Charged drop generator with guard system

Claim 1

In apparatus for the precise placement of liquid drops on a receiving surface, said apparatus including an orifice plate with a plurality of equally sized orifices, means for supplying liquid to all of said orifices at the same pressure, means stimulating the resulting liquid filaments at a common frequency to produce parallel streams of equally spaced drops having the same size, individual charging electrodes located adjacent each of the liquid filaments at the point where drops separate from the filaments, controls for the individual electrodes providing for selective charging of individual drops, means providing a deflection field along the drop trajectories downstream of said charging electrodes, and a catcher arranged to collect drops moved from their normal trajectory by action of the deflection field; the improvement comprising interconnected grounded guard electrodes supported between each of said charging electrodes and the deflection field to isolate each fluid filament from the deflection field and avoid inducing charges on the drops except by said charging electrodes.