Mathematical Modeling of Fruit Removal Force for Optimizing Selectivity of Mechanical Harvesting of Coffee Cherry
Keywords:
fruit removal force, fruit detachment force, Coffea canephora, selective harvesting, mathematical modelling, mechanical harvestingAbstract
Robusta coffee harvesting requires selective detachment strategies because cherries on the same branch often occur at different ripening stages. This study developed a mathematical model of fruit removal force (FRF), also known as fruit detachment force (FDF), using observed Robusta coffee cherries from Pakis Village, Sukorambi, Jember. Five coffee plants were evaluated, and mean FRF and fruit mass were tabulated for red, orange, and green cherries. The empirical maturity-index model showed that FRF increased consistently from red cherries (3.532 N) to orange cherries (5.966 N) and green cherries (8.034 N). A quadratic maturity model, FRF = 0.732 + 2.983M - 0.183M2, achieved high goodness of fit (R2 = 0.9996; RMSE = 0.036 N), indicating that fruit color can serve as a practical predictor of detachment resistance. Dynamic simulation using F = m(2πf)2A suggested that, at 2.0 mm vibration amplitude, the critical frequency for red cherries was approximately 122.32 Hz, while orange and green cherries required 159.13 Hz and 185.28 Hz. The optimum selective harvesting window was therefore estimated at 3.6–5.8 N or approximately 122–150 Hz at 2.0 mm amplitude. The model provides a quantitative basis for setting vibration-based selective coffee harvesters.
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