Image forming apparatus including a plurality of heating units and method of controlling the same

An image forming apparatus comprising:

• a fixing device to fix a toner image formed on a medium by applying pressure and heat onto the medium, the fixing device including a plurality of heating units having different power consumptions;
• a power supplying unit to supply a power to each of the plurality of heating units;
• and
• a control unit to control a supply of the power to the plurality of heating units by the power supplying unit at a control period T1, the control unit including,
• a first unit to set the control period T1,
• a second unit to set a power supply time t1 for a first heating unit having a largest power consumption among the plurality of heating units to which the power is supplied within the control period T1 and a power supply time t2 for a second heating unit having a second largest power consumption of the plurality of heating units,
• a third unit to supply the power to the first heating unit for a first period of the power supply time t1, the first period being from a beginning of the control period T1, and to supply the power to the second heating unit for a second period, the second period being from a point obtained by subtracting the power supply time t2 from an end of the control period T1,
• a fourth unit to set a power supply time t3 for a third heating unit, the third heating unit having a power consumption third largest next to the second heating unit, and
• a fifth unit to determine a point tc to start a supply of the power to the third heating unit such that at least one of the power supply time t3 does not overlap with both power supply time t1 and power supply time t2 within the control period T1 and minimizing the overlap of the power supply time t3 with both power supply time t1 and power supply time t2 within the control period T1.