## 3 Experimental Results and Discussion
\begin{table}
\begin{tabular}{l r} \hline \hline
**Characteristics** & **Value** \\ \hline Mean & \(-0.0281\) \\ Standard Error & \(0.0048\) \\ Median & \(-0.0317\) \\ Mode & \(0.0078\) \\ Standard Deviation & \(0.0713\) \\ Sample Variance & \(0.0051\) \\ Kurtosis & \(1.2310\) \\ Skewness & \(-0.3348\) \\ Range & \(0.5093\) \\ Minimum & \(-0.3603\) \\ Maximum & \(0.1489\) \\ Sum & \(-6.1856\) \\ Count & 220 \\ Largest (1) & \(0.1489\) \\ Smallest (1) & \(-0.3603\) \\ \hline \hline \end{tabular}
\end{table} 
Table 8: Statistical characteristics of the vibration signal of acceleration. The second constructed control charts according to (8)-(10) was the \(\bar{x}\)- diagram for the arithmetic mean. The value of the coefficient \(A_{2}=0.577\) was obtained from Table 5 of the STN ISO 8252 standard for \(n=5\). measurements, depending on the range of subgroups. The values of the central line of the control limits for the revolutions of the \(\bar{x}\)-control diagram are CL = 744, UCL = 819 and LCL = 668 (see Figure 10b). The \(\bar{x}\)-diagram shows that the sample arithmetic means are not outside the regulatory limits. However, it should be noted that the course of the control chart shows a periodic dependence of the evaluated technological parameter. Non-random causes of variability also influence the technological process. Nevertheless, the process is under statistical control. Subsequently, the control chart for the standard deviation \(s\) and the median \(\overline{x}\) were constructed. The values of coefficient \(B_{3}=0\), \(B_{4}=2.089\), and \(A_{4}=0.69\) for \(s\) and \(\overline{x}\)-diagram was obtained from the tables for  
Figure 10: Control charts for the technological parameter of revolutions: (**a**) diagram of variation range, (**b**) diagram of arithmetic mean, (**c**) diagram of standard deviation, (**d**) diagram of the median. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline  & \multicolumn{6}{c}{**Revolutions n (rpm)**} \\ \hline
**Process Quality Criteria** & \(R\) & \(\bar{x}\) & \(s\) & \(\overline{x}\) & \(\hat{R}_{\text{MR}}\) & \(X\) & \(\hat{X}_{MA}\) \\ \hline CL & 131 & 744 & 53 & 744 & 98 & 744 & 744 \\ UCL & 277 & 819 & 111 & 830 & 206 & 870 & 800 \\ LCL & 0 & 668 & 0 & 658 & 0 & 617 & 687 \\ \hline \hline \end{tabular}
\end{table} 
Table 9: Values of the center line and control limits for the revolutions. \(n=5\) measurements. The centerline and control limits for the \(s\)-diagram were calculated according to Equations (15)-(17). It applies in CL = 53, UCL = 111, and LCL = 0 (see Figure 10c). The centerline and control limits for the \(\overline{x}\)-control diagram were calculated according to Equations (19)-(21). The values are as follows CL = 744, UCL = 830 and LCL = 658 (see Figure 10d). There are several values in the chart close to the lower/upper control limit, so it would be appropriate to focus on this subgroup's values and determine the cause of such great variability. The technological process is based on \(s\), \(\overline{x}\) charts under statistical control. However, the property of the periodicity parameter reappears. Subsequently, control charts were constructed for the moving range \(\bar{R}_{MR}\), individual values \(X\), and moving averages \(\bar{X}_{MA}\) if the basic values are not determined (see Figure 11). Values of coefficients \(D_{3}=0\), \(D_{4}=3.267\) were obtained from (Table 5) for \(n=2\). The value of the central line and the control limits of the moving range \(\bar{R}_{MR}\) for revolutions are CL = 98, UCL = 206, LCL = 0 (see Figure 11a), for individual values \(X\), i.e., CL = 744, UCL = 870, LCL = 617 (see Figure 11b), and moving averages \(\bar{X}_{MA}\), i.e., CL = 744, UCL = 800, LCL = 687 (see Figure 11c). It is clear from the control charts that not all calculated points lie within the control limits. This was fundamentally reflected in the moving average diagram \(\bar{X}_{MA}\) (see Figure 11c). Several values are outside the range of the upper and lower control limits (see Table 9).