Patent attributes
A printing device is capable of externally detecting: (a) a toner concentration in a developing unit; and (b) a reduction in the usable amount of toner. This eliminates the conventional need of disposing the toner concentration sensor in a narrow developing unit or the need of disposing the toner remaining amount detection sensor in the toner supply unit. Further, it is possible to detect reduction in the amount of toner every time the toner in the developing unit is out, thereby detecting reduction in the usable amount of toner stepwise and issuing an adequate warning whose level is changed depending on the detection result. Thus, the printing device meets the need for miniaturization and is capable of favorably performing printing operation and maintenance work.
