# Evaluation of the Acceleration Vibration Signal for Aggregates of the Horizontal Drilling Stand
## 4 Experimental Results and Analysis
### Vibration Signal Processing in the Time Domain
The lowest statistical values are reached by mode VI, i.e., pump and hydro-generator \(x_{p}(t)=1.542\), \(x_{pp}(t)=3.622\), \(\text{RMS}=0.904\). It is clear from the time waveforms that the units in mode VI, i.e., the pump and the hydro-generator, are non-harmonic periodic signals, quasi-periodic with a stochastic component (see Figure 6e). It confirms the time waveform of the auto-correlation function (see Figure 6f). On the contrary, the signal waveforms of modes IV. and V. are strongly stochastic. The strong source of acceleration vibration is the motor unit. Regimes IV. and V. were successful. In a broader context, they have similar auto-correlation (see Figure 6b,d) and time waveforms (see Figure 6a,c). Figure 6: Time waveforms of the measured signals during the operation of the pair of aggregates in the operating modes IV.–VI. (**(a)** motor and pump vibration signal time waveform, **(b)** motor and pump auto-correlation function, **(c)** motor and hydro-generator vibration signal time waveform, **(d)** motor and hydro-generator vibration auto-correlation function, **(e)** pump and hydro-generator vibration signal time waveform, **(f)** autocorrelation function of pump and hydro-generator). Operating modes VII.-IX. compared to other regimes (see Figure 7), i.e., I.-VI., have significantly higher values of statistical characteristics (see Table 1). The reason is that all three aggregates are active during operating modes. In working mode VIII. a drill bit was installed on the spindle as part of the research and subsequent evaluation of the vibration signal (see Figure 7c,d). The proposed working mode VII. is without a drill bit on the spindle (see Figure 7a,b). In the last investigated regime IX., is a direct interaction of the drill bit with the andesite rock to disintegrate it (see Figure 7e,f). The revolutions and pressure force mode parameters were set to n = 1000 rpm and F = 8000 N. For this mode, the observed values of the vibration signal are clearly the highest, i.e., \(x_{p}(t)\) = 76.205, \(x_{pp}(t)\) = 160.711, and RMS = 21.978. The time waveforms of the signals are stochastic and stationary. It is clear  
Figure 7: Time waveforms of the measured signals during the operation of the pair of aggregates in the operating modes VII.–IX. ((**a**) time waveform of the signal of three aggregates without a drill bit, (**b**) auto-correlation function of three aggregates without a drill bit, (**c**) time waveform of the signal of three aggregates with a drill bit, (**d**) auto-correlation function of three aggregates with a drill bit, (**e**) time waveform of the andesite rock disintegrating signal, (**f**) auto-correlation function of the andesite rock disintegrating signal). from the time waveform of the autocorrelation function that the investigated processed signal also has periodic components. Figure 8a shows a histogram with a normal Gaussian distribution. It characterizes the operating modes in which the main vibration generator is the motor (i.e., modes I., IV., V., and VII.-IX.). For modes without motor operation (i.e., II., III., and VI.). The characteristic histogram in the figure is Figure 8b. It can be classified as a two-vertex histogram or a histogram with a non-Gaussian distribution. It indicates a superposition and a significant change in the position of the measured signals [57,58]. In the working modes I.-IV.-V. and VII.-VIII.-IX., the measured vibration signal of motor acceleration have higher statistics parameters; the highest contains IX. mode. When the drill bit was placed on the spindle, the values decreased. It suggests that the drill bit has a partially stabilizing character on the drilling stand. The complex classification of processed vibration signals in the time domain is complex. Acceleration vibration signals in operating modes I.-IV.-V. and VII.-VIII.-IX. are stochastic and stationary but have overlapping periodic and quasi-periodic components. The least significant statistical component appears to be the mean value of the signals.