Heat fixing device

Claim 1

A heat fixing device for use in a copying apparatus, including a heating roller subjected to heating control at high temperatures and a pressing roller held substantially in pressing contact with said heating roller and rotated together with said heating roller at the time of a fixing operation by said heat fixing device, said heat fixing device comprising: an ambient temperature sensor for detecting ambient temperature of said copying apparatus; first and second temperature sensors for detecting temperatures of said heating roller and said pressing roller, respectively; a decision means for determining whether or not the ambient temperature of said copying apparatus is above a predetermined temperature in response to detection of the ambient temperature by said ambient temperature sensor and for determining respective temperatures of said heating roller and pressing roller in response to detection of said respective temperatures by said first and second temperature sensors, said heating roller having been provided with a heater while said pressing roller is not provided with a heater; and an intermittent drive means which is so controlled by said decision means as to intermittently drive said heating roller and said pressing roller during a waiting mode of said copying apparatus when the ambient temperature is not more than said predetermined temperature and the temperature of said pressing roller is not at a predetermined temperature, so as to warm-up said pressing roller; said decision means also controlling heating of said heating roller so as to maintain said heating roller at a predetermined fixing temperature.