One of the most important design parameters for the inkjet printing device is the inkjet drop velocity, which changes along the falling path from the ejection out of a nozzle to the impact on a substrate. Therefore, in this study, the droplet velocity of the piezoelectric drop-on-demand inkjet was measured. The nozzle diameter was 70 µm and polyethylene glycol aqueous solution was used as ink. The inkjet droplets were generated within a range from 500 to 10000 Hz of frequencies at a reference piezoelectric input voltage. The successive inkjet droplets were captured by the high-speed camera with 100000 fps, then the inkjet droplet velocities were analyzed visually at each falling location. The velocity change of a drop up to its terminal velocity was calculated theoretically to be compared with the experimental results. This study found that the velocity of the continuously ejected droplets depended on the interval of the droplets, as well as the density and diameter of the droplet which are essential factors of the general velocity change of a falling drop. The inkjet droplets with the long interval can be considered as an independent droplet so that it can follow the terminal velocity curve of the general drop. However, the inkjet droplets with short interval have the higher velocity than the general terminal velocity curve. It is considered that each droplet gets into the wake field of the former droplet so that its drag force can decrease and the velocity can increase.

喷墨打印设备最重要的设计参数之一是喷墨墨滴速度，它沿着从喷嘴喷出到对基板的撞击的下降路径变化。因此，在这项研究中，测量了压电按需喷墨的液滴速度。喷嘴直径为70μm，将聚乙二醇水溶液用作墨。喷墨液滴是在参考压电输入电压下在500到10000 Hz的频率范围内生成的。连续的喷墨液滴被高速相机以100000 fps的速度捕获，然后在每个下落位置直观地分析喷墨液滴的速度。从理论上计算出液滴达到其最终速度的速度变化，并与实验结果进行比较。这项研究发现，连续喷射的液滴的速度取决于液滴的间隔以及液滴的密度和直径，而液滴的密度和直径是下降液滴总体速度变化的重要因素。具有较长间隔的喷墨墨滴可以被视为独立墨滴，因此它可以遵循普通墨滴的最终速度曲线。然而，具有短间隔的喷墨液滴具有比一般终端速度曲线更高的速度。认为每个液滴都进入前一个液滴的尾流场，因此其阻力可以减小，速度可以增大。液滴的密度和直径是下降液滴总体速度变化的重要因素。具有较长间隔的喷墨墨滴可以被视为独立墨滴，因此它可以遵循普通墨滴的最终速度曲线。然而，具有短间隔的喷墨液滴具有比一般终端速度曲线更高的速度。认为每个液滴都进入前一个液滴的尾流场，因此其阻力可以减小，速度可以增大。液滴的密度和直径是下降液滴总体速度变化的重要因素。具有较长间隔的喷墨墨滴可以被视为独立墨滴，因此它可以遵循普通墨滴的最终速度曲线。然而，具有短间隔的喷墨液滴具有比一般终端速度曲线更高的速度。认为每个液滴都进入前一个液滴的尾流场，因此其阻力可以减小，速度可以增大。