The effect of shaking frequency on fruit motion patterns and damage rate during cherry detaching process

High rate of harvest-induced fruit damage is the key obstacle of applying mechanical harvesting technologies on sweet cherry production. This study focused on investigating the effect of shaking frequency on the fruit motion patterns (pendulum, tilting and twisting), fruit removal and damage rate. Field test was conducted with a mechanical shaking device and a high-speed camera was used to capture the fruit motions during fruit detaching process. A total of thirty randomly selected limbs were shaken under the frequencies of 10, 14 and 18 Hz until all targeted fruits were removed. The motion of these fruits was recorded using the high-speed camera at a rate of 700 fps (frames per second). The detaching duration, cycle number of the motion patterns and times of fruit-to-fruit and fruit-to-limb impacting of each target fruit was extracted from the acquired images. The damage of harvested fruit was analyzed and sorted into four predefined levels according to the size of damaged area. Results showed that the average cycle numbers of pendulum and tilting motion patterns were much larger than twisting pattern. Much shorter duration needed to remove all fruits under 18 Hz shaking than that at lower frequencies. However, higher shaking frequency also resulted in higher levels of fruit damage, even fewer times of impacting were observed from higher shaking frequency. This finding implied that the harvest-induced fruit damage was caused mainly by few times of instantaneous and high-intensity impacting rather than many-times of low-intensity impacting.