Simulation and experiment of the rigid-flexible coupling for a pendulous type Camellia oleifera fruit picking machine

Mechanical harvesting is required for Camellia oleifera in hilly and mountainous regions. However, conventional harvesting cannot fully meet the large-scale production in recent years, due to the low efficiency and high labor intensity. In this study, a lateral branch shaking-type harvester was designed to enhance fruit harvesting efficiency with a low bud damage rate, particularly in hilly and mountainous terrain. A simulation model was developed to integrate the fruit detachment dynamics and the aerodynamic drag. Subsequently, the field tests were conducted to validate the mechanical harvesting of Camellia oleifera fruits. A single pendulum model was established to explore the dynamics between the fruit and its stem. The influencing factors on fruit detachment were identified during harvesting, such as shaking frequency, amplitude, and shaking position. The fruit's growth was also considered to accurately simulate the fruit detachment in the dynamic model. The frequency, amplitude, and shaking position were the most influential factors on the force of fruit detachment. Computational fluid dynamics (CFD) was employed to quantify the effect of aerodynamic drag on the fruit’s motion. There was also the relationship between the fruit’s velocity and the aerodynamic drag force acting on it. The aerodynamic drag was determined to affect the fruit's velocity and movement trajectory, as well as the overall harvesting. Subsequently, a coupled rigid-flexible simulation model was constructed to integrate the harvester, the Camellia oleifera tree, and the aerodynamic drag forces. The dynamic response of the tree and fruit was simulated under various operational parameters using the ADAMS simulation software. The results indicate that the fruit velocity initially increased but then decreased as the shaking frequency and distance increased. Once the frequency exceeded the threshold, the amplitude consistently increased the fruit velocity at a diminishing rate. The optimal shaking parameters were obtained for fruit harvesting. A three-factor, three-level orthogonal field test was also incorporated to evaluate the different operational parameters, including shaking frequency, amplitude, and shaking distance. Statistical analysis showed that the shaking frequency was the most significant factor influencing fruit removal efficiency and flower bud damage, followed by amplitude, and then shaking distance. The optimal combination of parameters was a shaking frequency of 8.87 Hz, amplitude of 51.79 mm, and shaking distance of 50.05 cm, after the response surface analysis. As such, the fruit removal rate was achieved 95.03%, while the flower bud damage rate was only 4.07%. Field trials were conducted to validate the simulation at a Camellia oleifera planting base in Poyang County, Jiangxi Province, China, in October 2025. The harvester’s shaking frequency was set as 9 Hz, the amplitude as 50 mm, and the shaking distance as 50 cm. The field results showed that better performance was achieved for practical applicability, with an average fruit removal rate of 94.24% and a flower bud damage rate of 5.27%. The simulation shared better agreement with the predicted values. The deviations in fruit removal rate and bud damage rate were 0.79 and 1.2 percentage points, respectively, indicating the high effectiveness and accuracy of the harvester after simulation and optimization. Comparative analysis revealed that the lateral branch shaking-type harvester outperformed conventional shaking machines, such as the branch-shaking and roller-type harvesters, in terms of both fruit removal efficiency and flower bud protection. Shaking force was transmitted from the ropes to the lateral branches, indicating less damage to the main tree trunk, particularly in uneven terrain. The optimal parameters were maintained for efficient harvesting to minimize bud damage, indicating the health and future fruit production of the trees. These findings can provide guidance to design the harvester with the optimal parameters for Camellia oleifera.