Piezo Drop on Demand
Written October 16, 2019
With piezo DOD, a piezoelectric crystal undergoes distortion when an electric field is applied. This distortion creates a pressure pulse in the ink chamber within the print head, which in turn, causes an ink droplet to be ejected from the nozzle onto the substrate.
Piezo DOD technology to print on a wide range of substrates using aqueous and/or UV curable inks. The print heads of these printers contain a series of chambers that are filled with ink. By applying voltages to the walls of these chambers, a distortion is caused that bows the walls outwards. This distortion causes the ink pressure to drop, drawing more ink into the chamber. When the voltage is released and the walls return to their original positions, an ink droplet is expelled through each selected print nozzle.
Collectively these droplets create high-resolution text, bar codes, graphics and variable data onto a wide range of uncoated and coated media, plastic cards and label stocks.
Sequence of an Ink Jet Firing Cycle:
There are a squence of events that all happen within millionths of a second. Consider that the rate of drop ejection ranges anywhere between 8,000 to 100,000 cycles per second, for each nozzle in any given ink jet head.
Voltage is applied
A voltage is applied to piezoelectric element or "transducer". This causes the piezoelectric ceramic material to shorten which draws back the "piston" or "foot" at the firing chamber. Transducer movement is measured in millionths of an inch.
Piezo element contracts
This in turn, pulls ink into the chamber from the ink manifold through the restrictor. The properties of the ink are such that the surface tension at the orifices prevents air from being pulled into the chamber during this phase of the firing cycle.
The voltage is then released, the piezo transducer expands to its original length expelling ink out of the orifices of the chamber.
After the ink droplets leave the firing chamber, the fluid stabilizes and chamber readies for another firing cycle.