Dynamic responses of sweet cherry trees under vibratory excitations

Current mechanical harvesters for sweet cherry use either impact or vibration excitations to remove fruit. A comprehensive understanding of dynamic responses of cherry trees to vibratory excitation is therefore important for designing efficient mechanical harvest systems. This research quantified the distribution and dissipation of applied vibratory energy within the woody structure of cherry trees. Limb acceleration responses to either a band of sinusoidal excitations ranging from 2 to 40 Hz, or a series of impact excitations were monitored and analysed. The kinetic energy transmitted to all monitored locations was also compared between sinusoidal and impact excitations. The results indicate that all primary resonant frequencies could be detected within the prime branches of test trees. Branch waving displacement responses became larger as monitoring points were located further from the excitation point. Further, vibratory energy was amplified on branches with acute angles between the nodes caused by pruning, and on branches with few short lateral branches. This suggests that higher energy distribution along the branch, therefore higher harvest efficiency, could be obtained on such branches.