Drop-on-Demand (DOD) print heads eject droplets through the air directly to a specified position on a media. Changes of shape and direction of the drops, which may also be followed by detached “satellite drops”, usually occur during the motion toward the target. The quality of printing depends on the velocity fluctuations and on the existence of secondary drops. A Laser Doppler Velocimetry technique was applied to analyze the performance of ink jet printing heads close to real operating conditions. The system can provide a statistical description, which includes distributions and average parameters of the main and lateral velocities of drops. In addition, the technique can also detect the time between appearances of ejected drops that can provide information about of satellite drops existence, and the drops' transit time in the measurement volume, which can be used as a rough estimate of the drop size. By using these parameters, it is possible to develop experimental techniques enabling the analysis of ink jet printing performance. The results reported here show the existence of more than one drop between ejection pulses. In addition to the main velocity, the lateral velocity distribution was measured. Multiple peak distributions were obtained, in some cases, for the velocity in both directions. Low ejection frequency has a higher tendency to produce multiple peak distributions. Optimal operating parameters could be extracted using the proposed experimental technique.
A. Blumberg, R. Semiat, "Velocity Measurements of Ink Drops Ejected from a Piezoelectric DOD Print Head—I. Technique Presentation" in Journal of Imaging Science and Technology, 2002, pp 171 - 181, https://doi.org/10.2352/J.ImagingSci.Technol.2002.46.2.art00013