## 3 Experimental Results and Discussion
It is possible to read the strong periodicity of the parameter from the control charts, and therefore the variability of the process is not under statistical control. It is, therefore, necessary to look for the cause of the instability of the analyzed parameter. Similarly, the second technological parameter, i.e., the pressure force, was analyzed. Control charts were constructed and subsequently analyzed (see Figure 12). The values for the \(R\)-control chart are CL = 988, UCL = 2087, LCL = 0. One subgroup is outside the upper limit, and there are several cases of non-random groupings (see Figure 12a). It was stated that the technological parameter pressure force is not under statistical control. The following charts also confirm the judgment. The values for the \(\bar{x}\)-control chart are CL = 7537, UCL = 8107, LCL = 6968 (see Figure 12b). Two subgroups are outside the upper limit, but several subgroups create a decreasing and increasing time trend. It is indicated that the parameter is not under statistical control. A similar partial conclusion can be drawn from the \(s\) and \(\overline{x}\)-control charts. The values for the \(s\)-control chart are CL = 399, UCL = 833, LCL = 0 (Figure 12c) and for \(\overline{x}\)-control chart are CL = 7588, UCL = 8260,  
Figure 11: Control charts for the technological parameter of revolutions (**a**) diagram of moving range, (**b**) diagram of individual values, (**c**) diagram of moving averages. LCL = 6915 (see Figure 12d). The technological parameter shows strong variability; it is necessary to look for its cause. The following values were obtained from the control charts for the moving range \(\bar{R}_{MR}\), individual values \(X\)., moving averages \(\bar{X}_{MA}\): the value of the center line and the control limits of the sliding range for the pressure are CL = 411, UCL = 870, LCL = 0 (see Figure 13a); for individual values they are CL = 7547, UCL = 8078, LCL = 7015 (see Figure 13b) and for moving averages they are CL = 7546, UCL = 7784, LCL = 7309 (see Figure 13c). Figure 12: Control charts for technological parameter pressure force (**a**) diagram of variation range, (**b**) diagram of arithmetic mean, (**c**) diagram of standard deviation, (**d**) diagram of the median. Figure 13: Control charts for technological parameter pressure force (**a**) diagram of moving range, (**b**) diagram of individual values, (**c**) diagram of moving averages. The values of pressure force that exceeded the control limits are in Table 10. It is clear from the charts that the process is not stable/not statistically mastered. The charts for individual values and moving averages show many samples outside the defined limits. It was stated that it is necessary to urgently find the causes of instability of the input technological parameter, i.e., the pressure force. After analyzing the process input parameters, the control charts of the output parameter vibration signal of acceleration were presented. The resulting control charts are shown in Figure 14.  
The values for \(R\)-control chart are CL = 0.161, UCL = 0.342, and LCL = 0. One subgroup is outside the upper limit, and there are several cases of non-random groupings (see Figure 14a). It was stated that the technological parameter vibration signal of acceleration is not under statistical control. There are several cases of non-random groupings of subgroups. The following charts confirm this. The values for \(\bar{x}\)-control chart are CL = 0.033, UCL = 0.342, and LCL = 0.126 (see Figure 14b). The subgroups are not outside the upper limit or the lower limit. This suggests that the parameter is under statistical control, but it is only a partial conclusion of one control diagram. A similar partial conclusion can be stated from the \(s\) and \(\overline{x}\) control charts.