Abstract: A developing unit including a housing having an opening defining a developing zone, an applicator for applying particulate developer through the opening towards an electrostatographic image to be developed, and a paddle wheel for agitating developer within the housing, for scooping up developer from within the housing and projecting scooped-up developer towards the applicator. A hopper, located outside the width of the development zone supplies toner to the housing, and a primary spiral screw conveys developer from the hopper across the width of the development zone in one direction, while a secondary spiral screw receives developer from the primary spiral screw and conveys developer across the width of the development zone in an opposite direction. A passageway outside the width of the development zone enables the return of developer from the secondary spiral screw to the primary spiral screw.

Abstract: An electrostatographic printer for forming a toner image onto a receptor element comprises: (i) at least one toner image-producing electrostatographic station comprising rotatable endless surface means onto which a toner image can be formed, means for forming an electrostatic latent image on the endless surface means and a developing unit for depositing electrostatically charged toner particles onto the electrostatic latent image; (ii) means for conveying a receptor element past the image-producing station; and (iii) transfer means for transferring the toner image on the rotatable surface means onto the receptor element web. The printer is characterized in that the developing unit is selectively moveable between an operative position and a non-operative position while the endless surface means rotates. The printer avoids smudging on the first few prints produced by the printer.

Abstract: An electrostatographic single-pass multiple station (e.g. multi-colour) duplex printer is described for forming an image onto a web. The printer has at least three toner image-producing electrostatographic stations. Each station has a rotatable endless surface in the form of a photoconductive drum onto which a toner image can be formed. The printer also includes drive rollers for conveying the web in succession past the stations. Corona discharge devices transfer the toner image on each rotatable surface onto the web. The image-producing stations are arranged in two sub-groups, the drum of one sub-group forming a backing roller for the other sub-group, and vice-versa, thereby to enable simultaneous duplex printing.