## 3 Experimental Results and Discussion  
To investigate the EPU effects on printing quality, we used the printing parameters of jetting frequency of 500 Hz, target drop placement spacing of 50 \(\upmu\)m, and printing speed of 25 mm/s. To clearly  
Figure 10: Flow chart for printing CAD-based line printing using the EPU. Figure 9: Built-in CAD software that is used to implement the EPU function (Supplementary Video, Ref. [10]). understand the effect according to the printing methods, printed dots are intended to be separated as shown in Figure 11. Figure 11a shows the printed result using the conventional constant frequency jetting for comparison purpose. As shown in the figure, the drop spacing increased from zero to target values during the acceleration region. As a result, a large number of droplets are overlapped at the initial part of the pattern. However, in the case of using encoder sensors to generate jetting triggers, there are no significant overlaps at the starting part (Figure 11b,c), and dots are placed at equally spaced distance, irrespective of printing speed. Figure 11b shows the printed results of using automatic trigger generation, including the acceleration and deceleration parts. This shows that the droplet size is smaller in the initial part in which the printing speed is low and becomes larger in the printing direction, until it reaches the target printing speed. The droplet amount is related to the jet frequency, and it becomes larger as the jet frequency increases [6; 8]. Note that in the acceleration and deceleration part, the jetting frequency should be very low to print dots at each equally spaced distance when it is compared to the target printing speed part. On the other hand, Figure 11c shows that using the so-called dummy distance approach significantly improved the droplet size uniformity. Nonetheless, the first droplet is smaller than the rest of the droplets. This might be related to the equivalent DC voltage behavior due to high-frequency pulse voltage, which will be discussed in detail later. In the case of high jetting frequency of more than 1 kHz and printing speed of more than 30 mm/s, the printing behavior might be slightly different, as shown in Figure 12, which shows that uniform line width at the initial part can be achieved by using the high jetting frequency. Here, dummy length is used to exclude the acceleration and deceleration regions. From the printing results shown in Figure 12, there are two interesting behaviors in the printing using high-frequency jetting: (1) There is printing position shift from the target location, and (2) There is a prolonged tail at the end of the printing line. The position shift is also related to the printing speed and increases slightly according to the printing speed increase. Figure 11: Jetting behavior due to different printing modes (**a**) Printing using conventional constant frequency jetting; (**b**) printing using the EPU including acceleration and deceleration; (**c**) printing using the EPU excluding acceleration and deceleration by using the dummy part. In the case of high-frequency jetting at more than 1.5 kHz, the equivalent DC voltage effects dominate the pulse voltage effects. The equivalent DC voltage effect can be written as:  
\[V_{\alpha q}=V_{dc}+V_{p\_ave},\hskip 14.226378 ptV_{p\_ave}=\frac{\int_{0}^{T}V_{p}(t )dt}{T} \tag{1}\]  
in which \(V_{\alpha q}\), \(V_{dc}\), \(V_{p}\), and \(V_{p\_ave}\) and \(T\) are the equivalent DC voltage, DC background voltage, pulse voltage for jetting, average of pulse voltage, and time of interest, respectively. Here, \(V_{p\_ave}\) will increase as the jetting frequency increases. To illustrate the equivalent DC voltage effect, the typical effect of \(V_{\alpha q}\) was plotted as dotted overlaid line in Figure 13. The figure shows that the equivalent DC voltage may be smaller in the initial jetting, which might result in non-jetting condition or smaller droplet size in the case of the first few jetting triggers, as shown in Figure 11c.