<b>Determination of modal properties of the coffee fruit-stem system using high speed digital video and digital image processing

Abstract

ABSTRACT. Detachment of coffee fruit is usually accomplished by means of mechanical impacts and vibrations applied to the plant. Modal properties of the coffee fruit-stem system represent important information for efficient and selective harvesting. This study aimed to determine the modal parameters of the coffee fruit-stem system, such as natural frequency and damping coefficient, using high speed digital videos. With image processing techniques, it was obtained the resulting displacement of the system subjected to an impulse. The modal parameters were determined by the logarithmic decrement method, considering the system as underdamped. The use of high-speed video and digital image processing techniques allowed the simple and reliable determination of modal parameters of the coffee fruit-stem system. Natural frequencies for the coffee fruit-stem system were 11.62 and 13.29 Hz; the damping coefficient was 0.0253 and 0.029 N s m -1, and the equivalent stiffness was 8.61 and 7.09 N m -1 for red and green ripening stages, respectively. It was found overlap of resonance bands, between the ripening stages red and green, hindering the selective mechanical detachment in the first natural frequency range of the coffee fruit-stem system. Keywords: image segmentation, mechanical harvesting, mechanical vibrations.Determinação das propriedades modais do sistema fruto-pedúnculo do café por vídeos de alta velocidade e processamento de imagens digitais RESUMO. A derriça dos frutos do cafeeiro é comumente realizada por meio de impactos e vibrações mecânicas aplicadas à planta. Propriedades modais do sistema fruto-pedúnculo do café são informações importantes para uma derriça eficiente e seletiva. Objetivou-se determinar os parâmetros modais do sistema fruto-pedúnculo do café, tais como frequência natural e coeficiente de amortecimento, empregando-se vídeos digitais de alta velocidade. Por meio de técnicas de processamento de imagens foi obtido o deslocamento resultante do sistema submetido a um impulso. A partir do método do decremento logarítmico foram obtidos os parâmetros modais, idealizando o sistema como subamortecido. A utilização de vídeos de alta velocidade e técnicas de processamento de imagens digitais permitiu a determinação dos parâmetros modais do sistema fruto-pedúnculo do café de forma simples e confiável. As frequências naturais do sistema foram de 11,62 e 13,29 Hz; os coeficientes de amortecimento foi de 0,029 e 0,0253 N s m -1 e a rigidez equivalente foi de 8,61 e 7,09 N m -1 para os estádios de maturação cereja e verde, respectivamente. Houve sobreposição de faixas de ressonância entre os estádios de maturação cereja e verde, dificultando a derriça mecânica seletiva do café na faixa da primeira frequência natural.Palavras-chave: segmentação de imagem, colheita mecanizada, vibrações mecânicas.

Mechanical properties of the macaw palm fruit-rachilla system1

“…This behavior is observed for the systems studied here. Coelho et al (2015) studied the fruit-peduncle system of coffee plants and found damping ratio values of 0.15 and 0.09 for the immature and cherry stages, respectively, while Villibor et al (2016) reported 0.149 and 0.126 for the immature and cherry stages, respectively. These values are close to those obtained in the present study for the fruitrachilla system of the macaw palm.…”

The effects of nuts per cluster and the fruit stem lengths on fruit detachment force/husky fruit weight ratio at different maturity times of hazelnut (cv. Yomra)

“…similarly revealed that the FDF/W reduced as the maturity increased. (Polat, 1999;Pozo et al, 2007;Civil, 2009;Rabcewicz and Danek, 2010;Polat et al, 2011;Khorsandi et al, 2012;Yousefi and Gholiyan, 2013;Villibor et al, 2016). Bora et al (2007) reported that fruit detachment force was lower for heavier oranges and the force required for the fruit detachment as the fruit (orange) ripens.…”

High-throughput Analysis of Arabidopsis Stem Vibrations to Identify Mutants with Altered Mechanical Properties

“…Another problem of measuring free vibration is that a high-speed camera or detector is required to obtain a sufficient resolution from the short-time displacement. Other studies of free vibration of plant stems used cameras with time resolutions of 200-1,000 fps (Der Loughian et al, 2014;Villibor et al, 2016;Zajaczkowska et al, 2017). In this study, we used high-speed shooting at 240 fps with the default function of an iPhone/iPad.…”

“…By assuming that the stem is a simple spring-mass-damper system ( Figure 7A), stiffness k and damping coefficient c can be estimated from ωd and logarithmic decrement (δ; Zebrowski, 1999;Villibor et al, 2016; Figure 7B). According to Zebrowski (1999) in tapered stems of Triticale and Triticum, the dynamic behaviors of the vertical columns were different from those of the horizontal beams.…”

“…Based on two previous reports (Zebrowski, 1999;Villibor et al, 2016), the damping ratio (ζ), the natural frequency (ωn), the damping coefficient (c) and the stiffness (k) were estimated from ωd and δ ( Figure 7B), as shown below.…”