Developing device of a copier

摘要

A developing device for a copier has a cartridge detachably attached to its housing. An outlet and an inlet provided with lids connect the interiors of the cartridge and the housing but developing agent can be supplied from the cartridge to the housing only if the cartridge is properly attached to the housing because the outlet lid is otherwise not opened. When developing agent is deteriorated and to be discarded for replacement, a transporting unit is activated and deteriorated developing agent is collected into the cartridge through its inlet. A sensor for detecting toner concentration inside the housing controls the operation of the transporting unit. Mechanisms are also provided to warn the user if a cartridge which has already been used is inadvertently set.