A Mechanical Model of Cutting Citrus Fruit Stems Based on Partial Least Squares Method

Accurately estimating the peak cutting force for cutting citrus fruit stems is helpful for the design of the end-effector of a harvesting robot and improves the harvesting success rate of the harvesting robot. In this study, five factors that influence the cutting of citrus fruit stems with a harvesting robot in a natural environment were analyzed, including cutting speed (v), the gap between the two cutting blades of the end-effector (s), the diameter of the stem (d), and the deflection (theta(def)) and inclination (theta(inc)) angles of the stem. An experimental platform was built for cutting citrus fruit stems with the blade gap (s) as a fixed value. A mechanical model for calculating the maximum cutting force was established based on the partial least squares method, and d, v, theta(def), and theta(inc) were the independent variables of the model and were verified by repeated tests. According to the test results, the mechanical model was modified when the citrus fruit stem diameter was greater than or equal to 3.2 mm, and the modified model was also verified by tests. The verification results indicated that, compared with the actual peak force for cutting citrus fruit stems, the percentage error of the peak force calculated with the model was 11.51% when the stem diameter was less than 3.2 mm and 4.94% when the stem diameter was greater than or equal to 3.2 mm, which can provide a significant reference for evaluating the peak force for cutting citrus fruit stems and designing the end-effector of citrus harvesting robots.