle of the alternating-current waveform and a wave number control waveform in which all current flows in a half-cycle of the alternating-current waveform, wherein as the control table, a plurality of control tables having different ratios of the phase control waveforms and the wave number control waveforms in the one control cycle have been set, and the control unit is configured to select one of the plurality of control tables depending on a set target temperature, and select a power level from the selected control table in accordance with the temperature of the fixing unit.