Abstract: In a thermal fixing device for an image forming apparatus, when a heat roller starts to be heated, a warm-up time matching the instantaneous roller temperature can be set and controlled with accuracy. The interval between the start of a paper after the start of a recording operation and the arrival of the paper at the fixing device is available for the elevation of the roller temperature to a fixable temperature. A period of time necessary for the roller temperature to reach a temperature at which the recording operation can be started is corrected on the basis of the instantaneous ambient temperature. The device therefore reduces the waiting time up to the time when the surface of the heat roller reaches a fixable temperature, and can control the surface of the heat roller to a stable fixable temperature.

Abstract: An image fixing apparatus includes a conductive fixing film, a pair of electrodes contacting the conductive fixing film, a supporting element supporting the electrodes, a pressing roller located on a side of the conductive fixing film opposite to the supporting element and having an outer elastic layer. The conductive fixing film is moved at a constant speed so that a transfer material having an unfixed toner image is nipped between the conductive fixing film and is moved. The transfer material is thus subjected to a heating and fixing operation. A thermometer detects a temperature of the electrode or one part of the supporting element. A memory stores a data-table having a relation between a power supply to the electrodes and a temperature of the thermometer. A control circuit both determines a suitable supply power from the data-table and the temperature detected by the thermometer, and controls the supply power supplied to the electrodes.