Heat fixing system in an electrophotographic copying machine having a temperature control device

Claim 1

A heat fixing system in an electrophotographic copying machine having a temperature control device, said device comprising: heat radiation means disposed adjacent the path traveled by copy papers; bracket means for mounting said heat radiation means, said bracket means being enclosed except for an open face directed to said path traveled by the copy papers; detecting means mounted in said bracket adjacent said path traveled by said copy papers for generating a sensing signal proportional to the heat capacity of the copy papers and the environmental conditions under which said copying machine is operated; means for setting said heat fixing system to a desired operating temperature, a setting signal being produced thereby representative of said desired operating temperatures; means responsive to the difference between said setting signal and said sensing signal for generating a control signal comprising a pulse train of variable width, constant period pulses, the width of the pulses being an inverse function of said average radiant temperature so that the fixing effected by said system is not influenced by variation in the said heat capacity of the copy paper and the said environmental conditions in the copying machine; and controllable means responsive to said control signal for regulating the power supplied to said heat radiation means.