Dynamic behavior of coffee fruit-stem system using modeling of flexible bodies

The objective was to analyze the dynamics of fruit-stem coffee system using flexible body modeling. A three-part model was defined: plagiotropic branch, stem and coffee fruit. The coffee stem was modeled as a flexible beam, discretized in four elements connected by torsional springs. The simulations were carried out to study the forces and torques in the connection between the coffee fruit and stem, the transmitted energy and the resultant force on the fruit. A sinusoidal displacement was applied at different vibration combinations of frequencies and amplitudes (13.33, 20.00 and 26.67 Hz combined with 5.00, 10.00 and 15.00 mm and 35, 45 and 55 Hz combined with 3.50, 5.00 and 6.50 mm). For validation, the coffee fruit-stem system displacement was monitored at the fruit free end, which was compared with the displacements obtained under laboratory conditions. The greatest difference in energy transmitted between maturation stages was observed at the frequency of 26.67 Hz associated with amplitudes of 10.00 and 15.00 mm, indicating a work range that could be favorable to the coffee fruits selective detaching. At high frequencies, the force and torque at the fruit-coffee stem linkage were smaller, evidencing the importance of the amplitude and the resonance bands to the detaching process efficiency.