Image forming apparatus that fixes toner image to recording medium using first and second heaters supplied with current during overlapping time periods

An image forming apparatus comprising:

• an image forming unit configured to form an image on a sheet;
• a fixing unit configured to fix the image to the sheet, the fixing unit including:
• a first heater to which is supplied current for generating heat;
• and
• a second heater to which is supplied current for generating heat;
• a temperature sensor configured to detect a temperature of the fixing unit;
• and
• a controller configured to:
• control a first current supplied to the first heater and a second current supplied to the second heater such that the temperature detected by the temperature sensor maintains a target temperature;
• in a case where the first current is supplied to the first heater, gradually increase the first current in a first period, supply the first current based on a first duty cycle in a second period that follows the first period, and gradually reduce the first current to stop supplying the first current in a third period that follows the second period;
• in a case where the second current is supplied to the second heater, gradually increase the second current in a fourth period, supply the second current based on a second duty cycle in a fifth period that follows the fourth period, and gradually reduce the second current to stop supplying the second current in a sixth period that follows the fifth period;
• and
• control the supply of the second current such that part of the fourth period overlaps with the third period,
• wherein the fourth period starts after a predetermined amount of time has passed from a timing at which the third period starts.