Evaluation of the transmissibility of vibration and dynamic behaviour of coffee plants under field conditions

Mechanical vibration-based harvesting can efficiently collect coffee fruits, but outcomes depend on machine type and plant factors. Therefore, it is crucial to determine the modal properties involved in this process. In this context, this study aimed to determine the dynamic behaviour of coffee plants through frequency scanning tests, considering different scenarios related to the plant and the ripening stages of the fruit. For this purpose, instrumentation was applied to fifteen plants chosen at random to collect field data for evaluating different scenarios. Through the induction of mechanical vibrations, it was possible to determine the vibration transmissibility in coffee plants, with 20 Hz induced frequency leading to greater transmissibility than the other induced frequencies. The dynamic behaviour of the coffee plants was evaluated using frequency sweep tests, which revealed a greater incidence of natural frequency peaks concentrated above 40 Hz. The analysis indicated that the selective harvesting of coffee fruits through the exclusive application of vibration is impractical in Arabica coffee plants. This is due to the absence of significant differences in the pending loads of fruits at different stages of maturation and the overlap in the frequency values identified in the investigated frequency bands.