Fruits are easily damaged by collision during mechanical harvesting of blueberries, affecting quality. In this study, theoretical analysis, numerical simulation, and experimental verification are comprehensively employed to investigate the mechanical behavior and damage mechanism of blueberry fruit collisions. A nonlinear collision dynamics model for fruits was constructed based on Hertzian theory; the collision force is found to be related to the mass, the coefficient of restitution, the material properties of the collided object, and the collision velocity. A discrete element simulation model was created, as was a finite element simulation model. The fruit collision type was determined, and the analysis showed that when the collision velocity of the fruit-rigid plate collision model was increased from 1 m/s to 3 m/s, the peak contact stress increased from 64 000 Pa to 110 000 Pa, the peak collision force increased from 1.85 N to 6.75 N, and the damage volume increased from 152.72 mm³ to 459.42 mm³, which is more likely to trigger compared to the fruit-fruit collision model plastic deformation. Through the collision test it was determined that blueberry fruit can withstand a maximum collision force in the range of 2.00-3.00 N. More than 300 mm of drop height will cause the damage surface ratio to increase dramatically. The results of this study identified the key factors and thresholds affecting damage, providing a theoretical basis for reducing the damage rate of blueberry fruit and also providing a reference for the mechanical harvesting of other berry fruits.

To solve the problem of soil loosening caused by whole plant vibration during the operation of a vibrating blueberry harvester, the force model of the blueberry tree containing root soil was established and analyzed. The main factors affecting the impact force of the shaker were the curvature of the shaker, the branch curvature, and the equivalent elastic modulus at the impact point. Through the analysis of the transfer law of vibration between the exciting force and the root-soil complex, it is concluded that the shear strength decreases with the decrease of the internal friction angle, resulting in loose soil and easy toppling of the fruit trees. Discrete element simulation was used to analyze the force of the blueberry model. The results showed that the lower the excitation height, the more drastic the fluctuation of the root-soil complex. In the range of excitation height from 200 mm to 500 mm, soil acceleration increased by 45.5% on average for every 150 mm decrease. From 200 mm to 50 mm, the average soil acceleration increased by 69.1%. Finally, through the field excitation sensor test, the sensor was buried in 200 mm, 100 mm, and 0 mm (that is, placed on the surface) of soil, and the exciting force was applied to blueberry branches at heights of 50 mm, 200 mm, 350 mm, and 500 mm, respectively, for four times, and then the soil acceleration was output. A total of 48 sets of experimental data were obtained. By combining the scattering data obtained from the experiment with the simulated curve, it can be analyzed that when the excitation heights were 50 mm and 500 mm, the soil fluctuation at the depth of 100 mm was close to the simulated average value. When the excitation heights were 200 mm and 350 mm, the fluctuation of surface soil with a depth of 0 mm was close to the simulated average value. When the excitation height was 500 mm, the root-soil complex fluctuated twice due to the obvious reciprocating swing of the fruit tree. Since very little vibration energy was consumed during transmission, the vibration was strongest in the surface soil. Soil with a depth of 200 mm was almost unaffected by the excitation force and excitation height because too much vibration energy was consumed during transmission. The results show that the established model and simulation scheme are reliable and can provide a theoretical basis for the optimization of the incentive parameters of blueberry fruit trees.