# Vibration from Electric Hand-Held Harvesters for Olives
## 3 Results
### Acceleration Components  
Figure 6 reports the fraction \(f_{wj}\) of the acceleration total value due to the \(j\)-axis component for each harvester head, defined as:  
\[f_{wj}=\frac{a_{hwj}}{a_{h_{w}}},\ (j=x,\ y,\ z-\text{axis}). \tag{5}\] \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Harvester** & \multicolumn{2}{c}{**Rod**} & \multicolumn{4}{c}{**Rod Angle**} & \multicolumn{2}{c}{**Measuring Point**} \\ \cline{2-9}
**Head** & **R4** & **R5** & **0\({}^{\circ}\)** & **45\({}^{\circ}\)** & **90\({}^{\circ}\)** & **Variable** & **M1** & **M2** \\ \hline H4 & 11.22 b  & 11.70 b  & 10.22 d  & 10.97 d  & 10.79 d  & 13.87 c  & 10.10 d  & 12.83 c  \\ H5 & 7.62 c  & 7.82 c  & 5.10 e  & 5.57 e  & 14.24 c  & 6.84 e  & 8.60 d  \\ H6 & 16.25 a  & 16.06 a  & 15.30 bc  & 16.12 ab  & 16.78 a  & 16.41 ab  & 15.20 b  & 17.11 a  \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Acceleration total values (m/s\({}^{2}\)) with harvester heads H4-H6 (mean separation by Kruskal–Wallis test for each interaction: means with the same letter are not statistically different at \(p\) = 0.05 level). Figure 6: Fraction of the acceleration total value due to the components for each axis as affected by harvester head, rod, and measuring point (symbols represent mean values). Considering the harvester heads H1-H3, Figure 6 shows that in the rear position (M1) the main acceleration component was always that along the \(x\)-axis, accounting for 81-92% of the acceleration total value at varying the rod. The lowest component was that along the \(y\)-axis for harvester heads H1 and H2 and that along the \(z\)-axis for harvester head H3. In the front position (M2) the lowest component was always that along the \(y\)-axis, whereas the main component was affected by the rod type. When the carbon fiber rod (R2) was used, the main acceleration component was again that along the \(x\)-axis (from 82 to 92%), whereas when the aluminum rods were used, the \(z\)-axis component was predominant for the harvester heads H1 and H2. When the harvester heads H4-H6 were used, the \(y\)-axis component was almost always predominant in both measuring points, accounting for 58-77% of the acceleration total value in the rear position and for 71-91% in the front position. Results on the acceleration components were strictly correlated with the harmonic content of the signals. As an example, Figure 7 shows the FFT spectra of the harvester heads H1-H3 applied to the rod R2 (carbon fiber) and H4-H6 applied to the rod R4 (telescopic, minimum length). To better analyze the results and highlight the main differences between and within the two groups of harvester heads, all FFT spectra were computed under idling conditions and in the most exposed measuring point (front position, M2). In addition, the frequency range in the plot was limited to 0-200 Hz, the effect of the higher frequencies being attenuated by the weighting curves stated by the EN ISO 5349-1:2001 regulation (Table 4). As it might be expected, the frequency of the first harmonic was around 18 Hz for all the harvester heads. In fact, all the machines were driven by the same engine model, the kinematics of the initial part of the motion transmission system was the same, as well as the reduction ratio. Comparing the acceleration values at the different frequencies, it is possible to point out that the arrangement of the arms carrying the sticks with respect to the transmission box had a significant effect on the results. In fact, with the harvesting heads H1 and H2, where the main arm oscillates orthogonally to the motor shaft, the highest acceleration values were recorded along \(x\)- and \(z\)-axes. Instead, in H3 the sticks oscillate around the motor shaft and this has resulted in an increase in acceleration values along the \(y\)-axis and in a decrease along the \(z\)-axis. In addition, the different disposition of the sticks in H2 with respect to H1 made the harmonics between 100 and 200 Hz of higher amplitude.