Fixing device, image forming apparatus, and method of controlling fixing device

A method of fixing a toner image on a printing medium by conveying the printing medium through a pressure contact section under heat and pressure, said method comprising:

• heating a fixing device;
• applying pressure to the fixing device at the pressure contact section;
• arranging an internal temperature detection device within a widthwise region corresponding to the heat generation section;
• detecting temperature of the fixing device using the internal temperature detection device;
• arranging an external temperature detection device at the outside of the widthwise region;
• detecting temperature of the fixing device using the external temperature detection device;
• controlling the heat generating device to approximate the temperature of the fixing device to a target level;
• and
• stopping heat generation of the heat generating device one of when the temperature reaches the first high temperature detection limit and a temperature rising amount exceeds a prescribed threshold in a prescribed time period after the first high temperature detection limit is reached, and when the temperature reaches a prescribed second high temperature detection limit, a temperature rising amount in a second prescribed time period after the second high temperature detection limit is reached exceeds a prescribed threshold, and the heat generating device continuously generates heat on the maximum heat generation condition for a prescribed time period within the second prescribed time period,
• wherein said second high temperature detection limit is automatically changed in accordance with a status of the fixing device.

A fixing apparatus, comprising:

• a rotatable fixing device configured to fix a toner image onto a printing medium with heat and pressure at a pressure contacting section;
• a heat generating device configured to generate and apply heat to the fixing device, said heat generating device having at least one heat generation section extending in a widthwise direction of the fixing device;
• a pressurizing device configured to pressure contact the fixing device at the pressure contacting section;
• an internal temperature detection device arranged within a heat generation region corresponding to the at least one heat generation section and configured to detect temperature of the fixing device;
• an external temperature detection device arranged at the outside of the heat generation region and configured to detect temperature of the fixing device;
• and
• a temperature control device configured to control the heat generating device to approximate the temperature of the fixing device to a target level based on the temperature detected by the internal temperature detection device;
• wherein heat generation of the heat generating device is stopped one of when temperature detected by the internal temperature detection device reaches a prescribed first high temperature detection limit and a temperature rising amount in a prescribed time period after the first high temperature detection limit is reached exceeds a prescribed threshold, and when temperature detected by the external temperature detection device reaches a prescribed second high temperature detection limit, a temperature rising amount detected in a prescribed time period after the second high temperature detection limit is reached exceeds a prescribed threshold, and the heat generating device continuously generates heat on a maximum heat generation condition for a prescribed time period within the second prescribed time period,
• wherein said second high temperature detection limit is different than the first high temperature detection limit, and
• wherein said second high temperature detection limit is lower than the maximum temperature detected by the external temperature detection device during a normal operation of the fixing device.