Simulation and Experiment of Optimal Conditions for Apple Harvesting with High Fruit Stalk Retention Rate

Apples are widely cultivated primarily for fresh consumption. During mechanized harvesting, the extraction of fruit stalks can significantly impact the storage duration of fresh apples. The tensile force applied to the abscission layers is a critical factor in retaining the stalks; yet, few researchers have focused on preventing stalk pull-out during picking. In this research, we studied the phenomenon of missing stalks during mechanical picking by analyzing the tensile force exerted on the abscission layer during picking and optimizing the attitude of the end effector to achieve the highest stalk retention rate. Firstly, the tangential and normal energy release rates of the abscission layer were used as key parameters to model the cohesive zone of the abscission layer, a finite element model of the fruit–stalk–branch system was developed, based on which the actual fruit picking process using direct-pulling and twisting was simulated. Subsequently, the data obtained from the simulation were analyzed using response surface analysis, and the maximum tensile force at the time of fracture of the delamination and the time of its fracture were used as optimization parameters to find the optimal solution of the angle, direct-pulling speed, and twisting speed d to achieve the highest stalk retention rate. Finally, through field experiments, it was demonstrated that the optimal picking conditions could effectively improve the picking success rate and stalk retention rate. The results show that, when the end effector picks close to the fruit at about 58°, the stalk retention rate can reach 94.0%.