Multistage Synchronous Telescopic Manipulator With End-Effector–Biased Rotating-Pulling Mode for Damage-Free Robotic Picking

Abstract

Fruit picking is one of the most time-consuming and labor-intensive stages of fruit production, characterized by high labor demands and significant labor costs. Traditional fruit-picking robotic manipulators typically adopt configurations similar to general-purpose industrial robots, following a predefined path and employing a direct-pulling mode to detach the fruit. However, due to the constraints of the orchard environment and the varying conditions of the fruit, manipulators should be designed to accommodate the specific horticultural characteristics of the trees to improve picking efficiency. Additionally, the picking process should be optimized based on the biological characteristics of the fruit to ensure quality. In this study, a five-degree-of-freedom manipulator based on a multistage synchronous telescopic mechanism is proposed for fruit picking. Workspace analysis indicates that the manipulator can cover more than 80% of the fruit distribution on the trees. To ensure motion accuracy, a FreeRTOS-based motion control system is developed for the manipulator. To evaluate picking efficiency and quality, fruit-picking experiments are conducted in an apple orchard. A rope-driven, three-finger end-effector is mounted in a biased position at the end of the manipulator, complemented by an RGB-D camera for fruit detection and a ROS-based control system for robotic operation. The performance of two picking modes (direct-pulling and biased rotating-pulling) are compared in these experiments. The results demonstrate that the biased rotating-pulling mode yields a higher picking success rate and a lower stem damage rate compared with the direct-pulling mode. Specifically, the damage-free success rate for the biased rotating-pulling mode is 80%, with a 9.18% reduction in stem damage compared with the direct-pulling mode. Furthermore, the average picking cycle time is approximately 14.5 s. In conclusion, the manipulator and its motion control system successfully achieve efficient, nondestructive fruit picking with a high success rate, offering valuable insights for the development of fully automated fruit-picking robots in the future.