Efeito da frequência e amplitude de vibração sobre a derriça de frutos de café

Abstract

RESUMOParâmetros de qualidade podem alterar significativamente o preço do café; entretanto, a colheita seletiva dos frutos é frequentemente associada à boa qualidade do produto, procedimento que pode ser realizado por meio de vibrações mecânicas. Desta forma, o estudo e a avaliação do efeito localizado de fatores como frequência, amplitude e grau de maturação dos frutos, são fundamentais para construção de máquinas adequadas a este tipo de prática. O trabalho foi desenvolvido com o objetivo de se avaliar os fatores frequência, amplitude, grau de maturação, direção de excitação e número de frutos por pedúnculo, na eficiência de derriça. Para a realização dos ensaios de vibração em laboratório utilizou-se uma máquina vibradora eletromagnética. Amplitudes na faixa de 3,75 a 7,50 mm e frequências na faixa de 13,33 a 26,67 Hz foram testadas para a variedade Mundo Novo, em que os resultados mostraram que a frequência de 26,67 Hz apresentou uma eficiência maior de derriça para os frutos cereja e a amplitude de 7,5 mm indicou maior eficiência de derriça. Verificou-se, também, que o número de frutos por pedúnculo influencia a eficiência de derriça dos frutos de café da variedade Mundo Novo. Palavras-chave: vibrações mecânicas, mecanização, colheita, grau de maturaçãoFrequency and amplitude of vibration on coffee harvesting ABSTRACT Quality parameters influence directly the coffee price. However, selective coffee harvesting is frequently associated to good quality of this product. This procedure can be performed by mechanical vibration. Therefore, the study of the frequency and amplitude parameters is important for the design of a specific harvesting machine. The objective of this work was to evaluate the effect of the frequency and amplitude of vibration, the coffee variety and the ripeness condition of the fruits upon the harvesting efficiency. The vibration tests were done in laboratory using an electromagnetic shaker. The tests were done using amplitudes in the range of 3.75 to 7.50 mm and frequencies in the range of 13.33 to 16.67 Hz. Branches of coffee plants of Mundo Novo variety were tested. The highest harvesting efficiency was obtained when using the 26.67 Hz frequency of vibration. The highest harvesting efficiency was obtained when an amplitude of 7.5 mm was used. It was also observed that the number of fruits per stem influences the harvesting efficiency of the coffee fruits of the Mundo Novo variety.

Detachment efficiency of fruits from coffee plants subjected to mechanical vibrations

“…Detachment efficiency increased with increasing vibration frequency and amplitude (Figure 2), corroborating the results found in similar researches (Ciro 2001, Souza 2004, Oliveira 2009, Santos et al 2010aand 2010b, Guedes 2011.…”

“…The significant interaction between frequency and amplitude, also found by Santos et al (2010a and2010b) and Guedes (2011), indicates the importance of choosing the right combination for these factors on harvesting. On the other hand, the significant interaction between amplitude and ripening stage points to the possibility of a selective harvesting through the appropriate selection of vibration amplitude and frequency (Santos 2008).…”

“…Thus, a single pass harvesting using such frequencies and amplitudes is not viable. On the other hand, Santos et al (2010a) …”

“…By assessing the detachment efficiency of coffee fruits, Santos et al (2010a) tested three branch lengths (5.0 mm, 10.0 mm and 15.0 mm) (Catuaí and Mundo Novo varieties) subjected to mechanical vibration. Branches were subjected to vibrations with different frequencies (13.33 Hz,16.67 Hz,20.00 Hz, 23.33 Hz and 26.67 Hz) and amplitudes (3.75 mm, 5.00 mm, 6.25 mm and 7.50 mm), in two different directions (longitudinal and transversal).…”

“…Even though the effects of vibration parameters on harvesting efficiency of coffee fruits have been investigated by several authors (Ciro 2001, Santos et al 2010aand 2010b, Guedes 2011, there is no record in the literature on the effects of vibration time in the detachment efficiency for coffee harvested by mechanical vibrations.…”