2.3.1. Establishment of Simulation Model
The RecurDyn 2023 multibody dynamics software was used to simulate the transmission of the seed discharge chain and the clearing brush in the chain–spoon seed discharger. The seed discharger model was created using the 3D modeling software 2023 SolidWorks. To improve the simulation efficiency, the model was simplified and converted to STEP format before being imported into RecurDyn for dynamic simulation [
23], as shown in
Figure 9.
The seed-metering device model was imported into RecurDyn, the material properties were set to steel, and contacts and constraints were added. The seed-clearing brush and the rubber plate at the bottom of the seed box were meshed as flexible bodies. The main constraints added were as follows: the drive sprocket, driven sprocket, vibrating sieve wheel, and seed-clearing brush were each added with a revolute joint relative to the ground reference frame; the seed protection trough and seed box were each added with a fixed joint relative to the ground reference frame; a fixed joint was added between the seed scoop and the outer link relative to the outer link reference frame, and a revolute joint was added between the inner link and outer link. The main contacts added were as follows: the drive sprocket and driven sprocket were each added with contact with the inner links of the transmission chain, and a flexible body contact was added between the vibrating sieve wheel and the rubber plate.
To ensure the coupling interface between EDEM and RecurDyn was connected, the components of the seed discharger model were exported as wall files and then imported into EDEM. The imported seed discharger model in EDEM is shown in
Figure 10.
After creating a 3D model of a seed potato in SolidWorks and converting it to STL format, the model was imported into EDEM. Using the particle fill function, the discrete element model of the seed potato was obtained, as shown in
Figure 11.
In EDEM, the contact model between the seed potato and between the seed potato and the seed discharger was the Hertz–Mindlin no-slip contact model. The main components in contact with the seed tubers were the seed spoon and the seed box, where the seed spoon is made of ABS plastic and the seed box is made of 65 Mn steel. The intrinsic parameters of the seed potato, 65 Mn steel, and ABS plastic, as well as the contact parameters between them, are shown in
Table 1 [
24].
2.3.2. Seed Filling Process Simulation Analysis
During the seed filling process with the seed spoon, the seed potatoes in the seed box are influenced by inter-seed forces, the vibration of the bottom rubber plate, and the agitation of each seed spoon. If the flowability of the seed potato in the seed box is too high, it can lead to an excessive accumulation of seed tubers in the discharge box, increasing the resistance for the seed spoon to rise. Conversely, if the flowability is too low, the quantity of seed tubers flowing into the discharge box will be insufficient, leading to potential seed loss.
The seed filling process of potatoes was analyzed by varying factors such as the seed chain wheel speed, the seed container height, and the seed spoon cavity tilt angle. During the post-processing phase in EDEM, the seed discharger was adjusted to a grid display, and the seed potato particle display state was set to the velocity. Four time points were captured to analyze the distribution of the seed tuber motion speed within the seed box, as shown in
Figure 12. In the figure, blue seed potatoes represent those with low instantaneous velocities, while red ones represent high instantaneous velocities. Due to the compression from the upper layer of seed potatoes and the agitation by the seed spoon, the high-speed seed potatoes were mainly concentrated at the bottom of the seed box. In the discharge box, seed potatoes on the left and right sides of the seed spoon, driven by the seed spoon, exhibited higher movement speeds. However, the seed spoon can only pick up a limited number of seed potatoes, causing the remaining seed potatoes to flow back and accumulate on both sides of the discharge box. As shown in
Figure 11, the number of blue seed potatoes on the left side of the seed box gradually increased, and the seed layer thickness in the seed box progressively thickened from the simulation’s initial 0.1 s, where the seed layer covered one seed spoon, to near the end of the simulation at 5.45 s, where the seed layer thickness covered two seed spoons.
In the simulation experiment, the seed chain wheel speed was set according to the RecurDyn simulation environment. The height of the baffle, which is the distance from the bottom edge of the baffle to the bottom edge of the seed box, is adjustable to allow for the modification of the connectivity area between the auxiliary seed box and the discharge box, thus adjusting the seed capacity height. During the modeling of the seed discharger in SolidWorks, different tilt angles of the seed spoon cavity were set and imported into RecurDyn. In the EDEM post-processing phase, a grid bin group (specifications: 100 mm × 50 mm × 100 mm) was set at the end of the seed filling area to create a filling monitor that tracked the seed spoon’s seed-picking performance [
25], as shown in
Figure 13 and
Figure 14.
To study the effect of the drive wheel speed on the seed filling performance of the seed discharger, single-factor simulation tests were conducted in the RecurDyn 2023 software with varying drive wheel speeds. Based on preliminary theoretical analysis, the drive wheel speeds were set at five levels: 14.0, 24.0, 34.0, 44.0, and 54.0 rpm, with all other factors kept constant. The experimental plan and results are shown in
Table 2.
To visually observe the impact of different operational speeds on various seed filling performance metrics, Origin 2021 was used to plot the relationship between the seeder’s performance metrics and the operational speed, as shown in
Figure 15.
From the test results and the relationship curves, it can be observed that at lower chain wheel speeds, the rates of qualified seeds and over-seeding showed more significant variations. As the speed increased, the changes in the performance metrics became more stable. When the speed exceeded 44 rpm, the over-seeding rate rose significantly. Therefore, the operational speed range for the drive chain wheel was preliminarily set between 34 and 54 rpm.
The angle of the seed scoop cavity plays a role in both the seeding and seed transportation processes, aiding in seed clearing. Based on previous theoretical analysis, the seed scoop cavity angles were set to 7.0°, 9.5°, 12°, 14.5°, and 17.0°, with all other factors held constant. Single-factor simulation tests were conducted, and the results are shown in
Table 3.
To observe the impact of different seed scoop cavity angles on various seeding performance metrics more intuitively, the relationships between the performance indicators and cavity angles were plotted using Origin 2021, as shown in
Figure 16.
From the above experimental results and relationship graphs, it can be seen that when the seed scoop cavity angle was greater than 7° and less than 9.5°, there were no significant changes in the performance indicators. However, when the cavity angle exceeded 14.5°, the missed seeding rate significantly increased, greatly affecting the performance of the seeder. Therefore, the seed scoop cavity angle was selected to be between 12.0° and 17.0°.
During the operation of the seeder, the accumulation of inter-seed forces can lead to the formation of strong force chains, affecting the seed filling performance. To improve the dispersion of seeds and prevent the formation of strong force chains, the seed capacity height should be limited during the design of the seed box. To analyze the effect of the seed capacity height on the seeder’s performance, the height of the baffle between the seed box and the seeding box was adjusted. The seed capacity heights were set to 0.12, 0.16, 0.20, 0.24, and 0.28 m, with other factors kept constant. Single-factor simulation tests were conducted, and the results are shown in
Table 4.
To more intuitively observe the effect of different seed scoop cavity angles on various seeding performance indicators, the relationships between the performance metrics of the seeder and the working speed were plotted using Origin 2021, as shown in
Figure 17.
From the above experimental results and the corresponding graphs, it can be seen that the single-seed qualification rate initially increased and then decreased with the increase in the seed capacity height, reaching a maximum value at a capacity height of 0.20 m. When the seed capacity height was less than 0.24 m, the missed seed rate decreased as the height increased, while the over-seeding rate increased with the height. Therefore, to ensure that the seed discharger maintains a low missed seed rate while keeping the over-seeding rate within an acceptable range, the optimal seed capacity height was determined to be between 0.16 and 0.24 m.
2.3.3. Seed Clearing Process Simulation and Analysis
The seed clearing stage is crucial for reducing the over-seeding rate. During the seeding phase, the seed scoop captures one or more seeds at a time. When the scoop enters the clearing zone, excess seeds outside the scoop cavity fall back into the seed box under the influence of gravity and the inertial force of the clearing brush. After the simulation was completed, the EDEM post-processing function was used to set up a grid bin group (100 mm × 100 mm × 100 mm) at the end of the clearing zone to monitor and count the number of seeds, as shown in
Figure 18.
To investigate the impact of the clearing distance on the seed clearing performance, the seed discharger model was adjusted in SolidWorks, with the clearing distances set at 20, 25, 30, 35, and 40 mm. All other factors were kept constant during the simulation trials. The test results are shown in
Table 5.
To more intuitively observe the impact of different clearing distances on the seed discharger’s clearing performance, the clearing performance of the seeder was plotted against the clearing distance using Origin 2021. The relationship curve is shown in
Figure 19.
From the results and corresponding relationship curves, it can be observed that as the clearing distance increased, the single-seed qualification rate initially increased and then decreased, the missed seed rate initially decreased and then increased, and the over-seeding rate gradually decreased. After the clearing distance exceeded 30 mm, the missed seed rate significantly increased. Therefore, a clearing distance of 30 mm was chosen, as it met the clearing requirements.
To explore the effect of the clearing brush’s rotational speed on the seeder’s clearing performance, and based on the preliminary experimental results indicating that the best clearing performance occurs with a clearing brush transmission ratio of 1:1.5 relative to the active chain wheel speed, the clearing brush rotational speeds were set to 51.0, 58.5, 66.0, 73.5, and 81.0 rpm. Other factors were kept constant for the single-factor simulation tests. The test results are shown in
Table 6.
To more intuitively observe the impact of different clearing distances on the seeder’s clearing performance, the clearing performance of the seeder was plotted against the clearing distance using Origin 2021. The relationship curve is shown in
Figure 20.
Based on the test results and corresponding curves, it can be observed that the over-seeding rate decreased as the clearing brush rotational speed increased, while the single-seed qualification rate initially increased and then decreased with the increasing rotational speed of the clearing brush. When the clearing brush rotational speed exceeded 66.0 rpm, the miss rate rose sharply. Therefore, the clearing brush rotational speed should not exceed 66.0 rpm.