Collision is one of the main causes of mechanical damage to the seedling during transplanting. To reveal the impact damage characteristics of plug seedlings, the kinetics equations of seedling collision were established based on Hertz’s contact theory, and the kinematic characteristics, elastoplastic deformation, and collision damage during seedling collision were analyzed using high-speed photography. Using the Tekscan pressure distribution measurement system, the significant levels of various factors that affect impact peak force (IPF) and damage of seedling pot (DSP) were studied, the change rule of contact pressure distribution of seedlings under significant factors was measured, and a regression model between IPF and DSP was established. The results showed that collision material, drop height and seedling pot size had significant effects on IPF and DSP. The contact pressure area of different collision materials from large to small was soil block, steel, and ABS plastic. The contact pressure area of seedlings of different pot sizes was big, medium, and small in descending order. At a dropping height of 50~350 mm, a contact pressure > 10 kPa accounted for the major contact pressure area, which is the main reason for collision damage of the seedling pot. Linear regression models between IPF and DSP under different factors were established, and the determination coefficients (R²) were 0.98 and 0.94, respectively. The results provided a theoretical basis for understanding the collision damage mechanism of the plug seedling and how to reduce damage during transplanting.

To improve the accuracy of simulation parameters used in discrete element simulation tests for the transplanting operation of the transplanting machine and to facilitate further optimization of crucial components of the transplanting machine, in this paper, the discrete element model of 50-hole plug seedling pots was calibrated and optimized based on the collision impact force between the plug seedling pot and the steel plate measured by a flexible film network tactile pressure sensor. Basic tests determined the contact parameters of the pot, and the initial parameters were screened for significance using the Plackett–Burman test. The pot-steel static friction coefficient, the pot-pot collision restitution coefficient, and the bond radius significantly affected the simulated collision impact force between the pot and the steel plate. According to the relative error value of the impact force between the pot and the steel plate as the evaluation index, the steepest climbing test was carried out on three significant parameters to optimize their value range. Based on the Box–Behnken test, a second-order regression model of the impact force and significant parameters regulating the interaction between the pot and the steel plate was established, where the target impact force between the pot and the steel plate was 11.78 N. The optimal parameter combination is obtained by optimizing the significance parameters: the static friction coefficient between the pot and steel is 0.790, the collision restitution coefficient between the pot and the pot is 0.325, and the bond radius is 1.542 mm. The test results show that the relative error between the actual and simulation tests is only 0.084%. The calibrated parameters of the discrete element model of plug seedling pots are accurate and reliable. The research results presented here can provide a reference for the subsequent transplanting operation simulation of the transplanter.

The movement of plug seedlings and the pots damage mechanism are deeply studied during the planting process, and the planting components are optimized. The Tekscan pressure distribution measurement system was used to measure the mechanical characteristics of the drop impact between the whole plug seedlings and the pots. The relative error between the collision impact force of the plug seedlings and the collision impact force of the pot is less than 20%. Therefore, a drop impact test using the pot allows the whole plug seedling to be characterized. The Hertz-Mindlin with bonding model was used to build a simulation model of the pot based on essential physical parameters. The Plackett-Burman test and the steepest climbing test determined the significant parameters and optimal intervals affecting the collision impact force: the rolling friction coefficient between the pot and pot was 0.35~0.38, the bond stiffness was 0.2~0.6 MN·m-3, and the bond radius was 1.56~1.98 mm. Finally, the Box-Behnken test was performed and the quadratic regression model of the collision impact force was developed. Taking the collision impact force with a drop height of 350 mm as the target, the optimal solution is obtained: the rolling friction coefficient between the pot and pot was 0.35, the bond stiffness was 0.53 MN·m-3, and bond radius 1.97 mm. The average value was used for other insignificant influence parameters. The simulation results are compared with the physical test, and the relative error is 3.65%. Therefore, the pot model established by this simulation parameter can represent the actual drop impact of the pots.

To accurately simulate the interactions between the plug seedlings and the planter during the planting process and explore the damage mechanism of the plug seedling substrate block, the bonding parameters of plug seedlings substrate block were calibrated by the discrete element method. The physical puncture test showed that the average of maximum force of the cone indenter on substrate block measured by texture analyzer was 4.633 N. A Hertz-Mindlin with the bonding model was established for the substrate block in EDEM software. A virtual calibration experiment was designed with the puncture force of substrate block as the evaluation index. The two-level factorial test and the steepest climbing test were used to screen out the significant parameters and the optimal interval. Then, the Box-Behnken test and the optimization solution were used to obtain the optimal bonding parameter combination of the substrate block particles. Finally, the optimal parameter combination was simulated and verified. The relative error of the maximum puncture force between the simulated value and the measured value was 1.88 %, which indicated that the bonding parameters of the substrate block obtained by calibration were accurate and reliable.

Currently, the simulation parameters for the model of the interaction between the transplanter, the plug seedlings, the soil, and the pot damage mechanism still need to be clarified. The optimization design of the planters and the improvement of planting quality are still urgent issues that need to be solved. In this paper, the simulation parameters of the pot and the soil were calibrated based on the pressure distribution measurement technology. With the actual collision impact force and matrix loss rate as the targets, a four-factor, three-level orthogonal test was designed to obtain the optimal parameters. Through the optimization analysis of the experimental results, it could be concluded that the pot–soil restitution coefficient, the pot–soil static friction coefficient, the pot–soil rolling friction coefficient, and the surface energy were 0.31, 0.88, 0.35, and 1.07 J/m², respectively. The experimental verification of the optimal parameter combination showed that the relative error of the collision impact force was 1.65% and that the relative error of the matrix loss rate was 2.32%, which verified the model’s reliability. Based on the optimal parameters, the movement law of the hole tray seedlings was studied at different positions during the transplanting process. The plug seedlings collided not only with the planter but also with the soil, which led to the breakage and looseness of the pot structure. The relative error between the matrix loss rate of the transplanter inserting soil, the matrix loss rate of the transplanter that did not enter the soil, and the simulated matrix loss rate was less than 10%, which further proved the accuracy of the simulation model.

This study provides a basis for designing and optimizing the key components of hanging-cup transplanters. The discrete element method, a high-speed photography test, and indoor soil bin tests were used to explore soil disturbance behavior during the hole drilling process. A comparative analysis of the discrete element method and the high-speed photography test indicated that soil particles are mainly affected by the coupled effects of the shear force and the squeezing force of the planter. The soil disturbance range in the horizontal and longitudinal sections gradually increases with the movement of the planter. The change in the soil particle velocity of the horizontal and longitudinal sections in different zones shows a trend of first increasing, then decreasing, and finally stabilizing. The velocity of soil particles in the longitudinal section varies significantly in the direction of burial. The soil in the horizontal section mainly moves to both sides when the duckbill is opened. The closer the soil particles are to the outer wall of the duckbill, the greater the change in velocity is. The soil bin tests and simulations were carried out under different conditions, but the change trend of the simulation results is consistent with the soil bin test results, proving that the simulation model is reliable. With the forward speed of the transplanter, planting depth, and soil compactness as the test factors, and the hole depth and hole longitudinal length as the response values, an orthogonal test of three factors and three levels was designed. A regression model between each element and response value was established. The optimal parameter combination was obtained when the forward speed was 1.25 km/h, the planting depth was 80 mm, and the soil firmness was 140~150 (N/cm²); these results were experimentally verified.