Xerographic Copying Apparatus

Claim 1

In a xerographic copying apparatus wherein a rotary drumshaped xerographic surface is arranged to carry electrostatic latent images along a predetermined path, a development unit for converting said latent images into powder image patterns, comprising a magazine for a supply of intermixed toner and carrier particles; and a conveyor arranged to withdraw intermixed particles from said supply and to cascade the thus witHdrawn particles over latent images in said path whereby the surplus of particles reenters said magazine and the particles become electrostatically charged as a result of triboelectrification during circulation in and back to said magazine, said conveyor including a series of discrete receptacles arranged to transport batches of intermixed particles from said magazine to a level above said supply and to dump the respective batches onto said xerographic surface upon reaching said level, said development unit having a plurality of particle-contacting surfaces including the particle-contacting surfaces of said magazine and said conveyor, said plurality of surfaces exhibiting neutral characteristics with respect to the overall triboelectric charge of said supply of particles and including a first group of surfaces which constitute the surfaces of said receptacles and move with said particles and a second group of surfaces, the particles which contact the surfaces of said first group being in motion relative to the surfaces of said second group, the surfaces of said first group consisting of insulating material and the surfaces of said second group consisting of currentconducting material and being connected to the ground, each of said receptacles consisting of current-conducting material having a coat of insulating material so that the surfaces of said second group are provided on said coats, said second group of surfaces comprising a first chute arranged to convey particles discharged by said conveyor into said path and a second chute for intercepting surplus particles in said path and for returning the intercepted particles into said magazine.