Modelagem do sistema fruto-pedúnculo no processo de derriça de café

• Autor(a) principal: Villibor, Geice Paula
• Data de Publicação: 2012
• Tipo de documento: Tese
• Idioma: por
• Título da fonte: LOCUS Repositório Institucional da UFV
• Texto Completo: http://locus.ufv.br/handle/123456789/734
• topic: Colheita de café; processamento de imagens; vibração; Coffee harvest; Image processing; Vibration; CNPQ::CIENCIAS AGRARIAS::AGRONOMIA::FITOTECNIA::MECANIZACAO AGRICOLA

The coffee crop has significant importance in Brazilian agriculture; and Brazil is the world's largest producer. Among all the field operations involved, the harvest is one of the most complex and costly to realize. The mechanization of the harvest is essential for the maintenance and sustainability of the coffee activity, since the costs involved with manpower are reduced and the time spent for the operation is minimized. Moreover the use of mechanical harvesting can reduce loss of quality because the operation can be performed when the fruits reach the ripeness stage those results in the best quality. The experimental determination of mechanical properties of the coffee fruit-stem system together the mathematical modeling and simulation is important for the development and improvement of harvesting devices. Understanding the system response subjected to vibration, assists in defining parameters that allow the selective detachment of the coffee fruits. The selective detachment of the coffee fruits contributes positively to the quality of the final beverage. The objective of this study was to determine the modal parameters including damping, natural frequency and stiffness, and transmissibility of vibration properties of the coffee fruit-stem system through high-speed digital video. Additionally, by means of computer simulation, the dynamics of the fruit-stem system subjected to forced vibration was analyzed. The modal parameters were determined by the logarithmic decrement for the season of 2010 and 2011. The transmissibility of vibration between an electromagnetic shaker and the coffee fruit-stem system in the direction and transversely to the displacement input was studied in two different experiments. The first experiment was performed using vibration frequencies in the range of commercial harvest devices. Frequencies between 13.33 and 26.67 Hz and amplitude of 5 to 15 mm were used. The second experiment was performed using higher frequencies and small amplitudes of 35 to 55 Hz and 3.5 to 6.5 mm, respectively. The resulting displacement of the coffee fruit was obtained by means of high-speed digital video and techniques of image processing. It was used a background image to provide information necessary to obtain the displacements of the coffee fruit-stem system in metric coordinates. The displacements obtained from the vibration transmissibility tests were used to validate the simulations performed. For the 2010 harvesting season, for ripe and green fruits, respectively, the natural frequencies of coffee fruit-stem system were 15.74 and 13.97 Hz; the damping coefficient was 0.053 and 0.032 N s m-1 and the stiffness was 14.40 and 8.32 N m-1. For the 2011 harvesting season, the natural frequencies of coffee fruit-stem system were 11.62 and 13.29 Hz; the damping coefficient was 0.029 and 0.0253 N s m-1 and the stiffness was 8.61 and 7.09 N m-1. The highest transmissibility of vibration in the coffee fruit-stem system was observed for bands near the frequency of 20 Hz for both ripeness stages. By means of simulations, utilizing this frequency as input, the larger efforts resulting in coffee fruit-stem system, were estimated for both ripeness stages. It was possible to determine the displacements resulting from the coffee fruit-stem system by means of high speed videos submitted to harmonic excitation with appropriateness. The obtained result showed that the coffee harvesting selectivity, using the range of the first natural frequency, seems to be is a difficult task because the difference between the modal parameters, transmissibility and efforts for the green and red ripeness stages are small.