Image forming apparatus that fixes toner image by thermal compression

An image forming apparatus comprising:

• a fixing device;
• a control device including a processor, and configured to act as a controller, when the processor executes a control program;
• and a transport device that transports a recording medium to the fixing device,
• wherein the fixing device includes:
• a heat roller extending in an orthogonal direction, orthogonal to a direction in which the transport device transports the recording medium;
• a pressure roller extending in the orthogonal direction opposite the heat roller, and defining, in collaboration with the heat roller, a nip region through which the recording medium to undergo a fixing process is to pass;
• and
• a heating device that heats the heat roller, the heating device being located inside the heat roller so as to extend in the orthogonal direction from an end portion of the heat roller to the other end portion thereof,
• the transport device transports the recording medium of a predetermined minimum size, through a predetermined region of the heat roller and the pressure roller, including a central portion of the heat roller and the pressure roller in the orthogonal direction,
• the fixing device further includes:
• a first temperature sensor that detects, as a first temperature, a temperature of the predetermined region in the heating device;
• a second temperature sensor that detects, as a second temperature, a temperature of a portion of the heating device between one end portion thereof in the orthogonal direction, and an end portion of the predetermined region on a side of the one end portion of the heating device;
• and
• a sheet sensor that detects presence of the recording medium passing through the nip region, the sheet sensor being located at a position in the nip region corresponding to a portion of the heating device between the other end portion thereof in the orthogonal direction, and the other end portion of the predetermined region on a side of the other end portion of the heating device, and
• the controller is configured to:
• control power supply to the heating device, to set the first temperature to a prespecified fixing temperature;
• start successive transport of the recording medium to the nip region by the transport device, at a predetermined first number of sheets per predetermined time;
• and
• change, upon deciding that a temperature difference between the first temperature and the second temperature is smaller than a predetermined first threshold of the temperature difference, and that the sheet sensor has not detected the recording medium, the number of sheets per predetermined time, of the successive transport of the recording medium to the nip region by the transport device, from the first number of sheets to a predetermined second number of sheets, fewer than the first number of sheets.