A drop is ejected from an inkjet by building a pressure upstream of the aperture. The pressure is built by applying a voltage waveform to some type of driver. In this study, the maximum required voltage to operate an inkjet was reduced by building the required pressure over multiple oscillations of the driver, prior to actual drop ejection. Hypothetically, multiple prepulses could be used, limited by the total period between drops, to be fired by the printer. When a prepulse was timed such that the energy added constructively with the main, firing, pulse, the required voltage of the firing pulse was reduced. Conversely, if the energy added destructively, the required voltage increased. The amplitude of the prepulse was limited by the following constraints: (1) it could not force air to be ingested into the inkjet; (2) it could not add enough energy to eject a drop itself or push the meniscus over the edge of the nozzle. In a typical situation, the prepulse reduced the required driving voltage by more than 20%. This improvement can be used in a few ways: (1) The drive voltage can be reduced (as discussed); or (2) a smaller driver can be used for the same voltage, allowing tighter packing of jets; or (3) an inkjet can be driven at a frequency further from its resonant frequency, which should reduce sensitivity to manufacturing variations.
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