Response of UFO (Upright Fruiting Offshoots) on Cherry Trees to Mechanical Harvest by Dynamic Vibratory Excitation

Abstract

<abstract><title><italic>Abstract.</italic></title> A series of mechanical harvest experiments was conducted in a high-density sweet cherry (Prunus avium L.) orchard to advance our knowledge of energy requirements and harvest efficiency. The primary goal of this research was to gain a better understanding of the dynamic response of fruiting wood to the forced vibrations and transmission patterns of vibratory energy on both the target and non-target trees. Experiments were conducted on UFO (upright fruiting offshoots) trees trained to an architecture consisting of unbranched upright offshoots. Field data collected from 31 tested trees revealed constant resonant frequencies within the upright offshoots at 8 to 10 Hz, which was attributed to the simple morphological structure. Single-impact excitation of the same peak force was also applied to the same offshoots. The resulting relative kinetic energy ratio (RKER) showed that resonant oscillation could obtain high amplification of vibratory energy, whereas the impact energy was attenuated. The supporting wire of the trellis system had little effect on the dynamic characteristics of tree limbs but could help in propagating vibratory energy within the tested tree and adjacent trees. In contrast, the foliage and fruits had a significant damping effect on both the dynamic response and vibratory energy transmission along limbs. The experimental assessment of mechanical harvest efficiency revealed a 77% fruit removal by vibratory force applied near the resonant frequency range of tested trees (between 12 and 16 Hz).