Fixing device

A fixing device, comprising:

• a fuser including a fixing member with a surface to contact a printable medium and a heat source for heating the fixing member;
• a first temperature sensor with a first sensing part that contacts a first region of the surface of the fixing member;
• a second temperature sensor with a second sensing part that contacts a second region of the surface of the fixing member;
• a heater control circuit configured to estimate a temperature of the surface of the fixing member based on a temperature measured by the first or second temperature sensors;
• a memory for storing estimated temperature values obtained over a prior time period by the heater control circuit;
• and
• a controller configured to determine whether there is an abnormality in the fixing device based on a difference between a maximum value and a minimum value of the estimated temperature values stored in the memory.

An image forming apparatus, comprising:

• an image forming unit configured to form a toner image on a printable medium;
• a fuser configured to receive the printable medium from the image forming unit and fix the toner image to the printable medium, the fuser including:
• a fixing member with a surface to contact the printable medium and a heat source for heating the fixing member,
• a first temperature sensor with a first sensing part that contacts a first region of the surface of the fixing member,
• a second temperature sensor with a second sensing part that contacts a second region of the surface of the fixing member,
• a heater control circuit configured to estimate a temperature of the surface of the fixing member based on a temperature measured by the first or second temperature sensors, and
• a memory for storing estimated temperature values obtained over a prior time period by the heater control circuit;
• and
• a controller configured to determine whether there is an abnormality based on a difference between a maximum value and a minimum value in the estimated temperature values stored in the memory.