Apparatus for developing electrostatic charge images

Abstract

An apparatus for developing electrostatic charge images on a moving support, e.g. on a photoconductive belt, by a developing powder composed of toner particles and magnetizable carrier particles, which powder is transported by a rotating magnetic roller from a reservoir through a developing zone where a magnetic roller from a reservoir through a developing zone where a magnetic brush is formed between the roller and the support, is provided with means for preventing variations of the quality of the developed images by supplying more developing powder to the brush than the roller transports through the developing zone. The excess powder flows away over a partition into a trough containing a rotor, to be remixed with powder from the reservoir and propelled by the rotor into a narrowing passage defined between the partition and the side of the magnetic roller that moves toward the support. Carrier particles staying on the support are removed by a magnetic field at the adjacent side of a nonmagnetic cylinder that bears through elastic end rings against the support at a location beyond the developing zone. Powder transported from the brush by the magnetic roller is received in a first mixing trough of a pair delivering into the reservoir, to which trough fresh developing powder is supplied for maintaining at a required value the concentration of toner particles in the developing powder. That concentration in the powder being returned on the magnetic roller is sensed, and the supply of fresh powder controlled, by an optical detecting device kept at a constant temperature above the ambient temperature. Further, frictional heat generated in powder mixed in the reservoir is dissipated by a cooling fluid passed through a double-walled bottom of the reservoir.