Color image forming apparatus

Abstract

A toner supplying system for use in combination with a developing device (100) of the type having a conveyor means (300) carrying a plurality of developing units (101) such as to bring the desired developing unit to the developing position for the development of a latent image on an image carrying member (1). The toner supplying system comprises a hopper (201) disposed outside the developing device, a shaft (310) provided in the toner conveyor means, a toner transportation means (202) for transporting the toner from the hopper to the shaft, and a toner passage means (310, 350) through which the toner is supplied from the shaft to respective developing units. The toner passage means includes annular chambers (351) formed between the hollow shaft (310) and an intermediate pipe (350). The annular chambers are separated axially by partition sealing means (354). Toner passage means (225, 450), switchable between open and shut-off states and adapted to take the open state only when their associated developing unit is in a toner supplying position, are also provided. The system further comprises a toner density detecting means (50) for detecting the toner density in the developing agent on the developing unit under development. The toner density detecting means produces, when the detected toner density is too low, a signal for bringing the developing unit to the toner supplying position after completion of the development of the final color on a copying paper under developing operation.