Developer material end of life sensing

An electrophotographic printing machine of the type having a developer roller transporting a developer material comprising at least carrier granules having toner particles adhering triboelectrically thereto closely adjacent to an electrostatic latent image recorded on a photoconductive surface so as to develop the latent image with toner particles, wherein the improvement includes:

• a member, positioned closely adjacent to the developer roller, adapted to attract at least a portion of the toner particles to at least one surface thereof;
• means for transmitting a beam of energy through said member onto the toner particles adhering to the surface thereof with the internal angle of incidence of the beam of energy being greater than the critical angle of incidence of said member;
• means for detecting the intensity of the beam of energy internally reflected through said member, said detecting means generating a signal indicative of the quantity of toner particles attracted to the surface of said member;
• and
• means for processing the signal received from said detecting means and transmitting a signal indicating the end of the useful life of the developer material.