GUARD DROP TECHNIQUE FOR INK JET SYSTEMS

1,219,711. Printing. A. B. DICK CO. 27 Feb., 1969 [28 Feb., 1968], No. 10511/69. Heading B6F. In a printing system wherein ink drops in a stream are variably charged in dependence upon electrical video-representative signals and are subsequently deflected in an electric field by an amount depending on the charge on each drop and then caused to impinge on a printing medium, means are provided whereby each drop charged by a signal is preceded and followed by one or more drops to which no charge is applied. To this end a known ink-drop printing system, Fig. 1 (not shown), is provided with gate means in the connections between the source of video signals and a nozzle and charging tunnel producing and charging the drops, the gate being connected to a frequency divider connected to a source of synchronizing signals. If the frequency divider is a bi-stable circuit, the gate allows a video signal to pass upon the occurrence of every other drop, the intermediate drops not being charged. A frequency divider which divides by three produces two uncharged drops between two charged drops. The effects of repulsion between adjacent charged drops are thus avoided. The uncharged drops are caught by a trough (38, Fig. 1).