Ink ejection type writing unit

摘要

A writing unit for applying fluid droplets to a surface includes a chamber which is divided into an outer chamber portion and an inner chamber portion which are connected by a connecting channel. A discharge channel is connected to the outer chamber portion in alignment with the connecting channel. A piezoelectrical transducer is provided adjacent the inner chamber portion opposite to the outer chamber portion to produce short duration pressure increases to eject the liquid in the chamber from the discharge channel in pulsed jets to the surface. The inner and outer chamber portions are communicated to the atmosphere by respective vent passageways to withdraw the air in the chamber when the writing unit is first loaded with liquid and the bubbles introduced into the liquid in the chamber during normal operation. The vent passageways are closed during ink ejection process.