Determining Adequate Vibration Frequency, Amplitude, and Time for Mechanical Harvesting of Fresh Mandarins

Abstract

Mechanical citrus harvesting systems in Spain can solve the problem of the high costs of manual harvesting. Previous results, without the use of abscission agents, have shown the effectiveness of trunk and limb shakers for mechanical citrus harvesting. It is crucial to define the adequate vibration time to achieve an acceptable removal percentage because a higher vibration time could render the operation economically unviable. To address mechanical citrus harvesting, it is also necessary to determine the vibration conditions (amplitude, frequency, and duration) to ensure maximum removal efficiency. The objective of this research is to determine the optimal combination of vibration frequency, amplitude, and duration that will ensure maximum removal efficiency in mechanical citrus harvesting. Marisol and Orogrande mandarin trees were tested and harvested with a commercial trunk shaker. The Marisol trees were shaken at a vibration of 15 Hz for 5 s with a 0.030 m displacement. The Orogrande trees were shaken at 15 and 20 Hz frequencies with two shakes, the first lasting 5 s and the second lasting 2 s, 3 to 4 s after the first shake, with a 0.030 m displacement. Due to the low trunk height of orchard trees in the Valencia region, it is impossible to study intermediate and high amplitudes with a commercial olive trunk shaker. To solve this limitation, a laboratory unidirectional vibratory device was used to shake the branches at a vibration frequency of 4.6 to 18.1 Hz and a vibration amplitude modified from 0.06 to 0.18m. The field and laboratory results show that the mechanical citrus removal percentage exhibits a logarithmic behavior with time. The laboratory test shows that high-amplitude and intermediate vibration frequencies in the branches achieve adequate removal percentages. Lengthening the shaking time and repeating the shaking process do not increase the removal efficiency. In the field test, almost all the detached fruit fell in the first 2 to 3 s of shaking. It was evident that two shakes were not necessary to obtain an acceptable removal percentage. The results found in the laboratory indicate the possibility of reducing the frequencies and increasing the amplitudes to achieve an optimal mechanical citrus harvest. In the fresh market for citrus from the Mediterranean region, with very low citrus trunk heights, mechanical harvesting equipment can be adapted to achieve high vibration amplitude and intermediate vibration frequencies in the branches.