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Coffee harvesting with the aid of mechanical means becomes impracticable for the immense majority of coffee producers in the world, due fundamentally to that, in general, in the moment of the crop, the plants contain fruits in all their maturation status and have not been able to be developed machines that guarantee a selective detachment of the cherries during harvest operation. In a first study (Symposio do Café do Brasil. EMBRAPA), a modal analysis of coffee fruit-stem system was made. Starting from this analysis, the possibility of achieving the selective detachment of the fruits (removing of a high percent of mature fruits and low percent of immature ones) can be expected if the vibrating frequencies of the machines that use this work principle, are selected in the surrounding of a vibration mode "in contrafase" of the fruit-pedicelo-peduncle system. In this first study, an analysis of the first twelve vibration modes of different configurations of the fruit-pedicelo-peduncle system of coffee, was carried out. This study resulted enough for the analysis of configurations with one fruit for peduncle, but it was insufficient for an analysis of the behavior of configurations with two or three fruits for peduncle. In this paper an study of 25 vibration modes of fruit-pedicelo-peduncle system of coffee (coffea arabica) varieties "Red Caturra" and "Yellow Caturra" is presented. As a result of the study four variants of counter-phase vibrating mode of the fruit-pedicelo-peduncle system were founded, being able to recommend the more promissory mode for selective harvest of coffee. [ABSTRACT FROM AUTHOR]

Recent studies involving selective coffee harvesting by shaking, indicates the necessity to apply to fruit -- stem system significantly high excitement frequencies in comparison with those that are habitually applied at the international practice. To reach the predicted frequency levels, in the order of 150-200 Hz, by mechanical, hydraulic or pneumatic means, is very difficult due to the presence of friction couples in these types of mechanisms that would suffer premature waste by the relative high speeds. It's for this reason that the development of electromagnetic vibrators in which the inertial mass, when moving inside a magnetic field, avoid the direct friction among kinematical couples, is a current task. In this paper, the mathematical modeling of a vibratory system of two degrees of freedom is made, using the method of the mechanical impedance, in order to obtain the frequency response of the system, and to determine the design parameters of a shaking device able to achieve certain levels of amplitude of the vibrations at the high required frequencies. From the study also emanates the conclusion that in such shaking device, the natural frequencies of the vibratory system should be contained in the range of the exciting force frequencies. [ABSTRACT FROM AUTHOR]

Researches directed to increase the indicators of efficiency and quality during coffee harvest mechanization constitutes an important topic at present time. The determination of the physical-mechanical properties of fruits and fruit-stem system is an indispensable stage during these investigations. In this paper the results on the determination of a group of dimensional, inertial and elastic properties of the fruit-stem system of coffea arabica variety Catuai in different ripening stages, related with mechanical harvesting of this crop, are presented. Also, the bending moment required for the rupture of the fruit-stem union is determined. Methods of processing of digital images, as well as strain gages techniques were used during the investigation. As result of measurement of the different properties, substantial differences on dimensional, inertial and elastic characteristics of green and ripe fruit were found, like as in the bending moment required to fruit detachment and in the detachment patterns. [ABSTRACT FROM AUTHOR]