Machine learning models for classifying coffee fruits detachment force

Abstract

The maturation process of coffee (Coffea arabica) trees exhibits inherent variability, producing fruits at various physiological maturity stages. This variability affects the resistance between the fruit and its peduncle, posing a challenge in mechanized harvesting: non-selective harvesting. A precise classification of coffee fruit detachment force is essential to address this challenge, ensuring coffee's quality and producer's profitability. This study assesses the efficacy of machine learning (ML) models in determining the detachment force across various coffee cultivars under drip-irrigated and rainfed conditions. The dataset included detachment force measurements from 24 cultivars—13 drip-irrigated and 11 rainfed—yielding 1152 data points. Variance analysis compared irrigation methods and three maturity stages: green, cherry, and dry. Detachment force was categorized into four classes based on the dataset's quartile distribution. The ML models utilized were random forest (RF), support vector machine (SVM), K-nearest neighbors, and artificial neural networks. The SVM model was notably effective in classifying detachment force for rainfed cultivars, with a Matthews correlation coefficient (MCC) of 0.78. In contrast, the RF model was particularly adept for drip-irrigated cultivars, with an MCC of 0.75. The highest classification accuracies were recorded for the extreme force classes I and IV, with precision values of 0.93 and 0.8, respectively, while classes II and III had lower precision at 0.57 and 0.69. Implementing these ML models for detachment force classification has been beneficial, improving decision-making in mechanized harvesting systems.