| 摘要 |
PROBLEM TO BE SOLVED: To obtain a fixing device and a fixing method for detecting the practical temperature of a nip part even when the size of paper is random and preventing the generation of defective fixing by a temperature drop due to the transfer of heat to recording paper. SOLUTION: A material to be heated is press-contacted between a fixing roller 2 having a heat source in its inside and a pressurizing roller 3 arranged so as to be press-contacted with the roller 2 and allowed to be rotated in cooperation with the rotation of the roller 2 and passed while being heated. The roller 2 has double structure having a surface layer 4 and an axial core 7 and having a space 6 between the layer 4 and the core 7, the space 6 is filled with gas of fixed pressure and the layer 4 or the core 7 is provided with an ultrasonic transducer 5 having a transmitter for radiating ultrasonic waves to the air and a receiver for receiving ultrasonic waves flying in the air. The layer 4 has flexibility, a distance between the layer 4 and the core 7 is detected by the transducer 5 and such a specific operation that the heating means of the fixing roller 2 is driven by a change of the distance is carried out.
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