Optimization of a Citrus Canopy Shaker Harvesting System: Mechanistic Tree Damage and Fruit Detachment Models

Mechanization of fruit and nut harvesting is becoming increasingly important because of a significant rise in the cost of manual harvesting. This work proposes a progressive analytical approach for the design and optimization of a citrus canopy shaker harvesting machine. The approach was formulated using finite element (FE) methods to find the optimum design parameters of the machine. The design parameters were defined in terms of a configuration (or stiffness) of shaking rods and two operating parameters: shaking frequency and shaking amplitude. The formulated methodology consists of determining the properties of wood, statistical modeling of the tree limbs, developing mechanistic models, and performing optimization using FE simulations. The proposed methodology employs the response surface methodology or surrogate models to quantify the objective functions, and Pareto-optimal search techniques to find the optimum designs. Three sets of machine parameters were proposed in this study to minimize tree damage and maximize fruit removal. These optimal parameters were proposed based on the configuration and distribution of limbs and fruits in a medium-size citrus tree. The optimized tine configuration of the middle and bottom section of the canopy shaker consists of a solid rod made of polyamide reinforced with 50% long glass fibers and a hollow tube made of hardened steel in a 3:1 ratio by length. These tines, when vibrating at a high frequency of 7.8 Hz and low amplitude of 3.81 to 5.08 cm (1.5 to 2 in.) and a low frequency of 3 to 3.5Â Hz and high amplitude of 13.9 to 15.2 cm (5.5 to 6 in.), provide a 25% to 30% reduction in damage to the tree limbs in the bottom and middle zones of the tree. Similarly, changes to the top sections of the canopy shaker with another set of optimized tine configurations resulted in a 40% to 45% reduction in the damage to the limbs of the top section of the tree canopy. The optimized tine configuration, thus proposed for the top section of the canopy shaker, is made of a solid rod of polyamide reinforced with 60% long glass fibers and vibrates at a frequency of 6.5 to 7.5 Hz with an amplitude of 7.6 to 8.9 cm (3 to 3.5 in.).