Design of End-effectors for Apple Robotic Thinning in the Green Fruit Stage

Thinning is an essential horticultural process that determines fruit quality in apple orchards. Hand and chemical thinning have historically been the two main fruit thinning practices. Recent advances in robotics have shown alternative automated thinning methods that potentially are precise and efficient. In robotic thinning, the end-effector acts as a "bridge" between the robotic arm and the apples in the orchard, connecting the automation system and the environment. Due to the high variability in field conditions, it is critical to design end-effectors that can adjust to the sizes and orientation of apples. Tension and bending experiments were conducted in the lab before the end-effector design, trying to find the best thinning method. Two models were designed based on different thinning approaches: the first end-effector model thins unwanted apples one by one, while the second end-effector model protects the king fruit of the cluster and simultaneously cuts off unwanted apples. Both models have been designed and simulated using SolidWorks® to test the end-effectors' motion. The fabricated end-effectors were tested in apple orchards during the thinning season, with Model 1 achieving a 100% success rate and Model 2 a 75% success rate.