Harmonic Vibration Simulation for Selective Robusta Coffee Cherry Detachment

Selective vibratory harvesting of robusta coffee requires a quantitative basis for detaching ripe cherries while retaining less mature fruits on the branch. This study simulated simple harmonic vibration on fruit-bearing coffee branches to screen amplitude-frequency combinations for selective ripe-fruit detachment. Fruit removal force (FRF) and fresh fruit mass were measured for red, orange, and green cherries collected in Pakis Village, Sukorambi District, Jember, Indonesia. Mean FRF values were 3.532 N for red cherries, 5.966 N for orange cherries, and 8.034 N for green cherries, with mean masses of 2.990, 2.984, and 2.964 g, respectively. The model treated the fruit as a lumped mass undergoing an idealized local harmonic branch displacement; damping and frequency-dependent transmissibility were not explicitly modelled, and unit displacement transmission was used as the baseline assumption. Model consistency was assessed by comparing simulated peak dynamic force with the measured maturity-specific FRF thresholds. The model predicted candidate selective conditions at 2 mm-140 Hz, 3 mm-120 Hz, and 4 mm-100 Hz. At 3 mm-120 Hz, the predicted peak force was 5.080 N, which was 1.548 N above the red-fruit mean FRF and 0.886 N below the orange-fruit mean FRF. These combinations should be interpreted as preliminary simulation-based screening conditions rather than field-validated operating settings and require confirmation through direct branch-vibration and prototype harvesting tests.