When a sensor in an image forming device detects fog on the photosensitive
belt, the CPU of the image forming device controls the shutter in each
toner hopper unit to open and drives a discharging auger to rotate,
causing degraded toner to be discharged from the developing chamber into a
waste toner accommodating chamber. After this discharging operation is
completed, the CPU closes the shutter and begins driving a supply auger to
rotate in order to supply new toner from the accommodating chamber into
the developing chamber, thereby replacing most of the old toner in the
developing chamber with new toner.
