## 4 Conclusions  
This work performed vibration analysis on coffee fruits (_Coffee arabica var_. [PERSON]). Vibrational signals were characterized by applying linear chirp excitation frequency and evaluating the response velocity measurements attained from a laser vibrometer. Two frequency intervals (10-100 Hz and 100-1000 Hz) were studied in three tested ripening stages. Initially, the ripening stages were classified according to a strategy based on measurements of CIELab color. Subsequently, the harmonic response of the fruits was analyzed by studying the application of time-frequency and CWT (bump wavelet) analysis. The signals analyzed were acquired in pursuance to detect the dynamic characteristics of the fruit-peduncle system. Using the traditional fast Fourier approach over the velocity measurements, it was possible to identify the mechanical resonances of each ripening stage. It was evidenced that between 10 and 100 Hz, resonances are more influenced by the lower stiffness (in the pedicel). For that reason, the unripe fruits start to resonate earlier and are more intense than the other rippeing stages. However, between 100 and 1000 Hz, the frequency of peaks was more influenced by the elasticity of the fruit since rip fruits resonate first and more than the others. In evaluating scaled mechanical impedance, we observed a range of frequency between 24 and 40 Hz that confirms the data determined in the velocity spectra. In this range of frequency, a positive indicator for selective harvesting  
Figure 10: Scalograms wavelet analysis for group 1 between 10 and 100 Hz measured in URI, SMR1, and RP1. (**a**) Analysis for P1. (**b**) Analysis for P2. means that the resonances were excited for semi-ripe and ripe fruits but not for the unripe ones. Therefore, according to measurements, we conclude that the differences among ripening stages are more visible in the frequency spectrum established for 10-100 Hz. Summarizing, we obtained in this interval the following values for both measuring points from velocity measurements: for P1, unripe 23.68 \(\pm\) 0.48 Hz, semi-ripe 33.94 \(\pm\) 7.50 Hz, and ripe 38.36 \(\pm\) 3.01; and for P2, unripe 25.66 \(\pm\) 0.30 Hz, semi-ripe 31.31 \(\pm\) 7.50 Hz, and ripe 43.88 \(\pm\) 1.50. The spectral characterization of the time-domain velocity measurements was achieved by decomposing the measured signals along the resulting amplitude scale by the function of the bump wavelet. The feature of impulsive signals was reflected in the computed scalograms taking advantage of the gradient information of the CWT as shown by the scale-space domain. The power of the solution scalograms permitted comprehending the shifts in the energy level of the vibrations for each ripening stage. The RP fruit exhibited a higher magnitude in the scalograms followed by the SMR and ended with the UR. This behavior was more clearly evidenced for the measured point P1. The average energy of the resolution window does not permit evidence of energy concentration at the geometrical center of the graph, which is logical due to the amplification of vibrational velocity varying from UR to RP. However, for the signals from 100 to 1000 Hz, it was not possible to obtain scalograms with a good resolution because the frequency concentration was lower than between 10 and 100 Hz. Then, the wider the resolution, the lower the frequency concentration that was presented. This study advances the condition monitoring of organic structures. It can be a helpful tool to understand the dynamic behavior of coffee fruits and fruits with other topologies that could be explored. Excitation frequencies between 24 and 45 Hz and close to 700 Hz could be assessed to develop vibration-based equipment for selective coffee fruit harvesting. Fatigue analysis could be proposed to evaluate the most effective frequency to detach the ripe fruits from the perspective of a real application in a selective coffee-harvesting scenario. However, experiments with more samples should be performed to evaluate deviations in the dynamic behavior of the fruits.