MECHANICAL HARVESTING TECHNOLOGY RESEARCH FOR FRESH MARKET SWEET CHERRY
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As labor cost keeps rising and labor availability remains increasingly uncertain, growers are seeking for mechanical harvesting solutions for tree fruit production. The goal of this research was to develop suitable vibratory harvesting technologies for fresh market sweet cherry to achieve high harvest efficiency and low fruit damage. The major objectives were to investigate the effect of shaking frequency, duration and excitation position on fruit removal and damage. To fulfill the goal, different prototypes of vibratory harvesting system were fabricated. The resonant frequencies of cherry trees were identified through analyzing their dynamic response to vibratory excitation. Experiments also showed that the majority of vibratory energy was transmitted to the excitation limbs, which could benefit the fruit catching. To find out the suitable shaking frequency and duration to achieve high fruit removal efficiency, harvesting tests were conducted in field condition. It was found that different combination of shaking frequency and duration had a big influence on fruit removal efficiency. The maximum fruit removal efficiency of 81% was achieved at 18 Hz with a 5-s shaking duration in total shaking time of 20 s. Among the fruit remaining on trees, over 60% were growing on long and slender twigs, which suggest that a proper pruning could increase the fruit removal efficiency. Additionally, excitation at different positions of a limb also resulted in different fruit removal efficiencies, which varied between 51 and 83% when a limb was excited in one position. It is also estimated that up to 97% of fruit could be removed if limbs were excited at two locations. The damage rates of harvested fruit were approximately 10% higher than that of handpicked fruit, but the rate was not affected by excitation positions. The fruit trajectory and damage source under vibratory excitation at different shaking frequencies were analyzed using high-speed camera images. It is found that detaching time of each fruit was closely related to its average kinetic energy, which resulted in higher harvesting efficiency at higher shaking frequency. Test results revealed that high fruit damage level at high shaking frequency was mainly caused by repeated high-intensity impacts on limbs.