Design and experiment of a dual-drive counter-rotating differential vibration pecan harvester

Existing pecan mechanized harvesters have been limited to the fruit removal efficiency and adaptability in recent years. In this study, a hydraulically-driven differential vibration was proposed with the dual-drive counter-rotating for pecan harvesting operations. Firstly, the overall structure was realized for the vibration-based shaker of the harvester suitable for the large pecan trees. A picking model was developed to couple rigid-flexible dynamic vibration, in order to simulate the interaction between the clamping-vibration component and the main trunk of the pecan tree. The clamping assembly was treated as a rigid body, while the tree trunk was modeled as a flexible body. A systematic analysis was also performed on their coupled vibratory dynamics. Then, the variation patterns were determined for the excitation force under counter-rotating differential vibration. The influencing factors on the harvesting performance were identified as the base rotational speed for one of the hydraulically driven motors, the differential rotation coefficient between the two hydraulically driven motors, and the vibration duration applied to the pecan tree. Secondly, finite element simulation software was adopted to design the structure and operation parameters of key parts of excitation and clamping, in order to enhance the performance of the system. Specifically, the geometry of the eccentric mass blocks was refined, including their structural configuration, eccentric offset distance, and mass moment of inertia, according to the structural parameters and material selection of the excitation main shaft. Additionally, the parameters of the dual hydraulic-driven motors were established to determine the design value of the clamping preload force. Finally, a pecan picking machine was trial-produced under picking test conditions. A full machine performance test was then conducted to verify the simulation. The results showed that the optimal operating parameters were a base rotational speed of 1 200 r/min, a rotational coefficient of 0.8 based on the base speed, and a vibration duration of 10 s, particularly for the mature pecan trees with trunk diameters of 35-45 cm, the harvester achieved a fruit picking rate of 88.8% in a single shaking pass per tree under this condition. Considering the damage caused by vibration to the tree body and the actual harvesting effect, adjust the optimal vibration time to 7 s, and The comprehensive performance verification test results of the whole machine under this condition showed that the average pecan picking rate was 85.0% in a single shaking pass per tree, without any destructive damage to the tree trunk. Meanwhile, the average harvesting efficiency was 40 trees per hour, which was approximately 16 times that of manual harvesting. The developed harvester fully met the high requirements of efficiency and adaptability during mechanical harvesting of pecan in orchards.