Optimization of vibration parameters for selective coffee fruit harvesting on the basis of branch energy transfer characteristics

To determine optimal vibration parameters for selective coffee harvesting, the vibration response and energy transfer of a coffee fruit–branch system were analyzed. A forced vibration model of the fruit–pedicel system was established to determine the critical acceleration for mature fruit detachment based on maturity-dependent connection forces. A rigid–flexible coupled dynamic model of the branch–vibrator system was developed by incorporating branch structure and mechanical properties. Single-factor simulations evaluated the effects of frequency, amplitude, and excitation position on kinetic energy transfer. The maximum kinetic energy increased from 0.162 to 0.987 J with increasing amplitude and reached 1.142 J at an excitation position of 47.98 mm. The 60–80 Hz frequency range provided high and controllable energy transfer while satisfying the critical acceleration required for ripe-fruit detachment. A test platform was then used to conduct a quadratic regression orthogonal rotational experiment, with the harvesting rates of ripe, semi-ripe, and unripe fruits as the response variables. Multi-objective optimization yielded optimal parameters of 75.75 Hz, 8.18 mm, and 109.54 mm for frequency, amplitude, and excitation position, respectively. Validation experiments conducted at 75 Hz, 8 mm, and 109 mm yielded harvesting rates of 94.62%, 8.84%, and 6.79% for ripe, semi-ripe, and unripe fruits, respectively, satisfying the predefined requirements. These results provide a theoretical basis for the design and parameter optimization of mechanized coffee harvesting equipment.