Abstract: A system is disclosed which will sense the image-development state of toner in the development subsystem of an electrophotographic copier apparatus. This image-development state is related to both toner concentration and the charge-to-mass ratio (q/m) existing on toner particles. The sensing system employs an optical fiber bundle having both transmitting and receiving fibers. At one end, herein referred to as the common end, and transmitting and receiving fibers are interspersed. This common end is positioned flush with the inside chamber wall on a developer housing. At the other end, the transmitting and receiving fibers are bifurcated. The transmitting fibers of the optical bundle are used to guide light from a light source to the common end, and part of the transmitted light is backscattered and guided through the receiving fibers to an optical sensor. The signal received is inversely proportional to the amount of toner deposited on the end of the bundle and the toner on the surface of carrier particles.

Abstract: A novel development system for controlling the flow rate of developer through a narrow development zone, using a reservoir which has a feed chamber for maintaining a constant pressure head at the entrance to the narrow development zone. Developer flow is initiated upon demand by virtue of actuation of a valve positioned between the feed chamber and the entrance to the development zone; since considerable developer mixing occurs in the developer reservoir, mixing devices for mixing added toner with carrier beads may be simplified.