| 摘要 |
PURPOSE:To detect whether or not fixation is defective instantaneously and securely by comparing the optical density of a toner picture formed on a recording medium with a predetermined value after a recording medium passes a heater. CONSTITUTION:A 1st photosensor 1 is provided on the exit side of the heater 2 and a photodetection part detects light which is emitted by an internal light emission part and reflected by a sheet S to detect the optical density of a density detection mark on the sheet S having already passed the heater 2. Then the toner picture on the sheet S is heated with radiant heat and fixed on the sheet S. Further, a 2nd photosensor 3 provided on the entrance side of the heater 2 and detects the optical density of the density detection mark before the fixation of the sheet S. Then detecting circuits 4 and 5 detect the outputs of the sensors 1 and 2 and a comparing circuit 6 compare their outputs with each other, thereby generating an alarm unless the output reaches a standard optical density difference. |
