Patent ID: 8358942

Claim:
Apparatus for measuring developer toner concentration in an electrophotographic system, comprising: a) a rotatable development member and a movable photoreceptor arranged so that a toning zone is defined between the development member and the photoreceptor, and the development member selectively supplies developer to the photoreceptor in the toning zone while it rotates, wherein the developer comprises toner and carrier particles; b) a patterning unit adapted to produce an electrostatic latent image on the photoreceptor; c) two sensors, one before and one after the toning zone in the direction of rotation of the development member, each sensor including a respective electrode arranged with respect to the development member to form a respective capacitance between the respective electrode and development member, and to define a respective working volume between the respective electrode and the development member, wherein developer passes through the respective working volume without contacting the electrode, and the respective electrode is electrically insulated from the development member by the respective working volume; d) a voltage source for selectively applying respective AC biases across the respective working volumes of the sensors; e) a meter for measuring respective currents across the respective working volumes while the respective biases are applied; and f) a controller adapted to perform the following functions: i) receive pixel data corresponding to toner to be applied to the photoreceptor; ii) cause the patterning unit to produce an electrostatic latent image corresponding to the received pixel data on the photoreceptor; iii) after the electrostatic latent image is patterned, cause the development member to rotate and the photoreceptor to move; iv) while the development member is rotating, receiving respective currents measured by the meter; and v) compute toner concentration using the respective received currents and the pixel data.