Piston-driven Inkjets

One reason why inkjet printers have become so inexpensive and their quality of printing so good is due to the research and development activities of competing manufacturers. The size of inkjets is typically in the range of 10 to 60 microns (a human hair is about 100 microns for comparison) and is so small that making experimental observations and measurements is difficult. For this reason, most research has included extensive computational modeling of print heads to provide guidance in how and where design improvements can be made. Simulations allow a researcher to study how the shape of ejected droplets is affected by parameters such as the driving pressure pulse, the shape of the nozzle, surface tension coefficient, and much more.

The example above shows the formation of a droplet from a nozzle that is driven by a moving piston. In this case the speed and displacement of the piston must be carefully selected to produce the proper amount of ink ejected and pinched off, while at the same time leaving a minimum disturbance in the ink remaining in the nozzle so that it can be quickly replaced by more ink from a reservoir. Usually, the replacement is by the action of surface tension pulling the ink up to the exit of the nozzle where it will be ready for the next pulse of the piston.