Serial dot printer for office machines.

摘要

Printing is effected on paper (82) passing over a platen (80) by applying high voltage pulses from a transformer (200) between electrically conductive ink (102) and a counter-electrode (89), so as to eject dots of ink through a nozzle (106). Each dot is created by a pulse of current I1 drawn from a storage capacitor (402) through the transformer primary (210) under control of a switching transistor (198) controlled in turn by pulses (TP). The pulses (TP) are provided by a monostable circuit (415) which has a time constant network (420, 421) energised by a potential divider (418,419) connected across the storage capacitor (402). The arrangement is such that, when the voltage across the capacitor (402) falls during rapidly repeated dot printing, the time constant of the monostable circuit (415) is increased and the total pulse energy supplied to the transformer (200) is maintained, thereby to maintain uniform dot density on the paper (82).