Toner projection printer with means to reduce toner spreading

摘要

A toner projection printer is provided with a developer surface which manifests a developer bias, and includes a cloud of entrained toner particles. A platen structure is positioned opposed to the developer surface and manifests a platen voltage that is attractive to the toner particles. An address plate is positioned between the developer surface and the platen structure. The address plate includes a determined thickness insulator with through pixel apertures. Each pixel aperture has at least first and second conductors that are electrically insulated from each other by the insulator, and a screen electrode for distorting the electric field between the address plate and the platen structure in a manner to reduce toner spreading. A first drive circuit is coupled to the first conductor for controllably applying a row drive voltage which is either a reference potential that exerts a repulsive force on the toner particles or a high voltage which is attractive to the toner particles. A second drive circuit is coupled to the second conductor for controllably applying a column voltage drive that is either a reference voltage (repulsive to the toner particles) or a high voltage (attractive to the toner particles). Both the column and row drive voltages are set at levels so that only when both are high can toner particles pass through the pixel aperture, be drawn towards the conductive platen and come under influence of the platen voltage. Control circuitry operates the first and second driver circuits to enable deposition of row and column dots of toner on a media sheet positioned on the platen, under influence of the platen potential. An improved platen structure is also shown which further reduces toner spreading.