## 4 Results and Analysis  
### Average Weight  
The dispenser jets 100 times for each run, and the weight of a single jetted dot is measured each time. The measured results are shown in Figure 5. Subsequently, the average weight and standard deviation of the results for each run are calculated and summarized in Table 6. The average weight of a single jetted dot ranges widely from 0.337 g (0.001 standard deviation, 5 th run) to 0.477 g (0.002 standard deviation, 12 th run) with respect to the operating parameter set. The measured results are analyzed by using a commercial statistical software package, Minitab (trial version 17 Minitab Inc., State College, PA, USA), and the level of significance is set to 0.1 (10%). The main effects and the interaction effects plots for the average weight of a single jetted dot are depicted in Figures 6 and 7, respectively. For the main effects plot, the parameters with a steep slope display a significant effect and the parameters with a gentle slope display a small effect on the average weight of a single jetted dot. As shown in Figure 6, the needle stroke (A) and open time (B) are evidently associated with a high effect on the average weight of a single jetted dot, and the rising time (C) and cooling pressure (D) exhibit a low effect on the average weight of a single jetted dot. The average weight of a single jetted dot decreases with decreases in the needle stroke and open time. \begin{table}
\begin{tabular}{c c c} \hline
**Run** & **Average (mg)** & **Standard Deviation** \\ \hline
1 & 0.344 & 0.005 \\
2 & 0.348 & 0.001 \\
3 & 0.416 & 0.012 \\
4 & 0.412 & 0.013 \\
5 & 0.337 & 0.001 \\
6 & 0.343 & 0.001 \\
7 & 0.400 & 0.013 \\
8 & 0.407 & 0.014 \\
9 & 0.367 & 0.014 \\
10 & 0.377 & 0.001 \\
11 & 0.471 & 0.003 \\
12 & 0.477 & 0.002 \\
13 & 0.388 & 0.001 \\
14 & 0.391 & 0.001 \\
15 & 0.469 & 0.002 \\
16 & 0.476 & 0.002 \\ \hline \end{tabular}
\end{table} 
Table 6: Average weight and standard deviation of the experimental results. Figure 5: Measured weight of a single dispensed dot. With respect to the interaction effects plot, the two parameters exhibit a high interaction effect when the two lines cross each other, whereas the parameters do not display any interaction effect when the two lines are parallel. The six interaction effects for the four parameters, AB, AC, AD, BC, BD, and CD, are plotted in Figure 7. As shown in Figure 7, the parameters exhibit small interaction effects on the average weight of a single jetted dot. The Pareto chart clearly explains the effectiveness of each parameter and is shown in Figure 8. It is noted here that any parameter with a bar that extends beyond the vertical red line (significant reference line) is potentially important. With the Minitab Software, the reference line for statistical significance is determined on the basis of the significance level and the [PERSON]'s method [21]. As shown in Figure 8, open time and needle stroke are the main parameters associated with a significant effect, and the rising time is also a main parameter with a low effect. The interactions stroke-open time, stroke-cooling pressure, and open time-cooling pressure are meaningful parameters, although their effect is very low for the average weight of a single jetted dot. The effects and estimated coefficients for the average weight of a single jetted dot are listed in Table 7. The \(p\)-value for each term is tested considering the null hypothesis in which the coefficient is equal to zero (no effect). A low \(p\)-value (less than 0.1 in this work) indicates that the null hypothesis can be rejected. In other words, a predictor that has a low \(p\)-value is likely to be a meaningful addition to the regression model because the changes in the predictor's value are related to the changes of the response variable. Conversely, a larger \(p\)-value (higher than 0.1 in this work) suggests that the changes in the predictor are not associated with the changes of the response [21].